Adjusting Prop Torque Effects in FSX
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Thread: Adjusting Prop Torque Effects in FSX

  1. #1

    Adjusting Prop Torque Effects in FSX

    Can anyone please tell me how to increase the responsiveness of an FSX aircraft to changes in applied propeller torque? Even with the sim's torque slider full right, I'm not seeing the variation in rolling moment I'd like. I'm familiar with editing AIR and CFG files, but don't see any particular single variable in either file which will give me direct control over this aspect of the FM. I'd like to avoid tampering with engine, prop, or inertia parameters if possible, as I'm happy with the FM in all other regards.

    Thanks,

    blue six

  2. #2
    SOH Staff Tako_Kichi's Avatar
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    Have a look in the [flight_tuning] section of the aircraft.cfg file and play with the following values to get what you want:

    p_factor_on_yaw=
    torque_on_roll=
    gyro_precession_on_roll=
    gyro_precession_on_yaw=
    Larry


  3. #3
    Cheers T-K, I'll give that a try. I've tried most of them in isolation, with no success; perhaps it's a case of having to work with several at once...

    If anyone else has any thoughts, I'm open to further suggestions.

    blue six

  4. #4
    You may find the best results in the primary aerodynamics tab in the .air file. Also remember that roll and yaw stability act against the derived torque values.

    Not able time wise (at the airport) to explain this further at the moment.

    Cheers. T

  5. #5
    I assume you are concerned with a single engine prop?

    I do not believe there is a Roll moment adjusting factor specifically for torque. However, decreasing roll damping a bit may give you what you wish. Cl_p roll damping is related to aileron deflection and aileron control (cl_da) factors. So varying either may produce the result you desire with some possibly undesireable increased roll with throttle adjustment in the air.

    Alternatively you could look at changing the weight of the prop (prop_moi) to assess impact aside from slower/faster rev up/down impacts.
    Milton Shupe
    FS9/FSX Modeler Hack

    My Uploads at SOH - Here
    Video Tutorials - Gmax for Beginners

  6. #6
    Thanks for your replies, fliger747 and Milton.

    For Milton, yes it is a high powered, single engine/prop aircraft. I suspect you are correct in thinking that FSX has no single adjusting factor specifically intended for torque effects - possibly this existed in earlier versions of MSFS but has been deleted?

    I'll do some further experimentation with roll stability and damping variables, plus roll and prop MOI, and see if I can induce the effect I'm after, without unduly compromising other aspects of the FM.

    Again, I greatly appreciate your assistance,

    blue six

  7. #7
    Cn_Dt Thrust effect on yaw moment has some bearing here (Pri aerodynamics)

    You also might look at record 1544 which has several propwash related derivitives.

    Remember that many factors are interrelated, fo instance you might be able to translate a prop induced yaw into a roll moment as well.

    Good luck! T

  8. #8
    More good ideas, thanks fliger747. Your suggestion to approach the problem indirectly, through yaw moment due to thrust and roll moment due to yaw rate, may just do the trick.

    I have to say I'm a bit fuzzy on record 1544 - I'd thought this was a FS2K2 record. Can it be "transplanted" from another air file to the FSX air file I'm working with, which has no records/tables beyond 1538? If so, do the values in it take precedence over those for any similar derivatives found in the original primary aero section?

    blue six

  9. #9
    With AirEd, you can copy tables to the clipboard and Paste from clipboard into another air file.

    EDIT: Seems the table entries in 1543 and 1544 are also in 1101 so not sure you need those tables. Tom?

    EDIT2: Have you looked at table 1530?
    Milton Shupe
    FS9/FSX Modeler Hack

    My Uploads at SOH - Here
    Video Tutorials - Gmax for Beginners

  10. #10
    Quote Originally Posted by Milton Shupe View Post
    EDIT2: Have you looked at table 1530?
    Hi Milton, table 1530 looks to be just what the doctor ordered, but isn't present in the FSX air file I'm tweaking. I've found an example of 1530 in the air file of an old FS2004/FSX add-on aircraft currently on my installation, and will try making some large variations in that, to see if this has any effect on how that add-on flies in FSX. If the changes are recognized, grafting a table 1530 into my FSX air file with AirEd may be the way to go. I'll let you know what transpires...

    Thanks again for your assistance.

    blue six

  11. #11
    A quick update, Milton. The only a/c on my FSX installation with a record 1530 (FS2K Torque Effect) entry is a Bristol F2B MkI biplane - a very nice freeware model which apparently had its roots in CFS3, but was largely rebuilt for FSX. Torque effect is evident in the FM, but slight, even during throttle slams at very low airspeeds.

    I made a series of progressively larger changes to 1530, testing at each stage (and swapping a/c types between each test to ensure my changes were loaded). Bumping the stock 1530 reading of 1.015000 to 1.500000 then 2.500000 and eventually up to 9.500000 had no perceptible impact on the torque effect. I suspect this particular entry is not being read by FSX and will explore some of the other options we've discussed.

    Any further thoughts on the "FS2K2" derivatives in the 1539-1544 range? I see them in the air file of the stock FSX deHavilland Beaver for example, as well as certain FSX add-on a/c, but am not clear whether or not they are being used as inputs, or how they relate to similar derivatives in the Primary Aero section, record 1101.

    blue six

  12. #12
    If the 1539-1547 tables are used, they take precedence over the 1101 table entries. I have found they are used in FS9, at least some of them relating to lift, drag, roll and pitch. If present, changes in 1101 are ignored.

    If you divide the table values in 1101 by 2048 you will find the equivalent value for the 1539-47 tables.
    Milton Shupe
    FS9/FSX Modeler Hack

    My Uploads at SOH - Here
    Video Tutorials - Gmax for Beginners

  13. #13
    Thanks for the explanation, Milton. I appreciate your patience!

    blue six

  14. #14
    Quote Originally Posted by Milton Shupe View Post
    If the 1539-1547 tables are used, they take precedence over the 1101 table entries. I have found they are used in FS9, at least some of them relating to lift, drag, roll and pitch. If present, changes in 1101 are ignored.
    Hi Milton - I can confirm this is also true with FSX. Thanks to your reply, I was finally able to sort out an issue with a different FS9/FSX add-on model. This one persisted in rolling in the wrong direction when rudder was applied. My changes to Cl_dr in table 1101 were having no effect. When I made the same changes to table 1543 (FS2K2 roll derivatives) further down in the air file, the response in the sim was clear and the problem was easily sorted.

    Getting back to my original question, adjusting roll due to torque in FSX, I had little success in attempting to translate a prop induced yaw into a roll moment. I went back to torque_on_roll in the [flight tuning] section of the CFG file, as suggested by T-K originally. I'd looked at this earlier, but saw no clear reaction in the sim to the changes I'd made in the CFG file. This time I made much more drastic changes and finally saw a response. This apparently is the way to go, in FSX. Thanks again, Tako_Kichi.

    blue six

  15. #15
    Cl_Dr in ROLL/Primarary Aerodyanmcs should be a negative number to get the plane to roll with the rudder. If this is positive the plane will fly a bit wierd and roll against the rudder input. However at low speed and lots of torque (say Corsair of Beercat) this will give you something extra to fight against turning into the short slot for deck landing....

    T

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