Calculating Power for Hovering Thrust of a Fan

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    Hovering Thrust
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Discussion Overview

The discussion revolves around calculating the power required for a fan to generate a specific thrust while hovering. Participants explore various equations and parameters involved in this calculation, including thrust, efficiency, and air density.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents an equation for power calculation: P^2 = (T^3) / ((eta^2)(rho)A) and questions its validity after obtaining a power value of 7322W for a thrust of 250kg.
  • Another participant suggests an alternative equation that replaces eta^2 with a factor of 4, potentially leading to a lower power estimate.
  • A third participant points out the need to convert thrust from kilograms to Newtons, implying that this might affect the calculations.
  • There is a humorous acknowledgment that the initial power estimate seems too low for the specified thrust and rotor diameter.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate equations to use for calculating power and whether the initial thrust value should be converted from kilograms to Newtons. The discussion remains unresolved with multiple competing views on the correct approach.

Contextual Notes

Participants note the importance of understanding the units of thrust and the implications of different equations on the power calculation. There are references to specific sources for further information, but no consensus on the correct formula is reached.

reebrah
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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!
 
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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?
 
Did you forget that thrust is in Newtons, not "kilograms"?
 
I think that might just solve my problem lolz
 
At least it will give you a bigger number. 7kW is obviously way too small for a quarter-tonne chopper with a teeny little 0.8m dia rotor :biggrin:
 

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