CS FP tradeoff

[glenmthompson]

I'd like to recognize and thank Gregory Young for his July 14, 2001 sincere report on his first and last RV flight. An excerpt is as follows.. (http://www.vansairforce.net/gregyoung.htm)


"....It wasn't slow and it wasn't pretty. I was
worried about maintaining speed during the turn and avoiding a stall/spin.
The descent rate was enormous with a windmilling CS prop......"

One more eye opening reason and justificatoin for stopping the prop (if able and you are capable) and/or knowing how an aircraft flies when the fan stops working....... in a CS engine failure situation.
Any questions?

Glen

[Bill Dicus]

Penguin: We've flown a Pitts S-2A for many years in a lot of acro including advanced competition. The plane has an angle valve 200HP Lycoming and a Hartzell CS prop. Despite all that acro, including much negative G and lots of transitions as well as zero G parabolas just for fun, the Hartzell never once showed any overspeed tendancy. Even with the Christen inverted system, oil pressure drops substantially for brief periods, one time being during any transition from pos to neg G and the worst in right knife-edge flight. We've also experimented with moving the prop control to coarse pitch (low RPM) and found the prop RPM on the Pitts does decrease (at 100 mph IAS) and so does the sink rate. It's still pretty high - a friend says he figures where he can throw his car keys and plans to land there - kidding a little! Have not stopped the prop on the Pitts S-2A but have done so on S-1S Pitts and Cessna 150's and 172's. In all cases the perceived decrease in drag and descent rate was striking. In all three airplanes it was necessary to really stall to stop the prop. The Pitts took 175 mph indicated to start the prop again. The Cessna's were restarted with the starter. The only attempted stopping of a CS was on a T-34A. The nose gear failed on TO and I orbited for over 2 hours while the authorities quarelled about who was going to foam the runway - so there was plenty of time to think. The T-34 has a special extra coarse (semi-feather) postion accessible on the prop control by going past a detent. The plane accelerates when you move to this position and rpm slows quite dramatically. Even so, I couldn't get that prop to stop at the forward CG condition of that flight, with a full stall. I wanted to stop the prop so it could be put in a horizontal postion before a dead-stick landing as this would avoid prop damage. As it turned out, the only damage was to the prop tips, the nose gear doors (minor) and the augmentors. I wonder what my RV-8 with Hartzell Blended Airfoil and Hi comp pistons will do when and if it's finally done? Bill

[glenmthompson]

Originally Posted by Bill Dicus

Penguin: We've flown a Pitts S-2A for many years in a lot of acro including advanced competition. The plane has an angle valve 200HP Lycoming and a Hartzell CS prop. Despite all that acro, including much negative G and lots of transitions as well as zero G parabolas just for fun, the Hartzell never once showed any overspeed tendancy. Even with the Christen inverted system, oil pressure drops substantially for brief periods, one time being during any transition from pos to neg G and the worst in right knife-edge flight. We've also experimented with moving the prop control to coarse pitch (low RPM) and found the prop RPM on the Pitts does decrease (at 100 mph IAS) and so does the sink rate. It's still pretty high - a friend says he figures where he can throw his car keys and plans to land there - kidding a little! Have not stopped the prop on the Pitts S-2A but have done so on S-1S Pitts and Cessna 150's and 172's. In all cases the perceived decrease in drag and descent rate was striking. In all three airplanes it was necessary to really stall to stop the prop. The Pitts took 175 mph indicated to start the prop again. The Cessna's were restarted with the starter. The only attempted stopping of a CS was on a T-34A. The nose gear failed on TO and I orbited for over 2 hours while the authorities quarelled about who was going to foam the runway - so there was plenty of time to think. The T-34 has a special extra coarse (semi-feather) postion accessible on the prop control by going past a detent. The plane accelerates when you move to this position and rpm slows quite dramatically. Even so, I couldn't get that prop to stop at the forward CG condition of that flight, with a full stall. I wanted to stop the prop so it could be put in a horizontal postion before a dead-stick landing as this would avoid prop damage. As it turned out, the only damage was to the prop tips, the nose gear doors (minor) and the augmentors. I wonder what my RV-8 with Hartzell Blended Airfoil and Hi comp pistons will do when and if it's finally done? Bill

This is what I/we/lurkers are looking for in posts!! Great info!!! Question though... When you said................" ...We've also experimented with moving the prop control to coarse pitch (low RPM) and found the prop RPM on the Pitts does decrease (at 100 mph IAS) and so does the sink rate. It's still pretty high - a friend says he figures where he can throw his car ...".................. Was that engine off or on?? Also, in the T-34 incident, did you try to stop the prop with the prop lever towards high RPM also? It appears to me the less the prop pitch, the harder to restart the prop..
Glen

[Bill Dicus]

Glen: Relative to Pitts glide, it seemed steep either way, just a little less so with engine stopped. The pitch attitude to maintain 100 mph IAS was not as nose down with the engine stopped as it was at idle. Neither Pitts of ours has a VSI, so these are really gross estimates. The T-34 - I never thought to try stopping the prop in low pitch/high rpm. I thought it would be harder to stop that way. Should I have tried that? Seemed to me it would be easier to stop it while in the lowest rpm mode (high pitch). Anybody have thoughts on that? Bill

[glenmthompson]

Originally Posted by Bill Dicus

Glen: Relative to Pitts glide, it seemed steep either way, just a little less so with engine stopped. The pitch attitude to maintain 100 mph IAS was not as nose down with the engine stopped as it was at idle. Neither Pitts of ours has a VSI, so these are really gross estimates. The T-34 - I never thought to try stopping the prop in low pitch/high rpm. I thought it would be harder to stop that way. Should I have tried that? Seemed to me it would be easier to stop it while in the lowest rpm mode (high pitch). Anybody have thoughts on that? Bill

Yep, flat pitch is the high drag reigime if engine is stopped, and course pitch impinges upon the prop in a more "torquing fashion". I proved with experimintain in my Kitfox (warp drive ground adjustable), that the prop is almost impossile to keep stopped with the higher cruise pitch setting (15 deg. at tip) as compared to the less pitched, power setting of 11 deg.

Glen