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<< Lancair Builders' Mail List >>
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As I change my focus from looking for new evidence in the engine failure,
and bring all the pieces together to make the final analysis, I believe we
have a fairly clear picture of what happened to DQ.
A brief analysis would be, that a kickback on engine start broke/cracked
the impulse coupling on the right mag. During decent parts/pieces fell into
the gear train in the accessory section. The Magneto drive gear from the
vacuum pump drive housing broke and went eccentric causing a severe
vibration.
Lightweight propellers are superior in reducing loads on crankshafts, engine
mounts, firewalls etc. (do you remember the last time you played with a toy
gyroscope and noted how much force was required to overcome the spinning
flywheel?). And the materials used (Woods) are harmonic/resonant frequency
resistant. Much more damage tolerant, and field repairable.
But, by being lightweight, they do not have as much of the flywheel effect
for engine start. With fixed magneto timing at 24 degrees BTC we have a
potential problem. If the engine has been primed, and the impulse coupling
has engaged the stop pin, and wound up the spring, it will fire nearly
instantaneously with the start switch. At 24 degrees BTC.
I intend to incorporate a change that should reduce my starting kickback
problems. It will include a modification that will remove the starter wiring
from the ignition switch and make it a independent circuit with its own
switch.
The new procedure will be to bring the engine up to cranking speed prior to
turning on the ignition, then priming.
Start-Ignition-Prime.
Is this problem an isolated case??
If you have experienced a kickback would you please send me the details---
CKohler1@cfl.rr.com
Charlie K.
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