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RV-3 Fuel flow question

F

Flyguysr5

Active Member
I have an early RV3A with fuselage tank. Typical dual diaphragm mechanical pump but no electric pump. If and when the mechanical pump fails will it allow enough fuel to flow through, with the little head pressure only, to supply the engine? I was installing a new mechanical pump on a Piper this weekend and decided to blow through it to see how free flowing it is. Not very.......

I do not have the original planes to see if an electric pump was originally recommended or not.
 
I would be very surprised if you could keep the engine going without a pump. One really needs a high wing aircraft for that, I'd say.
 
Fuel flow

I have done so in a flight attitude and it does not seem like it would be enough to get thru the needle and seat etc. But I'm also guessing the fuel vents sticking down provide some ram air at flight speeds that might help? Main question at this point since I do not have original drawings was is an electric pump part of the original plans?
 
Why would you want to take a chance with this and not just add a back-up fuel pump like every other RV we've all seen? Imagine that engine driven pump failing at the worst possible time - on final or during climb out. You're not flying a Champ or a Cub that has a low fuel flow demand. It seems to me that the RV-3 was very heavily influenced by the Piper design you were recently working on. I haven't researched the numbers, but I'm pretty comfortable saying that no Certificated aircraft (similar to the -3) would be approved w/o a back up fuel pump. Look at the drawings for the -3 or call the factory and see what they say.

Better safe than sorry that's what I say. Especially when it comes to fuel delivery issues.
 
RV-3A Fuel Sys. Set Up Fuse. tank

Some years ago I renovated an RV-3A with 22 gallons tank behind the panel, and removed the engine mounted fuel pump and replaced it with a std. Vans issue facet pump. Fuel flowed thru a filter and to the facet and then onto the carb. and during takeoff / landing I always used the facet, but (at altitude) also tested it at different fuel levels to simulate a climb out w/out the facet, and I never had it cough or sputter which was nice to know.

Doug Lomheim
RV-3A O-290G Sold
RV-9A FWF
 
My RV3 also has a fuselage tank. It has both a mechanical and an electric fuel pump. Recently the mechanical pump failed (spring under actuating arm broke), but I didn't notice until I was flying with some extreme nose-high attitudes. I.E. with the carburetor above the outflow valve on the fuel tank. The engine sputtered but would recover immediately once the electric pump was switched on. Without the electric pump, the engine would recover as soon the nose was lowered. Of course, if your pump has failed in such a way that there is debris within the pump that hinders fuel flow, your results may vary.
 
Fuel pump

Ours originally had no electric fuel pump and fed from the bottom rear of the tank closest to the pilot. I added an electric facet while putting inverted systems on it. Probably not necessary with the carb from before the conversion but I feel better having the backup with the Ellison TBI.
 
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