What prop size for three-blades on .25 twin (OV-10)?  
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All Forums >> RC Airplanes >> Twin & Multi Engine RC Aircraft >> What prop size for three-blades on .25 twin (OV-10)?
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What prop size for three-blades on .25 twin (OV-10)? - 7/3/2003 12:11:43 AM   
Don T. - NN4S



Posts: 59
Joined: 7/2/2003
From: Toney, AL, USA
Status: offline 		How do you go about selecting three blade props for an engine? I'd like to use a pair of them on the HH OV-10 I'm working on and have no idea how to choose them. Is there a rule of thumb that sizes them relative to a standrad two-blade prop? I'm also trying to decide which engines I'd like to use on it since I have a pair of Saito .30s I'm breaking in on other planes right now. I've also got a .25 schnurle BB that I can get a matching engine with a counter-rotation crank for so that the engines can operate the same as the full scale one. There's also the advantage of turning the cylinder to the other side on the new engine to change where the exhaust is; it can even be to the rear as long as I do it BEFORE I break it in. I was thinking that maybe I could rig it up for both engines to have the heads to the inside & exhausts along the bottom of the nacelles if I go 2c with it. Anyway, back to the original question: How do I select the props for these engines so that I can determine IF the reverse thrust prop is even available for this setup? Thanks for any help!

_____________________________

Don T. NN4S NN4SatARRLdotNET
Building again & loving it!
       Post #: 1

What prop size for three-blades on .25 twin (OV-10)? - 7/3/2003 3:08:27 AM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Don T:

I am a known nut as far as twins and 3-blade props are concerned.

General rule of thumb is down one inch in either pitch or diameter. That is, if you run a 9x6 two blade you'd go to a 9x5 three blade, or 8x6. This gives a good starting point, and in many cases it's all you need.

I have two engines running in your size range. The Magnum 25 is pulling an 8x6 three blade cut to 7" diameter, It's on a Goldberg Eaglet. The MDS 25 pulls a full 8x6 three blade. on a much larger, but slower flying, airplane.

Your Saito 30s should run the 8x6 3 blade props very nicely.

Grish (Tornado) and Zinger (J&Z, Zingali) both supply reverse rotation 3-blade props in this size range. Master AirScrew has none.

I like counter-rotating engines on twins, if you can find suuitable props it's well worth doing.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

(in reply to Don T. - NN4S)
       Post #: 2

What prop size for three-blades on .25 twin (OV-10)? - 7/3/2003 8:32:09 AM   
flying2bill



Posts: 485
Joined: 12/25/2001
From: Central City, IA, USA
Status: offline 		I would consider mounting the engines so that the glow plugs are to the outsides of thier respected sides, or use a remote glow system. I have a 52 inch Bronco that I just aquired and the port engine has the glow plug between the engine and center pod, reguires reaching around the center pod and under the wing which put my arm in a discomforting twist.


_____________________________

Rule of the 3 W's
If it involves Wheels, Wings, or Women, it's bound to be trouble.

(in reply to Don T. - NN4S)
       Post #: 3

What prop size for three-blades on .25 twin (OV-10)? - 7/3/2003 8:50:47 AM   
Don T. - NN4S



Posts: 59
Joined: 7/2/2003
From: Toney, AL, USA
Status: offline 		Thanks for the suggestions, guys! I'll look into the prop availability issue before committing to a course of action. The onboard glow system for low-speed/idle and boots that remain on the engines are an item that's been planned on; the gyro issue is being considered and a means of sycning the engines is a possibility if it looks like it'll be an issue. I'd even considered the possibility of a rudder gyro/FMA co-pilot combination for the plane's first flights; there's enough $$$ tied up in it to make me seriously nervous about meeting up with the ground at the wrong angle of attack!

Like I mentioned in another post, I'm still getting all of the ideas sorted through & on paper so that when the bench is clear I can get started and know where I'm headed with it. By the time I get finished I know I'll have a lot of EDF (Emotional Debt Factor) as well as $$$ tied up in it and want to make sure I've done everything possible to keep in in one piece while I get comfortable with it! No flying without the crutches until the knees stop shaking...


_____________________________

Don T. NN4S NN4SatARRLdotNET
Building again & loving it!

(in reply to Don T. - NN4S)
       Post #: 4

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