======================================================
= C-GPTR Ornithopter =
= for FlightGear with LaRCsim and the UIUC Aeromodel =
= =
= Flight model by: =
= Michael Selig, et al. (m-selig@uiuc.edu) =
= http://www.aae.uiuc.edu/m-selig/apasim.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
**************************************************