Control surface deflection due to downwash...

1st Official Post

    Is the effect of downwash angle variation affecting control surfaces in the tail ( namely the elevator ), on non FBW aircraft, modeled in AEFS2 - or possible to be modeled ?

    This applies, for instance to aircraft where the effect of lowering the flaps changes the AoA of the tail dramatically, and can even exert a force in the elevator that the pilot has to counter, because otherwise the sitck will move in the cockpit - ahed, in the case of a Spitfire for instance, causing the pitching down ...

    I know AEFS2 calculates downwash variations, but, could or is this already modeled ?

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    Yes I know it isn't the only factor...

    Because i do not have AEFS2 installed right now - problems with a very small SSD.... Working on it...

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    • Official Post

    1. Yes that is simulated

    2. Force on the stick is not simulated, rather pure stick position. Trim in the Cessna for example is currently only affecting your position of the stick it offsets your stick position back to center. And since the hardware isn't capable of providing better feedback than a spring back to the exact same position we can't really model the stick movement by force better. Sure we could try to optimize for force feedback instead of position feedback but people like me, that fly gliders don't usually fly by force (because there is barely any in a glider), we fly by stick deflection.

    And there are other problems... if I'm in a Cessna and hold my elevator fix (don't move my hand) then a pitch down trim would pitch the nose up since the trim tab acts like a little elevator and can't move the real elevator because I'm holding it. But the force moves the other way, so it's just impossible to model that with a spring force joystick. The attachment point of the other end of the spring would be moved by the trim but if I hold my stick fix the elevator is not going to move in the real world.

    And this is what Aerofly models. Stick + Trim move Elevator. And not Elevator + Trim moves Stick, stick moves elevator....

    Quote from bbrz

    And again (at least) one of my posts has vanished. Sorry guys, that's not acceptable anymore. I'm finally out of here.

    Bye.

    ???

    @bbrz, do you, by any chance, mean --> this one <-- ?

    Because if it's the one, you answered at a different thread...

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    Quote from Jet-Pack

    1. Yes that is simulated

    2. Force on the stick is not simulated, rather pure stick position. Trim in the Cessna for example is currently only affecting your position of the stick it offsets your stick position back to center. And since the hardware isn't capable of providing better feedback than a spring back to the exact same position we can't really model the stick movement by force better. Sure we could try to optimize for force feedback instead of position feedback but people like me, that fly gliders don't usually fly by force (because there is barely any in a glider), we fly by stick deflection.

    And there are other problems... if I'm in a Cessna and hold my elevator fix (don't move my hand) then a pitch down trim would pitch the nose up since the trim tab acts like a little elevator and can't move the real elevator because I'm holding it. But the force moves the other way, so it's just impossible to model that with a spring force joystick. The attachment point of the other end of the spring would be moved by the trim but if I hold my stick fix the elevator is not going to move in the real world.

    And this is what Aerofly models. Stick + Trim move Elevator. And not Elevator + Trim moves Stick, stick moves elevator....

    Jan, could you relatively easily setup an option where you could output that to a variable that a force feedback system would use?

    Then we could develop a stick for it (I think there is already someone that is developing a force feedback stick in another thread)

    Then people would have a choice: no FF joystick -it modifies position

    If FF joystick available, then it is implemented as force.

    And then even with a spring back joystick, they'd have 2 options to choose from, they could pick the one they like best as a simulation.

    I don't know how the other existing FF joystick read the info, but we can look into it, to try to make it a standard of some sort, but if it's not satisfying, then we can always develop a better model.

    • Official Post
    Quote from ussiowa

    Jan, could you relatively easily setup an option where you could output that to a variable that a force feedback system would use?

    Look at the cessna.tmd file and search for "SenderElevatorForceFree"... So there is already something like that in there. With the external dll from the developer tools you should be able to receive that message and do what ever you want with that force... Probably in newtons... Modify it so that it outputs as real force feedback...

    Quote from Jet-Pack

    Look at the cessna.tmd file and search for "SenderElevatorForceFree"... So there is already something like that in there. With the external dll from the developer tools you should be able to receive that message and do what ever you want with that force... Probably in newtons... Modify it so that it outputs as real force feedback...

    OK awesome, thanks.

    Further to these interesting suggestions / ideas we're sharing here, I'd say tha Yo-Yo gave the DCS user community the decision between implementing the effect of deflecting the flaps in the Spitfire: stick fixed or moving...

    For stick fixed, there should actually be a slight pitching up tendency, as it happens in IL-2 Battle of Staingrad, while in DCS as the flaps are lowered we can see the virtual stick moving fwd, and users with a FF joystick will see it also deflect fwd.

    The V-Pilot then has to pull the stick to counter the resulting pitching down moment.

    This appears to me as a better solution, even for non-FF joysticks, because it agrees with the Real World effect. All pilot notes for the Spitfire report the pitching down tendency, and a need to increase the force on the stick to avoid it. In IL-2, for instance, since there is no virtual stick deflection, the end result is actually a slight pitching up...

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    Edited once, last by jcomm (August 6, 2017 at 10:54 PM).

    • Official Post
    Quote from jcomm

    Further to these interesting suggestions / ideas we're sharing here, I'd say tha Yo-Yo gave the DCS user community the decision between implementing the effect of deflecting the flaps in the Spitfire.

    For stick fixed, there should actually be a slight pitching up tendency, as it happens in IL-2 Battle of Staingrad, while in DCS as the flaps are lowered we can see the virtual stick moving fwd, and users with a FF joystick will see it also deflect fwd.

    The V-Pilot then has to pull the stick to counter the resulting pitching down moment.

    This appears to me as a better solution, even for non-FF joysticks, becasue it agrees with the RW effect. All pilot notes for the Spitfire report the pitching down tendency, and a need to increase the force on the stick to avoid it. In IL-2, for instance, since there is no virtual stick deflection, the end result is actually a slight pitching up...

    As I said, two sides... If I completely remove my joystick spring DCS would simulate it incorrectly and IL-2 would simulate it correctly.

    When it comes to maximum deflections, how toes DCS get around the fact that they just shifted the center position and I still have full movement up an down?
    If before adding flaps the stick was neutral in the virtual cockpit and now it's further forward, what happens if I push forward all the way (slowly) does the movement stop before my real joystick hits the mechanical stop?
    What happens if I pull up? Do I still have full elevator up authority, now that the virtual center is forward and my mechanical stop would be hit before the virtual one?

    I'll check it in a couple of minutes, by displaying the controller reference axis in DCS, and will report back... Well, depending on PC slot available - wife on finals for Facebook....

    Ah! And just as a reference, this is the thread started by the main FDM developer at ED when they were still working on the Spitfire IX - worth reading, and starts exactly with the same remarks you've made Jan:

    https://forums.eagle.ru/showthread.php…t=flap+pitching

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    Edited once, last by jcomm (August 6, 2017 at 11:11 PM).

    • Official Post
    Quote from bbrz

    I'm not sure if I can follow the need of this discussion as there is no Spitfire in Aerofly FS2 and this aerodynamic effect can't be simply applied to any other plane.

    Considering that e.g. the Q400 and the C172 apparently simulate a moveable stabilizer instead of the correct elevator trim, I'd be already happy if the basics would be correct ;)

    Stabilizers are fixed (more or less, they have few mm movement as in real world due to bending etc.)

    @bbrz: it's MSFS that uses a stabilator-like modelling of pitch trim. In that simulator, when you trim in pitch, indeed the simulator assumes the whole HS moves, as if every aircraft was just like a typical airliner and most gliders, in terms of pitch trim.

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    Hey ussiowa

    I'm the guy behind the "other forum thread" developing FFB yoke with stick on to-do list. I am desperately looking for people to help me out with software suite for AFS2 interaction as there seems to be very few who understand this topic and even fewer who would have the time to write such program..

    Would you be interested to join forces and investigate the options we have regarding decent FFB system?

    Unfortunately I don't have programming skills to pull this of on my own but I'm pretty good with hardware. Check out these links for more details about the project.

    https://vrflightsim.wixsite.com/mysite

    3D Printed Force Feedback Yoke

    Programmer needed !! (FFB plugin)


    Regards Jay

    Over and Out

    Jay

    Quote from bbrz

    AFAIK MSFS doesn't use a stabilizer trim system for planes that are supposed to have only elevator trim.

    It moves the CG and/or the aerodynamic center forward and backward.

    From the MSFS Aerodynamics Reference DOC -Source AVSIM ( by Yves Guillaume ), linked from: https://www.aero.sors.fr/fsairfile.html

    This was long confirmed to me by a good source, and by Ron Freimuth, with whom I had the honour to learn a lot about the MSFS internals....

    "

    4.1 Elevator and Pitch Trim


    The main pitch control system in MSFS consists of an elevator and a stabilizer trim surface. The pitch trim concept is basically more the one of a moving horizontal stabilizer than that of an elevator with trim tabs. However, the additional lift and drag generated by the deflected stabilizer is not simulated in MSFS. Furthermore, the default autopilot only uses the stabilizer for trim and not the elevator. For consistency with the SDK the term Cm_detr is used although the elevator is not directly involved in trim.


    MS seems to have pitch controls designed for joysticks where the stick returns to a fixed center when hand force is released (such as most game sticks, e.g. Saitek X52). Zero hand force means zero elevator deflection in relation to stabilizer, so the stabilizer is the only trim surface.


    There are three components related to elevator and stabilizer trim: Stabilizer, elevator and an additional elevator effect due to stabilizer deflection.[...]

    "

    P.S.: Sorry for the out-of-context message - this is an AEFS2 Forum... I know :-/

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    Edited 3 times, last by jcomm (August 7, 2017 at 12:07 PM).