Chicken hoppers and fuel head issues

[Martin Harris - Moderator]

As suggested by Jon Harper (Laser Engines) I've started this thread as I have a few points to ponder on the subject...

Posted by Nigel R on 30/05/2019 14:09:12:

I found this diagram of a chicken hopper if anyone is interested.

The big tank will drain into the small tank, until the small tank vent is covered. That's the vent into the top of the big tank - not the air vent to atmosphere.

Looks quite a neat answer actually. To my mind, easier than trying to hack around to fit a big tank lower down.

Has anyone used this setup?

You are right Nigel but the problem is complexity. The one liner of 'fit a perry pump' does little to explain what is actually required, what specific pump you need, how to set it up and all the rest of it. Also how much is one of those pumps now? 50 quid? Which is why is easier to just put the tank in the right place and forget all about it.

The chicken hopper setup you have there is the same as the one i touched on before. A customer (steve where are you?) uses it but tells me filling and draining both tanks can be problematic. manufacturing it in the first place can also pose a challenge as you need a very specific setup and most freely available tanks would need modification. Get the mod wrong and you either have too much fuel or not enough. You could make your own, and that would certainly be an option, but how much work is that?

Again, its much easier to just move the tank. Why create all the extra work if you dont have to?

[Martin Harris - Moderator]

My "problem" is the tanks for my rather long winded Tempest build. While I fully understand why relocating the tanks would be the best solution for the engine, the unusually short nose on the Tempest makes this very impractical - the tanks would need to go through the front wing dowel fixing area...

I did take the plans and bucket cowl to Jon to check the suitability of a 200v - which is a lovely fit in the cavernous cowling and we discussed the tank position for 2 SLEC tanks which just squeezed into the tank bay which Jon agreed would work but not be ideal, being rather high.

My only alternative would seem to be a rather complex pair of separate custom tanks but this prompts a question. Why the requirement for a tank for each cylinder?

Edited By Martin Harris on 30/05/2019 15:16:18

[Don Fry]

Here is a copy of Jon's customers installation. For information, HobbyKing do fuel tanks with the necessary plumbing for chicken hopper tanks, To fill this, you ideally close the pipe to the carb, and also close the hopper fill line,.. To empty, use fill and drain pipe, and then turn aircraft upside down, and use the spill and drain..

my experience is the hopper fill line is best coming out of the upper tank bottom, any uphill fuel run tends to reduce flow to the lower tank. They work. You can put the upper tank on the centre of gravity. In a Tempest, above the engine if inverted, to the lower tank, which can have two clunk feed to the engine. I currently use a Yak 55m with a chicken hopper, Laser 80. For one reason and another butchery was not going to work. The lower tank is a 2 oz DuBro, shoehorned behind the engine.

but as Jon says, not a first option.

Edited By Don Fry on 30/05/2019 15:53:01

[GONZO]

There was an article in a past issue of RCM&E that used a Walbro carb to solve fuel tank location problems. Pressure pulses from crankcase drove the suction pump on the Walbro and the regulator part was used to control the fuel flow(sorry cant remember the issue). The 'Kline' and 'Iron Bay' (Webra also) regulator systems(pressure tap from crankcase feed via one way valve to sealed tank. High pressure fuel feed to demand regulator mounted by carb) would have been ideal but stopped production long ago. Very slim chance SH items available.

[Jon H]

Martin the reason for twin tanks is so that each cylinder has its own independent fuel supply. In the event of some drama the hope is that only one cylinder will fail and you can limp home on the other without a full deadstick. I did exactly this with my P39 on one occasion.

You can use a single tank with two clunks, but a T wont work im afraid.

One thing that has been done in the past with the BT Typhoon is to mount the tank in the wing and just disconnect it with the wing when its time to go home. Depending on the distance and space available this may be an option.

A reduction in tank size might also help with 20oz total being more than enough for a 200.

I cant remember how much we discussed this before, its been a while

[J D 8]

Plenty of stuff about chicken hopper systems in the control line world. Premade tanks are available in US.

Just a thought but with a twin cylinder would it not be possible to have one large tank feeding two chicken hopper tanks one for each cylinder ?

Edited By J D 8 on 30/05/2019 15:51:03

[Jon H]

Posted by GONZO on 30/05/2019 15:41:34:

There was an article in a past issue of RCM&E that used a Walbro carb to solve fuel tank location problems. Pressure pulses from crankcase drove the suction pump on the Walbro and the regulator part was used to control the fuel flow(sorry cant remember the issue). The 'Kline' and 'Iron Bay' (Webra also) regulator systems(pressure tap from crankcase feed via one way valve to sealed tank. High pressure fuel feed to demand regulator mounted by carb) would have been ideal but stopped production long ago. Very slim chance SH items available.

Ha! if only you knew the origins of this thread.

Not recommended at all im afraid and it causes way more trouble than its worth.

You cant take pressure from a V twin crankcase as the pulses are all out of whack with the induction cycles and many walbro type diaphragms are not suitable for long term use with methanol.

Numerous customers have tried cline regulators in some way shape or form. Results vary from 'it works ok' to 'oh no my engine melted'. In most cases the engines are difficult to tune and wont peak. If you want to use cline regs i think you need about 9psi fuel pressure, and if that is what you want buy a YS instead.

As its very possible to toast your engine to death due to the varying mixture caused by a dodgy regulator setup i wont warranty the engines if they are run that way as its a modification to the way they are intended to be used and as i result i cant guarantee their operation.

[J D 8]

P. S. The only experience I have with chicken hopper tanks is er - - - feeding chickens.

[GONZO]

Jon, I've only ever used the cline etc on 2st. It was just a suggestion. I thought 'chicken hopper' tanks required positive 'G' to work and were not 'happy' in inverted or negative 'G' situations.

[Nigel R]

Don raises some good points. Having an uphill run (i.e. using a clunk line) on the big tank's supply to the hopper could mean the system may have trouble getting a syphoning action going if for some reason both tubes become full of air (aerobatics).

Copied from the other thread:

Just a thought, would it be possible to use one of the square SLEC tanks as the hopper?

Two T pieces in a connection between the auxiliary "fuel level gauge" nipples could work as the two connections from the big tank to the small tank.

Excuse the quality of my ten minute paint masterpiece:

[Jon H]

Gonzo, 2 strokes are better suited to those sorts of regs as all the pulses are even.

Nigel, you need another pipe so you can drain the lower tank

The only way to totally drain the system would be through the clunk line..could you use one of those dubro fuel valve things?

Or could you break the link between the hopper fill and hopper breather, then T the hopper fill and use one arm to drain? mayb?

[Jon H]

hang on, dont you need another pipe in the top tank too as it needs to vent when filling the system?

[Nigel R]

It would vent through the bottom tank during filling, I think, via the same mechanism that keeps the hopper full to the level of the air release line. When the tanks both became full the pump would start forcing the level in the hopper up toward the vent line.

The hopper's vent line would need to be above the tee that connected the air release line.

The air release tee would need to be about half height of the hopper. I don't think the level of the tee that connects hopper fill line is that critical?

As drawn, yes, you'd have to drain via the carb line.

What we need here is a willing experimenter!

 

 

 

Edited By Nigel R on 30/05/2019 16:58:23

[Martin McIntosh]

I shall repeat a pic here of my Stampe tank set up for a Laser 155. Works great.

OK, a few then. The top 9oz feeds the lower 6oz. Both have clunks. Inverted flight is no problem.

[Nigel R]

I don't see a vacuum break? If none, that would mean the effective fuel head is simply the level in the top tank.

PS not doubting that the setup works!

[Steve Dunne]

Here is a sketch of my chicken hopper tank system, as shown in the Laser Tech thread.

The initial problems in draining the bottom tank were overcome by fitting a T-valve in the carb line.

It now flies very well in the Spitfire, fully (scale) aerobatic.

Please note: When filling the tank you must ensure that the top tank is completely full so that it starts feeding the bottom tank. Stop filling when the bottom tank starts spilling.

To empty the system, first drain the top tank, then invert the aircraft and drain the bottom tank.

The air release tube fitting is a fuel bottle fitting.

When building the system, ensure that the bottom tank spill tube end is above the bottom of the air release tube, so that the fuel level does not reach the spill tube before the air release tube is blocked by the rising fuel surface..

How does it work?

When the fuel level in the small tank falls, it allows air up the release line, which then allows fuel to come down the fill line into the small tank. When the fuel level in the small tank rises to block off the release line, a partial vacuum forms in the top tank, stopping the fuel feeding out and down the fill line.

Even the chickens can work it!

So far the system has worked very well for me, in a H9 81" Spitfire.

Steve.

[Martin Harris - Moderator]

Thanks chaps - some excellent ideas and info.

I assume you leave the spill and drain line open for flight and seal the fill and drain, Steve?

[Don Fry]

Yes, that's right.

in my case however, I found a clunk feed from the main tank did not feed the lower tank fast enough. I dropped the fuel through the tank floor, with a o ring sealed fitting. It does work very well.

[Steve Dunne]

Posted by Martin Harris on 05/06/2019 17:53:37:

I assume you leave the spill and drain line open for flight and seal the fill and drain, Steve?

Yes, fill and drain need to be sealed to allow the flow to work, and the spill and drain acts as a release.

Put a T-valve in the carb line, so that when draining, after the main tank has been emptied, the T-valve can be opened to drain the lower tank.

Let me know how you get on!

Steve.

[Martin Harris - Moderator]

Plumbing is a long way down the line but planning starts with the build...

Jon might appreciate an alternative version of the 6 Ps...planning plumbing prevents poorly performing powerplants.

Edited By Martin Harris on 06/06/2019 01:16:20

[John Stainforth]

We had this discussion about a year ago. I found that the chicken hopper system, illustrated very nicely by Steve Dunne above (and in the earlier discussion), is an elegant solution to problem of the position of Laser carburettors in some aircraft installations. This has to be a way more satisfactory solution than hacking away at the airframe. A well designed model does not have too much structural redundancy in the vicinity of the engine box and firewall.