[David-aviator]

Prop Damage...

Last week I did three full power runs with the airplane tied to a tractor to adjust the fine pitch stop with the MT prop. The run up was on a concrete pad at the hangar. A couple days later, while talking with a visitor, I noticed a major dent in one of the stainess leading edges, like it was a major ding, about 3/4" long, a quarter inch deep and a crack on the forward face of the blade. The airplane was about 15 feet from the concrete edge, which has a boarder of crushed rock. As near as I can tell, the prop sucked a piece of stone out of that boarder that far away.

The dent is definitely outside the envelope looking in the owners manual so I called MT-USA in Florida. Yes, it would have to repaired. Bummer, real bummer. The prospect of crating the darn thing just seemed like too much so I talked them into letting me take it apart and packing the blades and pieces in a much smaller UPS box. Shipping and crate cost savings, well over $300.

I had to call for assistance 3 times in getting the thing apart, but it is not a difficult task. It can be done in less than 2 hours easily once you know all the secrets. If anything good comes out of this, it is renewed confidence in the prop itself. It is an engineering marvel, right down to the 25 ball bearings that keep the blades in place.

I don't know what it will cost to repair or replace the blade, that will be determined after they look at it on Monday. The lesson learned is be sure the area in front of the prop is clear for well beyond 15 feet and watch out for runways not clean.

 

[SteinAir]

....it's not that dumb!

Hey David....you've got a ways to go before you get to truly feel dumb....try sticking your hand in a running prop and coming up with a good explanation for that one!

Glad to hear its going to turn out ok though.

Cheers,
Stein

P.S....don't worry too much about the $$'s...my "prop dumb dumb" cost in relation to airplane parts buys a couple brand new BA Hartzells!

 

[treeez]

Sometimes we need a reminder of just how much power we are handling with these planes. The law of physics for every action there is an equal and opposite reaction is still true. We know what prop wash does behind us but overlook what it is doing in front. Stay safe on the ground too folks.

 

[Walt]

Be Careful out there..

and don't underestimate the forces that are created by spinning props. Here's an interesting document that talks about some of the dangers of engine ingestion. I've seen the the concrete sucked right off the ramp doing power runs on large turbofans (basically a prop with a shroud)
http://www.flightsafety.org/amb/amb_mar-apr93.pdf

 

[Vern]

Prop /Jet inlet power

Over the years I've observed what looks like a small tornado when a prop or jet inlet was located over a puddle of rainwater. It's amazing to watch, especially on a larger airplane like a King Air, or a low to the ground jet intake like a B-737 or A-7.

 

[Rick6a]

That's a bummer Dave. I know how careful and conservative you tend to be. I'm not sure what lessons can be learned though. It sounds to me....as is your usual habit, that you took all reasonable precautions. One would think a rock impact generating that much damage would have been noticed during the runup. It may have happened as you suppose, still can you rule out a lawn mower throwing a rock while cutting the grass? Who can really say for sure what happened? Hopefully, MT will have it refurbished in short order. I know its little consolation but if you happened to watch the Red Bull race in Rio you would have witnessed frustrated and distracted racer Kirby Chandliss taxiing back to the ramp at a brisk pace after a disappointing race. At the last moment he spotted a parked airplane directly ahead and hit the brakes. In an instant, his plane nosed over just enough to seize the engine and shred the tips of his 3 bladed prop before plopping back down on its tail wheel. The lesson learned in that case is glaringly obvious. Your incident...however it happened...went unwitnessed and unnoticed for days. His episode was filmed for posterity.

 

[videobobk]

An instructor I know who teaches bush flying says the "tornado" effect that Vern mentioned is very real. He says it is the primary reason for not throttling up quickly unless necessary to clear the trees, especially on gravel. The tornado won't have time to form in front of a moving aircraft. Your runup area should be completely clear or you should limit the rpm/power. This is what "gets" most props! Let us know how this turns out for you.

Bob Kelly