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Push/Pull Fuel System Plumbing Trouble?

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Old 01-20-2003, 06:33 AM
  #1  
tyrolean_marcus
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Default Push/Pull Fuel System Plumbing Trouble?

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.
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Old 01-20-2003, 07:26 AM
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Hircflyer
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Default Push/Pull Fuel System Plumbing Trouble?

My suggestion is to remove the pressure check and then try it.

My opinion is, if the tank is placed in the correct position relative to the engine carbs. there is no reason you can't run any number of engines from the same tank. Time of run depending on size of tank.

If the engines are in proper tune and the tanks are in correct position normal muffler pressure is all that is required.
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Old 01-20-2003, 07:39 AM
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tyrolean_marcus
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Default Push/Pull Fuel System Plumbing Trouble?

How would removing the pressure check valve(s) from the fuel tank/exhaust pressure line result in better engine operation? Perhaps I'm missing some critical piece of information or knowledge here?

Could it be that the check valves result in the tank being "over pressurized" and the resultant fuel pressure to the engines being so great that they will flood the carb's?

I wonder if "over pressurizing" the fuel tank by the use of one way check valves would also contribute to the hydraulic lock that I am experiencing after trying to start the second engine with the first one running?

Cheers,

Marcus.
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Old 01-20-2003, 08:01 AM
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Robby
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Default Push/Pull Fuel System Plumbing Trouble?

Marcus,,
One would think that as each engine has pressure to its own tank, that running two engines would require two pressure lines..
Answer: NOT ..
Only run ONE line from one engine to presurre the fuel tank.. Even
as such, the first engine will pressure the tank and can cause second engine to flood, so start first one and then right away
start second one..
I have one plane that is using this set-up.. It is also the last time I will feed two engines from one tank.. Too much pumbing and too
much aggravation if done as a direct hook up..

Robby
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Old 01-20-2003, 06:46 PM
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Default Push/Pull Fuel System Plumbing Trouble?

Use 2 tanks
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Old 01-20-2003, 09:50 PM
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Ernie Misner
 
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Default Push/Pull Fuel System Plumbing Trouble?

Pinch off the fuel line to the second engine until ready to fire it up. At the very least make sure the carb throttle is in the closed position on the 2nd engine until firing it up, this will help.

BTW, two clunks in one tank work great for twin engine setups...

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