What goes on inside your tank

[cymaz]

I found this on poo tube and thought it would be good to post. It really does show how much the fuel is thrown about and how hard the clunk has to work to keep up with it...just a shame the tank is the wrong way round. It is demo but interesting nevertheless

 

HERE

Edited By cymaz on 31/08/2015 07:32:04

Edited By Chris Bott - Moderator on 31/08/2015 09:36:40

[..]

Interesting cymaz the clunk is exposed for longer than you would think.

[Peter Miller]

It would seem that a small reservior in the fuel line would be a good idea.

Funny that engines never seem to cough in spite of the fact that there must be a lot of air drawn into the line.

[..]

My thoughts exactly Peter , I initially started thinking a small header on the fuel intake etc but if it ain't broke.....

[Jack Banner]

Quite interesting but that tank isn't under pressure. My understanding is that back pressure from the muffler pressurises the tank and forces fuel through to the engine, along with the draw pressure from the engine. Neither of those forces are acting on this test tank. It would be great to re-run it with an engine attached.

[Bob Cotsford]

but Jack, neither factor would affect the position that the fuel falls to in the tank, which means that the clunk would still be exposed for long periods.

The clunk line looks to me to be Tygon, so if the tank contents are just dyed water then it will be much stiffer than it would be in petrol.

I think we can assume that the fuel in the model's functional tank is performing similar antics, so for periods of several seconds at a time the engine is running on the fuel pipe contents, apparently with no ill effects.

It does show the value of bubble-free felt or sintered clunks though.

[cymaz]

If you notice the tank is the wrong way round and its only a demo.

What surprised me is how the fuel is chucked around so having a clunk that will surpress any bubbles up the delivery tube is vital.

Do some fuels incorporate foam surpression additives....? I hope so

[John Privett]

I don't think the tank is the wrong way round. The nose of the aircraft is on the left.

When diving vertically, and the clunk is exposed, the engine will (usually) be at idle, hence using very little fuel and so only a small amount of air will be drawn into the fuel pipe. The one vertical dive shown on the video under power shows the fuel moving all over the place! So some air will enter the fuel pipe. I guess a prolonged vertical dive under power may still end up with the plane accelerating slower than it needs (g, 9.81m/s^2) to keep the fuel at the back of the tank. In that case the engine may eventually cut - if the wings haven't folded first!

[Stevo]

"When diving vertically, and the clunk is exposed, the engine will (usually) be at idle"

Not the way I dive

Yes, as per the collective, it really is suprising the amount of time that the clunk is totally exposed! When we run one up on the bench, or an un-cowled model, we are always looking for that tell tale microbubble that makes its way into the carb. However in this scenario the fuel is cut completely and it survives - as they all do!

I almost exclusively use SLEC tanks (marmite) so any sintered or felt clunk is n non-starter. I was put off the conventional brass tubed tanks by the number I've had that have corroded and given me endless trouble.

Don't suppose anyone has any suggestions? The tank is a vital part of the chain and IMHO should never be overlooked.

Edited By Stevo on 31/08/2015 11:37:46

Edited By Stevo on 31/08/2015 11:39:04

[Mr.B.]

Very interesting. Thanks Cymaz. I have recently been wondering how fuel behaves in the tank as my saito powered Wots wot will fly inverted all day, knife edge either way from horizon to horizon, lomchavak, inverted spin....but....after 1 turn of a normal spin either way the engine will stop. I suspect this is because the engine is at idle for a long time prior to entering the spin and not drawing fuel hard.

[Dave Bran]

ALL my engine powered Heli's have header tanks. NONE of my fixed wing do. What does that say??

This is partially due to the normal location of a Heli tank being well off the correct level for balanced flow, partially a vision thing, (easier to see a header tank is still fuel filled, particularly on a scale bodied bird)

[Bob Cotsford]

Posted by Mr.B. on 31/08/2015 14:10:28:

Very interesting. Thanks Cymaz. I have recently been wondering how fuel behaves in the tank as my saito powered Wots wot will fly inverted all day, knife edge either way from horizon to horizon, lomchavak, inverted spin....but....after 1 turn of a normal spin either way the engine will stop. I suspect this is because the engine is at idle for a long time prior to entering the spin and not drawing fuel hard.

I've had this on a few models, usually those with a low tickover and a fast spin or violent spin entry. The only certain cure seems to be to raise the tickover with an idle-up mix for aerobatics. Other models will spin forever without cutting, particularly my Wot 4/ASP52 which will spin from tiny spec down to hedge trimming without missing a beat.

[Don Fry]

I can believe it, try climbing to hight towards the end of a flight, 20 turns high,and spin the model, and on recovery slam the throttle open. Dead stick every time. Drift he throttle open and you can get away with it.

[Tony Read]

Very interesting topic. I've just replaced the round SLEC tank in one of my models as the brass pipes had split and corroded like Stevo had experienced. I've had to use the same type of tank but when testing I've noticed that the clunk pipe is too stiff and exposes the supplied clunk to air when the models nose is pushed down too far, causing the FS glow to cut. Is there a better flexible pipe or clunk suitable for glow fuel than the one supplied? I'm thinking one of these might help-

[Don Fry]

Re stiff clunk pipe, silicone comes in 2 varieties, thin wall and thick wall tube. You need the thin wall variety for a clunk tube, much more floppy. As an aside I had delivered this week some of the HK fuel tube they describe as suitable for gas or glo motors. Don't know how long it lasts, very very pale green stuff, stretchy, and thin walled good for clunk tubes. Nice to use, will see if it lasts.

[ASH.]

Posted by Donald Fry on 31/08/2015 17:32:54:

"I can believe it, try climbing to hight towards the end of a flight, 20 turns high,and spin the model, and on recovery slam the throttle open. Dead stick every time. Drift he throttle open and you can get away with it."

That's good to know.. thanks.

This is an interesting subject.. thanks cymaz. I'm intrigued now how it survives with the clunk exposed for so long.

I'm quite anal when it comes to plumbing a tank.. it has to be just right because the majority of engine problems are down to fuel supply, and it's a pain having to go into the tank.

I have considered thin-walled tubing but think it will split easily. I use a standard thick-walled fluorescent coloured tubing (TowerHobbies US) which works beautifully because it's very flexible! It has a slightly smaller ID so less chance of slipping-off clunks and fuel flow is fine. I'm saving what I have left for all future tank installations. I am also going to try aluminium tubes instead of brass (believe it corrodes more slowly) so it's a 'fit and forget' job.

PS. Forgot to mention- this tubing is impossible to remove from clunk when fitted from new. I use standard metal clunks (Dubro tanks) with a Sullivan in-line filter on carb line which can be visually checked and replaced at anytime.

 

 

 

Edited By ASH. on 19/09/2015 21:17:06

Edited By ASH. on 19/09/2015 21:45:53