I wrote: > Jim Wilson wrote: > > 4) Fixed rpm/power numbers under the prop tags. They need to be > > scaled back according to the gear ratio. Someone with a better > > understanding of mech engineering might be able to explain why the > > BHP on the prop shaft is reduced by a factor of 0.35 when that's > > the gear ratio, or maybe that is wrong and there is something going > > on in the YASim calcs. > > Yeah, that's a bug. Power is power. If the prop wants to sync X > horsepower at Y RPM, then the engine ought to be defined as producing > the same X hp at Y/gear-ratio RPM. > > Let me take a look.
Indeed, there was yet another spot I missed when adding the gear-ratio stuff. The torque conversion from "propeller side" to "engine side" worked correctly during solution, but not at runtime. This is fixed now, so you should be able to use real numbers in your propeller tags. FWIW, I also took the opportunity to re-visit the P-51D configuration that I promised (long ago) to hack at. Attached is a version that should perform more realistically. The biggest change is that I reduced the cruise speed (360->310) to represent what a typical aircraft "should" be able to achieve with 50% fuel. The resulting aircraft is a *lot* less slick (it produces almost three times as much parasite drag), and should perform more realistically at low altitudes. You should still be able to hit the textbook numbers with a stripped aircraft and empty tanks. Also, there is a syntax fix: the <piston-engine> tag should be a subtag of the <propeller> tag. Putting it immediately after the propeller definition works only due to a lucky interaction with the way the parser stores its "current object" pointer. It doesn't clear the value when it sees </propeller>, so you can get away with putting the engine at any point in the file before the next tag that sets a current object. I haven't flown this enough to say whether it's worth checking in. Let me know if anyone tries it and likes it. Andy
<?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: http://www.hq.nasa.gov/office/pao/History/SP-468/app-a2.htm http://www.olympicflightmuseum.com/aircraft_gallery/p51d_mustang.htm http://www.btinternet.com/~lee_mail/P51.html http://www.sprucegoose.org/pdfs/planes/P51Mustang.pdf Weight and balance: http://www.p51.wjackparker.com/P51_Additional_reference_material/x_maintenance.htm http://www.nzfpm.co.nz/aircraft/p51d.htm http://www.wpafb.af.mil/museum/engines/eng33.htm Three-view: http://members.optushome.com.au/gjmustang/docs/3-View.html (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="7125"> <!-- Approach configuration --> <approach speed="87" aoa="13"> <control-setting axis="/controls/engines/engine[0]/throttle" value="0.3"/> <control-setting axis="/controls/engines/engine[0]/mixture" value="1.0"/> <control-setting axis="/controls/engines/engine[0]/propeller-pitch" value="0.5"/> <control-setting axis="/controls/flight/flaps" value="1.0"/> <control-setting axis="/controls/gear/gear-down" value="1"/> </approach> <!-- Cruise configuration --> <!-- 360ktas is often quoted as the top speed for a mustang, but that - is almost certainly for a stripped aircraft. In this cruise - condition, we are carrying about 1100 lbs of fuel that the - record-setting aircraft was (probably) not. Since drag goes - (very roughly) as the square of both weight and speed, a 14% - increase in weight should come out to a proportional reduction - in maximum speed, thus this value. This results in an aircraft - that is much less "slippery" in descents. --> <cruise speed="310" alt="25000"> <control-setting axis="/controls/engines/engine[0]/throttle" value="1.00"/> <control-setting axis="/controls/engines/engine[0]/mixture" value="0.65"/> <control-setting axis="/controls/engines/engine[0]/propeller-pitch" value="1.0"/> <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"/> </cruise> <!-- 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="1.0" length="5.16" chord="2.845" sweep="-3.5" dihedral="5" camber="0.1"> <stall aoa="16" 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" split="true"/> <control-input axis="/controls/flight/aileron-trim" control="FLAP1" split="true"/> </wing> <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="2"> <stall aoa="15" 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" prop="/surface-positions/elevator-pos-norm"/> </hstab> <!-- 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" invert="true"/> <control-output control="FLAP0" prop="/surface-positions/rudder-pos-norm" min="1" max="-1"/> </vstab> <!-- 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 --> <!-- FIXME: 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. The second stage should boost at 17000ft. --> <!-- cruise-rpm roughly estimated from documented gear ratio of 0.479 --> <!-- Give the "book" numbers a hand by tuning the propeller for its best performance at the 360ktas maximum speed. -Andy --> <propeller x="-0.75" y="0" z="0" radius="1.75" mass="1690" moment="94.5" cruise-alt="25000" cruise-power="1695" cruise-speed="360" cruise-rpm="1437" gear-ratio="0.479" min-rpm="766" max-rpm="1437" > <actionpt x="-1.25" y="0" z="0"/> <control-input axis="/controls/engines/engine[0]/propeller-pitch" control="ADVANCE" /> <!-- Similarly, favor high performance by guessing at the high end of the engine boost values. --> <piston-engine eng-power="1695" eng-rpm="3000" turbo-mul="5.5" wastegate-mp="61" > <control-input axis="/controls/engines/engine[0]/throttle" control="THROTTLE"/> <control-input axis="/controls/engines/engine[0]/starter" control="STARTER"/> <control-input axis="/controls/engines/engine[0]/magnetos" control="MAGNETOS"/> <control-input axis="/controls/engines/engine[0]/mixture" control="MIXTURE"/> <control-input axis="/controls/engines/engine[0]/boost" control="BOOST"/> </piston-engine> </propeller> <!-- 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" square="true" src0="-1.0" src1="1.0" dst0="0.5" dst1="-0.5"/> </gear> <!-- left main --> <gear x="-2.79" y="1.81" z="-2.20" compression="0.4" spring="0.7" damp="3.0"> <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-speed control="EXTEND" transition-time="6"/> <control-output control="EXTEND" prop="/gear/gear[0]/position-norm"/> </gear> <!-- right main --> <gear x="-2.79" y="-1.81" z="-2.20" compression="0.4" spring="0.7" damp="3.0"> <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-speed control="EXTEND" transition-time="6"/> <control-output control="EXTEND" prop="/gear/gear[1]/position-norm"/> </gear> <!-- 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"/> --> </airplane>
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