I wrote
> Jim Wilson wrote
> > 
> > I can see a difference,  but it is still broken.  No matter
> > what the setting, now the engine RPM is either way to high or 
> > way to low.
> > 
> > It'd be great if someone else could look at the P51D fdm.
> > I'm lost.  Flight dynamics is neither my area of expertise or 
> > interest.  The only reason I did it in the first place is I 
> > had a 3D model that Jon supposedly had a JSBsim config for 
> > that never materialized.
> > 
> > In short, the major issues are with the propeller rpm (as
> > Vivian noted) and probably more significant, the thing still 
> > flies like it has the glide ration of a 30m soaring plane.  
> > Any help is appreciated.
> > 
> Jim, it's a super model, and deserves to fly well. Once we 
> get the Merlin
> sorted for the Spitfire, we should be able to fix up the 
> p51d. It's a bit
> hard to separate the various effects at the moment.

PS - here's a quick fix - I think your stall AoA was too close to your
approach AoA, which was forcing a wheel landing rather than a 3 point. The
wing should stall before the tail, so I adjusted the incidences, and I think
the engine/prop mass position and the prop action point were the wrong way
round. Anyway, until the engine bug is fixed I can't test it properly, but
the stall speed is about right, and it lands well. Won't fly fast enough

See what you think

<?xml version="1.0"?>

YASim aerodynamic model for a P-51D mustang
Started 2003-04-24 by Jim Wilson

This aerodynamic model is based on three-views, unauthoritative
performance data, and wild guesses.  These sites provided particularly
useful information or were simply fun to visit:

Performance data:

Weight and balance:

(Note: I have local copies if this url becomes un-available)

The reference datum for measurements is the nose.

<!-- Weight of everything but fuel  (7010 empty) -->
<airplane mass="7190">

<!-- Approach configuration -->
<approach speed="87" aoa="13">
  <control-setting axis="/controls/engines/engine[0]/throttle" value="0.2"/>
  <control-setting axis="/controls/engines/engine[0]/mixture" value="1.0"/>
  <control-setting axis="/controls/engines/engine[0]/propeller-pitch"
  <control-setting axis="/controls/flight/flaps" value="1.0"/>
  <control-setting axis="/controls/gear/gear-down" value="1"/>

<!-- Cruise configuration -->
<cruise speed="380" alt="25000">
  <control-setting axis="/controls/engines/engine[0]/throttle"
  <control-setting axis="/controls/engines/engine[0]/mixture" value="1.00"/>
  <control-setting axis="/controls/engines/engine[0]/propeller-pitch"
  <control-setting axis="/controls/engines/engine[0]/boost" value="1.0"/>
  <control-setting axis="/controls/flight/flaps" value="0.0"/>
  <control-setting axis="/controls/gear/gear-down" value="0"/>

<!-- pilot's eyepoint -->
<cockpit x="-4.495" y="0" z="0.689"/>

<fuselage ax="0.0" ay="0.0" az="0.0" bx="-9.9" by="0.0" bz="0.0"
          width="0.94" taper="0.38"/>

stall aoa not available
flap drag not available
<wing x="-3.96" y="0.55" z="-0.60" taper="0.466" incidence="2"
      length="5.16" chord="2.845" sweep="-3.5" dihedral="5" camber="0.1">
  <stall aoa="20" width="4" peak="1.5"/>
  <flap0 start="0.024" end="0.543" lift="1.2" drag="1.8"/>
  <flap1 start="0.543" end="0.945" lift="1.3" drag="1.4"/>
  <control-input axis="/controls/flight/flaps" control="FLAP0"/>
  <control-output control="FLAP0" prop="/surface-positions/flap-pos-norm"/>
  <control-speed control="FLAP0" transition-time="5"/>
  <control-input axis="/controls/flight/aileron" control="FLAP1"
  <control-input axis="/controls/flight/aileron-trim" control="FLAP1"

<hstab x="-8.62" y="0.18" z="0.34" taper="0.639" effectiveness="3.5"
       length="1.834" chord="1.256" sweep="0" incidence="0">
  <stall aoa="20" width="4" peak="1.5"/>
  <flap0 start="0.0" end="1.8" lift="1.65" drag="1.2"/>
  <control-input axis="/controls/flight/elevator" control="FLAP0"/>
  <control-input axis="/controls/flight/elevator-trim" control="FLAP0"/>
  <control-output control="FLAP0"

<!-- rudder has to be able to counteract aileron drag -->
<vstab x="-9.30" y="0" z="-0.37" taper="0.432" effectiveness="3.5"
       length="1.971" chord="2.65" sweep="25"  incidence="-0.58">
  <stall aoa="15" width="4" peak="1.5"/>
  <flap0 start="0" end="1" lift="1.3" drag="1.2"/>
  <control-input axis="/controls/flight/rudder" square="true"
control="FLAP0" invert="true"/>
  <control-input axis="/controls/flight/rudder-trim" control="FLAP0"
  <control-output control="FLAP0" prop="/surface-positions/rudder-pos-norm"
                  min="1" max="-1"/>

<!-- moment calculated using formula submitted by Donald Simon:
      MOI = # of Blades * (8.2*(10^-5))*(D^5), slug-ft^2
      then converted to kg-m^2 and finally square root to kg-m for torque
value -->
<!-- wastegate setting should not apply.  set here so that calculations
would approximate.
      YASim doesn't model gear supercharger.  Have read various figures
(turbo-mul) 4.0 to 5.8 for 
      running the second stage blower.  Fixing this would probably give more
      performance at lower altitude -->
<!-- cruise-rpm roughly estimated from documented gear ratio of 0.479 -->
<propeller x="-1.25" y="0" z="0"
           mass="2000" moment="35"
           eng-power="1590" eng-rpm="3000"
           turbo-mul="4.0" wastegate-mp="61"
           cruise-alt="21400" cruise-power="1370"
           cruise-speed="380" cruise-rpm="2900"
           manual-pitch="true" >
  <actionpt x="-0.75" y="0" z="0"/>
  <control-input axis="/controls/engines/engine[0]/throttle"
  <control-input axis="/controls/engines/engine[0]/starter"
  <control-input axis="/controls/engines/engine[0]/magnetos"
  <control-input axis="/controls/engines/engine[0]/mixture"
  <control-input axis="/controls/engines/engine[0]/propeller-pitch"
                 src0="0" src1="1" dst0="0.40" dst1="0.82"/>
  <control-input axis="/controls/engines/engine[0]/boost" control="BOOST"/>

<!-- Tail wheel -->
<!-- tail wheel "steerable" in p-51d (in stick back locked position it
actually should be limited to 6deg +/-) -->
<gear x="-7.90" y="0" z="-0.96" compression="0.2">
  <control-input axis="/controls/flight/rudder" control="STEER"
                 src0="-1.0" src1="1.0"
                 dst0="0.5" dst1="-0.5"/>

 <!-- left main -->
<gear x="-2.79" y="1.81" z="-2.20" compression="0.4" spring="0.7"
  <control-input axis="/controls/gear/brake-left" control="BRAKE"/>
  <control-input axis="/controls/gear/brake-parking" control="BRAKE"
  <control-input axis="/controls/gear/gear-down" control="EXTEND"/>
  <control-speed control="EXTEND" transition-time="6"/>
  <control-output control="EXTEND" prop="/gear/gear[0]/position-norm"/>

 <!-- right main -->
<gear x="-2.79" y="-1.81" z="-2.20" compression="0.4" spring="0.7"
  <control-input axis="/controls/gear/brake-right" control="BRAKE"/>
  <control-input axis="/controls/gear/brake-parking" control="BRAKE"
  <control-input axis="/controls/gear/gear-down" control="EXTEND"/>
  <control-speed control="EXTEND" transition-time="6"/>
  <control-output control="EXTEND" prop="/gear/gear[1]/position-norm"/>

<!-- Guess on wing tank positions -->
<tank x="-3.50" y="1.0" z="-0.61" capacity="726"/> 
<tank x="-3.50" y="-1.0" z="-0.61" capacity="726"/> 
<tank x="-6.50" y="0" z="0" capacity="671"/> 

<!-- pilot -->
<ballast x="-4.495" y="0" z="0.689" mass="180"/>

<!-- armament -->
<!--  Had too much weight I think...disable until stall speed fixed
<ballast x="-3.20" y="0.7" z="-0.60" mass="800"/> 
<ballast x="-3.20" y="-0.7" z="-0.60" mass="800"/> 

<!-- prop -->
<ballast x="0.1" y="0" z="0.0" mass="200"/>


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