On Sunday, June 19, 2011 09:58:48 AM Bertrand Coconnier wrote:
> 2011/6/19 Ron Jensen <w...@jentronics.com>:
> > On Saturday 18 June 2011 21:00:41 Jon S. Berndt wrote:
> >> Here's an example from Hal's P-51D Mustang. This is from an old version,
> >> so it may have changed by now, but it illustrates the approach. In the
> >> <aerodynamics> section of the config file - but outside of any <axis>
> >> element - is this definition of qbar due to propwash:
> >>
> >> [Note: <v> is shorthand for "value", and <p> is shorthand for
> >> "property".]
> >>
> >> <function name="aero/thrust-qbar_psf">
> >> <product>
> >> <v> 0.5 </v>
> >> <p> atmosphere/rho-slugs_ft3 </p>
> >> <pow>
> >> <sum>
> >> <p> velocities/u-aero-fps </p>
> >> <product>
> >> <p> propulsion/engine/prop-induced-velocity_fps </p>
> >> <v> 2.0 </v>
> >> </product>
> >> </sum>
> >> <v> 2.0 </v>
> >> </pow>
> >> </product>
> >> </function>
> >
> > I recently added this function to the A6M2 Zero. I placed it on CYdr
> > (rudder yaw) and dCLdf (flap lift delta) as well as CMde. It makes the
> > plane fly much, much better during the initial takeoff roll. It probably
> > should be used with CMdf (pitch due to flaps) as well.
> >
> > But why are you multiplying propulsion/engine/prop-induced-velocity_fps
> > by 2?
>
> The total velocity of the air flow in the far slipstream is V+2*w
> where V is the velocity of the airplane and w is the induced velocity
> as computed by the momentum theory. See the following discussion in
> the JSBSim mailing list :
>
> http://sourceforge.net/mailarchive/forum.php?thread_name=201004181833.32417
> .ghmalau%40gmail.com&forum_name=jsbsim-devel
>
> Bertrand.
I just added this to the P-51D this morning. I have this setup so that the
propwash affects Roll_moment_due_to_rudder Cldr, Pitch_moment_due_to_flaps
Cmflap, Delta_Lift_due_to_flaps dCLflap, Lift_due_to_Elevator_Deflection CLde,
Pitch_moment_due_to_gear Cmgear, Pitch_moment_due_to_elevator Cmde and
Pitch_moment_due_to_alpha_horiz_tail Cmht. It had a significant impact on low
speed high power handling. The rudder has authority much earlier during take
off and the tail lifts in a very natural way during the take off run. Over
all
these changes made take offs easier and more natural feeling. This also made
it less likely to ground loop during the engine runup. This is an easy
enhancement to do and it appears to improve ground handling and take off
significantly.
I have these changes checked in to my fgdata GIT clone if anyone wants to try
them.
Hal
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