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

[Tony P. <ap...@ea...>]

Steven's F-16 data is tail-on and these parameters are not needed unless you 
are deriving your own data. 

On Monday 10 September 2001 12:05 am, you wrote:
> 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
> >
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>
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-- 
Tony Peden
ap...@ea...
We all know Linux is great ... it does infinite loops in 5 seconds. 
-- attributed to Linus Torvalds