The Tdngand Modbatbn d a FulCZCork OmMoptw

Bruce Aiexander Fenton

A thesis submitted in conformity Ath the requimments for the degree of Masters uf Applid Science Graduate Department of Aeros~aceScience and Engineering Unkeraity d Toronto

@ Copyrîght by Bruce A. Fenton 1999 National Libiary Bibliothèque nationale du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, rue Welington OttewaON K1AW Ottawa ON KIA ON4 Canada Canada

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The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. An importânt rest~ttd the testing has beeri to shoReci the nose gear d aie air#dt to duce the average lii during the td

Thanks ahto Dr. Delaurier, who has done so much mom than just give me a dream topic for my thesis. His unwavering trust in me has been a tremendous bwst to my confidence and has ailowed me to complete this wok.

The omithopter pro- has been blessed with a remarkable pilot in Paûicia Jones-

Bowman. Her well thought out approach b the taxi trials has been a key factor in getting as close as we have to sucœss. Also, her bravery has been and continues to be an inspiration.

I could not have finished this without the bve and support of rny wife Jennifer. She has been ümre through the good times and the bad times.

I would also like to thank my farnily and friends. Their enthusiasm for the omithopter has been a reminder to me of how fortunate Iam to be working on this project.

Finally, 1 must express my gratitude to the curent members of "Team Omithoptef. it has been a pleasure to work with al1 of you. To James Avew Fenton AbPct ii Ack-nB iii Tabk of Conbbntb v UstofTa~ viii List of Figuir# & 1 INfROWCTM 1 1.1 Flipping FlbM 1 1.2 PikCd Flapphg FlgM 2 1.3 The FullScale Ornithopaer 2 1A Transport Cam& lnvohnmrnt 5 1.5 TgahO Location 5 1.6 Pilot Bitkgtwnd 7 1.7 Gemral Test Pdum 8 2 DATA ACQUISKmN SYSTEIiII 11 2.1 HardniiPre 11 2.2 mm 13 2.3 Calibntkn procedure 14 2.4 Data collectkn and mductkn pdum 15 2.5 V#eo Sysoimi 16 2.6 Noise Problems 16 3 PRE-1997 MODIFICATIONS 18 3.1 Nm Smikrg and hkingSysbms 18 3.2 lUewUndercarrirg@ 19 3.3 Nswzerosm~ 20 4 1897 TESTS AND M0DlFICATK))rlS 22 4.1 1997 Test Program 22 4.2 Zero Sb@# 25 4.3 bih 28 4.4 ThoroxStnrctum 30 4.5 Nœe Ckrr Suppocaig Stnichin 32 4.6 InstnirnenfPokn 34 4.7 Sumiry of 1997 Rrub 35 5 1997 DATA REWCTION 5.1 mIkb 5.2 P~~rW as w~~~nrlyib 5.4 Summary 6 OFF SEASON ANALYSW AND MOMFICATW 6.1 Structural Modification8 6.1.1 CadeFramehatysh 6.1.2 -Repair~ 6.1.3 Thara#Repairs 6.1.4 NewCmsMemberin DriveMUdule 6.2 Simubtkn 6.2.1 Obtaniig Sphg Caaitenls and Dampiirg fMb 6.2.2 Simulabioii Resub 6.2.3 FutureWorlr~rrtheSimulation 6.3 InanimeMath 6.3.1 Ptessure Transduoer Calikatior, 6.3.2 Nemr Prsssurefrawducer 6.3.3 SWlaWAngle Inchdor 6.3.4 Frequency Meter 6.3.5 New- 64 f niIing.Edge Clips 6.5 Whg Reprim 6.6 Throttle Mschanh 6.7 EngimRestrakit 7 1998 TESTS AND MûD1FICATK)NS 7.1 1998 Test Pmgtam 7.2 Hinge Modillcrtbns 7.3 Wng R#Lr 7.3.1 Shedf Repair 7.3.2 Fkating Panel wr 7.4 NOWGear 7.4.1 NosewDgnpjng 7.4.2 Stnidural 7.5 Other devekpmsnt kucw 7.5.1 Stsering 7.5.2 Aqparentasymneby pro#ems 7.5.3 1- 7 J Summry d 1998 Test R#ulb 8 1- DATA REDUCTION 8.1 Wkig 8.2 Po@nWmbrDrfi 8.3 Air Spwâ va Fbppkig Fmqamcy

8.6 Run 2 ori -ber 8,1988 8.6 Sumiiy 9 PREPARATtûNS FOR FURTHER TESTlNG

9.2 Nour Gear IlkdHicdom 9.3 oula?Modmaaons 9.4 Test Piogmm lbr 1999 10 CONCLUSDN REFERENCES

APPENDK A: 1997 BENDING DATA APPENDIX 6: 1997 POTENTmETER DATA APPENDIX C: 1998 BENDING DATA APPENDK O: 1998 PûTENTIûMEER AND ACCELEROMETER DATA Tabie4.1. Canpletelistd1997teatsfranAugust 1 ttm~@1Se@mbm16...... 24 Ta5.1. WdomW Ranges artd Posilive Dirieebrons ...... 42 Taüe 6.1 : Prr#nilre Tranaduoer Canpahm ...... 62 Ta7.1.Cmpktelistdtestsin 1988...... 72 Table8.1. Sequenee~Eventsfor~HopAttemptonIrkvember8. 1998 ...... 101 Figun 1.1 : Three-Vi (Drauiing by D. beum) ...... 3 Figun1.2:The-ontheRufnii~y(-byJ.D. DeCauier) ...... 4 Figum 21: Angle Mer...... 12 Figuis 3.1: Stedng Pedals (Nae the heel kakss) (Phdogqh by J.O. DeLaurier)...... 19 Figum h2: Noee Gear and Sm\Mres (PhaBogra9h by J.D. Oel#aer)...... 20 Figum 3.3 ïm Stage Wnand Sptodret Diive (Phobgaph hy J.D. Delaurier)...... 21 Figun H:Zero Sage vvith New 6earing and CWn Guard (Phdapph by J.D. Delaurler) ...... 26 Figun~:\IViiI1Oemageon~Panel~DrivingHi~.(~byJ.D.DeCauler) ...... 29 Figure 43: Reinforcement d Riblet to S- AtEachment (Mby J.O. Deîaurier) ...... 29 Figum4A: itemChmged to Strengaien Nose Gear Support (Skebch by J.O. DeLawiw) ...... 34 Figun 48: New Tubes Aâded to Strengthen the Nom Gear support (Smby J.D. DeLaurier) ...... 34 Figun 61: ûmiing Manent DaEa han Third Run on 15, 1987 ...... 38 Figum 5.2. 8ending Manent D& from Second Run on 1, 1997 ...... 39 Figure &3: Bending Manent Oata fran Second Run on Sepdember 15, 1997 ...... 41 Figure 54: PdeMuneW Data fran Second Run on -ber 1, 1997 ...... 44 Figun 55: pctentlana(a aatafrom Ssond Rur on Se@ambf 15, 1987 ...... 45 Figum 5.6: FWai View d the Data in Figure 5.5 ...... 46 Figure 5.7. -OatafFom Thid Run on Segtember 15, 1997 ...... 47 Flgui. 58: pdenGaeter Data from Second Run on Sepanber 16, 1997...... 48 Figun 6.l. Dmaged Lelt Oubgger (mdogmphby J.D. Delaurier)...... 52 Figure 6.2. Bent Tube in Ledt Oubigger (Phobog~by J.D. -der) ...... 53 Figura 6.3. Straigiltening üw LamLangaron (- by J.D. Delwrier) ...... 54 Figun 6.4: MnUwWwniage Drop AppWus (PMqlraph by J.D. DsLauier)...... 57 Figure Bb: Piegue Traskicar Cdiôdion...... 59 Figum 6.6. Cdibration d 1987 Pmsure Tmsducer...... BO Fîgun 6.7: Air Speed Data and TrendYne ...... 61 Figure 6.8: Camd 1988 P~nnrrr,Traisducer ...... 62 Figun 6.9 Staülrbr Aigle Indiroloc ...... 83 Figun 6.10: Rwrto ln= SM(Skdai by J.O. Delarier) ...... 66 Figun 6.11: ThWe Resparwt afb 1- d New Meehariism ...... 67 FQun 6.12. EMne R-nt (Ridogaph by J.D. DeiarW)...... û8 FCun 7.1. TraiHng-Edge c# Pîywod SM...... 74 Figun 7.2. Teer the Rœting Panl Me&s the Spar...... 75 Figum 7.3. Stripe d Kevtar Uard For the Repair ...... -75 Figun 7.4: Scissx-Type Dmpef ...... TI Fîgun 7.S: Bioyde Dsmper ...... 78 Figure 7.6:ModSfied RMorqâe ...... 79 Fbun7.I: Noae Geer Support Sbii$ ...... 81 ~igum7a: ~rolrenN- GW ...... 82 Fîgun û.1. Bending Mcmmb vs Flapp'ng F- ...... 88 Figure û2Bendirig Mornerit DaEa from flrst Run on November 8. 1998 ...... 89 Figure IL3: FWmWmWiWa frPm Rist Run uii 19, 1908 ...... 91 Fi~urs8.4:PdedbmWDataffun FourthRunon -24, lm...... 92 Fbum 8.6: Data from Third Run oii ûctobef 16, 1998 ...... 94 Figure 8.6. PdedhmW Diata ftom fia Run on Fkvember8, 19Qû...... 95 Figum BI: Air Sr##l W. Flappng Frequency ...... 96 Figum 8.8. AamhmeW Data from Second Run on Nommber 8, 1998 ...... 98 FQum 8.9. WngFrequeney û&a fran Second Run on Nomnôer 8. 1008 ...... 89 FigumatO: PdentimeWDatafromCrowHop~onNavember8. 1998 ...... 100 Figun 9.1. Bent linch Aluninuni Tube ...... 104 Figum 9.2. Steel Plug Inserîed in 1-inch AIuninun Tube ...... 105 Figure 9.3. New StdTube Hiiai Machined End ...... 106 Fbum SA: Cart for Testing Steering Gemmetry ...... 108 The twentieth cenhrry has brought with it an unpreceâented rate of tedxiobgical

advancement The aviation industry is an exœlknt example of mis rapïd development This

industry was. for al1 inam$ and purposes, bom on Oecernber 17, 1903 when the Wright Flyer

made b historic fimt flight, less than 100 pars ago. Smœ then the iecords have fallen quickly:

non-stop flights across the gmt oœans, supersonic flight, around the world fllghts, hurnan

powered fiiiht, the list goes on. Arnong aie ever decreasing list of aemnautical adiievements

which riemain, piloteâ flapping wing flight is aie one which has captured imaginatins for

centuries.

1.1 Fîapping Wing FligM

Humanity's onginal dmam of flight was to fly like the birds. it was logical for people to

assume that this was how to fly because their only knowledge of fiigM was that of aie birds.

Consequently, eariy attempts at fiight were essentialiy mimicking birds. The earliest known

serious design of a flying machine is that of Leonardo DaVinci's human powered ornithopter.

Many inventors followed DaVinci's dream and buik flapping conttaptions of al1 sorts. They al1 haà

one thing in common: they did nat work. Eventually, the eady pioneers of aviation shifted their attention to fixed wing fîighf separating the fundons of lift and thnist Once the Wright brothers made fixed wing flight a reality, there was no tuming back. People now take to the skiby the millions evew day without giving it a thought, b~4no one ha$ yet fbwn in a bird-like manner.

Thmghout the rapid devebprnent of hed wing flight, DaMnci's dmhas not died. Tiem have been attempts at mechanical flappîrtg wing fligM, mostly on a mode1 sak. Alexander

Lippisch buiit a human-powemd ornithopter in the 1920'9, but never mamged anythhg more than exteruid glidas'. Percîval Spencer had some sucœss mth his engine-powered models in the 19ûû's. but he never biad anything on a larget scaie. Milsof Spencer's design have only mtlyoDme to lighf Mer neady decales of mearchl James DeLauriet and Jeremy Hanis designed and built 'Mr. Bill". On September 4, 1991, 'Mr. Bill" flew twiœ: once for 1 minute

46 seconds and again for 2 minutes 46 s6conds. These wre the first tnily successful ornithopter fiights because they wem engine pouiered, sustained and conbollable and they wem only limited in duration by the s~eof the fud tank. The devekpment of the airdlwhich fiapped its way into the history books, is described in detail in Rebrenœs 1,3,4 and 5.

1.2 PHUFlappirig Wing FlipM

More than just a modd, 'Mr. Bill" was also intended to invesügate the feasibility of mechanical fiapping wing flight on a larger $cale. fothat end, 1 was a quarter sale mode1 of a full site, piloteâ orniaiopter. DeLaurier and Hams founded a company called "Project Ornithopter" with the goal of building and Qing Ihe full ske ornithopter. After a period of analysis and design, the omithopter was wmpleted in 1996 and started taxi trials. The design of the full sue ornithopter is describeci in detail in Reference 6 and bnefty in Section 1.3.

The time sale of this projet3 is such that it couiâ not be mvered by a single two-year thesis, and there has hem more than enough research and data pmâuced to support several mastem' theses. To date, however, the published work has been largely theoretical (Machaœk7 and ~ashagor roaising on the wings (FOWI~and ~ehbr'?.As the taxi trials have progresse& a large amount of data has Mncoliected on the perfomanœ of the air& as a whoie. This thesis serves to canünue Mehler's wrk on the wings, (which in tum was a continuation of

Fowler's) and more importantly, b discuss new data collecteci relating to the pilot's control of the aircraft.

1.3 The FulCScpk Ornithopter

Figure 1.1 is a three-view drawing of the fulCscale omithopter as it appeared in 1998, and

Figure 1.2 is a photograph taken in 1998. The orQinal design in 1996 had some important dibrences, whidi will be discussed throrylhout this document Figure t .l: Ornithopter Three-Viw by o. ~oemin)

One of the key features of the omithopter wing, (which is essentially the same design as that for the model), is the thisspanel configuration, as can be seen in the front view. There is a

'centm sectionndimctly above the fuselage, or 'Yhorax" for the omithopter, and two 'outer panelsn, which are hinged to aie centre section. These outer panels are connected to the thorax via outnggers, on which the outer panels pivot for flapping. The engine drive is conneded to a 'drive module", which reduœs aie engine's rotational speeâ by a ratio of approximately W:1 and terminates in a Scotch yoke mechanism. The Scotch yoke converts the rotary input to a sinusoiiôal output and drives the centta sedion sûaight up and down. As the centte sedion moves up, the outer panels pivot on aie outriggers and the outer portions of the wings go down.

The purpose of the thriee-panel design is to even out the lift produced during the flapping cycle, which has two ben&. First, it bnngs the peak power raquimâ fmn tha engine down to a value doser to the average, meaning that the engine does not have to be unmœssarily powemd and therebre heavy (sinœ emgine sùing is based on peak power). Second, it reduces the heaving eripsrienced by îhe~fuselage, which is qui te^ important for a pibted ornithopter.

Rgun 1.2: The OrnihpW on the Runway J.D. Daaukr)

The other important feature of aie ornithopber wing is its ability to twist in respnse to aerodynamic bads. Bneîly, the trailingdge is split in twa and aiese two edges are allowed to slie past each oîher in a spanwise diredion. OpenMg up the torsion box in aiis way allows the wing to twist without the skin buckling. The two trailingsdges are held together by alurninum clips, which are aitemately glued to the upper and lower trailing-edges. This idea, calied shearflexing, is explained in more detaii in Refemœs 1 and 5. Only the portions of the outer panels beyond the outrtggers are capable of shearfiexing. The centre section and the innemast paît of the outer panel are essentially rigid. To accommodate for the shearflexing, each wing has a '(loating panel" on its upper surfaœ at the piwt point (top of the outriggers), which is where the shearflexing portion meets the Mid portion. The fbating panel is allowed to slide on top of the

@id part of the whg. There is also a fioating panel at the wing tip. The shearlbxing wing and the three panel configurdon have pabents in the United States and Canada.

In most other respects, the ornithopter is a faidy standad âesign. The ertgine is a three cylinder, two stroke which produces 24 hompower, made by Konig. The control surfaces am a nidder and an al1 rnoving hobonta1 stabilizer, or stabiiator. There are no ailerons on the

ornithopter, as incorporatirtg them into the shearflexing wings wouîâ have been a difficult

devakpmentai ta&. The nidder is used to tum by taking advantage of yaw-rol coupling. The

yaw-roll coupling is present because of the average positive dihedral of the wings. The tuming

was accomplished the same way for the rnodel, and it was seem b work very well. Both control

surfaces, Ndder and stabiiator, are controlied by the pikt with a centrie mounted contml stick. The

nose wheel is stserabîe for ground control. The nose gear steeiiig and brakes will be disaisseci

in Section 3.1.

14 Transport Canaâa Involvement

Before any aircraft can be fiorni, t must first be given a Certificate of Aimorthinesa The

design team was aware of this, so Transport Canada was contacteâ very early in the project,

when the fuli-scale ornithopter was still being designeci. The people at Transport Canada have

been very helpful airoughout the project and have been kept infonned of the progress with the

aircraft. Throughout the design process, Transport Canada has been invohred and ensured that

the design WOU# comply with the neœsary safety requirements. The aircraft was officially

registered and assigned the cal1 letters CGPTR, which are the letten by which the aircraft is

identified.

When it became apparent in the fall of 1998 that the aircraft was very close to its first fiight, the representatii from Transport Canada visbd the hangar, where the aircraft was stored

between tes&, for an inspection. They had seen the aircraft several times before, so this

inspection was mainly a fonality. They were then willing to issue a Special CertiFiite of

Airworthiness for C-GPTR.

1.5 Testing Locrition

The initial tests of the omithopbr in 1996 were (no foward motion) flapping bsts.

These boak place in the Air Cushion Vehicle dome at the lnstitute for Aerospaœ Studies. The subsequent taxi bsts in 1996 were conducteci at Toronto's Downsview Airport, which is a fomr

Canadian Forœs base and the location of the de Havilbnd plant. All of the 1996 tests and the

initial static flapping tests of 1997 (in the ACV dome) are discussed in Refetence 10. Sinœ the

conclusion of Mehler's worlr there were further sedes of tests in 1997 and in 1998. All of these

tests wem carried out at Downsview and are the subject of this thesis. Sorne of these are static

fbpping , but most wwe taxi tests. The uNmate goal of these taxi tests has kena "crow hopwfor

the ornithopter. A cmw hop is a very short flight, followed by an immediate landing on the same

ninway. For the orniaiopter, the cmw hop should be long enough to inchde two full cycles of the

wings, b prove sustained fliht, and the landing should be by choiœ.

There are twa runways at Downsview. The main runway, calleâ 15/33, is 7000 feet bng

and is used primarily by de Havilland for their newly buit aircraft. Student pilots and a few othan

also use it. In general, it sees very little traffic. The other runway is no longer acüve because it is

only 2500 feet long; it was shortened significantly when Allen Road was buik alongside

Downsview. Throughout this document, it is refemû to as the ?axiwayn.

The Certificate of Airworaiiness is 'Special" because the ornithopter is experimental, so

there are several limitations imposed on its operation. The most important is that the aircraft can

not be fkwn omr any buiit up area. Ideally, this would mean testing at an airport in a niml area;

however, Downsview Airport is locateâ in a very buitt up area. This location is prderabie for tesüng because of its proximity to the Asrospaœ lnstihite and b the team rnernbets homes.

Relocating the testing elsewhere wouid be logistically and financialîy difî~cult.Transport Canada

has given permission for COPTR's fia fligM at Domisview, under the strkt provis0 that the

air& does not bave the confines of the airport This means that the ai- must bnd on oie same ninway as it departs hm. Therefom, the acceleration up to takdw, rotation, flight, landing and slowing to a stop must al1 take place within the îength of the runway. This distance limitation has had an irrffuenœ on the demlopment of the airctaft, as will be shown in Chapders 7 and 8. 1.6 Pikt Bac@mund

The pilot for the ornithopter prow hss been Patricia JoneçBowman. Ms. JomeBowman

EB very experienced. having bgged 2300 houm of fliiht time, 2100 of which are as pibtin-

command. She has fbwn a iarge vam of malRwed whg aiicran, mostfv single engine, but

absome muhngine. 500 of her hours were log@ am in float planes as a bush pilot. She has

a commercial pilot's license (number C-097314) wilh a dass 2 inotnidoh rafing, IFR nüng and a

Singb and Mulo Engine. Land and Sm' rdng. hrextensive pibting experience is not her only

asset as an omithopkr pilot she also weighs only 93 pounds.

In testing the omithopter, Ms. Jones-Bowman has had to cal1 on al1 of her experience and

then some. Pibting the ornithopber is anything but easy whik 1 is on the ground. Once in the air,

the flapping wings will cause the aircraft to heave a Iimited amount. The degm of this motion

was calailated and a simulator at the University of Tomto pcograrnmeû accorâingly. Mer being

subpckâ to this motion, Ms. Jones-Bowrnan declared it acwptable. When the aircraft is on the

ground, however, ground contact issues make the mowment a much harsher one. To make

matters more dinicult, the movernent is not a regular, periodic motion, but almost chaoüc. Ms.

Jones-Bowman has described taxihg the omithopter as, at times, "like fiying in exberne turbulence". One of the main devebpment issues with the omithopter, if not h main issue, has

been reducing this motion in the takeoff run. ft is more than a amfort issue for the pilot; it is

essential to behg able to pilot the aircraft to a successful takeoff. The shaky cockpit environment

means that al1 of the ordhary indicators that a pilot WOU# use to identify the attitude of the aircraft, such as the distance behiveen the horizon and the top of the instrument panel, are wmpromised.

The constant shaking rnakes it difficult for the pilot to Md the conbol stick at a precise position

and alsa rneans that she has no inhennt feel for the stabaador position, as slie would in an ordinary airdThese dewbpment issues wül be discussed thrwghout this thesis. Ahugh 1

is of iiicornfort to the pilot, it shouid be mted that almost al1 hW& aircraft have been dinicuît to fiy. The relationship between the pibt and the design team has been crucial in Mngthe ornithopter and trying ta aaiieve the historic first flight. The designers have a thorough understanding of the thaory behbid what wil make the ornithopter sucœssful, but they lad< tho familiaiity with acbially fiying an aircraft and what it feds like to be inside. At the same time, the pilot has the flight expeciance. but needs the input frorn the designers to help in detenining a course of action. The two parties are equally important b success. As such, it is important that they be abb to communicate with each omr. The pilot must be receptive to the suggestions of the enginsers and the engineen must try to understand the pilots point of view.

When developing a totally unique ai- such as the ornithopter, the test procedurs employed must be very deiiberate. It cannot sirnply be taken out of the hangar and Rown. If fiapping wing flight were that simple, it would have been achieved a long time ago. To try to make the aircnR do too much, too won, would be a dangerous situation and cauld put üm pibYs life in danger. Sinœ nothing was known about the behaviour and handling of an ornithopter on aie ground More 1996, each test W a smll step fornard and every time the air- is taken out of the hangar, sornething new is ieamed. It is criocal that everyone on the team, the pibt and the entire gmund CM, ôe aware of what is intended for each test and that any member of the team can bring the test to a stop if they notice ciomething wrong. Over the three seasons of testhg, the test procedure has evohred into one which meets these goals, whik at the same tirne albwing for progress toward eventual flight

Prior to each day of Wngthe goals for that day are disaissed and agreed upon by the pilot and ground aew. To detemine these goals and what steps should be taken to achieve thern, the data and videos from the previous te& am reviewed. These discussions have equal input from the ground aew and the pibt busel requim the experiencct and training of booi.

Onœ the procedum for the next test is establirrhed and the ai- is reaây, the barn wab for a weather opportunity. The ornithopter is v8ry semitive b cross winds, so the wind must be veq

light and aligned with the runway for the testing to proœed. The pilot checks the uveather upda@s

at Buttonville Airport and Lester 8. Pearson International Airport and uses the wind

rneasurememts over the past sereral hours along, with the pmdicbms, to decida l testing will be

on for that moming. The tests are geriemlly carned out at dawn so that the winds will be as ligM

as possible.

On the day the tesüng is to take place the ground crew mets at the hangar to prepare the

aircraft. The calibmtion of the onboard instruments is compîeted, as demibeâ in Section 2.3, and

al1 of the batbries an plugged in to make sure mat they am fully charged. Once the pibt and

oaier crew members anive, a pre-test briefing is held. This meeting is to ensure that everyone in

the gmund mwis aware of what will be happening in that day's tes$ and to detemine more

precisely the exad pmcedure for that day. The aimis then rolled out of the hangar and the

pilot does her walk around. Then she gets in the aircraft and starts to get ready while it is rolled

out onto the apron. Once on the apron, the final checklist is run through. This indudes starting the

data acquisition system and the engine, a radio check, anning the BaY*tic Recowry System ad

securing the nose cone on the front of the aiW.

During a test, there are two chase cars drNing along with the ornithopter. Thchief fieid engineer drives one, staying sligMly attead of the ornithopter. From this car, sameone is communicaüng with Re pikt on a twIway radio. The pilot radios back her cummt speed, fbpping fmquency and stick control position. The other car is beside the ornithopter and has one of the ground crew rnembers with a vide0 camera recording the test. The grounâ aew is in constant communication with the pibt so they are awam what is happening and can radio to her

if a different stick position is desired or if the test needs to be terrninated because of some probîern.

Afkr the testing is completed for the day, the aircraft is mlied back to the hangar where oie post calibration is completed. Then the grwnd ann and pibt discuss îhe day's events and detemine a preliminary course of adion for aie next bsts and whether the aidneeds to be repaiied or rnodM. The cycle is then repeateâ b-re the next day of testing with the data Ming ieducd and sîudieâ and the videos being revieweâ by al1 the membs of the team. This testhg procedure has sen& the team wdl up b this point in the program, which has bmdoser than anyone in history to achieving pibted flappmg wing fiight. This pmcedum will continue to be followed until a sucœssful flight and, under no circumstanœs, will the pilot or anyone else be put in any danger. There is an extensive data acquisition system onboard the fuli-scale omithopter.

Throughout the development of the omîthopter, the data acquisition system has been an

important tool. The data wllected serves two main purpases: to help the team get doser to the

ulümate goal of fliM; and it provides a weatth of valuable information on the performance of a

completely nm type of airdThe data acquisiion systern is a testament to the experimental

research aspect of the omithopter. Attt~oughthe goal of the propct is to aehieve flight, it is equalty

important ta the tearn that data be colkbâ during the tests.

2.1 Hardwaiie

The data acquisition hardware and original instruments are âescribed in Reference 10. To summarize, the data acquisition unit is a NetDAQ 264s by Ftuke Eîetdronics. The NetDAQ, which processes the data from the various instnrments onboard, is connected to a notebook computer with a network cabie. The computer mrdsthe data on its hard drive for subseguent processing. In 1996, tttere were 16 sets of sûain gauges in the wings to measure the bending and hvisting mornerits. There were four to measure bending and four to measure twisting in each outer panel, at four different locations along the span. In addition to the mingauges in the wings, there was one on each pylon, a frequency meter to mord thet fiapping frequency and a cycle tngger. The cycle tngger r%caids when the œnûe section is at the bottom of ib stroke, meaning the wings are at th& maximum dihedral angle.

Unfoitunately, some of the sets of mingauges œased to funetion pmperfy. However, this meant that they cou# be disconneded and the availabk NetDAQ channels used for new instruments. Before tests were resumed in 1997, instruments were added to albw for recording the pibt's conW inputs and the rasponse of the omithopter. These new instruments included two potmtiometers on the antrol stick to meaaure the stabihtor and nidder inputs, a potentiometer to masure the th- input, a pressure transducer to meesum air speed, a üiemocouple to record the cylinâer head temperature and an angle of a- meder. The angle of attack meter is mounted on the staboard outRgger at the bottom of the vertical link As ahown in Figure 2.1, it consists of a wather vane device, which is free to rotate in the X-Z plane, con- to a pottmliomster at its tuming as.Som of these new instruments were instalîeâ More the tesang starteâ in 1997, while others were instalkd as the besting progressai. The chmnology of when the naw instnrmem were added wÎY bemme dear in Chapter 4. mer changes to the data acquisition systern in 1997 were to change the cyde bgger to a mechanical deviœ and changing the frequency meter in an attempt to make it function property. The data collecbed in 1997 is discussed in Chapter 5.

Figure 2.1 :Angle of Aî!ack Meter

As testing resumed in 1998, it was found that more of the sets of $train gauges had stopped working property. Consquentiy, three of them were disconnectecl to up the channels for a new 3-axis accelerometer. The other work on the data acquisition system prior to

1998 was to replace the pressure tranducer (as discussed in Section 6.3) and to continue working on aie frequency mbr. By the conclusion of the 1998 tests, the frequency meter fmally worked properly. The author is lwking fornard to taking nifl advantage d mat instrument in 1999. The number of funcbning strain gauge channels has now diminished to the point where very litlle goad data is being colleded from the wings. tf it is deaded thpt sorne of these ndto be mpbced, that will be on, of the adMies barntdng in 1099. tt is quite a delicate operation to replace these strain gauges because they am attached dimcüy to aie spar and covemd by the wing CoMmg fabnc. The data collected frorn the strah gauges up to ihis point has btwn very useful, so it rnight be prudent to replace them. However, the data has also been faidy consistent, so it may be deciûed that the risk of damaging the spar is too gmat and the effort would be best dire- elsewhere because aie future data is likely to be similar to past data.

2.2 $0-rie

The software used for data acquisition is the NetDAQ software by Fluke Eledronia. This is a Windows based package devebped by Fluke foc use with their data acquisition unb. It albws for full control of the 20 analog channels in the NetûAQ. Using nie software, the user can tum each channel on or off, specify the type of data bemg iecorded (i.e.: DC Vol$, Ohms etc.) and the range of the signal. It ais0 has a choiœ of sampling rate and data file types. To maximue the amwnt of data riecordeci on the ornithopter, the data is recordeci at the fast setüng in a binary file mode. The data is later converteci to an ASCII file format (comma separated values) using a utility in the NetûAQ sufhvare. Another important featum of the software is that there are two rnethods of starting the data collecoon. When (he play button in the software is pressed. data collection will begin immediately if the "Trigger Typenis set et "lntewar. f the TrQger Type is set to 'ExtemaIn, a switch can be wired into the back of the NetOAQ and data collection will begin when the switch is dosed. The latter method is used in the omithopbr so that the pilot has control over the data colledion. This ensures that the data files do not become unmanag8ably large. The NetDAQ software is rich in features, as documented in Referenœ 11, but aie above rnentioned items are the primary ones of interest for this work. The data reductkm software is MiuosoR Excd 97. 2.3 Cklibretkn pr#.duir,

Before each series of lmb, data is recorded which is used to calibrate the instruments for mat day of Mng.The calibration p&um for th mingauges W to record data with the wings level at four dinerent loads. The fi& data is recordeci with no weight on the wings. Then three dilietant sets of data are recordeci; eadi with a dinerent known weight hung on each wing tip.

Finally, another set of data is recordeci with no weight on the wing tips. The first and last sets of data are averageâ to find a "zeronreading. it is not a ûue zero because of the weight of the wings, but it is considerd to be zero. This procedure is completed before and atler a series of tests. The mubfrom both caiibrations are avemged to get aie rem mading and mingauge constant for that day's data. In general, the mingauge constant does not change much, but the zero may fluctuate a bit.

The basic idea of this strain gauge calibrath has not changeci dunng the devebpment of the ornithopter. However, the original procedure invaiveci mcording al1 of the calibration data in one file. This producd a file with six distinct regions in it: one for each dinerant weight and a zero reading before each weight When reduœd, the file was examined graphically to detemine the six ranges to be averaged. This was time consuming and it could be dficult to find a good stable mgion of the data because the data was mcorded continuously hile the weights were hung on the wing tips and rernoved. For 1998, the procedure was modifieâ slightty so that the calibration is recordeci in fiw separate files: one at zero load, one at each of the thme wights and one at zero again. The averaging is much easier and faster wiai mis new sysdem because the entire data file can be avemged.

The other calibraüon carried out is that for the potentiometers. For each potentiometer, data is recorded at each exberne of the range of motion. As wilh the new strain gauge calibraüon procedure, the data for each point is recorâed in a separab file. The potmtiometer signal is assurnecl to be linear wiîh the angular input. ît was disoovered that the signal from the podentiornetier varies with the excitation voitage, which is directty hmthe onbard battery. The onboard battery is a t2 Voit gel œll, which is not getüng any charge from the engine, sa its voltage is constantiy dmpping during a test secwion. The NetDAQ mrds the voltage from the battery, so it is used to corred the signal from aie potentiometers. The signal from each potentiometer is divided by the excitation voitage at that moment and muiüplied by 12. The result of this correcüon is aiat the pobntiorneter signal for a given mput is reasonably constant.

2.4 Macdkcllon and duc-n pdure Data is coliected in a file that has a four digit code for the date, the word fhp to indicate that it is a flapping test, a number b indicate what test series it k for that day and a letber. For example. the file OQl9fiaplbcontains the data for the Septamber 19" flapping tests. tt was the first series of tests that day and this is the second data file in that series. The data file name is changed Mer hrvo or thme tests so that if a problem arises with the date acquisition system it will not affect that data already recorâed. The year of the data is kept track of by the diredory name.

On the notebook which collscts the data, only the current yeats data is stored. if aie O# data files ever get mixed up, they can be easily so- out by looking at the date stamp recordeci by the

NetDAQ at the beginning of the file. The calibntion files for a given day are stored in the same directory as the test data. The word "prie"or "po* is used to indicate that it is a calibration file and wheaier it was taken More or after the tests. The sarne number is used in aie calibration file name as the test file name (Le.: one in the example gkm) and the letters a thmugh f are used to distinguish the different calibdon data.

Before going onto the runway for a test, the filename for the data is set and the play button is presssi in the data acquisition software. Then the computer is put into the nose of the air& and the nose cone is secumd in place. lrnmediately tefore statting a test, the pilot flips the data switch on and data starts to be recarded. At the end of the test nin the pilot bms the data switch off. RATA Mm 8Vm 16

As rnentioned, aie data is recorded in a biriary format and eonverteâ to ASCII later. The

ASCII files produω by the conversion can be opened di- by Excel. This powerful

spreadsheet program can handie the someb'mes very large data files qub easily. A number of templates and macms have been dewloped to speed the reduûion. Ushg the calibration values for that day. the data is converteci to uuseful units (such as Ibot-pounds for the bending moments) and plottd. These plots can be found in Appendices A îhrough D.

2.6 Video S-m

There are two srnall video cameras onboard the ornithopter. One of them is rnounted on top of the vertical tail, pointing at the port wing to mord the twisting of the wing as it fiaps. The other is rnounW in the thorax koking dom at the drive train. Of panicubc inberest for mis second camera is stage zero of the drive train because it had been gMng probiems in 1996 and 1997.

These cameas are conneded to a switch box in the cockpit so that the pilot cm tum them on and select which camera will record for that test. The 8mm-video recorder is sbapped into the nose of the aircraft and has to be staited by one of the gmund crew before putting on the nose cone.

Although they am not onboard the ornithopter, the extemal video cameras and stiH cameras shouid still km cansidered part of the data colledion system. At each test, there is akays a SupeNHS viâeo camera being operated by one of the ground crew and, if people are avaiiabîe, a three CCD digital video camera is used as well. Also, for the high-speed taxi tests,

David Stringer, a professional videographer, is on hand to record the events with his Betacam.

Dr. DeLaurier is the chief still photographer for the barn.

2.6 NoiiseProbIenrs

There have been ongoing pmblems with electrornagnetic interference on the ornithopter.

The source is ôelived to be the engine ignition system. This noise has caused problems with some of the instrumentation and some of the data collection. During 1997 very little was recordecl from the onboard cameras because of the elecbomagnstic nom. A gmt deal of time and effort was expemded trying to tmubleshoot the video system, with libenefit During the off-season, the entire camera system was rewired with higher quality shielded cables and the shields wece grounded to the fmme of the aid.At the start of the 1998 season, the cameras were working and video was racorded from them for the first féw tests. Hmver. at some point they started to cut out again. possibly because of radio interfaremce. Sinœ besting was going on at the the and the team could not afford to lose any pobntial tedng days in order to debug the video system, the problem was ignored and the onboard cameras were not used. For the tests der Odot>er 12, 1998, a small 8mm-video camera was strapped into aie cockpit just abow aie pibfs left shoulder. it was positioned in such a way an to show al1 the instruments and some of the ground outside. This carnera provided some excellent footage. One of ths t~sprior to starting testhg in 1999 will be to get the onboard video system working and moue the carnera fmthe thorax to the cockpit, because the probhms with stage zero of the drive train appear to have been sohred.

There have beem problems with the data frorn the pressure transducer, used for recording air speed, because of this noise. Ttw first pressure traneducer, instalkd in 1997. had a vefy small output signai, on the order of lx104 Vol$ for the speeds at which the ornithopter is tested. In

1998 it was replaœd with a more sensitive one, which had an amplioutput signal. The new pressure transduœr ha$ an output on the orcier of 2.5 Vob for the same spseds. The piessure transducers and their calibrahion are discussed in Sections 6.3.1 and 6.3.2.

The other vidim of the electromagmtic noim has been the f'requency meter- The freguency mebr has undergone an exte~nskedavebpment and several design changes.

Although there were design issues wi(h the eadiir fmquency meters, eecbomagnetic noise was the uttirnate cause of their failures. As mentioned earlir, the only tests for which ttiere was a consisteritiy fundionhg frequency meter mmr on Nowmber 8, 1998. This insbument is aitical in the ornithopter, as will be discussed in Chapter 5. Af'ter the 1996 test season, a substantial wing npair was required as documented in

Referenœ 10. In addition to thc3 whg mpair. other major changes mfm made to the aircraft to improve the gmund handling. In fa4 the ornithopter which took to the runway in 1997 had many differences from the 1996 version. These changes am discussed in References 6 and 10, but this chapter is intenâed to provide more deCail.

3.1 New Stœring and Bmkhig Syaûms In 1996, the nose whegl steering was coupîeâ wîth the nidder movement on the control stick. A left or right movement of the stick would defled the Ndder arid turn the nose wheel. The pilot was unsatisfied wilti îhis arrangement, so it was changexi before testing man 1997. The new system, which is cumntly in use, still has the rudder controlled by kit or right movement of the stick, but the nose wheel is conttolled with foot pedals. The pedals are rigidiy connected b each other and pivot about a point at the centûeline of the aircraft, so as the left foot moves forward, the right fwt mu& move aft. The pedals am directly connected to a control hom, which rotates witfi the pedals. Coming off each end of the control hom is a cable, which ans forward to a pulley, amund aie pulley, and back to another control hom that is attached ta the top of the nose gear. The stsering is arranged with the pulieys so that when the left foot is pushed fonnrard, the aircraff will stwr left. The control hom on the pedals has four diffbrent connection points for the steering cables to allow for adjustment of the steering sensitivity.

The brakes were modîfiied at the same tirne. The 1996 system utilized drum brakes on the main wheels, acaiated by cables. The pilot input for the brakes was through foot pedals hinged at the floar. A desire b improve the baking pehnnance and the change b the &-ring system necessitabd a change to the brakes, which are now hydraulic disc brakes on the main wheels.

The hydraulic fluid used is automatic transmission fkiiâ. The sysliem katureg independent master cylinders for the Mt and right whee(s, so the pilot can empky braûe-stmring. These masbr cylinders are incorporated into the stwring mals w that the pilot can push on them wiai her heels. The $teering is don, pfimarily wi(h her bes. Figure 3.1 shows the sdeering and braking arrangement.

Figun 3.1 : Steering Pedds (Note the hed mes) (- by J.D. ~aawkr)

3.2 NewUndemni.ge

After the testing in 1996, it was decided that a taller, wider undercarnage was needed, for two reasans. First, the ornithopter dispiayed a tendency to tip in even a slight cross wind, so the undercaniage needed to be wider to combat this tendency. Second, the wing tips came alarmingiy dose to the ground at the bottom of their stroke. PJaiough the wing tips never touched the ground, more distance betvueen the wing tips and the ground was desired for safety.

Grove Aidin California, a# same Company that made üte original main landing gear, made tfte he one. The r#w gear was one bot talier and thm feet wbrthan the original. tt also incorporated larger diamter wheeb than bsfore, which have the disk brakes mentioned in

Section 3.1.

The new fanding gear attadid to aie fuselage in much the same manner as the O# one. and in the same location. It did, howewr, neassilate a major change to the nose gear. The nose gear abhad to be talier ta accammodab the larger main gear. This was accomplished by exbnding the nose gear stnR and supporting it wiai 3 guy wim as show in Figum 3.2.

Rgun 3.2: Nose Gear and Support Wires (~#aographby J.O. ~e~auler)

3.3 NewZem Sbge

From the 1996 data and videos, it was deterrnined that the belt drive from the engine to the first stage of the drive module (the "zero me-s siipping. The evidenœ of this was that the down stmke of the wings was taking up to Nice as long as the upstroke, and that the plots of bending and torsion moment in the wings had thrw distinct bumps on the down stroke. The reason a belt ha$ been used ominally was to allow for a clutch, which auld be used to engage or disengage the wings from the drive. This is desirable in case of an engine out sibation mile the wings are in aie down position. ît was found that even with a direct drive, the wings cauld back drive the engine and retum to a stable positive dihedal angle, unless the engine seizeâ.

Amr discussions wiîh the pilot, it was decided that the Ekelihood of a seued engine is bss d a risk than a siiiping belin the drive train. The solution was to change the bdt and pulky stage to a chain and spmcke~tstage. The sprockets were sekW to provide the same gear ratio as the bett and pulleys. An idler sprocket was incorparatecl as a chah bnsioner b eliminab sîadt in the chain. The arrangement is show in Figure 3.3.

Figure 3.3: Zero Stage Chain and Sprocket Drive by J.O. oecaurler) 4 1997 Tusts and IlllodMkaüom

The 1997 test program began with a sefies of statk fhpping tests, whidi wmmducteâ

in the ACV Dom at UTIAS. The iesults of these tests have ben dhssed by ~ehler'~,along

with the 1996 tests. AMr the &tic flapping tests, the aircraft was moved to the taxi test kation

at Oownsview Airport. The tests that wem conducbed in 1997 from the time the aircraft was

moved and the îests in 1998 are the subject of mis thesis. This chapter will aver the 1997 taxi

tests and the devekpment of aie airuaft which took place during that tirne.

4.1 1997TeitRogmm

The primary goai of the 1997 test program was to amplete a 'cmw hopn (Defineci in

Section 1.5) on the main ninway at Domisview, which is a uucial step towards full Riht The

specifi tasks Mingup ta this were as follows:

a Assess the new hydraulic brakes and nose gear steering.

a Continue leaming how the aircraft handles on the ground.

Condud taxi tests at incrementally higher speeds than 1996, when the maximum speed was 22 mph. first goal was 30 mph, then 40 mph and finally 50 mph befom attempting a crow hop.

a As the taxi Mals progress, develop a takeM drategy . A sacondary goal was to get the onboard video system to work pqely. The team was

well aware of specific itiems on the aircraft which needed to be watched closely afbr the

experiences of 1996. One of the primary concems was for the tratniling-edge dips because they

had demonsbated a tendancy b corne off during the taxi tests. Therefore, the clips on neach wing

wem counted after every test to make sure they were al1 süll there. fhe team was also bok-mgfor

smoolher wing operation because the zero stage belt had been replaced with a chan, and the

perfomanœ d the wing tip modificab'ons would be manitomcl. Other Lmsto in- afbr each test session were the driva moâub bol$ (for tightn8ss) and the thorax rtiuctum. Table 4.1 lists the tests conducteâ from August 1, 1BQ7 to Septamber 16, 1997. Note that the "Apron" is the pamâ area immediateîy outside the hangar and mat th hangar itsel was large enough for some of the static flapping tests.

Run #

Apron

Main Taxi up b 22 mph, top Runway speeâ mached in 1996. Go toahigherapeieâif commabb.

Hangar Yes

Main Runway Apron Static flapping a. ide. tcr test z=-wmodrficabons Spring sliffness is nryyi. Zero No stageperformed~l. I-- Yes

- - Hangar Yes

Main Runway Hangar

Hangar Stsilicfla#Pingtotestnew engine mouit Date I~unt)~odlon 1 PutPo- 1 R-lt No - Yes

------sept Main 40mptlreechedm!3ityorirun Yes 1 Runway 2.Run3wascutshort beeause dabarigng noise. ImpeJdhn~no pioblems,so~n4~ ~.Thenwi~sdoQped aam-ddamagie to~=~=supCIorbng stnidue. - Hangar Tests to cfmck the PmssWeT-aid Yes instdlalioridtwnew ~tomeaswe instnments. th- input chedc out. - sept Taxiway Taxiupto4ûmphwithttie Reaehed3ûrnph,kRnoee Yes 15 stkkshghtîyhirtherback HkieelstillWngaIdd ttiailm-1. &use. - _1 sept Taxiway As abare, but mth the stick Reached 40 mph and air#dt Yes 15 aîiifwa#rbedc aatdtobowiee. ------Sept 3 Taxiway Asabcle,kituiiththeirck Yes 15 inbetweeritheposioons used in nins 1 and 2. - Sept 1,2 Main Trytoreaeatetk!j0cond Thefirst mn ~iescut short Yes 16 Runway runfruntW1S"andhdd because of a radio prohiem. In on through the bancest0 the second nin, txnincing try to get &the gmnd. statedat35aidcauldr#1be contmw. Testmninded vuhen a wing dip came M. . ------Table H:Camplete list of 1997 test&m August 1 thrwgti Septmbsr 16.

Insteaâ of disaissing al1 of the modilications made to the ornithopter during these tests in a chronobgical manner, the following sections detail the devebprnent of the aimon a systern basis. For exampie, Setcüon 4.2 deah with the pmbierns found with h3zero stage of the drive train and the changes made to try to sobe them, whiie Section 4.3 describes the mpairs and modifications that were mquired for the wing. Many of the adiviin these separade sections happeneci at the same time. As menhioneâ in Chapter 3, the zero stage was changed from a beit and pulley system to a chain and sprockets after 1996. This change to a chah and apmcket system had pecfomed quite well in the sWc flapping tests, but had yet 10 be testecl durhg a taxi test. In the first taxi tests on

August 7. then, wsrs no probiems mth the drhre train. Aithough no data was collected to ver* the wing perionanœ, the motion appeamd to be much smoother and the down stioke was taking approxitnately the sarne amount of the as the upstmke, thus indicating that slippage (or skipping) was not occurring.

In the next test on August 8, hower, the zero stage chah jurnped off the sprockets just afbr the pilot had moved the throttla fornard. lt was thought that perhaps the pikt was accelerating too aggressively. However, even if she does acceletate aggressively, the chah should not jump off the sprockets. Three modifications wem made to the zero stage so that the chah woukî stay on:

1) The spring in the tensioner was changed for a strffer one so that the chain wouM be ûghter.

2) Aluminum chain guards were added dose to the sprockets at the top and bottom of the mge. These wece intendeci to keep the chah on the sprockets if it starteci to corne off again.

3) A bearing was added to the emd of the engine drive shaf?. This shaR is extendd out from the^ engine and had no support, so it was essenüally cantilevereâ. The bearing, which was boited to the drive moduie, would support the end of the shaft and reduce the radial movement of the lower sprocket.

The next fgw tests were conducteci to evaluate these modifications, shown in Figure 4.1.

August 15 was a static flapping test to check the zero stage perfamance. No data was collected for these tests because the engine was MIvar hcreasd hmidle. The chan guards were not in plaœ so that the relative mowment between the zero stage spmckets could be observed. The movement of the lower spmcket was gmatiy mduœd, as was the action of the tensiawr. After a

1O minute nin, the engine was shut dawn and the zero stage was examined. R was quite wann uimparsd to other cwnponents d the driva train. suggesting that the hensioner was too ttght The spring was modMto ducethe tension slihlfy and the chain guards were installed. On August

16, anoaier staac flapping test at ale ckmonstrated that the system was working well. The movernent of lensioner was more than the day before, but stil less than it was onginally. None of the components seemed bo be ovenieating.

On August 18. more static flapping tests wre conduded as a final check on the zero stage before going badc to the runway. These tests wem at fiapping fmquencies up to 1.O Hz to fully test the system. Unfodunately, the bearing in the iâler sprocket had a pbstic component, which melted under the higher bad. This bearing was replaced wfi an al1 steel ove and the test repealed on August 20. It was ahnoted that although the bearing on the end of the drive shaft limiteâ the radial motion of the bwer spmcket, them was dl1 a substanoPI amount of relative motion betwem tt# zero stage sprockets; a total of about Ycindi. The conœm was that the drive shaft exbnsion was slaing in and out dthe beanng, which cwld damage the bearing andlor the end of the drive shaft. The inte- betwem the drive diaft eutension and the haring was lubricated with a MolyWenum Disulphide grnase called 'Moty-Slipw.

Finalîy, on August 25, the airuat was ready for more taxi tests after this trwbla shoothg of the zem stage. However, just as on August 8, as soon as the airciaft started to roll, the cham fell off. This time the diain hdopened at aie masbr link. Mough the master link itself was not damaged (it was found on the ground), one of the chain's rotîers did have a fraduiie in it. It was belied that aie km and aft motion of the lower sprocket, as noted earlier, was aie primary reason for the conünued difficulaes with the zero stage chah However, it was unknown what was adually causing (his motion. Sereral staüc fiapping tests mm, conduded bber mat day and the relative motion of diffemnt mmponents wre measured with a dial gauge (i.e.: drive module to îhorax). Atter several of aiese tests, no single cornpanent cou# be id8ntiTied as the cause of the relative motion between the upper and lower spmckets. Howwr, aie engine was mounbed ta aie thorax with rubber between aie steel mwnt and aie thorax frame. This was inbended to provide shock absorption and isolate the ainraft stnicture from the engine vibrations The cydic load on the engine was causmg it to rock back and forth on aiese mounts. Sinœ the engine itself is some distance above the mounts, a small movement at the mounting point translates to a s$rificant mowment at the drive shaR. This rocking resulbed in a fore and aft motion d the bwer sprocket, which is attached to the drive shaft The rocking motion was observeci to be mom in the aft diredion than foiward. A temporary solution was to diange the mar engine mounts so that them was hard Teilon behniwn the mount and the thorax. Static flapping up O 1.O Hz on August

26 showed that the relative motion betwwn the zero stage sprockets haâ beem reduœâ and it was decided to prooeed with further taud tests.

This modification to the engine mounts was by no means a permanent solution. lt was, however, suniCient to alkw taxi ûsting to continue, and them were no hrrther problems. The deam maked Ihat it wwld not be aeceptaMe to atbmpt full flight m this condition busea zero stage

failure cou# be disastrous. A more permanent solution would be sought in the off season.

4.3 Wing min

Priw to the 1997 tesüng. a substanüal wing repair was compîeted on both the ldt and right

wing tip, as documented by ~ohkr''. Hnmtver, before taxi tests couid begin, another minor

repair was requirsd. The innemost riblat on each outer panel (at the driving hinge) had started to

pull away hmthe Supe&ox, whkh is the rigid mner portion of each panel. They were reattached

by overîapping the joint wilh a piece of thin prywood. These pieces were glued on with 3-hour

epoxy*

This repair held the riblet in pbœ for the early tests, but Mer the bsts on Septernber 1, the

area had becorne damaged again. This time, aie barn riblet itself had cracked abng a diagonal

and the thin plywood panels in the upper and lower surfaces of the wing had started to tear away

hm the Superbox, as sketchai in Figure 4.2. This damage was surprising because the

Superbox is designed to handle al1 of the torsion loads from the wing twisting. The aft portion of the wing is considered to be an aemdynamic fairing. However, a riepair and modification were

clearly indicated by the damage present.

First, the pieœs of plywood that had bwn aiHached in the previous repair were removeci by grinding Wrn away with a Dremel tool. Then the upper and bwer piywood panels were

reattached to the Superbox with cyanoaaylate giue. The bond betwem thme panels and the

Superbox was reinforcd with *ps of fiveounœ fibregîass doth along the ham with the fibms oriented at O and 90 degrees to the pint. The bond between the ribiet and aie Superbox was also

reinforced with fivgounœ fbmglass cloth, but the fibres were oriented at pludminw 45 degm.

A piece of 11321nch plywaod was glwd on top d the fibmbss, both to repair the crack in Ihe

nblet and to minforce the bond betwieen the ribiet and ttie Superbox. The fibreglass and ptywood were al1 glued on with a 24-hour epoxy. This mpair is sketched in Fium 4.3. Figura 4.2: Wing Damage on Outer Panel at Onving Hinge. (sketch by J.D. ~elaurki)

Figura 4.3: Reinforcement of RiMet to Superbox Attachment (seleh by J.D. ~e~aurier)

As mentioned, the cause of this wing damage was a rnystery. Subsequent to the 1997 testing, an undergraduate thedawas compW which rnoâelled the shearîiexing wmg in C

MAS.a finite alement prognm. The resub showed that a shearfiehg wing shoufd ideally have inner Roating panels on the top and bottom, as opposeci to just on the top as is the case for the ornithopter's wing. Such a modification is not essential, and it would basically amount to rebuilâing the wing. Therem, the wings still have an inner fioaüng panel on the top only, but if another set of wings wm built, îhey would most likely have floating panels on the top and

bottom.

The tmiling4ge dips continuad to be a source of conami in 1997. After the tmts on

September la,inspectbn of the clips back in the hangar ieweled mat Ihe sbdh clip in from the wing tip on the rîght wing had corne bose. The seventh clip in was damaged in that it had bent open slightly. Both clips wen remowâ and reattached with a thick cyanoacrylate glue called

'Powergel". These dips were not among those which mwe reglued during the wing tip repair of eady 1997.

The repaired clips bMup during the tests on September 15", but during the second test

on September 16", a dip mis seen to mme off, which brought an irnmediate stop to the test The clip which had come off bimed out to be the sndh one in fmm the tight wing tip agah. The ai- was taken back to aie hangar with the intention of reaüaching the clip and continuing the taxi tests. At the same time, however, other probiems with the thorax structure (see Section 4.4) were noticeci. The combination of aiese probiems and the imminent departure of Dr. DeLaurier for his sabbatical rneant that the team decided to suspend testing for the season. The issue of clip attachment was addressed in the off season and is detailed in Section 6.4

4.4 ThotaxSbructum

The thorax stnicture performed well thmugh the static bsb and low speed taxi tests and remained unmodified from its original design. Whiie it was not subjecbed to any serious bads from the landing gear, the bads frorn fîapping are substantial, paitiailarly for the oMggers. On some of Via testsl particubriy on Septeinber la, the main wtteek WR kaving the ground by about six inches, but there was no obsenmd damage sustained by the ouûiggers or thorax. On

September 15", however, We aimraft wemt (hrough several niY bounces, with al1 lhrw wtreels leavng the ground when the wings wem on the down stroke, but King the ground quite forcefully when the wings went airough the upshke. As the aimafl was b&~pushed out for fuither taxi tests on Septetnber 16'. the ground crew noted some strange noises from the thorax. Inspection of the thorax revealed that several rivets had sheared, the strange noises being the rivet bodies raffling amnd inside the tubes.

Sinœ the team was assembled and everything was ready for a taxi test, inciuding the weather, it was decided b mvethe aimait to th side of the taxiway and repair the damage immediately.

The hales where aie rivets had gone thmugh aie guseb no bnger Iined up with the holes in the tubes, so new hoies wem dnlled. In some cases the holes almost lined up, so they were simply drilled out to a larger size and a 5/32-inch diameter rivet was used instead of the otiginal

118-inch diameter. Riece mm, also several missing rivets in the top part of the thorax structure, which provides lateral bdngfor the drive moduls. These rivets were replaceci without having to drill new hoies. All of the new rivets were stronger stainiess steel, as opposed to the aluminum rivets used originally.

After cornpleting this repair, while the pilot waited patientty in the cockpit, the aircraft was rolled out to the main runway. Two test nins were completed with the intention of recreating the second fun from the day before, but keeping the throttle up for bnger. The bounces on the 15" had been progressively brger, and it appeared that afbr a few more bounces the aircraft would becorne airborne. The first fun was cut short when radio communication faim, and the second nin was knninated when a trailingdge clip came off. When the clip came off, the aircraff was going through a series of large bounces as it had the day before. The aircraft was taken back to the hangar and inspeded. The same problems as had been noticed just befare the tests wre notiœd again. The sheared rivets had allowed the structure to becorne flexible to the extent that the foam fairing on the Ming-edge of the right pylon had a large scrape mark. The mpetition of the rivet failure and the unknown extent of the damage didated that the tesüng shoukl be stopped for the day. it was clear Bat a full inylection of the thorax structure was required, and possibly =me signifiant strengüwniig. In orrkr to alkw for a pmper analysis and design of the thorax, and to address other issues such as the trailing4ge clips, aie 1997 tests were conckided.

4.5 Nose Gear Supporling Stmdum

For the tests on Sep(8mher 1: the pian wes to try b achieve 40 miles per hour on the fimt wn, then 50 on the next if ewrything went smoothîy. An ear(iir study of the takeoff strategy7 suggested that aie pikt shouiâ hold the stick fornard so that the aircraft would stay on the ground until she reabied the takeoff speed of 51 mph. The first run went very well, and 40 mph was easiiy achieueâ. The second fun was cut short because the pilot bard a banging noise.

Inspection of the aircraft mvealed no problems, and it was decided to proceed with the third test.

This tirne, the pibt stopped acceierating at 40 mph because she fett that the nose gear steering was not working praperfy. Frorn outsiâe aie aircraft, it cou# be seen that the rear guy wires had perrnanmtîy slackened. An inspecûon showed that the support sûucture for the nose gear sûut had yieldec(, allowing the strut to bend bacicwards.

The guy wires, as disaissed in Section 3.2, am meant to support the nose gear from lateral and longitudinal movement relative to the fuselage, but they only do so when they are in tension.

During these test runs, the forward stick position resuited in an extreme bad on the nose gear.

Wiai the flappmg driving the nose dom, the tire was cornpressing to the point that the rim was slightly bent. tt was suspecaed Bat the excessive load on the nose gear had yieîded the support structure in a vertical diredion first, which meant that the forward guy wire was no bnger in tension to pmvent the wheel frorn bemg pushed aft. The continueci force of the bouncing and the fridion betweeri the wheel and the runway caused the support structure to yield futther and the nose gear was pushed aft. The stm itself did not berid, just the fuselage tubes to which 1 attaches.

As well as causing darnage to the nose getar support sbuctum, the tests of Ssptember 1* revealeb a fundamental pruôîem with the takeoff strategy. While the nose gear was king forced into the giound, the main wheek mm, Ming off the gmnâ by about six inches. This situation, whm the nose wheel is the only one on the ground, is calied 'Meel bamwing'. Wheel barrowing is a pdentially dangerous situation becau= of the dynarnic instability. WRn oie centre of gmwty so far behind the grourid contact point, the ai- cou# quickty spin 90 degm and end up on its side. At 40 miles per hour, this would happen too quickly for aie pilot to be able to conttol it. tt was decideci that for the next test, a more aft stick position WOU# be used with the hope of avoiding wheel krrowing. This WOU# have the added ben& of reducing the load on the nose wheel.

In repairing the damage, it was most critical to strengthen aie structure against vertical deRcctDn bacause if the structure can wa#tsnd the vertical bad, the guy wires wil prevent the nose wheel from movmg, as the original design intended. Referring to Figures 4.4 and 4.5, the following modifications were made:

The upper gusset plates, Mm 1 in Figure 4.4, were imreased in thickness from 0.020 inches to 0.063 inches. The load from the nose gear is transferred directly into these pieces, and they had failed.

The vertical tubes (item 2), which transfer the bad into the upper plates, were changed from 6061-T6 alurninum to 2024T3 ahminum.

The lower hoaontal tube (im 3) was changed from 6061-T6 akiminum to 4130 -1.

Two new tubes were added, strown in Figure 4.5. These tubes were inlnded to add fore and aft support to aie vertical tubes. Figure 4.4: Items Changed to Sberrgthm Nose Gear Support (Skm by J.O. Wauder)

Figun 4.5: New Tubes Added to Strengthen aie Nose Gear Support (Sketch by J.D. Delaurler)

In addition to these changes, al1 of the riveted joints were reinforcd with VHB tape from

3M, which has very high &mgth in shsat. Also, strongar rteinkss steel rivets were usd. This repair allowed the nose gear structure to wwithstand the subaequent abuse it saw on September

15m and 16'.

4.6 ImtnimenQition

Of the new instniments for 1997, listed in Section 2.1, the mes which were in place krttie finst taxi îests were the potentbmebrs for rneasuririg the ruâder and stabilator inputs and aie angle of attack meter. The thennocouple b mcod the cyEnder hed temperature was added on

August 21: The pressure transduœr b recoid air speed and the potenthmeter to measure the throttle input were added on September 12". All of these imibuments fundioned properly, although them wem some problems wiai ebdrornagmüc noise in the pressure transducer

signal. In spite of this noise, uduldata was obtahed.

The frequency meter was a continuing effort during the 1997 test seam, with little success. The frequemcy meter took its input from an optical sensor in the drive module. The sensor was ciose to a hub in the zero stage. HaIf of the hub was painted white and the oaier half was biack, so that the sensor picked up altemating high and low signais. This was ~onverbedto flapping fmquency by a circuit board behind the instrument panel. After the drive module was opemM, the painted suifaces wwld becorne dirty. Thinking that this was the cause of the probîem, the hub was repainted twice. Each time it was repainted the frequency rneter seemed to work, but oniy bndly. The lad< of a funcüoning frequençy mebr made P dimailt for the pilot to know what the flapping frequmcy was, because the tachomebr signal fiuctuatd wiidly. This probîem is apparent when looking at the data.

The oaier activi which was considered instrumentation worlc was the onboard video system. A number of ideas were tned in an effort to gel the video cameras to wrk with the engine running. The most promising idea was to have a dedicated battery for the video system and use fully shielded cables everywhere. Unfortunately, this was never properiy implemented, so the onboard cameras never worlced in 1997.

4.7 Summrry of 1997 hub

The 1997 season was considemû a success, in spite of the fact that the ornithopder did not fly. The bounoes on Septembr 15" and len weie very enauraging. Refem'ng badc to the goab listed in Sdon4.1, the conclusions can be summarized as follows:

a The nose gear skmring works well.

0 The brakes, while better than before, still leave something to be desired. It was thought that perhaps the brake discs neeâed to "break inn. A gleat deal was leamed about the aiiaafYs gmund handling. The pilot was geüing very accustomeci to tha cockpit environment and even getting used to the bouncing.

40 miles per hour was mched on several occasions, but gang beyond that speed without whwl bamwing or bainMg was dimcuk

The takeoff sûategy was developing. It appeared that them migM be a small window for the stick position which wuid allow the aircraft to accelerate beyond 40 mibper hour.

The video system and frequency meter still nwâed work.

Other conclusions which were drawn:

a The thorax structure and outriggers needed to be repaired and strengthened.

a The trailingdge clip attachment should be more robust.

a In other respects, the wings perfomed very well.

The zero stage required modlcaüon to prevent the chah hmcoming off, or to be changed from a chan to something else.

These items would be attended to in the off season, as discussed in Chapter 6. Data was not colleded for al1 of the tests in Table 4.1, as indicated by the last coiumn in that tabk. Of the data, only that colkbd dunng taxi tests will be discussed hem, as that is the foais of this thesis. Thercfore, the oniy data of significance is from the four taxi tests on

Septernùer la,three on Septernber 15" and two on September 16". The data is d Mded mto two categories for discussion: wing data, which is in Appendk A, and potmtiometer data, which is in

Appendix B. Some portions of the wing data for staüc Rapping, coliected on August 20", are also pmsented in Appenâix A for cornparison purposes The other data which was collededl that is not discussed here, was the cylinder head temperature. This data is not particularly interesting; it simply confimis that the engine did nat overtieat.

5.1 Wing Data

As mentioned in Sedion 2.1, several of the strain gauge channels were disconneded after the 1996 tests. Of the ones which were still conneded, sow of them did not work properîy either.

The channets which did work reliabty WE: the four stations in bending on the right wing, the first station in beriding on the Mt wing and the third station in torsion on the right wing. For reasons expiained in Reference 10, the Mt wing data is not conskfered rieliable. However, it was plotted and compared to the rigM wing and was found ta match reasonably wel in most cases. The torsion data is not discussed hem because, with only one torsion channetl working properfy, there is not Mcient data to draw any condusions. The graphs of right wing torsion are pmented in the appendix for camplefeness.

The most striking aspect of the wing data is the extremeiy high bending moments which were recordeci. The e-ed maximum Ming moment, which was used in designing the wings, was 2318.7 foot-p~unds'~.For several of the runs in Sepbmber, the peak bending moments mrm wdl over 3000 foot-pounds. At fimt glana, mis was quite aiarming. and iead to thoughts that (he original anaîysis used in the wing design was fiawed (A cornputer code calkd tOQI DATA m

FulWig. desciibed in Refennœ 9). It was ahconsidereâ biieffy that the raw data or the caïbration was wrong, but thecie thoughts wem quiçkly disrnissed. A doser inspetcüon to determine the flapping frequency corresponding to these high bending moments rev8aled that mis was prqbably the mason. Figure 5.1 shows a portion of the right wing bending moment data hmthe miid run on September 15". The peak bending moments lor the part show are appmimateiy 3400 foot-pounds. The average fiapping fiwquancy for this sequenœ is 1.3 He&

Bmding moments of this magnitude are corisirftmt whsuch a high Rapping hequency.

I

1-RW ~endrl-RW esndn RW -RW BOMW -~riggor -Arrstmdj I ïigum 5.1 :Mdng Mamerit Data from Third Run ori September 15,1997

Taking into amnt the high fiapping hequenq restores faim in the original anawcal melhods. but these Mingmoments an, ail dihüy higher than p~~.ît is thought that the mason fbr this discriepancy is that the aiMan had not yet reaMits takeoff speed. At bwer speds, there are substantial mgions of stalied flow, which tha original analysis does not fully take into account because the soîution is assumed to be sinusoidal. A current research efbt at the Insütute for Asro!3paa3 Studies is a time rnarctiing anaîysii, whidi should be able to predict the lads at any air spmd. Rambod Larijani is complethg this analysis for his Dodorate thesii

His initial resub show much beüer cornparison with the experimental data.

1-RW Rend Ul -RW Wnd $2 RW Bond #3 -RW Band 14 -~niggar] Figun 5.2: Bending Manent Data from Second Run cm September 1,1997

From Figure 5.1, it is akro interesting to no@ that the air speed has relativeiy Iittle effsct on the positive peak Ming moments. Rie positive peaks are about the same for the portion show; yet the air speed inaeases hm20 miles pet hou 0 37 miles per hour. Compafing

Figure 5.1 with Figure 5.2 conf~nnsthe notion that flappinq fmqumcy is the primary factor, not air speed. Fiun, 5.2 is a portion frwn the second nin on September 1: in which the peak bending moments are about 2800 foot-pounds. The average ihpping fiequency in Figure 5.2 is 1.16

He-. Although aie air speed was not recorded because the pressure bansduœr was not yet installed, the pilot reportecl that it was approxirnateîy 40 miles per hour. The fact that the peak

ôending moments am bwrin Figure 5.2, even though the air speed is slightiy higher, suggests that fiapping frequency is aie prime factor.

Figure 5.1 shows that the negative pks,unlike the pasiave ones, do show a shiR as the air speed increases in aiat they become srnalier. This shift is most likeiy because the wings are canying more of the aimfk's inreight as air speed increases. It is also worth noting the blips in the bending moment traœs, which am in the negative peaks at the higher speeds in Fiiwe 5.2. The negaüve bsnding moment peak corresponds to when the wmgs wem half way through the up stroke, which is when the main wheels wre hitthg the ground. The blips reflect that this contact with the ground was being transmiüed to the wings. The blips are not present at bwer speeds because the aircraft is not bouncing.

Although the peak bending moments were quite high, there was no wing darnage apart frorn the minor probkms discussed in Sedion 4.3. The wings were designeci with a factor of safety of 5.7Q1'0,so none muid be expected. The fact that these high bending moments did not cause damage to the wings is a testament to their design and construction. However, it woukî be undesirable ta continue relying on the factor of safety when the aireraft is in nomal operaüan.

The high flapping frequencies which were seen in sevenl of the runs emphasized the need for a properîy fundicning fmquency meter. The pikt canne be biarned for Rapping the wings too fast, as she did not have the insbumentation to be able 10 know the fiapping fmquency. The fretquency meter was useless and the tachomeber was not diable either. The fmquericy m&er became a priority in the off season. [-RW 8end Ul -RW BsndU2 RW Bsnd t3 -RW Band 14 -Trlgger -Air Spesd 1 Figun 5.3: Bmding Mornerit Data from Secocid Run an Septanber 15,1997

The high fiapping frequencies lead to the question of whether or not they are required ta mach takeoff speed. Companng the air speed traces from several diffemnt nins shows that the higher fbpping frequencies do result in faster acceîeraüon. For exampie, the time taken to accelerate from 25 miles per hour to 35 miles per hour in Figure 5.1 is appmximately eight seconds, at an average fiapping fmquency of 1.3 He&. In Figure 5.3, on the other hand, the aircraft requid 12 seconds b accelerate over the same qmd range. The average fiapping frequency m Fiurp 5.3 is 1.17 Hem. Note onœ again mat the peak bending moments are signficantly lower at the lower fiapping fmqumcy, with blips in the negative paks as discussed eailier. Cieady, the highew fiapping fmquemcy generates mon, thrust, but it was not kmnif this extra thnist wouiâ be requinxi to mam taMspeed. Lookng at Figure 5.3, aie airddoes continue to accelerab at the lower flapping fmquency, albdt at a dower rab. Of course, even the lower ffapping frequency in Figure 5.3 fe süY higher than the design vabd 1.05 Hertz. None of the tests in 1997 mched a steady air speed, so it was not known what sped those high flapping frequencies wwld have attahd, or what fiapping fmquency wouid be~requimd lo mach takeoff speed. There is not sumQent data hm1997 at bwer flsppmg frequencies to answer aiat important question. This issue will be discusseû again with reference to the 1998 data. On a posiove note, the high flapping frequencks indicate that the 24 honiepower engine is moie than adequate.

5.2 Po~nüonreberData

As with the wing data, only the data hmthe taxi nins in September will be discussed hem.

The reason for adding the potentiometen msto mard the pibYs contrd inputs during taxiing, so the static fîapping tests were of lm significanœ. There are tour potentiometers to consider. stabilator, angle of attack, Ridder and throttle. The potentbmeter to masure the throtüe input was not instalîed until September 12", so b data was only recorôed on Septernber 15" and q6".

Rudder

Angle of Attack Nose up 1 -45degm 45- Throt" OF O pmt 100 percent TiMe 5.1: Pdentiometer Ranges and Positive Directions

The definition of posh diredons and the ranges of motion used to calibrate the four potmtiomebrs afe presended in Table 5.1. For the stabibtor, nidder and airattle, this range of motion are the physical limits of the input for that control. The angle of attack meter has no physical stops, so the range useâ for calibration was chosen arbibarily. The air& wiU not see such a range of angles of attack in normal operation. The angle of atfack king meawmd is that of the fuselage, mth the top of the fuselage taken as zero. The calibntbn of the angle of attack potentiorneter was net wry accurate because it was done by eye. When the data was duced using the caliôration fmm the appropriate day, the angle of attack traces for Seplember 15" lookeâ most realwtic. Themfore, that calibration was used for September 1 and 16. nie potentiometer calibratbn, once comrded for excitation voltage, does not Vary much from one day to the next, so this is valid.

For the stabilator angle, posMis dehed as trailingdge dom. This conventkm is used because it is an al1 moving suffaœ, and trailingedge dom repreaents a positive angle of attack for the surface. Note that this is the coWinput which wwld make the aifcraft's nose go down, or stick forward. Zero fcr the stabilator is paralid to the top of the fuselage. 60th the stabilator and rudder potentiorneten am connectecl to the cocont ml, so if thete is any cabb stretch, it is not accainted for. At the operathg qmeds of the ornithopter, cable saetch should not ôe significant.

Figure 5.4 is the potenbiometer data for the second Rin on September la.As disaidin

SedDn 4.5, the tak80ffstrategy at this point was to keep the stick fornard until51 miles per hour was reached. This can be seen in the trace of stabilator angle; it is virhially full forward for the entire run. It can be secln that the nidder is slîghüy to the right in this nin. This was not intentional on the pilot's part, but a natural consequena of holding the ambe mounted conbol stick with her right hand. The weight of her antends to pull the stick slighüy over. This tendency with the rudder is piesent in several of the runs, as can be seen in the graphs in Appendix B. Them is no other signifcanœ to the rudder data, because the pilot was not exdgany tums. Therefore, the Rdder trace is left off of the othar graphs preaented in thb duipter. The angle of attock trace in Figure 5.4 is also interesting. For the earîy part of the fun, the air speed is nd high enough to make the angle of attack meter align with the airibw, so the angle of attack is not really minus 7 degrws. Onœ the air spaed is high enough, the angle of attack meter staits to measus the actual behaviour of the aircraft. The angle of attack is generaliy negaüve because the nose gear is slighüy shorter than the main, and knauzm of the full forward sück input. As the fiucbiatkns in angle of attack inmas8 because of the bouncing, notice mat the angle becornes gemrally more negaüve. This is beause d the whed barmwiig, whem the main uiheels wem lifting off the

stick steady. It is likely that the incread sticû movemnt then furlher augments the bounces.

The fluctuations in the stabilator angle am nd as pronound in Figure 5.4 beceuse the stick is

ful fornard. so it is king heîd against the physbl stop.

[-~n~ls d At- -Slabllatw -- Trigger -lhmltie Posltlon -Ali Spa& ] Figura 5.5: Potenticmeter Data fran Semd Run on September t 5,1997

Figure 5.6 is a partial view of the sarne data shom in Figure 5.5, covering the period fmm

40 secondg to one minute after the start of the run. For danty, the air speed tram has been mmoved from this partial view. At 40 seconds, the stabilator angle is about th- degmes. and the boundng is inmashg in severity. Afkr 45 seconds, the bwncaig is takng the aidalmost ngM Mthe gmund. At this point, Ms. Jones-Bowman pulls back on the sück and the aircraft goes through several large bounces. Each bounce is merand highet than Ihe previous, to the point that the airmît was 2 or 3 htoff the ground. The Pikt mornentafliy increases the thmttle to maa.mum, but then wWeiy backs off, as Oie aircraft was becomkig dimcult to contrd. Aftsr reducing the thmttk, the aircraft bounces two more times before settling on its main wheels with

the nose wheel still up in the air. The angle of attack gradually decreases as the nose wheel

Paft d Sopbmkr 15,1997 Run 2: P-r D.tr

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figure 5.6: Padid View of the Data in Figure 5.5

Figure 5.7 shows the antire third run on September 15". and Figure 5.8 the entire second

run on September 16". These two runs retlect a fundamental shin in approach. Until the large

bounces shown in Figure 5.6, each taxi test was a small step towad eventual flight and was just that, a taxi test. ARer the large bounces, which suggested that the aircraft was on the verge of

flight, the mentality changed to om of getting the aircraft airborne. This change is reflected in the

pilot controls, which are much more aggressive. Noting the different time scale in Figure 5.7 from

Figure 5.5, it can be seen that the throttle was applied more rapidly, all the way to 100 percent.

This resulted in a much higher flapping frequency and faster awekration, as noted in Section 1OQI -TA CI

5.1. The startirtg stick position was slbhtiy more fotward, in the hopes of finding the fine the

exœsdve bouncing and wheel banowmg. \Illhen back stick was applied, it was dom much quicker and to a gmber degm. The mit was anottar =ries of large bounces, but with kss control end more violerit than befom. Onœ again, the aircraft settled on iE8 main wheels with the nose wheel stil up. This time the nose did not corne domi as quiddy, and the aircraft started to hmto the right. The pibt dïd not iaelize that the nose was off lh gmund and bied to counter this by turning the nose wheel ngM This had no MW, of course, and when the nose finalty did corne down, the sudden side load on the nose gear stmtched one of the guy wiies. The airueR was taken back to the hangar and desting was stopped for the day. Figure 5.8: Potenticmeter Data from Secoiid Run on Septmber 16, 1997

Figure 5.8 shows the same aggressive approach the folbwing day. The first run fmm

Septamber 16" is not shown because it was cut short when the pilot kst communication with the ground crew. The second run was similar to the 4st one on the previous day. The throMe was incread quite rapidly up to 100 percent. This time, huwewr, the stick position at the start was neutral. Once the bouncing starts, as indicated by the angle of attack fluctuations, the stick shifted back (tfailing-edge up for the stabilator). Notice the increaseâ severity of the bouncing as the aircmft is accelenting, even bafore the pilot puk back the stick. The pilot pulls the stick back at a lower air speed Umn the day before, and almost sirnultaneoudy reduœs the thmttie because the bounciig is so Severn. Then she ckcicks to continue the run and rapidiy in-= the throttle to

100 percent At this point, the ground crew noticed a ûailmg4ge dip corne off, so aie nin was

-pped. The change in apprcrach did not work out; the aiddid not fty. The large bounœs wre not considered flight because the airmft did not stay aihome when the wings came up. Ciearty, patience wouiâ süll have to be pracüsecl b get this aircraft to its first flight Howewr, the change was not just on ttie part of the pilot. The entire team was veiy excW by the bounœs on

September 15" because lhis was the fimt tirne thst the ornithopder was "aYbomn,albeit bnefly, and perhaps the barn got a bit amed away. Aftw the tests on September 16". when the ainraft was back in the hangar, it was dBCided to suspend tesüng for the season.

5.3 Vid.oAiwlyrb

The video analysis of the aimafVs movements confimieci the findings hmthe data discusseâ above. Wdeo of the stabifator deflections was also used to confimi the data madings fmm September la.As nobd in Section 4.6, the onboard cameras never worked for long enough to record any useful footage, so no anaiysis cou# be done. Frorn the outsiâe cameras, only qualitative conclusions could be drawn. The Mts on the upper surface of the ieft wing confimeci that there are substantial regions of stalied fiow when the wings ara on the down stroke. The size of ais region diminished with air speed, but even at 40 miles per hour, them was still about 3 feet at each wing tip where the MEs stood straight up. These regions shouîd virtually vanish when the air& maches 50 miles per hour.

5.4 Summay

The data coliected in 1997 was very useful. From the bnding moment data, it was ciear that the flapping ftequmcy woutd have to be kept under control. Apart fiwn that, however, lhe bending moment data was encouraging because it was not egregiously dilferent hmthe predidions. The po@ntiometerdata was helping to establish the takeoff procedure. This data is especially important because of the shaky cockpit environment. It is very difficult for the pilot to say preciseiy Mat 9tie did afkr a test nin. As sudi, the data is good for boai the pilot and the engineen to see what she did. The approach used in the la& few tests of 1997 did not wrk, but it was an experiment. tt would not have been masonable to expect to get the produre exadly mht the first tirne. The aircraft was damaged, but repairable, and the team was looking forward to continuing testhg the folbwing year. Between the destin9 =sons of 1997 and 1998 a gmat deal of work was armpieted,

foawing on the items liin Sedion 4.7. This chapter dedbee the analysis and design

invohied in improving the ornithopter for another season of tmting. h the intsrest of brevity, the

focus is on the final modificaüons wtiich wem irnpîemented, as opposai to al1 of the options

which were considered.

6.1 S~ralModifkatbm

The onginal fuselage design foaised primarily on h-fïgM bads. In designing for these

loads, steel was chosen for the forward mernbers of the thorax and outriggers, because they are

closest to tfre wing spar and drive module. Alurninurn was adequate for the more lightly loaded aft

members. How~w~,the main landing gear is locateâ very close to these members.

Consequentiy, these were darnaged as a result of the bouncing. From the damage sustained, it was apparent that sirnply riepairhg these areas to their original condition would not be sufiicient. lt was hoped that an improved takeoff procedum would eliminate the bouncing, but this was not certain. Tberefom, the thorax and outriggers had to be strengtheried to withstand the bouncing

loads.

6.11 ClChieFtameAniilyris

h order to evaiuabe potential modifications, a stnichrral anaiysis was conduded by Patrick

Zdunich using a hite dement program called Cadre1? Each thorax and outnOger tube was an eîernent in the model, wîîh the ends of the tubes bemg the nodes. Alaiough the focus was on the thorax, the entire fuselage was modelled so that the loads fmm the empennage, nose gear and cockpit would be accurateiy transfed to the thorax. To test the model, a 1-G lad case was considered, to simulate the static ornithopter. The reaction forees at each wheel were calailateâ hmthe mode1 and found to be within five percent of the measured loads. Next, tfte mode1 was subjeded to a 3.86 landing on only one of (he main wheek. ît showed that the potential probkm amas wem Be same as the ones which had been damaged. Tbee dests validateci the madel so

that new designs cou# be diecked. A detaiîed description of this mode1 and the mults are in

Refemnce 13. M.2 QJmWw- Figures 6.1 and 6.2 show the damage to the aft members of the left ouûigger, whiai was

typical of b@h oubiggers. There was aacking and bcaiized budding where the diagonal paon

mets aie hokontal portion, and them was a bend in aie diagonal tube away from the

connedion point. Strengthming of the outriggem was accomplished by mplacing both af&

members, whidr wre 1-inch 00 by 0.035-inch wall thickness ahiminum, wiai strpnger tubes.

The new tubs rn titanium of the same diametsr wiai 0.051-inch wall thickness. fhe total extra

weight hmthis modification was about thme pounds. For aie strength gained, this weight

increase was wll worth while.

The outrigger repairs took oom tim, because gmat Gare had to be taken to ensure that them would be no alignment problems when the aircraft was masaembbd. They were then recovared wiîh the Polyfibm fabric, which was used to cover the entire ornithopter. All of these tasks wem complicated by the fact aiat the original team mernbers who built the outnggers, and had experience working with the mvering material, were! no longer part of the ieaearch grwp.

Such is the nature of an academic proied, that team membem graduate and move on.

Fiaun 6.2: Bent Tube in Left OuMgger (n#bograp~iby J.O.

6.1.3 ThorUr -&S

The major concem with the thorax was that the lower bngemn tubes wie slightly bent in a downward and outward direction. This was why new holes had b be drilled as part of the fieu repair describecl in Sedon 4.4. These tubes are welâed into the thorax and serve as the rnounting points for the drive module, outnggers and, indiredfy, the engine. Therefore, replacing thern woulq essentially be a cornpiete rekiild of the thorax, which œrtainly would have meant no taxi testing in 199û. lt was decided to straighten the tubes using standard aircraft repair techniques.

Before beginning the tube straightening, the magnitude of the bend was quantifid by careful measurements with a dial gauge and found to be approximately ?/&inch. The tube straightming procedure is shown in Figure 6.3. At the bwer bngeron, the tube to be straighteneâ, a wooden bbck was used to transfer aie force from the pipe clamp ta the tube. This block had a semi-circular surface to match the tub on one side and a îlat surface for the damp on the oppgsite Me. The clamp was positioned at the point of maximum bend in the lower tube.

At the top, a large^ mctaqubr piece of alumlwm was used lo tramfer the damping force, via the wooden blocks at the left and right, to hard points on aie thorax. The dial gauge, Mich can be seen in the jWbm of Figure 6.3,was useci to metawre how far the tube had ddïecW hmthe cfamping force. Unforhrcately, when the clamp was released, the tube rehirned almost to its original position. Several attempts were made, each one using a gmter denedion than the previous, but aie tube wwld not sariighten compledeiy. An alaming amount of force was required, and it was decüed that using more force could msuY in other damage such as flPt$ning or cracking the kwer bngemn tube.

Figure 6.3: Straightening the imm Longeron {mctqpph by J.O. ~elaurki)

After the tube sbaightening, a dye penetrant test was useâ on the lower kngerons to check for cracks in the weids. This was a three part process invohn'ng a cîeaner, a pmetmting dye and a de!#-, al1 made by Magnafiux. The tube was cieaned aionxighly with the cleanet, and then the dye was appli. Afàer one hour b albw the dye to seep into any cracks, the excess dye was wiped off with the cieaner and the developer was appiii. The developer praduced a white background on which the cracks wld show up rd. No crad

ChenyMAX rivets had been udpmiously in the outnggem, and wen useâ again when they were môuiit. The team met with Tony Starcevic of Textron Aerospace fastsners to get technical atjviœ on the suitability of aiese rivets for use in the thorax. He assured the team mat the rivets would be suitable and he was vwy enthusiastk about the project. He ofbred adviœ on installing the rivets and donaa number of rivets to the project. He also loaned out a hydraulic rivet gun to make installing the rivets much easbr. One conœrn was that ctven though the

CheiryMAX rivets are strong in shear, Me holets in the gussets might not be sttong enough. Mr.

Zdunich investigated this posdbility with cakulations on the holes considering three modes of failun". He found that hmwould be no pmblems with most of the holes. The only one that may be a problem is one of the hoies in an ahminum gusset. The hole in question is easily inspecteci afbr taxi tests. ln addition to using ChenyMAX. rivets mrywhere that a tube was mplaced, a number of the unfaiied oid rivets were replaœd in crucial bcations,

6.1.4 hbwCrcmha&whûfive'Iyiiiir The final modification ta the thorax was to install a îateral cross member connedhg the legs of the drive module. This aoss membetr was part of the dnie module when it was buiit, kit it was not inatslbd originally. The part of th drive module that it supports is quite robust, so it was decideci that the cross member was not needed. The designer of the drive moduk, Jeremy

Hanis, was coriwlted about mis. He confimed that the part was not esseritid, but said mat it woulâ not be dstnrnental to install it. The weight of aie extra part was minimal, so it was installed.

The pnmary macon for adding this pke was that the other thorex madificaoons support the lower longem tubes in the vettical plane, but do fiito heip them in the horizontal plane. This pieœ shwid heip suppoit aie hrion- tubes from bowing out as they did befom.

6.2 Simuiaîion

To help give some guidanœ befom the 1998 test s8ason, a non-linear, timeniarching simulation of the takeoff was programmed on a cornputer by Dave Lmn.The main questions for which amenwere sought, through the simulation, were:

ûoes the main undercamage need to be modified to increase damphg?

Is them any takeoff approach that can avoid the dangerous bouncing?

What modifications am necessary ta minimite the bouncing if it can? be avoided?

0 What flapin will be required to achieve fiight?

The ~imulationonly consiâered longitudinal motion, which alioW8d it to be prograrnmed as a (WQ dimensional mode1 by assurning symmetry. The simulation was programmed in Working

Mode120 and reîii on output from FulWmg for the aerodynamic charaderistics of the fiapping wings. Th$ aerodynamic charadeniltics of the other components, such as the fuselage and empennage, wem modelled based on cornmon analybcal rnethods for conventional airenft.

6.2.1 o#i~SpmOConrbinbndDmphORiQ.

Some of the important variabk of the simulation are the characteristics of the undetcarriaga These were detemined experimentally by mounting the main undercaniage on a rig, shami in Figure 6.4, which alwik to be raniaed and them dmpped. These dmp teas were video taw and the motion of the rig weo pbW as a funrlkn of tnne. Again ushg Working

Mode1 20. the spring constant and damping ratio of a cornputer mode1 of the test apparatus wem

adjustetd until the motion of the mode1 dosely matched that of the experiment Thevalues wre

used in Ihe takeoff simulation.

6.22 Shnilatknb~lg

The fimt important mit from the simulation was that the damping already present in the

main undenarriage seemed to be sulficient. lncreasing the darnping in the cornputer model did not change the resub enough b suggest that Wilying the undemamage to incorporate mom damping would be wocthwhila. Such moditications wouki require a great deal of Orne and effort. and add weigM and drag to the aimait.

The simulation indicated that, basd on the amni( air- configuration, the bouncing was inevitabte regardless of stick position. Howiever, shortming the nose gear of the cornputer mdel reduced the bouncing significantly. The reamn is easily understood when one examines the perfonnanœ of the flapping wings. The whgs generate M in much oie same way as fixed wings, so the average IR increases with dynamic pmssure and angle of attack. For îhe aimait to Ry, the average IM must ex- the wight, which shwid ocarr at an air spemd just over 50 mibs pr hour. Aiaio@ aie flapping fr6qwncy has liieflect on the average Mt. the fhpping dasr impose an osdlîatory IYt onto the average lii The magnitude of the oscillatory IR depends quite strongly on the flapping fmquency! As the average Mt is approadiing the weQht of the ai-, the oscillatory ln causes the total I'R to exceeâ the weight of the aircd when the hgsam on the down sboke and be hss than the weight on the upetroke, which causes th8 bouncing. Shortening the nose gear reducss th angle of attack and mean IR, which alkws the aimaft to reach a sufkbnt for fliht without the oscillatory liR causing bounung. Badon mese rwuits, the

gear sûut was shoctend by three inches.

The final impoitent resul frorn the simulation was that a small variation in stick position wouîd make a large dihrenœ to tha airaaR it seemed that, with the shortening d the nose gear, there wu# be a stabilator angle that wu# albw the aitcraft to mach 50 miles per hour without wheel bamnning or bouncing. However, when rotations were ttied in the simulation, it was found that a very small stick movement woulâ cause the aircraft to lift off very quiddy. It was this finding which rnotivated the addition of a new instrument to indicate aie stabilator angle of attack to the pilot.

6.23 Future WMICon Um Simubtbn

Aithough oie simulation did provide some useful mults, which albwed the 1998 testing to get doser 19 flight than ever More, t dœs have some shortcornings. One potemtial source of inacairacy is in the use of FulWiig data for lhe piformana, of the wings. When the previously mentioned tirne-maraiing analysis is complete, 1 might be woramhile to update tha simulation accordingîy, Amther amd unceitainty is in the downwash model. Dr. Delaurbr has devekped a theoretical mode1 of the downwash of the fiapping wings, but it has not been experimentally validated. Future thesis topics may be to experimentaliy determine the downwash of a Rspping wing or to refine the simulation and test it eqmrimmtally with an already exisüng quaiter+cale model. 6.3 înstnmiençotion

As a resuk of the findings hmthe 1997 tests, and the msub of the simulation, some work was done on the instnimentation. This hduded calibating the pressure transducer and installing some new instruments as described bdow.

6.3.1 PnwuribTmmâuœrCdihdon

Figun 6.5: Pressure Transducer Calibraticm

In the interest of gettMg it onboard as soon as possible, the pressure transduœr fhat was instalied in 1997 was not calibrated beforehand. Instead, it was post-calibrated in the bw speed wind tuinel pl UTlAS during the winter of 199748. ln order to get an accurate calbration, the pitot tube, air speed indicator, pressure ûansduœr and al1 of aie conneding tubing were set up in the wind tunnel the same way as they wra in the omithopter. The pibt tube was mounted in the wind tunml so that it was approximately in the centre of the lail sedion, as show in Fiium 6.5.

The data was recordecl using the same sarnpling rate and file type used on the omithopter.

Calibraüon tests were camed out at several difbrent speeâs on a few dihrerit days. Eadi time it was tested, the zen, readhg for the pressure tranaduœr was elightiy dilfarent The zero mdng for the day ywas subtfaded from al1 of the madings in wch calibration mn. The results are pbtted against dynamic p

6.6. Figure 6.6: Calibraüon of 1997 Pressure Transducer

The average dope of these lines was taken as the conversion factor for the pressure transducer. To leduce the ornithopter data, the zero readmg is found by averaging the signal hmthe pressure transduœr dunng the pm and post calibration. Onœ the zero reading for that day has been subtracded fmm the piiessure transduœr signal, the resuit is multiplied by the conversion factor to get a dynamic pressure. The dynamic pressure is then converted to air speed usîqg the standard abnosphedc density of 1.225 kg/m3, which ghs the equivalent air speed. Air speed indicators are calibrated to read equivalent air speed, so this method gives results whidr agree well with the air spdindicator.

As rnmtioned, the@ was a pmblem with eiectromagnetic noise interfenng with the signal fmm the pressum transduœr. To produœ the gmphs, the air speed data was appna'mated by a bendline. Plotüng al1 of the air speed data WOU# obscure the other data on the graph. Figure 6.7 shows the air speed data for one run and the tmdlhe which has been used ta approximabe it. The ûendline, ealled a "moving avemge", average$ a number of data points for each pont in the

trendline. In dohg $0, it duces fhe fluctuations and makes the data more understandable.

Figure 6.7: Air Spmd Data and Trendline

6.3.2 New Pmswrr, Transâuc8r

In an effort to eliminate the noise pmbbm with the pressure transduœr signal, a new pressure tqnsducer was installed for 1998. it was thought that using a more sensitive deviœ, with an amplifii output, WOU# reduœ the pmblem by improving the signal to noise rab. Table

6.1 is a cornparison of the O# and new pressure transduœrs.

When orQinally instalkd, the old pressun, trensduœr had a dedicated 6 Volt powr supply, because that was thought to be requirsd. tt tumed out (ha it awld be powersd by up to 16 Volts, and that Re output signal was pmporbnal to the excitation voltage. Tkefore, using only a 6

Volt power supply had fumer ihduced the output @ml. The new pressure transduœr b also ratiomebic, so it is powered by the onboard battery, whkh is nommally 12 Volts. As with the

polrmtbmeWs, the signal recorded hmthe pressun transducer is diviied by the main baüery

voltoge at fbt ürne and mulopli by 12 to cormdfor changes in the excitelion vo~.

MPX 201 0 DP

TaMo 6.1: Pressure Transduœr Cornparison

The new pressure transâucer was calibrated in the same manner as the old one. Three di#femt excitation voltages wre used to check the ratiomefnc bahaviour. The rewb anshown

in Figum 6.8, etsubtrading the rem mdmg and armcting for excication vd$ge. The pilot had commented in 1907 on the difficutty of Mingthe stabilator at a pmsçnbed

angîe because of the bouncing, which moved her am and inhibbd her inhensnt feel for the stick

position. Al=, the simulation had shown that the stabilator angle must be mûolled very

precjm)y. For these reasons, a new brbumetnt was added b indicab the angîe of aie stabilator

to the pibt. nie indicetor conaists of a vertical mw of LED's: four red for sück back, One yelbw for

neutral and four green for Sb'& fornard. On, of the LED's îights up to indicade at a glanœ the

current angk of the stabilator. The signal for this instrument Is taken hmthe same potentiometer

that is used to mord the stidr position in the NetDAQ. The instrument, show in Figure 6.9, and

its assocjafed cirwitry wre built by Rambod Larijani and Jasmine ECKhatib.

Figun 6.9: Staôilatar Angle lndicator

6.3.4 Fmqumcy mir

As shcwn in Sadion 5.1, the bemding moment data fr#n 1997 showsd that me peak

bending moments in the wings am very mgly a hindion of the flapphg frequency, emphasising the need for a hindioning fiequency meter. A mm fraquency mkrwas built which incorporateci a horizontal rniv of LEUS: eigM grwn to indiab flapphg frequencies up to 1.0

Hertz, one yeNow to inbicate 1.O b 1.2 Hertz and one rdabow 1.2 Hertz. The optjcal sensor was replaceci with a magnetic pick up and two magnets wem embedded in the wheel which had pmviously been painted bîack and white for the optical sensor. The idea was similar to the O# frequency mkw, but insbad of the bbck and white paint providing the on/M signal, it would be the magnets pssing by the magnetic pkk up. This frequency meter mwiiâ also go through developmerit problems, as described in Section 7.5.3.

6.3.5 Pbw Compubr

A new notebook cornpmr was purdiasecl to use far the data alledion onboard the omiaiopbr. The new computer, a Sony, is smakr and lighter than the pmvious one, and it can be closeâ al1 the way wiaiout entering a power saving mode. Recall that no data was recorcied on

August 7". 1997 for that reason. The new computer also has a faster procassor to improve the samQling rate and data redudion prooess.

6.4 Tniiing-Mge Clips

The mason that the trailingdge dips have been the focus of so much attention is that it is critical that they stay on. if one cornes off, the clips bideit are Iikely to corn off as well because the trailingdges try ta pull apart. If two adjacent clips corne off, the lin and thrust generated by that wing are severeiy compromised. If this shou# happen while the ornithopter is in the air, the resub could be disastrous. The original rnethod of attachment was a cyanoacrybte glue, or Zap, similar to what is commonly used by mode1 airplane buiîders. The clips that were reattached as part of the wing repair were installed with a dfirent adhesk called Powergel. This is also a cyanoacrylatie based adhesive, but it is a thick pasde as opposd to aie thin lquid used barn. It was hoped that the thicker pasbe wwkl allaw for more fknbility in the bond. Howver, during the

1997 tests there wre süll problems with the troiling4ge clips, mduding the ones rvhich had been reattadied with Powergel. WhCeline Bernard hm3M visii to see the ornithopder, she suggestd that an epoxy would k better because it allows for a more flexible bond. She providecl some sampies of a 3M produd she mmmended cailed ûP42û. In order to assess the sûength of mis epoxy. samples wre tested by Don Morison in a tedie besting machine. Three sampies iniiem made with each adhesive: Zap, Powel~eland DP-

420. One sample of each was tested to failum in order b find ib ultimate -th. it became immediably apparsnt that the DM20 was stmng because oie sample broke in the aluminurn body athef than at the glue bond. New samples were made which used thicker aluminum strips and it was found that the DP420 was 6.2 tirnes stranger than the Powergel and 8.4 times stronger aian the Zap. Then two fatigue tes@for each type of adhesive were carried out at 80 pemnt aqd 60 peroent of that adhesive's ultnnate faikire bad. On these bsts the DP-420 appeared to do poorly, because it lasded for a lowec number of cycbs than aie other two.

Howewr, the ularnate falure load for DP420 was signifkantly higher than that for the other two, so the load it was subjected to during aie fatgue tests was also much higher. It was decideci to do ami more f-ue test on the OP420 with a simiiar Mingto that which was used on the Zap sample. In this test, the DP-420 perfomed exfremely -Il, lasting for more than 2 million cycles without failing. Based on these resub, the team decided that it would be worth the effort of removing al1 of the old clips and replacing them with new ones attached with DP420. This decisin was verified by the ease with which aie okl clips wre removed.

6.5 Win# min In addition to the wrk on the trailing4ge clips, a minor repair to each wing was required.

Recall, frorn SeWn 1.3, that there is a floating panel at the inderface betwm the shearfiexing portion of (Ire wmg and the rigid poition (nearthe fiapping hinge). The piece that the fkating panel siides over, called a "sher, is a non-structural, aerodynamic bar&. The aft portion of the shel is attached b the cap sbip of the outemost nblet Mind the Supe~rbox,as sketched in the left of

Figure 6.10. As show in the sketch, thb portion had tom away from the foam riblet. This was glwd back down to the riblet with epoxy and ceLiforcd wÎth a bridging strip as shown in the dght of the figure. The bricjging sûip overiappeâ both the top and bottom cap stnpd so that the load which caused the upper cap stnp to pull away would be better distfibubed. Access to the area was gmMby an eWng hok in the bwer wrrfPce of the wing whem the pivot hhge plaie is bolteû to the back of the Superbox. The final stq, of thb mpair was to glue he trailuig-edge of the plywood sheW bsa down tc~the carbon fke traiiiidge arip.

After discussions with the pilot, it was desid to refine the throttle msponse airva to give her batter control Mar the top end. The original throttle mechanism gave an essentially linear response, 80 that a given amount of movement of the handie would move the catbumttor the same amount airoughout the range of motion. However, this gave non-linear engine RPM response. A new linkage was designed by Helen Tsai and Lorenzo Aurio using Working Model

20 to de$miim the response. The final mechanisrn mat was buiit and installed gave the response show in Figure 6.1 1. Fmm the figure, t can be smthat the throttîe is more sensitive in the eady portion of the handle movement than at the end. This was so hat the pibt cou# have finer conûoî over the throttîe when the flapping frecluericy is above 1.O Hertz. lt was decided that the best way to deal with the problems with the zero stage chah would be to eliminate the engine's rocking motion, which wouid eliminab the dative motion between the two sprockets. Changing the zero stage to a different type of drive woukl be a major modification and would inevitably be heavier than aie existing chain and sprockets. To eliminate aie rocking motion, the engine was rigidly con- to the drive modub with a steel bracket.

This bradret was cusbm made b attach to the drive module at two existing boit bations and ta the engine at the cylinder head. The bob which hold the cooling fins on the top of the cylinder wem npbced with longer ones to hold the bradgt as well as the cooling fins. Two pieœs of nibber were used betwwn the bradiet and the drive module to duce aie engine vibrations transmilted to the drive moduk. The instaled engh restraint is shown in Fium 6.12.

TWng in 1998 bagan witt~the team fieelmg very opthnislic about the possibility of a sucœssfui crow hop. The final tests of 1997, when al1 three wheels of aie aimait were wei off the ground, had kept the team mtivated thmugh the bng period of analysis and rnodhtian dmin Chapter 6. The bam was confident that the shortened nose gear wouid reduœ the bounàig prior ta fwchmg 50 miles per hour, and #at the structural changes would make the airdstrong enough to withstand some bouncing. Finalty, on August 26, 1998, the ornithopder was modbadr to Downsview. The aircraft had a new home for this seasan of testng in the

Toronto Aerospaœ Museum, Mich was süll under dersiopment The management at oie museurn agmd to let the ornithopter stay in their hangar mt fm in the hopes mat they might evemtually be able to put it on display as the world's first successful piloted ornithopber.

This chapbr is structured in a simiiar way ta Chapter 4. Section 7.1 presents the test program for 1998 and lists the tests Wch were cornpieted wMout going into detail on the modifications. The other sections of this chapter will detail the modifications and repairs that were made belween tests. The data reduetion will be discussed, in detail, in the following chapter.

7.1 1998 Tmt Pmgram

As with the previws two seasons of testing, the goal in 1998 was to comptete a uccrow hopn

(Defineci in Secbion 1.5) on the main ninway at D~sviewAirpoR. As before, the testing was approached in a well thought out, rneasured fashion. tt was necessaiy to asses the en$d of the signlcant shoidening of the nose gear on the handling of hairwft. tt was also desired to obtan data to validate the simulation of the taûeoff. The pnmary kst goals were as folbws:

0 Hoid the air speed at 30 miles per hour and find the necessary fiapping frequmcy. Whiie doing mis, experiment with stick angle to find what position will minirnize wheel bamwing without causing bwncing.

- SePt 1 1 IAP~1 Tastfrequaicy-m Ïislsdidndwork 4 shiie 1 - - -- Apmn G~~.Fi~run mth the niings on. Everyttrng msmoahty-

No

- No

- Sept 1,2 Apron Static fbppng with @ot at Fta(39ing at 0.7,0.8, 0.9 and Yes 18 four ancrent frequencies. 1.O Hz cmpk!ed. Stabilaor Test stabibtari-. iridieator did nâ w#lc Testfikm~. TachomeWw. - Sept 1,2,3, Main Ta#i at 0.7 Hz and find 0.7Hz~iieslessthan10mph. Yes 19 43 Runway quilibiiun 8pd.Then tiy 0.8 M wer, up b 20 mph. 0.88 0.8 and 0.9. EKperinierit Hzwsupto28mph.AUd Hiiaistidtarigk pitdûngwhenthridtlefirst applii.Neubdstidrbest. Sept 1,2,3, Main CoritinuetesWruniasttnne Lastrmreachea42mph. Yes 24 4,5 Runway athi-wig SligMbadcstidrdlaiiRdnoge frequencies. Hiheelto'itaydfrnostdthe tirne at 38 mph. - Sept 1,2 Main Testthenewnoeegear ~~suppOrt~Yes 29 Runway sbii$. Taxi up to 40 be(tar. low pitchig mph. reduoed. Steeringw - Sept 1 Main Testaieseissor-type ~W=jpibehim~ Yes 30 Runway dômpf. Aeeeleae 10 40 rcrdiced. Tna noises M:a mm* --am dlmk. - Oct 1 Main Testthebicydedmper. BicydedampersmnstoW Yes 11 Runway TeMng oghtsr -1. Stêefiig is beiter, kd di CableSTest~krshings ndgm&Nos$aigenoises and wing repairs. heewd.Newkishingsanâ Mng riepairs held up HRH. Test sbppdb#wMMnd. Oct. 1 -7 Taxiway Seriesdaoeelerationand Reacned40mphin Yes 12 bakingtests. 1280 fbd anci stogped in &Jout250feet - Run t eu- - Main Runway

oct. Main Yes 30 Runway

Nov Main Yes 8 Runway - - Nov Main Yes 8 Runway

table 7.1 :Complet8 list of tests in 1998

7.2 Hinge Modificridkm

The taxi run on September 30" was cut short when the pilot heard two odd noises hmthe wings. One of these was a cyclic clunking conesponding to the fiapping hquency and the other was des- as sounding like a woodpecker (a rapiâ clicking iike a wooden ratchet). The second noise was of unknown ongin, but it was not hewd again after the wing repairs which are descnbed in Section 7.3. The first nom was beiiiveâ to be a result of the hole at the top of the vertical Iink having becorne slighüy defoned so that it was not round. This allowed the boit through the hhge to shift up and down sligm with each fbp of the wings. The soiution was to replace the bushings in (ha hinges at the top and bottom of the wrtical links. The new bushings, pumhaaed fmm Leavens Aviation in Miss'iuga, wem oilimpmgnated bronze. They had a lager outside diameter, which meant drïling the hoks out to a iarger sire. Ahio, the new bushings had a smaller inner diameBr which wu# fit amund the bat better. The wings were

taken off the aircraft so that the hinges car# be modifted.

The bushings wem ûimmed appmpriabeîy for the plate in which they wem instalîed. Some

of them are in 3ilGnch ttiick aluminum, whiîe others am in l/lGindi thick steel. The aiuminum

pbtes which am attached to the wings wem riemoud so that the holes could be drilled out on the ddll press. Rien the bushings wem pressed in to ensurie a tight fit ît was not possible to use the drill press for the holes in the vertical links, so aiey were carefully drilled out with a hand drill.

Then the plates were heated with a blowtorch before installing the bushings, ensuring a tigM fit.

7.3 Wing min

When the wings were off for the hinge work to be done, they were thoroughly inspecteû.

The trailingdge clips were holding up well, none of them showing any signs of koseness or other damage. The Superbox area appeared soiid, although it is difficutt ta properly inspect a glu& closed structure. mer8 were, however, two problems discovered. These problerns and the repair techniques used for each am discussed below.

7.3.1 SMRspeir

Section 6.5 describeci a =pair to the piywood shelf whidi is below the inner floating panel.

Recall that part of that repair was to glue the trailingdge of the plywood shel back down to the carbon fibm trailing4ge strip. On inspection, the plywood had once again lRed away from the carbon fibre trailing-edge. This was not surprising sinœ the pfeviws repair did not involve any modification to make the bond stronger in mis am. Ahough this is not a strudural part of the wing, the noise of these two pieces nibbing agamst each other wuld be quite alaming. The structure of the wing is such that 1 amplifies any small noises like a drum.

The shell was reglueci to the heiling me, but lhis tim the epoxy was mixed with a micro- balloon filler to fonn a thick paste. This mixture was pushed inb the spaœ between the plywwd shelf and the carbon fibm trailing edge. Tha thickness of (he mixture meant that it formed a fillet betwieen aie two pieœs, as opposeci to a thin epoxy, which will only bond where thtwo surfaces

touch. This inmascd the sbength of th bond because of a greater surface ama. but this was

not the only change. The outside of the joint waa wrapped with lightweight fiôreglass cbth with

the fibms oriented at plusJminus 45 degrees to the trailingedp. This fibre orientation was used

because it alkwed the clath to wrap amund the sharp traiiing-edge. This area was inspecteci after

subsequent taxi tests and no problerns uuem fwnd. Figure 7.1 shows the trailing4ge of the

piywood shef on aie right wing beforet it war wrapped with the fibreghss. At the extreme right of the figure, the innermost trailing-edge dip can be seen.

7.3.2 FwPIi#l mir

The other problem, which was discovend abr the shef repair was completed, was that the inner floating panel was starüng to bar away from the spar. Fiure 7.2 shows aie bar on the right wing after the surrounding area had been sanded, with the ieading-edge outside of the top of the pidure. The tsar on the len wing was similar. At Ihe time that this was discoveied, the work on the hinges was ahost ample@ and the weather boked good for tesüng the folbwing day, so a gui& repair was sought The easiest solution was to attach strips of Kevlar across the bar, which would hou the fioating panel to Iha spar. Three Mps of five-ounœ Kevlar doth were used, as show in Figure 7.3. The smalkrt piece (IR-inch by 8 inches) was laid down fi&, then the middle one (I-inch by 7 inches) and the la- (2 inches by 9 inches) was on top. The fint two piemi were ait so that the fibres were orknted at O and 90 degrees, while the fibres in the top one wem at pluslminus 45 degrees. Thet fibre orientation of the top piecet was chosen to albw a bit of flexibiîii because aie fkathg panel bas to move as aie wing twists. The two smalîer pieces wem orienteci to maximize their sbength in the chordwicw didm so that if the first piece starded to bar, the bar would stop when it readied the ooier pimes. As such, aie smaller pieces wrie posiooned doser to the end of th crack (to the right in Figure 7.2). In the interest of complethg the repair quidcfy, the epoxy used for this was a Wo-ton adhesive with a 30 minute worttmg time and a 3 hour cure time.

Figuiru 7.2: Tear Where the FWngPanel Meeîs the Figura 7.3: Strips of Kevlar Used For the Repair

7.4 Nose Geat

One of the prknary goals of the 1998 bating was to detemine the effect of shortening the nose gear. As well as finding this out, the nose gear undernt substantial devebpment in 1998.

This âevelopment can be divided inb two main cabgories: damping and structural. 7.41 mObY[kmpine

The ofiginal design of the nose gear suopension had a spnng inside the &rut and an

additional sprnig outside the sûut as shown in Figum 3.2, but no damping other thon lhet offered

by the fridion of the tubsliding inside each other and aie tire. One of aie first effeds of

shoidening the nose gear seemed b be increased pitching at bw speeds. When the pilot

accebrated wiy gradually, there was no problern, but if she acœlerated even slighüy more

quickly the aircraft starteci ta pitdr aggressivdy. The main gear WOU# stay finnly planbed on the

ground while the front of the airaaft bwnœcl on th nose gear like a pogo stick. This motion

staW to disappear once the air speed exded 15 miles per hour and would be virtually eliminated once the air speed was above 20. There was no stabilator angle that wouid eliminate the pitching at Iower speeds because there was not enough dynamic pressure at the stabilator for

it to have an effect Once the air speeû reached 20 miles per hour, the stabibtor started to take efFect and the pitching was mduced. Experimenüng with dinemt stabilator angles at higher air speeds showed that a neutral stick or slightîy aft stick (trailing4ge up) resuM in a nice smooth ride, as disaissed in Section 8.2. However, the pitching at bwer speeds was a problem because the oniy way to avoid it seemed to be to accelerate extrerneîy skwly. With the length of aie ninway limited to 7000 Mt, it was important to be able to mach takeoff speed as quickly as possible.

After Ihe taxi tBSfS on September 2gnI the team decided that some soit of damping shaiM be implernented on the nose gear. With no tirne to source a damper of the right sire and type for this application, if one even existeci, the damper shown in Figure 7.4 was made by Derek Bilyk and Rambod Larijani. In between the two pieces of metal angle is a stack of washen, alternating metal and rubber, lubricaded wiîh grease. A bolt with a locknut holds the two pieœs of metal angle together, and the washers in behnreen. One of ths pieces of angle is aüach8d to the nose gear near the forks while the other is attached to the faed part of the nose gear strut. When the wspnsion mrnpmsses, the two pieces of angle rdak relative to eaai other. This rotation is transferred to the stack of washers, which provide damping because of the friction between them.

Tightening or kosetning the boit will change the fricüon betwa the wadrem, changing the amount of damping.

This uscissor-type" damper was instalied before the next taxi tast on September 30". To maximire the Iength of ninway available for this test, the aircraft was positioned close to the end, which meant that it was on a slight incline. This meant that the pilot had to use quite a high flapping frequency just to get moving, which was the sort of situation which would have cause severe pitching before. On this test, however, the pitching was minimal and the aircraft won starbed to mow forward. This proved that additional nose gear damping wouid blp. Due to failing light and noises bard from the wings, the tesüng wâs stopped for the day, but the team was happy mat the nose gear damping appeand to heb signaicontly.

Before the next taxi tests there was an exbnded gap whik the work descnbed in Sections

7.2 and 7.3 was compleW. During this time, it was decided that the scissor-type damper, whiie dküw, was heavy and would cause ex- dmg. This damper was replaced with a basic dashpot damper intended for a rnountain bike suspension, show in Figure 7.5, which was much lighter and smaller. The fixed part of the damper (Black paR in the figure) was attachai to the outside of the nom gear sûut ud4h tuuo horie damps. A malhok was drilled in the end of the piston and bdmire was used to hdd the piston to the nose geai fork.

The bnyde damper worked for the test on Odobar 1lm and for the eeven tests on Ocbober

12". A# of these tests were below 40 rniies per hour and invohnd no serious boundng. Howewr, on Odober 16", oie air& madied 46 miles per hour and started to bounce a lot. On each of the four tests, the bicycle damper was knocked off. tt seemed that the damper couid not handle the severity of the nose gear compression at these speeds. When it was installed, it was determineci that the damper could handle the amount of travel in the nose gear suspension, but perhaps the rate of compression was too fast Wm the nose gear compmssing so quickly, the load imposed on the body of the darnper by the piston was so much that it wu# come off. The team agrwd that a more mbust damper and attachment were needed.

Dave Loewen located such a damper at a used motorcycle shop. This unit was a shock absorber for a small motorcycle, inarporating a damper and a spring. The spring on the shock absorber was very SM,so it was repîaced with a @Mer one. The shock absorber was srnall enough in diamebr bat it was able to fÏt inside the nose gear sûut in place of the spring thal was there, onœ the mounîing ends were ait off of the shodc absorber, as seen in Fiiure 7.6. The only draw back to this shock absorber was mat it had a limited amount of allowabb travel. A spaœr had to be instalîed to îiml the ûavel of the nose gear suspension so that the spring would not fully compm.

Figure 7.6: ModiReâ Motorcyde Damper

This new damping system was first tried in a taxi test on October 30". and it appeared to perfon well. However, because of a cross wind, only two wns were compkted on that day.

Nebrof these runs fulîy tested the damper because the acceieration was not very fast and the maximum speeds wem moâerate. On Nowmber 8". the conditions albwed for a ttue test of the damper and it perfomied we9. Rie acceîeration was quite aggressive on the second test fun and the pitchhg was not unacceptable.

7.4.2 Sbucbital

In addiüon to the damping pmbiems smin the early tests of 1998, a stnichral probiem with the nose gear was noîiœd. Whm tho ai- was pitching and had started to rnove, the fridion ktween the wheel and thet ninway inboduced a mamard moment into the nose gear stnR. The stnR is supportecl by cabk to handle this type of baâ, but the nose gear could be swn to dafied aft eacb tim it hit the ground. Inspecüon of the nose geai and ils supporthg structure after the tests on Sepbmûer 24' revealed that the rear guy wirerr had becorna pemanently sladcened and the supppoiling sbudure had yielded sîïghtfy. The fear was lhat if taxi testing continued Wout some modification, aie no= gear supporting structure could becorne

damaged in a simikir way as on SepWmber la, 1997. Tbsdubbn was to replaœ the mar guy

wim with tubes, as shown in Figun 7.7. The guy wim obviwsly mu# not resist any

compression, which meant that the forward guy wire was üte ooly mmber to resist the aft

deflection of the nose wheel. The tubes in plaœ of the rear guy wires would resist the aft

detlection of the nose wheel and sbiengthen and stiffen the entire sysbm.

The tubes used weiie 4130 steel, 5Mnch OD by 0.035-incti wall thidmess. The wires were

steel and had relatively heavy devises at eact, end, so the new tubes were not rnuch heaviet.

The same attadiment points b the nose gear stnR which had been used for the wires were used for the tubes, The tubes had a skt cut in one end and a I/IG-inch thick steel tab was welded in. A

hok was drilled in the tab so Lhat it auld be boMthe to nase gear strut whem aie wiw had

been attacheci. The tubes were attachecl to the bottom of the fusebge wrth the same 1184ndi aluminum gussets lhat the wim used. The end of the tube was heated with a blowtordr and crushed flat so that a bolt could be run thmugh it and the gusset. tt was decided to altach the tube so that it was on the outside of the gusset, Aich was rivetecl to the outside of the bwer fuselage longeron. Although this method of attachment is not the best from a load path perspecûve, it was

used for safety reasons. k was intended that if the nose gear strut were pushed bad, the tube would break away from the fusebge. Had the tube been connecded on the inside of the fuselage, it could have been deflected inwards when it bmke. In that event, it cou# have gone into the cockpit and injured the pibt. Figun 7.7: Nose Gear Support Wts

These support &ub, installed bdom the tests on September 29", prwed to be a great help, totally eliminahg the aft rnovernent of the nose gear noted earlier. They alsa reduœd the low speed pitdring siighüy, as this was before any of the dampen had hem tried. The stnik did, however, seem to cause pmbkms with the nose gear steering, Wich are addriessed in Section

7.5.1.

Uitimately, 1was the nose gear which brought the tetsting season to a dose. On November

8", afbr acceîeraüng masonably quickly to 50 miles per hour, the pibt sbwly rnoved the sW< back to attempt a crow hop. The stick movement was slow because the simulation had predicted that only a small stick mowment would be mquired to becorne airborne. This caused the aircraft to start bouncing, and several of these bounces were mosüy on the nose gear. After a few bounœs, the nose gear broke at th point whem ihe forks meet ttie main sû'ut, as show in

Figure 7.8, and aie sûut scraped akmg the ninway. These evients will be discussed in detail in

Chapter 8. When the sbut scraped akng the Rinway, the extra friction force caused soma significant damage to the nose gear support sbuûure. The support sûuts described eariier m this sedon bmlce away hmthe fuselage in pcaciaely the rnanner inbded, and no hancame to the pikt The repair of this damage will be discussed in Chapter 9. 7.5 Other development hum

In addition to the major developrnent actMties described in Seaions 7.2 to 7.4, there were a number of smaller issues which were not critical because they elher invohre minor changes or were considemcl acceptable far the time beig.

7.5.1 Sm

The steering system in 1997, which had been substantially mâesigned from 1996, was not an iswe. The pibt felt at all times that the steering was controllable enough. However, in 19981 the steehg hecame an issue again, partiarlarly after the installation of the support struts for the nose gear as ddbedin Section 7.49. tt was thought at the time that support sbuts might have increased the steering sensiüvii by eliminaa'ng the laberal cornpliance in the nose gear. The sensamty was reduœd by adjusting the connecüor~point of the steering cabks to the pedals so that they am doser to the turning axis. This adjustment, which was designed into the system, reducss the amount that the cablecl are movd for a ghpedal delledion, si, the wheel is tumed less. it also has the undesirable e(led of increasing the minimum tuming radius of the ornithopber, because the maximum deflection of the pedals is unchangeci. A slight increase was considsrsd acceptable to the pibt if it wouîâ mean that the stemhg was easier to control. fnioally ais adjustment did not improve the situation, but them it was noticed that the steering cables wm not as tight as they should be. Any slack in mese cables cwld cause pmblerns with the sbeering.

Once they wem adjusted to be tighter, the -ring improved slightty, but was still a constant souree of concern for me pilot. The pilot desaibed the steering as Wichynand said that she was constanüy working to keep the ai& going sbaight. Even a slight cross wind was too much to handle with the steeting mis way, but taxi tests mtinued on the days whem the wind was light enough.

The author suspects mat the pmblem with the steenng is due to the geornetry of the nose gear stnit, specificalty the angle the strut makes with oie ground. Like most general aviation ai- the omithopteh nose gear was originally designecl with a fornard rake angle. Withe shortening of the nose gear, this angle was reduced significanüy. Then, when the support struts were added, the angle was fuRher reduoed so that the fonward guy wire would be in tension.

Also, when the nose gear is compressed, the angle becornes ewn less and can be seen to be slightly negative. This is an unstable ateering configuration, which would indeed require constant effort to stay sbaight Wh the nose gear now being iebuilt, this geometry is being camfully assessed, as described in Chapter 9.

7.12 Appiiient-

Throughout the testing of 1997 and 1998, the ornithopter has dispiayed a tendency for the rigM wheel to bounca more than the M.This situation has been tolenble exœpt in a mht cross wind, which exacerbates the probiem. One possible cause is that the landing gear Îtself is not symmetric, with the right side king sMbr than the left This seems highly unlikely, as the gear was manufadured by Gmve Ai- in Caliimia, who spedalbe in making this type of landing gear. A more probable cause is asymmetry in the aiditse, either in the wings or in the outriggen. Sinœ the distance between the driving hinge and the pivot hinge (at the top of the vectical hk) is precisely the same on each wing, the ampli&& of üt8 fbpping is the same.

Measurements on the oulriggers suggesbd that the right outrQger is slightly higher than the left, which would man that the right wing is slightiy higher than the left throughout the cycîe. A measurement of the wing tip to gmund distana, &med mis, but the dn8rence was only about

3 inches. Sinœ Ihe cause d the asymmetry is not knm, and them WOU# likely be no easy way to fix it, nothing has been done to rernedy the situation. lt simply emphas~esthe neeâ for calm weather when conducting taxi tests (or winds siightiy from the Mt).

7.S.3 lnsbunsnfstkn

The frequency meter describecl in Section 6.3.4 did not funcüon corredly at first because of intefiremce probkms. A number of aie eady statc Rnpping tests were conducted to determine the source of this interference. it was also noted that the tachometer reading fluctuated by as rnuch as pluslminus 1000 rpm. A certain amount of fluctuation in the mading is expected, as the angine experiences a varying bad fmm the flapping wings, but the magnituâe was suiprising. A filter, consisting of a mistor and a capacitor, was installed in the wire leading to the tachometer from the engine. This reduœd the fluctuations in the tachometer reading b a believable pluslminus 100 rpm and seemed to help with he elebrornagnetic noise probiem. The frequancy meter still did not fundion entirely corredly, so work on it was continued. For the tests on

November 8,1998 the new fmquency meber, built by Rambod Larijani, was functioning propedy.

The homontal row of LED's was repbced with the original digital display on the instrument panel, which shows the fiapping frequency numencally. The same magnetic input as described earlier was used. The new fmquency meter also has an output to the NetDAQ so that the fmquency can be recordai.

An accekromelsr was added aîbr the tests on Septembew 19". it was mounted at the top of the nose gear strut because that location provided a @id fîat surface away fmm the elacbomagnetk noise of the engine. The accelerorneter, moâel AD XL 05 EM-3 by Analog

Devices, is a th~xisun&. This provided some inkresting data, discuSSBd in Chapter 8.

A new interference probiem was experienced in 1908 with the pilot's radio. This was most notiœable with the pressure transducer, but it also Medd the acœierometer. The pressure tranaducer $$na1 frwn 1998 has occasknal peaks to over 10 Vob. The signal jump to mis high level for a few wnds Wore mtuming to the proper kwl (About 2 voits). This signal was compared against a recordhg of the pilot's communications owr the radio, and the peaks wiere found to cornpond exactty to when she pushed the button ta transmit. The exact cause of the probkm has yet b be inVBSfiZ1atwd, but it is thought that thare may be a pmbîem with the grounding of the antenna.

7.6 Summay of 1998 Test R-ulb

The 1998 test season was wry sucassful. One of the crucial conœms since the founding of Project Omiaiopbr had bwn whether or not the aimft would be capable of propelling itsel to

50 miles per hour. The tests on November 8" pmved that it cm. These tests also showed that thete is an appmpriate stabibtor angle which will keep the airdon the ground, suppressing bouncing, untit it reaches mtation speeû. The other posiove aspect of the tdng season was the continued development of the pilot-togmundcmw interaction, which will be cntical for achieving flîght. Although the airdwas damaged, no one was hamied and the darnage was remarkably srnall considering the forces invohred. The mpairs of September la,1997 had held up well, even afbr the nose gear broke. Also, the timing of the damage cou# not have bwn better, with the

1998 test season drawing b a cbse anyway because of the weather. tt was good that the darnage occurreâ then insteed of during the first test of 1999. Refening back to the introducüon to the chapter, the other conclusions wem:

A number of difietent flapping frequencies wem maintained and the equilibnum air speed detemiid. See Section 8.3.

0 The a&al time to accelemb fiPm 30 to 40 miles per hour is gnrater han that predicteâ by the simulation.

0 There were no problems wÎth the zero stage after the addition of the engine restraint. The nose gear shorteming muses increased bw speed pitching, but this can be eliminated with appropria@ damping in the nose gear suapension.

The aircraR can mach 50 mph within a masonabla distance, but the length of ninway does not îeave much time to ansider the decision of whether or not to try a crow hop. However, 7000 feet does appear to be adquate.

A crow hop was attempted, but 1 was not successhrl. The aircraft stayed up for more than one full cyde of tha wings, but it cannot be considerd a uow hop. The rotation procedune wilt be changed b moving the stick more quicicly so as b get oie aircmft airbome quickîy.

Also, the wings continued to perfam well. The repairs describeci in Sedion 7.3 were relaüveîy minor, and all of the trailing-edge clips stayed on ttiroughout al1 of the tests. In 1998, data was collected during 29 taxi tests and one static fiapping test. This provided a large amount of information to be stuâkâ, al1 of which is p~1~~~11tedin the appendices. The graphs of aie 1998 wing data cari be found in Appendix Cl and those for aie rest of the data are in Appendix O. As with the 1997 data, a 'moving average" trenâline has ben used b show the air speed. In addition, because of the probiern with radio interfbrience, whicti showed the air sped to jumping to over 100 mües per hour, some portions of the air qmed data have been omitted.

8.1 Whig-

The purpose of the static ffapping on September 18" mis primarily a final check before proceeding with taxi tests the folbwing day. The first test was mnducted at four different fiapping frequencies, with about 20 seconds of data recorded at each frequency. The second test was conducted at one flappmg frequency. For each sedion of data, the average fiapping fmquency and the average peak bending moments were detemined. The resuiting frequency/bending- moment mlationship, shown in Figure 8.1 as squares, agtees well with that from previous static flapping tesis in 1996 and 1907'~.This not oniy confirmed that the data acquisition system was working, but also that there were no problems with the installation of the trailing-edge clips. lmproper dip installation cou# have inhibiteâ aie shearflexhg adion of the wing, which wouid have mMin very high bending moments.

Aise shown in Figure 8.1, as triingles, am the peak bending moments for a given fbpping frequency during taxi tests. The= data points were taken hmregions of the data mat had at hast five seconds of constant air speed and constant flapping fmquency. This data confimis the earlier noüon that air speed has less effed on the positive peak bending moments than the fîapping frequemcy. As further evidenœ of this trend, Figure 8.2 is a portion of the bending moment data when the air speed was 50 miles per hour. AIlhough lhis air sped is much higher than any from 1997, the peak bending moments am mich lower. (As compand to Figura 5.1)

The average flapphg frepuency in Figure 82 is 1.17 Hertz.

Figure 8.1 :Bending Manents vs. Flapping Frequency

The emphasis for the early taxi tests was on maintaining a given flapping freqwncy and detemining the equilibrium opeed. whik exprimenting to find the best stabilator angle. This pmvided for much more taxi test data at constant flapping frequencks than 1997, when the emphasis was on attaining a givm air speed. One of the reasons for this new approach was to keep the peak Rapping frequencies, and Iherefore peak bending moments, lower than in 1907.

Consequently, the peak bending moments were rnuch more masonable than those seen in 1997.

The peaks wem only higher than 3000 foot-pounds when the aircraft went through several bounœs on Odoôer 16" and on ~wemberam, suggestîng mat angk d attack rnay hava a mapr ekct on the peak ôending moments. This will not be confimed unül in fliqht data is obtained. Figure 8.2: Bending Moment Data from First Run on November 8, 1998

The number of fundioning strain gauges continueci to dedine in 1998. As the season

progressed, the first and second stations in bending and the third station in torsion on the rigM

wing stopped working. This left only thme channek recording good data: the third and fourth

stations in bending on the right wing and the first station in bending on the leR wing. In Referenœ

10, the left wing data is not considemci reliable and is exciuded. However, the plots in Appendix A

of the 1997 wing data show that the bending moments fmm the îeft wing generally agree with

those hmaie right wing. In Appendix C, the bending moment data from the three fundioning

channels (L& wing #1, rigM wing W and rigM wmg 114) are show on the same gmphs for the

data colkcted afbr Septembr 19".

The mason for the continued demise of the strain gauges is unknown. For each channel that recorded emw\eous data, the raw data mis doseîy examined to debennine if the problem was stricüy with the calibration or with the raw data. In each case, it was found that the raw data was bad. it is possible mat the pmblem is simply a îoose conmction. Before any repair work on the mingauges is started, a methad will be devised far dedennining if îhe gauges aiemselves are faulty, or !he wiring.

8.2 PobentiomederData

The potentiometers used in 1998 were the same as those in 1997: nidder, stabilator, angle of attack and thmttle. Once again, the Ndder angle has hem ornitteci from the figures presented hem, but inckided in the appendix. The reader shauld be aware that the graphs of throtHe input show the movement of the handle, as opposed to the oping of the throttle on the carburettor.

The differenœ is a result of the new airottle mechanism, described in Section 6.6. it was decided not to adjust the data for the response airve show in Fgum 6.1 1, because it was more useful to have a graph of the pilot's input. Howewr, this means that 50 percent thmttle on the graphs actualîy rep~e~~ntsabout 80 percent of full throttle at the carburettor. Anoaier change was the addition of a voltage regulator to the sbibilator potemtiomeber. The new stabibbr angle indicator, described in Section 6.3.3,took L input signal from this potentiorneter. Howver, it was noted earlier that the potentiomter output is dependent on the excitation voltage. Since the main batteiy voltage drops dumg a test session, so do the signais hmthe potentiometers. This is easily acoounted for in the data redudion, but it was having an adverse affed on the dispby. The addition of a voltage mgubtor ensured th& the output voltage for a given stick position would remain constant.

From aie experiences of 1997 it was leamed that the stabilator angle is a critical factor in successfully reaching takMspeed. tf the stick was held bofar forwarâ (positive stabilator), as it was on Sepbmber 1, 1997, there was a serious pmbkm with wheel bamwing. However, if 1 was held bo far back, th airdwould start to bounœ wll bebw 50 miles per hour. The simulation had predicted that the shoctened nose gear, ahgwith a moderate amount of fornard stick, WOU#alkw the aircraft to mach takeoff speed wilhout wt#el banaMng or bouncing. Sinœ reaching this sped was crucial to achievhg a aanr hop, one of the primaiy test goals was to validate this pdidion.

l11111111111111111111 I IlII II II IIIII /,Il IIIII

Figure 8.3: Potentirneter Data from First Run m September 19,1998

As expbined in Sedion 7.4.1, a problem with low speed pitching was notiœd very early in the test program. The first attempts at countenng this behaviour were to move Ihe stick fornard, as shown in Figure 8.3, until1was aY the way forward, which appeared to hep the pmblem in the test shown. The air speed was quite low in this run, so it has been left off the figure. On the next few nns, the bw spaed pitching was sW a problem, regardles of stabilator angle. In realii, the stabilator had little or no efkt at very bw air speds, and the pitching in aie first nin diminished because oie acceieration had stopped. In subsequent tests at higher air speeds,the forward stick position actually seemed to make the pitching wom. The positive stabilator angle wwld drive Lhe IIIIIIIII

IlII 1111111111111111 attack seen in the figure at this point are a muk of the slight heaving of the airuaR, not pitchwig.

This stabibtor angle appeaied to provide the Meal situation which had been sought

The sligMly aft stick position continued ta be used for the ned few tests, most of which dealt with Ihe issues described in Chapbr 7. These tests conhued to irdicate that this stabilator angle WOU# work for the entire takeofî run. However, the maximum air speed in these tests was never grnater than 40 miles pet hour. On Odober 16", the goal was to use this stick position to accekrate to over 45 mibs per hour. It was thought the aircraft wwld continue b accelerate and essentialîy Ry off the gmund waMut much change in stick position. In the fimt test tha aircraft reached 45 mibs per hour easily, then stadeci a series of lage bounces. Ms. Jones-üowman them reduced the throttle because the nose gear damper had corn lwse (see Secüon 7.4.1).

The bouncirg was very similar to that seen on September 15" and lem,1997, but the bounœs occuired at a higher air speed in 1998 because of the sholtend nose gear. From outside the ai- it appeareâ that each bounce was larger than the previous, and that the hncmwould lead to a crow hop. In between tests, the gmund ~iewmbyed to the pilot mir impressions that the aircraft was on the verge d flight, and that if the throtlk input was rnaintained, the air& would pmbably fly. Although the bounœs wsre quite severe, inspection of the fuselage reveaied no damage, so furaier atternpts wem made. However, each attempt ieâ to the same resuit, and maintaining the throttk input did not help.

In the hird run, shown in Figure 8.5, the pilot momentarily ieduced the thmttle once the bouncing staited, then increased it again in an attempt to continue the accebration. As with the previous tests, once the bouncing staited, the ai- œased to acceierate. Anoaier important point about the boundng is that it makes it difficuh for the pibt to maintain a specific stabilator angle, whidr swrned to rnake the bouncing wom. Figun 8.5: Potentirneter Data from Third Run on Odober 16,1998

After a period of analysis to consider how to avoiâ the bouncing, the next serious attempt at ieaching 50 miies per hour was on November 8". It was decideci that the stick should be heu slighüy forward (slightly positive stabilator) to amid bOun&g. On the fmt attempt, shown in

Figure 8.6,50 miles per hour was easiiy reached. There was a small amount of wheel bamwing, with aie main whlscomng about 3 inches di the gmund. This amount of wheel bamming was not considered a major problem, and it was decided to pmaeed with another test. The se- run is discussed in detail in Section 8.5. Figure 8.6: Potentirneter Data fram First Run on November 8, 1998

This stick position was the most successful to date, albwing the aircraft to get cbser than ever to its first Riht However, the fact that there was still a small amount of wheel banowing is a conœm. At the tirne of writing, further shortening of the nose gear is being considered. it is belied that this would eliminate the whlbamming because a neutrai stick position could be uS0d.

8.3 Air Speeâ m. Fkpping Fmqwmy

During the eady taxi tests, the flapping frequency was held constant much of the time and the air speed albwd to stabilize. From the sections of data with rebttiveiy constant air speeâ, 10 second segments wem examined to determine the awmge air spwâ and flapping frequency.

The collection of data points, shom in Figure 8.7, roughiy shows the relationship between the flapping fmquency and the a~ spwâ. Thare is quk a scalier to the points butssome of them are taken from near the end of a nin, whik olhers are clwiet to the begînning of a fun. It is passible that the grade of the Rinway was a f'ador. The Nmay is at its highest point in the

rniddk, so that the airaaft was ahways on a veiy slight indine for the first hdl of a run and a very

slight dedine for the second haW.

1l111:!ll1111111111III ------+------IIIllllllllllllllll III Illlllllllltlllllll III1

1111111111t11111111III -l '1- ' ' I- -1- l' - -1- ' - -,------l- c-7- ~IIIIIIIII~IIIIIIIJIII -l-_i--~--~--L-J--~--'--Lf.J--~--~--I-J--~--~--L-J--~--~--L-1- 1111111111111111 IIIII llllllllllllllll?,llll

IIII II 1 1 IIIIIIIIIIIIII IIII Il IllllllllllllIll 7- -1- -r- -7 --l--r-r - -r-r-7--l- -l--r-f - - -! r-, - -1- iiiiiiiiiriitiii'~iiiii

Figura 8.7: Air Speed vs. Flapping Frequency

The uppmost point in Figure 8.7 was taken from the Crst run on Odober 16". The validity of mis data point is questionable because of aie bouncing experienced by the aifcraft. tt is thocight mat had the airaaR not been bouncing, a hîgher air speed coukl have been reachd with this fiapping frequency. Takirtg this into aaxrunt, the figus wggests mat the design point of 51 miles prhour at 1.O5 HertzQmay be possible. h praaice, however, it will take tao much Rinway to mach the takeof'f speed at that freqwncy. Higher fmquencies will acœlemte the aircraft more quickly, but abwill increase the lift variation, whkh is a problem for rotation. A higher fbpping ftaquency couid also owr kad the wings. A teasonable compromise may be to use a fiapping frequency as high as 1.2 Hertz up to 50 miles per haut and ttm lhmtîk back to 1.O5 Hertz just

before rotation. Sinœ the wings am designed primarily for cnrising fiîîht at that ftequency, this

soit of compromise is not surprising.

8.4 Other-tp

In addition to aie wing data and potentiorneter data, them wem two other types of data

recorded in 1998. A threegxis accelerometer was instalied at the top of aie nose gear stmt, as

discussed in Çecoon 7.5.3, and the controCpand mounted fmquency meter finally worked on

November 8"'.

1 kœbmm@rDQfs

The continued trouble with some of the strain gauges in the wings albwed for the

accelerometer, rnentioned in Section 7.5.3, to be connecded to three of the NetDAQ channeis

previoudy used for that data. This was instalbd after the first set of taxi tests, on September 19", sa them are no accelerometer graphs for those bsts. The accelerometer makes no distinction

between modes of vibration, so high frequency vibration dominates rnost of the graphs. Figure

8.8 is typicaJ d the graphs of accelerometer data, which are in Appendix 0.

it is inbresting to note that the acœierations in the z diredion are offset by about negative

1-G because of the eWof gravity. ît is negative because the accelerometer was most easily installed upside down. In the figure, which is fmm the nin in which a crow hop was atternpted, a few large spikes can be seen just after 1:45 inb the nin. This is when the pilot sta- to pull the stick back and there were several bounœs on the nose gear, one of which caused it to break.

Afbr mis, the accelerometer traces are al1 mlatively quiet. During mis time the nose gear was off the ground, as was the entire aircraft for some of it. The high frequency vibrations disappear because the nose gear is not in contact with the grwnd. Noinmbu8, t @URun 2: Accdmmm Dib

Figure 8.8: Aceelerometer Data frm Seccwid Run ori November 8,1998

842 Frequmcym

As noteci in Section 7.5.3, the fmquency meber was a work in pmgress for much of the

1998 test season. However, it worked wel for tha fmal two tests, on November 8'. The recordeci signal from the freguency meter was checked by determining the achial flapping frequency hm the cyde tngger (as was done for the Rins with no fmquency meter) and faund to be 5.6 percent lower. This can be easiiy correcfed before tesong mils in 1999.

it is inteWng to compare the signal frwn the fmquency meter to the thmm input, as show in Fiure 8.9. A kg can be seen betwem me the the thcoltle is moved and when the fmquency changes. it is not suiprising, because of the inertia of the drive train and flywheel, that the engine rpm does not change irnmediately when the throttîe is moveâ. This same inertia is taken avantage of to even out the pawer mquirernents hmthe angine during the fiapping cycle. NoviHnkr 8,îm Run 2 Clrpplng Fmquoncy

1oa 1 -. I i I I I I I I I I I I I I ,-1.4 I 1 I I I I I I I 1 I t I 1 I I I I I I I I i I I I t I 1 I m.- - - ,- - - - - .- . , . . ,- - 7- - -, - - -1- - -1- - . . r. -r. -r. -r-

7--r-- -

Tlmo dnem uml d CI (nmrl)

1--Tngger -fhioWa PoJtlon -Flwping Fmqwncy -Alr s~wJ] figure 8.9: Ffapping Frequency Data from Secorid Run m Nomber 8,1998

8.5 Run 2 on November 8,1998

The events of the second run on November 8'" have received considerable attention. For the second nin it was decided to accebrate more quickly and by b exceed 50 miles per hour. It was also decided that if mom than half of aie ninway hgth was available and the speed was at least 50, a crow hop shoulâ be atternpteâ. Through rapid application of the throttle, îhe aircraft readied 50 miles per hout in 1:25, comparecl to about 2:30 for the fird nin. However, the acceîeration viitually stopped at this speed. W~ the halliway point of the runway rapidly approaching, and the requisîb speed having benreached, a crow hop was attempted. The stick movement to attempt the crow hop was very gadual, as the simulation had predicted that only a small movement wu# be requiried. UnforhrnaWy, the maIl change in stabilator angle did not initiate full ftight, but caused aie aircaft b start bouncing. Several of these bounces were mostly on the nose whed, and one of them caused it to break. The aircraft went through two more 1- MTA 100 bounœs on ¶henose wheel aiter aie pibt had reduced aie throttle and started ta apply full back stick. WRh the application of full back sticlt, the aireraft îei€ the gfound and stayed up for about one and a haîf flapping cycles of the wings. it shouid be notecl that the redudion in flapping frequency, whidi reduced the livariation, had a kt to do with the air& staying off the gmund as the wings went thmugh the upsûoke. The aircraft then went thmugh mveral bounces on the main whwls befare the nose finally came down and the aircraft came to a sbop.

Figure 8.10 shows the portion of run 2 from the time the pilot started ta move the stick to whm the aixraft carne to a stop. Akr studyhg a slow motion video of the cmw hop attempt and the data, certain important points were denalied. These pomts am marked on the graph in Figure

8.10 and listed in Table 8.1. R is important to remember that the angle of attack tace is not the pitch angle of the ai- so it will go down when aie aircraft heaves up and vice uersa.

I Part of Nov«nkr 8,1898 Ru, 2: Pot~~efMa

figure 8.10: Potentiameter Data fiCm Hop Attempt on November 8,1998 Point on Graph Event l~ra~hTtne - I 3 First Bounœ 101 :42.8 !secondBounœ 1 01 A3.7 Reduœ Throttle 01:44.0 Nose Gear Breaks 101:44.7 - - -- First Scrape [01:44.8 seconci scrape 101 :45.3 Main Gear Leaves O1 :46.7 Ground

Lighuy

ppppp - Gear Leaves Grounâ 101 :49.0

Main Gear Touches 01 :51.2 Gear Leaves Ground 01 :51.4 15 1 ina al Touch Down 101:51.9 -. .- - .- .- -. .------. 16 $ose Gear Touches 101:52.1 TaMe 8.1: Sequence of Events for Crow Hop Attempt on Nomber 8,1998

Close inspacbon of the data shows that the throta was adually reduced (point 3) before the nose gear broke (point 4). There were two îarge hnœson the nose wheel More it broke on the third. The second of these bounces produœ a loud bang, which can be bard on the video frorn the cockpit camera, when the nose gear suspension fully compressed. The bang was bud enough that Ms. Jones-Bowman thoupM that the nom gear had broken at that point. In the slow motion video shot from outside the airupff, the nom gear breaks on the next bounce, but it may have starteci to break on that previous bounce. Afbr the nose gear broke, the aiwaft scraped on the nose gear strut Iwice, mlag in very low angks of attack and spikes in the acœlarometar signal (points 5 and 6). From the video, the aidleaves the ground about 1A seconds after the second scrape (point f),and stays up for 1.4 seconds. The rest of the bounces are indicated in the table and on the graph. After one of the bounces, the pilot increased the throttle whiîe the

aircraft was in the air (point 10). Anerwards, she said that increasing the thcbttie abr a bounœ is

standard pradice in fixed wing aircraft, in order to sofben the impact the next time the air&

cornes down. Since she is an instructor, with a great deal of experieriœ with bouneed landings

hmstudents, this is an automatic riesponse for her. it probably does not help in an ornithopter

because the air speed will not incriease immediately. In fact, the increase in flapping frequency

might make the next bounœ harder. In this case, the increase in throttle was so brief that it had rieffect

8.6 Summay

The data acquisition system continued to ôe an important tool for the devebpment of the ornithopter. In particular, the potentiorneter data helped immensely in developing the takeoff

strategy. In addition, the new stabilator angle indicator helped Ms. Jones-Bowman in canying out the plan. tt is unfortunata that there are now only three sets of strain gauges that worlc properly, but the data continued to confimi that the wings are operating within their structural lirnits. Some of the maifundioning strain gauges may be repaired phor b starting ttie 1999 testing. A very

positii note was the frequency meter. This will help both the pibt, because she will know exactly what the flapping frequency is, and in the data reduction.

Although the hilunt of the nose gear was disappointing, the sacond nin on Novernber 8" wes an important step forward in deteminng the takedf strategy. Finrt, it was found that the aircraft can mach 50 miles p8r hour. Also, there are two other conclusions that can be made.

The first amciusion is that the mowment of the contra1 stick must be fairty brisk. However, how much to change it by is süll not certain. Too much hck stick could result in a bss of air speed because the thrust of a fiapping wing dirninishea with inmasing angle of attackO.A sudden bss of air speed could be qu& dangerous. However, too lit* back stick will essentially be a mpeat of

November 8". The author feets that it is probably betbr to move Ît too much than too Ti.On= the aircraft is ofF aie gmund, the pibt will bnng the stick fornard sliihtty to amid stalling and to avoiâ a signihcant kss in thnist. Less thnist, hough. should be needed once ths air& is off (he ground and there is no rolling mistance. The second conclusion is that 1 may be neœssary to duce aie throttle prior to rotation, whidi may approadred in two ways. The airottk cou# be reddsignificantly, as it was on Novetmber 8", and then inmseâ agan once the aircmft is air borne; or it ewld be reduced slghtly, to a fbpping frequency of 1.0 Herb, as was suggested earlkr. The reason for reducing aie fiapping friequmcy before rotation is to duce the magnitude of the lift variation, so that the aircraft does not touch aie ground as the wings go up.

These conciusions am sirnply ideas at this point. As the neiseason of testing approaches, they will be discussed thomughly with Be pibt and the takeoff sûategy will uîtirnateîy be decided. At the time of writing, preparaüons for another season of testing are undemay. These pmpaiatioms are minly foaia4d on repairing the darnage fmm the cmw hop atternpt, but a few other modifications are being considemi as well. Due b budget constraints and severe manpower limitations, most of the efforts are on essential modincaoons. Thentire barn, and the pilot in parücular, is eagerly awaiong the opportunity to resume teeüng and make the ornithopter's historic first flight.

9.1 FurdrgeRepain

As a mit of the nose gear brieaking and the subsequent scrape along the wnway, some of the stnidural tubes in the front of the fuselage wem darnaged. Most of these can easily k replaced wîth new tubes, but the ber 1-inch diameter tubes wem sevemiy bent, as shown in figure 9.1. This bend had resuM in some localized budtling, so they cou# not simpîy be straightened as was done previously with the steel tubes in the thorax. In addition, because they are 6061-T6 aluminum, a new piece of tube couîâ not be welded to the existhg tube without compromiqing the material properbs. It was decided to cut the darnaged portion out and join the replacement tube to ththe existing tuba with a plug. The pkg will be a tube that fits inside the aluminum and overiaps both pieces, with rivets holding the pkig inside the tubes.

Figun 9.1: Bent 1inch Aluminum Tube

One proMem wilh this method d joining the hnro pieaa, was a deliberab bend in the original tube. When the ornithopber was buiît, the l-indi akiminum tubes were bent b help gh CllLCAlU~1O11RI(CIW'~ 106

the nose of the aimait a sbeamlined ahape. One of thess bends was located very dose to the

point whem the phig is to be inseided, whia, would Ernit the amount of ovedap between the pl&

and the new piece of aluminum tube. To avoid this problem, it was ôecided to maice the bend in

the plug and shorten the new piece of aluminum. For ease of fabricating. it was furaier daedto

mplace the bend in the plug with a bevel cut and a weûi, so the plug would have to be steel.

Therefore, the plug is achialiy two pisaw wnlded bgether, and the new piece of aluminum will

not butt up apainst the existing ph.

The milthiclaiess of the pbg was se3û3cted so that it will be at hast as stmng in bending as

the aluminum which used to be them. In fact, the pkyl will b sbonger because it is steel. A

potential weak point in the plug is at he bevel, because it will be a sharp bend insteaâ of a

gradua1 one and it will be weldeâ. However, the welder who has worked on the ornithopter is

highly skilled, and the plug is over s~edb handk the bending bad, so the stms concentration

should not be a probîem.

Figun 8.2: SW Ptug lnserted in 14mh Aluminurn Tube

The plugs wm made by machining a pieœ of l-inch OD by O.OW)-inch wall thkkness

4130 steel to an outside diameter of 0.920 inches, leaving a wall thiekness of -050 inches. The

inside diameter of the aluminum is 0.930 inches, sa there is enough chrance for the plug to be

inserted easily. The pbgs were bevelled so that the angle, when they are put bgeîher, is the

same as the Mdwhich used to be in the aluminum at that kcooon. At the time of W.this woric has bem completed. fo take the pichm in Figure 9.2, aie two pieces wre epoxrrd togemer. The final step in making the pbgs will be to weld the pieces togmr.

The &et plug rnethod of joining a new tube to an emgtube was abusd kr the Iwo vertical tubec, whidi are direcüy above the end of the nom gear sbut (Item 2 in Figure 4.4)

Redthat at aie top of ofese tubes is a box structure which was reinforceci afkr it was damaged on September la,1997. (Section 4.5) The reinforcement of this ama proved to be adequate, as there was no damage sustaineâ aiis tirne. Homnier, it 1 quite an intricate structure of vertical and horizontal pbes and two large guswt plam. To save time and ellott it was decideâ to salvage this box structure by mgthe vertical tubes just below the bottom of the gusset plates. To sirnplify the repair, the new tubes and the plugs to jon them to the existing tubes are one pieœ.

Three inches of the end of a YSinch OD by O.OgO.inch waY steel tube was rnachined to fit Mnsiûe the ahminurn tube, as shown in Figure 9.3.The remaining portion of the tube, down to the nose gear &rut, is (ha 5Mchdiameter by 0.0901nch wall thickmss. This is significantly stronger than the pmvious alurninum, and is possibly unnecessarily tteavy, but the additional weight is kss than one pound and this rnethod of repair is much easier.

Fîgun 9.3: New Steel Tube with Machined End

All of the other damageâ tubas wiW be replaced with ones of the sasame material and wall thMess. It is apparent mat had the nom wheal foik not brd

Onœ the rivets sheared, the bending bad was taken entireiy by the botbm tubes. Had the ûuss structure ramaind intact, the damage wu# have been much less because the bending bad wouM have been distributeci to the top and ôoüorn tubes, which am a considerable distance apaR As wps done with the thorax repairs earCar, merChenyMAX rivai will be used eveiyutiem in the rebuitt nose Sedion of aie ofnithopter. Akm, the existing intact rivets will be replaœd wilh ChenyMAX rivets in the cockpit uuhem euer possible.

8.2 Nose Geat MOdificaliom

Once the structural repaim an cornplete, the nose gear stnit will ôe rebuiît The nose wheel itself will be mplaced with one of a brger diameber. The wheels which were used on the main undercamage in 1996 are a good sbe for this and are very light because they have plalc rims. Using one of these also ensures that a spam is avaibble. The laiger nose wheel will duce the rolling resistanœ of oie air- and should eliminate the kndency for the tire to becorne cornpletely compressed when the aircraft is nose down during high-speed taxi tests. The larger wheel wll require a larger fork, and the foR neeâs to be much stronger, paiticubrty at the point where it attaches to the nose gear sûut The sûut will havs to be shoitened to accommodate the larger nose wheel without raising the nose of the ai& it will most likely be shortened by an additional inch, to increase to nose down attitude.

Since the nose gear is king rebuit, this is a possible opportunity to make a viWout of a necessity. nie first issue is that the pilot is not keen on the steeràig bar, because it means that the piane of her foot changes when she $teers. She has said that this makes it difficult at times to kaep her fbt on the pedals. The stwring mals johed by a @id bat could be replaced by independently mounted pedals which are hinged at the fkor. Allemately. two pedals could be joined in a paralb~ramfadiion ao that the hœs of the mais are always in the same plans.

How~w~,either of these ideas WOU# requim a bt of time to redes'in because of the severe space limbtkns in the nose of the aircraff. The eiaisong steerhg method is aâequate and the

pilot ha$ bcorne acarsdomed b it now, so the steering sctuaoon will not be redes'ined.

Rie other issue is the probkm with the sbeerlrg king 'hinichy". which started afbr the

addition of the nose gear struts. This is a pobntially dangernus pmbîem if aie pilot cannot steer

the air#aft reliably. As discusaed in Section 7.5.1, it is thought mat the geornetry of the nose gear

strut, speaklly #e angle it rnakes with the gmnd (oie 'rake" angk) is the cause of the

problem. Sinœ the nom gear is likely to be shortend by another inch, mis problem will get

wom if it is not addresseci. Now is a bgical tim ta do so, because the nose gear has b be

rebuilt.

it is known that a fornard rak angle on (he rose gear will resut in a stable ste8Wg configuration. Howwer. it was desid to muse the existing nose gear sûut because of the time invohred in designing and building a new one. What mis uncertain was Iha enect of intmducing an offset to the nose gear, SQ mat the axle of the whed is not on the (uming axis. In order ta investigîte the he al ddmt rake angko and dinelient offset$, (he tricycb catt show in Figure 9.4 was buitt. The nke angle couid easÿr be adjusted by bending aie front Wi's

support to a dinerent angle, and a straight York" could b exchangeci for a bent one. ûiimt

configurations mm tdd by btag the art roll down a ramp. with perturbations being

inboduϞ by bumps. Based on the mtts O# these tests it was decicfed to muse the eWng

nose gear sPnrt and inaoduœ same trail in aie design of aie fork. This will mean essentially no

fonnrard rab, but the axle wheel will &ail behind the sbeering axis ta provide stewing stability

(sirnilar to ttm configuration shown in the figum). This design tums out to be veiy sirnilar to that

employed by a Hohrn Qing wing15.

The final consideration wiîh the nose gear design will be the suspension. As documenteâ

in Section 7.4.1, thme different dampers wem tried on the nose gear in 1998. All of them had

their stmgths and weaknesses. With the introduction of tail in the fork, the suspension could be

redesigned b give a larger amount of travel, or at least recapture the original fiv8 inches of travel.

Flom the experiences of 1998, it is knmthat damping in the nose gear is essential, and this will

be incorpoated in the new dqn.

9.3 0th ModMcations

There are omr possible modifications to the ornithopter, which will be undertaken if time

pennits. Nme of these madifications are as ensential as reôuilding the ncse gear and front fuselage, without which the ornithopter cannot continue taxi testing. Pemaps the highest priority of aiese 0thmodificahions are aie brakes. The pibt has mentioned on occasion mat the brakes are not strong enough. This is an important issue because the braking distance rnust be kept to a minimum if a aow hop is to be compkted *in the bngth of ninway available. The solution

WOU#be to incorporate levers into the brake systetm so that the pilot has a mianical advantage when pushing on the brakes. With the cumt setup, she pushes directty on the master cylindem. There is no danger of over pn#ieuring the sys$mi, even with a 4:1 advantage on the brakes. However, this modification is not essential because the brakes were warking better as aie &&hg pmgresseâ m 1998, and on some occasions she was able to stop qub quicùly.

Anoüwr action item rnay be to repair some of the strain gauges on the wings. Ideally, Wre should be stations in bending and hiK, M torsion on each wing, for a total of eight. Originally there were 16 strah gauges in the wings, but many of those dataacquisition channels are now bemg used for other instruments. However, eight channetls cou# easily be made available. This work is not essential eîther, because it does not prevent the aircraft hmattempting a crow hop.

Howewr, @ewing load data is very useful, and it will be particularly intemsting to have infiight data. The problern wioi mpairing the strain gauges, as mentioned before, is that they are mounted diredly on the spar, which is now wvered with fabric. Removing the fabric can be accomplished, but removing the strain gauges aiemseks without damaging the Kevlar skin of the spar might be quite difficult.

As usuat, ümre is a certain amwnt of instrumentafion wotk fo be done. The reason for the radio inteNrenœ with aie pressure transduœr must be detemined, and fixed. It is likely that once that problem is SOM,the onboard video cameras will begin to fundion again as they did in the early part of Vie 1998 bst season. In addition, a new instniment will be added to indicate the

~dderangle to the pilot. This cou# take a similar form b the stabihtor angle indicator, with a horizontal row of LED's instead of vertical. Altemabely, it cou# be a single light to indicate when aie ~dderis centred, since that is the only position of significance for these tests. The pilot has also suggesbed an angle of attack indicator and an aceelerometer indicator on the instrument panel. Homwer, she is alraady very busy, and ewry new instrument will occupy sonte of her attention.

9.4 Test Pmgmm for 1988

The tesüng in 1999 will ecrsentialîy be a continuath of 1998, but it will not pW up rîght where 199û îeft off, with a crow hop atbernpt The fimt few tests will be similar to the tests on Septmbey 24", 1998. A constant flapping fnquemy Al be heu, and the best stabiletor angle detenined. h will be a slightty different angle from that used in 1998 because the nose gear will be shorter. Also, the pilot will have to a feél for steering with the new nose gear design.

Hopefuliy it lwill be easier ta control and inspire mon confidence than the Ywitdiy" steering of

1998.

Once these issues are sorteci out and aie pilot is reacquainted with the cockpit environmenh the will pmgmss to higher speieds. Y wouîd be interesting, though not

~ss~ntial,t~ conduct more of the constant air spd tests at flapping frequencies between 0.95 and 1.05 Hertz. These tests would provide more points for the graph in Figure 8.7. More attempting a crow hop, it wuld be worthwhiie to test the hypothesis of ducing the throttle immediately befom rotation by doing so without pulling ais stick back. The purpose of this wouid be to see how dramatically the aiwaft skws with a eEgM dudion in airottle. if at all. h dll also be intetre&ng to see if the aircraft can axelerate past 50 mites per hour before attempting a mw hop. It is ho* that this will be possible with the reâuced mWing mistance ofkred by the new nose whegl. In addition, the more nose down attitude should provide morie thrust whiie eliminating the wheel bamming, both of which should impmve the gnund spwâ. f it is found that the aircraft cannot exceed 50 miles per hour, then any cmw hop attempts will have to be approached with caution. The original design was for cruising RigM at 51 miles pet hour, and the aiTcraft is about 50 pounds heavier than it was originally. However, Ihem an, a number of aerodynamic effeds, such as ground effed which were not accounted for in the otiginal analysis.

The author believes that 1999 will be either the year of a successful crow hop, or the year that the limitations of this aircraft are fully revealeâ. This thesis has dacurnenteâ the testing and dewlopment of a fulCscaîe, pibted ornithopter over the last two pars. The approach to modifications during the devebpment has been largely experienœ baseid. In other words, modifications wem made lo address speafic needs which arose fmm the testing. In the case of the field @pairs describeci in Chapters 4 and 7, the cîesign of the modifications was bated on experieriœ and fundamental engineering principies. with less emphasis on anaîysis. The offaason period, as dewibd in Chapter 6, allowed for a full anaiysis of each modification. Ail of aiese acüvitks were the resuît of a team effort, with the indiviiuals noted king major conbibutors. The author was involved in alrnost al1 of aie actMties, and was exclusively mponsible for the data collection and redudion, discussed in Chapters 5 and 8. For 1999, the author is pleased to be the chief field engineer. This will allow the opportunity to continue working on ttiis exciting project, and to continue documentation to serve as an addendum to this report Delaurier, James D., "An Ornithopber Wing Design", Canadian Aemnautks and Space Journal, Vol. 40, No. 1, March 1994, p. 10-18.

Stilley, Faye, 'Spencer's Omithoptef, Mode1 Airplane News, February 1999, p. 4045.

Dalaurier, James 0. and Harris, Jemmy M., 'A Study of Mechanical Flapping-Ww Fliht", The Aemautkal Journal, Vol. 97, Odober 1993, p. 277-286.

Delaurier, Jams O., 'An Aerodynamic Model for Flapping-W'i Flight", The Aemau&l Journal, Vol. 97, April 1993, p. 125-130.

Delaurier, James D., "The Oevebpment of an Efficient Ornithopter Wingn, The Aemautkal Journal, Vol. 97, May 1993, p. 153-162.

DeLaurier, James O., The Devebpmt and Tesüng of a FulCScale Piloted Omithoptef, Canadien Aemnaufics and Space Journa/, to be publishd in 1999.

Machaœk, Todd J., 'A ûynarnic Anabsis and Femibility Study of a FulCScale Ornithopter's Take-On Proceduren, M.A.Sc. thesis, UnkrsRy of Toronto InsüMe for Aerospace Studies, 1995.

Rashid, Tahir, The Flight Dynamics of a FulCScaie Ornithopter", M.A.Sc. thesis, Univermty of Toronto InstiMe for Aemspace Sbidies, 1995. Fowîer, Stuart J., The Design and Dewlopment of a Wing for a FulCScaie Piloted Engine-Powared FiappingWing Aircraft (Ornithopter)', MASc. thesis, University of Toronto InetiMe for Aerospace Studies, 1995.

10. Mehier, Felix M., "The Structural TBStjng and Modification of a FuYScaie Omithoptets Wng Sparsn, MA-Sc. thesis, University of Totwito Institute for Aerospaœ Studies, 1997.

11. 'Fluke NetDAQ Data Logger User's Manual", Fluke Corporation, 1995.

12. Fermira, Sandra, 'Defornation Geometries On Shearflex Wingsn. B.ASc. thesis, Univermty of Toronto, Depaitment of Meduinid Engineering, 1998. 13. Zdunich, Patrick J., 'Finite Ebment Analysis of Omithapter Fuselagen, Unpublished report, UniversRy of Toronto Institut8 for Aerospaœ Studies, 1998.

14. Zdunich, PaWJ. and Fenton, Bruce A., '1998 Orniaiopter Repair Work", Unpublished laboratory noims, University of Toronto Insütute fPr Aempaœ Studies, 1998.

15. Dabrowski, HansPeber, 'Flying Wmgs of the Hoilen Bmthenr', A ShiRer Military Histoiy Book, 1995, p. 39.

August 18,1997: RW Bending Moments Static Flapping at 0.58 Hz

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