Dennis Michelini is a U.S. Border Patrol pilot.

Airplanes have a great proclivity to flight. Anyone who has ever flown a small airplane will tell you that you have to bring the engine down just about to idle in order to get the thing to land. Helicopters, on the other hand, claw their way into the air. They fight for every inch, and they do it with too many moving parts. It's unnatural. Unlike an airplane, when the throttle of a helicopter is brought down to idle, it drops like a rock from the sky.

PRINTDISCUSSE-MAILRSSRECOMMEND...SINGLE PAGE

FacebookMySpace Mixx Digg Reddit del.icio.us Furl Ma.gnolia SphereStumbleUponCLOSE

The Border Patrol utilizes airplanes and helicopters. Throughout the year, we have flight training in both types of aircraft. Today I flew with an instructor practicing "engine out" procedures and auto-rotations in a helicopter. In simpler terms, I practiced falling out of the sky like a rock.

Whether you see a helicopter in the air or one running at full power on the ground, the rotation of the blades is the same. What needs to change to lift it off the ground is the pitch angle of the blades. It's the same effect as sticking your hand out the window of a moving car. With the palm down flat, horizontal with the ground, your hand buffets with the wind but stays basically stable. When you add a slight angle to your palm, bringing the thumb up a little into the wind, you'll feel pressure on your hand: It wants to rise. When a pilot raises the collective in a helicopter, each blade does what your palm just did; they pitch up, bite into the air, and lift the craft off the ground. It's much harder (requires more torque) for the engine to rotate pitched blades than flat blades. Of course, while flat blades spin freely through the air, they produce almost no lift.

When a helicopter loses power, the pilot tries to maintain rotor rpm. The only way to do this is to flatten the pitch angle on the blades. Unfortunately blades without pitch do not produce lift. With the flattened pitch, the helicopter begins to drop anywhere from 1,500 to 2,200 feet per minute toward the ground. The good thing about dropping so quickly is that as long as the blades remain flat, they will continue to rotate as if they had an engine; they retain their rpms. The bad thing is, of course, impacting the ground at 2,200 feet per minute. There is another little problem. The helicopter is also traveling forward at about 70 to 80 miles an hour.

There is an expression pilots use to describe the mental state they are usually in before things begin to go wrong. It goes like this, "So there I was fat, dumb, and happy when …"

When an engine fails in a helicopter, the pilot has a second, or maybe two, to lower the collective (flatten the pitch of the blades). If the pilot doesn't, the combination of a large angle on the blades and no engine from which to generate torque will quickly erode the rpms of the rotor past a recoverable point. The blades will no longer produce lift, and the tremendous speed at which the helicopter is falling still will be insufficient to regain the original rpms.

So, here comes the trick. About 50 feet off the ground, the pilot lifts the nose of the helicopter—like reigning in a horse—and slows the forward air speed. All that extra air speed (think of it as wind) gets pushed through the blades and can be used as surplus energy. As a result, the pitch of the blades can be increased without too much loss of rpm. The aircraft is going from 80 knots to 20 knots, and the extra energy is going into a slight pitch increase, which slows the descent.

Almost immediately the nose of the helicopter has to be lowered—the helicopter leveled—or the tail rotor and tail boom will strike the ground and break off. Now the last bit of pitch is brought in as the rotor speed degrades past a recoverable point. But by this time, or, I should say, at this exact moment, the helicopter has landed, and what was left of lift in the blades has been spent.

In theory that is how it goes. Pilots like me practice this maneuver so that real life resembles theory and so that you may be fortunate some day, fortunate enough to start a story that begins with, "So there I was, fat, dumb, and happy when …"

PRINTE-MAILRECOMMEND...RSS

FacebookMySpace Mixx Digg Reddit del.icio.us Furl Ma.gnolia SphereStumbleUponCLOSE

SPONSORED CONTENT