Simple Torque calc?

[hardlock]

I'm scratch building a micro heli and need a simple way to determine the thrust needed for the tail rotor. The main rotor is 10 inche dia. turning at about 4000 rpm. Tail moment arm can be changed but at present is about 8 inches.

I realize I can rig a test stand to weigh the load on the tail boom with a scale but there is no easy way to do this with the current motor installation.

Even a rough estimate will help a lot.

Thanks,

Ken

[Plantoflap]

Hi, I think this will work:

Inch ounces=1352 X (Watts in) X (motor efficiency) X (gear box efficiency) X (gear ratio) / (motor rpm)

inch ounces/tail arm = ounces of thrust needed at tail

Watts= (volts at motor) X (amps)

Try motor eff.=.5 and gear eff.=.92

If this gives an absurd result then I made an error and I will look it up.

GB

[hardlock]

I'm using a brushless outrunner direct drive so I think that formula can be much less complex?

[hardlock]

I ran it for the fun of it leaving out the gear box stuff and came up with about 1 oz. Does this sound realistic? Of course to be able to swing the tail in yaw against torque I'd need more than that, maybe figure 2 oz total for good measure?

[Plantoflap]

Hardlock, Right, Just x out the gear ratio and gearbox efficiency.

It's easier to measure Amps ,Volts and rpm than use a scale.

GB