Q1 prop size?

As you increase pitch the the prop will also slow down. So if you have a 44" prop that is spinning too fast then increase the pitch until it slows down. I've heard positive reviews of these props.

www.propsinc.net/

Oh and btw, the standard cruise prop for the upgraded 22hp Onan was a Cowley 44 x 42. No longer being manufactured, unfortunately.

SteveC68 wrote:

As you increase pitch the the prop will also slow down. So if you have a 44" prop that is spinning too fast then increase the pitch until it slows down.

Not so simple, increasing the pitch also affects climb rate. A 27 deg prop will climb well, but have a low top speed. A 42 deg prop will climb poorly, but have a high top speed.

It's all compromise. That's why variable speed props came into being. Check out the Ivoprop.

haiqu wrote:

SteveC68 wrote:

As you increase pitch the the prop will also slow down. So if you have a 44" prop that is spinning too fast then increase the pitch until it slows down.

Not so simple, increasing the pitch also affects climb rate. A 27 deg prop will climb well, but have a low top speed. A 42 deg prop will climb poorly, but have a high top speed.

It's all compromise. That's why variable speed props came into being. Check out the Ivoprop.

Increasing pitch WILL decrease RPM keeping diameter constant. Conversely I could decrease pitch to like 5" and the engine will make tons of thrust but never get off the ground. Also pitch isn't measured in degrees it's inches. A 42" pitch prop moves the propeller forward 42" for 1 revolution in ideal conditions. If it were measured in degrees then a 44" diameter prop that was 42 degrees "pitch" would have a different pitch speed than a 54" diameter prop that was 42 degrees "pitch" at the same RPM. That's not the case.

SteveC68 wrote:

Increasing pitch WILL decrease RPM keeping diameter constant. Conversely I could decrease pitch to like 5" and the engine will make tons of thrust but never get off the ground.

No disagreement there. It would make a great cooling fan.

Also pitch isn't measured in degrees it's inches. A 42" pitch prop moves the propeller forward 42" for 1 revolution in ideal conditions. If it were measured in degrees then a 44" diameter prop that was 42 degrees "pitch" would have a different pitch speed than a 54" diameter prop that was 42 degrees "pitch" at the same RPM. That's not the case.

Thanks for clarifying this, I had been looking for an explanation of why there were two different measurements, both in inches.

Some further data from Lonnie Prince, of Prince Propellers:

"There are many factors to a propeller other than pitch and diameter such as hub thickness, blade width, airfoil thickness, helical twist etc. To determine the proper propeller (you need to specify) the HP, Propeller RPM, and Airspeed, all determined in the full throttle level flight condition."

Just managed to dig out some more data. The original Cowley prop was evidently a 42" x 30". A Ritz 44" x 22" prop was also tried, and seemed to be an improvement.

Found in QuickTalk newsletter #18 summary. I don't have the original article here, but this seems to indicate that my earlier 44" x 42" was way wrong.

From data supplied on a possible 28hp engine, Lonnie Prince quoted me on a 40" x 32" prop today. N.B. His p-tip design reduces the size needed by 2" at this diameter.