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MD-81-yasim.xml
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MD-81-yasim.xml
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<?xml version="1.0"?>
<!-- YASim Aerodynamic Model for the McDonnell Douglas MD-81 -->
<!-- Gary Neely aka 'Buckaroo' -->
<!--
Based on MD-81 model with upgraded engines:
Empty: 77888 lbs
Zero Fuel: 118000 lbs
Max Fuel load: 39128 lbs
Max Payload: 40112 lbs
Max Take-Off: 140000 lbs
Max Land: 128000 lbs
Cruise: Mach 0.76 @ 35000'
-->
<airplane mass="77888">
<!-- Approach configuration -->
<!--
These values are selected largely on the basis of meeting minimum stall speeds for various
weight configurations, based on MD-80 flight tables and lots of trial-and-error. Approach
AoA really should be 3 degrees, but 4 works better for the FDM solution.
-->
<approach speed="135" aoa="4" fuel="0.3">
<control-setting axis="/controls/engines/engine[0]/throttle-fdm" value="0.2"/>
<control-setting axis="/controls/engines/engine[1]/throttle-fdm" value="0.2"/>
<control-setting axis="/controls/flight/flaps" value="1.0"/>
<control-setting axis="/controls/flight/slats" value="1.0"/>
<control-setting axis="/controls/gear/gear-down" value="1"/>
<solve-weight idx="0" weight="360"/>
<solve-weight idx="1" weight="30000"/>
</approach>
<!-- Cruise configuration -->
<!--
I use a throttle value of 0.9 based on the 90% maximum continuous setting of the JT8D-217.
Speed is based on max Mach at FL350 of 0.82.
-->
<cruise speed="472" alt="35000" fuel="0.59">
<control-setting axis="/controls/engines/engine[0]/throttle-fdm" value="0.9"/>
<control-setting axis="/controls/engines/engine[1]/throttle-fdm" value="0.9"/>
<control-setting axis="/controls/flight/flaps" value="0.0"/>
<control-setting axis="/controls/flight/slats" value="0.0"/>
<control-setting axis="/controls/gear/gear-down" value="0"/>
<solve-weight idx="0" weight="360"/>
<solve-weight idx="1" weight="30000"/>
</cruise>
<!-- Pilot viewpoint -->
<cockpit x="-2.9" y="0.5" z="1.2"/>
<!-- Fuselage, essentially a nose cone + a body cylinder + a tail cone -->
<fuselage ax="0.0" ay="0.0" az="-0.263" bx="-5.087" by="0.0" bz="0.506"
width="3.328" taper="0.3" midpoint="1.0" />
<fuselage ax="-5.087" ay="0.0" az="0.506" bx="-32.160" by="0.0" bz="0.506"
width="3.328" taper="1.0" midpoint="0.5" />
<fuselage ax="-32.160" ay="0.0" az="0.506" bx="-41.889" by="0.0" bz="1.158"
width="3.328" taper="0.0" midpoint="0.0" />
<!-- Engine Nacelles, true width of 1.7 halved for a guess at effective drag width -->
<!-- Left engine -->
<fuselage ax="-30.845" ay="2.7" az="0.738" bx="-37.246" by="2.7" bz="0.516"
width="0.85" taper="0.5" midpoint="0.3" />
<!-- Right engine -->
<fuselage ax="-30.845" ay="-2.7" az="0.738" bx="-37.246" by="-2.7" bz="0.516"
width="0.85" taper="0.5" midpoint="0.3" />
<!--
Airfoils are not accurately modeled; I wasn't able to find profiles, and one source
indicates they are proprietary. Not that it matters much, but I would have liked
proper profiles for the model. The profile used is a generic thin semi-symmetrical.
Update: Airfoils may be DSMA-433A/-434A at root, DSMA-435A/436A at tip.
I would prefer to divide the wing into two sections for inboard and outboard geometry,
but YASim allows only one 'wing'. I believe a vstab/mstab could be used, but YASim docs say
it isn't used by the solver computation, so for the moment I leave things simple until
my understanding improves. My single-geometry solution yields too much wing area and
too much lift aft. To compensate for the latter, I have the wing artificially placed
just under 1 meter forward of the actual position (which is not precisely known). The
position on the model is -23.034.
Beyond basic geometry, this is guesswork. Some reports have the MD-80's as slightly
slow to roll, but that is a comparison with the smaller DC-9 which pilots say is very
responsive on the roll. Also note that though the 80's have a very slight dihedral, they
are said to be very stable on the roll axis, therefore I've increased the dihedral a bit
beyond what the model geometry suggests. I have one source that lists the dihedral as
3 degees, so this guess may be correct.
I'm not happy with the mushy stall characteristics, but in reasonable flight the plane
shouldn't get near stall conditions anyway. The MD-80's are subject to deep stalls due
to rear mounted engines and high tail configurations, and have many control and warning
measures to get the pilots into recovery mode before things get dangerous.
Unused:
<control-output control="SPOILER" side="left" prop="/surface-positions/left-spoiler-pos-norm"/>
<control-output control="SPOILER" side="right" prop="/surface-positions/right-spoiler-pos-norm"/>
Spoilers without flight/ground mode distinction:
<spoiler start="0.078" end="0.554" lift="0.7" drag="2.0"/>
And with flight/ground mode distinction:
<spoiler start="0.078" end="0.554" lift="0.55" drag="3.0"/>
For flight operation, spoiler control value is cut by 2/3, so in effect we usually see the former
values, but when on the ground we get the latter, reflecting the setting of ground spoilers. Note
that flight mode is restricted to 50% full setting, so we in effect we only see have the former
setting in flight. See spoilers.nas for details.
<spoiler start="0.078" end="0.554" lift="0.55" drag="3.0"/>
-->
<wing x="-22.25" y="1.630" z="-0.648"
length="15.632"
chord="6.308"
taper="0.17"
sweep="19"
dihedral="3"
incidence="1.5"
camber="0.1"
twist="-2.0">
<stall aoa="10" width="2" peak="1.5"/>
<flap0 start="0" end="0.597" lift="1.5" drag="1.9"/>
<flap1 start="0.597" end="0.824" lift="1.25" drag="1.2"/>
<slat start="0" end="1" aoa="3" drag="1.1"/>
<spoiler start="0.078" end="0.554" lift="0.7" drag="2.0"/>
<control-input axis="/controls/flight/flaps" control="FLAP0"/>
<control-input axis="/controls/flight/aileron" control="FLAP1" split="true"/>
<control-input axis="/controls/flight/slats" control="SLAT"/>
<control-input axis="/controls/flight/spoilers" control="SPOILER"/>
<control-output control="FLAP0" prop="/surface-positions/flap-pos-norm"/>
<control-output control="SLAT" prop="/surface-positions/slat-pos-norm"/>
<control-output control="FLAP1" side="left" prop="/surface-positions/left-aileron-pos-norm"/>
<control-output control="FLAP1" side="right" prop="/surface-positions/right-aileron-pos-norm"/>
<control-output control="SPOILER" prop="/surface-positions/spoiler-pos-norm"/>
<control-speed control="FLAP0" transition-time="10"/>
<control-speed control="SLAT" transition-time="10"/>
<control-speed control="SPOILER" transition-time="1"/>
</wing>
<!--
-3 dihedral based on several unofficial sources.
Note that the hstab may have a negative camber. I haven't confirmed this.
-->
<hstab x="-41.691" y="0.220" z="5.727"
length="6.520"
chord="3.602"
taper="0.392"
sweep="26.5"
dihedral="-3"
incidence="0"
camber="0">
<stall aoa="15" width="4" peak="1.5"/>
<flap0 start="0" end="1" lift="1.3" drag="1.3"/>
<control-input axis="/controls/flight/elevator" control="FLAP0" />
<control-input axis="/controls/flight/elevator-trim" control="FLAP0"/>
<control-output control="FLAP0" prop="/surface-positions/elevator-pos-norm"/>
</hstab>
<vstab x="-38.578" y="0" z="1.952"
length="5.185"
chord="4.507"
taper="0.928"
sweep="44">
<stall aoa="15" width="2" peak="1.5"/>
<flap0 start="0" end="0.829" lift="1.4" drag="1.3"/>
<control-input axis="/controls/flight/rudder" control="FLAP0" invert="true"/>
<control-input axis="/controls/flight/rudder-trim" control="FLAP0" invert="true"/>
<control-output control="FLAP0" prop="/surface-positions/rudder-pos-norm"/>
</vstab>
<!--
Early 81's used Pratt & Whitney JT8D-209 18,500 lb (8,391 kg) and were generally considered
underpowered. Most have been upgraded to the -217 series with 20,000 lb thrust. I use the
latter as most -209's have been upgraded to -217's.
Known values for the JT8D-217:
mass="4567" egt="625" tsfc="0.518" n1-idle="30" n2-idle="60" n1-max="99.2" n2-max="102.5"
(tsfc based on one engine maintenance report for T/O value, tsfc=0.492 at cruise)
oil pressure 40-55 PSI
The JT8D-217 is rated at 20000 lbs thrust at sea level and a temperature of 25C. YASim uses a
standard atmosphere temp of 15C. So, assuming a dewpoint of 0 for atmosphere density calculations,
that gives 0.0347% more thrust in YASim than indicated by the rating, or 20694 lbs. This may be
conservative based on new engine data I've not yet fully interpreted.
Authoritative sources report reversal time to be about 2 secs.
Note that the JT8D-217 has 850 lbs of reserve thrust which I currently don't factor in as I don't
know exactly how it's used; is it in addition to rated thrust, or factored into rated thrust? Using
this with the above factor would give another 880 lbs of thrust per engine (21573), but it seems to
be available only for emergency situations involving failure of one engine.
FDM throttles are mapped such that the engines idle at 7% rated thrust with throttle controls at the
full backstop.
-->
<jet x="-33.757" y="2.7" z="0.687" mass="4567" thrust="20694" egt="625" tsfc="0.518" n1-idle="30" n2-idle="60" n1-max="99.2" n2-max="102.5" epr="2.12">
<control-input axis="/controls/engines/engine[0]/throttle-fdm" control="THROTTLE"/>
<control-input axis="/controls/engines/engine[0]/reverser" control="REVERSE_THRUST"/>
<control-output control="REVERSE_THRUST" prop="/surface-positions/reverser-norm[0]"/>
<control-speed control="REVERSE_THRUST" transition-time="2"/>
<actionpt x="-35.0" y="2.7" z="0.687"/>
</jet>
<jet x="-33.757" y="-2.7" z="0.687" mass="4567" thrust="20694" egt="625" tsfc="0.518" n1-idle="30" n2-idle="60" n1-max="99.2" n2-max="102.5" epr="2.12">
<control-input axis="/controls/engines/engine[1]/throttle-fdm" control="THROTTLE"/>
<control-input axis="/controls/engines/engine[1]/reverser" control="REVERSE_THRUST"/>
<control-output control="REVERSE_THRUST" prop="/surface-positions/reverser-norm[1]"/>
<control-speed control="REVERSE_THRUST" transition-time="2"/>
<actionpt x="-35.0" y="-2.7" z="0.687"/>
</jet>
<!-- Gear -->
<!--
I'm aware that the nose sits a bit too high on the ground, but am unable to resolve the problem without
compromising either the compression throw or realistic compression behavior under YASim.
Steering is 27 deg side to side.
-->
<!-- Nose -->
<gear x="-2.476" y="0" z="-2.451"
compression="0.38"
spring="0.5"
damp="4"
>
<control-input axis="/controls/flight/rudder" control="STEER" square="true"/>
<control-input axis="/controls/gear/gear-down" control="EXTEND"/>
<control-output control="EXTEND" prop="/gear/gear[0]/position-norm"/>
<control-speed control="EXTEND" transition-time="10"/>
</gear>
<!-- Left main -->
<gear x="-24.5" y="3.112" z="-2.949"
compression="0.55"
spring="0.35"
>
<control-input axis="/controls/gear/brake-left" control="BRAKE"/>
<control-input axis="/controls/gear/brake-parking" control="BRAKE" split="true"/>
<control-input axis="/controls/gear/gear-down" control="EXTEND"/>
<control-output control="EXTEND" prop="/gear/gear[1]/position-norm"/>
<control-speed control="EXTEND" transition-time="10"/>
</gear>
<!-- Right main -->
<gear x="-24.5" y="-3.112" z="-2.949"
compression="0.55"
spring="0.35"
>
<control-input axis="/controls/gear/brake-right" control="BRAKE"/>
<control-input axis="/controls/gear/brake-parking" control="BRAKE" split="true"/>
<control-input axis="/controls/gear/gear-down" control="EXTEND"/>
<control-output control="EXTEND" prop="/gear/gear[2]/position-norm"/>
<control-speed control="EXTEND" transition-time="10"/>
</gear>
<!--
Approximate tank locations. The MD-80's have three tanks, one in each wing and a central
tank in the fuselage between the wings. The MD-83 adds two small auxillary tanks of about
500 gallons each just before and aft of the wing section, not used here. Note that the APU
draws from the right wing tank.
-->
<tank x="-22.4" y="5.7" z="-0.465" capacity="9266" jet="true"/>
<tank x="-22.4" y="-5.7" z="-0.465" capacity="9266" jet="true"/>
<tank x="-22.4" y="0" z="-0.465" capacity="20596" jet="true"/>
<!-- Forward ballast for nose gear, batteries, avionics, etc. -->
<ballast x="-2.0" y="0.0" z="0.0" mass="7000.0" />
<!-- Some ballast for mass of main landing gear assemblies -->
<ballast x="-24.390" y="-2.0" z="-0.658" mass="3000.0" />
<ballast x="-24.390" y="2.0" z="-0.658" mass="3000.0" />
<weight x="-2.9" y="0.0" z="0.6" mass-prop="/sim/weight[0]/weight-lb"/> <!-- Crew -->
<!-- Crude initial positioning of cargo/passengers. Would like to itemize this by location later. -->
<weight x="-23.0" y="0.0" z="0.0" mass-prop="/sim/weight[1]/weight-lb"/> <!-- Cargo/Passengers -->
</airplane>