Man Flies Like Bird! Film at 11!

I wrote five years ago about one of the remarkable things that I found on YouTube: the use of wingsuits in sky diving and base jumping. A wingsuit consists basically of some fabric membranes stretched between arms and legs and between the legs. It increases the area and improves the shape of the jumper’s planform, making him or her look a bit like a flying squirrel. Some of the most startling daredevil stunts on YouTube — and there are many — involve guys in wingsuits barreling down mountainsides, seemingly inches away from some very abrasive-looking rocks. A good wingsuit can attain a glide ratio of 2:1 or so; in 2010 an Army jumper glided 11.5 miles after jumping out of a C-17 at FL 320.

Normally, wingsuit jumps end with a parachute deployment. But the last time I looked, a fellow was trying to figure out how to flare and land without a chute, just using the lifting capacity of the wingsuit. He may have given up by now. I doubt it is possible, but you could certainly get killed trying. Perhaps one could calculate a flare factor — the product of lift-drag ratio and wing loading, with suitable exponents, required to permit a given touchdown speed — in order to know what kind of wing would be required to allow a man to touch down at, say, 25 feet per second with a survivable vertical velocity. Hang gliders do it all the time, but a hang glider is a far cry from a wingsuit.

Speaking of flaring, a magnificent super-slo-mo video of an owl flaring to pounce upon a bait can — and must — be seen below. It certainly makes human attempts at “variable geometry” appear contemptible.

Another surprising example of airplane-as-clothing is Swiss pilot Yves Rossy’s jet-powered strap-on wing. Rossy has used several different wings, all more or less conventional-appearing, of about eight-foot span, somewhat swept, of carbon-fiber construction, with four model-airplane jet engines slung underneath them.

Each engine weighs five pounds, produces 50 pounds of thrust and burns a pound and a half of kerosene per minute at full throttle. The wing has ailerons, but there is no empennage, and I imagine pitch must be controlled with elevons or small fore-and-aft weight shifts. A former Swiss Air Force fighter pilot who now flies for Swiss International Air Lines, Rossy, 52, jumps out of an airplane or helicopter or balloon with the wing on his back, and is able to fly level and maneuver for some time. There is a YouTube video of him racing about among the Swiss Alps, in formation with a couple of jets, and another of him crossing the Grand Canyon. He crossed the English Channel but failed because of weather to make it across the much narrower Strait of Gibraltar, ending up in the drink.

Startling stunts can get millions of hits on YouTube. A couple of years ago there was the airplane that appeared to lose a wing during an aerobatic routine but managed to land nonetheless. This was a rather obvious fake, but it still fooled a great many people.

A less obvious fake that recently excited millions is the purported achievement of one Jarno Smeets, a Dutch engineer presented, in a series of videos, as having constructed a wing that allows him to rise, flapping, into the air. It is not clear to me that Jarno Smeets actually exists; he may just be a persona of a filmmaker named Floris Kaayk, but that is unimportant, since what is interesting to me is the project’s technical plausibility, or lack of it.

It is well established that human strength and endurance are sufficient to get an airplane aloft and keep it aloft for a long enough period to fly a considerable distance. The record, unlikely ever to be broken, is held by Kanellos Kanellopoulos, an Olympic cyclist who, in 1988, covered 71.5 miles in three hours and 54 sweaty minutes in the MIT-built Daedalus 88. Perhaps in the first sentence of this paragraph the word human should be replaced with superhuman.

It is also well established that, even though birds move their wings in complex and nuanced ways, simplified flapping-wing machines can be built and will fly. There are plenty of flapping-wing toys on the market.

Smeets’ ornithopter does not rely on human strength for propulsion. It uses several small electric motors and some lithium polymer batteries. What is ingenious about it is the way in which the flapping is controlled. He uses, or rather claims to use, an electronic motion-control system like those in Wii and Kinect consumer games. Sensors detect the movements of Smeets’ arms and reproduce those motions in the wings. Thus, Smeets can flap with very little effort while the batteries and motors do the heavy lifting.

The climactic video in a 14-segment series on this project shows the birdman running along a large open space in a park, then rising into the air and flapping along for a little while before gliding down to a surprisingly smooth and skillful landing. The video is of rather poor quality — that is part of The Blair Witch Project-style pseudo-realism — but the flying motion looks plausible enough if you aren’t disturbed by the fact that the wings never seem to load up: They don’t bend upward, and the fabric between the ribs does not bulge as you would expect it to if it were supporting a good deal of weight. There is also some question about why this contraption would be longitudinally stable or even controllable. But despite these faults, the appearance of flight is quite persuasive.

The filmmaker said that he was surprised that so many people were taken in; to him the video was obviously fake. But people will be taken in by almost any hoax, no matter how transparent it may appear to the perpetrator; the desire to believe creates its own momentum and continues to roll along so long as it does not encounter a barrier of certain knowledge. When a magician saws a woman in half, you do not expect to see a heap of blood and entrails on the floor. However persuasive the illusion, you know that you are not assisting at a murder. But with something like flight, the boundaries of the plausible are less distinct. And Smeets’ concept was, in fact, quite plausible.

So why was it too good to be true?

The basic problem is getting into the air. A running man encumbered by a large wing will be hard-pressed to reach 15 miles an hour. At this speed the dynamic pressure of air is around three-quarters of a pound per square foot. Assuming that the total weight of man, wing, motors and batteries is 200 pounds, the area of the wing would have to be on the order of 300 square feet just to get airborne in the first place, and twice that if the runner reaches only 10 mph instead of 15.

The area of Smeets’ wing is only around 100 square feet, and so there is simply no way it could support a man at running speed. But on a sufficiently large scale the idea of a powered ornithopter with electro-imitative motion control and artificial stability is not implausible. In fact, now that it has been broached I would not be surprised to see it done.

While perusing the various Kaayk/Smeets videos I came upon a couple of a man-powered ornithopter called Sunbird built by students at the University of Toronto. It has the 100-foot wingspan typical of human-powered craft — induced drag is the big problem at very low airspeeds, and pure wingspan is the solution — and this enormous wing flapping is something to behold. Sunbird appears just able to maintain height after being towed into the air by a car. There are also some human-powered helicopters. The record for hovering is 19.46 seconds a few inches above the ground, set by a gigantic four-rotor Japanese thing in 1994.

*Yawn*

That’s enough for one YouTube session. I guess it’s time for bed.