Custom plane laggy in FS2

  • Jan,


    Airfoil TMD data. I assume everything is in radians.

    "Attached Center" is that the AOA of the middle of the Cl/Alpha curve, or is it the AOA at which Cl = 0?


    For exemple I have an airfoil -7 +14 thus a range of 21deg (to put in radian) so "attached range" is 21deg

    The "center" of that curve is at 4deg AoA with Cl of 0.5, is that my "attached center" value, or is it the AOA where Cl =0 (-1deg in this case)?


    Also in your graphs on the wiki, for the attached range, the upper graph (alpha) shows that it goes between - and + (thus the number is the full range) on the graph below (with airfoil pict) it is represented as half (once between 0 and minus, and one between 0 and plus). I assumed it's the former.

    Stall range is also represented twice, but I believe that is probably correct.

  • The full linear range of the airfoil goes from -AttachedRange - AttachedCenter to +AttachedRange - AttachedCenter.

    The AttachedCenter shifts the center of the attached range but I think the sign is counter-intuitive here... I have not checked the code but it feels like that more negative values shift the range towards a more positive angle. I think of it like:

    aoa += AttachedRange

    if ( aoa > -AttachedRange && aoa < AttachedRange )

    -> cl = Cl0 + aoa * ClAlpha


    To the left and to the right of that you add the StallRange angle to get the stalled region.


    The angle for cl=0 is not defined in the airfoil parameters, you have your ClAlpha 2 pi slope and your Cl0 lift at zero angle of attack instead.


    AttachedRange is 0.5 * ( max - min ) and AttachedCenter is -0.5 * ( max + min ).


    So for you that is

    0.5 * ( 14 - (-7) ) = 0.5 * 21 = 10.5 degrees attached range

    And -0.5 * ( 14 + (-7) ) = -0.5 * 7 = -3.5 degrees attached center.

    If I did my maths right. It's before the first coffee ^^

  • OK Thanks.

    So attached range is indeed the value in the positive region, and same in the negative region, thus 1/2 of the maximum span 1/2(max -min) [0.5(14-(-7)) or 1/2*21 or 10.5]

    The attached center is the offset of the real center, compared to the mathematical center.

    Here the math center is at -10.5 from max or +10.5 from min

    But the real center is with 14 to max and -7 to min, so I have to move the center by the distance between my max and min

    or 1/2 (|max|-|min|). So here 1/2 (|14| -|-7|) or 0.5 (14-7) or 3.5

    And I give it a negative sign to move the center below the math center, so -3.5

    Which indeed gives me an upper of 3.5 + 10.5 = 14

    and a lower range of -10.5 - (-3.5) or -7


    Here with more exact values:

  • Okay guys, some updates, since I had time to test the new airfoils that ussiowa gave me.


    First, I had to tweak the CG so that the flying is stable (like in your story, I have experimented, and I didn't rely on theory ;) ). After some tweaking, I was able to observe some stable flying behavior. However, I couldn't experiment much, since I somehow wasn't able to steer the glider.


    I hooked up the pitch and roll input from the simulator to a linear joint, and to the graphics. The graphical part works, because when I steer the glider, I actually see the pilot's graphics pitching/rolling. However, I am dubious that the linear joint is working because steering doesn't have an effect on the flying behavior... So I have to fix this...


    Does anyone know if there is a way to debug the rigidbodies while in the simulator ? I would really like to be able to verify that the pilot's rigidbody pitches/rolls when I control the plane in the simulator.


    Anyway, thank you guys for your involvment in the project !


    Antoine

  • I hooked up the pitch and roll input from the simulator to a linear joint, and to the graphics. The graphical part works, because when I steer the glider, I actually see the pilot's graphics pitching/rolling.

    You don't have to animate the graphics if you already simulate it in the physics!

    Just attach your pilot graphics to your rigidbody that is moving in the physics....


    In Aerofly FS we only animate things that do not have physical properties.

    For example: almost all of the landing gear parts are not animated. Only the locking mechanisms are actually an animation, the test is pure physics simulation and thus always looks physically correct. That includes gear contraction, gear retraction, wheel deformation, gear bending, wing bending as the gear hits the ground and what not.


    Similarly if you hinge your pilot in the physics you can expect it to collide with the ground correctly (if you attach a collisionhull) and the center of mass moves correctly and the graphics always moves with it.

  • Well the question could be as to whether the CG of the group of rigidbodies is dynamically calculated or not?

    If it is, then at least we know the physics dynamics of the masses could be correct, yet somehow the "plane" is not reacting properly. We can continue investigating that way.

    If the CG is calculated once only (at load up or something similar, which could be very possible with a regular aircraft since it is not expected to change during flight (except Concorde and other limited exceptions)), then we'd have to find another way to simulate that part. We can introduce "virtual" control surfaces that would move from the dynamic standpoint (ailerons, rudder and elevator), but that would not exit graphically. That way the "plane" would react properly, and the graphics would be proper as well (only pilot moving).

  • Okay guys, some updates, since I had time to test the new airfoils that ussiowa gave me.


    First, I had to tweak the CG so that the flying is stable (like in your story, I have experimented, and I didn't rely on theory ;) ). After some tweaking, I was able to observe some stable flying behavior. However, I couldn't experiment much, since I somehow wasn't able to steer the glider.


    Antoine

    Remember that the positions of the CG with the pilot and without are fundamental to the behavior. I'm thinking that the CG without should be at 25% MAC (I will tell you what that is in a few minutes, I have to calculate), and that the CG of the pilot itself should be located like a normal human being.

    Provided that the suspension of the control bar is at the right point, then it should work somewhat.

    I don't know yet about "joints" but I'd think that a rotating joint at the point of control bar suspension would be more accurate (to the reality) than a linear one. But linear may work too.

  • Yes of course it is :)

    Neat! Sorry for questioning, I guess I'm too used to old sims and low computing power, where everything had to be "simplified" to fit the computing power and time.:)


    So great, that makes things easier for us in a sense, all we have to do is model the reality correctly.


    Jan, any input on this CG location. I'm thinking the CG of the glider is at 25% MAC and then the addition of the pilot moves it forward enough to create the static margin in essence. Or could it be that the glider itself has the static margin (CG forward from AC) in that it would fly "empty" correctly, and then the pilot is loaded at that particular CG (except lower of course) and then its motion laterally and longitudinally from the neutral point is what steers the glider?

  • OK so MAC (Main Aerodynamic Chord) is at 215.86 cm from center line and is 142.20 cm.

    That means that the Aerodynamic Center (AC) for that wing is at 131.58 cm from the nose of the wing (25%).


    Antoine that should be the starting point for the CG of the empty glider. I would expect that the CG point for all together in flight be around 125.4 cm from the nose and in the horizontal plane (20% of MAC or a 5% static margin).

    These should be good numbers to start and should provide a flyable system. We can fine tune later.


    The vertical position of the CG is whatever it is vertically from that point (125.4 from the nose, center line)