Band Powered Ornithopters
Some of the first successful
ornithopters were powered by rubber band. Their goal was to figure
out another way for people to fly after balloons. Experiments with
rubber-powered ornithopters did help pave the way for Schmid's manned
ornithopters of the 1940s. However, the rubber-band-powered ornithopter
is a fascinating endeavor in its own right, today providing an excellent
educational opportunity for students, as well as great enjoyment
Here are some rubber-powered
ornithopters developed in France during the 1870s. Starting
from the left, Jobert flew this ornithopter powered by a stretched
rubber band turning a crank. In
the following year, he built a biplane ornithopter with the twisted
rubber band motor more common today. The use of four wings was a
clever innovation that reduced the amount of torque needed to flap
the wings. The other ornithopters shown here were built by Alphonse
Penaud and Hureau de Villeneuve, respectively, in 1872.
In 1874, Victor
Tatin devised a more complicated crank mechanism that actively drove
the twisting of the wings. His ornithopter shown here is on exhibit
at the National Air & Space Museum in Washington. Most of the
mechanism was fashioned from bent wire, and it is quite interesting
to examine up close. A similar mechanism was used by Pichancourt
in his toy bird, "l'oiseau mécanique". This was
perhaps the first commercial venture involving ornithopters. Pichancourt
is shown at right with his lovely assistant and the biggest rubber-powered
ornithopter I have ever seen! He must have needed a huge bundle
of rubber to flap those huge wings.
In fact, the
thickness of the rubber band has to increase faster than the scale
of the ornithopter. If you double the wingspan and every other dimension,
the rubber band needs to be more than twice the thickness
of the original. This could be corrected by using some sort of gear
reduction to amplify the torque of the rubber band. However, that
is not so easy to do. Lawrence Hargrave, working in the 1890s, discovered
an easier solution, which many people after him have adopted. To
reduce the torque requirement, he made the flapping wings smaller
and provided a large fixed wing. Two examples are shown below. At
left is one of Hargrave's ornithopters. The center photo shows an
ornithopter built by Alexander Lippisch.
led a group of aviation students during the 1930s. He and his students
built many large ornithopters powered by rubber band and by internal
combustion engines. The science of aeronautics had advanced greatly
since Hargrave. These ornithopers had better airfoils and more efficient
flappers, even though the flapping wings remained comparatively
Erich von Holst
experimented with various bird and dragonfly ornithopter configurations
in the 1930s. His work included experimentation with biplane wing
phasing and hinged outer wing panels. Some of his rubber-powered
ornithopters achieved a very high level of realism, as in the example
shown above. He used pulleys to increase the torque.
ornithopter contests began in the 1930s. A model airplane club called
the Chicago Aeronuts was holding various contests for the indoor
flying of model airplanes. For some extra challenge, they decided
to add ornithopters to the list of events. Ed Lidgard's design shown
here could be built from magazine plans, and many of the rubber-band-powered
ornithopters built over the subsequent decades followed a similar
pattern. Eventually the ornithopter event became part of the national
contest arranged by the Academy of Model Aeronautics.
the 1980s, it was found that biplane ornithopters had a huge advantage
in these indoor flying contests. With monoplane ornithopters, much
energy was lost at the end of each wingstroke, when the crank went
through its "dead center" position and snapped forward
without doing any useful work. With four wings, you can set it up
so one pair of wings is in mid-stroke, maintaining a load on the
crank, while the other pair is at the end of its stroke. The cranks
don't reach dead center at the same time, so the crank doesn't snap
forward, we can harness the energy of its full rotation, and the
smoother flapping motion allows overall weight reduction.
the upstroke of one wing to the downstroke of another, two other
benefits were achieved. First, the upstroke could procede more slowly,
so the wing could continue producing lift during the upstroke. Second,
the lift on that wing would partially offset the force required
for the other wing's downstroke, reducing the overall torque requirement.
modification was to move the stabilizer to the front of the model.
With the flapping wings at the back of the motor stick, the stabilizer
could be positioned directly above the motor stick and in clean
air where it could function more effectively as a lifting surface.
With these innovations,
ornithopter flight times increased from around four minutes, to
the current record of 21 minutes, 44 seconds held by Roy White.
Successful competition models are extremely light-weight and delicate.
Careful adjustments must be made to maximize the flight time without
hitting the ceiling. Perhaps as you refine your ornithopter skills,
you will be able to log some impressive flight times of your own.
ornithopter also offers a range of interesting projects, aside from
duration contests. Shown above: Ken Johnson's lifelike butterfly
model. John White's ornithopter in which the tail moves as well
as the wings. Albert Kempf's dragonfly using a geared rubber band
motor and foam wings.