Unit systems to be used with VSPAERO

[Andrey Piatygin]

While reading "Using VSPAERO", I have noticed only feets and slugs/cubic foot and no meters and kg/m3. Does the software work with imperial units only? Isn't it just a matter of using a consistent unit system throughout the project starting from geometry and ending with a VSPAERO Setup file?

Thank you in advance for an answer.

Andrey

[Rob McDonald]

You are correct. Everything will work if you input density in consistent units.

I.e. if your model is in meters, put in density in kg/m^3.

For most of VSPAERO, the units don't matter at all. It gets a little
tricky when it has to convert actuator disk thrust/pressure
coefficients into a form that works with drag coefficient. So if you
aren't using those features, you won't notice any change at all.

lbf-slug-ft-second or N-kg-m-second are both easy to work with.

The tricky one is that a lot of people build their aircraft model in
inches -- but they want to work with forces in lbf -- which means they
need to figure out air density in a very unusual mass unit...

Rob

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[Andrey Piatygin]

Thanks a lot Rob.

Best regards,

Andrey

[Jeffrey Wang]

Hello,

Some questions have arose since I am not familiar with imperial unit... 

While I input the Ct and Cp to designate my thrust, I put rho as slug/ft^3 and diameter as ft. So does that mean the unit of power is going to be horsepower and the thrust is in pound?

Thank you for the response.

Jeff

Rob McDonald於 2016年7月20日星期三 UTC+2下午8時05分04秒寫道：

[Rob McDonald]

You can instead use SI - meter, kg, Newton, sec, Watt, etc.

If your model length units are in feet, then you want mass in slug/ft^3 and then

Force will be in pounds - lbf

Power will need to be in foot pound per second ((ft lbf) / s)

1 Hp = 550 ft lbf / s

CP and CT will need the propeller speed as well -- in revolutions per second

Though for VSPAERO itself, you input propeller speed in RPM.

Rob

[Jeffrey Wang]

Thanks !

Jeff

Rob McDonald於 2016年10月16日星期日 UTC+2上午1時57分56秒寫道：