Prop Strike for Cont Engine

[Bill Greenwood]

I 'd like to know if anyone has ever had a "prop strike" for an engine that was not running, just parked and if you disassembled the engine as Cont advises, did you find any internal damage? Thanks of any help.

I have a J3 Cub with a C90 that was tied down, with FBO supplied ropes that were worn out, and yes I should have spent $20 at the hardware store for chains that would have held. I wasn't expecting 50 mph wind in the middle of winter.
The plane hit hard enough to crack the wood prop.
Cont Service Bulletin says a static impact is really the same as when running, doesn't sound logical, but there it is and advises full disassembly and check internal parts. I would have thought a checkout of runout of the prop flange with a dial micrometer would be the first step, but Cont doesn't even mention that.
A Cub is to airplanes as a golden retriever is to dogs.

[cub builder]

Unfortunately, static prop strikes can cause cracks at the flange itself. I wouldn't sweat having the rods and gears magnifluxed, but the crank should be. I bought a C-85 from a friend after it had what I considered to be a pretty minor static prop strike. Flange dialed good, so I figured it was probably OK. I didn't think there was enough impact to damage it. Put it on my experimental and flew behind if for 350 hrs to run it out. Upon tear down, sure enough, when we magnifluxed the crank, the flange was cracked. I won't chance another "prop strike" engine without a tear down.

[Scooper]

Bill, since the prop is wood, I wouldn't think the engine suffered any damage.

Check out this article on pipercubforum.com.

https://www.pipercubforum.com/woodprop.htm (https://www.pipercubforum.com/woodprop.htm)



Wood is great stuff. "Compared with other materials, wood, with its inherent damping, tends to run smoother. It's also the material you want, if you have a tip strike; it acts as a 'fuse' when you get a tip strike -- the strike makes a bunch of toothpicks; but your engine probably won't be wrecked -- it's cheaper to replace a prop than a crankshaft."

[enginesrus]

A person could do a quicky magnetic particle inspection of the flange engine on plane. The wood would have cushioned it. And yes a dial indicator check is needed.

[Bob H]

If engine was not running and any impact loading from prop would be in bending of flange, I would not expect crank to have damage. Certainly you should indicate flange and assure it is within normal runout.
And give a 10X visual inspection for cracks. Tearing down engine for what sounds like a relatively minor impact seems like overkill to me.

[bfinney]

Yes I've had a "prop" strike. Airplane was in the hangar, no prop wings or tail feathers, inadvertantly dump it on the nose, i.e. engine flange, took a small divit out of the concrete floor. I went through all of the senarios posted above, had a conversation with my A&P, the result, I called my insurance company, prop strike inspection was covered, insurance paid the bill. No damage found from the "prop" strike.

My advice, if you have hull insurance coverage, call your agent.

[Bill Greenwood]

Thanks Bruce and all you guys. And no, I didn't have hull insurance. I tried to save premiums, so only liability. A Cub is not high dollar value and as long as the engine ran, I assumed I would fly it safely. I never thought about damage while being tied down, and I wasn't expecting high winds, 60 mph in the middle of winter. The FBO was sold, the new one was a really sketchy marginal one and they put out old used tie down ropes. I was " penny wise and pound foolish" for sure, I could have bought tie down chains for $20 at the hardware store 5 miles away. Then that FBO went out of business. The one now seems good, has good ropes.
I expect I am going to do the full inspection as Cont says, to be safe. We'll see.

[thisadviceisworthles]

Bill, forgive me for taking this a little off topic, but about how much did you save be dropping hull on the Cub?

[Bill Greenwood]

I think it was $700, or maybe that was the whole premium, I cant recall. I wasn't flying the Cub in the middle of the winter. Just goes to show you that we can all do some dumb things, in this case it was like the perfect storm as the new FBO came in and they were a low level operation. The one there now has 3 strong ropes in good shape at each tiedown.

[rwanttaja]

I think it was $700, or maybe that was the whole premium, I cant recall. I wasn't flying the Cub in the middle of the winter. Just goes to show you that we can all do some dumb things....
I don't think it was that dumb. Depending on how much the inspection and prop costs and how long you'd owned the airplane, you'd still come out positive on that deal.

Every time I buy a new cell phone, they try to sell me insurance for ~$20/month. Then I explained how I haven't damaged or lost a cell phone in ~25 years, and have saved enough to buy ten new phones.....

Ron Wanttaja

[Bill Greenwood]

Ron your logic may have worked with cell phones, but it was really stupid of me to discontinue the Cub hull ins. It cost thousands to repair the damage, and we haven't even gotten to the engine yet. The flip over was the same year as stopping the ins. And even dumber was not just going to buy tie down chains, which I thought about, literally would have been $25.

[rwanttaja]

Ron your logic may have worked with cell phones, but it was really stupid of me to discontinue the Cub hull ins. It cost thousands to repair the damage, and we haven't even gotten to the engine yet. The flip over was the same year as stopping the ins. And even dumber was not just going to buy tie down chains, which I thought about, literally would have been $25.

It really depends on how long you owned the aircraft, and how long you *didn't* spend money on the hull insurance.

I don't have hull on my Fly Baby. But if the worst happens, I can sublet my hangar for two years and earn the value of the plane back.....

Hindsight is always 20/20. Probably few folks check the tiedown ropes. I learned my lesson back when I was flying the (starterless) Fly Baby prototype. It had a glider hook on the tail, and I'd loop a tiedown rope around it to start. But I'd pull test the rope first...and was surprised at how often they'd break at a single tug. Carried a hank of rope in the airplane and would cut off some to use when necessary.

Ron Wanttaja

[Sam Buchanan]

Just as a datapoint--my hangar is located in tornado alley. I carry GNIM (ground not in motion) policies on my aircraft which are not much more costly than liability-only. This covers the hull until the aircraft begins moving under its own power. If the hangar gets blown away I have full hull coverage for very little cost.