Simple thrust measurement stand

[motthomas]

I have a thrust producing engine and I would like to measure the thrust from it as accurately as possible without needing the use of scales, rollers, load cells, etc.

Anyway a friend of mine suggested I suspend the engine from four wires so that the wires are vertical when the engine is switched off. The idea would be that when the engine is started, it would push forward and cause the supporting wires to rotate through an angle which would be dependant on the thrust produced.

Would it be right to assume that if I measure the angle the wires are rotated through i could then calculate the thrust through the equation F=mg(L-LCos(theta)) where m would be the mass of the engine and L would be the length of the supporting wires? It seems pretty straightforward but I am not sure if I am missing something. Seeing as the engine is producing horizontal thrust and I am using the height difference to calculate thrust do I need to allow for this?

 

[phyzguy]

I think your concept is good, but according to my analysis your equation is wrong. I calculate that the result is F = m g tan(theta). Your equation is not even dimensionally correct, since mg is a force, so mgL is an energy.