Propeller thrust equation discrepancy with online calculators

[nickpark83]

can anyone confirm this equation?? Prop. Thrust

there are many websites that calculate propeller Thrust, and they never show any formulas for it... and i somehow manage to find the formula from NASA website, but when i compare the result with each other, i get totally different numbers...

Thrust = (density)(pi)(radius of prop)^2(2)[(2Vk(RPM) + k(RPM^2)]

where k is coefficient of efficiency of prop.
V = speed, V=0 when static

if i just work with the units only, i get the force unit no problem, but the result is way off from the number from websites..
anyone know which one is correct?

 

[FredGarvin]

You might want to try this one:

$$T=P_{io}^{2/3}(2 \rho A)^{1/3}$$ where

$$T$$ = thrust
$$P_{io}$$ = (induced) power of the engine
$$\rho$$ = density
$$A$$ = propeller area