Posts by ussiowa

    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)

    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?

    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.

    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).

    Well it's not "unforeseen difficulties", more like it's a whole lot of work, and we all have a life outside of FS2 that includes full time work or other more prioritized obligations for some members of the team. So it takes time and longer than first anticipated sometimes. We're stuck on time and volunteering availability.


    It's 95%+ complete and in terms of "difficulties", no we didn't bite more than we could chew, actually quite the opposite, we could bite much more if we'd be given the food to be chewed to continue with that metaphor.

    As a matter of fact, we did chew much more than we bit as the original idea/project didn't include many animations and features that ultimately ended up in the final product (including tech optimization required because of complexity and size of scenery)

    It deserves and requires a certain standard of excellence, thus we want to do what is needed, and that takes times, more time as affected by conditions as Zosochile explained.


    More importantly, we also wanted to pace ourselves so as not to get more praises and mark of confidence than we could reasonably handle.;)


    Bottom line, it's coming for sure, hopefully by 2021, but no firm date at this stage. Stay tuned!

    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:

    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.

    Hello Phil,


    Any progress on these standard sensor modules?

    I'm thinking 90deg rotation module, and then mechanically we can add spring and damper as needed (also in modular form maybe), in particular two configs:

    Center with spring return so -45,0,+45 typical for joystick, rudder, etc..

    Center with no spring, for helo cyclic

    0-90 for throttles, flaps, wheels, etc..

    :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.

    I do ask myself why I do these updates, well it's to show just how much work and time these things take, so next time we ask for this and that aircraft please give some thought for the poor designer and the months and months of work

    Yep, that's the spirit. I can't yet imagine the amount of time spent on developing an entire aircraft, but I've seen the incredible amount of work spent by an entire team (Apollo or Hawaii) to do just scenery, and it's always a lot more than people imagine.

    "Oh why don't they do ...." well that simple thing is easily 8 hours and more. I know I've easily spent 2 digits hours developing a single building volume, and then the same amount is spent to texture, convert, position.

    I'm slowly getting into aircraft devt, and so far I've already spent close to 20 hours on it and nothing to show for it but a little bit of fundamental research (data, type, etc..)


    We do this because we love it, we offer it for free because we want to and can, but it certainly doesn't mean that it's just a Sunday cruise.

    Yet people will always ask. There are people that recognize and are sometimes (mostly?) silent out of humility, and then there are people that are just gimme, gimme. It is what it is, and we have to try to not let that stop us.

    The most difficult is when people ask for things that are obvious to us (but not done for whatever reason, or not YET done), but they think they have such a great insight as they looked at the product for 10mn.^^

    That's the nature of the beast!


    So thanks Steve, Jan, and all others at IPACS and every person that contributes or ever contributed.

    Jan, thanks.

    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?

    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.

    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

    Well you and I wish!


    The USS Iowa is 3D because we got generous benefactors that made it an extra contribution that we can install:):thumbup::thumbup:. You can also install some autogen for Los Angeles, other than that there is not much for Los Angeles unfortunately at this point (Downtown exists in the sim and maybe a few other places around, and I believe all airports are there (can't remember if Hawthorne is there, Van Nuys?))

    So, what we'd need is a team project to develop the whole area, especially the whole harbor with bridges, cranes, ships, containers, etc.. It's a BIG job

    There are tons of iconic places we could do.

    We do have 4 sim stations as part of the exhibit on the Iowa, so it would be great enhancement (that and having the aircrafts related to the museum A HUP helicopter, and a Kingfisher airplane). At some point I was hoping to gather a team or create one (get some volunteers to learn how to do it) to do just that. Unfortunately for now because of COVID the sim stations are not available temporarily, so maybe one day.