CorvAircraft> Fuel system opinions.

[Dave Morris "BigD"]

People have used the mechanical fuel pump in the past.  The problem 
with using the Corvair mechanical fuel pump is this: a failure of the 
diaphragm will leak the fuel directly into the crankcase.  Other fuel 
pumps have different failure modes that are not as 
disastrous.  William finally contradicted his own earlier advice and 
eliminated the mechanical fuel pump to reduce that possibility.  He 
did say that gravity feed would be a good way of doing it, if you can 
develop sufficient head and flow rate between the tank and the 
carb.  My own choice would be a main tank(s) feeding a header tank 
with at least 45 minute reserve capacity, and an electric boost pump 
for backup.

Dave Morris

At 08:23 AM 4/13/2007, you wrote:
>
>   Ok guys I have a questions for the group about fuel systems that 
> my EAA technical advisor (TA) asked us.  First some 
> background.  Our advisor has built and flown behind many 
> aircraft.  He has restored several classic aircraft, is a retired 
> airline captain and currently spends his days flying corporate and 
> running an airport.  He is the kind of guy who has, or will, fly 
> behind everything he suggests..  Our project is a Zenith 601 HDS 
> that has 2 ten gallon leading edge wing tanks.  It currently calls 
> for a plain vanilla corvair engine and an MA3 carb.  TA has warmed 
> to the idea of Corvair, although he is not crazy about it.  He has 
> helped people in the past with other auto-conversion and was 
> helpful, but not overly enthusiastic.  All that being said, here is 
> the issue.  During a conversation on fuel system design we showed 
> him the WW design for the Zenith XL, using the 2 in series 
> electrical pumps and no mechanical pump.  He recommended against it 
> on the principle that we
>  had placed all our eggs in the one basket, that being the 
> electrical system.  His suggestion was to use one electrical pump 
> and the corvair mechanical pump and fly it like a Cherokee using 
> the electrical pump as a boost pump and only during take off and 
> landing.  Alternatively, he suggested a header tank, pumping fuel 
> to the header and gravity feeding the carb.  This would probably 
> require a return line to the wing tank.   We discussed this for 
> sometime and then he asked me this.  Could I name a certificated 
> aircraft, low wing, that only had one type of pump to move fuel to 
> the carb?  If not, why did I think that was?  Interesting question 
> as the FAA guys "fly behind" lots of airplanes.  I would be 
> interested in any help or suggestion I can get with fuel systems, 
> especially flying airplanes and their different fuel systems.  Thanks phill
>
>
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