Debra
01-04-2007, 11:34 AM
After flying RC for 30 years and owning and building the real thing, I’m finally stumped and need some help.
I recently purchased a Great Planes Super Sky Bolt and in it, I put an O.S. FX .91 (Two Stroke). I was very careful to follow all the break-in instructions and did so on a test bench. The engine ran great until I put it in the airplane with a Bison Pitts style muffler. The plane flew great but the engine over heated and I landed immediately. I have tried many different props and different brands. I seem to have narrowed it down to a 14X6 or a 14X8; one lugs the engine down and the other over speeds it?
I’ve had every pro at the field (My RC Club) look at the plane and we all agree it has plenty of cooling and yet it still over heats?
I called O.S. but they only suggested I run it rich (less power, more mess) or go to a cooler plug, neither of which helped? Shouldn’t a new engine come with this figured out?
Please help me, I’m near tears and no one has an answer?
Sincerely,
Jeff R.
Dear Mr. R,
Three things are going to cause an engine to over heat: insufficient cooling, running the engine too lean, or using a fuel with low lubrication content.
You say that you have ample cooling, but how much air exit area do you have? It should be at least 1 1/2 time larger than the entrance. Otherwise pressure builds within the cowl and the air just goes around rather than through.
You did not say what you are using for fuel. on the market now days contain about 17 - 18% less. Try adding 3 or 4 ounces of castor oil see if this doesn't help.
How are you setting the mixture? The engine should be set to run in a rich 2-cycle and crack rich at the bottom of loops, etc. If you are running it in a screaming 2-cycle from beginning to end of the flight it is too lean - especially at the end of the flight. Don't try to get every last rpm out of the engine especially when using a Pitts style muffler that is pretty restrictive.
I would appreciate hearing what you find.
Yours,
Clarence Lee
(to write to Clarence, please email man@airage.com)
I recently purchased a Great Planes Super Sky Bolt and in it, I put an O.S. FX .91 (Two Stroke). I was very careful to follow all the break-in instructions and did so on a test bench. The engine ran great until I put it in the airplane with a Bison Pitts style muffler. The plane flew great but the engine over heated and I landed immediately. I have tried many different props and different brands. I seem to have narrowed it down to a 14X6 or a 14X8; one lugs the engine down and the other over speeds it?
I’ve had every pro at the field (My RC Club) look at the plane and we all agree it has plenty of cooling and yet it still over heats?
I called O.S. but they only suggested I run it rich (less power, more mess) or go to a cooler plug, neither of which helped? Shouldn’t a new engine come with this figured out?
Please help me, I’m near tears and no one has an answer?
Sincerely,
Jeff R.
Dear Mr. R,
Three things are going to cause an engine to over heat: insufficient cooling, running the engine too lean, or using a fuel with low lubrication content.
You say that you have ample cooling, but how much air exit area do you have? It should be at least 1 1/2 time larger than the entrance. Otherwise pressure builds within the cowl and the air just goes around rather than through.
You did not say what you are using for fuel. on the market now days contain about 17 - 18% less. Try adding 3 or 4 ounces of castor oil see if this doesn't help.
How are you setting the mixture? The engine should be set to run in a rich 2-cycle and crack rich at the bottom of loops, etc. If you are running it in a screaming 2-cycle from beginning to end of the flight it is too lean - especially at the end of the flight. Don't try to get every last rpm out of the engine especially when using a Pitts style muffler that is pretty restrictive.
I would appreciate hearing what you find.
Yours,
Clarence Lee
(to write to Clarence, please email man@airage.com)