Jeff's Lunchbreak: Gamera Human Powered Helicopter

From time to time, I actually read the newsletter from the engineering department from my alma mater, the University of Maryland. The latest had an interesting story. Some students built a human powered helicopter, and managed to get it airborne (around 6" off the ground for just a few seconds, but still, it took off under its own power).

Human powered flight in fixed wing airplanes, if not exactly common place, has been accomplished numerous times by now. The record holder is the MIT Daedalus, which flew 71.5 miles from the island of Crete to the island of Santorini, staying aloft for 3 hours and 54 minutes. A flight that long is more than just a hop, but human powered flight is still pretty demanding. It took an Olympic cyclist to pilot that aircraft, and the structure was so optimized (the plane itself only weighed 69 lbs), that it couldn't handle the winds in Santorini and was blown apart before the pilot landed (he did escape unharmed). Other notable human powered airplanes include Southampton University's Man Powered Aircraft (the first human powered aircraft to take off under its own power in 1961), the Gossamer Condor (which won the first Kremer prize in 1977 by flying a designated course), the Gossamer Albatross (which crossed the English Channel in 1979), and the Musculair 1 (the first human powered aircraft to carry a passenger in 1984).

But if fixed wing airplanes are a challenge, human powered helicopters are next to impossible. I've only heard of 3 that have actually managed to lift off - California Polytechnic State University's Da Vinci III, which flew for 7.1 seconds at a height of around 8" back in 1989, Nihon Aero Student Group's Yuri I, which flew for 24 seconds and reached 27.5" in 1994, and now University of Maryland's Gamera, which flew for 10.8 seconds at around 6". Although certainly impressive technically, none of those results are very awe inspiring. It just goes to show how thin air really is, and why flight is such a challenge that humans weren't able to conquer until last century.

There's an Official Gamera Website where you can see pictures of the aircraft and read more about it. There's also a Wikipedia entry. To get a better idea of the scale of the aircraft, you really should watch the video of it flying (the flight starts at around 3 minutes into the video).

From the above websites, I gathered the following data. The empty weight of the aircraft was only 101 lbs, and with the pilot included the gross weight was only 208 lbs. The helicopter had 4 rotors, each with a 42' diameter.

A metric that rotorcraft engineers like to use is disc loading. You divide the weight of the aircraft by the disc area of the rotors. This is all to do with efficiency - the lower the disc loading, the more efficient the rotor can be. When you calculate disc loading for this aircraft, you get 0.0375 lb/ft². That's incredibly low. For comparison, the Robinson R-22, a lightweight helicopter with a relatively low disc loading itself, has a gross weight of 1370 lbs and a rotor diameter of 25'-2", giving a disc loading of 2.75 lb/ft². Gamera's disc loading is more than 70x lower than the R-22's! For another comparison, the V-22 Osprey has a relatively high disc loading of 26.7 lb/ft² (part of the reason why it will never do as good as a pure helicopter in hover), 712x higher than the Gamera.

I can't help but put up a picture of da Vinci's helicopter concept here. Everyone knows that his concept wouldn't work, but I don't think most people realize just how far from a workable design it really is. You can't be too hard on da Vinci given the state of aerodynamic knowledge in his time, but compare this to the Gamera.

da Vinci Helicopter Concept

On a less technical note, Maryland's human powered helicopter was the first to be powered by a woman, 24 year old biology student, Judy Wexler. I wonder if they chose a woman just to be the first, or if it was more to do with improved power to weight ratio (she only weighs 107 lbs).

So, my hat's off to the students at the University of Maryland who built this aircraft. It was an incredible technical accomplishment. I gather that they're going to attempt more flights and try to claim the Sikorsky Prize. I wish them luck.

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