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Old May 06, 2002, 04:49 PM
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Dallas TX
Joined May 2002
4 Posts
motor/prop test bench

Hi,

I'm new to this forum and just started flying electrics a couple of months ago. I flew alot of gas about ten years ago.

I'm trying to design and build a test bench to measure thrust using a postal scale of some sort. I've ordered a Wattmeter for the electrical measurements.

I would greatly appreciate any advice / designs you guys have tried.

Thanks
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Old May 06, 2002, 05:39 PM
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Dick Curtis's Avatar
Santa Barbara, California, United States
Joined Mar 2002
97 Posts
I have been using a test stand to measure static thrust, current, voltage,watts, RPM, and temperature.
It is a rolling platform mounted on screen door ballbearing wheels that run on an aluminum
angle track and pull a linear scale. It is set up for 15 pounds thrust but a differnt scale would work fine for lower thrust values. I am measuring 26/14 props on 48, 3000nimh cells,which unfortunatley hits the stops so I need to get a 20 pound scale. Fish weighing scales are not too expensive and work OK.
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Old May 06, 2002, 05:44 PM
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Dallas TX
Joined May 2002
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Thanks Dick. Do you have a bigger picture or can you email me the one you posted so I can zoom in to see more detail.

Dale Troutt (txzagi)
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Old May 06, 2002, 05:57 PM
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sneu's Avatar
United States, CA, San Diego
Joined Dec 1999
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I hate to toss cold water on the idea your test bench but the fact is that static thrust measurements are not very useful for getting a idea how your palne will perform. The better prop--a smaller diameter high pitch prop may well be stalled in the static condition and will look worse than a low pitch larger diameter prop. Have fun playing but don't take the data too seriously.
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Old May 06, 2002, 06:46 PM
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Dick Curtis's Avatar
Santa Barbara, California, United States
Joined Mar 2002
97 Posts
Sneu and Tzagi,
At initial launch, when the propellor parameter V/nD =0, the first motion is related to static thrust and the kick to start accelerating. As the plane gains velocity, the blades, if high pitched, start to lessen angle of attack, are no longer stalled, speed up , and the thrust changes. So static is only one point on the curve-but it is a point. I use a high speed blower to simulate "V" up to 30 mph but only on props less than ten inches. For the test stand pictured, we mount it on a pickup and calibrate at speeds to 40 mph. Not as good as a wind tunnel but better than guessing the coefficient of thrust (Ct) for the particuliar blade shape, aspect ratio, pitch, and tip shape. As per the request for better graphic, I'll send E-mail.
...Dick
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Old May 07, 2002, 11:50 AM
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Dick Huang's Avatar
Dallas,TX, USA
Joined Mar 1999
834 Posts
Here is another test stand for 400 motors.
Dick Huang
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Old May 07, 2002, 12:03 PM
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Dick Huang's Avatar
Dallas,TX, USA
Joined Mar 1999
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try
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Old May 07, 2002, 12:05 PM
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Dick Huang's Avatar
Dallas,TX, USA
Joined Mar 1999
834 Posts
second try
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Old May 07, 2002, 02:46 PM
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Dallas TX
Joined May 2002
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DH,

Thanks. Is there a pivot point that can't be seen in this view that allows the motor/prop to pull the weight up?

Dale Troutt (txzagi)
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Old May 08, 2002, 04:36 PM
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Dick Huang's Avatar
Dallas,TX, USA
Joined Mar 1999
834 Posts
Dale,
There is a linear motion slide with ballbearings that holds the motor mount to the vertical poast which has less than one gram of tare. My scale is zeroed with the lead weight and reads thrust in minus numbers.
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