    ======================================================
    = C-GPTR Ornithopter                                 =
    = for FlightGear with LaRCsim and the UIUC Aeromodel =
    =                                                    =
    = Flight model by:                                   =
    = Michael Selig, et al. (m-selig@uiuc.edu)           =
    = http://m-selig.ae.illinois.edu/apasim/Aircraft-uiuc.html     =
    =                                                    =
    = External model by:                                 =
    = Lee Elliott                                        =
    ======================================================

    To run, try:

    fgfs --aircraft=ornithopter-uiuc

    Files and directory structure required in $FG_ROOT/Aircraft/ to fly the
    model:

    ornithopter-uiuc-set.xml
    ornithopter/Models/C-GPTR-8-4.ac
    ornithopter/Models/ornithopter-8-4-model.xml
    ornithopter/Models/C-GPTR-003.rgb
    ornithopter/Sounds/ornithopter-sound.xml
    UIUC/ornithopter/aircraft.dat
    UIUC/ornithopter/flap.dat
    UIUC/ornithopter/README.orni.html

    These files above come with the FlightGear base package.

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Model description and updates:

    6/3/03: First FGFS release, as outlined in an email to the FlightGear
    mailing list:

    Earlier today I added an ornithopter model to FlightGear.  The model
    simulates the full scale piloted C-GPTR ornithopter designed by Prof
    DeLaurier and his group at the University of Toronto Institute for
    Aerospace Studies (UTIAS).

    A web link detailing the design is here: http://www.ornithopter.net

    Credits for the simulation model go to:

    - Prof DeLaurier and his group for input on several topics ranging
      from aerodynamics to mass data to gear parameters and more

    - Rambod Larijani (UTIAS) for the predicted force and moment data
      produced by the flapping wing (lift, thrust, moment and inertia).
      This data is encapsulated in a 9 MB file (124,000 lines give or take
      a few).  He did this work for his PhD.

    - Theresa Robinson (UTIAS) for writing the 4D interpolation code that
      finds the force/moment data as a function of airspeed, flapping
      frequency, wing phase, and angle of attack.  This effort was part of
      her MS work.

    - Rob Deters (UIUC) for taking Theresa's code and integrating it w/
      FlightGear (LaRCsim/UIUC-Aeromodel)

    - Lee Elliott for making the wonderful 3D model w/ all the trimmings,
      including sponsor logos, stabilator mass balancers, nicely detailed
      front nose gear strut, pilot, twisted wings, and much more.

    - My work involved pulling all of this data together and making sense
      of it.  I also added in aero characteristics and other data to fill
      in the gaps.  An interesting part was working out the model
      animations using Matlab to find the positions for all the flapping
      wing bits, which were then put into the -model.xml file.  The
      illusion of wing twist is created by flapping 5 different wings
      together, but only one is displayed at any given time depending on
      the phase in the flapping cycle.

    - Of course, thanks go the FlightGear group for the wonderful
      infrastructure that made it all work!

    Things to note:

    - The flapping wing data is limited to certain parameter ranges which
      are:

      Angle of Attack: -15 to 15 deg
      Velocity: 5 to 100 ft/s
      Flapping Frequency: 0.8 to 1.25 Hz
      Phase: 0 to 360 deg

      It is easy to pitch up into a high angle of attack regime, in which
      case, the simulation is going to be off.  If the angle of attack or
      velocity goes outside this range, then the last interpolated values
      are held.  The throttle controls the flapping frequency from 0.8 to
      1.25 Hz, so it is not possible to stop the wings.

    - In high speed taxi trails of the real aircraft, one of the
      challenges has been setting up the optimum undercarriage
      configuration and characteristics (spring and damping
      characteristics).  For certain setups, the aircraft will bounce on
      the nose wheel or "hop" on all three wheels.  These pesky
      tendencies, which have led to airframe damage, which can be
      demonstrated by changing the front gear strut length in the
      aircraft.dat file.

    - As the wings flap up and down, the ornithopter center of gravity
      moves in sync like a bird.  This behavior can be sensed from the
      cockpit, and in the HUD the g-load can be seen to vary from ~0.7 to
      ~1.3g.  When viewing the aircraft in chase mode, it's not so easy to
      sense and see this effect because the target spot is centered on the
      screen and held fixed to the center of gravity.  In this view it is
      actually the ground that appears to be moving.

    - The goal of the real bird is to be the first full-scale piloted
      ornithopter.  If it happens this year (and flight attempts are
      planned) ... well then, it only took 100 yrs since the last group was
      trying it.  Clearly separating lift from thrust is the easier route.
      We have the Wright Brothers to thank for that.

    - One other thought, it's worth mentioning that this type of airplane is
      not envisioned as an "ultra-light" for the masses.  The handling
      qualities leave a couple of things to be desired.  In pitch, it has
      massive authority by design.  A full-flying stabilator design can be
      set to trim for any position, which ultimately might not match the
      engineering predictions for this first of type.  So in the design
      there's inherently room for error, and hence the pitch/trim authority
      is conservative.  As for lateral/directional control, it does not have
      much.  But come to think of it neither did the 1903 Wright Flyer.  The
      goal of the C-GPTR ornithopter is to fly once in a straight flight
      down the runway.  The mission is simple: takeoff, fly straight, land.

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    **************************************************
     Prof. Michael S. Selig
     Dept. of Aerospace Engineering
     University of Illinois at Urbana-Champaign
     306 Talbot Laboratory
     104 South Wright Street
     Urbana, IL 61801-2935
     (217) 244-5757 (o), (509) 691-1373 (fax)
     m-selig@uiuc.edu
     http://www.aae.uiuc.edu/m-selig
    **************************************************