flyrotary@lancaironline.net Mailing List Archive

Todd, My understanding is when the prop stalls it is not loaded as heavily as when "unstalled". If that is the case, then it would seem a stalled prop would cause a higher rpm at the same throttle setting than in the "unstalled" state.

----- Original Message -----

From: Todd Bartrim

To: Rotary motors in aircraft

Sent: Sunday, December 11, 2005 4:27 AM

Subject: [FlyRotary] Prop stall?

Hi Ed;

    This talk of stalled props brings up another question. Last week when I was doing circuits, on one of the touch & goes, moments after I'd applied power, the engine suddenly revved up momentarily much the same way as when you hit a patch of ice while driving a vehicle with a heavy foot. This happened very fast so I wasn't able to check the RPM (sure wish I had a datalogger), but both my buddy & I heard/felt it. My first thought was the PSRU had slipped, but it had no accompanying mechanical noise (like broken gears) then second thought was prop stall. I held it on the ground a little longer without reducing power, but as we pulled through 90mph with no further indication of a problem ( I still had several thousand feet of runway ahead of me) I let her lift off and then went on to complete another dozen circuits with no further incidents. But afterwards we discussed it further and I recalled Dave's broken PSRU shaft, but if I recall his was a clean break without any sort of preceding slip. This just leaves a prop stall as the likely culprit, but I wouldn't expect that a prop would stall when at approx. 50mph. At the time my electronic prop governor was on auto and had been performing well and in any case the electric IVO prop is too slow to have gone full fine momentarily so I can almost discount this as being related.

    Any thoughts on whether this could have simply been a momentarily stalled prop?

Todd

Interestingly enough before I had the prop shortened, I was a Tracy Crooks and was doing a run up to get some exhaust sound readings. It was a cool morning and the engine was turning around 5800-6000. Tracy and I (as well as the sound meter) could hear the prop blade stalling and unstalling (apparently as the blade rotate different orientation with respect to the cowl and effect the airflow enough to cause it to stall and that point and then recover). You could hear a distinct "wop! wop! Wop!" sound as the prop stalled and unstalled.