RV-9A True Usable Fuel???

[GETST8FRM]

I recently purchased an RV-9A with standard 18 Gal. tanks. I have been getting usable fuel info. all over the map..ie: 1/2 gal. un-usable per tank, up to 2 gal. un-usable per tank.
Is there a standard answer for true usable & un-usable fuel per tank??
By the way, I could not be more happy with my purchase. Great speed & I can't get it to burn any fuel <----Joke. I appreciate your help.

[scard]

It is generally accepted (but best proven by testing your own setup) that un-usable is just a few ounces. As it is in my -9A tanks.

[flyboy1963]

I also bought a 9a and wondered about the fuel, but am too chicken to run a tank dry!
I just drained a tank to seal leaky fuel sender screws, and looking into the tank with a mirror ( too find out why gas was still squirting out the holes!) i see it's fairly open thru the nose ribs.
If you look at the drawings, the tank lets fuel run down to the pickup, but in a prolonged turn ( or bank, such as an approach into a strong x-wind) toward the low tank, it appears the pickup will be sucking air if less than half a tank is present!
I recall seeing a drawing with a little one-way flapper door which is common in wing tanks, so maybe some builders can help us out here!

My bigger boggle is how to accurately 'dip' the tanks, when only the top half can be accessed thru the filler cap! I'm thinking a plastic ( glass?) sight gauge on the cabin wall would be a welcome addition, if all the fittings were in the wing root to preclude leaks, fire hazard etc.

enjoy!

[9Driver]

We pumped our tanks dry using fuel pump (tri gear) and wound up with 4 ounces unuseable in each tank. However I decided to use 3 gal as a more realistic figure because of the posibility of fuel sloshing away from the pickup in rough air. We made our own calibrated dipstick by adding 2 measured gallons at a time and marking the tube at that point. Incidentaly at four gallons fuel is just visible directly below the gas cap.

[Kevin Horton]

Originally Posted by flyboy1963

If you look at the drawings, the tank lets fuel run down to the pickup, but in a prolonged turn ( or bank, such as an approach into a strong x-wind) toward the low tank, it appears the pickup will be sucking air if less than half a tank is present!
I recall seeing a drawing with a little one-way flapper door which is common in wing tanks, so maybe some builders can help us out here!

If you fly in a prolonged turn, where is the ball on the turn coordinator? I'm betting it is pretty close to the middle (the lowest point of the curved tube it rolls in). The same force that keeps the ball in the middle will keep the fuel in the inboard end of the tanks.

During a crosswind approach, why not simply crab with the wings level during the approach, and switch to the wing down method late in the game? If you want to use the wing down method for the whole approach, I'd put the fuel selector on the high tank.

[kentb]

18.1 gal.

I have run my tanks dry in flight. I was a little supprised that the tank took 18.1 to fill to the bottom of the filler neck. I usually like to leave a 1/4 inch below to the bottom to allow for expansion, but wanted to see how much I could add.

Kent

[rvbuilder2002]

Originally Posted by scard

It is generally accepted (but best proven by testing your own setup) that un-usable is just a few ounces. As it is in my -9A tanks.

It is usually a very small amount but as Scott already mentioned...It is important that you verify what the unusable fuel is for your airplane. There have been accidents related to the variables that are possible. It is easiest to do it in flight but the thought is un-nerving to some people. Using the electric boost pump to drain the tank in to fuel jugs works also.

[GETST8FRM]

I like to land with a minimim 45 minuite fuel reserve. I have a hard time getting my 0-320 to burn 8 gal / hr. If there is 1/2 gal. un-usable in each tank, that means I need to have 3.5 gal. in each tank at my minimums ( I can accept this number). If there is 2 gal. un-usable in each tank that would mean I need 5 gal. in each tank at my minimums. (5 gal. in each tank =10 gal. total. Seem like a lot of un-usable fuel)
What are the minimum's other RV-9A pilot's use???
What is the safest way to to determine un-usable fuel per tank???
By the way, I am seeing Van's published performance numbers easily. I am surprised / pleased. I picked up my 9A 3 weeks ago in Oshkosh, flew it home to an airport just outside of Jackson, MS & averaged 7.1 GPH. Love my 9A!!!

[N941WR]

Originally Posted by GETST8FRM

...
What are the minimum's other RV-9A pilot's use???

30 minutes for DVFR, 45 for NVFR translates to three & 4.5 gallons.

Originally Posted by GETST8FRM

What is the safest way to to determine un-usable fuel per tank??? ...

If you don't want to run a tank dry in flight, run both tanks down down low. Level the aircraft. Pull the quick drains out and empty the tanks. Re-install the quick drains, pour a 1/2 gallon in each side. Disconnect the fuel line at the carb and point it into a calibrated gallon jug. Turn on your electric pump and run each tank dry. Look at how much is in the jug after the electric pump starts sucking air. The difference is your "unusable".

[kentb]

My tanks are placard for 18 gal. After running the tank dry (engine starts to stumble), I switched to the other tank. When I got back to the airport I added 18.1 gals to that side. I repeated the process on the other tank and got the same answer.

We each build the tanks slightly different, so the quantity will very with your plane. I don't know how much is unusable in my tank, but I do know that the engine will stop after using 18.1 gal.

I would not normally run my tanks dry, but did this for testing purposes during phase I.

During normal flight I would switch off of a tank that got down to 3 gal. I would land somewhere before the second tank got to the 3 gal point.

Kent