Aircraft Development

  • I would also like to point out, if your using VR then check it out early. You may notice that switches, knobs etc are smaller that you would expect even if modelled to the exact size. I scaled mine by 30% where I could and they do look a lot better but still not big enough.

    I assume it's a VR projection problem as anything closer to the projection point gets smaller. I tried to add an oxygen mask and it came out looking very thin.

  • Hi there,

    it is really cool, that the aircraft development get's a boost in the last days.

    I've been experimenting with the subject for a while now. Due to a lack of time I am only now able to move on a little. I have to say that I am an absolute newcomer to texturing and modeling etc. . Maybe someone of you can explain the following question to me. With my converted model, I get some kind of shimmer effects at specific points (seen in the picture). What could be the reason for this?



    • Official Post

    That happens when the uv map for that triangle has no area on the texture, the entire triangle gets mapped to a line.

    Or in other words you are projecting the texture not onto the surface but along the surface and it never hits the triangle.... texture projection is 90° to the surface normal...

    Change the uv coordinate for one of the vertices and the issue will go away.

  • Thanks so much Steve for those tips, they are incredibly useful!

    I havn't had much of a chance to do anything today but I think I understand how the gear works (including joints etc). Very cool.

    That being said I'm a little confused on how I'd set-up the Tail Wheel for the spit. It has the main strut, then the free-castering part with the wheel attached. Should the free-castering part be its own RB, or is that handled by the wheel?

    Also, does the mass of the fuselage take into account the loaded fuel, oil etc, or is just purely the 'empty' fuselage?

    And what do the parameters of the collisionhull represent? Particularly K and D?


    Edit: Spoke too soon, aircraft now explodes upon spawn thanks to some dodgy gears :D

    Would this be the connection between the wing (I know it says fuselage) and the gear that rotates it up into the gear bay? Not too sure what the parameters mean.

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    • Official Post

    Hi Alex,

    the wheel can only rotate around its normal rotation axis, any steering requires an extra rigidbody.

    For your tailwheel you can probably copy the pitts or f4u tail gear construction and then delete the steering input and set the K and D properties of that joint to 0.

    K and D are spring and damping constants, K in N/m or Nm/rad and D in N/(m/s) or Nm/(rad/s).

    Increasing K makes the connection stiffer (oscillating frequency goes up) and leads to less gear contraction at a static load, making D higher dampens any movements but does not affect stationary deflections.

    If you make K and D too high it gets nummerically unstable, essentially the update rate of the physics engine falls below the frequency of the oscillation and things blow up and explode. Either parts fly away or you are stuck in an endless repositioning loop, in both cases check the leverage like tail gear joint to tail gear center of mass (R0 of rigidbody should be near the rotation axis) and if that doesn't hep then reduce K and D, e.g. setting them to K = 10 and D = 0.01 or something like that or straight to zero.

    Collision hull K and D are like spring and damping constants when the mesh goes below the terrain. Higher damping means less of a bounce when the part hits the ground.

    Weight and balance is currently not implemented as such, but we have prepared "passengers" and "fuel" masses in some of the airplanes. If you want to do that then use the empty weight of the fuselage + engine + oil + unusable fuel. And then add a fuel mass where the tank is actually located in 3D and set its mass to either full or some intermediate value. None zero though.

    hydraulic_cylinder is a contraction device, it pulls the the two bodies together or pushes them apart. It defines the maximum retraction but not the actual pivot and rotation axis of the landing gear (just like IRL)

  • Thanks for the explanation Jan!

    I think I've made a little bit of progress but alas my plane is still exploding :D Is the inertia length considered to be 'local'? For instance the tail wheel is rotated at say, a 45 degree angle. Is the X distance the distance from the start of the tailwheel strut to the end, or from the xMin bounding box to the xMax?



    • Official Post

    I think I already put that in the wiki...

    InertiaLength is the size of a box that is representative for the inertia. If there is a lot of mass concentrated in the center and only light structure around that, then the inertia lengths are smaller than the bounding box. If it's just an empty shell then it should be bigger.

    Take the bounding box for now but it's numerically more stable with bigger boxes

    Lengths are relative, so from r0 half a length in each direction, r0 is center of mass

    • Official Post

    I think it's got to do with the gear rigidbodies, nothing else had changed (and the tm.log is not reporting any different errors). Think I might start the TMD again.

    Nah... just remove one joint after another, until it works again. Then add them back in in a different order until it breaks again, then you know which joint needs other K and D values or needs to have their input, axis and pivots checked

  • Yeap that did the trick (mostly).

    I noticed the F4u has 3 gear rigidbodies, just wondering what the third is? The F4u's landing gear is a lot more complex (at least it looks like it) than the Spitfire - would I only need two? One for the main strut and one for the wheel connection?

    Here's how I'd imagine it to be?

    EDIT: Whoops, I think the Hydraulic Cylinder and Joint should be swapped

  • I think you might have something extra to be excited about Mr Spit40 ;)

    Roger that...

    Mk. IX hopefully



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    • Official Post

    That is a correct imagination (sounds weird, is this even english) :D

    Replace hyd. cylinder with damper though. cylinder would be diagonally to pull in the gear.

    F4u also rotates the landing gear as it is being retracted, thats why there is an extra body, that you probably wont need.

  • That is a correct imagination (sounds weird, is this even english) :D

    Replace hyd. cylinder with damper though. cylinder would be diagonally to pull in the gear.

    F4u also rotates the landing gear as it is being retracted, thats why there is an extra body, that you probably wont need.


    Is this the damper you're talking about?


    Edit: Ah I misunderstood you, I see what you mean now :)

    I've done it :') Gear is now not exploding! A little rigid and I still need to set up the dampers, but progress!