Gear positions

[Zaretto]

• Nose wheel in the air
• Main gear sunk into ground

The basic coordinates are correct so it is possibly the location of the masses that is wrong; although the model file could also need adjustment.

It should sit level on the runway - but a quick investigation showed unequal gear compression on the main gear

[AxelPaccalin]

In Mirage2000-vsp.xml

Nose contact point: <z>-1.518</z> Rear contact point: <z>-1.458</z>

This could be as simple as that, however, we will have to cross-check with the gear models to be 100% sure.

[AxelPaccalin]

The gears are indeed at the same vertical position in Models/m2000-5.ac.

[paccalin]

The gear position is now synchronized with the ground position.

Fully extended (should only happen after takeoff):

Fully compressed (should never happen):

Since we cannot set the maximum stroke of the damper in jsbsim, if you exceed maximum compression, the gear will go into the ground:

[paccalin]

Tested and tweaked with the new fuel system.

Compression for dry weight:

Compression for MTOW (16.5T: full fuel + full ventral):

[paccalin]

The horizontal adjustment of the wheel is not very precise, if someone know how to calculate precisely the VRP in mirage2000-vsp.xml, the whells will follow the ground more properly when rolling!

[Zaretto]

VRP is the matrix used to adjust from the 3d model to the JSBSim model, based on the origin of both.

After a quick check it appears that I didn't really check that the VRP was correct when I made the aero.

VRP(x) should therefore be -1.726m; I haven't calculated the Z VRP.

Getting the tyres into exactly the right place can be tricky but firstly it is important to have the gear in the correct position in the JSBSim but also VRP(x,z) needs to be correct as otherwise the 3d models for the wheels will be in the wrong place when rendered.

[AxelPaccalin]

VRP(x) should therefore be -1.726m; I haven't calculated the Z VRP.

Okay, I'll test with the new VRP(x) later in the day ! Thank you for calculating it precisely !

The VRP(z) sems relatively ok, judging from how the plane look like on the ground with gear retracted

[AxelPaccalin]

According to the gear compression, this VRP value is incorrect. The eyeballed VRP value I found (which should be in the vicinity of the true value) was 290'' (7.366 meters). Could you explain to me what this 6.834 figure is ?

[AxelPaccalin]

I think I figured that out ! (all following vectors are in the metric system).

Soo, if we consider the jsbsim main-gear contact point to be the "true/official" contact point for the MLG, the contact point is [8.76, ..., ...].

We know that the most bottom vertices of the MLG wheels in the model are at [1.94771, ..., ...] relative to the model origin.

So if my math is correct, to put the MLG vertex (of the model) on the MLG contact point (in JSBSIM) we need to have a bias translation of [6.812, 0, ?].

[Zaretto]

The 6.834 is the 3d model X origin measured from the nose; so calculated from the JSBSim offset using an offset -f -1.94771 will result at the same point.

[AxelPaccalin]

With the proper VRP, the gear now follows the ground even when the plane doesn't sit flat on the ground.