Fuel Tank flapper door

[Goingmach_1]

Hi,

I have just started my wing kit and am looking at the drawings. It shows a 1 1/2" hole in the bottom of the fuel tank nose ribs. Obviously to let the fuel travel between the cells. The drawings show a flapper door on a hinge to cover the same hole. Again obviously to stop the fuel from travelling outboard and starving the fuel pickup when your down to the short strokes of fuel quantity.

Question, did everybody install these flappers? The reason I ask is because a friend of mine has a completed RV8 and I looked in his fuel tank and see this hole but there is no flapper door.

Your thoughts?

Thanks

 

[Andy Hill]

The Flap is fitted only if you fit a Flop Tube... I think

 

[Lemmingman]

I installed one flop tube in my right wing. I have the flapper in both wings. It's not strictly necessary for the normal pickup tube or the flop tube. It is just there to slow down the fuel draining from that bay during prolonged uncoordinated flight situations.

 

[chaskuss]

Here's mine

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The red item in the foreground is a flush fuel drain off of a Beech King Air. I machined up a couple of bungs to make them work with the RV fuel tank.

Charlie

 

[DaAV8R]

The red item in the foreground is a flush fuel drain off of a Beech King Air. I machined up a couple of bungs to make them work with the RV fuel tank.

Charlie

How does the water get out? Is there a hole in the drain housing near the skin?

In other words, have you created a lip that will prevent the escape of water?

 

[ronschreck]

I wish I had installed a flapper door.

The flapper door also keeps fuel from migrating toward the wing tips during prolonged spins. Depending on the fuel level, I find that my engine quits on the 5th or 6th turn of a spin.

 

[Michael White]

The flapper door also keeps fuel from migrating toward the wing tips during prolonged spins. Depending on the fuel level, I find that my engine quits on the 5th or 6th turn of a spin.

Well, other than scaring the cr@p out of your passengers, that certainly makes for a nice reminder that it's time to break the spin....

 

[ronschreck]

Well, other than scaring the cr@p out of your passengers, that certainly makes for a nice reminder that it's time to break the spin....

Actually, no! I live about 5 miles east of the CLT class-B airspace. I overfly at 11,500 feet when returning from the west. It's fun and instructional to fly over my field and spin down. About twenty turns is all I've done.

Interesting things I've learned on the way down:

A. Relaxing back pressure while spinning causes the spin to accelerate.
B. If you release the stick in an established spin it will stay in the full aft position. You have to force it to neutral to break the spin.
C. The engine quits after 5 or 6 turns.
D. The engine re-starts before you can pull out of the dive during spin recovery. (Good to know!)
E. If you neutralize rudder but keep the stick full aft the spin will probably keep turning. Rudder has little effect in a full stall/spin at idle power.
F. If you add power (before the engine quits) the spin will flatten out some. (Never could get the RV-8 into a flat spin. I tried!)
G. Foolproof RV 4-step spin recovery:
* 1. Throttle - Idle
* 2. Controls - FORCE to neutral position
* 3. Airspeed - Wait for 100 KIAS
* 4. Recover from the dive

Also, I never do spins with a passenger, so there is nobody to scare the cr@p out of except me. I recover well above 3,000 feet; plenty of time to set up for a dead stick landing if the fan quits for good.

Disclaimer: Please get some dual spin training from a qualified instructor before doing any of the above.

 

[chaskuss]

Flush fuel tank drains

How does the water get out? Is there a hole in the drain housing near the skin?

In other words, have you created a lip that will prevent the escape of water?

Robert,
Notice that the ProSeal on the bung does not go all the way around. That is because the bung has 4 cut outs to allow fuel to drain all the way to the bottom. Viewed from above, the bung is shaped sort of like the Nazi "Iron Cross" medal. There is also an annulus on the ID of the bung, at the bottom, to allow the fuel to reach the very bottom of the drain fitting. See crappy photos and drawing below. [This was done about 13 years ago. Photos then were taken with a disposal camera]

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The drain threads into the bung. Hard to see, but there are indentations to use a spanner wrench to tighten the drain into the bung. The drain seals to the tank skin via an O-ring. The drain can be disassembled and both the internal and external O-rings replaced.

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Assembled flush drain mounted to a test piece of .032" aluminum.

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Cocktail Napkin drawing of the bung.

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Left fuel tank with flop tube [brass weight for the end removed], anti hang up bars [for flop tube], capacitance fuel sender and flush drain. This four piece design of the anti hang up bar [unlike Vans design] allows easy and unfettered access to the inside of the fuel tank via the access plate.

Charlie