FMS 2 alpha 8.5 par file description
by Gary Gunnerson, Feb 6th, 2004

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Note 5/2008: This description of the FMS alpha 2.8 .par file pre-dates any nice .par editor. All things known here were reverse-engineered or discovered by trial-and-error. Today, Mr. Masuoka's .par editor is invaluable in making a correct .par file and serves as a better explanation in how the .par file is configured. Get ParEdit.exe here: or in japanese at:

* * * * M A I N * * * *

The MAIN section is comprised of model mass, moments of inertia and model height above ground. Reducing mass makes the model fly more spritely. Above ground height is related to the 3D modelname.x file and the wheel height above ground. Wheel height should never be below ground height but can be above ground height.

* * * * M O T O R * * * *

MOTOR elements control the amount of thrust for the model. I've not toyed with these except to increase the motor power and adjust the prop diameter and pitch. As you'd expect increasing them increases thrust. Not played with the fuel/battery consumption yet to see how it's modeled. The Transall model has a second motor entry.

Note 5/2008: The fastest way to increase thrust for ELECTRIC motors is to increase the number of battery cells for which each cell is 1.2 volts. Remember, this version of FMS pre-dates LiPoly cells. Next up for thrust increase is to increase blocking current and max RPM. Also, a way to kill adverse yaw for a motor is to double the motor count, halve the thrust and reverse the direction of the second motor RIGHT to LEFT in the same x,y,z location as the first motor. If the motor takes awhile to spool up, the motor "moment of inertia" needs to be decreased.

If the model climbs under power with a tractor motor, increase the down motor thrust angle incidence. Typical down and side motor thrust angles are 3.0 and 3.0 degrees.

* * * * W I N G * * * *

WING elements are comprised of surfaces that provide control and/or lift. Position is calculated by the spreadsheet with it loosely defined as the moment center or center of lift. The X coordinate is 25% back from the leading edge or 25% in front of the object center. Unit vectors (ex,ey) indicate dihedral, sweep or both. Check out the top swept wing of the Pitts and the bottom dihedral wing of the Pitts or the Transall wing for typical values. See the spreadsheet for the degree of sweep or dihedral and how these elements change. You basically rotate the object around the Z (up/down) axis for sweep and the X (fore/aft) axis for dihedral. The POLAR number refers to one of the POLAR tables further down in the file and assigns lift, drag and moment factors for different angles of attack.

Note 5/2008: Using Mr. Masuoka's ParEdit.exe, you simply choose a left or right wing and input the x,y,z position, dihedral angle in degrees, half-span for one wing, starting and ending chord etc. Use the 3D view from the TOP and see how well your .par wing aligns with the 3D model wing. When first editing the .par, put in the left and right wing spans and click on Y-Auto in the 3D window pane to align the .par wing span with the 3D model wing span. Numbers between 100 and 200 are acceptable, over 200 percent is bad and requires scaling of the 3D model to compensate. The obvious conclusion here is that the 3D model scale and .par file scale do not need to be the same. Another note, the ParEdit program has 4 types of wings, left, right, sym and std. Left and right are indicated from the pilots point of view. Sym=symmetrical and most often used for the horizontal stab. Std=standard is used for other asymmetric wing surfaces, typically the fin or vertical stab.

Surface width is the object span. The number of elements are 4 for AUTOELEMENT wings, 3 for AUTOELEMENT fuselage and could be a larger number for ELEMENTDATA points. The surface angle of attack is self-evident. Chord length at the first end (left end) and at the second end (right end) provide surface taper. Chord length of the flap is the flap depth. Start position is meters from the left side of the surface and end flap position is also from the left side to indicate the width of the flap. Max deflection is the degrees the surface can travel. Increasing flap length, width or deflection angle will increase the control effect. Channel refers to the radio channel that controls the movable surface. Follow the sign of flap deflection from other models.

Note 5/2008: Using Mr. Masuoka's ParEdit is more intuitive than editing the .par file directly. Remember that the wing incidence angle is a comination of the wing incidence angle (usually positive) and the horizontal stab incidence angle (usually negative). A truly neutral pattern plane will usually have zeros for both. Typical numbers are 1.0 for wing incidence and -1.0 for stab. If the model climbs too much, reduce incidence angles.

Left wings, right wings and elevator all follow the same general concept. The rudder however, is a little different. The rudder span is the height of the rudder, chord 1st is the bottom, chord 2nd is the top, start flap is the bottom and end flap is the top. This gets a bit confusing when the rudder/vertical stabilizer is not square or even regularly shaped. The best way to make sure this section is accurate is to draw it out on paper, use custom ELEMENTDATA and calculate the sweep correctly. Note 5/2008: Or use Mr. Masuoka's ParEdit and compare the 3D model to the .par file using the SIDE view.

ELEMENTDATA is the method used for expressing irregular shapes within the surface. As an example look at the Elements for the Diamant surface number one (left wing). The first element is different than the others and starts with a chord length instead of a relative position. This length is the width of the wing at the farthest left point of the surface. For the Diamant, that number is .113 meters. Element 2 relative position is the percent of span from the left edge of the wing. In this case it's .0778 or 7.78 percent. Multiply that times the span of 0.8 to get the position on the wing that is .158 meters wide (chord) and starts a flap depth of .04 meters. The aileron (flap) progresses for two more elements before stopping and at .6556 of the span the wing is up to .23 meters chord. See the Suchoi rudder for an interesting use of ELEMENTDATA combined with sweep to show an irregular rudder configuration.

There are 3 AUTOELEMENT elements in the surface 5 fuselage. It's mostly width (span) times length (chord).

* * * * D R A G * * * *

DRAG is a general number used for the overall model. I'm not sure if it's derived from some physical model property or not. If your model seems too twitchy or too spritely overall, increase the DRAG coefficient. You have position x,y,z, reference cross-section area and coefficient. Increasing either parameter will increase drag. You can also trigger drag with a channel to allow for increased drag from flaps or spoilers.

* * * * P O L A R * * * *

We already discussed the POLAR sections that are used by surfaces to show coefficients for lift, drag and moment for various angles of attack. I've plotted each of the POLAR tables directly to the right of each section. You'll see that most of the drag and moments look very close to each other. Where you see variance is in the lift component associated with the Pitts Polar 2 as compared to the Transall Polar 3, both used for Surface 5, the fuselage. The fuselage show a dramatic drop in lift at 9 degrees of attack, but the Pitts shows a marked increase over the Transall at the 50 degree mark.

* * * * P O I N T S * * * *

POINTS are collision detection points usually associated with wing tips, nose and top of rudder/tail. Breaking load refers to how hard the point has to hit to cause a collision. If this is set too low, you'll collide with the slightest touch. Too high, and you'll seldom collide with anything unless hitting the ground in a full dive. Note 5/2008: Remember that points are directly related to the 3D model only and may differ from .par file objects.

* * * * W H E E L * * * *

In the WHEEL section, three sets of wheels are indicated for models with landing gear. The parallel pair are listed first followed by the single center wheel either a tail dragger or front wheel. Tail draggers use channel 1 while front steering uses channel 3. Note 5/2008: Wheel points are also directly related to the 3D model only.

If the model steers the wrong direction on the ground, reverse the sign of the angle for the steering wheel.

* * * * H O O K AND V M I X * * * *

Finally you'll see the HOOK and VMIX vmixer used with the glider or v-tails.



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