Re: [Jsbsim-devel] Horizontal tail arm

[Fabian G. <fab...@gm...>]

Hi Tony and Jon,
I think your answers made me open my eyes:

> 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.

Since what I'm calculating is the downwash angle and not a force or a
moment, I cannot treat this parameter as other coefficients. BUT, I've just
discovered the property "inertia/cg-x-in" is available and updated at
runtime, so I guess I can do the following:
STA_HT = 600 'the known location of the tail quarter chord'
LHT_CG = STA_HT - inertia/cg-x-in

I'll try that.
Thank you.
Fabian.

On 7/22/08, Tony Peden <ton...@co...> wrote:

>  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
>