Page 1 of 2 1 2 LastLast
Results 1 to 10 of 20

Thread: Inertia?

  1. Default Inertia?

    I was just thinking about how inertia effects the turns of an aircraft. Am I correct in assuming that a plane can roll out of a turn to straight and level flight but still have a slight "drift" in the direction of the turn for a few seconds?

    Or does the rudder cancel it out if the turn was coordinated? Just wondering because I noticed even with autorudder in fsx it seems there is still that slight drift for a moment but it seems to be less if I bank the other direction for a second and then return to straight flight.

    I have also noticed that even autopilot seems to have this issue with the larger planes.

  2. #2

    Default

    No the intertia of the turning moment is way too weak. But there is "adverse yaw", an aerodynamic effect that yaws the aircraft in the opposite direction of the roll. You find more information about this in the net.

  3. #3
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    6,876

    Default

    You have a good eye -- congratulations, you are one of the very few people who seem to notice that problem. You are noticing a phenomenon unique to FS. Aircraft do NOT drift in that fashion, though all the default aircraft and many (most??) add-ons do so. A friend and I call it the slip/skid problem, though it's something that can be alleviated by adjusting some of the yaw parameters in the .air file (AirED is good for this). However it does take experimenting, since no two aircraft react the same to the adjustments.

    Section 1101 (Primary Aerodynamics) has various yaw parameters which you can try. I'd suggest, for the C-172 in FSX, that changing:

    Cl_da - Airleron (Control) to -500
    Cl_P - Roll Rate (damping) to -1200
    Cmo to -140
    Cm_de - Elevator (Control) to -1800
    Cn_beta Sideslip to 300
    Cn_dr Rudder (Control) to 200
    Cn_R - Yaw Rate to -1000
    Cy_Beta Sideslip to -1400
    Cy_dr Rudder to 100

    would be a good start. Be certain that you save a copy of the .air file as is before you start changing anything. Do note that most (not all) of the values I list above are negative numbers, so pay attention to sign. The above will also make a few other slight changes, so check out the handling and see what you think. Remember, save a copy of the original .air file before making any changes.
    Last edited by lnuss; 10-10-2019 at 08:58 AM.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  4. #4
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    6,876

    Default

    Quote Originally Posted by mga010 View Post
    No the intertia of the turning moment is way too weak. But there is "adverse yaw", an aerodynamic effect that yaws the aircraft in the opposite direction of the roll. You find more information about this in the net.
    Adverse yaw is not what he's talking about. Adverse yaw is the reaction of the nose in yaw to application of aileron, while he's talking about after the wings are level and controls are neutral. See my post above.

    Though this behavior is always there in aircraft so affected, it's easiest to see this behavior from the spot view (roughly at 6 o'clock) in slow flight, not too high off the ground, perhaps 500 feet or so.
    Last edited by lnuss; 10-10-2019 at 09:01 AM.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  5. Default

    Quote Originally Posted by lnuss View Post
    Adverse yaw is not what he's talking about. Adverse yaw is the reaction of the nose in yaw to application of aileron, while he's talking about after the wings are level and controls are neutral. See my post above.

    Though this behavior is always there in aircraft so affected, it's easiest to see this behavior from the spot view (roughly at 6 o'clock) in slow flight, not too high off the ground, perhaps 500 feet or so.
    Also seems easier to see in the larger jets. I do remember asking before about this and you let me know about it. But I wasn't sure if it was also happening to the larger planes or if it was inertia effects for them.

    I had made the changes to the c172 you recommend a while back and it did help with that one. I just needed to know if inertia played a part in it at all. Thanks again!

  6. Default

    Quote Originally Posted by lnuss View Post
    You have a good eye -- congratulations, you are one of the very few people who seem to notice that problem. You are noticing a phenomenon unique to FS. Aircraft do NOT drift in that fashion, though all the default aircraft and many (most??) add-ons do so. A friend and I call it the slip/skid problem, though it's something that can be alleviated by adjusting some of the yaw parameters in the .air file (AirED is good for this). However it does take experimenting, since no two aircraft react the same to the adjustments.

    Section 1101 (Primary Aerodynamics) has various yaw parameters which you can try. I'd suggest, for the C-172 in FSX, that changing:

    Cl_da - Airleron (Control) to -500
    Cl_P - Roll Rate (damping) to -1200
    Cmo to -140
    Cm_de - Elevator (Control) to -1800
    Cn_beta Sideslip to 300
    Cn_dr Rudder (Control) to 200
    Cn_R - Yaw Rate to -1000
    Cy_Beta Sideslip to -1400
    Cy_dr Rudder to 100

    would be a good start. Be certain that you save a copy of the .air file as is before you start changing anything. Do note that most (not all) of the values I list above are negative numbers, so pay attention to sign. The above will also make a few other slight changes, so check out the handling and see what you think. Remember, save a copy of the original .air file before making any changes.
    By the way, just so I get a good idea of WHY it works what is it about these particular settings that makes it help? I mean, why does adjusting Cmo to -140 help? and what is Cmo?

    Oh, and another thing...I think you would be proud of me. I've gotten the hang of hitting center line even with this issue lol.

  7. #7
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    6,876

    Default

    Quote Originally Posted by jbearnolimits View Post
    By the way, just so I get a good idea of WHY it works what is it about these particular settings that makes it help? I mean, why does adjusting Cmo to -140 help? and what is Cmo?
    I don't really know, and I'm not sure anyone can really provide an answer. Also, I didn't work out these settings. A friend of mine, who had much more patience for this sort of thing than I ever would, spent many, many hours of trial and error developing this. FS "aerodynamics" are table driven, rather than trying to be a true physics engine, and so these factors are what control aircraft behavior. Many of these factors work with and/or against each other, thus changing one has effects from other factors too, making things even more complex.

    Quote Originally Posted by jbearnolimits View Post
    Oh, and another thing...I think you would be proud of me. I've gotten the hang of hitting center line even with this issue lol.
    You should be proud of making good progress -- I'm happy for you.

    So make the changes and let me know how it works out for you.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  8. #8

    Default

    Quote Originally Posted by jbearnolimits View Post
    By the way, just so I get a good idea of WHY it works what is it about these particular settings that makes it help? I mean, why does adjusting Cmo to -140 help? and what is Cmo?

    Oh, and another thing...I think you would be proud of me. I've gotten the hang of hitting center line even with this issue lol.
    Messing with the .air file is for experts only. If you have to ask, you're not one. Leave it alone.
    `Cmo` is something to do with Coefficient of Restitution in Centre of Mass Frame.
    Precisely what is beyond the scope of this forum.

  9. #9
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    6,876

    Default

    Messing with the .air file is for experts only.
    So long as you save a copy of the original, you can't really hurt anything, just perhaps have some weird experiences "in flight," easily rectified by going back to the original. Since there's a rather strong lack of documentation from MS about what these various factors do, how do you become an expert except for years of experimentation or by learning from someone who did that?

    Besides, these particular changes are helpful, and are easily done, once you know the desired values. So I wouldn't consider this operation to "need" an expert.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  10. #10

    Default

    Quote Originally Posted by lnuss View Post
    So long as you save a copy of the original, you can't really hurt anything, just perhaps have some weird experiences "in flight," easily rectified by going back to the original. Since there's a rather strong lack of documentation from MS about what these various factors do, how do you become an expert except for years of experimentation or by learning from someone who did that?

    Besides, these particular changes are helpful, and are easily done, once you know the desired values. So I wouldn't consider this operation to "need" an expert.
    Disagree, One becomes an expert by hours of learning and understanding the innate issues between various parameters in the .air file (and the interrelationship between the .air and aircraft.cfg file).
    One cannot do it in five minutes (or else you would have answered the question about Cmo and why it's important).

    I calculated that with `a bit`of aviating knowledge (about five years worth derived from building my own piston single, twin seat Europa) one can have a reasonable stab at air file development but not without help and guidance - random `stabs in the dark` are tantamount to learning how can screw it up.

    And even then I needed the hand of the late, great Ron Freimuth to put me right in several areas. And where would you suggest one can get the values? Not from Cessna, Piper, Lockheed Martin, Boeing?
    X-Plane is a far better place to start with Blade Elemt Theory, which can be worked into a halfway decent flight model in about six months. And that can be done by plugging-in known parameters.

    There are NO such education resources for the .air flight model - not even who the proprietor of the software was, because it wasn't Microsoft...
    All knowledge has come from re-engineering and reverse engineering, and filtering out the fields that don't work with the various elements that variously form FS2004, FSX, and P3D.

    So who out there claims to be an `expert`? And where are their published works for review by other experts?

    You can ONLY screw it up by `hitting and hoping`, so advising anyone to go ahead and try in this early stage of their flight simming career leads ONLY to disaster.
    But don't let me stop you from confirming that.
    FSX has been out for 13 years now, while our new arrival only found flight sim about 6 mths ago. And no evidence to this point that he has `aviating experience` in the real world...
    Do you REALLY want to advise him to play with something even we, with many years of experience, can't claim the first thing about..?

Page 1 of 2 1 2 LastLast

Similar Threads

  1. Overcoming Inertia
    By okdaley in forum General Support
    Replies: 0
    Last Post: 06-06-2018, 03:39 PM
  2. Roll Inertia
    By Gimli Glider in forum Aircraft Design
    Replies: 13
    Last Post: 04-08-2011, 09:36 AM
  3. Inertia Start?
    By FlightOntario in forum Panel & Gauge Design
    Replies: 1
    Last Post: 04-13-2008, 12:01 PM
  4. Stop view inertia movement ???
    By wbf in forum FSX
    Replies: 2
    Last Post: 05-29-2007, 10:53 PM
  5. Exceess banking inertia in FS04 default B737-400
    By arttreichler in forum FS2004
    Replies: 2
    Last Post: 01-20-2004, 11:28 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •