Lead Computer Configuration:
The following properties will need to be set to configure the lead computer for your aircraft.
These are set in the aircraft's *set.xml file in the section where you are setting initialization values
for various properties. This MUST happen before the nasal section in the *set.xml file.
The following five values can be found in the submodels.xml configuration file where the guns
ballistics are configured.
/controls/armament/gunsight/z-gunOffsetFeet = Gun position on z axis relative to the sight line in feet.
Will = <z-offset>offset value</z-offset> + distance from aircraft center line to sight line height in feet.
/controls/armament/gunsight/y-gunOffsetFeet = Gun position on y axis relative to the sight line in feet.
Will = <y-offset>abs value</y-offset> if the guns are equally distributed about the aircraft center line
set this to 0. If this value in non-zero this is in feet.
/controls/armament/gunsight/gunElevationDegrees = <pitch-offset>gun pitch setting</pitch-offset> in degrees.
/controls/armament/gunsight/ballisticCoefficienct = <eda>xxxxx</eda>
/controls/armament/gunsight/muzzleVelocity = <speed>xxxxx</speed> = In feet per second
Additional parameters need to be set that are not in the submodels.xml file.
/controls/armament/gunsight/gunHarminizationRangeFeet = Range where the sight and the bullet
path cross is straight and level flight in feet.
/controls/armament/gunsight/timeStep = The computer cycle time in seconds.
This will typically be values between 0.5 and 0.05. These correspond to
lead computer update frequencies of 2 to 20 times per second. Use a slower update
rate for older purely mechanical gun sights and faster rates for newer fully
digital gun sights. Slower rates will tend to make the gun sight lag.
/controls/armament/gunsight/dampingFactor = The computer damping factor adjustment.
The optimum dampingFactor is 1.0. Lower values will make the reticle less stable and
prone to over shoot and jitter. However using lower values may result in a more
accurate simulation of older mechanical gun sights which were under damped. Modern
gun sights will be well damped and for those this should be set to 1.0. This value is
capped by the lead computer and values above 1.0 will result in 1.0 being used and
values below 0.3 will result in 0.3 being used.
/controls/armament/gunsight/MaxAzimuth and /controls/armament/gunsight/MaxElevation = The
maximum deflection of the sight reticle in mils. Used to limit the movement of the reticle
to the mechanical limits of sight being simulated.
Lead Computer Input Values:
/controls/armament/gunsight/range = The range to the target in feet.
With radar ranging this value will be constantly changing. Internally the lead computer
also uses this data to calculate the rate at which the range changes (IE. how fast
the target is being closed in on).
/controls/armament/gunsight/computer-on = 0 to turn the lead computer off and 1 to start the
lead computer. Cycling power will reinitialize the lead computer.
Lead Computer Output:
/controls/armament/gunsight/azimuth and /controls/armament/gunsight/elevation = Deflection
needed to hit the target in mils. 1 mil = 1 foot at a 1000 foot range. These values are
used to drive the sight reticle animation. This is usually done by applying these to a
factor that is then using the resulting product to move the reticle in the animation code.
Including the Lead Computer in the Aircraft's Set File:
For the lead computer to function it needs to be added to the aircrafts *set.xml file's nasal section.
This will look something like this.
<nasal>
<!-- your other nasal files -->
<!-- the following three lines must be exactly like this -->
<name of you gun sight>
<file>Aircraft/Instruments-3d/computing-gun-sights/Nasal/lead-computer.nas</file>
</name of your gun sight>
</nasal>
