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attack from the ADCs) and aircraft
motion (from the IRSs.) The “control
laws” in its program decided what
to do with the controls, and signaled
hydraulic control actuators
electrically. Sensor feedback loops
supplied info on how the controls
responded. There was no direct
mechanical connection between
control surfaces and the pilot, who
never actually knew what the control
surfaces were doing.
The FC could move the controls
faster than a pilot’s mind could
react. Not only could it fly the statically
unstable airplane perfectly
well, it could do a lot of other
things, such as smoothing out the
effects of configuration changes
and protecting the airplane from
exceeding limitations such as load
factor and AOA limits. The latter
was big for the military. Prior to
FBW they lost many fighters in
94 PROFESSIONAL PILOT / September 2004
By Don Witt
ATP/CFII. Boeing 737, 757,
Airbus A320, Learjet series.
AVIONICS
Introducing full FBW for business av
Safety and economy spur drive to high-tech flightdeck.
Dassault’s Falcon 7X, with full FBW flight controls, is due to fly in the first quarter of 2005.
Illustrations and photos courtesy Dassault
W
combat when their pilots pulled
through the AOA limit in the heat
of battle and the aircraft departed
into an unrecoverable spin.
Soon the civilian world saw
advantages to FBW too—specifically
safety and ease of control. With
built-in “hard limits” an FBWequipped
aircraft cannot be stalled
or over-G’d. Just as important, it’s
easier to fly, freeing the pilot’s
attention for higher-order tasks.
Airbus Industrie, followed by
Boeing, chose FBW for its new airliners.
Fly-by-wire is not a simple technology,
nor is it without hazard. In
fact, it has the potential for new
kinds of accidents—for example,
certain combinations of control system
lag (measured in fractions of a
second) and actuator rate limits
(how fast a control surface can be
moved) can allow aircraft-pilot
coupling events, similar to PIOs,
that have caused loss of control,
such as the Aug 1993 crash of a
Saab Gripen in Sweden.
In FBW systems, multiple computation
channels are required for
safety in case of failure. Multiple
channels monitor each other and/or
“vote.” This is a highly complex
communication task, and Boeing
struggled with this aspect of the
777’s FBW until late in its development
program.
Dassault and FBW
Dassault’s experience with FBW
goes back as far as 1963, when the
Balzac—a VTOL development of
the Mirage III fighter—transitioned
to horizontal flight through FBW
control of its tailpipes.
Since 1954 Dassault has manufactured
most flight control components
in house. The Mirage 2000 is
full-FBW with 4 analog computers.
The Dassault Rafale fighter, which
flew in 1986, has 3 digital FCs and
an analog backup.
According to Dassault Senior VP
Civil Aircraft Olivier Villa, the
Falcon 7X will be significantly
more fuel-efficient than its predecessors.
In part this is due to the
7X’s FBW system, which is a major
contributor to reducing the drag
induced by the horizontal stabilizer.
Overall, Dassault says it has
reduced the size of the stabilizer by
roughly 20%.
Flying the Falcon 7X
When Dassault brought the 7X
simulator to EBACE, I was able to
fly it with Test Pilot Philippe Deleume.
The 7X’s sidestick is comfortable
to the hand. Dassault has put much
thought into ergonomics. For example,
the artificial feel or force needed
to displace the sidestick has
been tailored and is not symmetrical
from left to right. This is
because a pilot (or anyone else) has
less strength available to rotate the
wrist outboard than to rotate it
inboard.
The sidestick has 4 switches available
to thumb and forefinger. They
are the radio push-to-talk switch,
the TCS switch (TCS is an autopilot
mode—the FBW equivalent of control
wheel steering), the HUD declutter
switch, and a 4th switch
which serves 2 functions—autopilot
disconnect and sidestick priority.
In the 7X, as in the A320, dual
sidestick inputs are summed algebraically.
For example, if the captain
has full left stick and the FO
has full right, the algebraic sum is
zero and the aircraft will not roll. A
sidestick priority switch gives one
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