Good Day All,

I've bashed together a one-off push/pull twin. The aircraft employs two 0.40 size motors from different manufacturer's.

I'm having trouble with the fuel system plumbing.

Currently I'm using one fuel tank to supply both engines, and have both engines supplying exhaust pressurization to the single fuel tank. The fuel supply line originates from a single tank clunker and splits to two lines by using a fuel line splitting "T". The fuel lines then run from the splitter "T" to each engine.

Additionally the engine exhaust port pressure supply lines each flow through a one-way valve prior to connecting via an in line "T", and then provide pressurization to the fuel tank via a single pressure hose.

I tried the first test engine run today and had a variety of troubles. Firstly, the tail engine ran rich to the point of quitting when I tilted the aircraft nose up (i.e. engine lower than the fuel tank). I suspect that the siphoning effect of the fuel from the tank to the engine resulted in just way too much fuel arriving at the carb. Any thoughts on this?

Additionally, I had a great deal of trouble trying to start the second engine after the first one was running. The problem seemed to be that the fuel tank pressurization from the operating engine was so great, that the fuel to the engine being started was over supplied (i.e. flooding). In fact, I was often getting hydraulic lock on the second engine during start attempts.

This is my first attempt at operating two engines simultaneously from one tank. What am I doing wrong?

How should I set up the fuel system in order to run two engines in a push/pull configuration?

I have two Perry Fuel pumps, but have not installed them yet. In fact, I don't have any experience with Perry style fuel pumps. Would these pumps eliminate the requirement for fuel tank pressurization? Would Perry pumps (one for each engine) provide a metered flow of fuel to the engine avoiding the change in mixture that results when the aircraft pitch is changed from nose up to nose down?

Any help from the experts out there would be greatly appreciated.

I'm struggling but having fun.

Cheers,

Marcus.

First of all you need to remove the oneway or check valves, if you run a check valve then you need something to regulate the fuel pressure, also a clunk for each engine would work much better, my Laser V twin has two carbs and Laser recommends a clunk for each cylinder. The way you're set up now with the check valves you have too much tank pressure when you reduce the throttle setting. If you use the Perrys you can get away with one clunk and a tee and no tank pressure.

If it's an in-line twin, (nose and tail mounted) then the simplest way is with two small tanks as close as possible to each engine with only muffler pressure and no pumps. Mount the rear tank backwards (clunk in rear) so it doesn't starve in climb.

If you must use one tank, put it as close as possible to one engine, plumb that engine normally and pump to the other.

If the tank has to be in the center, you must pump to each engine separately or with one pump and 'T' fittings but return lines bust be used then or you will still have the same problem with gravity flooding the 'lowest' eng.

Kirk

Boomstriker,

Yes this is an in-line twin (nose & tail mounted engines).

I understand the concept of using one Perry pump and a "T" splitter to provide fuel to both engines.

However, you mention using "return lines" in the tail engine installation to avoid the problem of gravity feed flooding the rear engine during a climb.

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"If the tank has to be in the center, you must pump to each engine separately or with one pump and 'T' fittings but return lines bust be used then or you will still have the same problem with gravity flooding the 'lowest' eng. "


Quote from Boomstriker
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I don't understand exactly what you mean by this statement . Aside from using a "pressure return line" I haven't ever used a "fuel return line".

Could you please provide either a more detailed explanation, or a diagram that will help to clarify the use of a return line as mentioned in your post.

Cheers,

Marcus.

Let's see if I can make some sense.

There are several ways to plumb a pump.

*) Pump from tank to carb., no return.
With this set-up, the higher pressure at the carb gives the most consistent runs but causes a rich midrange because with a two needle carb., you can lean the top and bottom but not the mid. A larger bore or Perry carb will compensate with less draw at mid and give a tad more power at top. Perry advises not to use muff press. just vent the tank, but I never could tell any difference.

*) Pump from tank to a 'T' just before to carb. then a smaller return back to a vented tank or muff pressure.
This method is good if you your carb is too rich with the above method or you have an air bleed carb and can't close down the fuel at idle. Fuel will always be 'at the carb' when nose-up so it doesn't have far to draw but will only be under the pressure of gravity when nose-down.

*) Pump from a main tank on CG to a small header tank behind the eng. Vent (overflow) it out the top and back to main, which can be vented or to muff pressure. The carb just draws out a clunk in the header tank and the pump keeps the header full till the main is dry. This method is much like the 'T' with gravity still having an affect.

*) I've even heard of pumping air into a sealed tank so the fuel is pressure fed to the carb from the clunk. This method may work but will flood a stalled eng until the pressure equalizes.

*) Some guys swear by the 'uniflow' or two line method, though I don't think it will work with a pump. I've never tried it.

Some set-ups may require a restrictor, check valve or creative fill/drain system but most can be made to work with one of the above methods.

Give me all the details on your plane - maybe I can help and fax you a diagram or something.

Hope this helps!!! Kirk

Wouldn't it be better to use 2 tanks? If you have a fuel problem or run out of fuel, both engines are going to shut down with one tank. At least you would still have one running, so you could make it back to the field and land if you had two tanks.
Boomstriker said to mount the rear tank 'back wards"...no, it should be mounted just like the front tank, facing forward, with the lines going back over the tank to the engine. Just for my planes safety, I would use 2 tanks myself.
Suptter

Hello!
The eaysiest way to solve this problem is to use two tanks as close to each engine as possible!
And use no pumps !!!
You could skip the clunk in the reartank as long as you do not fly inverted for more than 5-10 seconds ( is it an airobatic airplane?)

If you want to fly aerobatic manuvers tye best tank to use is the Tettra "bubbleless" fueltanks from performance specialties in Nevada( also US YS-importer) as these does not have clunks at all!

Regards!
Jan k

Re-read the earlier posts guys- this is exactly what I said.

The simplest way is with two tanks but some designs don't allow for it or it may be after the fact.

The rear tank should be back-wards with respect to the back-wards engine - facing forward - you know what I mean ---"clunk to the rear". (:

Marcus, You may try to make room for the two tanks now before you get any further along. It will be cheaper and save a lot of headaches later.


Kirk