A thought occurred to me last night on the modelling of gear reactions, and a possible
way to solve some or all of the related problems that have been discussed on the list
over the past few months.
I wasn't even trying to think about the problem so if anyone else had the same ideas
at about 10:30pm UK time, I apologise for telepathic theft of your ideas.
1) For each wheel (or group of wheels), we keep a coefficient of friction in the
rolling direction and a coefficient of friction perpendicular to this.
2) The vertical force on the wheel is multiplied by the two coefficients to get a
maximum force in each direction that the wheel will "absorb" before it starts to move,
that is the drag.
3) The horizontal force on the wheel is resolved into two components, one parallel to
the rolling direction and one perpendicular to it.
4) Each horizontal force component is modified according to the following rules:
If it is less than or equal to the drag in the same direction calculated in
step 2 then it is set to 0.
If it is greater than the drag calculated in step 2, then it is reduced by the
drag.
5) The modified horizontal forces are recombined to get a force which can be used to
accelerate the aircraft.
I suggest that the coefficients of friction stored are for a tyre at correct pressure
on dry tarmac, and then the could be modified according to ground type and tyre
condition automatically. For instance grass will increase the rolling coefficient, but
decrease the perpendicular coefficient. Additionally, we may want to include a
mechanism to store coefficients for different ground types.
Unfortunately I don't have the skill or time to implement this at the moment, but I
think that some others are working on the problem, so I offer the ideas to the group
as brain fodder.
Richard
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