Tinisn Tor - View Site

DESIGN AND BUILD AN RC BIRD MDDEL
A little more sheeting and a couple
of balsa blocks carved to shape,
and you'll almost be finished.
CONTROL
Two methods for pitch control
have been tried—a standard
elevator at the rear of the tail
and the single-piece tail hinged
at the wing's trailing edge. The
elevator at the rear is the most
effective.
Because of the large adverse yaw associated
with ailerons, they don't work well
when there is no vertical tail. A rolling tail
(horizontal tail that tilts
around a longitudinal
axis for controlling turns)
works OK depending on
the CG location but is not
very powerful. If used
with a pitch-stable air-
Here's the completed fuselage ready to cover with
MonoKote. To make it easier to finish, I simply painted
the head and beak.
plane (forward CG), the model flies well,
but the control action is opposite to the
way birds really fly (the model will turn in
the same direction as the tilted tail, but
During the past 11 years, many encounters have occurred between these models and real birds.
Unfortunately, these encounters are usually spontaneous and take place at a fairly high altitude, so I
have no photographic evidence of them.
There are lots of ravens around here; they are gregarious birds, and quite inquisitive. The models
circle easily and climb with the real birds in thermals. Often, one or two ravens fly formation with the
model and follow it as it circles in a thermal (or, just as often, I follow them). Occasionally, one will
come in quite close. Because the wing loadings of the models are lighter than their real counterparts,
the models can fly more slowly. Sometimes, I slow the model to near-stall and then watch as the poor
birds stall or flap off to one side.
One warm, still day, I thermalled a Raven model with about 25 real ravens for about half an hour. The
entire gaggle got so high that I had trouble distinguishing the model from the real birds. I made step
inputs in roll control, and then flew the bird that rolled abruptly. From my notes on the day of the flight:
"Finally I got too high to see well, so I put in full forward trim and flew straight. One bird followed,
matching the model's speed and descent rate, and joined up in formation. I pulled up into a loop. He
watched, then joined up again. I went into a full-up, full-left spiral for about 5 turns to lose altitude,
then recovered. The raven pulled his wings in and did about 3 half-rolls, then some other maneuvers,
then joined up again. I continued trying to descend, and eventually he left.
"The fixed-geometry, under-cambered wing of the models is no match for the refined, variablegeometry
wing of the real birds in straight, high-speed flight. The model quickly drops below and
behind. On several occasions, ravens have followed the model down to about 20 feet altitude, and
then circled overhead squawking loudly as the model lands. One raven landed nearby and walked all
the way around the model (it was probably puzzled by my belly landing}."
I have also thermalled the Turkey Vulture model with real turkey vultures. The appearance and climb
performance were similar, but real vultures aren't as friendly as ravens; they completely ignored the
model.
/ used a 0.063-inch-thick piece of aluminum for
my wing dihedral brace. Note that the fulldepth
spars slide into place in the slots cut
into the brace.
The wing is built with a front and rear portion
glued to the main spar. Here you see the wing root
and the slots in the ribs for the aluminum brace.
no one will notice!). Drag flaps on the
lower wing surface (or spoilers on the
upper surface) also work well for initiating
turns, but they aren't very efficient or
realistic. Since they rely on dihedral effect
to control turns, they often require larger
wing dihedral than that observed on a
real bird.
Wingtip ailerons (feathers) are the most
bird-like roll-control method. They are
very sensitive to the initial incidence setting
of the two ailerons. I use a bias control
through the throttle channel to help
locate the proper angle in flight. For land
birds, use the forward three feathers as a
single aileron surface that rotates around
a spanwise axis (detailed on the plan). For
sea birds, use the outer 22 percent of the
semi-span as an aileron, rotating around a
I've had the most fun with hawks. They will dive at any of the models (raven, seagull, or turkey vulture) from out of nowhere. They have never touched or damaged a model but
usually go screaming by with their wings folded. I once watched a hawk regain altitude
after the attack and then begin circling off to the side. He stayed there until I did something
abnormal, such as a stall, with the model. He then folded his wings and came right
at the model, aborting at the last minute. I triggered three attacks this way. Apparently,
the hawks thought they were watching a wounded or sick bird. Recently, a hawk zoomed in
and established a position directly above the seagull model just a few inches away. He
stayed in that position for about 15 seconds as I made turns with the model. Eventually,
he flew away. I expected to find claw marks on the model but saw no evidence of any contact. Hawk attacks on the Turkey Vulture model are more cautious—usually from above
and directly behind. They fly in trail with the model for awhile until they are satisfied that I
it is not a wounded, easy target. I hope to eventually install one of the new, tiny video cameras in a model to document
some of these encounters-up close and personal.
90 MODEL AIRPLANE NEWS
'ere, the two wing panels have been joined. Note the reflex
hape of the airfoil. The wingtip aileron feathers and the
'ding-edge sheeting still have to be installed.