Using weighing machine to measure thrust.

[Babylon5]

Hi, at one time I was contemplating to use the weighing machine to measure thrust beside weighing the model.


However, there are problems(accuracies) to be ironed out as follow:-

1) How to keep the plane perpendicular to the weighing machine at full power at all time.

2) How to keep the plane from squirrelling of the weighing machine due to the torque effect at full power.

3) How to determine the location of the line force in which the trust is acting through the model plane when the model plane is a irregular body. This is pure physics


Would appreciate if anyone can share your experience and help us come up with a more accurate thrust readings.

[Super-Hornet]

If u talking about helicopter... I done that before.

I just put my heli on top of the scale. Do inverse of the pitch curve so it become -ve pitch instead. Get the reading from scale and that will be the dead weight. Or just do an offset setting for the scale to set it back to 0gram. Make sure heli is properly tied onto the scale. Spin it up and measure the weight. That value will be the thrust of lifting (or have to minus away the deadweight if it not using offset).

For airplane, I did saw a few examples on the past edition of R/C model magazines.

What it does is actually connect/tie the plane to a string. The other end of string is connected to a one end of "L" shape linkage. That other end of linkage is connected to a ball or a wider surface and it is seat on top of the scale.

SH

[pilot_bear]

i have seen something like that, but most is just for mounting the motor + prop, not the whole plane.

[kenshinz]

Hi, at one time I was contemplating to use the weighing machine to measure thrust beside weighing the model.


However, there are problems(accuracies) to be ironed out as follow:-

1) How to keep the plane perpendicular to the weighing machine at full power at all time.

2) How to keep the plane from squirrelling of the weighing machine due to the torque effect at full power.

3) How to determine the location of the line force in which the trust is acting through the model plane when the model plane is a irregular body. This is pure physics


Would appreciate if anyone can share your experience and help us come up with a more accurate thrust readings.

Hmm for 1 and 2, why not keep "clamp" the plane fixed to your workdesk, and make the weighing machine perpendicular to the plane instead. Make a 90 degrees L shape frame, and fix the weighing machine (assuming those flat digital ones) to the frame. Should work I think.

Disclaimer.... this is just something which I thot of on the fly.... nvr tried b4, so dunno if it is even feasible.

[Brandon Chng]

possible, but not accurate unless you have a pusher prop. the thrust generated is moving air, or air at a high pressure. high pressure air tries to equalise with the surrounding air, thus the slip stream is not straight but divergent. as for helicopter, measuring the the negative thrust is not very accurate if you wanna test for thrust upright. as any pilot who can fly inverted would say, the heli flies better inverted because there is not obstruction in the slip stream. for all theoretical purposes, thus the lift is actually less than that seen on the scale, unless you wanna lift something by taking off inverted

[Babylon5]

Hi, usually I want to measure the thrust on a pusher or an EDF mounted model RC plane. Just want to find out how you guys did it and whether the result is reasonably accurate.

Anyway thanks for all the ideas and contribution.

Cheers

[Brandon Chng]

sorry forgot to add that in flight, thrust would also be different as the angle of attack of incoming air changes with airspeed... the thrust measured from experiments would be the max static thrust.

[Adrianli]

Why not use those karang guni type of weighing scale and attach it to the aircraft or heli n full throttle it?