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

[Steve Hosgood]

Dave Culp wrote: On Thursday 11 May 2006 11:08 am, Steve Hosgood wrote: 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. Tell you what: a "tweaker's guide" would be a useful document! For instance, how do you tweak the output of Aeromatic to model the fact that your aircraft (Colditz Glider in my case) has almost no dihedral on the main wing. 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. Now that you've pointed it out, I can see the relative merits of both routes. I have no argument with jsbsim's methodology, just a slight misunderstanding to do with just how much the physical model is "missing" from jsbsim's .xml files! 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). What I meant was, regardless that most of the physical measurements are missing from jsbsim's .xml files, **Aeromatic** should have a way of specifying them so that it can produce the right "magic" coefficients. Yet it doesn't. Aeromatic is good at what it does, but would be nice it it handled some of the other possible physical parameters of a basic aircraft. Dihedral and wing incidence would seem obvious ones. Steve. Steve.