VSP Aero Coefficient definitions

[Luka]

Hi to all,

I've been using VSPAero to calculate power requirements for a helicopter blade in progressive flight and can not find definitions of following designations:

- Station (x-axis when plotting Load Dist.)

- CPo_H (I assumed profile power for helicopter rotor, but is less then CP_H)

- ^ for CT_H and CS_H

- Momenti

- Momento

- Thrusti

- Thrusto (I assume the -i / -o suffix applies to all other coefficients as well)

- CDi vs CDi_Un

Also, when looking at Unsteady plots, I have an option to choose between 'History', 'Group' and 'Rotor'.

The 'Rotor' is self-explanatory, I assume that 'Group' divides rotating and non-rotating parts (fuselage and rotor), but what is 'History'?

Also, does VSPaero use the same empirical approximation based on 0012 data for CD0 of the rotor blade?

Thanks,

Luka

[Rob McDonald]

Luka,

The _H indicates that the coefficients are normalized following Helicopter conventions rather than Propeller conventions.  CT, CP, CQ are symbols used for both propellers and rotors -- but with slightly different definitions.  VSPAERO can calculate both (depending on the context), so the _H is used to indicate when helicopter rotor nondimensionalization is used.

the _i is for induced or inviscid and the _o is for profile.  So, hopefully CP_H=CPo_H+CPi_H

The _Un is the unsteady term.

For unsteady motion, aircraft components can be placed into groups to capture motion and to help sum forces.  For example, if you had a fuel tank dropping away from an aircraft, you would use two groups.  Rotors are a special group that sum forces and moments according to rotor conventions -- specifically, thrust and power are calculated.

The OpenVSP VSPAERO GUI sets up the most simple possible groups -- everything static in one group, rotors blades handled with rotor groups.  For anything more complex, you will need to set up the files on your own outside of the GUI.

History should show the time history of all forces / moments in a global frame.

Yes, the same simple 0012 data is used to come up with the parasite term for the rotating blades.

Rob

--
You received this message because you are subscribed to the Google Groups "OpenVSP" group.
To unsubscribe from this group and stop receiving emails from it, send an email to openvsp+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/075c2859-15f8-40de-b409-fb131227fdd1n%40googlegroups.com.

[Luka]

Hi Rob,

thank you for your reply!

I have another question.

I'm analyzing a single rotor blade in progressive helicopter flight. The helicopter's velocity vector is co-planar to the rotor disc plane.

The blades are producing zero-lift (collective is set to ~Alpha_n).

What I'm trying to determine is the drag force the blade is producing, in the helicopter velocity vector (in the X-axis).

I'm especially interested in the drag the blade is producing in the X-axis when the blade is parallel with the helicopter progressive speed, and what kind of drag the blade produces 30° after this position.

What I believe is happening is that VSPAERO is giving me the drag coefficient of the blade in regards to the blade tangential vector at any point, thus showing a perpendicular projection to what I'm interested in, or am I wrong?

The reason I'm looking for X-axis drag is, that I've already determined the span-wise drag of the blade at each angle with a Matlab script of mine, and thus have the torque and consequently shaft-power required for turning the rotor and confirmed my findings with VSPAERO

Now I'm interested in what the increase in drag would be for the aircraft in the X-axis solely so I can get a feeling on the impact of the rotor on the aircraft polar.

So, my question is, if VSPAERO does not show X-axis drag by default, what can I do to get this result?

Kind regards,

Luka

[Rob McDonald]

I think you're looking for CFx.

Rob

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/13bc02fb-70f6-455e-9784-c62def5e361dn%40googlegroups.com.

[Luka]

Hi Rob,

thanks!

Now that I'm looking at CFx, one last question.

When trying to calculate Fx, the rho and S_ref values are clear (the ones defined in VSPaero by the user), but which speed should be used for the Coefficient to Force calculation, since I have both a rotational and progressive speed.

It this speed the optional Vref, Vtip, V_75%R, or something else?

Of course, if there is documentation available on this matter, you can just point me there and I'll take a look myself.

Many thanks and kind regards,

Luka

[Kun Drew]

Hi Rob， 

I have some confusion about the unit of Thrust, Power and Moment.

 After making aerodynamic calculations on a single propeller, I compared the results with the performance data on the official website of the propeller.

My model took m as the unit, and found that Thrust (N) and Power (W) were roughly the same, but the difference in Moment (N*m) was too large.

Now I cannot determine whether it is the problem of the unit, the problem of the propeller model import, or the problem of my application of vspaero calculation process.
kind regards!kun

[Rob McDonald]

Power and moment are essentially the same thing -- one is multiplied by propeller speed.

So, if you're not matching, I suspect you aren't doing the units correct.

Since you haven't shared any other information, I can't be of any more help.

Rob

[Kun Drew]

thanks！