Re: [Flightgear-devel] Frames of Reference in jsbsim

[Dave C. <dav...@co...>]

On Thursday 11 May 2006 11:08 am, Steve Hosgood wrote:

> Things are becoming a bit more transparent. Trouble is, an aircraft
> modeller usually starts by knowing just physical parameters (location of
> wings and things, location of tail, rudder etc along with amount of
> dihedral, angle of incidence of wing). Deriving the parameters like "yaw
> moment due to beta" and other such magic numbers from physical
> parameters is going to be pretty non-trivial.


You can use "common numbers" from some hard to find sources.  To get fancy you 
can use DATCOM+ to calculate them.


> Hence the existance of Aeromatic I presume.


Yes, that takes the pain out of getting a good first cut at a config file.  
You can tweak stuff afterwards.

> And that's fair enough, having a "compiler" that takes "high level
> language" (a description of the physical layout of a plane) and compiles
> it down to "assembly languuage" (the 20 or so entries in the
> <aerodynamics> section).


Look at it this way.  The process of getting an FDM to model a particular 
aircraft can be broken down into  3 steps:

1)  define the airplane parts
2)  define the effects of the airplane parts
3)  render the airplane state during simulation

Using YASim you do step 1, and YASim does steps 2 and 3.  Using JSBSim you do 
steps 1 and 2, and JSBSim does step 3.  The two methods each have their own 
advantages.


> However, it doesn't seem possible to specify 
> the things I was griping about to Aeromatic (wing incidence, dihedral,
> vertical dispacement of rudder w.r.t centerline etc).

You don't specify the measurements, you specify the effects.  (Except wing 
incidence).

Dave