Bob Paris

My Feedback: (13)

I am building a P-38 with two K&B .61 Twister engines, and found that the fuel tanks are very low in the engine pods. I bought two Perry fuel pumps (P-30) and wonder if I can just tap the center of the back plate as the instructions say, with out any running issues, to power the pump.

Does anyone out there have any experience with the Perry P-30 fuel pumps ?

Thanks and Soft Landings Always,
Bobby of Maui

w8ye

My Feedback: (16)

They may work better with the Perry pump carbs for the K&B

earlwb

Yes, that is what many of us do it, is to drill and tab a hole in the center of the backplate for a small muffler pressure fitting.
Granted the hole doesn't have to be perfectly in the center either. But that is the usual place to put it.

If the fuel tanks are positioned low in the engine pods, that tends to imply that the plane was setup for a inverted engine arrangement. Is that how your plane is setup?  Just curious as to what you have there.

cjet

Here is my setup in a scratch built fiberglass A-7 prop jet that three of us designed and constructed back in 1991. Two of us still fly them some today. We made about 8. I wanted the tank on the CG. for better balance.

Photo one is inside from the tank forward to the firewall. Photo two is the pump mount less my standard silver K&B .61. Photo three is my friend's Twister mounted on a test stand. His pump has red because it is over 10 years old while mine is blue, but they are both VP 30s.

We use standard K&B carbs that came on the engines and a check valve in the plumbing as per Perry's directions. On the Twister photo you can see the plumbing layout better. The yellow thrid line from the tank would go to a check valve mounted on a Tee fitting to vent fill up overflow to the outside of the fuse.

We always wondered how a backplate pressure tap could be trouble free since we were concerned about having enough thickness there to tap into. So we went with the pressure tap on the case mounting lugs. If anyone has photos or input on that I would like to hear more about it.

The twister photo has the tank about 18" back and I am flying my A-7 with the tank about 14" back from the carb. I think we tested up to 22" back and quit there.

I am so far very pleased with the setup in flight, no problems to date.

Just follow the Perry directions and all should be fine. Good luck!

cjet

One more photo showing the red return fuel line on a T fitting to the carb (plane in front). This allows excess fuel from the pump to get back to the tank. The A-7 in back has the Twister.

No muffler pressure hooked up and note the angle of the brass tubing down from the firewall. The tank is almost on the bottom of the fuse. A 12" section of brass runs back into the fuse and then is connected with several inches of fuel tubing to the tank.

mike31

My Feedback: (67)

If you drill and tap the back plate make sure nothing protrudes into the crank case. The crank will remove it if any interferences are there.

earlwb

well it depends on the connecting rod. If you had a recessed middle section on the rod, and put the fitting in the center of the backplate, and the fitting only protruded a little bit, it would clear the rod as it is articulated. But you are correct.


CJET, I love the idea of drilling in through the mounting lug. Not bad at all.

The ideal pressure fitting, has something shaped more like a tiny rocket nozzle inside where the hole is. It is tapered on the engine side but flat on the fuel tank side. This makes it easy to squirt some crankcase pressure into the fuel tubing going to the fuel tank, but forms a resistance to bleeding off the pressure as it is built up. No fancy valves are needed.

The other method you see on some engines is to use a timed pressure tap. It is located just under the carb at about 90 degrees on the side. You see this method on Cox Tee Dee engines with the little side nipple on them. But some engines have a small reinforced flat spot there for drilling and tapping it out for a fitting too. The timed pressure tap makes it easier to hand start a engine that way. Sometimes the pressure tap on the back plate can make hand starting nearly impossible (but we have electric starters right?).

Kweasel

My Feedback: (29)

The only issues with P30 pumps will be getting the slow needle lean enough at half throttle without cutting fuel at low idle. Even with the pump it will still lean with positive Gs and richen with negative. I have never found a backplate too thin to work with a HH Big Tap since it uses 3/16 threads.

Bob Paris

My Feedback: (13)

Thanks Guys for the information.
Bob Paris