Coordinate system notes: All positions specified are in meters (which
is weird, since all other units in the file are English). The X axis
points forward, Y is left, and Z is up. Take your right hand, and
hold it like a gun. Your first and second fingers are the X and Y
axes, and your upwards-pointing thumb is the Z. This is slightly
different from the coordinate system used by JSBSim. Sorry. The
origin can be placed anywhere, so long as you are consistent. I use
the nose of the aircraft.
XML Tags
--------
airplane: The top-level tag for the file. It contains only one
attribute:
mass: The empty (no fuel) weight, in pounds.
approach: The approach parameters for the aircraft. The solver will
generate an aircraft that matches these settings. The tag
can (and should) contain <control> tags indicating pilot
input settings, such as flaps and throttle, for the
approach.
speed: The approach airspeed, in knots TAS.
aoa: The approach angle of attack, in degrees
cruise: The cruise speed and altitude for the solver to match. As
above, this should contain <control> tags indicating
aircraft configuration. Especially, make sure the engines
are generating enough thrust at cruise!
speed: The cruise speed, in knots TAS.
alt: The cruise altitude, in feet MSL.
cockpit: The location of the cockpit (pilot eyepoint).
x,y,z: eyepoint location (see coordinates note)
fuselage: This defines a tubelike structure. It will be given an even
mass and aerodynamic force distribution by the solver. You
can have as many as you like, in any orientation you please.
ax,ay,az: One end of the tube (typically the front)
bx,by,bz: The other ("back") end.
width: The width of the tube, in meters.
wing: This defines the main wing of the aircraft. You can have
only one (but see below about using vstab objects for extra
lifting surfaces). The wing should have a <stall> subtag to
indicate stall behavior, control surface subtags (flap0,
flap1, spoiler, slat) to indicate what and where the control
surfaces are, and <control> subtags to map user input
properties to the control surfaces.
x,y,z: The "base" of the wing, specified as the location of
the mid-chord (not leading edge, trailing edge, or
aerodynamic center) point at the root of the LEFT
(!) wing.
length: The length from the base of the wing to the midchord
point at the tip. Note that this is not the same
thing as span.
chord: The chord of the wing at its base, along the X axis
(not normal to the leading edge, as it is
sometimes defined).
taper: The taper fraction, expressed as the tip chord
divided by the root chord. A taper of one is a
hershey bar wing, and zero would be a wing ending
at a point. Defaults to one.
sweep: The sweep angle of the wing, in degrees. Zero is
no sweep, positive angles are swept back.
Defaults to zero.
dihedral: The dihedral angle of the wing. Positive angles
are upward dihedral. Defaults to zero.
idrag: Multiplier for the "induced drag" generated by this
surface. In general, low aspect wings will
generate less induced drag per-AoA than high
aspect (glider) wings. This value isn't
constrained well by the solution process, and may
require tuning to get throttle settings correct in
high AoA (approach) situations.
hstab: These defines the horizontal stabilizer of the aircraft.
Internally, it is just awing objects and therefore work the
same in XML. You are allowed only one hstab object; the
solver needs to know which wing's incidence to play with to
get the aircraft trimmed correctly.
vstab: A "vertical" stabilizer. Like hstab, this is just another
wing, with a few special properties. The surface is not
"mirrored" as are wing and hstab objects. If you define a
left wing only, you'll only get a left wing. The default
dihedral, if unspecified, is 90 degrees instead of zero.
But all parameters are equally settable, so there's no
requirement that this object be "vertical" at all. You can
use it for anything you like, such as extra wings for
biplanes. Most importantly, these surfaces are not involved
with the solver computation, so you can have none, or as
many as you like.
stall: A subtag of a wing (or hstab/vstab) that specifies the stall
behavior.
aoa: The stall angle (maximum lift) in degrees.
width: The "width" of the stall, in degrees. A high value
indicates a gentle stall. Low values are viscious.
peak: The height of the lift peak, relative to the
post-stall secondary lift peak at 45 degrees.
Defaults to 1.5. This one is deep voodoo, and
probably doesn't need to change much. Bug me for an
explanation if you're curious.
flap0, flap1, slat, spoiler:
These are subtags of wing/hstab/vstab objects, and specify
the location and effectiveness of the control surfaces.
start: The positition along the wing where the control
surface begins. Zero is the root, one is the tip.
end: The position where the surface ends, as above.
lift: The lift multiplier for a flap or slat at full
extension. One is a no-op, a typical aileron might
be 1.2 or so, a giant jetliner flap 2.0, and a
spoiler 0.0. For spoilers, the interpretation is a
little different -- they spoil only "prestall" lift.
Lift due purely to "flat plate" effects isn't
affected. For typical wings that stall at low AoA's
essentially all lift is pre-stall and you don't have
to care. Jet fighters tend not to have wing
spoilers, for exactly this reason. This value is
not applicable to slats, which affect stall AoA
only.
drag: The drag multiplier, as above. Typically should be
higher than the lift multiplier for flaps.
aoa: Applicable only to slats. This indicates the
angle by which the stall AoA is translated by the
slat extension.
jet: A turbojet/fan engine. Really cheezy right now, so there's
not much to set. It accepts a <control> subtag to map a
property to its throttle setting, and an <actionpt> subtag
to place the action point of the thrust at a different
position than the mass of the engine.
x,y,z: The location of the engine, as a point mass. If no
actionpt is specified, this will also be the point of
application of thrust.
mass: The mass of the engine, in pounds.
thrust: The maximum sea-level thrust, in pounds.
propeller: A propeller connected to a non-turbocharged piston engine
The engine model is evolving, this tag is likely to change
radically in the future.
x,y,z: The position of the mass (!) of the
engine/propeller combination. If the point
of force application is different (and it
will be) it should be set with an <actionpt>
subtag.
mass: The mass of the engine/propeller, in pounds.
moment: The moment, in kg-meters. This has to be
hand calculated and guessed at for now. A
more automated system will be forthcoming.
radius: The radius, in meters, or the propeller.
cruise-speed: The max efficiency cruise speed of the
propeller. Generally not the same as the
aircraft's cruise speed.
cruise-rpm: The RPM of the propeller at max-eff. cruise.
alt: The cruise altitude.
takeoff-power: The takeoff power required by the propeller...
takeoff-rpm: ...at the given takeoff RPM.
actionpt: Defines an "action point" for an enclosing jet or propeller
tag. This is the location where the force from the thruster
will be applied.
x,y,z: The location of force application.
gear: Defines a landing gear. Accepts <control> subtags to map
properties to steering and braking.
x,y,z: The location of the fully-extended gear tip.
compression: The distance along the Z axis that the gear
will compress. Compression along other
vectors is supported internally, but not in
the XML parser. Bug me if you wantthis
added.
sfric: Static (non-skidding) coefficient of
friction. Defaults to 0.8.
dfric: Dynamic friction. Defaults to 0.7.
retract-time: The time, in seconds, that the gear takes to
fully retract or extend. Defaults to zero,
which indicates a non-retractable gear.
spring: A dimensionless multiplier for the automatically
generated spring constant. Increase to make
the gear stiffer, decrease to make it
squishier.
damp: A dimensionless multipler for the automatically
generated damping coefficient. Decrease to
make the gear "bouncier", increase to make it
"slower". Beware of increasing this too far:
very high damping forces can result and make
the numerics unstable. If you can't make the
gear stop bouncing with this number, try
increasing the compression length instead.
tank: A fuel tank. Tanks in the aircraft are identified
numerically (starting from zero), in the order they are
defined in the file. If the left tank is first, "tank[0]"
will be the left tank.
x,y,z: The location of the tank.
capacity: The maximum contents of the tank, in pounds. Not
gallons -- YASim supports fuels of varying
densities.
jet: A boolean. If present, this causes the fuel
density to be treated as Jet-A. Otherwise,
gasoline density is used. A more elaborate
density setting (in pounds per gallon, for
example) would be easy to implement. Bug me.
ballast: This is a mechanism for modifying the mass distribution of
the aircraft. A ballast setting specifies that a particular
amount of the empty weight of the aircraft must be placed at
a given location. The remaining non-ballast weight will be
distributed "intelligently" across the fuselage and wing
objects. Note again: this does NOT change the empty weight
of the aircraft.
x,y,z: The location of the ballast.
mass: How much mass, in pounds, to put there. Note that
this value can be negative. I find that I often need
to "lighten" the tail of the aircraft.
weight: This is an added weight, something not part of the empty
weight of the aircraft, like passengers, cargo, or external
stores. The actual value of the mass is not specified here,
instead, a mapping to a propery is used. This allows
external code, such as the panel, to control the weight
(loading a given cargo configuration from preference files,
dropping bombs at runtime, etc...)
x,y,z: The location of the weight.
mass-prop: The name of the fgfs property containing the
mass, in pounds, of this weight.
size: The aerodynamic "size", in meters, of the
object. This is important for external stores,
which will cause drag. For reasonably
aerodynamic stuff like bombs, the size should be
roughly the width of the object. For other
stuff, you're on your own. The default is zero,
which results in no aerodynamic force (internal
cargo).
control: This tag, which can appear in two different contexts,
manages a mapping from fgfs properties (user input) to
settable values on the aircraft's objects. Note that the
value to be set MUST (!) be valid on the given object type.
This is not checked for by the parser, and will cause a
runtime crash if you try it. Wing's don't have throttle
controls, etc... Note that multiple axes may be set on the
same value. They are summed before setting.
One serious shortcoming of the current implementation is
that there is no provision for modifying the values read
from properties. There needs to be a way to scale,
translate and truncate the values. On its way, I promise.
axis: The name of the double-valued fgfs property "axis" to
use as input, such as "/controls/aileron".
output: Which property to set on the objects. It can have
the following values:
THROTTLE - The throttle on a jet or propeller.
MIXTURE - The mixture on a propeller.
REHEAT - The afterburner on a jet (unimpl.).
PROP - The propeller advance (unimpl.)
BRAKE - The brake on a gear.
STEER - The steering angle on a gear.
INCIDENCE - The incidence angle of a wing.
FLAP0 - The flap0 deflection of a wing.
FLAP1 - The flap1 deflection of a wing.
SLAT - The slat extension of a wing.
SPOILER - The spoiler extension for a wing.
invert: Negate the value of the property before setting on
the object.
split: Applicable to wing control surfaces. Sets the
normal value on the left wing, and a negated value
on the right wing.
square: Squares the value before setting. Useful for
controls like steering that need a wide range, yet
lots of sensitiviy in the center. Obviously only
applicable to values that have a range of [-1:1] or
[0:1].
A control tag can also appear inside of an <approach> or
<cruise> tag. Here, it specifies a particular value of an
axis mapping that should be true under the given
conditions. At cruise, the throttle is generally at a high
setting, the flaps and slats are up During approach
the flaps and slats are down, etc...
axis: As above, the name of the input property.
value: A floating point number that the property is expected
to hold.
