Re: [Flightgear-devel] dc3 effectiveness="nnn" for both hstab andvstab
Arnt Karlsen wrote: > ..one idea; try make the effectiveness'es a function of the propwash, > or thrust initially, and from each engine. May help to get a feel for > it, I'm not that sure this is the _right_ way to model it. Negative > thrust (say on decent/approach, does not need negative prop pitch, > only negative prop blade aoa) also has an impact on the tail surfaces. My current thinking, actually, isn't to treat propellers specially at all. Every surface (propeller, jet, wing, whatever) generates an aerodynamic force, and every surface has a characteristic size. You can use, with a little heuristic handwaving, to determine a downstream wash field for each surface. Basically, how much air at ambient density must be flowing through a "tube" the size of the surface to create that force? Then you get all sorts of nifty effects for free: + Propwash and jetwash, of course. + Asymmetric stalls when slipping, because the fuselage masks one wing. + Loss of tail authority in T-tail aircraft during stall. The hard part here is deciding what the wash field should look like. It should spread out gradually along some vector between the global velocity and the perturbed velocity, but which? Dunno. There is also a potential performance issue, since the extra calculations will go as O(N^2) in the number of surfaces; I think this isn't likely to be significant in practice, though. Andy -- Andrew J. RossNextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] dc3 effectiveness="nnn" for both hstab andvstab
Andy Ross writes: > If you get the model to a place where you're happy with it, would you > be willing to post it so we can try it out and get it into the > archive? I'm no expert on tail draggers, so I haven't done as much > testing on this model as it needs. David is the only one who has > spent significant time with it, I think. The model, not the real aircraft, for the record. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] dc3 effectiveness="nnn" for both hstab andvstab
This is great stuff; apologies for forgetting to respond yesterday. :) Dave Perry wrote: > I was able to get good control (vtab effectiveness) and early tail up > (htab effectiveness) with both values at 2.25. It was easier with > both values at 2.5. I then shot a number of touch-n-goes using wheel > landings. It still seems that it is very easy to over control in > pitch while trying to stay on the mains. One effect that you may be missing is prop wash effects. During the takeoff roll in the real aircraft, the tail surfaces will be much more effective due to back blast from the propellers. YASim doesn't model this, so in order to get good controllability during takeoff you are probably having to increase the effectiveness more than is strictly correct. This makes the whole tail surface, including elevator and rudder authority, more effective and you get the pitch sensitivity that you mention. You could try to treat this by tuning down the flap effectiveness of the elevator (or increasing that of the rudder and turning down the overall effectiveness). Inter-surface wash effects are on a list of stuff that would be cool to implement (they get you asymmetric stall effects too, which would be nice to have modeled). I've been spending most of my time recently with the jet models, which don't really need them. Taildraggers do, though, so maybe I should give it some thought. > For normal full stop landings, it is best to lock the tail wheel and do > a full stall landing, brake, get rid of the flaps, and then unlock the > tailwheel to turn off the active. I've found that to be true with the YASim model as well, although some articles at douglas-dc3.com indicate that normal practice was to never do a three point landing and instead plant the mains as early as possible. As you mention, the YASim model makes that difficult. If you get the model to a place where you're happy with it, would you be willing to post it so we can try it out and get it into the archive? I'm no expert on tail draggers, so I haven't done as much testing on this model as it needs. David is the only one who has spent significant time with it, I think. Andy -- Andrew J. RossNextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
