Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
2002-08-09
2003-04-29
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C241S003000
Reexamination Certificate
active
06556897
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to aircraft control systems and more particularly to aircraft sensor systems.
An aircraft is a vessel that is free to move in three dimensional space.
FIG. 1
depicts a typical coordinate system useful for describing aircraft motion in three dimensions. In the body fixed coordinate system of
FIG. 1
, the aircraft has a longitudinal axis x
b
which extends along the length of the airplane. Rotation about the X
b
axis, L, is called roll. The coordinate system of
FIG. 1
further includes a lateral axis y
b
extending parallel to the aircraft wing. Rotation about the y
b
axis, M, is called pitch. The z
b
axis extends perpendicular to the remaining axes as shown. Rotation about the z
b
axis, N, is called yaw.
Equations of motion can be derived to describe the aircraft movement using the axes shown in FIG.
1
. Unfortunately, the orientation and position of the aircraft in space cannot be truly understood with the coordinate system of
FIG. 1
since the coordinate system is moving with and is always centered on the body of the aircraft. For this reason, it is common to transform the parameters of
FIG. 1
to describe the angular displacement of the aircraft in space. These angular displacements, or Euler angles, are as shown in FIG.
2
.
In good weather, under visual flight conditions, pilots of conventional aircraft control the aircraft motions and the resulting angular displacements in three dimensional space by visual reference to the natural horizon. The natural horizon serves as a visual clue from which the pilot can determine if the airplane is climbing, descending or turning. In low visibility conditions, such as, for example: nighttime, haze, or flight in clouds; the natural horizon can become obscured and the pilot is unable to control the aircraft by reference to the natural horizon. Conventional aircraft are therefore equipped with several instruments to assist the pilot in visualizing the aircraft's movement in three dimensional space. These instruments also provide the pilot with supporting data from which to confirm control of aircraft even when the natural horizon is visible.
FIGS. 3A-3G
show a conventional aircraft panel for a contemporary airplane having such standard instrumentation. The control panel of
FIG. 3A
includes: an altimeter
2
that provides the pilot with information on aircraft altitude; an airspeed indicator
4
, that provides information on the aircraft speed through the air; and a vertical speed indicator
6
, that provides data on the rate of climb and descent. Instruments
2
,
4
and
6
comprise the pitot-static, or pneumatic, instruments since they operate by sensing air pressures exterior to the aircraft. In certain larger aircraft, the pitot static instrument sensors are combined into a single box called an air data computer. The air data computer then outputs the altimetry and airspeed data to a cockpit display and/or to other avionics equipment requiring such data.
Also included in the standard control panel of
FIG. 3A
are the gyroscopic instruments. The gyroscopic instruments provide the pilot with a pictorial view of the airplane's rate of turn, attitude and heading. These instruments include a turn coordinator
8
, an attitude indicator
10
, and a heading indicator
12
. A wet magnetic compass
13
, may also be used to provide heading information. Wet compass
13
does not contain a gyro.
FIGS. 4A-4B
illustrate aircraft turn coordinator
8
in greater detail. Turn coordinator
8
senses yaw, r, and roll, p, movement about the aircraft z
b
and x
b
axes. When the miniature airplane
14
is level as shown in
FIG. 4A
, the aircraft is neither turning nor rolling. When the aircraft banks, miniature airplane
14
also banks. In the drawing of
FIG. 4B
, miniature airplane
14
indicates a turn to the right.
FIGS. 5A-5D
illustrate operation of aircraft attitude indicator
10
also known as an artificial horizon. Attitude indicator
10
senses pitching, &THgr;, and rolling, ø, movements about the airplane's lateral and longitudinal axes. Attitude indicator
10
is the only flight instrument that provides both pitch and bank information to the pilot. Attitude indicator
10
presents a view of the aircraft, as represented by miniature airplane
20
, as the aircraft would appear to someone standing behind it. The pitch attitude of the aircraft is shown by noting the position of the nose
22
of miniature airplane
20
relative to the artificial horizon
24
. Bank information is shown both by noting the position of miniature airplane
20
relative to the deflected artificial horizon
24
and by the alignment of bank angle pointer
28
with the graduated bank angle indexes located on the perimeter of the device.
FIG. 5A
shows the aircraft in level flight and no turn.
FIG. 5B
shows the aircraft in a level turn to the left.
FIG. 5C
shows a level climb and
FIG. 5D
shows a descending left turn.
Heading indicator
12
, also known as a directional gyro, serves as a means to indicate the aircraft magnetic heading without the limitations of using wet compass
13
. Wet compass
13
is prone to various turning and acceleration errors. Heading indicator
12
is not subject to these errors and thus provides the pilot with a more stable indication of aircraft heading throughout the flight.
Each of turn coordinator
8
, attitude indicator
10
, and heading indicator
12
includes a gyroscope needed for proper operation of these instruments. Typically, the gyroscopes in attitude indicator
10
and heading indicator
12
are powered by a vacuum pump. Turn coordinator
8
is normally powered using an electric motor. The gyroscopes contained within each of these instruments also have operating limitations. For example, if the aircraft enters an extreme or unusual flight attitude, the gyroscope can tumble rendering the associated instrument inoperative.
Similar to the air data computer, the gyroscopic instruments are occasionally on larger aircraft combined into a single integrated sensor package called an attitude heading reference system, or AHRS. The AHRS system outputs the attitude data to a cockpit display and to other avionics equipment requiring such data.
In airplanes with autopilots, the autopilot uses the attitude information supplied by these gyroscopic instruments or AHRS instrument suite to fly the aircraft. Thus, when an instrumentation fault occurs, the autopilot is also affected.
Gyroscopic instruments are also prone to various types of errors during normal operations.
FIG. 6
is a cut away view of a gyroscope and gimbal structure representative of those used in aircraft applications such as directional gyro
12
. The gyroscope of
FIG. 6
includes gyro wheel
30
mounted on an inner gimbal
36
which is in turn mounted on an outer gimbal
37
. Directional gyro
12
and the heading gyro used in AHRS applications work best when the inner gimbal is exactly perpendicular to the outer gimbal. When the inner gimbal is correctly oriented, the gyro is said to be ‘erect.’ When the gyro is not erect, its output is inaccurate.
Modem gyros use an automatic erection system to maintain the gimbals in the proper orientation. In one such system, an inclinometer, in the form of a pendulum or an accelerometer is used.
FIGS. 7A and 7B
show a pendulum erection system used with vacuum driven gyros. In
FIG. 7A
, the pendulum
40
hangs in a first orientation when the gimbals are properly aligned. In
FIG. 7B
, pendulum
40
is displaced when the gimbals are not properly aligned, opening air vents
42
which then cause the gyro to move to the desired position under the force of the resulting air flow.
Accelerometer based systems work identical to the pendulum based systems. Both systems are sensitive to the acceleration of gravity and actual aircraft accelerations. Under steady state conditions, or with no aircraft accelerations, both (accelerometer and pendulum) will sense a proper vertical position or “locally level” direction.
In some circumstances, the pendulum may cause op
Katz Kenneth P.
Lehfeldt James J.
Oberg Joseph M.
Sample William G.
Wilson Ronald D.
Camby Richard M.
Honeywell International , Inc.
Honeywell International Inc.
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