Gry101

My Feedback: (8)

I ma looking for some help. I have a George miller A-10 with OS46 turning Turbax I fans. I have perry pumps to draw the fuel from the tank located on the CG to the engines. I can get the motors running but individually. However, when I run them together, one always goes lean and quits. I have been banging my head against the wall for the past two years off and on trying to make these runs well enough to fly the plane. There is plenty of fuel getting to the motors, and there is a good smoke trail. However, they are just not reliable. I was wondering if there was anyone in the Ventura County area that has experience with these and could come to my field or I can go to theirs, and try one last time to get these reliable for flight. Otherwise, I am canning the glow and going electric. But before spending 3K I want to make one last attempt. Thank you to anyone that can help me.

Andrew

rjbob

My Feedback: (8)

I don't know the plumbing situation you have but it sounds like you are using one tank for both engines. If you switch to a two tank system, the problems will probably disappear.

With one tank and one fuel pick-up, the fuel tubing is probably not capable of passing enough fuel for two methanol-thirsty engines.

It is difficult to troubleshoot effectively, however, without having more facts.

Gry101

My Feedback: (8)

rjbob, sorry I forgot the particulars, just a little frustrated here.

OK, I have one 40oz tank. However, each motor has its very own fuel pick-up. There is one vent line and one fill line, though I think that should not matter. The tank is around 12 inches away from the engines themselves and the pumps draw the fuel through fine after a little priming. Thank you for the fast response.

rjbob

My Feedback: (8)

Besides the tank, the only shared component is the vent then, correct? Does it keep up with the fuel flow at full throttle?

Puzzler.

invertmast

My Feedback: (23)

just a thought, but maybe the single vent line isn't up to the task, and when both engines are running they are beginning to suck the tank in a bit and cause one to run lean and quit? Maybe try a larger size vent tubing system than the fuel supply system.

Gry101

My Feedback: (8)

Hmm, I will have to try a second vent. I will probably change the fuel fill line into a vent and put a T in one of the draw lines to fill the tank. Thank you guys. I will modify and give it a shot....

JohnnyA

My Feedback: (1)

I've never used a pump with a 46VRDF(I assume you're talking about a DF engine), but I did use a DuBro fueler and found that it wouldn't flow enough fuel.
I had to go to a fueler for a large glow engine to get it to run.
I suspect your shared vent is the problem: It's big enough to supply vent for 1 engine, but not for both.

joeflyer

My Feedback: (48)

Get rid of the pumps. Historically they never have worked very well with DF engines, probably due to the high rpm. Install separate tanks and vents for each engine and use standard pipe pressure.

Joe

L Turner

My Feedback: (3)

I second the motion: get rid of the pumps. As I understand it, the oscillating piston with flap valves in the pumps are unable to keep up with the high vibrational frequency of .45 DF engines turning 22-23k.

You are going to have a problem with a DF A10 and any fuel system (single or separate tanks) with main tanks located down near the wing and the cg: could be 4-6 inches lower than the carburators/venturis. Reminds me of my 45 DF Sabre with its tank mounted low-actually in the wing root center section. It will forever be difficult to consistently get the right amount of carb suction & pipe pressure. The amount of exhaust pressure transmitted to the tanks will depend greatly on the rpm and what type of exhaust system you are using. Are you using a standard exhaust mufflers, or some type of short (Weston) tuned pipe?

You might consider moving the tanks higher and more aftwards in the fuse to reduce the gravity gradient as well as the length of the fuel tubing runs. You could test that on the ground by seeing if external tanks mounted as high in the fuse as they could be possibly installed give you more consistent engine runs. If that helps, then reinstall the tanks high and aftwards in the fuse and balance the A10 with full tanks (using nose weight/battery packs, etc) and an aftwards as possible CG. As fuel burns off it should become more nose heavy.

joeflyer

My Feedback: (48)

I concur with L Turner's comments. Ideally each tank should be centered on the carb centerline. If you can't get reasonably close to that then you should install a small header tank near each engine that is centered on the carb. If you don't do that your fuel delivery will not be uniform as the tanks empty.

That will flood one of the engines when you fill the tank.

Joe

Gry101

My Feedback: (8)

The pumps that I am using work off of the crank case pressure. So in theory, they should pump fuel every revolution and not be dependent on the vibrations. Removing the pumps and going to pressure could help with the header tanks.

I have the tank right on the CG and almost at the high point of the fuse and actually even with the carbs if not a bit higher.

I am already at 26 pounds and 28 pounds wet. If I move the tank back to get them closer to the motors, then I will need to add even more weight. Moving 2 pounds of fuel behind the CG will force me to add another pound or two to the nose where I already have a little over three pounds.

I am using short pipes that I got from Dub Jett and they do have a pressure nipple available already drilled.

Well, I really do appreciate the help. I will look into seeing what I can do and if it will work for me.

Andrew

Kevin Greene

My Feedback: (85)

The pumps still have a diaphram that cannot keep up with the RPM...As suggested, pipe pressure with header tanks are the way to go...Run the largest fuel line that you can to help with any long tubing runs...

Kevin

surferman

[quote]ORIGINAL: Gry101

The pumps that I am using work off of the crank case pressure. So in theory, they should pump fuel every revolution and not be dependent on the vibrations.

Maybe the design of the pumps are not capable of the high RPM pulsations? There is mass in terms of fuel and in the pump parts, at some point ( rpm) this mass can act as a dampener to itself.
I think you do best in removing the pumps as the other posters suggests.
Go step by step for trouble shooting on ground:
First separate tanks with separate pressure at carb level, then play around one step at the time with tank height/one tank setup and so on.....


Fuel supply need to be free flowing into the carb - Make sure you have the largest high quality fuel line dimension as the carb has a bigger than usual bore and therefore less natural fuel suction.
Check that you have clips on the fuel line to keep the fittings at the carb and tank air-leak free

all the best

craigdyer

Hi All

Maybe run pressurised fuel tanks with cline regulators at each engine. Pressurise the tank/s with a crankcase pressure from one engine. This system works great with Moki engines etc. Seeing the tank is under pressure it can be installed any where in the airframe.

Kind Regards, Craig Dyer

Mace

My Feedback: (21)

After reading about his problem, I would suggest the same. Header tanks with pipe pressure, large fuel line, individual systems simplified for each engine will gain reliability as these engine fan combos have a rep for a good reliability. Get rid of all pumps and in line filler valves, they fail and cause bottlenecks.

MACE