02/03/93
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STANFORD - If you have never flown a helicopter, don't even think about taking off in one - not even if your life depended on it.
Helicopters are notoriously difficult machines to control, and even experienced pilots frequently have trouble negotiating simple maneuvers. If a measure of complexity is added, such as carrying a suspended weight or trying to hold a steady hover in windy conditions, the task becomes daunting.
Professor Arthur Bryson at Stanford's department of aeronautics and astronautics and his Stanford/NASA research team, however, are trying to change all that.
Using advanced control systems and computer modeling concepts, they are perfecting a system in which helicopter pilots play the role of flight managers, instead of having to constantly worry about controlling the machine.
"We wanted to move the pilot's emphasis from controlling the helicopter to other tasks - like monitoring the meters and looking out the window more often to see if there's a risk of a mid-air collision," said Chris R. Purvis, a doctoral student on Bryson's research team.
"Neglecting these 'discretionary' tasks frequently causes accidents. The pilot is often too busy with the controls to pay much attention to them."
Helicopter pilots simultaneously have to manage the altitude, speed and direction of the machine. This is especially difficult when approaching a hovering position, and requires unusual coordination among the pilot's mind, hands and feet.
Acceleration in any direction is achieved by changing the angle of the rotor, which changes the direction of the rotor's thrust. To change the hover position, for example, the rotor must be tilted to accelerate the machine, then tilted in the opposite direction to bring it to a standstill at the desired point.
"It's something like bringing a ship into a dock," said Bryson, the Paul Pigott Professor of Engineering. "You have to reverse the propellers and start slowing the ship long before you've actually reached the dock. The only difference is that in a helicopter everything is happening a lot faster."
The research team's basic task was to develop a computer program that would model an expert pilot.
When the pilot indicates he wants to turn, climb or change velocity at a certain rate, the computer computes the difference between what the helicopter is doing and what the model says it should do. The computer then automatically adjusts the helicopter controls to achieve the desired maneuver.
Bryson acknowledges that a part of his inspiration from the project came from listening to the stories of pilots describing the difficulties of flying helicopters.
"I recall the helicopter pilot's difficulty immediately after the Apollo [mission]," he says. "He was to pick up the Apollo craft after it landed in the ocean and had to struggle for several minutes just trying to get the hook to the astronauts to connect to their craft."
If that pilot had possessed Bryson's technology, all he would have needed to do was move the control stick to the point on the display that showed where he wanted to go. He then would have released the stick, which would have clicked back into neutral and let the computer take over, moving the helicopter to the desired position and altitude.
"We could now get that hook to those astronauts in seconds," Bryson said.
Bryson and his team felt that such a system would not be accepted unless the pilots felt that they - not the computer - were in control of the aircraft. Purvis, who is an experienced pilot, pointed out that no pilot would want to have the helicopter seem to fly on its own.
The most mathematically efficient way to fly the machine is not necessarily the way an expert pilot would have flown the chopper in every instance.
"It was important that the computer issued commands to fly the helicopter the way an expert pilot would," Bryson said. "Otherwise, he is not likely to use the automatic system."
The initial test flights of the model won the approval of expert pilots at the NASA/Ames Research Center.
"They disliked it at first," Bryson said with a smile. "It didn't sound very macho. But they later said it was pretty good."
To avoid "pilot boredom," the system was not automated to the point where the pilot could simply type in his commands over a keyboard, Bryson said.
"We want the pilot to stay alert and in control of the craft," he said. "Our aim is to make helicopters easier to fly - we don't want the pilot to get careless and lose touch with the controls."
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This story was written by Shankar Vedantam, a science writing intern at the Stanford News Service.
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