Due to a large number of fatal crashes during training, students are not allowed into a Robinson R22 2-seat helicopter, even with an instructor, until they’ve had some ground training. If you believe that you have some special mission on this planet the grounnd training might cause you to terminate your.
Here’s what I learned about the hazards inherent in flying helicopters…
As with airplanes, the key to being safe in a helicopter is energy management. In an airplane you have potential energy (altitude) and kinetic energy (forward speed) that can be traded off against each other to bring the airplane down gently in the event of an engine failure or ordinary landing. The helicopter has three kinds of energy: potential (altitude), kinetic (forward speed), and angular momentum (blade speed).
In an airplane you can make decisions about trading forms of energy very late in the day. For example, if you pull the stick all the way back at 6000′ above the ground you will gradually slow down and eventually stall and perhaps enter a spin. With many airplanes you could spin nearly all the way to the ground before applying forward stick and opposite rudder to get back to a normal flight condition. All without an engine.
In a helicopter, by contrast, if the blades spin down more than 10-15% from their normal velocity, there is no way to convert potential or kinetic energy into spinning such that the helicopter will start to fly again. If you don’t have an engine, therefore, your helicopter can very quickly become a rock.
In a turbine-powered helicopter like the Jet Rangers that are typically used for sightseeing the blades are heavy and the blades won’t slow down for several seconds after an engine failure. The Robinson, however, is designed for super high efficiency and therefore everything is as light as possible. After an engine failure you have no more than 1.2 seconds to take exactly the right actions or the helicopter cannot be recovered.
What if you do take all the right actions? Suppose that you’re up at 4000′ and the engine quits. You lower the collective pitch (lever on your left) immediately to flatten the blades and allow them to be driven by the wind through which the helicopter is now falling at 2000 feet-per-minute. You adjust the cyclic (stick in front of you) for about 65 knots of forward speed. You aim for a landing zone. The good news is that you don’t need a very large one but the bad news is that the glide ratio is 2:1 instead of an airplane’s 10:1 and therefore you don’t have as large an area from which to choose. As you get within about 50′ from the ground you pull back the cyclic to flare the helicopter and shed most of the forward speed. Just as in an airplane this flare also arrests most of the vertical speed. At the second to last moment you stop flaring and return the helicopter to being parallel to the ground. Ideally at this point you are hovering 5′ or so above a soccer field and the blades are still spinning. Finally you raise the collective as the helicopter falls, using the stored energy in the blades against the force of gravity. You land gently on the skids. (In practice the cyclic flare is more important than the “hovering autorotation” at the end; a lot of people walk away from helicopter engine failures if they get the cyclic flare right but can’t manage to pull the collective smoothly at the last moment.)
This all sounded good until we looked at the “deadman’s curve”. The marketing literature for helicopters says “if the engine fails, you can autorotate down to a smooth landing.” The owner’s manual, however, contains a little chart of flight conditions from which it is impossible to landing without at least bending the helicopter. Unfortunately these conditions are the very ones in which nearly all helicopters seem to operate. If you’re above 500′, for example, you’re pretty safe. But TV station helicopters are often lower than that when filming. Flying along at 65 knots is also good but if the camera needs the pilot to hover the helicopter slows to a crawl.
After a couple of hours of theory we went to the hangar and preflighted the helicopter. The engine is flapping in the breeze on an R22 and therefore you can inspect a lot of linkages and lines that are hidden on most airplanes. Most of the other critical mechanical components are open to the air or accessible via covers that you open during the inspection.
Four hours after the lesson started we were ready to fly… but the ceiling was 900 overcast with visibility 4 miles in mist. So we gave up and went home.
Hell, I thought that when a helicopter’s engine failed you just dropped out of the sky like a rock and died when you hit the ground at several hundreds of miles an hour. So that actually sounds better than what I thought would happen. Thanks for the explanation on how a rotating wing can (sort of) work like a fixed wing for trading potential and kinetic energy. What jumps into my mind is that a computer should (in a perfect world) be much better at this sort of recovery than a human, even a Greenspun 1000XL, in any case.
I had that idea too. You need quick reaction time and nothing is quicker than a computer. The instructor ridiculed my implied reliance on automated systems. In any case a combination of small market and government regulation has conspired to make helicopter autopilots cost $250,000+ (i.e., more than the $180k cost of a brand-new R22 trainer). I don’t think these autopilots do anything in an emergency except disengage.
Maybe because most of the stuff flying was designed in the 1950s and built in the 1970s the prevailing philosophy in aviation is that all mechanical and electronic systems are crap and prone to break. Consequently what you learn as a pilot is to pull circuit breakers and fly with some part of your airplane disengage. So you’d think flying a 767 would be simpler than flying a Cessna because of all the fancy computers but in fact the 767 guys need a tremendous amount of training to deal with their ability to, in-flight, selectively disable computers and other bits of automation.