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helinewbie
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Hello, I'm creating an excel file to calculate the velocity of one rotor of a helicopter, and I'm getting really weird answer, in comparison to the one a friend of my who does aerospace engineering give me.
I don't do an aerospace engineering course but this is a project I've been researching at my own time so I'm really eager to learn how to work out equations by myself. And I've lost contact to that friend who gives me his excel file so I don't have anyone to help me really.
I have attached 2 XLS files.
- Basic Aero Dynamics of Helicopter.XLS is from my friend
- VelocityCalculation.xls is what I'm trying to achieve
The formula I was using is Force of Lift = p * Cl * U^2 * S/2 = Kl * w^2
where
p is air density
Cl is lift coefficient
U is flow velocity
S is the reference area
Kl is some K variable I don't understand.
Also, Force of Drag = p * Cd * U^2 * S/2 = Kd * w^2
where Cd is the drag coefficient
If you can help explaining what U really represent, it would be really helpful. I looked it up for aerodynamics of helicopter lift equation (http://helicopterflight.net/lift_equation.htm ) and find U is the same as w. Is this correct?
Another thing I don't quite get how my friend work out the velocity by sqrt(2*Force/(Density*Span*CoefficientLift)) What is the reference area of a helicopter? From http://www.aerospaceweb.org/question/aerodynamics/q0015b.shtml, it's the 2*PI*span, but he uses the span as the reference area.
His answer however is a lot more sensible than mine: ~1200RPM compared to ~153RPM. It's a small RC helicopter I'm looking at, and most commercial ones are 1200RPM-2000RPM. So I'm really confused.
Please have a look at the Excel Files. Thanks.
I don't do an aerospace engineering course but this is a project I've been researching at my own time so I'm really eager to learn how to work out equations by myself. And I've lost contact to that friend who gives me his excel file so I don't have anyone to help me really.
I have attached 2 XLS files.
- Basic Aero Dynamics of Helicopter.XLS is from my friend
- VelocityCalculation.xls is what I'm trying to achieve
The formula I was using is Force of Lift = p * Cl * U^2 * S/2 = Kl * w^2
where
p is air density
Cl is lift coefficient
U is flow velocity
S is the reference area
Kl is some K variable I don't understand.
Also, Force of Drag = p * Cd * U^2 * S/2 = Kd * w^2
where Cd is the drag coefficient
If you can help explaining what U really represent, it would be really helpful. I looked it up for aerodynamics of helicopter lift equation (http://helicopterflight.net/lift_equation.htm ) and find U is the same as w. Is this correct?
Another thing I don't quite get how my friend work out the velocity by sqrt(2*Force/(Density*Span*CoefficientLift)) What is the reference area of a helicopter? From http://www.aerospaceweb.org/question/aerodynamics/q0015b.shtml, it's the 2*PI*span, but he uses the span as the reference area.
His answer however is a lot more sensible than mine: ~1200RPM compared to ~153RPM. It's a small RC helicopter I'm looking at, and most commercial ones are 1200RPM-2000RPM. So I'm really confused.
Please have a look at the Excel Files. Thanks.
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