• Tutorial: Tweaking Flight Dynamics

    Tweaking the Flight Dynamics of Aircraft in Microsoft Flight Simulator

    By Bob Chicilo

    WARNING: DO NOT MAKE CHANGES IN AIR OR AIRCRAFT.CFG FILES YOU HAVE NOT BACKED UP.

    To more fully understand each section of the aircraft.cfg file download the Aircraft Container SDK, from Microsoft. It goes line by line telling something of what each line is for. For FSX this is on the first DVD and has to be installed manually. It does not load with the simulator.

    First of all, some, maybe most, model makers do not complete the job they started before they upload it to a site for others to download and enjoy.

    Where some of them fall down is in putting the information in the [aircraft geometry] section that they have, or at least could have, by writing things down as they make the model. I refer to the wing apex and height, horizontal tail position and height, wing sweep (if any), etc. that they at least knew when making the model.

    This also applies to the engine section(s) and propeller section of the aircraft.cfg file that they have at least some of the information for, and don't always enter it accurately, if at all.

    This info is used every second by the flight engine of the flight sim to tell the simulator how the aircraft is flying. So not having this information as correct as possible is a mistake that at least some model makers have been making. That is, if they want the aircraft to fly the best it can in the sim.

    THE ABOVE IS NOT MEANT AS A PUT DOWN TO ANY PLANE MAKERS. AT LEAST SOME OF YOU, MAYBE MOST OF YOU, DIDN'T KNOW BEFORE YOU READ THIS THAT YOU WERE FALLING DOWN ON THE JOB.

    Because of the above, the first thing you need to do is find the specifications for the aircraft in question and see if the model maker at least tried to make the aircraft.cfg file match the aircraft it belongs to.

    The bad thing is that, if you look at three or four places on the Internet that has specifications for the aircraft, they won't all necessarily agree on every point, such as empty weight, or max gross weight, or on almost any other point. They usually do agree for the most part, but rarely on everything, even for the same model of the same aircraft.

    Therefore the best source for the info is a book by someone known for attempting to be accurate with such information, like Jane's various books on aircraft. Your library may have a copy of one or more editions of Jane's All The World's Aircraft.

    Link: https://en.wikipedia.org/wiki/Jane%27s_All_the_World%27s_Aircraft

    Something like this is the best source that I am presently aware of.

    You can use the info from the web, most of it is reasonably accurate, but it's just like anything else on the web, it is only as accurate as the person who entered the information.

    The next thing to do is put a new nav light into the lights section of the aircraft.cfg file. You do this so you can use it to find out the positions of the wing apex and height; wing root chord, (the distance from the front of the wing to the trailing edge, measured next to the fuselage) horizontal tail position, height, and span; vertical tail position, height, and span; (rarely is the span for the horizontal tail or vertical tail correct on an aircraft that is not flying well). If you think the engine or wheel positions are incorrect you can use the light to check on them as well.

    Note: This goes double for float points (if any) plus contact points that are otherwise invisible.

    For each position on the aircraft that you check with the light this way, you may have to move the light six or more times to accurately find the position you are attempting to establish, such as wing apex and height.

    Note: When you change something in the aircraft.cfg file, you must change planes and then go back to the one you are working on for the changes to show up. For FSX I use an aircraft on the same line of pictures, or on the line of pictures just below the one I am working on.

    A few things to know about using a nav light to find positions: There are only 19 lights possible at present in the lights section; from 0 to 18. Any other numbers will be ignored. In FSX this has changed to any number of lights you want to put in.

    You can skip numbers, but you cannot put them out of order, such as light 5 before light 3.

    The first number after the = sign is the type of light it is.

    The second number is the longitudinal (forward or back) position of the light, measured from the datum point.

    The third number after the = sign is the position left or right of center.

    The fourth number is the height above or below the datum point.

    After the fourth number is the type of light, or effect, it is: e.g. fx_navred.

    Each of these values is separated by a comma; and sometimes, in addition, by one or more spaces.

    If, as sometimes happens, all the lights are used, go to a light the color you want to use, remark it out with either ; or // in front of the line for the light. Then go to the beginning of the next line and hit enter two or three times. This will make a space for you to write a line for the light you will use. Write in a new light with the same number as the one you remarked out, or copy the line you remarked out (not including the //) paste it in the space, and change the position numbers to match where you wish to start.

    Note: If you have all the position numbers for the light at 0, the light will almost certainly be inside the aircraft fuselage. So you should start with it far enough left or right, and, or high enough so this won't happen. Sometimes just left or right leaves it inside the wing. Also if you have the sim start without the nav lights on by default, you will need to turn them on.

    The thing to remember once you have found, and written down, all the information you need, is to delete the new light you made, and maybe, remove the // or ; from in front of the light position you used.


    7 Comments
    1. shanwick's Avatar
      shanwick -
      Great stuff - thank you!

      Is it possible to make this article available as a PDF download, please?

      Dijvid
    1. Barkingside's Avatar
      Barkingside -
      Ctrl C & Ctrl V into MS Word worked OK for me.
    1. fly1937's Avatar
      fly1937 -
      Thank.. precious!
    1. pinkyjr's Avatar
      pinkyjr -
      By far the best mods Ive made are eliminating assymetric thrust, so I can taxi twin engine jetliners on a single engine without needing steering correction.
    1. napamule2's Avatar
      napamule2 -
      You can download this article at Simviation. 'Bob_sFlightDynamicsRevised2.zip', 2.2 Mb. Then you can print it out the 23 page PDF and keep it handy. Thanks Bob. You the man.
      Chuck B
    1. flightman's Avatar
      flightman -
      This is a useful introduction to tuning a flight model but it could do with putting in a more usable order. For example, you should sort drag out before adjusting thrust to change maximum airspeed.

      I hate to be picky but it's quite wrong to say, as on page 5,

      "Unless the elevator and horizontal stabilizer are one and the same, as on some aircraft, the horizontal stabilizer never supplies any lift. It just supplies stability if it is located behind the wings, nothing else. Any forces acting on it are not lift. The wings do the lifting, the horizontal tail, when behind the wings, helps the wings stay at whatever angle of attack they are flying at, at any given moment. The forces generated to do this are not lift that is holding the aircraft up, even though those forces may seem the same as positive or negative lift."

      Any lift generated by the stabiliser will also contribute to the total lift generated. It makes no difference whether it's forward of the wing, behind the wing are an all moving surface.
    1. rockinrobin's Avatar
      rockinrobin -
      Quote Originally Posted by napamule2 View Post
      You can download this article at Simviation. 'Bob_sFlightDynamicsRevised2.zip', 2.2 Mb. Then you can print it out the 23 page PDF and keep it handy. Thanks Bob. You the man.
      Chuck B
      Noticed that the document is now here on Flightsim as well.
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