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 Elements
------------
airplane: The top-level element 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 element
can (and should) contain <control> elements 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
fuel: Fraction (0-1) of fuel in the tanks. Default is 0.2.
cruise: The cruise speed and altitude for the solver to match. As
above, this should contain <control> elements 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.
fuel: Fraction (0-1) of fuel in the tanks. Default is 0.2.
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> subelement to
indicate stall behavior, control surface subelements (flap0,
flap1, spoiler, slat) to indicate what and where the control
surfaces are, and <control> subelements 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).
incidence: The incidence angle at the wing root, in degrees.
Zero is level with the fuselage (as in an
aerobatic plane), positive means that the leading
edge is higher than the trailing edge (as in a
trainer).
twist: The difference between the incidence angle at the
wing root and the incidence angle at the wing
tip. Typically, this is a negative number so
that the wing tips have a lower angle of attack
and stall after the wing root (washout).
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.
mstab: A mirrored horizontal stabilizer. Exactly the same as wing, but
not involved with the solver computation, so you can have none,
or as many as you like.
stall: A subelement of a wing (or hstab/vstab/mstab) that specifies the
stall behavior.
aoa: The stall angle (maximum lift) in degrees. Note that
this is relative to the wing, not the fuselage (since
the wing may have a non-zero incidence angle).
width: The "width" of the stall, in degrees. A high value
indicates a gentle stall. Low values are viscious
for a non-twisted wing, but are acceptable for a
twisted one (since the whole wing will not stall at
the same time).
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 subelements 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. It accepts a <control> subelement to map a
property to its throttle setting, and an <actionpt> subelement
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.
afterburner: Maximum additional thrust from the afterburner,
in pounds [0].
rotate: Vector angle of the thrust in degrees about the
Y axis [0].
n1-idle: Idling rotor speed [55].
n1-max: Maximum rotor speed [102].
n2-idle: Idling compressor speed [73].
n2-max: Maximum compressor speed [103].
tsfc: Thrust-specific fuel consumption [0.8].
This should be considerably lower for modern
turbofans.
egt: Exhaust gas temperature at takeoff [1050].
epr: Engine pressure ratio at takeoff [3.0].
exhaust-speed: The maximum exhaust speed in knots [~1555].
propeller: A propeller connected to a non-turbocharged piston engine
The engine model is evolving, this element 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>
subelement.
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.
cruise-power: The power produced at cruise, in horsepower.
cruise-alt: The reference cruise altitude in feet.
eng-power: The brake horsepower at cruise.
eng-rpm: The engine RPM at cruise (for geared engines?).
takeoff-power: The takeoff power required by the propeller...
takeoff-rpm: ...at the given takeoff RPM.
displacement: The engine displacement in cubic inches.
compression: The engine compression [??]
turbo-mul: The turbocharger multiplier.
wastegate-mp: The manifold pressure to activate the wastegate
(inHG).
min-rpm: The minimum operational RPM.
max-rpm: The maximum operational RPM.
gear-ratio: The factor by which the engine RPM is multiplied
to produce the propeller RPM. Optional (defaults
to 1.0).
actionpt: Defines an "action point" for an enclosing jet or propeller
element. 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> subelements 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).
solve-weight:
Subtag of approach and cruise parameters. Used to specify a
non-zero setting for a <weight> tag during solution. The
default is to assume all weights are zero at the given
performance numbers.
idx: Index of the weight in the file (starting with zero).
weight: Weight setting in pounds.
control: This element, 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/flight/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.
CYCLICAIL - The "aileron" cyclic input of a rotor
CYCLICELE - The "elevator" cyclic input of a rotor
COLLECTIVE - The collective input of a rotor
ROTORENGINEON - If not equal zero the rotor is rotating
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 element can also appear inside of an <approach> or
<cruise> element. 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.
rotor: A rotor. Used for simulating helicopters. You can have one, two
or even more.
If you specify a rotor, you do not need to specify a wing or hstab,
the settings for approach and cruise will be ignored then. Instead
stored results from the c182 will be used.
name: The name of the rotor.
(some data is stored at /rotors/name/)
The rpm, cone angle, yaw angle and roll angle are stored
for the complete rotor. For every blade the position
angle, the flap angle and the incidence angle are stored.
All angles are in degree, positive values always mean "up".
This is not completely tested, but seem to work at least
for rotors rotating counterclockwise.
x,y,z: The position of the rotor center
nx,ny,nz: The normal of the rotor (pointing upwards, will be
normalized by the computer)
fx,fy,fz: A Vector pointing forward, if not perpendicular to the
normal it will be corrected by the computer
diameter: The diameter in meter
numblades: The number of blades
weightperblade: The weight per blade in pounds
relbladecenter: The relative center of gravity of the blade. Maybe
not 100% correct interpreted; use 0.5 for the start and
change in small steps
rpm: rounds per minute.
ccw: determines if the rotor rotates clockwise (="false") or
counterclockwise (="true"), (if you look on the top of the
normal, so the bo105 has counterclockwise rotor)
maxcollective: The maximum of the collective incidence in degree
mincollective: The minimum of the collective incidence in degree
maxcyclicele: The maximum of the cyclic incidence in degree for
the elevator like function
mincyclicele: The minimum of the cyclic incidence in degree for
the elevator like function
maxcyclicail: The maximum of the cyclic incidence in degree for
the aileron like function
mincyclicail: The minimum of the cyclic incidence in degree for
the aileron like function
pitch_a: A collective incidence angle, used for the next token
forceatpitch_a: The force, the rotor is producing when the incident
angle is equal pitch_a. I.e. hover-pitch and a force
equivalent to the weight. (in pounds of force)
pitch_b: A collective incidence angle, used for the next token
poweratpitch_b: the power the rotor needs at pitch_b. (i.e. at the
bo105 the main rotor consumes bout 90% of the engine power,
and 9% the tail rotor. In kW. Used for calculation of the
torque.
poweratpitch_0: the power the rotor needs at zero pitch.
In kW. Used for calculation of the torque.
notorque: If set to "true" the calculated torque is always zero.
Very helpful while adjusting rotor parameters.
flapmin: Minimum flapping angle. (Should normally never reached)
flapmax: Maximum flapping angle. (Should normally never reached)
flap0: Flapping angle at no rotation, i.e. -5
dynamic: this changes the reactions peed of the rotor to an input.
normally 1 (Maybe there are rotors with a little faster
reaction, than use a value a little greater than one.
A value greater than one will result in a more inert,
system. Maybe it's useful for simulating the rotor of the
Bell UH1
rellenflaphinge: The relative length from the center of the rotor
to the flapping hinge. Can be taken from pictures of the
helicopter (i.e. 0 for Bell206, about 0.05 for most
rotors) For rotors without flapping hinge (where the blade
are twisted instead, i.e. Bo 105, Lynx) use a mean value,
maybe 0.2. This value has a extreme result in the behavior
of the rotor
delta3: Some rotors have a delta3 effect, which results in a
decreasing of the incidence when the rotor is flapping.
A value of 0 (as most helicopters have) means no change in
incidence, a value of 1 result in a decreases of one degree
per one degree flapping.
So delta3 is the proportional factor between flapping and
decrease of incidence. I.e. the tail rotor of a Bo105 has
a delta3 of 1.
delta: A factor for the damping constant for the flapping. 1 means
a analytical result, which is only a approximation. Has a
very strong result in the reaction of the rotor system on
control inputs.
If you know the flapping angle for a given cyclic input you
can adjust this by changing this value. Or if you now the
maximum roll rate or ...
translift: Helicopters have "translational lift", which is due to
turbulence and hard to calculate, so this simulation uses
a phenomenological ansatz. Use .1 for the start value
dragfactor: The drag of the rotating rotor perpendicular to the
rotor plane is larger than the drag of the not rotating
rotor. Hard to calculate, so it is added phenomenological
Any rotor needs a <control> subelement for the engine
(ROTORENGINEON) and can have <control> subelements for the cyclic
(CYCLICELE, CYCLICAIL) and collective (COLLECTIVE) input.
The rotor simulation is very "beta" and not finished yet. So don't
spend too much time to adjust a flight behavior to the smallest
details now.
