Alant wrote in Tue Jun 02, 2020 10:03 pm:If JSBSim rotation is set to 360deg, you should get castoring and hence no side force.
Good reminder.
The /fdm/jsbsim/gear/unit :
steering-angle-deg can be calculated by:
- in castor mode,
/gear/gear :
steering-norm * 360 and (please fix me if I'm wrong)
- in steerable mode,
/gear/gear :
steering-norm * max-steerSee also
/fdm/jsbsim/fcs/
steer-cmd-norm/fdm/jsbsim/fcs/
steer-pos-degJSBSim Reference Manual v1.0 (2011), p.40 (PDF 51/158) Ground reactions (search word: "Castered", "steering").
The steering-angle-deg works well for animation of the rotation angle for the tail wheel.
In particular, also well for animation in castor mode (360).
However, the castor mode is wrong from the FDM and mechanical point of view because
in real life the springs exert a return (or restoring?) moment on the rotating wheel (moment and force on the aircraft) if the wheel angle is greater than the rudder angle (+/- 30 deg max IRL, actual rudder angle depends on the control).
IRL, with this aircraft, there is no "free" castor mode.
[EDIT]
Unless it would be declutchable (unlockable). Just found
This video 1:45.
[/EDIT]
Suggestion: (to be considered critically, please)
- In the FDM, set
steering mode, max_steer angle +/- 30 deg (it cannot be steered farther than rudder amplitude)
steering-angle-deg = /gear/gear : steering-norm * 30.
(to be calculated and added in the Property tree)In FG, using differential braking and / or rudder propwash, the tail wheel will laterally slip on the ground thanks to the moderate dynamic friction (that's cheating, I admit, but that's mechanically acceptable for approximation of the behavior).
-
For animation of the rotation angle, use:
(/fdm/jsbsim/gear/unit )
steering-angle-deg + slip-angle-deg,
If it is declutchable, a true castor wheel when beyond +/- 30° rotation is the better way. But quite difficult IMO. Worst, switching should be based on lateral force exerted on the tail wheel, even if the rudder and wheel rotation are at zero.
Even if it is declutchable, a low friction can approximate. Although the dynamic friction should if possible be lower when beyond +/- 30° rotation.