In the process of working up my JSBSim FDM for the P-51D I had added some functions to make the behavior at stall more realistic. In FG 2.0 before adding these functions were added the stall was like a (very fast) trainer - a straight ahead mush but it would drop a wing if enough rudder was added at the stall. Basically what I did in the stall/spin function was to increase yaw forces to the left as the alpha angle reached the stall point.
Since I have started using FG GIT with it's newer versions of JSBSIm I have noticed that the behavior I had created with the stall/spin function was much more pronounced and today I had a closer look at this. With current versions of FG and JSBSim even with my stall/spin function removed I am seeing a very pronounced tendency to drop the left wing at the stall and this now acts much like it did in FG 2.0 with my stall/spin function included. Although I think the effect is more pronounced with a tendency to snap to the left when doing high G maneuvers that was not there with my function and FG 2.0. It appears that there has been some work done on JSBSim to get more realistic stall/spin/snap behavior. Is this correct or am I imagining things? Here are my thoughts about what I am seeing. 1. This is a step in the right direction that should result in a immediate improvement to the stall/spin/snap behavior for most existing models. 2. My stall/spin function was actually a very crude attempt at this and I had intended to revisit it to make it more generalized. One issue is that it always drops the left wing regardless of the beta angle. In an aircraft like the P-51D there is almost always some beta angle (in this case it almost always has a little beta to the left since the fin has a 2 degree angle to the AC centerline) and in most cases this will result in the left wing dropping during a stall but I don't think it should always drop the left wing regardless of the beta angle. I think it should drop the left wing if the beta angle is to the left and it should drop the right wing if the beta angle to the right with perhaps a slight tendency to favor dropping the left or right wing depending on the direction of rotation of the prop and/or some other factors. 3. I think the current setup has too much tendency to drop the wing but this likely depends on the aircraft being modeled. Perhaps some kind of property can be exposed so that those creating models can control how strong this is. That is a C172 should only drop a wing in a very deep stall with a significant (larger) beta angle but a WWII fighter or an air racer should drop the wing earlier in the stall with much smaller beta angles. Those creating models need some way to control this so that this can be tuned to the aircraft being modeled. Hal ------------------------------------------------------------------------------ Sell apps to millions through the Intel(R) Atom(Tm) Developer Program Be part of this innovative community and reach millions of netbook users worldwide. Take advantage of special opportunities to increase revenue and speed time-to-market. Join now, and jumpstart your future. http://p.sf.net/sfu/intel-atom-d2d _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
