Re: [Flightgear-flightmodel] New properties in c172.xml

[Roman G. <rgr...@ho...>]

Thanx Tony for your reply but I try to make F16 XML file and what to better
understand following values:
RegisterVariable(FG_LBARH,           " h-tail arm " );
  RegisterVariable(FG_LBARV,           " v-tail arm " );
  RegisterVariable(FG_HTAILAREA,       " h-tail area " );
  RegisterVariable(FG_VTAILAREA,       " v-tail area " );
  RegisterVariable(FG_VBARH,           " h-tail volume " );
  RegisterVariable(FG_VBARV,           " v-tail volume " );
Could you please explain what is arm and volume and how it can be calculated
Sorry for my lamely question
Thanx in advance
Bye

----- Original Message -----
From: "Tony Peden" <ap...@ea...>
To: <fli...@li...>
Sent: Saturday, September 08, 2001 3:11 AM
Subject: Re: [Flightgear-flightmodel] New properties in c172.xml


> On Friday 07 September 2001 05:01 am, you wrote:
> > > Thanx Tony for your reply
> > > but could you please explain what does this values mean?
> > >
> > > > They are parameters needed for tail-off aero models.  If you don't
use:
> > > > FG_LBARH
> > > > FG_LBARV
> > > > FG_HTAILAREA
> > > > FG_VTAILAREA
> > > > FG_VBARH
> > > > FG_VBARV
> > > >
> > > > in any of your coefficients then you need not supply values for
these.
> >
> > Could you restate what tail-off aero is, too, while you answer Roman's
> > question?
>
> For an aircraft like the c172, the pitching moment sum is primarily
composed
> of contributions from the wing, fuselage, thrust and horizontal tail.   So
I
> can write:
> Cm = Cmwing + Cmbody + Cmthrust + Cmhtail
> The primary sources of lift are:
> CL = CLwing + CLbody + CLhtail
> That lift from the tail is generally the largest contributor to tail
pitching
> moment (there will be a relatively small Cmo from the tail):
> Cmhtail = -lh / cbar * CLhtail
> where lh is the distance from the aero reference point to the MAC of the
> horizontal tail.  Note the minus sign, positve tail lift produces negative
or
> nose down pitching moment.
>
> OK, so now if I derive Cmhtail offline and separate out the elevator
effects
> so that I've got:
> Cmhtail = Cmstabilizer + Cmde
> Then realize that the  stabilizer is fixed relative to the body in the
case
> of the c172, I can combine some terms and reduce the amount of data I need
in
> the config file:
> Cm = Cmwbh + Cmthrust + Cmde
> where
> Cmwbh = Cmwing + Cmbody + Cmstabilizer
> A similar sort of reasoning can be followed for the lift equation:
> CL = CLwbh + CLde
>
> That's a tail-on model.
>
> On the other hand, if I wanted to take a little more fundamental approach
I
> can build an aero model that always calculates the tail pitching moment
from
> the tail lift.  Many people like this approach because it preserves the
> physical relationship that we know must exist between the tail lift and
its
> contribution to the total aircraft pitching moment.  Also, if you design
an
> airplane, you pretty much have to look at it this way so that you can make
> good choices regarding the tail airfoil section and planform.
>
> The downside to a tail-off model is that it can be harder to make changes
to
> the model data to get the simulation to match flight.  How much harder
> depends on both what you can measure on board and how you go about
>  reducing the flight data down into something that can be applied to the
> simulation.
>
> A similar sort of approach can be applied to the vertical tail (though my
> understanding is that tail-off vertical models are even harder to get
right)
>
> Does that help?
>
>
>
>
>
> >
> > Jon
> >
> >
> > _______________________________________________
> > Flightgear-flightmodel mailing list
> > Fli...@li...
> > https://lists.sourceforge.net/lists/listinfo/flightgear-flightmodel
>
> --
> Tony Peden
> ap...@ea...
> We all know Linux is great ... it does infinite loops in 5 seconds.
> -- attributed to Linus Torvalds
>
> _______________________________________________
> Flightgear-flightmodel mailing list
> Fli...@li...
> https://lists.sourceforge.net/lists/listinfo/flightgear-flightmodel
>