David Megginson wrote:
> I'm controlling the (simulated) bo105 helicopter much better by
> picking an airspeed (say, 10 kt when maneuvering for a landing) and
> holding it as closely as possible with the cyclic.

Out of curiosity, how do pilots do this in real helicopters?  I
wouldn't think a traditional ASI would work very well at 10 kts...

> Even as slow as 10 kt, the bo105 barely needs any input from the
> anti-torque pedals.  How realistic is this?  It certainly makes flying
> easy.

Here's a candidate solution for that problem (I didn't test it).  It's
not that the aero force is too high, it's that the moment of inertia
of the helicopter is too low.  I see the following in the YASim
definition:

  <airplane mass="2813">
  ...
  <ballast x="-3.0" y="-.0" z="1" mass="1820"/>

So 2/3 of the craft's weight is modeled as a point mass at a location
that, one presumes, is right under the rotor.  Point masses don't
oppose torques very well. :)

Really, what's needed here is a "shell" configuration, where several
point masses are placed on the edge of the fuselage where the weight
is concentrated.  YASim's built-in fuselage and wing declarations
models the airframe as strings of point masses.  This works OK for
long-aspect things like (heh) wings and fuselages.  It's not going to
produce good results for a spheroidal helicopter fuselage.

It wouldn't be too hard to write an "ellipsoid" declaration for
low-aspect fuselages, I guess.  But a quick hack would be to split out
that ballast point into, say, a square of masses of the right size and
centered on the c.g. (the c.g. is really easy to find on a helicopter,
BTW: by design, it has to lie very close to axis of the rotor).

Andy


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