Insects Can't Fly

"The fundamental laws of aero-
nautics, dynamics, and what ever
must soon convince the unbeliever
that bees were built to such a model,
they scarcely could do more than waddle.

The ratio of their body weight
to wing-span, he could demonstrate,
prelude takeoff, much less flight."
Sheenagh Pugh, 'Bumblebees and the Scientific Method'

    Flying insects are a miracle of robotics. They can turn left and right, go up and down, hover and avoid obstacles with ease with 'less computational power than a toaster', according to Rafal Zbikowski. Zbikowski is an engineer at Cranfield University working on flapping flight. For a long time, conventional theories of flight could not account for the amount of lift generated by insects. The equation used says that such creatures should not be able to fly. But in recent studies, biologists have began to unravel the complexity of insect flight and brought the science to the point where engineers can contemplate making flying vehicles that can flap their wings.
    In 1996, the US Defense Advanced Research Projects Agency (Darpa) initiated this research with $35 million to develop 'micro aerial vehicles (MAVs)'. The target was to create a flying object that could fit in a 15 cm sphere, weigh no more than 140 g, fly up to 2 hours and have a range of 10 km, operate in winds up to 50 kph, and be able to manoeuvre without a remote pilot. Zbikowski is working on a machine at the 15 cm limit while Ron Fearing is working on the much smaller scale of the blowfly.
    When you look at a wing of an airplane and how it works, it is much different than an insect. An airplane's wings move horizontal through the air to generate enough power to lift it. To do this, the upper surface off the wing is rounded and then flattens toward the rear, almost like a tear drop. The airflow has to split to pass over the wing which produces lift. If you imagine the air as visible particles then you can see the air particles as streamlines. The streamlines are symmetrical before it hits the wing but once the air hits the wings then they become asymmetrical. The streamlines are being pushed closer together. The only way to the air to move pass the wing without compression is to move faster than the air below the wing. Thus, the pressure above the wing is lower than the pressure below and the result is an upward pressure on the wing: lift, as shown above.
There are differences in the flight of an airplane and the flight of an insect. The main battle for a plane is gravity. For insects, gravity is less important. It is hard for engineers to design a machine to mimic the flight pattern of a fly because they use wheels, axles, ball bearing, and linkages while nature uses stretchy muscles and bendy hinges. It's challenging to find materials that can flex 200 times a second without breaking. It is also challenging to match their three basic movement (up and down, sweeping, and twisting).
    In 1996, Charlie Ellington had a breakthrough in his studies of insect flight. Using stereophotography, Ellington captured the flow of smoke around a tethered hawkmoth. He says he saw vortexes (whirls of air like miniature tornadoes) form along the front of the wing on the down stroke to create additional  lift. Ellington build a mechanical flapper about 10 times bigger than the hawkmoth to demonstrate his technique. This work was a great inspiration on the MAV movement but it had a lot of biomechanic skepticism.
    Ron Fearing began to work on an MAV and his version is known as the Micromechanical Flying Insect (MIF). The model is a blowfish which has a wingspan of 25 mm and flaps 150 times a second.

There is no attempt to copy the fly's exact appearance, he also is working making the machine out of sheets of carbon fibre to make it lighter than an actual fly.
    Scientists stress that a fly does not have to think about how to move it's wings, they just do it. Just like humans don't think about throwing an object, they just do it. A fly's sensory system is highly developed. They are able to process 150-200 pictures per second. This is an important aspect of how a fly can fly and this is why they are so hard to catch. The last thing that scientists need to apply to a robotic is this sensory system. They say that a sensory-rich feedback to control system will be the key to controlling MAVs.