Thorp Air Command - T18.net

Gent's,

I took a friend of mine who owns a Cessna 185 for a ride in a real airplane and he couldn't get over the fact that I only get 2150 rpm on take off. I explained the prop pitch for the Thorp, but he wasn't buying. As he put it, I'm causing premature detonation and will prematurely destroy the engine. I unfortunately don't have the mechanical knowledge to debate him on the subject, can the brain trust help me out with some knowledge?

Thanks

Chuck Kincer

Sure;
Your aircraft engine is equipped with magnetos, whose timing is established by the factory to prevent detonation when operating under the conditions defined by the engines type certificate.
2150 RPM might actually be the lower permissible Static RPM.
You should be just fine if you use fuel within the engine's octane rating and operate within the range of permissible temperatures.
How's That??
Added Link!!
http://www.7ts0.com/manuals/lycoming/32 ... 320_OM.pdf
This is a PDF file of the Lycoming operating manual for the O-320 series engine.
I did not see a reference to minimum static RPM, but lots of the power graphs show full power data for 2200 RPM.
Lee;
You may want to add this file to your archive for future reference if it isn't already there??

Hi Chuck, assuming you have a fixed pitch,when you power up for take off the prop is loaded. In other words the plane is just starting to move, as you gain speed the prop starts unloading this is evident as the rpm will increase as the plane moves faster. IF your static rpm is at red line while doing a full power run up, and you then start gaining speed and the prop unloads your RPM will be past the engine red line before you get into the air. Take off rpm will be far below red line and then progressively gain as the speed of the airplane picks up. As was said in a prior mail, during the loaded condition of the prop timing being regulated by the mags and the octane rating being where it is supposed to be detination should be of no concern all things being the way they should be. Hope this makes a little sence,I am not the expert by any means and this was explained to me in Lyman's terms so I would half way understand...Dan

Thanks for your input.

I have an O-320 (150 HP)in my T18 and pull 2050 RPM @ 29"mp FT static. Through 80 Kts I see about 2300. It will go 100 RPM past red line FT straight and level. I always use AVGAS.
If you use AVGAS I wouldn't worry about it, you only loiter there for a short time.
Tony
ZK-VMS
T18C