Re: [Jsbsim-devel] Horizontal tail arm

[Tony P. <ton...@co...>]

That's but one way to do it.
 
I believe its still true that all aerodynamic forces and moments in JSBSim
are calculated relative to the Aerodynamic Reference Point.  The location of
this point generally depends on how the coefficients were derived and is
most often the quarter chord of the wing.
 
Once all the forces and moments are summed, they are shifted to the CG.
 
So, to use your parameter in JSBSim, define the tail arm as the distance
from the quarter chord of the wing to the quarter chord of the tail and
treat it like other coefficients.
 

  _____  

From: jsb...@li...
[mailto:jsb...@li...] On Behalf Of Jon S.
Berndt
Sent: Monday, July 21, 2008 8:26 PM
To: 'Development issues'
Subject: Re: [Jsbsim-devel] Horizontal tail arm



Hi, Fabian,

 

The horizontal (and also vertical) tail arm is supposed to be the length
from the CG to the quarter chord of the tail (horizontal or vertical as the
case may be), as you stated. The only thing that is done with that value is
it is tied to a property. There is also the normalized version, which is
divided by cbar. It is not updated at runtime.

 

Maybe that should be changed someday, but that's all that happens, now. It
should not change enough normally to make a noticeable difference.

 

Jon

 

 

Hello,

In the aerodynamic model I would need to include alpha_dot effect on
alpha_tail:

dEPS_alphadot = 57.3 * (AlphaDot * LHT_CG / Velocity) * dEps_dalpha

 

For this, I need the value of LHT_CG - the distance from the horizontal tail
25% chord to the actual CG.

 

Is this parameter available? For what I understand, the parameter
metrics/lh-ft or (htailarm) is the distance to the reference CG, not the
actual CG. Is that right?

 

(The same is needed for the pitch rate (q) effect on alpha_tail).

 

Fabian