Hi All,

Was wondering if I could get some advice on a header tank that basically doesn't work.
Normally when fitting out a jet I use a commercial header such as the UAT, MAP, Intairco etc.

I thought I would make a "dodgy" one for my Xcalibur using an ultra flash header tank. Pictures attached.

So when I take off the header is pretty much full. Fly a straight and level flight and you land with a full header. Do slow roll and you can just hear the engine starting to get a few bubbles. If you really push it you get the nice white smoke flame out that we have all seen. Upon landing the header is still pretty much full.

Why is it so? You would think that a small air space in the header wouldn't really matter that much but my testing proves it does.Does anyone have a good theory on what is happening?

Paul.

What pick up did you put in the hopper?

If it's not a felt, paper or sintered type, that's your issue.

Your header is not the problem i would say
but your pickup in the main tank .It gets out from the fuel when you turn upside down.
Maybe you want to change to something like this

?????? ???????? - www.petame.gr

But again you can trace the problem easy :

Start your engine.
Wear earplugs.
Go half throtle.
Hold your header tank and turn it upside down.Check for any changes.
If all ok place header back in the model and turn all airframe upside down and check again.

my2c

I know it may sound obvious, but is your fill line closed while is flight ?

The WHOLE point of the hopper is that it copes with a main fuel pick up coming in and out of fuel. If the main pick up was at fault there would be lots of air in the hopper, I read it as not much.

It should have a felt main clunk and absorbent pick up in the hopper ideally.

As Dave said, during maneuvering, the air bubble is moving around the header and at some point travels over the pickup and you are getting a bubble to the turbine.

You need something to "Wick" the fuel in the header tank. That way you get fuel, and the bubbles stay in the header. I personally like the felt filters that are used in the chainsaw, and weedeater markets.

With that said... I've had issues with commercially made header tanks... so I only make my own now. Spend half as much, and never have an issue.

I'm interested to see what the problem turns out to be.

I use a similar system to yours & have had no problems at all, I'm about to
fit a simple header tank to a little Bobcat 50 as the engine sometimes stops
when the fuel level is low & the nose is down on the approach (no header,
felt clunk in the fuel tank).

Thanks for the reply's everyone.

Dave - I haven't used anything on the pickup. It's just open tube. What I will do is use the filter that comes with the UF and see how that goes.
Maybe it's obvious that this is the issue. Thanks for the feedback.

DelGatoGrande- I don't think its a main tank issue as there is very little air in the header on landing. I do however like your home made pickup. Nice!!

RobinLeblond - An open fill like in this kind of system would result in a flame out shortly after take off. There could however be a leak in the fill like but I don't think so. The plumbing is pretty solid.

Dr Honda - I will give the felt filter a go. Never had a problem with commercial headers. You may ask why I am not using one then

Mr Matt - That has to be the issue. I would have thought a slow roll would have been pretty gentle of everything and allowed the bubble to roll around the outside of the tank.. I guess not.

Boomerang1 - I will put the felt filter on and report back.

​​​​​​​Paul.

so you where able to cause the problem on the ground
by turning just your header with your hands
while engine in half throttle?

...never hapen this to me with the headers i have like yours..

So I managed to get 6 flights in this afternoon with the felt clunk installed in my header tank. It now looks something like the attached drawing.
No issues now.. very happy !!

Glad to hear it.

I discovered those felt clunks about 10 years back, when I needed a rather small tank in a gas (petrol) model. Someone told me that they will get every last drop of fuel out before letting air pass... and they were right!!! When I built my first jet, I bought a UAT and spent $50 on it... but after a while, I noticed that there was some wetness around it, and I couldn't ever get the cap to seal 100%. Then, I built a small jet (wren 44) and my $50 UAT was causing flam-outs. (getting a little air past the cap) So... I grabbed a 4oz dubro tank, petrol stopper, and a felt clunk. Never had an issue with that, and it cost about $10. Ever since then... I just build my own.

Glad you find a solution, Felt clunks work very well, and some people even use them in the main tanks without a header tank or a uat with success.

The original problem with your header tank is that it is quite small, and its standing in the up position, with a small cross section area. I always used bigger ones, with at least 10oz and the tank shape itself as close as a cube as I can find, with the biggest cross section area in the horizontal position.

The only disadvantage of the felt clunk is that it needs inspection every flying season or so, and it increases fhe workload of the fuel pump. This is not a issue at all for the pump mechanics by itself, but for helping avoiding trigger that dreaded watchdog function some, if not most, turbines have.

Paul

Just a plain tube will suck a bubble straight down the hole! The felt type breaks these up, holds a certain amount of fuel and maintains the supply.
I now only use MAP (Canada) bubble traps, same all the people around me, plus we use the Hi Flow felt clunks we sell, no air in the hoppers and just about 100% success always. People discus flame out issues after they are highlighted like in this thread, my lot just shrug as they follow a path and don't change from it. Obviously building a tight fuel system is critical, but we don't suffer with flame outs in my group.
Just keep an eye on your pump voltages, this now will give you a fuel system health check, we only use premium paraffin and we don't suffer algae like Jet A1 users.

Glad you are sorted

Dave