Even before I saw Little Nellie in You Only LIve Twice in 1967, I was in love with gyrocopters.
They were so ugly, they were cute, they were much simpler than a helicopter, could get off the ground in just a few feet, and could often land on a dime. If the engine quit, you could safely autorotate to the ground. I can’t tell you how many of my childroom fantasies included traipsing around the Texas Gulf Coast in one of those. Ah, how naive we can be. They looked so simple. So, in other words, I was in love with the idea of gyrocopters, but didn’t have a clue about their problems.
Gyrocopters have been subject to one main problem ever since they were invented, something called Pilot Induced Oscilation, or, PIO. A lot of people skid off the road in their cars due to PIO, too, so it’s not totally the problem of gyro’s. Basically, if you oversteer, you have a tendency, of course, to steer back the opposite way. But if you oversteer the opposite way, then you have to steer back again the other way. Each time you try to correct, you simply make it worse, but in the opposite direction. This oscillation isn’t caused by the machine, but by the person operating it. Consequently, designing a gyrocopter (or a car, for that matter) that makes it difficult to start these kinds of oscillations would be a good thing.
The other day I was out and about and saw this fellow (below) very happily taxiing his gyrocopter (officially, the FAA calls them rotorcraft). He probably would have liked to have had a few missles on it like James Bond had on Little Nellie, but, hey, these days, people get upset over little things like that.
A minute or two after I took the picture, he was at 1000 feet, buzzing around the runway. If you look at this photo carefully, you’ll notice that the engine is set rather high and is, in fact, directly behind the pilot. Of the many things you can do to reduce PIO in a gyro, this is one of the major ones. By having the engine, and thus the prop, directly behind the principle mass in the machine (the pilot), then when accelerating, the thrust of the prop doesn’t try to push him down, or push him up. If the line that passes through the engine/prop was higher than the line through the pilot, and the pilot goosed it, the nose woujld try to dive. The pilot would try to compensate for this, possibly causing a PIO. This is the thrust line, and you want it directly in line with the primary masses, the engine/prop and the pilot.
You may be able to see, also, that the rotor blades are pretty simple. They are essentially free-wheeling. The engine behind the pilot pushes the craft forward, and that results in wind being pushed through the blades, which then spin round and round, faster and faster, until they produce enough lift to suck the gyrocopter up into the air. The rotor then, like a helicopter, provides the primary lift for the craft. The engine simply keeps the whole mechanism moving forward through the air. To steer, you push the stick around and that causes the rotors to tilt one way or another.
One of the worst things you can do in a gyro is to perform any maneuver which will stop that forward progress. If the wind stops being pushed through the rotor, then you lose your lift, and you stall. If you have a lot of altitude and time, you may be able to get the craft pushed through the air enough to create enough lift again, but it’s much harder than it would be in a standard 3-axis aircraft.
Learning to fly a gyrocopter requires quite a number of different kinds of skills and knowledge. I certainly would never jump into one without the proper training, any more than I would into a helicopter or a trike. Each one of those types of aircraft require lots of training and are different enough from a regular 3-axis aircraft that, without the specialized training, you could easily and quickly get into trouble.