Page 127 - Understanding Flight

CH04_Anderson 7/25/01 8:57 AM Page 114

114 CHAPTER FOUR

actions are transmitted by wire. The pilot inputs a command on the
yoke, which is read by a computer. The computer translates the
command, along with its own inputs to augment stability, to an
electrical signal. A wire then connects the cockpit to various actuators,
which convert the signal into a mechanical action, like moving the
elevator.
There are a few interesting side effects of fly-by-wire. One is that an
intelligent computer can be used to make decisions. For example, the
computer may monitor the angle of attack and not allow the aircraft
to reach the stall angle of attack. Thus, no matter how hard the pilot
pulls back on the control yoke, the airplane will not increase its angle
of attack to a stall. This can be useful in a fighter aircraft where the
pilot in combat does not have time to watch the angle of attack
indicator. Another example is that the computer might turn a sloppy,
pilot-controlled landing into a smooth landing. In essence, the pilot
and the computer both fly the airplane.

An unfortunate incident happened at a French air show in 1988.
An Airbus A-320 on a demonstration flight crashed off the end
of the runway.The jet was scheduled to do a flyby. But the
computer interpreted the approach as an approach to landing.
The subsequent confusion between the pilot and the computer
resulted in neither a controlled flyby nor a controlled landing.
Instead, the airplane crashed and was destroyed.The A-320 was
the first civilian airplane to use fly-by-wire control.

In Sioux City, Iowa, on July 19, Another side effect worth noting is the effect on stick
1989, a DC-10 landed after force. Flying an airplane with a joystick is no different from
losing all tail surface controls flying in a computer simulation with a joystick. The joystick
due to an explosion in the on the computer has no way of giving mechanical feedback
middle tail engine. The pilot in terms of resistance to turning. So it takes the same force to
miraculously maneuvered the make a tight turn at low speed as at high speed. This
airplane to a crash landing using feedback is a point of contention between pilots and
the thrust from the two wing designers. The pilots want the mechanical feedback. Now at
engines to turn. least one airplane manufacturer has developed springs and
linkages that are controlled by the computer system that give