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Todd,
I've
heard the exact same noise that you described on 2 occasions. When I heard
it the first time, I also thought that I had a issue with the PSRU, because it
felt and sounded like something slipping. Both times, mine occurred
when powering up from idle to take off power. The second time it happened
I glanced at the mixture, and it was bottomed out on the lean side. I
think that the noise was caused by detonation cause by a very lean fuel
mixture. I immediately reduced throttle, and then advanced throttle again
with no problem. Since then, I've been trying to advance the throttle more
slowly, hoping to avoid the problem. I think that it may be caused by the
spooling of the turbo driving the mixture lean, or else the EC2 MAP table may
have a borderline mixture somewhere. Not sure.
Steve
Brooks
[Steve
Brooks]
-----Original
Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]On Behalf Of Todd
Bartrim
Sent: Sunday, December 11, 2005 4:27 AM
To: Rotary
motors in aircraft
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.
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