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what rpm to operate at?

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what rpm to operate at?

Old 03-19-2007, 08:18 PM
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Default what rpm to operate at?

I tend to run props on my o.s. .50 engine that are on the smaller end of the suggested spectrum(10x8,11x6). Wide open, in cooler weather, it will regularly run at 15000 rpm. I normally just fly sport/ aerobatic routines. I've looked at prop charts before and have done testing with other size props so please don't suggest those as answers. I want to know from science or experience whether its generally better to run that engine near its peak rpm with a smaller prop like I've been doing, or settle for less rpm with a larger prop. I'm concerned that the engine is being overworked and will have a much shorter life. It doesnt overheat, but seems like it's ready to explode when I have it on the ground and am tuning/testing. I know at high rpm nylon blades can distort and lose efficiency so I should maybe consider a wood prop.
Any help on this matter would help alot.
Old 03-19-2007, 08:42 PM
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Default RE: what rpm to operate at?

H.P. cool, but Toruqe is were it`s at, big or small.
Old 03-19-2007, 08:49 PM
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Default RE: what rpm to operate at?

Empirical data obtained from controlled, scientific testing can be obtained for about $500.00/hour from Sonex Labs in Maryland. On the other hand, it's about the type of flying you want to do, how fast it has to go, how much torque is required, and the type of airframe. If you're runnng your engines at the maximun possible peak rpm then you are not using the engine in a manner that would fly the plane the best. I'll venture that the aerobatic up lines suffer badly and that you have trouble managing the excessive speed in the horizontal. The down lines must be real screamers, and everyone covers their ears when you fly.

Use a bigger prop and lower the rpm. Find the one that pulls the plane effectively in all attitudes. It's always a trial and error thing.
Old 03-19-2007, 09:21 PM
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Default RE: what rpm to operate at?

Although the OS 50 will turn faster I prefer to run mine in the 13,000 rpm range. I run a 10 x 8 MA Simitar on a 6 1/2 pound airplane at 13,100/13,200, which is about 500 rpm off peak.

Old 03-20-2007, 06:53 AM
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Default RE: what rpm to operate at?

I agree with Silversurfer. I played with a lot of props from 10x6 to 12x6 an even a couple of 3 blades with my OS .46 SF. An 11X7 had enough speed and enough "dig" with my Sig Kougar (6lb) to get good uplines and managable downlines. It turns about 10-11k on the ground.
Old 03-20-2007, 04:16 PM
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Default RE: what rpm to operate at?

All you have to do is tell us what plane you have and how big it is and we will tell you what prop that works best!
That simple!
15000rpm is just too much if you use the OS .50 engine in a sport type aerobatic model.
Aim for a rpm around 11000-13000. APC is the best prop around. Never go with a 3 -blade prop.

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