flyrotary@lancaironline.net Mailing List Archive

Subject: [FlyRotary] Re: idle speeds (prop stopped flight)

Hi Charlie,

I had a cruise prop (80 inch pitch) sensenich metal prop on the 6A. When I was doing engine off glide testing, some thought I would do better with engine stopped rather than turning. Really had to slow way down to get prop to stop. Could not measure the difference in glide engine stopped or windmilling. Really had to go fast, over a hundred to get it going again!

Bernie Kerr, painting the 9A waiting to get rotary back from Bruce T at SnF

A stopped prop is in a complete stall condition, and would be expected to provide less drag than one that is turning at an RPM of incipient stall. There will be some RPM for a given pitch and touchdown speed that will provide the most drag. We just have to figure out what that is.

Landing speed in Kts times 100 gives you ft/min. Pitch divided by 12 gives you ft/min per revolution of the prop for neutral thrust (approx.). So my 85 pitch prop at 70 kt landing speed is neutral at 1000 RPM. So maybe the max drag point is somewhere around 650 RPM (mas o menos 100). Just a guess. Someone less propeller-design challenged than I may have a better answer.

Al