> Curtis L. Olson writes: > > David, I'm starting to get nit-picky here :-) but one more thing > > ... the elevator doesn't seem to be responding to elevator trim. In a > > real life C172 the elevator trim is a little tab on the trailing edge > > of the elevator that causes the elevator to actually change position > > ... kind of like an elevator elevator.
David's excuse (grin): > I haven't added a tab object to the 3-D model yet, but I'd like to > understand more about how it actually works first (ditto for elevator > and rudder trim). The motion of the trim tab is only a function of trim wheel position, so it should be easy to show the tab itself in the model. The force of the trim tab on the whole aircraft is minimal and can be ignored. The position of the elevator is a force balance, consisting of the aero force on the elevator, the aero force on the tab and the muscle force on the yoke. All of these forces are linear with position, but the aero forces are also proportional to the square of airspeed. The apparent spring constant for the pilot therefore has a range of a factor of nine (141kias/47kias)^2 according to the situation. However, we ignore spring constant for non-force-feedback controllers. The aircraft motion is determined by the net elevator position, so you should simply draw the elevator in whatever position is being used by the FDM. No other correction is needed. For zero force yoke (aka centered joystick), motion of the trim causes the tab to move one way and the elevator to move the other. The ratio of the two angular rates is about equal to the ratio of the two lengths of the movable pieces of metal. I don't know what it is offhand; it should be apparent from any photo of that area. Hope that helps ... _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
