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Prop Strike questions

B

bob turner

Registered User
I am aware of AD 2004-10-14c. As I recall, before that, one would often "dial in" the crankshaft flange and bolt another prop on. Indeed I did that once in West Texas many decades ago.

So - question: part 91, is it still legal to do that on Continentals? Yes, I have seen broken cranks on small Continentals, most likely due to a prop strike in the distant past, but just asking about legalities.

Trigger for the question - low speed nose-over on a 180. Very little damage other than to prop blades, and he is considering "dial it in" and a new set of blades. All I could say is "that's what we did in the 1960s."
 
To quote just a small part of the article above:

"To be undiplomatic, dialing in a crank after a prop strike or sudden stoppage as has been defined by both the manufacturers and the FAA is essentially a fools errand-at least as possible decision making criteria on the serviceability of the crank. Unfortunately, disassembly and nondestructive testing procedures are the only way to provide a reasonable level of assurance that the engine is truly fit for continued service."
 
Do the tear down. We had a crank crack 200 hours after we bought a 185 with “lost” engine log book from a lawyer. Low speed slight bend are many times worse then a full power full curl on a prop.


Sent from my iPhone using SuperCub.Org
 
How do you do a slow nose-over in a 180? Parking a plane that weighs over 2000# on its prop is pretty unusual. Nosing a 180 over generally can’t be done “slow”.

How about you IAs out there. would you sign your name to a dial indicator test and return it to service?
 
Last edited:
I was advised by a Alaska engine shop that Continental crank shafts are made of glass (not literally, obviously, but I got the jest) and to tear it down. They were right. Cracked. Not a hard hit...which some say is worse.
 
You guys are ok. This is what I need.

Stewart: I flew tailwheels daily for fifty years before I discovered this - and fortunately my discovery was not the hard way.
A slow speed panic application of brakes, at least on pavement, will put you on your nose almost instantaneously.

You can lock them on landing if you want, and nothing worse than a blown tire or tube will happen, but slow speed? In a heartbeat.

I kept wondering how acquaintances were doing nose overs on the taxiway (!) - then one day the tower said "cancel takeoff clearance; hold short of . . ." - Instant brake application. Fifty years of training told me to get off the brakes when the tail left the ground, so not an expensive lesson.

First thing I tell a new tailwheel student - "low speed and panic brakes = disaster."
 
By the way, Mike, my mentor says the same thing. Crank cracks are far more likely at low power settings. Doesn't make sense, but you guys are seeing it.
 
It would be really difficult to put a typically loaded 180 on its nose, even if you bury the mains in soft sand, which will put a Cub on its nose faster than most guys can react.

Back the the IA question. Is a dial indicator good enough for you IAs to return it to service with your signature on the line?

How about perspective buyers? You find a nice 180 with a recent prop strike and dial indicator inspection. How do you value that engine? Myself? It's a core.
 
gbflyer said:
I was advised by a Alaska engine shop that Continental crank shafts are made of glass (not literally, obviously, but I got the jest) and to tear it down. They were right. Cracked. Not a hard hit...which some say is worse.
Click to expand...

Sounds like the same thing I heard from a friend after he had a prop strike in an O-300 powered 172. The shop told him the crankshaft, "won't be bent, but might be broke." They were right. Totally straight, but cracked. They told him that Continental cranks were hardened surfaces, so they generally responded with cracking instead of warping/bending.
 
Have heard the same- straight but cracked continental cranks. Lots of lycoming cranks straightened with a big crescent wrench and a dial indicator back in the day, and go on to live long happy lives- but every once in a while those crack too...
 
Continental nitrides the crank flange area. Lycoming doesn't. Consequently, the Continentals are hardened and crack while the softer Lycomings bend. You can even straighten a bent Lycoming flange if it isn't bent too badly.

-Cub Builder
 
This is all true. Lycoming cranks bend, Continentals crack and it doesn't matter how fast they were tuning! I've seen them break with improperly installed propellers as well as bumps with a tug/tractor.
AND...
Many people don't know that the magnetos take a hit as well. Both Magneto overhaul manuals call for overhaul and or replacement after a prop strike.
 
stewartb said:
How do you do a slow nose-over in a 180? Parking a plane that weighs over 2000# on its prop is pretty unusual. Nosing a 180 over generally can’t be done “slow”.

How about you IAs out there. would you sign your name to a dial indicator test and return it to service?
Click to expand...

Not a chance that I would accept any prop strike, especially on a Continental. On the late model engine i.e. 550's, the overhaul manual states to tear down any blade contact that requires more than minor prop dressing. I recently had a very low time 520 that sustained an unknown strike that the pilot did not realize had happened, a divot about the size to put my index fingertip in and it had a cracked crank. Was found at the end of a 3 hour flight when pushing back into the hangar.

It would keep me awake at night to go against the overhaul manual but then I also frame things as an IA as if I were on the wrong side of the table with the investigators after the worst has happened. Been there and it sucks beyond belief even when you are in the clear.
 
Ken Robbins said:
Not a chance that I would accept any prop strike, especially on a Continental. On the late model engine i.e. 550's, the overhaul manual states to tear down any blade contact that requires more than minor prop dressing. I recently had a very low time 520 that sustained an unknown strike that the pilot did not realize had happened, a divot about the size to put my index fingertip in and it had a cracked crank. Was found at the end of a 3 hour flight when pushing back into the hangar.

It would keep me awake at night to go against the overhaul manual but then I also frame things as an IA as if I were on the wrong side of the table with the investigators after the worst has happened. Been there and it sucks beyond belief even when you are in the clear.
Click to expand...

My stepfather had got stuck on a beach with gar-areos 29”. He got unstuck, broke the guys nose pushing on strut from rock. Had a chunk out of prop less than foot from spinner I could lay my thumb in. He just wanted to dress it out. I was like no, the prop shop can bless it. He was like they won’t. Yup new blades. That prop lasted 6 DAYS before the 185 got blown over in amber bay long after landing. And the tide got it.... Also destroyed exhaust headers, which I never had time to install the new ones before it was totaled.


Sent from my iPhone using SuperCub.Org mobile app
 
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