Note: Descriptions are shown in the official language in which they were submitted.
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AIRCRAFT PRECISION APPROACH CONTROL SYSTE~
BACKGROUND OF THE INVENTION
The present invention relates generally to a
Precision Approach Control (PAC) system for stabilizing an
aircraft during landing thereof, such as during a relatively
precise landing on an aircraft carrier, and more particularly
pertains to a precision approach control system which
provides the pilot with precise control over the flight path
rate and flight path angle of the aircraft during landing.
The precision approach control system also maintains the
aircraft at a predetermined angle of attack during landing.
Precise control of the flight path of an aircraft
should be maintained throughout a landing approach to an
aircraft carrier, which makes this a very demanding task for
; 5 a pilot. During such a landing, the pilot is presented with
a relatively narrow landing window along an ideal glide slope
path. The landing is further complicated by uncertain
aircraft carrier motions and also by atmospheric and
ship-induced turbulences.
The landing approach of high-performance,
relatively unstable aircraft on an aircraft carrier is an
even more demanding task, requiring precision control of the
~light path by the pilot. The prior art has used Stability
Augmentation Systems (SAS), Approach Power Compensators
~APC), and Direct Lift Control (DLC) subsystems to augment
the basic aircraft flying qualities and control systems, but
using separate design criteria for each of these dif~erent
subsystems. With the main objectives of these subsystems
(shor~ period response, phugoid damping, g control) achievedr
3 the pilot is given improved control over the aircraft.
However, in ~igh-performance, relatively unstable aircraft
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requiring exceptional flight path control, this design
methodology is generally insufficient since it does not
assure precise flight path control.
However, none of the prior art approaches has
resulted in an entirely satisfactory solution to the problem
of providing a pilot with precise flight path control over an
aircraft during a relatively critical landing thereof such as
on an aircraft carrier.
Manual and Automatic Carrier Landing (ACL) designs
resulting rrom an integrated approach to the flight path
control problem, as well as the application of qualitative
flight path control eriteria, have achieved superior flight
path response in a Grumman F-14 aircraft with minor
modifications to its existing hardware, which has been
demonstrated in studies and piloted simulations.
The present invention relates to a precision
approach control system for an aircraft during landingr
comprising: a said aireraft having a plurality o~ operating
control surfaces thereon, an autosystem for maintaining the
aircraft at a predetermined angle of attack during landing
thereof, a control system for ma~intaining the inertial flight
path angle of the aircraft constant during landing thereof,
and a controller, operated by the pilot, for controlling the
flight path rate of the aircraft.
The present invention provides a precision approach
cvntrol system or mode of operation for an aircraft which
allows landing thereof in a more stable and easier manner
~han with existing and available control systems.
Improved control over an aircraft during landing
should result in significantly ~nhanced flight safety and
3 also in substantial savings in fuel sinee fewer bolters and
wave-offs ean be expected, which will result in fewer landing
approaches. Fewer landing approaches eombined with
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significantly enhanced aircraft control by the pilot should
reduce the number of critical piloting situations, thereby
significantly enhancing flight safety.
The subject invention also provides a precision
approach control system for an aircraft which essentially
provides the pilot with
a flight path angle rate ( ~ ) controller, and which
utilizes the autothrottle system to maintain the aircraft at
a predetermined angle of attack
( ~<), thereby defining aircraft approach speed with weight.
In one embodiment in the X-29 aircraft, the controller in the
cockpit that is normally the pitch rate comnland stick
controller during a Power Approach landing is converted into
a flight path angle rate ( ~ ) controller. The precision
approach control mode of the present invention provides true
control of the inertial flight path and velocity vector of
the aircraft, providing the pilot with rapid and precise
control over the aircraft during a landing approach. The
precision approach control mode also uses the autothrottle
control subsystem to maintain the aircraft at a predetermined
angle of attack ~c~ ~ during landing, which in a particular
disclosed embodiment for the X-29 aircraft was selected to be
8.75, which defines the aircraft approach speed with weight.
The predetermined angle of attack ( ~ ) would normally be
different for different types of aircraft, and could even be
desi~ned to be variable and selected by the pilot.
The precision approach control system or mode of
operation of the present invention is designed to control th~
approach of an aircraft during landing to provide a more
stable flight path and easier mode of landing, which is very
3 important in critical landing situations, such as during the
landing of an aircraft on an aircraft carrier or on a
relatively short runway.
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1 In operation of the precision approach control
system, when the aircraft is subjected to vertical or
horizontal winds or wind shear, the system controls the
aircraft to maintain the inertial flight path angle
constant, which essentially defines operation in the
precision approach control mode.
One embodiment of the precision approach control
system was designed for operation in an existing aircraft,
the Grumman X-29, and the particular PAC system implemented
therein used the existing controls and control subsystems
onboard that aircraft. The Grumman X-29 aircraft is designed
with three pilot-operated controllers, a throttle, a control
command stick, and rudder pedal controls.
Disengagement of operation in the PAC mode will
cause operation to revert to normal operation in the power
approach mode. The precision approach control mode in the
X-29 aircraft is designed to be capable of being overridden
by the pilot by engaging the throttle controller with a force
in excess of a given threshold force, such as above eight
pounds. Moreover, the PAC mode of operation is designed to
be disengaged by closure of weight-on-wheels switches on the
aircraft, which indicates landing contact. Accordingly, it
should be recognized that the P~C mode of operation of the
present invention can be designed to be suspended by a higher
priority operating system or subsystem or by the pilot.
In the precision approach control embodiment in the
X-2~ aircraft, the PAC mode of operation was designed to be
engaged by first selecting a normal power approach mode of
operation, then by engaging the autothrottle system, and then
by engaging the PAC mode, with all engagements being by
normal electrical switches in the cockpit. For engagement to
be complete, several other conditions must exist within
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proper predefined limits, such as angle of attack probe data,
attitude reference data, normal acceleration data, etc. The
trim button is then operated to stabilize the rate-of-climb
(descent) of the aircraft, which is shown on a needle gage,
and additional trim control should not normally be required
thereafter. This trim requirement is only required in the
X-29 control arrangement embodiment, and alternative
embodiments do not necessarily require this feature. The
stic~ controller which is normally the pitch-command stick
controller in the cockpit is then operated in the PAC mode by
the pilot to control the rate of descent of the aircraft.
The present invention for a PAC system is designed
to reduce pilot workload by minimizing aircraft flight path
deviations caused by atmospheric disturbances, by maintaining
a stable, trimmed approach airspeed/ and by providiny an
optimum flight path response to pilot commands through the
pitch-command stick controller (single control input), with
response characteristics which are more easily perceived and
predicted by the pilot. The improved performance is attained
while providing for acceptable transient e~cursions in
angle-of-attack and control surfaces relative to aerodynamic
limits, in engine thrust (throttle3 variations, and also in
short-period attitude excursions and damping.
The precision approach control system implemented
in the X-29 aircraft automatically modulates the thrust
through the throttle to hold the angle-of-attack of the
aircraft constant and hence the airspeed constant. This
provides the pilot with direct control over the aircraft's
fligh~ path angle and speed with the pitch-command center
stick controller. Moreover, improved phugoid damping is
; 3 obtained via thrust modulation, eliminating any tendency for
an oscillator~ flight path. Direct lift control is obtained
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with incremental flap motion upon stick movement, with the
canard cancelling flap pitching moments with a flap canard
interconnect. Other systems, such as the F-14, use spoilers
as the direct lift command controllers which would move with
the center stick.
The present invention for an aircraft precision
approach control system may be more readlly understood by one
skilled in the art with reference being had to the following
detailed description of a preferred embodiment thereof, taken
in conjunction with the accompanying drawings, wherein like
elements are designated by identical reference numerals
throughout the several views, and in which:
Figure 1 is a schematic illustration of an
exemplary embodiment of a canard-equipped aircraft, such as
the Grumman X-29, which can be operated in a PAC mode of
operation pursuant to the teachings of the present invention;
Figure 2 is a functional block diagram of a PAC
outer loop control system pursuant to the subject invention;
and
Figure 3 is a functional block diagram of a PAC
modified auto throttle system in accordance with the present
invention.
Referring to the drawi:ngs in detail, Figure 1
illustrates a canard-equipped aircra~t, such as the Grumman
~ X-29 aircraft, and illustrates in a schematic manner an
; 5 aircraft having a canard control surface 2at a wing flap
control sur~ace 2b, and a stra};e flap 2c, all of which are
employed in the X-29 jet aircraft. Actuators 3 variably
position the control surfaces 2a, 2b and 2c. A flight
control digital computer 4 of ~nown design has a number of
3 inputs thereto including pilot command inputs, and data
inputs from accelerometers and gyros, collectively referred
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to by reference numeral 5. The X-~9 control system employs
known components and subsystems to achieve stability for an
inherently unstable aircraft by multi-control surfaces.
Figure 1 also illustrates on the right side thereof
the centerline ~ of the aircraft, the horizon, the velocity
vector V of the aircraft, the flight path angle ~ of the
aircraft, and the angle of attack c~ of the aircraft, all as
~ are well known in the art.
- It should be realized that the PAC mode of
operation is applicable to many different types of aircraft
other than the canard-equipped aircraft of Figure 1.
Moreover, the particular design of a PAC system for a
particular type of aircraft will depend to a large extent on
the operating and control systems already existing onboard
that aircraft, and the extent to which the design can be
implemented ~rom an existing design or from an original
design.
The following description is specifically with
reference to a PAC system implemented in a Grumman X-29
aircraft. Upon engagement of the PAC mode~ a PAC mode light
indicator in the cockpit is energized. If the speed
stability mode which is part of normal power approach had
been previously selected by the pilot, the spee~ stability
switch will go off. If speed stability is automatically
i engaged because the aircraft speed is below 148 I~ts. when the
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P~C mode is selected, speed stability will also disengage.
Disengagement of the PAC mode and reversion back to the
normal power approach mode can be achieved by overriding the
throttle motion with a pilot force in excess of eight pounds.
Upon disengagement, a PAC solenoid held switch will
3 disengage. Re-engagement of the PAC mode can be achieved
only by pilot action through reselecting the PAC mode via the
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PAC switch. The PAC mode will also be disengaged upon
closure of a weight on wheels switch on the aircraft.
The operational procedure to engage the PAC mode is
to first engage the normal/PA mode (flap handle in MCC,
thumbwheel switch - TW=9). Next, the boost switch and
autothrottle is engaged, and then the PAC switch is engaged.
The trim button is then operated to stop any motion of the
rate-of-climb needle (h). Further trim control should not be
needed thereafter. The desired rate of descent and flight
path angle is then controlled by operation of the stick
controller.
Figure 2 illustrates a functional block design of
one embodiment o~ a precision approach control outer loop
control system, which illustrates the control systems of the
longitudinal control surfaces. Referring to the left side of
Figure 2, a ~ stick command signal from the controller is
multiplied at 20 by a gravity constant G divided by the
aircraft speed CAPV to obtain a signal GAMDL, which is then
multiplied at 22 by a constant representing the stick gear
gain to obtain a ~ command signal. This multiplication is
used because the stick throw was originally scaled for
incremental load factor (DNZ). An upper control branch
multiplies the ~ command signal by a constant at 24 to
provide a lead of the ~ stick command signal.
A DNZ signal (DNZBody cos ~ cos ~ ) represents a
feedback signal, which is also multiplied at 26 by the same
constant as at 20 to provide a ~ actual signal, which is
then summed at 28 with the ~ command signal. The ~ signal
could also be obtained directly from an inertial navigation
system, when available onboard the aircraft. The output
3 of 28 is integrated at 30 to obtain an integrated signal
which is multiplied by a constant at 32. The actual signal
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is also multiplied by a constant at 34 to provide damping and
stability. The three signals from 24, 32 and 34 are then
summed at 36 to obtain a PAC command signal.
A Q signal, representing the pitch rate of the
aircraft, is also directed to a washout filter multiplier 38,
which stabilizes the signal to zero at steady state, and the
output thereof is then multiplied by a constant at ~0 to
provide additional damping. The output thereo~ is summed at
42 with the PAC command signal from 36 to provide a PAC inner
loop pitch rate command signal. This signal is then applied
to the existing X~29 inner control loop o~ the X-29 aircraft,
and the output thereof is applied to a summing circuit 50.
The ~ command signal from 22 is also multiplied
by a constant at 44 and directed through a limit circuit 46,
which provides position limits of ~ 2 to provide a ~ flap
5 command signal. The ~ flap command signal is then multiplied
by a constant at 48 to provide a DC PAC signal which is
summed at 50 with the PAC mode si~nal from 42 to provide a
canard command signal.
A primary flap command signal ~rom the pilot is
also summed at 52 with the ~ flap command signal from ~6 to
provide a ~ total flap command signal ~or the Grumman X-29
aircraft.
Figure 3 is a functional block diagram of the X-29
auto throttle system modified for the PAC mode of operation.
An oC ref si~nal, representing 8.75, is summed at 60 with a
signal representing the actual angle of attack of the
aircraft. The resultant ~ ~C signal is multiplied by a
constant at 62 to obtain a ~ ~ o~ signal which is
multiplied by a further constant at 6~, integrated at 66, and
3 limited at 68 to obtain a TD thrust signal.
A DNZ signal is also multiplied by a constant at
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70, an~ then multiplled at 72 by the sos ( 0 ) ~ 30,
wherein o is the bank angle of the aircraft, the output of
which is summed at 74 with the signal from 62. The
output of 74 is then fed through a lag ~1 sec.) filter 76 to
produce a TE signal.
A J stick command signal is also multiplied by a
constant at 78, the output of which is fed through a 10
second washout filter 80 to provide a TF signal, which is
summed at 82 with the TD and TE signals to provide an
incremental thrust signal. The incremental thrust signal is
multiplied at 84 to provide an incremental power lever
signal.
A pilot thrust command signal tbefore PAC) is then
summed at 86 with the incremental power signal, and the
output thereof is limited at 88 to provide limits for the PAC
power lever command signal at 90 for the X-29 aircraft.
In summary, Figure 2 illustrates a functional block
diagram of the control laws commanding the longitudinal
control surfaces, and Figure 3 illustrates a functional bloc]c
diagram of the control laws commanding the autothrottle.
The control law is a ~ command, ~ hold, with the
autothrottle holding ~ . In order to maintain an adequate
stall margin for the aircraft, t:he speed is increased in
banked turns.
While one embodiment of the present invention for a
~` 5 precision approach control system is described in detail
herein along with several variations thereon, it should be
apparent that the disclosure and teachings of the present
invention will suggest many alternative designs to those
skilled in the art.
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