Would anyone on this list have ideas on the propeller size for a Quadra 200cc with a belt reduction drive (2.72:1) . The engine combo is installed on a 1/3 scale Beaver that a friend of mine is building.
http://www.geocities.com/roger_forgues/Works.html
Right now he has a 42" x 25" propeller on it, but because the Beaver is on floats, the diameter is too large because of water splash.

Roger

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Use the largest prop that will fit and still clear the water...I turned a 30-10 with a Mick Reeves drive on a G62, 4000 rpm..

Roger

I think you should look at props with much less pitch. I would guess the 42x25 was a prop designed around going fast, not sport flying.

What size prop diameter will meet your needs?

As Ralph suggested use the largest diameter prop that will clear.

mgalvin, with that much reduction he will have to run a much higher pitch especially if he reduces the diameter to clear the water. Simple example: in theory a 25" pitch prop at 3500 rpm should be flying the same speed as a 12.5" at 7000 rpm keeping the same diameter. I suspect he will be turning the prop well below 3500 rpm. Yes I know about slip, efficiency, etc. Maybe a 3 blade prop might be in order.

Ken

Hi Roger,

Put some more pictures up on your site of the Beaver. It looks great. I wish they had projects like that when I was in school. All I got to do in shop class is make enameled ash trays.

I see the numbers like this:

7,000rpm @ 12.5" pitch = 82.26mph @ 444lbs. thrust

7,000 divided by 2.72 reduction 2,573rpm; 25" pitch prop =65.18mph @ 68.74lbs. thrust

Reducing the diamter of the prop to say 38" looks like this:

2,573rpm, 25" pitch = 65.18 mph @ 40.24lbs. thrust

2,573rpm, 12.5" pitch = 30.46mph @ 40.24lbs. thrust

It looks like to me the key here is going to be developing more thrust at a higher rpm with the reduced size propellor. Pitch only effects "MPH", and has little to no effect on static thrust.

How about a 36/12 @ 5,000rpm developing 122lbs. of thrust at 56mph...

Multiply the scale 56mph by the reduction in size of the model its actually traveling at 168mph...

Thanks Michael, Bill, and the rest of you for your fine answers. I will tabulate all this and the decision will come from Roger Lalonde the school teacher that built this airplane.
I plan to take more photos and repost them for you guys.

Roger

Team ACM
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Forgues Propellers
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I'd just like to say what a cool thing your doing with your class and these kids. It makes me want to go back to high school....your school though. Can I join your class(at 39)? Really inspiring, and beautiful workmanship on the plane. Very admirable and definately commendable. Good luck with it, those kids will have memories of that for life.

Thanks Dale, I will also take the compliments to its rightfull owner. Roger Lalonde the teacher, I'm just the messanger.
Roger

Team ACM
Fiber Optic Servo Extensions
Forgues Propellers
Multiplex Dealer
http://www.aerografixs.com
Model-Scan Frequency Analyzer