Custom plane laggy in FS2

    • Official Post

    You can use two joint_multi or one jointlinear with two axes of rotation.

    Both methods should work since you can actually change the center of mass by moving the pilot body.

    E.g. the CG of the P38 moves significantly as the gear is retracted in Aerofly FS :)

    OK guys, Ive been wanting to get into aircraft devt, not yet possible (not the right hardware), etc..)

    However in the mean time if I can help, I will gladly do so.

    I know about aircraft dynamics, physics, and so on, so in that sense maybe I can give some help short of having experience developing my own aircraft. I don't know about TMD stuff yet.

    Oh and I can do 3D modeling in Sketchup if needed (already do that for scenery), but I can't convert to FS2.

    Great graphics so far Antoine.

    For the hanglider (and I've never flown one) I imagine if the physics are real (which they reportedly are) then joystick control of pilot moving left and right, extending arms forward or not, and gear control of him standing and extending his leg (into the bag or whatever they use) would do the whole job from a physics standpoint, the "plane" would react properly automatically (with real physics). Like Jan said, 2 rotations (lateral and longitudinal), with center at pilot "hanging" point" . Interestingly, that point may or may not be the CG of "empty of pilot" hanglider. It could be the same point although a different point could be used to create some static margin (stability), I'm curious.

    Even the legs hanging or extending could automatically take into account induced drag, just like gears.

    Then all it needs after that is a graphic "animation" of a pilot body, if desired, to coincide with the physics.

    I don't know if livery could include weight change in FS2, probably not, then even pilot weight and size could be considered. Alternatively creating three models with three graphics (small, med and large persons) and three respective weight files would do the trick too.

    There may be one issue of dynamic stability (I'm not sure how stability is achieved on handgliders, most likely reflexed airfoils, and/or direct CG feedback), but that can be worked on (short of using an invisible tail)

    I also don't know how FS2 implements different wing shapes/airfoils, etc for flight dynamics, but it can be started simple (Cessna airfoil for example) and then evolve from there to simulate the corrections needed once the FS2 action/reaction principles are understood.

    I don't believe a hanglider has evolving airfoils (like a paraglider) so that probably makes it simpler so far. Not sure how FS2 could handle wing warping (paraglider, early aircrafts, transient effect of wing loading and structural reaction) or wingerons, but that is a problem for another day.

    Et si vous avez besoin de ca en Francais pour etre plus clair si l'Anglais pose probleme , pas de problemes non plus.

    PS, my short list of aircraft I want to do:

    - Superhornet

    - SR71

    - A10

    - DC3

    - F86 Sabre

    - F16

    Hello ussiowa !

    Thank you for your message ! I don't have a lot of time those days since I am doing a master in computer science, but I try to work on the hangglider in my free time.

    I was thinking that you probably have the knowledge to help me with the dynamics of the hangglider, because I encounter some stability issues. The hangglider is stuck in a stall behaviour where it constantly rotates forward or backward, I guess that I may need to tweak the horizontal position of the pilot, so that the load on the wing is more stable. Also, I think it has to do with the fact that the initial speed of the glider is too slow, so it doesn't glide at all, but rather falls straight from the start.

    If you want to know more about that project, you can send me an email at brunnerant@gmail.com and I will be happy to discuss in more depth about it ;).

    Thank you so much for the interest, I really appreciate !

    Antoine

    Jan, I've started working with Antoine on the subject. There is definitely some answers to the problem, airfoil is one of them, and dynamic stability the other (positions of CGs and so on).

    I was reading the airfoil wiki and there are small issues, which threw me off for a second, especially working on hanglider which may have inflatable airfoils and thus a "chamber". How can I contact you to change them?

    For example it says "chamber" when it means camber (AOA paragraph, CL0 first paragraph, Cmalpha first paragraph,...)

    And since you mention model planes, how did you guys factor in the influence of mass (inertia really) towards the stall behavior, if you did?

    Let me get into somewhat technical details: stall characteristics of an airfoil is typically studied in a wind tunnel, this is however limiting and theoretical and overly simplifying (which his actually good). Among others it makes the assumption that stalled flight is stable (continuous flying attitude in a stalled AOA).

    In reality if I use the same airfoil (thus same stalling "coefficient" and parameters (from the wind tunnel)) on a very light airplane (think balsa model) and a heavy plane (think real plane) the stall behavior will be significantly different.

    The light model will essentially never stall (dynamic stall) as there is never enough inertia to "stall" the wing , the plane will rotate and react. The only stall will come from lack of speed, thus lift, not from excessive AOA ( where the plane will react and change trajectory instead).

    On a heavy plane the wing will dynamically stall because the forces induced by "excessive" AOA are not sufficient to modify significantly (or enough) the trajectory to prevent stall.

    Thus Concorde could land, planes can do cobra maneuvers and so on.

    From the wiki It seems that maybe the modelization doesn't take this into consideration, as it relies on the pure fixed parameters (Cm, Cl0, attached range), or does it?

    Is that why the parameter "attached center" is used? Which BTW I don't understand what it is and does from the wiki description. "assymetric" from what? Where is the separation point symmetric to anything?

    I assume the "attached range" is to "decide" stall.

    It is the AOA at which Cl decreases significantly, or is it the maximum point for Cl/AOA?

    In the intro there is a mention of a "stallrange" parameter, but no other info on it, anything?

    This leads me to believe that the physics model considers "stall" when AOA reaches "+attachedrange". If the forces of flight and dynamics are used (which I'm sure they are) then maybe that could take care of inertia, unless airfoil and flight dynamics is not modeled beyond "stall" point.

    I'd still be very curious to see a real concorde in FS2 and a model one in FS2 or aerofly RC, or a sukhoi doing cobra.:/:)

    Anyway I hope you're interested and have some time for this, if not, that's OK too, I'll figure it out.

    • Official Post
    Quote from ussiowa

    it says "chamber"

    That wiki airfoil chapter is super old :D I'm not sure I knew how to spell my name when I wrote it. - I changed it, thanks :)

    seeing the wiki page:
    OHH NO WHERE ARE ALL THE IMAGES?

    That would make it so much easier...

    The Aerofly FS flight simulation has two core parts that contribute to the simulation of the flight characteristics and the stall:

    The rigidbody simulation: a multibody simulation of all moving airframe parts. Those dictate the inertia, mass and how flexible the airframe is.

    And the aerodynamic simulation: Each of the moving airframe parts can have multiple aerodynamic wings and bodies attached to them. They only calculate the forces of the air and apply them to the rigidbodies, which in turn get accelerated and moved because of these forces.

    It's these rigidbodies that define how quickly the airplane changes it's attitude. In general and in a stall. So if you have a light aircraft you have a low inertia and therefor you don't need a lot of lift to stop a wing from dropping and there is not much momentum to cause it to drop through. Increase the mass by a factor of two or so and the same aircraft behaves very differently.

    By definition the stall occurs when the flow separates from the airfoil, which happens at a given angle of attack, not airspeed. I wish this was forever deleted from all of the aviation books ever written. Stall does not happen because of low speed. You can comfortably fly at zero speed as long as you follow the path of a thrown rock :) You need speed to maintain altitude, not to prevent a stall.

    If you fly slow and try to maintain altitude you increase your angle of attack. And that is why you stall.

    There several other ways to increase your angle of attack and all of them lead to stalling:

    - Speed reducing and maintaining altitude, keep pulling up -> aoa increases, stall

    - High angle of bank and staying at the same speed and pulling up -> aoa increases, you can stall.

    - Pulling into a maneuver with more than 1g -> aoa increases you can stall.

    - Sideslip, effective wing area may decrease, you need to pull a bit -> aoa increase, you can stall.

    - Extend the spoilers, useful wing area decreases, you have to pull up -> aoa increases, stall.

    - Flying a parabola with 0g -> angle of attack stays constant. NO STALL. YAY.

    I should get a sticker or t-shirt for that.

    Low Speed != Stall ... Fly the AOA not the IAS.


    The stall behavior is mainly affected by the center of gravity, mass, the airfoil characteristics, wing geometry and things like flap deflections. In Aerofly and in the real world. It's the combination of the mass and wing geometry that affects most of the behavior and is responsible for the effects that you mention. How drastically the wing stalls is a mere function of wing loading, not necessarily the size of the airplane. A small and heavy RC aircraft stalls the same as a big aircraft. If you just increase the mass of the small rc plane it can make it fly terrible, too :)

    Scaling the airplane up produces nearly the same lift, drag and moment coefficients BUT there are also viscosity effects that change the behavior. Those are Reynolds and Mach effects. Those mainly affect the laminar flow fraction as well as the compressibility of the flow. If you don't go too small or too fast the aerodynamic factors can be considered identical for a small or large aircraft.

    Dynamic stalls happen just as much in a 1m aerobatic rc plane as in a 10m big airplane. It may just happen much quicker in the RC world so that actuator speed actually plays a big role. Slowed down to the same speed it would be like "pulling back gently".

    Now to the airfoil in aerofly. We need to simulate the lift, drag and moment coefficient somehow for the entire 360° angle of attack range.

    The real world airfoil show a near linear range between the start of the negative stall and the beginning of the positive stall. That delta angle is the attached range. The middle is the attached center.

    Above that angle the stall is slowly introduced throughout the stall range angle. Stall range small = aggressive stall, sudden decrease in lift coefficient as you increase AOA. Stall range high = very soft stall, lift coefficient may continue to rise for quite some time after the first bit of separation at the trailing edge.

    Jan, thanks.

    Quote from Jet-Pack (IPACS)

    By definition the stall occurs when the flow separates from the airfoil, which happens at a given angle of attack, not airspeed. I wish this was forever deleted from all of the aviation books ever written. Stall does not happen because of low speed. You can comfortably fly at zero speed as long as you follow the path of a thrown rock :) You need speed to maintain altitude, not to prevent a stall.

    Well yes, agreed, hence Concorde stalls its wings at landing (significant IAS, high AOA), and the sukhoi can do cobra (again super high AOA, some IAS. Got it.

    And yes it's the mass that matters, I used the real plane/RC plane analogy to make it more visual. I get it that the same RC plane made of balsa and or aluminium will have different stall behavior.

    I also get Reynolds and Mach, viscosity.

    The question was more is it modeled accurately in FS2, the answer I gather from your reply is yes, because you modeled real physics throughout, mass, aero forces, even "flexibility", which is usually complex structure calculation. I haven't dug into tmd yet, but so you have spring/damper constants (Young modulus,... and damping factors) modeled? Probably using the same for the whole rigidbody too (no detail of frame versus skin, etc..). WOW color me impressed nonetheless.

    Quote

    The real world airfoil show a near linear range between the start of the negative stall and the beginning of the positive stall. That delta angle is the attached range. The middle is the attached center.

    Above that angle the stall is slowly introduced throughout the stall range angle. Stall range small = aggressive stall, sudden decrease in lift coefficient as you increase AOA. Stall range high = very soft stall, lift coefficient may continue to rise for quite some time after the first bit of separation at the trailing edge.

    OK got it. So:

    1) -attached range is AOA of negative AO for maximum negative lift

    2) +attached range is AOA for maximum positive lift

    3) attached center is the offset, which for symetrical airfoil would be 0, in all other cases it really defines the asymmetry of the particular airfoil shape beyond the necessary simplification that Cl/AOA is linear in between.

    4) stallrange parameter essentially defines/models the derivative of the Cl/AOA line after the maximum Cl point.

    That last sentence (lift coefficient may continue to rise for quite some time after the first bit of separation at the trailing edge.) however confuses me a bit. maybe you didn't simplify that attachedrange point to max Cl/AOA, but rather more like in reality it is defined when the separation point becomes different than TE. Thus indeed we could reach Cl maximum AFTER theoretical stall (or beginning of stall, separation point not being on TE). Never the case if we assume stall starts at max Cl (which is not the case IRL I know, but close enough)

    Then to determine attachedrange AOA I would need to read the Cl/x/c separation curve for particular airfoils and translate into AOA, not just use the Cl/AOA curve?

    Count me in, fascinating stuff for us developers and aerodynamics nerds :D

    This is what I love (and hate) about FS2, its just so accurate. Why do I hate it I hear some ask..., well, if you want an accurate aircraft/helicopter there is just so much work involved and FS2 will let you do pretty much anything you want so you keep adding and adding and adding

    Steve

    Quote from larrylynx

    This is what I love (and hate) about FS2, its just so accurate.

    Steve

    :D:D:D

    Well, 2 doctors in physics and a university degree in aerospace engineering counts a lot for accuracy.

    I'll be interested as well, at least to follow the conversation. Perhaps I learn to avoid my rc models from crashing ;)

    Quote from Rodeo

    :D:D:D

    Well, 2 doctors in physics and a university degree in aerospace engineering counts a lot for accuracy.

    I'll be interested as well, at least to follow the conversation. Perhaps I learn to avoid my rc models from crashing ;)

    I'm more of the former, certainly not a magician. I haven't yet been able to avoid my models from crashing, yet.^^;(

    And since I fly on a cliff, I use good shoes and climbing gear to rappel down when necessary.

    Although I'll tell you of a humbling story. This WE we have this kid that is really good flyer, and mostly an artist, he shows up at the bluff (slope flying) with a "plane" of his design. Zero notion of physics, the plane is a triangle of flat foam, with elevons. The two outside points of the triangle are on servos and he can bring them up (like vertical stabilizer) or bring them down (making the triangle plate a flat triangle plate).

    I ask about CG, his answer, "hmm I don't know about CG I just put it somewhere and felt the plane is not pitching much", so no calculation of any kind, or concept for that matter.

    My bet was the plane would tumble down the cliff. First, sloping a delta wing is typically never a good experience (I've heard and tried personally), then kind of arbitrary CG, no airfoil whatsoever, the result would be entertaining, but not as expected.

    So maiden flight we're ready for anything, and the thing FLEW! and was controllable, a little bit of rolling oscillations in certain extreme attitudes, but nothing crazy. Then he puts the tips down (vert stabilizer) and he still could turn and control.

    That is just incredible, oh and the "plane" flew with a nose down attitude too (about 10deg), the opposite of what I would have thought, especially for a flat plank.

    Over the years, and having been a test engineer, I've know better than to always solely rely on theory and this is another proof of it, but still it's humbling. Knowing theory is great, but we've got to remain humble, reminded again.

    I cannot yet explain why or how, maybe I'll dig into it. Or maybe we can check how accurate the physics are in Aerofly RC 8 (RC version of FS2) :P, but I don't have that one.

    Oh and his hope by dropping the V stab down is to be able to perform a flat spin. That was just no way, he had another weird contraption before that he was hoping for the same (that looked a bit more like a conventional airplane), he is just too far from understanding basic physics for that to work the way he pictures it, but who knows maybe he'll figure out something (although it's a very complex problem, pure yaw rotation in flight).

    I've seen the LE fish do pure pitch rotation (with madstab) but even that is not what people really think is happening.

    They think 'I put the stab at 90 vertical and so normal the plane is flipping' (like the loop is getting tighter, to the point of pitch roll), well it's not that simple since all forward momentum is lost. Iv'e thought and analyze that one for a while and my suspicion is that they're just evolving the regime of a machine from a regular forward flight (airplane) to a vertical axis wind turbine configuration, and that config if done wrong (stab axis lower on WL) it may not work. Theory not tested yet.

    But that again was thinking outside the box by people that thought one way (one logic) and obtained the result even though it works a different way.

    Back to work on hanggliders, I found some interesting stuff for those interested.

    That too is a more complex problem that it looks at first. Working on airfoils for now, then CG. The hope is to get decent flight from one model, then we can make all kind of different one.

    Anyway we'll carry on here for now, thanks for the interest.

    Reminds me of my days building RC and some weird stuff, I got bored with the run of the mill stuff so I experimented

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    Lynx, SU and "Warbird" were all mine. Lynx was a TRex 450

    Music was nothing to do with me..=O

    Oh, it's a great but rather old version aerofly professional deluxe, called AFPD.

    You can download lot of sceneries and models for it at rc-sim.de, Higgy's server for sim stuff.

    After AFPD IPACS published aerofly rc5, rc7 and currently rc8.