Saturday, March 11, 2006

Real Life AT

From time to time, I plan to post some photos of real-life Adventure Team vehicles.

This very nice gyrocopter was photographed by my wife in Tillamook, Oregon a few years back. Not only is it an interesting little aircraft, somebody (consciously or not) has already painted it AT yellow!

For those who don't know, a gyrocopter, or gyroplane as they're sometimes called, is not the same as a helicopter. A helicopter has a powered rotor (or two) that is powered to lift and propel the vehicle. (There are also "compound" helicopters which may add auxiliary propulsion from propellers or jet engines, and sometimes auxiliary lift from small wings, for better high-speed performance, but these are rare, and I don't think any have seen actual service beyond experimental programs.)

A gyrocopter has a normally unpowered rotor. It simply turns in the airflow like a windmill, and in the process generates lift in the same way a conventional wing does as wind flows over it. The propulsion usually comes from a conventional airplane motor with a propeller. To get its rotor turning fast enough for flight, a simple gyrocopter usually will simply turn into the wind and taxi until the rotor is turning fast enough.

Unlike a helicopter, a gyrocopter generally can't take off vertically (though with a good head-wind, some can come close), but they can land with minimal runway, and fly slow. And they can land almost vertically, though it's a rapid decent with no hovering.

That's another rule for gyrocopters that doesn't apply to helicopters. No hovering.

So why would anybody want one? Well, they're very simple and rugged. They cost a tiny fraction of what a helicopter does, are far easier to maintain, and can do some of the same jobs (scouting, observation, aerial photography, access to short, rugged fields) almost as well.

There's one other thing that I've saved until now, just to avoid confusing the issue. Some gyrocopters cheat a bit on the vertical take-off business. They use a power system (either a separate gasoline motor, or a drive shaft connected to the propulsion motor with a clutch) to power the rotor up to flying speed. Then the motor is disengaged, the rotors are quickly turned to "bite" the air, the throttle on the propulsion motor is gunned, and the gyrocopter uses the stored energy in the rotors (which act like a bit flywheel) and "hop" into the air. In some designs, all this stuff is coordinated through the operation of one lever. The pilot waits till the rotors hit proper speed, activates the lever, and then fly for all they're worth.

You may be asking, if there's a system to drive the rotor with a motor, why not keep it connected in the air? The answer is: torque. Real helicopters (single rotor ones, anyway) have a tail rotor that counters torque. Without it, as the helicopter tried to spin its rotor, torque would cause the rotor to try and turn the body of the helicopter, until you're quickly flying a human Cuisinart and crash. As long as the body of the helicopter (or qyrocopter with powered rotor) is sitting firmly on the ground, torque isn't much of an issue, but the instant it leaves the ground torque takes over.

Why not add a tail-rotor to the gyrocopter? Because then it becomes a bad helicopter, and by the time you add all the things it needs to become a good helicopter, it's just as expensive, complex, and hard to maintain as the real thing. In fact, it is the real thing.

One last reason that the Adventure Team should have a gyrocopter is that it has a solid place in the Adventure culture that spawned it. Gyrocopters were all over TV in the 60s. Jacques Cousteau used one on occasion in filming his TV specials, and his son Phillipe was badly injured when one crashed on Easter Island. James Bond use a rocket firing gyrocopter in You Only Live Twice. And of course, there's a late comer in the form of Mad Max's "Gyro-Pilot."

So, Joe never had his gyrocopter, but it seems reasonable that he should have. Why not? Perhaps the AT was so well financed he never had to cut corners. Perhaps AT logistics were so good that maintaining and supporting actual helicopters in isolated jungles and deserts was never a problem. So look on this little craft as a missed opportunity for the AT.

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