What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Unusable Fuel Query

Hello

I am in the final stages of assembly with my RV7 and last weekend I completed my fuel flows and measuring the unusable fuel.

My question is what are other people's unusable fuel quantity WITH Flop Tubes installed?

Both my Left and Right tanks are measuring around 2.5L or 0.66 US Gallons. The reason I am asking the question is my friends RV7 with fixed fuel pickups has much less unusable fuel around 0.5L or 0.13 US Gallons.

Does 2.5L or 0.66 US Gallons sound reasonable with flop tubes installed?

Thanks
 
Virtually zero fuel unusable

I've ran both of my RV6 fuel tanks dry (on purpose and not on the same flight:)) to check how much fuel is unusable. When I filled the tanks they took exactly the tank capacity which is 19 gal. in a RV6. FYI this is without flop tube and would depend how low the intake tube was positioned in the tank.
 
Possible explanation, your friend may have his stock pickup tube right down near the floor of the tank (where it should be). That is 3/8" above the floor if the tank, so next to no 'unusable'.
The flop tube pickup is much thicker, about 5/8" diameter (plus o-ring) and has holes on the end and around it's perimeter, so it becomes un-ported at a level higher than the standard pickup, therefore has more 'unusable' in the tank.

Easy way to check if your 2.5L is reasonable is get a large pan or tub that you can tilt at same angle as the wing dihedral, pore 2.5L of water in it & see if the deep end is about 5/8 to 3/4" deep (simulating the diameter of the flop pickup).
 
Hello

I am in the final stages of assembly with my RV7 and last weekend I completed my fuel flows and measuring the unusable fuel.

My question is what are other people's unusable fuel quantity WITH Flop Tubes installed?

Both my Left and Right tanks are measuring around 2.5L or 0.66 US Gallons. The reason I am asking the question is my friends RV7 with fixed fuel pickups has much less unusable fuel around 0.5L or 0.13 US Gallons.

Does 2.5L or 0.66 US Gallons sound reasonable with flop tubes installed?

Thanks

That's a huge amount of unusable fuel. During prep for A/W inspection, when measuring fuel flow, we ran the tanks dry and then sumped the drains. Got just a couple of drains full (the longer, thin ones like this
13-18464.jpg
) on one tank and 5-1/2 IIRC on the other. I thus consider unusable fuel to be < 1/10 gal on either tank, and plan to never be in a position to need to know that. :) Oh, yeah, flop tube on the left tank. I don't remember which one was which for measuring, but I'd guess the slightly higher amount was on the left tank.
 
My tanks ran almost completely dry in both flight attitude and tail low (RV7). My calcs are at the hangar but only a couple ounces left in either tank and both have flop tubes.
 
Something wrong

I have both types of pickup in my RV-7 and got about 200ml unusable in the tank with flop tube, barely 50ml in the tank with standard pickup. This was done in normal tail dragger attitude.
 
Our RV-6

In getting ready for a weigh-in, I used the electric pump to run both tanks dry on our RV-6. Tail was up, in level flight attitude. Ran the pump until fuel stopped coming out of the fuel line, took the weights with unusable fuel. Then we drained each tank into a cup. We got maybe 2 ounces out of both tanks. Right tank has a flop tube. Practically no significant unusable fuel. Amazing.
 
Back
Top