Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

OS 91 FX WHAT PROP

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Old 02-07-2009, 04:14 AM
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ALO 111
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Default OS 91 FX WHAT PROP

I HAVE A SUNDOWNER 50 WITH A OS 91 FX SPINNING A 12/8 APC AT 11500.
I SEE SOME GUYS TALKING ABOUT 11/10, s .COULD THIS WORK OR WILL I OVERREV THE MOTOR? WHAT ARE THREE BLADE PROPS LIKE FOR SPEED?
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Old 02-07-2009, 07:16 AM
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nesikachad
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Default RE: OS 91 FX WHAT PROP

No three blade props when hunting for speed. just too much dead mass.

According to OS the engine you have peters out around 15K for rpm. I'm guessing that if you tach the prop on the ground to peak around 12,500, it'll unwind in the air another 2500 to 3K.

So long as your within that window I'd say your ok. APC and Zinger props seem to be the two that get the best speed from this plane. I'd be curious to see what a DF engine does. That might be pretty cool with the right prop.

With your engine I spec you'll top out in the 130-140mph range. The extra displacement helps but the increase in weight will affect it some too. Take offs will be a little longer and landing will require some extra work to get the speed bled off.

I don't mean to sound "know it all" so if your an experience pilot just disregard this. On my SD I start waaaayyy out and I chop back to idle. As I get "close" I start to do some high rate turns to scrub the speed off. It's a guess as to how much and I never seem to get quite enough off. She always comes in hot and I just end up holding it a foot or so off the ground until it can't ground effect anymore. It's not a textbook picture perfect landing process but it's safe, controlled, and results in the plane keeping all its parts together.

If your radio has it, maybe slow down the throttle servo a bit. I dialed mine back to take 1.5 seconds to go from idle to WFO. (JR12X radio) This has been nice because take offs are much smoother. I can just mash it and then start dancing the rudder to keep it straight. It was far more work to do that before I slowed things down. This is a speed plane so in the air it's always on the gas anyway so there it matters little. Just seems to help me so thought I'd share it.
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Old 02-08-2009, 08:19 PM
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Default RE: OS 91 FX WHAT PROP

If you can find an APC 11x9 or 11x10 that might help. Mine is quite happy turning an APC 13x8 on a Delta Vortex, which can be quite quick in spite of the signifigant induced drag.
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