Alum. header tank question. KF IV

[beeryboats]

As a fairly new owner, the first thing I noticed is that there was no low point sump drain in my aircraft. But then again my poly tank was not placed in the correct place. Now that I've installed the aluminum tank in the proper place, it is the low point sump drain for water and general crap that can get in the fuel. Then again mine is a tail dragger and the low point may be very different for a nose wheel aircraft.

[Av8r3400]

Header tank, one major reason.

The fuel pickup in the main tanks is located such that they drain from the rear of the tank to facilitate pluming during the wing fold.

During low angle of attack or decent with lower levels of fuel in the tanks, these pickups can become un-ported, sucking air instead of fuel.

The header tank gives a reserve of fuel in this instance to keep the pilot cooling fan running.

[Paul Z]

Here is where my 7 Super Sport has the header tank behind the passenger.

[PapuaPilot]

There are several reasons that planes have header tank(s). Some of them have been mentioned. Let me list what I understand about them.

1. The header tank is the low point in the plane. It is there to collect water, dirt, sediment, etc. so you can drain it. Note that the fuel outlet to the engine is slightly above the bottom of the header tank to leave some room to collect stuff and still allow clean fuel to go to your engine.

NOTE: You should drain the header tank on preflight, after every flight and after refueling. If you get too much stuff in the bottom then it will go into your engine.

2. It is there to provide some usable fuel in case the fuel tanks become unported. This happens especially when you have low fuel in the main tanks and pitch or yaw (slips or poor coordination). When you do any of these things the fuel in the tank(s) can move away from the pickup hose. The header tank will have enough fuel for the engine to keep running for several minutes if you are unported.

Example: If the header tank holds a half gallon of fuel and your fuel burn is 8 GPH at full power then you have about 3.75 minutes of fuel in the header tank at takeoff power that you can fly unported before the engine quits. If you are at a lower power settings then you have more time.

3. It functions as a place to separate air from the fuel. If you have fuel returning from you engine/fuel pump notice that this line goes into the top of the header tank. This allows the air to separate at the top and go back to the fuel tank(s). The fuel stays in the header tank and goes back to the engine.

Don't remove the header tank! That would be a recipe for disaster. Hopefully this makes it clear that you want, no need, a header tank.

If you have the poly header tank don't even bother using it. Bite the bullet and buy an aluminum one. I just threw my "new" poly tank in the trash recently after buying the aluminum one.

[Paul Z]

I agree with Phil Nelson. This is why I wouldn't use the Poly Tanks
Original Tank that came with the plane. I couldn't get it to stop leaking.
IMG_0761.jpg

Replacement tank after replacing the 1st Tank. I was surprised how much fuel that had leaked. Definitely a safety issue!
IMG_0709.JPG

[kitfoxrk]

Thanks to all for the great comments. I am enlightened. It is greatly appreciated.

[PapuaPilot]

Paul Z,

Wow, your pictures really drive the point home of why you shouldn't use the poly tank!

What did you use to attempt to seal the threads on the poly tanks? What did you use on the aluminum tank?

[Dave S]

Phil,

I think Kitfox uses Permatex 80938 in their kits (formerly Permatex 9AR) It is a white sealant that is fuel proof and does not harden.

Same stuff recommended for poly and aluminum tanks and wing tanks & any other screw in fuel fitting....... now the poly tanks?....what can I say...... .....

Used it to seal all fuel fittings....6 years....no leaks.


Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

St Paul, MN

[Paul Z]

I used the Permatex 80938 that comes in their kits. I believe the treads are tapped to deep. I removed, reinstalled just to watch it happen again. The treads are so weak you have to worry about stripping the threads out. For me it's the aluminum tank or a funeral, pick one. If you look at the Poly tank that leaked on the sides, you can see the treads are not stripped. I wouldnt waist the time or risk my life putting in one of those crappy plastic ploy tanks.

[jiott]

Here's my 2 cent opinion on why the threads leak on the poly tanks even when sealed with the 9AR which is really good stuff. I think it is because the poly threads are so soft that they conform perfectly to the fitting threads and thereby essentially wipe off most of the 9AR sealant as you are screwing in the fitting, along with the fact that the threads are tapped deep and you can't tighten the fitting very much. The same 9AR sealent works very well when the mating part is aluminum (header tank) or fiberglass (wing tanks) because those are harder materials. Just a thought.