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Need more giddy up.....

BH1166

Well Known Member
I own a 28 year old 6A with a O320 with a 28 year old Bernie Warnke almost constant speed wood prop. Prop is 72 x 72, urethane edge, and is in like new condition. Prop is great at cruise, 7 gallon an hour at 2350 rpm / 150 TAS. Static 2400 rpm, WOT 2480 rpm. On a budget, aka I’m a tight wad. Would like to improve takeoff ( takes a long time/ distance to get to rotate speed) maybe better climb as well.

Question, could someone in the wood prop business, cut this prop down to ??? in to increase rpm and enhance TO roll / climb with minimal impact my cruise?
 

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While not the 'cheap route', have you considered a ground adjustable composite prop such as the WhirlWind?
 
Wouldn't the pitch have to change to see significant gains in takeoff distance? I see spinning faster with a shorter prop but I can't imagine the difference is that much.
 
You already see a higher static RPM than many with fixed pitch which makes it a bit of a climb prop already. If you have it re-pitched for higher static RPM, it will hurt your top speed unless you are willing to perhaps exceed redline. Cutting the diameter will have similar results, higher static RPM and probably lower top/cruise speed.

If your wot 2480 RPM is in cruise, perhaps a little less pitch would help speed by getting you some more power from higher RPM. Perhaps the wood prop is thicker than optimum and a composite prop would be more efficient for both climb and cruise. Craig Catto?

Ed Holyoke
 
Thanks

You don’t know what ya don’t know. Thank you for the input. I have reached out to Frank Johnson at performance propeller.
 
If you want real improvement, and the engine is properly configured, go to CS. It deals very well with the takeoff condition and the cruise condition. Probably similar cruise, but takeoff would be greatly improved.
With fixed pitch you either get takeoff/climb performance or cruise, or somewhere in between but not all like CS.
 
Butch,

You have what we call a Warnke Toothpick. Sounds like it's going into flutter at higher rpm, thats why you can't achieve more than 2480 wot. Typically, if you make 2400 static you should see at least 2700-2800 wot. I'm happy to help.

Give me a call, 713-417-2519
Frank
 
There's a comment from Van himself on the Front Page today, Friday October 23. (Now it's on post #12 below).

It's pretty interesting....

Dave
 
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Warnke prop

I bought one of the very first Warnke almost constant speed props about 40 years ago for use on my Bushby Midget Mustang. Its performance was a mix of good and bad.

It was a very thin propeller with very little area both in the sense of disk loading and also in the sense of strength. This is why it was made from a very large number of laminations (30+). The workmanship was beautiful.

It has been a long time, but my memory is that it turned about 2500 rpm static and about 2700 WOT in level flight (170 knots or so) with an O-235. It was very smooth, with very little inertia. It also exhibited what I thought was blade stall during the early seconds of takeoff. Somewhere around 20 knots the blades would finally get a grip and the acceleration was pretty good. Up to that point there was a sound like cavitation and acceleration was weak.

The thin blades were also very flexible. It was easy to twist the blades a few degrees and I am sure this was the key to the constant rpm.

I considered the prop to be experimental aviation at its finest, offering some real opportunities for some airplanes. I was never tempted to replace it (where it has replaced a cut down and brutally twisted Sensenich club) but neither was I a big fan.
 
Van's comment, etc

Some really good comments re fixed pitch, particularly Mr. Van G's on the front page with Propman and others in the thread.

I have used Javaprop to do light a/c prop design simulations for many years as a hobby. Van's analysis is totally in sync with some of the results I have produced with Javaprop. The program has shown that a prop design similar to the one in question will be maybe 70 or 80 percent stalled at static. This will reduce loading and static thrust as well as increase static RPM. I have also seen design examples of a prop loading up with increasing forward speed and a subsequent small drop in RPM as speed increases, just as in a previous comment by dart11. So its nice to know that the wiggly lines produced in Javaprop can be real in the real world.

Once upon a time, more than half a century ago, I competed in model a/c speed contests. Making the blades thinner than stock would = faster up a point, then a further thinning would result in a drastic loss of speed. Propeller flutter may be more common than is thought.

A very flexible prop is bound to flutter at some point with an increase in flex or speed if special attention is not given to increasing torsional stiffness or forward load the section CG. It is SOP with helicopter rotor blades to weight the leading edge, for example. For light a/c wood props, metal edging can help serve this function. So, yes, Propman keyed in on flutter. He may have something for you.

Ron
 
Dick VanGrunsven input....

Dick V. saw this thread and emailed me the following to add:

VAFDR_85%20Oct.%2022%2015.51.jpg

VAFDR_86%20Oct.%2022%2015.51.jpg

v/r,dr
 
Warnke "Almost Constant Speed" was pretty much in name only. Prior to those his standard props had a wider chord and performed very well. I had one on my O-360 RV-4. Similar props today are made by Performance Propeller which was first owned by Warnke's ex son-in-law who copied his design.

Warnke was always experimenting with new designs, ie the "Toothpick." My hangar was next to his and I tested many but none ever surpassed his original wider chord "Club" as I would tease him.

Bernie was a great guy....hard to believe that was 30+ years ago.
 
GT Propellers

I'd give GT propellers a close look. I use one of their props on my radial RV and love it. They worked with me to engineer a blade for my specific installation. They also make replacement blades for a hartzell hub. In fact they have a blade that is modeled after the spitfire blade.
 
Your prop tips are still pretty wide. I had a Performance Prop giving me about the same RPM you discussed. I drew a line along the leading edge and cut down the tips thinner, worked the wood to match the existing profile, rebalanced it, also glassed it but that was just to make sure it was stiff enough. Pics are before and during the glass application. It gave me about 125 more RPM. (the dots are lead shot to balance it)
 

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