Propeller stone damage

[boofhead]

Can anyone point me to a good source of information relating to how much stone damage a prop can have before it is unsafe to fly? How deep, long, location, shape etc of knicks and scratches etc.
Much obliged, and any stories of prop failure to illustrate the paper I need to write on the subject also appreciated.

[StopStart]

Not seen any failures but we were getting through quite a few C130J props out in Afghanistan. Our limits on damage are, in my opinion, overly cautious - small dents being enough to render the prop unserviceable. Ours is a composite blade with steel leading edge stone guard. I suspect there are fears about delamination of the prop or the shedding of a damaged stone guard in flight. The older C130 with the all metal prop has far fewer problems with dents and knicks just being filed down :)

[Short_Circuit]

Surely the Aircraft Maintenance Manual will have very specific
damage assessment criteria ie size and position of allowable damage.

[411A]

Any really good propellor overhaul shop can supply the relevant data, and it is surprising how some metal props can continue in service with what might seem rather drastic nicks, etc, IF properly attended to by the maintenance staff.

Composite props...wouldn't have one.:eek:

[johnriketes]

Not a lot of damage can be tolerated.

We operated large piston nose wheel twins on gravel strips for years and the prop tips were very close to the ground. Damage was kept to a minimum by doing run ups/power checks with forward motion (EG.,while back tracking) and riding the brakes so not to let the speed get too high. We operated single crew so you needed to be very careful. Two crew of course the duties could be shared IE., one looking out, controlling speed and steering.

Possible prop damage was taken very seriously in the company as loosing even the tip off a prop blade at the damage point (weakest) could be catastrophic.

You can do a "C of A" preflight but remember, one cannot inspect for prop damage after engine start, until after the flight.

[stevef]

What you don't want is damage to the inner third of a prop blade. You'll get away with polishing out VERY slight nicks or dings but anything more than that is going to be expensive.

[boofhead]

The airplanes I am responsible for range from Beavers through Cessna172,182,185,206, all single engine types, and a couple of Cessna twins, PA31 and a Kingair. They all operate on gravel at times, some on skis in the winter. I need something for the typical 300 hour private pilot to use to determine if a prop is good to go or if he needs to call a mechanic to help with the decision. I don't want them to whip out a file and start dressing a prop in the field either.
I also run a composite prop on my own airplane, a pusher amphibian and it is eroded by water just above the nickel leading edge cuff but I hope that does not meet the criteria for this discussion.
The local prop shop is giving me some good stuff but I need to make it interesting or the pilots will not read it.
I have seen prop blades that have knicks as small as the head of a pin that have failed or cracked, and others with pieces out that you can put your finger in that continued to operate without cracking or failing. If I make it too frightening I will have airplanes grounded all over the state. Typically it is safe to return to base, since it takes some time and engine vibration to cause a blade failure, but I could be wrong. One of the mechanics working on airplanes I fly always dresses the props when he personally flies out of gravel and does not accept any damage. We had a blade fail last year with only a small chip out of a blade (cannot be sure because the piece was not recovered). In that case we think the blade hit a runway light (the runway owner reported a damaged light after the event) and the blade failed minutes later on takeoff. Since it was a twin, the pilot shut it down immediately but we still lost the prop and had to overhaul the engine, big expense.
I know I was willing to accept quite a lot of damage before I was acquainted with the dangers, and one of my crews flew an airplane with three big pieces out of two of three blades (one piece was big enough to put a pencil in, and that blade also had a curled over tip caused by hitting something metallic) seemingly without concern, which is what has prompted this topic. They were experienced pilots, one was an instructor and they conferred together before accepting the airplane. They could have called a nearby mechanic but did not feel it necessary. The engine and prop had to be overhauled of course, but I am more concerned by the fact that they did not think it hazardous to fly an airplane in that condition. And would others do the same as they did?
Thus a desire to put something together that I can put out for everyone to read that helps them to make that decision. Any help from you guys would be appreciated. Stories of failures, guidance on damage, precautions and the like, especially with links to sites that have pictures...