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Old 02-18-2008, 09:25 PM   #1
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static thrust

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how does static thrust relate to the wieght of an airplane? ie if a r/c duct fan unit only puts out 16 oz of thrust does that mean 16 oz is the max wieght of your airplane? thanks for your help
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Old 02-19-2008, 03:10 AM   #2
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Re: static thrust

Originally Posted by igor27
how does static thrust relate to the wieght of an airplane? ie if a r/c duct fan unit only puts out 16 oz of thrust does that mean 16 oz is the max wieght of your airplane? thanks for your help
this is the way i was told it works.

im going to make a thrust gauge to find out actuall thrust figures of EDF and 2 strokes of what the EDF will take place of.
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Old 03-08-2008, 08:55 AM   #3
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Static thrust is how much push the fan unit puts out at full throttle sitting still.

I suspect that the manufacturers do this with the fan unit mounted in a test rig so that the maximum amount of air can be drawn into the unit.

Of course, static versus dynamic thrust (dynamiic is what you get with the plane in motion) is dependent upon the design of the fan unit.

The old Byron units were designed for sttic thrust and acceleration (getting the plane going and into the air as quickly as possible, hence the large diameter and size of the blades.) Beyond a certain point, the fan unit would "choke" and actually slow the plane down -- that is, the fan unit could not move air through the unit faster than the airplane was flying at.)

By comparision, the Dynamax unit (a generation later in designs) was aimed at dynamic thrust -- getting the plane to go as fast as possible in the air. Static thrust was lower than for the Byron unit, and that's why the Dynamax-powerd planes would need more runway to get into the air. Once they got "up on the step" and were operating in the correct speed range, the same sized motor would be revving higher and pushing more air through when the same engine on a Byron unit would be maxed out and "choking".


Now getting to the maximum weight of the airframe.... the calculation for the IC fan units is that the worst-case weight to thrust ratio is .5 (a 32-ounce airframe fuelled and ready to fly) can be moved by a 16-ounce static thrust.) Getting closer to 1.0 and better is "a good thing" to quote Ms Stewart.

Of course, there are variables galore -- eg, grass versus asphalt versus catapult, type of fan unit, ducting, wing lift, total drag.

Best way of looking at what should work for electrics is to get the details for similar aircraft -- size, weight, fan unit, motor -- to what you want to fly.

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