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IAC Discussion Summary

"Raked and thinned" propeller.

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Disclaimer: These IAC pages are developed by individual IAC members and do not represent official IAC policy or opinion.


Collected by: Doug Sowder DSowder@AOL.COM


Question

Is anyone familiar with the concept of a "raked and thinned" propeller as it relates to the usual Sensenich fixed pitch metal prop on an S-1S? These look radically different from the stock Sensenich on my particular S-1, much less massive looking. What's the story? Upsides, downsides?

From: Doug Sowder DSowder@AOL.COM


Answers:

The guy to talk to about raked props is Jim Stanton if you can find him. He did his own and it was really an awsome prop. don't tell Sensenich about it.they will dis-own you. Very narrow and the back of the prop has a little camber to it.

Last I heard, Lim was in PHX flying air ambulance. good luck.

From: mattcap231@earthlink.net (Matt Chapman)


I have run direct comparisons with a stock metal 76x60 Sensenich and an Anderson Raked and Profiled 76x60 on my Pitts. Tested them back to back on the same day.

I ran numerous performance points as well as flying a sequence.

Bottom line-

The only benefit I could find was that the Raked prop ran a little smoother. All performance points were either a tie or the stock Sensenich won out. For the majority of the perfomace points the Sensenich won.

Guess they knew what they were doing at Sensenich!

Also check back a few years ago when Van did a series of test on his RV-6A. It was written up in Sport Aviation as well as Kitplanes. I thought the stock Sensenich was the winner here as well.

From: Dan Rihn danrihn@aol.com


I have a S-2 w/230HP HIO360, used a constant speed, to heavy, went to a Racked and Thinned prop from Anderson in Chicago, a normal prop for an S-1 w/ 180-200 HP Lycoming is 76X62,60,or59pitch. Weight is 37 lbs stock from Lancaster, when racked and thinned approx. 10lbs of meat is removed then repitched for the above numbers. My experience is that the prop is so thin then that after a few hours the tips went out of track and actually we bending and I could not get them back in track. That prop is on the wall in my hangar. I now use a Performance 3 Blade Prop and it is fantastic, 13lbs and rugged, if your interested talk to Clark Lydick at Performance 520-394-2059.

From: Kelkensmgr

I didn't think to compare the weights of the two props. I don't think that the Raked prop was 2/3rds the weight though. I would have noticed that. I do agree that it must be lighter, but the hub is still the same. The prop I had was also reduced in chord, most of the reducetion was beyond the 50% prop station.

Also I agree that it will be easier on the crank. I'll have to check my memory (read textbook) but as I recall the polar momnet of inetia will be reduced by the 4th power of the weight.

I took comparison pictures of the two props. I can e-mial you a jpeg if you like. I'll look for my performance comparison numbers. Don't hold your breath on that one....it's right here in my files!!!!

From: Dan Rihn danrihn@aol.com


Any propeller that has been modified from original, certified dimensional limitations is dangerous unless a full vibration survey with strain gages has been performed. When you change the blade profile and planform, especially out near the tips, the natural frequencies of the propeller change dramatically and may enter the region where excitation from the engine causes a resonant condition. Blade failure is soon to follow if the resonance is bad enough. The effect is more pronounced for constant speed installations, but just as applicable for fixed pitch. I spent 5 years at Hartzell doing vibration surveys and certifying propellers. I would NEVER fly behind a propeller that had been modified beyond manufacturer approved limits, especially doing aerobatics.

From: Skybolt540@aol.com Scott Rodriguez



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Last Update: Sat Aug 29 16:11:25 2009


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