morlove3

My Feedback: (14)

I have a Patriot XL with an OS 91 FX and a MACs tuned pipe. Everything is new so I'm only getting 10,100 rmp on the engine. The plane hasn't been flown yet. I have a perry VP-30 pump which I plane to use and a 4 oz header tank. The main 12oz tank is located over the CG, so it's a long run (about 18 inches to the engine) which is why I plan on using the pump. Has anyone done this and if so how did it turn out?

r-c-guy

My Feedback: (37)

Hi,
I have used such a setup in a 330 extra with an os 91 fx and tuned pipe. The engine and system performed well using only pipe pressure.

That rpm appears a bit low. What prop and fuel are you using? How long is the pipe and what size is it?

The specs say you should expect somewhere around 15000 if propped for maximum power (2.8 hp @ 15,000) but it will be with a smaller prop (maybe 11-6 or 11-8). With Tower's and OS's prop recommendations, it will not turn that high - they get 10000-10400rpm with 15-6 and 13-8 ; 13-6 turns 12500rpm.

randy

morlove3

My Feedback: (14)

Randy, I'm using Powermaster 15% and an APC 13 X 8. The folks at OS said when the engine is broken in the RPM's will increase. The pipe has not been tapped so I don't have any pipe pressure, I guess that's easy enough to fix. The reason for the pump was the long run from the tank to the header to the engine. I need to measure the pipe but I've cut about3 inches off of the brand new header.

r-c-guy

My Feedback: (37)

Hi
That sounds about right. If pipe pressure isn't enough you may need the pump. That pump may need a carb designed for pressure. I have seen guys use them with normal carbs but at least half have had midrange trouble.(too rich).
Maybe try a 12-8.

randy

bob27s

My Feedback: (19)

What prop are you using ???

On the patriot, you want nothing larger than a 12x9 on that engine. An 11x9 or 11x10 works well too.

You want to shoot for somewhere between 12,000 and 13,000 rpm with the engine.

How is your pipe set up? What is the length from the glow plug to the divergent section (fat part) of the pipe ?
(for that rpm range, something around 14" would be about right for starters )

Maybe if Vic is reading here, and can give some numbers from his SU-27 setup

Keep in mind, your pipe tuning length has EVERYTHING to do with the rpm you engine will perform at. IT can work to boost, but it can also work to govern or limit rpm.

If you have the header tank, try it without the pump first. Pick up the pipe pressure from just forward of the pipe weld. You might be surprised.

Bob

kmtranmd

My Feedback: (71)

I've done that pump setup and having trouble with carb adjustment. I'm using 11x9 apc and can get 12,400 on the ground but the plane flies slow and sounds rich in the air. I'm guessing it's my stock muffler hindering the engine, not allowing it to pipe up to high rpms in the air. I'm going to try the jettstream muffler next. Then, if still having problem with the pump adjustments, I'll just switch to 4oz header tank set up and lose the pump. I'm guessing that the stock carb on that os 91fx may not run well with Perry pressure driven pump. You guys agree on this plan or have better approach??

bob27s

My Feedback: (19)

the key is to first setup the engine so it runs without the pump - then add the pump in line, and adjust the PUMP until the engine runs pretty much the same as it did. Small tweeks on the low end and high end at that point.

That aside, 11x9 at 12.4K is pretty good on a stock muffler. You should see a good improvment with the JS

morlove3

My Feedback: (14)

Bob, thanks for the input. I've already installed the pump and it seems to be running a little rich, so I may have to back pedal. The OS calls for a 13 size prop, per instructions, but I'll try a 12 X 8 to see what happens. -Phil

bob27s

My Feedback: (19)

Consider the OS91FX an over-grown .61 engine That was its intended market.

Only a recommended prop size. Prop selection has to be made dependant on application - a match between the needs of aircraft and powerplant (and exhaust system if you are using a tuned system)

What is your pipe length set at currently? (measure glow plug, to fat part of pipe)

If the engine is a bit rich, reduce flow/pressure from the pump (See the perry instructions - adjust accordingly).

Rich condition may also be due to the pipe set a bit long - getting through the pipe step in that case, the engine will load up quite a bit. Engine/pipe/prop have to be matched for the top end rpm, then the rest of the adjustments can be made.

morlove3

My Feedback: (14)

Bob I measured as you suggested and the pipe from the glow plug to the divergent part is 14 inches, so I was happy to see that was right. I will try the pump adjustment this weekend and see if I can get it in the air. I have also switched to a 12 X 8. Thanks again. I'll let you know what happens.

bob27s

My Feedback: (19)

outstanding... lets see what happens