CAVEAT EMPTOR ... (Continued from Preceding Page) facturer allows becaus e harmonith f o e c vibratio- en n tanglements that are set up. Third, to complicate the matter further . whic e proin s pitche th ,4 s pwa hi 6 o dt again way over the manufacturer's limit. With three strikes against it, that prop was bound to go out and it just about took me with it. Icing On this subjec f buyino t g e homebuiltpropth r sfo I , ha a dlon g chat with Steve Wittma t Oshkosa n d an h have subsequently talke o t othed r well qualified, knowledgeable people. Base n whado t I've learnedd I' , like to submit these recommendations: 1. If interested in buying a "reconditioned" prop Iml Control from a shop not well-known to you, check with the FAA to find out if they are a certified prop shop. My supplier was not certified. This will not make them liable for an experimental prop that they sell you, but at least they'l e limius l t tables, etc. n makini , youp u g r prop. Get a yellow tag! f 2buyinI . a gpro p fro a mprivat e source, check Shivers,B. ByC. (EAAJr. 49289) with the FAA or other facility to determine that the prop model wile suitablb l r youfo e r purposes. Just 8928 Valleybrook Road becaus t bolfite i th st pattern doesn't mea nthinga . Birmingham, Alabama buyinf - I . de 3 thae s gbrana on propwa t w y dne bu , signed for a similar application to yours. In my case, a prop for a 125-hp "Swift" might be the answer, or per- hap e "Yankeeth s " prop n thaI . t waye b t t i wil, no l necessary to cut it down much nor will it be neces- sary to change the pitch much from the original. 4. If you don't know all the facts about that prop V^ARBURETO e th hazard f Ro s ICINGE ON , you're thinking about bolting onto your machine, stopd ,an don't make another move! Get the facts! Talk to the guys of primary concer o pilott n f ligho s f t o aircraft e on s i , e mosth t controversial subjects connected wit e fielhth d in the "know", look up the specs, and make certain of aviation. My interest in this subject increased as that you aren't being eased down the primrose path. the result of a landing, with a dead engine, at the Birming- In my case, I was lucky. I'm still around to tell the Municipam ha l Airpor Februarn o t , 1963 10 ye air Th .- I full tald y an e expec o havt t e "Tailwind" N-312t Sa craft involved, Piper "Super Cruiser", N-4297Ms wa , Oshkos t n '72whai hbu , t about you? Before grabbing also the first aircraft on which the Shivers carburetor up that bargain, beware!!! indicator was installed. Prio thio t r s collected timha eI d several informative articles relating to carburetor icing (AOPA Pilot, De- cember, 1959 and Flying, February and December, The failure of fixed metal propellers on home- 1960) in an effort to become better acquainted with builts problema is of great concernHead-EAA to the problems involved in an effective means of detec- quarters. Several accidents of this type have occured tion of ice in an aircraft engine induction system. in the past few years and have been the probable Assuming tha informatione th t s providea , thesn di e cause somein fatal accidents. manyIn casesthe articles, was correct as to location of ice build-up, metal propeller has been a cut down, repitched one the only problem appeared to be the construction of a such as in the story. Often, they are damaged suitable detection device e uniTh .t used provide- de a d propellers that have been straightened before other tection rangdegree6 3 f eo s below freezin degree2 3 ( g s modifications are accomplished. An added element F to -4 degrees F or 0 to -20 degrees C) providing (althoughShafer's Mr. casefactora the of in not the necessary temperature detection range as suggested "Tailwind" accident) has been the use of these props by these articles accumulateIce . thiin d s temperature with shaft extensions. range woul indicatede db . HeadquartersEAA wants compileto a report on Initial ground test, conducted wite "Supeth h r the use (and misuse) of cut down metal propellers. Cruiser" durin e springth f 1963go , revealed thae th t We would appreciate any and all information probe wire installed adjacent to the valve pro- members have that would apply to this particular vide desiree dth d indication, under simulated conditions. problem area.resultsThe willprintedbe in (The hol n whici e e prob s th hfirs wa et locate s proi d - SPORT AVIATION. vide e opposit drillinr th dfo n o e idl t egth e e je sid th f eo In addition to the advice and warnings contained in carbureto s alsri e locatio waloe th d Richte th an l f no r the article, EAA advises that the builder contact carburetor temperature probe and the ARP ice detector.) originalthe manufacturer metalhis of propeller On November 8, 1963, after completion of the required providing the model number, the new length and paperwork, STC SA217SO was issued by the FAA ap- pitch you plan to use, and the anticipated rpm provin e installatiogth e carburetoth f no indicatoe ic r r operating range. their Ask feasi- the adviceto as on the "Super Cruiser". bility of your modifications - particularly with re- Flight test, conducted wite "Supeth h r Cruiser", metallurgicalgardsthe to considerations. Secondly, soon revealed that actua accumulatioe ic l sufficienn ni t wooda of considerpropelleruse "Spit-the the - quantit causo yt e powe t providrno los d indican di sea - fire" OJf.did with wooden blades! tion at the probe location. It was determined that the deflection of the fuel air mixture by the throttle valve provided a temperature consistently 15 to 40 degrees 48 SEPTEMBER 1972 colder than the same point (idle jet location) on the coming air freezes as it passes the outer rim of the throttle opposit e carburetor th wal f o l e temperaturth , e differ- valve, restricting the air inlet and also resulting in ential determined by the throttle setting. Continued test, an overrich mixture. Corrective procedure for this type of actual and simulated, revealed that the probe provided engine failure is to advance the throttle to cruise or full a flat surface (the type probe presently used by the ARP open position (correct fuel/air ratio supplie e maith ny db ice detector) on which ice particles deflected past the fuel nozzle o restort ) e heath e e carburetot th ris o t e r throttle valve roul trappee db r flo ai provido wt y db n ea heat shrou appld dan y sufficienheaa r fo t t lengt timf ho e erroneous indication ot' ice but did not provide an indica- to clear the ice formation, this condition indicated when tion of ice when power loss was experienced due to actual the throttle can be retarded to the closed position and the icing. Additional test revealed conclusively tha onle th t y engine idles normally. This type of icing was the cause point wher e accumulatesic e , causing power d losan s e enginoth f e failure experience- de s wa t 196n i di d 3an engine roughness, is on the throttle assembly and the termined after landing that a throttle setting of 1600 probe wire was relocated on the throttle valve under rpm would permit engine operation; however time th et a , SA316SOC ST . Although thi- s ac informatio e ic o t s (a n landine ofth t attribute failure no g th s ewa carburetoo dt r cumulatio throttle th n no e assembly rather than closinr go ice. restrictin e inductiogth n passag s previouslea y depicted Noticeable throttle valve icing of this type can also l illustrationial n f carburetoo s r t presentlicingno s i ) y be expecte occuo t d r during ground o idling150t 0 060 , accepte e FAAth y b d, despite letter d flighan s t demon- rpm with most aircraft, when the OAT is 40 to 60 strations including total power loss and restart demon- degrees F and the relative is 80 to 100 percent. strations, continued test under actual conditions further Engine roughnes higd san h magneto drop, during engine substantiat previoue eth s findings. run-up e alsar , o associated with this typ f icingo e f I . The vaporization process, cause of temperature reduc- n accumulatioa s undetectei n d prio take-offo t r , severe carburetore t a th tio x n i n mi r ai , occurd e fueth an l s sa power loss may be experienced on take-off. If in doubt the point of fuel discharge, a nozzle located in the center abou e availabilitth t f fulo y l power a stati, c check e venturioth f . shoul made db e prio take-offo t r . As the fuel is changed from a liquid to a vapor, e secon Th d moran d e serious typ f engineo e failure evaporation cause a sreductio n temperaturi n e th f o e occurs at intermediate to full power settings, when the incoming air and the adjoining carburetor wall. The ice mass projects into the venturi opening as described temperature dro s dependeni p e throttlth n o t e setting, above, and has the same effect on engine operation as a slight drop below outsid r temperaturai e e (OATt a ) closin e throttlth f g o r placineo e mixturgth e contron i l idle and a severe drop at full throttle. If the incoming air f positionof e idlt th cu e . Unde e mosth r t favorable con- contains sufficient moistur throttld ean e setting provides ditions engine failure from this cause is preceded by the correct temperature droe moisturth p e begino t s only a slight loss of manifold pressure or rpm followed e supercooleth for n mo d surface carburetoth f o e r wall by a complete power loss resulting from a lean mixture. and discharge nozzle. Maximum condensation of moisture Although the cause of power failure is lack of fuel (im- on the carburetor wall or fastest rate of accumulation proper fuel/air ratio) some fuel continues to flow from the accompanie a noticeabl y b d e manifold pressur r rpo e m main discharge nozzle, maintaining the temperature drop los r engino s e roughness occurs whe e temperaturth n e cause vaporizationy e continueb d ic e th o built sd an ,d differential between the incoming air and the inside sur- even thoug e engin longeo th hn s i e r developing power. faces of the carburetor are maintained at a given tempera- Corrective procedure for this type of engine failure is to ture sprea a prolonge r dfo d perio f timedo simplA . - il e apply full throttle, , and operate the engine lustration of the required temperature spread, as related primer (pump rapidly) to restart the engine, also to to condensation, is provided by observing the condensa- restore the heat rise to the carburetor heat shroud. Primer tio f moisturo n e supercooleth n o e d surfac a glas f o es operation can normally be discontinued after 30 to 60 containing an iced beverage. It will be noted that con- seconds of operation or when the engine resumes normal densatio s greateni r during condition f higo s h humidity operation without the aid of the fuel supplied by the (summer months certaid an ) n frer temperaturesai e . primer. During restart procedure engine roughnesy ma s e moistureTh , deposite e supercooleth n do d surfacf o e occul cylinder al t equippe f i rno e sar d with primer lines; the carburetor wall and fuel discharge nozzle, is moved however, the heat rise is sufficient to melt the ice accumu- toward the throttle valve by the velocity of the incoming lation for engine restart. mase ic se beginth d throttle builan o st th r n ai di e valve This typ f engino e e failur s firswa et experiencen do whe throttle nth e assembly reaches freezing temperature. Marc , 196419 h t ,Vera o Beach, Florida while demon- (Ice build-u e throttlth n o p e assembly projects inte oth stratin e carburetoth g e indicatoic r o Pipet r r Aircraft low pressure area of the venturi and interferes with the Corp. on "Cherokee", N-8500W. However, the corrective fuel/air ratio.) The ice builds until detected by procedur r enginfo e t eknow no restar t s thaa n wa tt noticeable manifold pressure/rpm los r engino s e rough- time, necessitatin a gforce d landinge seconth r dfo , ness. time resula s a ,carburetof o t r ice. Engine failur thin eo s occasion occurred at 7000 ft. and all attempts to restart Prolonged ice accumulation can result in complete the engine, except primer operation, failed and a forced power loss occurring primarily from two causes. The landing was made at the Vero Beach Airport. After first and less serious is caused by formation of ice on th minute5 e1 groune th o t e enginn n so dth te e started dan idle-je e tthrottl th sid f o e e valve, while operatinn i g ran normally without any modification. This demonstra- cruise configuration. If a loss of manifold pressure or tiosubsequend nan t loa Piper'f no s Experimental "Chero- rpm is not noticed because of slow accumulation, the kee", N-280 furtheo 0t e studth r carburetof yo r icing re- ics detectei e d onl n closine o ythrottle th f o g f cari , - sulte thesn di e conclusive findings N-2800f o e Us . W pro- bureto rt applie hea no sufficiena s r i t dfo t lengt timf ho e vided comparative study of multiple probes, in the car- to melt completely an ice accumulation prior to power buretor, not allowed on standard category aircraft. This reduction. (Ice accumulatio e throttlth n o n e valve, idle typ enginf eo e demonstratede failurb n ca e timy an e t a , t sideje , provide a sprematur e relationship betweee nth e 145-h degree5 th 4 n s o i p , T ContinentaF s OA tha e th t l idle jet opening and the throttle valve — creating suction or the 150-hp Lycoming engines. The amount of water prematurel supplied an y— s additional fuel fro e idlmth e required normall causo yt e total power loss t ful,a l throttle, t sourceje , causing engine failure fro n overricma h mix- thres i fivo et e tablespoons. ture.) Idling failur n alsca eo occu- moisturf i in r e th n ei (Continue Nexn do t Page) SPORT AVIATIO9 N4 CARBURETOR ICING ... (Continued from Preceding Page) e mosTh t likely tim encounteo et r carburetor icing, contrar e generath o yt l consensu f opiniono s s durini , g take-off, climb cruisd an , e configurations where heas i t seldom used unles noticeablsa e los manifolf so d pressure occursm orp r . Temperature t whica s e foric hm vary wit individuae hth l aircraft becaus cowlingf eo r intak,ai e design, location of the carburetor in relation to the engine, and numerous other factors, but will be found to occur with most aircraft at 40 to 55 degrees F OAT if sufficient moisture is present in the incoming air. All (Photo Left) The redesigned gauge and throttle assembly aircraft, on which the indicator has been installed, have which compris e completth e e carburetor-ice-indicator been found to accumulate ice while operating in this OAT installation kit. (Photo Right) Marvel-Schebler MA-4-5 range moisture Th . e conten incomine th f o t r controlgai s carburetor reflect e installeth s d modified throttl- as e the rate of accumulation if the throttle setting and OAT sembly. This carbureto commonls ri yCessne useth n do a provide the correct temperature differential for condensa- 182, Mooney "Statesman" Piped an , r PA-28-180. tion. One of the primary sources of water, providing fast ice accumulation s througi , e aircrafth h t fuel system. Carbureto froe ic rm this sourc occun e ca t lowea rT OA r and at any time the water is not frozen in the fuel tanks. e improvemenTh fuef to l handlin provisiod gan quicf no k drainfuee th l n tanki s s greatlsha y reduced carburetor icing from this cause. Use of partial carburetor heat can also cause carbure- icinr to g when operatin lowet ga r outsid temperaturesr eai , this being the case at the time of the engine failure while test flying "Cherokee", N-8500W bees ha nt I .determine d that icin s mori g e likel o occut y r whe e temperath n - ture, as measured at the Richter carburetor probe loca- tion, is between 0 and 12 degrees C (32 to 55 degrees F), this temperature range comprising the yellow and green arc, or caution and safe operating ranges, of the Richter carburetor temperature gauge. The application of partial hea provido tt e these suggested operating tempera- ture mors si e likely, under condition higf so h humiditr yo moisture content causo t , e carburetor critica e icinth t ga l point rather than prevent its formation. Further evidence of this hazard is evident in reading the article regarding engine failure as a result of carburetor icing in the September, 1965 Flying, page 104 f hea.I s usei t n i d mannee th r suggeste Richtery db reserve th , e heat rise (full-on position) may be insufficient to clear the ice accu- mulation or addition of the heat reserve may increase the The blac throttlke th are n ao e plate indicatee ic e sth rat accumulationf eo . build-u e pthrottl th are n o ea flye dotte.Th d lines Wit informatioe hth n provided during developmental indicatin closen i y fl de positiogth same n th sho ew who testing the suggested use of carburetor heat would be full build-up of ice will close off the idle jets. heat if engine roughness or a loss of manifold pressure occursm orrp , returnin heae gth t contro ofe fth positioo lt n when the manifold pressure or rpm is regained. Carburetor remain in the extreme left edge of the red arc for an ex- heat should als minuteo appliee ob tw o t t leas da se on t tended lengt f time o hn resul ca , n completi t e power prior to power reduction and for a sufficient length of time failure as described above, necessitating restart procedure. to melt any undetected ice accumulation. If no engine Application of full carburetor heat and clearing of the ice roughness occurs, that would indicate ingestion of water formation wil e indicateb l d whe e indicatoth n r needle enginee byth carburetoe th , placee e r b th hea n n di ca t return greee th no st arc. off position if desired. After power reduction very little Earl yn preven detectioca e ic t f damago ne th o t e hea provides i t d fro carburetoe mth r heat shrous i d dan engine as a result of prolonged operation with a lean inadequate to melt an accumulation present prior to mixture (slow accumulation may prevent detection power reduction. through roughness or loss of manifold pressure or rpm). Utilizin Shivere gth indicatoe sic piloe rth t is warned Formation of ice on the throttle valve, cause of the lean e accumulatiooic f n e timprioth ea noticeablo t r e loss mixture occun ca , r whe mixture nth efule controth l n i s i l of manifold pressur occurm rp r seo (normally5 1 fiv o t e rich position. A slight roughness from this cause may not minutes depending on the rate of accumulation), the e e noticepilotb th y .b dMinimu f carburetoo e mus r presence of an ice accumulation of minute thickness pro- heat will save d increasfuean l e range additionn I . r fo , vidin indicationn ga formatioe Ic . indicates ni movey db - maximum power densese th , coldesr o tdesirables i r ai t , ment of the indicating needle into the red arc as the ice and the Shivers ice indicator allows the maximum use formation begin betweep bridgo t sga e e probth enth e of cold filterean d r (excepai d t when hea s actualli t y electrode throttlth d ean e valve. Whe e indicatinth n g neede combao dt t icing). needle moves inte extremoth c ar ed lefre t e edgth f eo Unlike the carburetor temperature gauges, the car- the ice mass has increased in size and will begin to bureto indicatoe ric r is dependen neithen to r temperature affect engine operation if it is not cleared. Prolonged humidityr no , onl actuae yth l presencformatioe ic n a f eo n ice accumulation, allowin e indicatinth g g needlo t e for an indication. £)

50 SEPTEMBER 1972