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How were you able to trace this back to the prop with 100% certainty out of curiosity. |
Too many hours, tool little service
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Just thinking out loud, but could the common cause for this type of failure be a nasty kickback from a flooded engine? I know that is ripped started castings apart (skytech). It wouldn't surprise me if it could strip a plastic gear. But I don't have direct experience with that, and hope not acquire any.
Nice to hear that it ended uneventfully. Our engines are so reliable these days that most of us never get a forced landing so most of us don't have any experience with them. We just hope that our training was good enough and we are current enough and we are lucky enough that if it does happen it will be a situation with some options. |
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What no one could answer is if the prop caused internal damage to his engine and no one wanted to pay for it to be disassembled, inspected, and put back together. |
Makes a good case for eliminating the mags and installing electronic ignition!
I went with EFII ignition only and couldn't be happier. I know that's not an option for certified birds......too bad!:eek: |
Update
After a two hour flight with the new mags, the engine became rough and upon inspection, several teeth had been lost on the mags!
A mechanic in Florida found what he thought to be the problem. The airplane has air conditioning and the drive pulley has two rubber cushions to soften the engagement torque of the a/c compressor, when it's engaged. the rubbers are 7 years old and not soft anymore. The jarring of the accessory gears as the compressor is engaged, causes the backlash that damages the plastic mag gears! So they went out and flew several flights without engaging the a/c compressor and examined the mag gears...no damage. They flew a few more times and engaged/disengaged the compressor and came back and found damage to the gears in the mags. The cushioning effect of the rubbers in the drive had hardened with age and seem to be the culprit! Even though the compressor is belt driven, the rubbers still play a big role. Whodathunk? Best, |
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POSTSCRIPT: Found it: http://cirrusengineering.blogspot.co...-bushings.html This photo from 2010; apparently they started out with no soft elements in the drive pulley. http://1.bp.blogspot.com/_6NMZbtOd12...0/IMG_7354.JPG Don't know if this is the latest: http://cirrusengineering.blogspot.co...g-washers.html Given that the problem has been going on four or five years, I question that this particular mag failure was caused by an AC drive bushing issue. |
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The little 4 cyl Continentals have a design flaw... they have no flywheel!!! The carbon fiber prop on Lycs are not experiencing this issue because Lycs have flywheels which dampen out these high order harmonics. |
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In general, the very large prop MMI is the anchor against which the other components oscillate, so yes, the amplitude of torsional vibration tends to be worst at the accessory end of the system. A prop is typically modeled as a spring-mass system, with the blade roots being the spring and the blades themselves being the mass. Very stiff blade roots would tend to increase oscillation amplitude at the accessory end. The Lycoming flywheel has little or no effect on torsional vibration in the first vibratory mode, because it is located near the node, the point in the system with no oscillation. Its effect at higher orders would require analysis, but again, it is a relatively small inertia located in proximity to a huge inertia with no significant connecting spring between them, other than the blade roots. I would predict its effect to be pretty near zip. IIRC, pendulum absorbers on Lycoming cranks are tuned to the 6th and 8th orders. I don't know about Continental cranks. |
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