Aircraft sinking on takeoff (SFM)

[No1sonuk]

Anyone got any idea why this is happening?
 

It looks like the undercarriage is collapsing on takeoff (Taxi is OK), but I can't figure out why.

Collision lines and shells are in place on all 3 wheels, and another puzzle is why the tail wheel is part-submerged.

 

[western_JPN]

Hi, does this trouble still need some help ?

The movie looks like main (left and right) gears get damaged and separated in physics calculation, it leads the fuserage sinking .... fuserage doesn't have a collision .... pivot (0, 0, 0) goes under the ground .... exploding judgement is done !

I cannot figure out why gears get damaged.
Main wheels' collisions are too low ? not following the suspension's animation shorten by Gravity ? too weak values set in the flightmodel ?
Umm ....

The tail wheel submerging maybe the mismatch of nose_gear_pos value in the lua.
How about decreasing its second (Z position) value ?
Or its suspension stroke value (optional in lua) is too big than its animation ? Its default (no value set) stroke maybe fitting to modern jets' nose gear and too big for WWII tail gear.

Edited November 16, 2022 by western_JPN

[No1sonuk]

It's definitely something to do with the undercarriage collapsing at about 58 to 61 knots. The sink position changes when I alter the main gear collision lines.

I have no idea why, but I think it might be related to the tail wheel being sunk. I still have no idea why that's happening either.

[western_JPN]

How about removing collisions from undercarriage ?

I have less information about collisions and damages , cannot instruct them for you.

[No1sonuk]

If I remove all the collision features, it still sinks, but will take off and fly as it takes no damage.

Also, I don't have any suspension code in the lua - neither do some other mods I've looked at.

[No1sonuk]

I'm getting nowhere with this.  There's insufficient information, so I've decided to abandon the idea entirely.

[SkateZilla]

Change the main and nose/tail gear position in the AC LUA to make the Aircraft sit higher off the ground,
Also change the compression strokes for those gears.

ie:

-Landing Gear Specifics
nose_gear_pos                               =   {4.149,    -2.140,    0}, --Position in M of Nose Gear, Y, Z, X
nose_gear_wheel_diameter                    =   0.541, -- Diameter in M of Nose Gear
nose_gear_amortizer_direct_stroke           =   0.000, -- Full Strut Expansion
nose_gear_amortizer_normal_weight_stroke    =  -0.196, -- Strut Weight Compression
nose_gear_amortizer_reversal_stroke         =  -0.393, -- Full Strut Compression

main_gear_pos                               =   {-1.662,-2.567,    1.603}, -- Position in M, Y, Z, X for Main Gear Tire, Automatically Mirrored.
main_gear_wheel_diameter                    =   0.802, -- Diameter in M of Main Gear
main_gear_amortizer_direct_stroke           =   0.000, -- Full Strut Expansion 
main_gear_amortizer_normal_weight_stroke    =  -0.532, -- Strut Weight Compression (Distance in Z Axis (Up/Down))
main_gear_amortizer_reversal_stroke         =  -0.580, -- Full Strut Compression  (Distance in Z Axis (Up/Down))

        

[No1sonuk]

Are you sure those coordinates are Y,Z, X, and not X,Z,Y?

[SkateZilla]

15 minutes ago, No1sonuk said:

Are you sure those coordinates are Y,Z, X, and not X,Z,Y?

Yes, Front/Back, Up/Down, Left/Right

[No1sonuk]

In Max, front/back is +- X. Left/right is +- Y.

[western_JPN]

5 hours ago, No1sonuk said:

In Max, front/back is +- X. Left/right is +- Y.

That looks like not to follow DCS's rule.
As SkateZilla wrote, DCS models are in X+ Right / X- Left , Y+ Front / Y- Back , Z+ Up / Z- Down coordinate.

Each abc_klm_pos(,,) lines in lua means (Front or Back, Up or Down, Right or Left) ; equaling (Y, Z, X) in model's coordinate.

Or ? that orientation mismatch might cause the undercarriage breaking ?  not sure not sure ...

[No1sonuk]

If I put the model in with x left/right, it goes in game sideways.

[western_JPN]

6 hours ago, No1sonuk said:

If I put the model in with x left/right, it goes in game sideways.

How about applying "Reset XForm" and "Collapse" after rotating the model ?

This operation may reset all sub-nodes' orientation. Some reworks or parameter reminds maybe needed. 

[No1sonuk]

Reset Xform just blew up the model.

[western_JPN]

16 hours ago, No1sonuk said:

Reset Xform just blew up the model.

I know it and advised as :
 

Quote

Some reworks or parameter reminds maybe needed. 

But perhaps it's only way to adjust the model's total coordinate after built in wrong direction.