# Hovering thrust calulation

by reebrah
Tags: calulation, hovering, thrust
 P: 10 Basically I am doing work that requires me to calculate power for given thrust of a fan which is hovering. Variables known: diameter of fan: 0.8m, thrust output of fan: 250kg, rho=1.1455 kg/m^3 which is the density of air at 35Celcius , and eta which is the fan efficiency = 0.8 I tried this equation I found on wikipedia: P^2 = (T^3) / ( (eta^2)(rho)A) using this equation I got 7322w of power to attain a thrust of 250kg...This seems a little off. What is wrong here? does anyone know if this is even the correct value or even correct equation? thank you and appreciate it!
 P: 546 You can always use this equation which is valid for cases when the initial velocity of the air is 0. Here is the link: http://en.wikipedia.org/wiki/Thrust#Thrust_to_power and in case you are feeling lazy: $P^2 = T^3 / {4 \rho A}$
 P: 10 True but in this equation the eta^2 is replaced with a 4. This would then further decrease the power estimated from this relation. Anybody else know anything for hovering thrust?
P: 546

## Hovering thrust calulation

Visit this link, specifically check pages 281. I think it has the equations you are looking for. The book also has a nomenclature section at the front of the text. Hopefully this helps: