I have a hard time beleiving that this can be leagally done.  The prop has to be balanced, if you get a thicker coat of paint on one side the prop will be out of balance.

   Dave

If you believe a propeller is statically balanced this close have I got a deal for you.

If you're talking about repainting just the spot where the maintainance was done on the nick...I don't think that calls
for repainting the whole prop.  A quick "phsssft" on the
exposed metal should do it.  The amount of paint shold
be pretty darned inconsequential, I would think.

Michael

Under FAR43, you can paint the prop but are not allowed to dress the prop unless you are a certified mechanic.

<...rips the engine off of the airplane.> 

Seems like this should be the design criteria for the engine mounts. 1/2 Prop separates at full throttle.  Anyone know what it is?

Makes the case for wearing a parachute!

[Hmm? How heavy do you think that kind of engine mount would be?? A 1/4" STEEL firewall to mount it to?? A big truss?? Think it would fly?]

Don't know what the forces would be without a calc to answer that question. 

The real question is do you want to fly a plane where the engine can be ripped off by a very plausible and possible failure mechanism for an active component.  Nevertheless, seems like this kind of thing can and does happen.   I wasn't aware that this was a real risk and I am very surprised!

Has there been any operating experience reports of this happening?

Jack,

A 3 lb mass spinning at 2600 rpm 2 feet from the center of the rotating shaft can generate that amount of force on the shaft.  I believe you!

What I'm surprised about is that I did not understand the risk associated with this type of failure.

The next time I preflight, I'm going to spend a little more time looking for stress concentrations on the prop!

For those interested:
I worked out some very rough numbers to get a sense of what's happening.  When on the ground, each mount at the firewall must withstand in addition to the forces produced by the engine:

[This doesn’t account for the load being applied rapidly and using a simple geometry with just the static loads in a direction that produces the least amount of force on each!]

6500 lbf in shear  (Assuming 4 mounts 26,000 lbf / 4))

In addition, to compensate for the moment applied each of the 4 mounts at the firewall must withstand loads in tension or compression:

26,000 lbf in Tension or compression
(Assuming each mount is 1 ft from the shaft and 4 ft from the prop)

Steve,
Dynamic balancing the propeller has little effect on propeller stress and therefore propeller service life. Those little weights added to the spinner backplate do not change the bending stress created as the blades pull through air. Vibrations caused by imbalance - stress the propeller attachment and everything downstream which includes the passengers, but not the blades.. Your one ounce weight added 2" from the rotational axis only created a force of @ 21 lbs.. Your propeller blades generates some 13 tons of force so it really wasn't concerned with the 21 lbs of imbalance. Your smoothing from 3.1 to 0.6 was a nice thing to do for your airplane. It was money well spent......Many times the Static Balance from Propeller shops lacks the fine tuning that Dynamic balance accomplishes.    Another Propeller Subject - Metal Props operating off Grass Strips....easy to spot by the 1/4 inch foreward curl at the blade tips.....Now that's ugly!!!!jack

Steve,
Usually it is not the attachment that fails but somewhere within the outer 8 inches of the blade. It is the thinner part of the blade with the less strutural mass with the highest flex...So the most critical.
Yes, The Spinner is not the best place to attach weight.  The Lycoming has holes in the flywheel that can be used but you have to be careful because the added weight may not clear the passage through the flywheel/Starter slot..
Continentals - Most times the weight is added to the Spinner Bulkhead.
Grass Strips... Well, if you think about it, the grass strips very on grass depth - Freshly mowed to needing cut.  So, when you line up for take-off and you apply full power, your plane does not immediately move because of the turf drag on the tires. This is the point where the  Aluminum Propeller tips bow foreward....It's all action - reaction,  caused by the natural tendency of the Propeller.. It is designed to move foreward no matter if the plane is going or not... The Wood propellers on grass strips are not susceptible to this bow. If you bow a wood prop, it  springs back or breaks. If you bow aluminum just a bit too much, it bends.  I had a conversation with my friend who has operated a propeller shop for 30 years and he said that the Sensenich propellers are really not designed heavy enough to be operating on grass strips.. (They come into his shop all the time and he reworks them back to specs.)  He said the same thing will happen if you get the tires stuck in snow or mud.. Anytime the propeller has a high demand and the plane is not moving - then those forces cause the tips to curl.. Sight down the leading edge of your blades.. If they are curled foreward - you will see it ... It is not critical to flight but it will cause the propeller to be a little less efficient....I guess the secret is to  apply the power slowly and let the plane pick up momentum - hopefully the strip is long enough to allow this safely...  I guess I rambled... Sorry!  jack

OK, this has been getting my attention.

So how much "dressing" is safe for the average prop.  And how do we mere mortals evaluate whether or not our A&P has done a satisfactory job.  Even more to the point - what signs can you reasonably see that would predict a prop getting ready to fail? 

(I tap on the prop to hear that nice "tone" but have never felt I'm doing much more than a ritual here...)

To those that choose to post about my mentioned balance the prop, kiss off!  I simply made a comment based on what I felt and I get smacked around for it.  Geez, makes a guy NOT want to post around here!

    Dave