I have continued to work with the dc3.xml for yasim and some of the
numbers in the original file seem inconsistent with the 3D model. Here
are my questions:
1. Shouldn't the z value for the wing be -0.95 as the z for the wing is
for the root mid cord. This is a low wing. This matches the tank and
the engines better also. This looks like a typo.
2. The z value for the tail wheel, z=-1.5, seems to leave the tail off
the ground at rest in the 3D model with compression="0.2". I have tried
increasing the compression to 0.3 to 0.5 or increasing z to -1.0. Then
the over-the-nose visibility is terrible. In a real dc3 it was not so
great until the tail came up in the takeoff roll.
3. Is there a way to add damping or make the stiffness of the
compression for the main gear? It is very easy to get an oscillation
the feels like a pre-bounce while accellerating on the mains or while
rolling out from a wheel landing.
4. Does yasim report an actual Center of Gravity? I know that it
checks to see if the approach config can be achieve with trim. This
would tell me if I was going overboard with the ballast.
The xml file I am attaching allows take off accelerating on the mains
with only rudder inputs to keep the nose straight down the runway if you
add just one "tic" of up trim. I did switch to a negative mass in the
tail for ballast to move the CG forward. The main gear are back in
their original position.
Dave
<airplane mass="16865">
<approach speed="58" aoa="13">
<control-setting axis="/controls/throttle[0]" value="0.4"/>
<control-setting axis="/controls/throttle[1]" value="0.4"/>
<control-setting axis="/controls/mixture[0]" value="1.0"/>
<control-setting axis="/controls/mixture[1]" value="1.0"/>
<control-setting axis="/controls/propeller-pitch[0]" value="0.5"/>
<control-setting axis="/controls/propeller-pitch[1]" value="0.5"/>
<control-setting axis="/controls/flaps" value="1.0"/>
<control-setting axis="/controls/gear-down" value="1"/>
</approach>
<cruise speed="180" alt="23200">
<control-setting axis="/controls/throttle[0]" value="1.0"/>
<control-setting axis="/controls/throttle[1]" value="1.0"/>
<control-setting axis="/controls/mixture[0]" value="1.0"/>
<control-setting axis="/controls/mixture[1]" value="1.0"/>
<control-setting axis="/controls/propeller-pitch[0]" value="1.0"/>
<control-setting axis="/controls/propeller-pitch[1]" value="1.0"/>
<control-setting axis="/controls/boost[0]" value="1.0"/>
<control-setting axis="/controls/boost[1]" value="1.0"/>
<control-setting axis="/controls/flaps" value="0.0"/>
<control-setting axis="/controls/gear-down" value="0"/>
</cruise>
<cockpit x="-1.63" y="0.41" z="0.76"/>
<fuselage ax="0" ay="0" az="0" bx="-19.75" by="0" bz="0"
width="2" taper="0.5" midpoint="0.25"/>
<wing x="-7.02" y="1.09" z="-0.95" length="11.58" camber="0.1"
chord="4.77" taper=".286" sweep="19" dihedral="4">
<stall aoa="14" width="6" peak="1.5"/>
<flap0 start="0.04" end="0.38" lift="1.5" drag="1.2"/>
<flap1 start="0.38" end="0.97" lift="1.2" drag="1.2"/>
<control-input axis="/controls/flaps" control="FLAP0"/>
<control-input axis="/controls/aileron" control="FLAP1" split="true"/>
<control-input axis="/controls/aileron-trim" control="FLAP1" split="true"/>
<control-output control="FLAP0" prop="/surface-positions/flap-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-speed control="FLAP0" transition-time="5"/>
</wing>
<hstab x="-18.12" y="0.41" z="0.27" effectiveness="4.0" length="3.00"
chord="3" taper=".545" sweep="15">
<stall aoa="18" width="6" peak="1.5"/>
<flap0 start="0" end="1" lift="1.5" drag="1.2" effectiveness="0.25"/>
<control-input axis="/controls/elevator" control="FLAP0"/>
<control-input axis="/controls/elevator-trim" control="FLAP0"/>
<control-output control="FLAP0" prop="/surface-positions/elevator-pos-norm"/>
</hstab>
<vstab x="-18.12" y="0" z="0.95" effectiveness="2.0" length="2.72"
chord="3.95" taper=".462" sweep="2">
<stall aoa="14" width="4" peak="1.5"/>
<flap0 start="0" end="1" lift="1.5" drag="1.2" effectiveness="2.5"/>
<control-input axis="/controls/rudder" control="FLAP0" invert="true"/>
<control-input axis="/controls/rudder-trim" control="FLAP0" invert="true"/>
<control-output control="FLAP0" prop="/surface-positions/rudder-pos-norm"/>
</vstab>
<propeller x="-4.09" y="2.52" z="-0.95"
mass="2000" moment="35" radius="1.4"
eng-power="1200" eng-rpm="2700"
turbo-mul="1.5"
cruise-power="660" cruise-speed="195"
cruise-rpm="2100" cruise-alt="20000"
min-rpm="1600" max-rpm="2700">
<actionpt x="-2.45" y="2.52" z="-0.95"/>
<control-input axis="/controls/throttle[0]" control="THROTTLE"/>
<control-input axis="/controls/starter[0]" control="STARTER"/>
<control-input axis="/controls/magnetos[0]" control="MAGNETOS"/>
<control-input axis="/controls/mixture[0]" control="MIXTURE"/>
<control-input axis="/controls/propeller-pitch[0]" control="ADVANCE"/>
<control-input axis="/controls/boost[0]" control="BOOST"/>
</propeller>
<propeller x="-4.09" y="-2.52" z="-0.95"
mass="2000" moment="-35" radius="1.4"
eng-power="1200" eng-rpm="2700"
turbo-mul="1.5"
cruise-power="660" cruise-speed="195"
cruise-rpm="2100" cruise-alt="20000"
min-rpm="1600" max-rpm="2700">
<actionpt x="-2.45" y="-2.52" z="-0.95"/>
<control-input axis="/controls/throttle[1]" control="THROTTLE"/>
<control-input axis="/controls/starter[1]" control="STARTER"/>
<control-input axis="/controls/magnetos[1]" control="MAGNETOS"/>
<control-input axis="/controls/mixture[1]" control="MIXTURE"/>
<control-input axis="/controls/propeller-pitch[1]" control="ADVANCE"/>
<control-input axis="/controls/boost[1]" control="BOOST"/>
</propeller>
<!-- Tail wheel; has castering selectable by a wheel lock -->
<gear x="-17.3" y="0" z="-1.5" compression="0.3">
<control-input axis="/controls/tailwheel-castering" control="CASTERING"/>
</gear>
<!-- Main wheels; note decreased compression -->
<gear x="-6.08" y="2.52" z="-3.49" compression="0.75" retract-time="7">
<control-input axis="/controls/parking-brake" control="BRAKE"/>
<control-input axis="/controls/brakes[0]" control="BRAKE"/>
<control-input axis="/controls/gear-down" control="EXTEND"/>
<control-speed control="EXTEND" transition-time="7"/>
<control-output control="EXTEND" prop="/gear/gear[0]/position-norm"/>
</gear>
<gear x="-6.08" y="-2.52" z="-3.49" compression="0.75" retract-time="7">
<control-input axis="/controls/parking-brake" control="BRAKE"/>
<control-input axis="/controls/brakes[1]" control="BRAKE"/>
<control-input axis="/controls/gear-down" control="EXTEND"/>
<control-speed control="EXTEND" transition-time="7"/>
<control-output control="EXTEND" prop="/gear/gear[1]/position-norm"/>
</gear>
<!-- From the type certificate: "Fuel capacity: 822 gals. (4 tanks in
center section wing: 2 main including fuel system 210 gals. each
(+48) and 2 aux. 201 gals. each (+83.5)" -->
<tank x="-7.02" y="0" z="-0.95" capacity="4932"/>
<ballast x="-18.0" y="0.0" z="0.6" mass="-1400"/> <!-- move CG forward -->
</airplane>
