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. Carburetor 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!!! ice 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 throttle 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 d fo 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 humidity 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.