Almost lost prop

[krwalsh]

This is common on wood and wood/composite propellors on the EZs. The solution is to use a stack of Belleville washers in a very specific stack order and to torque the stack a fixed number of turns instead of to a torque value. Contact me off-line and I can provide the details and contact information.

[dealfair]

Yes Willy, thanks again for that report and using those eyeballs. A great lesson there for prop inspection. I like to think I pay close attention to the prop; but this will be in my mind from now on. Catching this on the ground is mucho better. A great lesson!!!

___________________________
Deal Fair
RV-4 (34CB)
George West, TX (8T6)

[MikeS]

How much does vibration play a part in prop problems like this?

I made the investment three-four years ago of a Dyna-Vibe and it's been well worth it just for the smoothness. I do other people's planes all the time so it earns it's keep.

Mike

[MNForrest]

Asside from his questionable treatment of a pretty wooden prop, Bill is a great guy, and a heck of a pilot. He finished well flying Sportsman last November at the Keystone IAC contest near Daytona. This spring, he finished second (in a field of eleven). He has done a great job adapting the RV performance characteristics to the maneuvers required, flying them better and safer than many of the guys/gals floundering about in Pitt's and Extras. He listens to comments from more experienced pilots and really works hard to "fly it right". Anybody interested in IAC aerobatics in an RV should pick Bills brain bare. He's a good example of an RV guy operating in "less charted" territory.

Forrest

[sandifer]

Originally Posted by MNForrest

Asside from his questionable treatment of a pretty wooden prop, Bill is a great guy, and a heck of a pilot. He finished well flying Sportsman last November at the Keystone IAC contest near Daytona. This spring, he finished second (in a field of eleven). He has done a great job adapting the RV performance characteristics to the maneuvers required, flying them better and safer than many of the guys/gals floundering about in Pitt's and Extras. He listens to comments from more experienced pilots and really works hard to "fly it right". Anybody interested in IAC aerobatics in an RV should pick Bills brain bare. He's a good example of an RV guy operating in "less charted" territory.

Forrest

According to the IAC contest results this Forrest fella is pretty good in his S-1S too. Did you fly Sebring a couple weeks ago? I attempted to CD the Carolina Boogie last weekend, but had to cancel due to Wx. Major bummer.

[Bob Axsom]

Several posts seemed to gloss over the part about false torque indication caused by long bolts bottoming out. If they are marginal to start with, repeated torquing will eventually use up the threads and you will no longer be tightening down against the prop.

Bob Axsom

[smokyray]

Willy,

Nicely done. Been there, done that brother. Now you know.
Having removed and installed "several" wood props on RV's what Bob said above is key. Make sure the bolt grip length is correct. Also a crush plate should be there, I don't see one. That would make up the space difference for the bolt length. Dial the crank before you tear the engine down. Unless you shook it off the mounts, it should be OK.
My buddy JJ had a wood prop split apart inflight and made a nice forced landing at an airport. He said the vibration was so intense he thought it would break off the tail. The engine was fine and he went with a Sensy metal although he liked my Catto.

Most all the wood props will give you very long life with proper care and feeding. Having said all that, the composite props (Catto, MT, Hertzler, P-Tip) hold their torque longer. I still check them every oil change.

Smokey

[DanH]

Originally Posted by WillyEyeBall

Conditional inspection with torque of prop bolts checked at 22 ft-lbs....

Prop material is sugar maple, yellow birch, or something else?

My A&P mechanic thinks that the long prop bolts may have bottomed out, and created a false torque value when the bolts were retorqued on the conditional inspection.

Very possible and easy to measure.

The previous engine overhaul company thinks the 8 ? inch bolts through the spacer were a contributing factor when the aircraft is used extensively for aerobatics.

If installed correctly length doesn't matter. The bolts are clamping devices, nothing more. Engine torque is transmitted by static friction between the flange face and the rear face of the wood prop. If static friction fails the design backup is generally engineered sizing of the flange bushings. When they wallow out (and they will in short order) the prop bolts will see bending loads and fail....as you've seen.

[Ron Lee]

Let's assume that if you put a prop bolt in a flange without the prop and loosely tighten it until it stops (bottoms out). The distance from the lug forward point to the bottom of the bolt head is 8.0 inches.

How much MORE than 8.0 inches should all the prop bulkheads, crush plate and prop be to ensure that the bolts do not bottom out?

1/8 inch ?

3/16 inch ?

[DanH]

Originally Posted by Ron Lee

Let's assume that if you put a prop bolt in a flange without the prop and loosely tighten it until it stops (bottoms out). The distance from the lug forward point to the bottom of the bolt head is 8.0 inches. How much MORE than 8.0 inches should all the prop bulkheads, crush plate and prop be to ensure that the bolts do not bottom out? 1/8 inch ? 3/16 inch ?

This should help Ron....written by Henry S. Rose, Chief Engineer, Sensenich, back in the good 'ole days: