richard.goode(at)russiana
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 Posted: Mon Apr 24, 2006 6:55 am Post subject: Ground Strikes with M14P |
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Ground Strikes with M14P
I am alarmed that people consider it to be general practise to replace a prop after ground strike and go on flying.
The issues to consider are:
There are several areas where the M14P can suffer in a ground strike:
- The satellite gears in the gearbox are small and can crack with a shock-load.
- The crankshaft is pinned together and a shock can move the separate parts of the crankshaft in relation to each other.
- The supercharger assembly is turning at over eight times engine speed and even at idle has a fair amount of inertia.
- The manufacturer,s strict instruction is that any ground strike must have an engine replacement. This is over-cautious, and the real issues are the speed of which the engine was turning; whether it came to an immediate stop or continued; and the amount of prop damage, which will indicate the blow to the engine.
We have a Sukhoi customer who had a significant ground strike, but at idle; changed the prop, and about ten hours flying later one of the satellite gears broke up, and the engine locked solid. Fortunately he was taxiing in after an aerobatic sequence. Had it happened a minute earlier the engine would almost certainly have been torn out.
The prudent approach is to say that a small amount of propeller damage, and where the prop was not totally stopped should mean that a prop change alone is fine.
If the engine was at higher power, then the gearbox should be removed and the components crack tested.
If the prop stopped suddenly I personally believe the whole engine should be checked or changed.
Richard Goode
Richard Goode Aerobatics
Rhodds Farm
Lyonshall
Herefordshire
HR5 3LW
United Kingdom
Tel: +44 (0) 1544 340120
Fax: +44 (0) 1544 340129
www.russianaeros.com
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