Ornithopters: Making Maximally-Efficient Man-Made Wings
Researchers have crunched the numbers to develop extremely efficient wings and fins that could help future flying and swimming drones.
Fixed-wing aircraft have been all the rage the past century or so but such winged flying machines are hardly the only way to do it. Rotary aircraft like helicopters are amazing machines as well and fill a much needed niche that even many VTOL (vertical take-off and landing) craft cannot. The first attempts at winged flight are lost in the contrails of time but there were surely were many misguided attempts over the centuries and even millennia. There had to be some caveman named Grog or Atouk who died jumping out of a tree feverishly flapping his arms in an attempt to fly (hopefully before he added his genes to our gene-pool).
Such attempts make sense since the efficacy of such flapping is literally in front of our noses with birds, insects, and bats constantly flying around. Early serious attempts at mechanized flight therefore often employed a flapping wing approach, all of which failed miserably and hilariously. Ultimately though, the biggest downside to flapping flight would have to be its inefficiency, especially while hovering or at slow speeds. The rapid flapping required to put a person in the air is just too difficult and complex, especially in the low-tech era of pre-early human flight. Even a lightweight pigeon in flight needs about 4 times the power that an equivalent helicopter would need. Those wonderful humming birds pay a stiff price for their amazing aerial acrobatics. They expend more relative energy than any mammal (10 times that of humans). This leaves them constantly on the verge of starvation and understandably perpetually ravenous. Spinning propellers and rigid wings clearly have the edge over nature which is kind of unusual since leveraging the work evolution has done (bio-mimicry) has been such a boon to high-tech product design. I guess we can forgive evolution since evolving biological structures that spin like propellers might be nigh impossible.
This hasn’t stopped researchers like Professor of Mathematics Nick Moore at Florida State University from publishing a new paper about this in the academic journal Physics of Fluids. His approach was to ask something like…If you had to design a wing or fin from scratch, what properties would it have? Since natural wings are fairly flexible, Moore wanted to also find out what the optimal flexibility would be. He said:
“We want to understand how wings and fins perform differently when they are made of flexible material…Sometimes, flexibility can really boost performance, but too much flexibility can be a bad thing. We want to find the happy medium.”
These big-picture ornithopter investigations have historically received very little attention. Moore guesses it may be because the work involved requires complex math that would normally be run on a supercomputer. To make his work accessible and replicable by a wider audience, he spent a great deal of time simplifying the mathematics so that calculations could be run on a simple laptop. His results showed that if the wing were more flexible at the leading edge and less so towards the back, it could increase performance by 36 percent compared to wings with a uniform flexibility. Moore believes his model not only can help researchers understand the biological underpinning of winged flight, he hopes this model could someday be used by researchers to improve current designs or even to create maximally efficient wings or fins from scratch.
The potential applications for such efficient ornithopter technology is quite interesting. The primary research is focusing on small very efficient vehicles like drones rather than larger vehicles. The most fascinating are drones that take the shape of common flying creatures, primarily insects. Using these diminutive flappers, search and rescue after natural disasters would be greatly facilitated especially where there’s a need to fly or crawl through tiny nooks and crannies of fallen debris. Discrete surveillance is another no brainer application. Being the literal equivalent of a “fly on the wall” would certainly be an intriguing if scary form of covert intelligence gathering. I often think of the ultimate form of this type of surveillance tech using dust-mote sized camera and audio equipment. Quintillions could be released over an area subject to prevailing winds or perhaps minute wings to direct motion. Orwell would be quite proud. Of course the scientific use of such devices would be a game changer in terms of studying the earth’s surface in detail or taking atmospheric measurements and improving weather prediction to a degree permitted by the chaos inherent in weather systems.
Another way cool possibility for this technology is an improvement of a type of helicopter that is a fusion of a rotary aircraft and an ornithopter. Developed in 2002 at Delft University of Technology in The Netherlands, this has been referred to as an OrniCopter and it has two key differences. Primarily, the blades not only rotate around as usual, they flap up and down at the same time (this is called active flapping). The range of flapping is not a lot; perhaps a few feet or more at the tips for a large-ish ornicopter but the benefit is quite extraordinary because it obviates the need for a tail rotor. This tail rotor is absolutely critical for conventional helicopters (at less than cruising speed with one rotor) because of its anti-torque properties. As the main rotor spins, the fuselage of the copter naturally tries to counteract that movement by spinning in the opposite direction. For a Dizzy Machine that would be perfect but for almost anything else, it’s a deal breaker. This tail rotor stops this spin and also allows for precise control of the orientation of the helicopter. Despite these benefits, tail rotors have always been seen as a necessary evil for the following reasons:
- It’s a complicated mechanism.
- It saps some of the engine power to operate.
- It’s an especially vulnerable part of the helicopter. How many movies show disabled copters due to tail rotor damage?
- It’s notoriously terrible in high wind situations.
The flapping and rotating blades (which I will now call FlapTating) of an OrniCopter counterintuitively do away with the need of a tail rotor. This is basically because the rotors in this design do not generate torque so there is no need for an anti-torque tail rotor. The flaptating blades provide both lift and propulsion. Increasing or decreasing the flapping is used to change the direction of the fuselage and changing the angle of the blades provides movement similar to a conventional helicopter. If OrniCopters ever find a solid niche in the our suite of flying machines, Moore’s model for developing ultra-efficient flapping wings may just provide the extra efficiency that such a machine needs.
Check out these other cool ways to remove a tail rotor
Image credits: Douglas Olivier