Need some help selecting a propeller

BarryHay

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Mar 9, 2016
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Location
vancouver, Wa
I have a KB2 gyrocopter that is 95% complete - all I need is the pusher prop and a tuned exhaust for my yamaha 540. I could use some direction where I can find some info to help me select a prop with a reasonable level of confidence that it will work for my HP and RPM setup.

Here is what i have - 60 HP 6700 RPM reduced to 2900 RPM with a belt drive reduction.

Looking at the Tennessee Prop website I am guessing I can use something like a 58" dia with 42deg pitch.

Any members want to give there 2cents?

thanks!
 
I don't understand what a manufacturer means by 42 "degree" pitch as the pitch varies along the length of the blade. The closer to the hub, the greater the pitch as the prop is spinning slower at the hub than at the tips. When I was flying fixed pitch Troyer props in the 1970's if I recall properly, the pitches were actually identified in "inches". The inches being the distance that the prop would move forward with one revolution. The tip, which is traveling faster than the root, needs less pitch than the root to keep the travel the same along the length of the blade.

You should buy an adjustable pitch prop (like a Warp Drive) and set the pitch to maintain engine rpm just below red line. I can't see trying to calculate the optimum prop pitch and purchasing a fixed pitch prop when most of the new props have adjustable pitch. The prop will also have greater resale value as it will be more versatile, allowing it to be configured for different machines.
 
The biggest prop I have seen in a stock KB2 is 54", unless you raise the mast. Measure to see, bigger is better as long as it fits.

With 60 HP you will need a 3 blade prop to use the power. I would go with an Ivo prop because the are so easy to adjust. If you are flying of a dirt strip a Warp Drive will probably last longer.

My 2 cents
 
Not 42 Deqree!

Not 42 Deqree!

...I don't understand what a manufacturer means by 42 "degree" pitch as the pitch varies along the length of the blade. ...

The 2nd number is how far a prop would screw forward in 1 revolution if it was 100% efficient (like a screw beinq tiqhtened into wood)

a 42`` pitch prop would carry your qyro forward 42`` in one revolution if it didn`t ``slip`` in the air.

It has NOThINq to do with deqrees of pitch.


The two articles below will help select a prop for any engine.

https://www.cps-parts.com/cps/pdf/Part5.pdf
https://www.cps-parts.com/cps/pdf/Part6.pdf
 
I agree with Cesphil. With an adjustable prop you won't get stuck with something that may not work out just right.
I have always used Ivo and am very happy.
 
If that is the snowmobile engine 535 cc it don't hold up well to belt drives and prop use, of the three in my area none reached ten hours on an airboat, the one I had got to six hours and after the second time I replaced it with a 552 rotax which now has over six hundred hours on the same belt drive that was on the Yamaha.
Norm.
 
I have found that the proper pitch is not determined by the RPM but more so determined by the EGT. Am I wrong
 
The ideal pitch is where you just barely reach max rpm at WOT.
This is the point where the max hp is transfered into the prop.
This will vary with flight speed and altitude, so a compromise is required with a fixed pitched prop.

You may want to select best performance for climb or cruise, or get a variable pitch prop and get the best of both worlds..
Too much pitch causes lugging with excessive MAP with its associated excessive temperatures.
Too little pitch causes over reving, the lessor of the two evils.
 
When you have 54 inches max. for prop size, take a look
at the "Kharkov" propellers from Ukraine (here on forum). They
make a 3-bladed 140 cm version. 54" x 2.54 cm = 137.2 cm.

I'm contemplating their 3-blade 160 cm for my Rotax 503.

Cheers
Erik
 
Last edited:
Belt drive

Belt drive

If that is the snowmobile engine 535 cc it don't hold up well to belt drives and prop use, of the three in my area none reached ten hours on an airboat, the one I had got to six hours and after the second time I replaced it with a 552 rotax which now has over six hundred hours on the same belt drive that was on the Yamaha.
Norm.

Norm:
Was this belt drive made by you?
If not, by whom?
How many belts does it use?
Was the failure of the 535cc engine due to lack of bearings supporting the PTO?
 
It is a cog belt system which puts very little stress on the crank, the failure was the crank between the cylinders, I have seen hirth 2703 fail the same way.
Norm.
 
Depending on the configuration of the redrive-engine combination, a stock KB-2 with a redrive engine can end up with the prop thrustline quite a bit above the aircraft's CG.

Unless opposed by a large, functional horizontal stabilizer, this arrangement can kill you (as it has done to scores of gyro pilots over the decades). Have you dealt with this issue? How?

We want all our gyro brothers to remain alive and intact.
 
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