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JonathanMilbank
Joined: 14 Apr 2012
Posts: 390
Location: Aberdeen area
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 Posted: Fri Apr 02, 2021 11:49 am Post subject: Acceptable prop strike damage? |
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Getting straight to the point, is there a "rule of thumb" for how much damage a propeller can sustain before a shock load engine strip-down is necessary? I suspect that the decision lies with the engineer making the assessment.
Today a friend was flying his tail wheel RV6 in a strong crosswind on a tarred runway and while landing he was dumped by a gust while attempting to go around, perhaps over-rotated when pushing the stick forward and heard a sound like kerbing a car's wheels, as he described it. He didn't really feel a vibration, nor did he hear the engine note change. So it was a fleeting "brrrrt" on the tar and following the go around pattern flown, a later inspection showing no evidence on the runway surface.
The engine is an IO320 (I think), the propeller is fixed pitch metal and last 3 to 4 inches of the tips are now curled forward through a full 90 degrees. My instinct is that a shock load engine strip-down isn't necessary in the circumstances, but what do I know? Very little indeed, apart from a slight recollection that damage like minor nicks in prop leading edges can be dressed out provided that they're not along the 1/3 nearest the hub.
I look forward to your replies, thanks.
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Matt Dovey
Joined: 13 May 2017
Posts: 48
Location: st albans, england
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Peter jeffers
Joined: 24 Aug 2020
Posts: 20
Location: hp143hr
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| Posted: Sat Apr 03, 2021 12:46 am Post subject: Acceptable prop strike damage? |
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Hi Matt,
When I answered your request re grease for Arplast PV50 I was unaware of the
prop strike. Whilst a PV 50 prop is not in any way related to Lycoming
engines or associated props a lot of the advice given in the linked article
is entirely relevant and should be taken notice of. I have seen PV50 hubs
cracked by prop strikes without significant damage to blades. So beware.
Pete J
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 287
Location: Florida USA
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| Posted: Sat Apr 03, 2021 4:44 am Post subject: Acceptable prop strike damage? |
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Jonathan,
Any propeller contact is a shock to the engine and prop.
Hollow or foam filled composite props made from carbon fiber tend to crack and tear inside and there is hidden damage. As a rule, I replace damaged carbon fiber blades.
Solid Carbon fiber is only a bit tougher. Even Warp Drive prefers to just throw away the blades and replace them. Their ground adjustable hubs are prone to cracking on sudden stoppage but the cracks only show on NDI testing. The low power hubs cand bend slightly out of shape on "the minor prop strike". This is standard for aluminum. Always have the hub mic checked and I prefer to let the factory do that now as I have made mistakes and missed things that the factory would have caught.
Metal fixed pitch propellers, I recommend shipping back to the factory for redo and static rebalance. The slight brrrt can twist the tip making for unusual harmonics in the prop and eventual problems. Beware of the used aircraft with a minor prop strike. It reeks of cheap owner, lax maintainer, and eventual vibrational issues.
Wood props are a mixed bag, but normally the glue joints fail and the prop is toast. Ultrasound and X rays don't work well with wood props.
Constant speed props are a mixed bag. Any prop strike should be sent to the factory. The bearing surface at the collar and down in the hub can be distorted with any shock load. The bearings are designed for rotational loads not bending loads. As stated above, only through de-painting and NDI inspection can a hub be returned to service. Hence, I believe in sending the hub back and have it rebuilt.
Engine damage is also a mixed bag. Slipper clutches, types of gearboxes, crank shafts, depend on the engine. I personally take a day and pull the engine, run it to the facility and have the inspection done. It takes about 3-4 hours to do it by the book.
No matter what, the pilot owner needs to pay the "dumb tax" if he made the mistake. We all do and we also know that flying is not cheap. Bad maintenance will degrade an aircraft into a flying heap. Pilot wise, if it was necessary to ground loop to prevent destruction of the aircraft, insurance will pay for it.
One thing I know for sure is, aircraft damage is easy to repair. It will be time consuming, inconvenient, and destroy the pocket book and pride but we own our mistakes. If done right, the plane is as good or better than new. Cut corners and it will bite you eventually.
Prop rebuilds on an Airmaster average is about $3-4000. Gearbox teardown/rebuild and engine inspection is in $2-3000 range for a Rotax. Lycoming/Continental I don't have as much experience with.
Treat any prop strike as serious. I have yet to find a simple one.
Regards,
Bud Yerly
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Matt Dovey
Joined: 13 May 2017
Posts: 48
Location: st albans, england
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| Posted: Sat Apr 03, 2021 9:44 am Post subject: Re: Acceptable prop strike damage? |
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Peter I havent had a prop strike!!! Jonathan, the guy who started the thread his buddy has pranged his RV.
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