Hovering thrust calulation


by reebrah
Tags: calulation, hovering, thrust
reebrah
reebrah is offline
#1
Dec5-12, 06:09 PM
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!
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Aero51
Aero51 is offline
#2
Dec5-12, 07:03 PM
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:

[itex]P^2 = T^3 / {4 \rho A}[/itex]
reebrah
reebrah is offline
#3
Dec5-12, 07:08 PM
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?

Aero51
Aero51 is offline
#4
Dec5-12, 07:21 PM
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:
http://books.google.com/books?id=SgZ...page&q&f=false
AlephZero
AlephZero is offline
#5
Dec5-12, 07:40 PM
Engineering
Sci Advisor
HW Helper
Thanks
P: 6,344
Did you forget that thrust is in Newtons, not "kilograms"?
reebrah
reebrah is offline
#6
Dec5-12, 07:50 PM
P: 10
I think that might just solve my problem lolz
AlephZero
AlephZero is offline
#7
Dec5-12, 10:51 PM
Engineering
Sci Advisor
HW Helper
Thanks
P: 6,344
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


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