Aeronautics and astronautics – Aircraft control
Reexamination Certificate
2001-08-14
2003-11-04
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Aircraft control
Reexamination Certificate
active
06641086
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of aircraft and, more specifically, to systems and methods for controlling aircraft.
BACKGROUND OF THE INVENTION
Aircraft generally have a variety of control surfaces that can be deflected to cause the aircraft to perform maneuvers during flight.
FIG. 1
illustrates an aircraft
8
having typical control surfaces. Aircraft
8
includes an airframe
10
, a first wing
13
, a second wing
16
, and a rudder
19
. Movably coupled to first wing
13
is a flap
14
and an aileron
15
, and movably coupled to second wing
16
is a flap
17
and an aileron
18
. Flap
14
and flap
17
can be extended from the trailing edge of first wing
13
and second wing
16
, respectively, to generate increased lift for aircraft
8
, which can cause aircraft
8
to climb. Aileron
15
and aileron
18
, on the other hand, are hingedly coupled to first wing
13
and second wing
16
, respectively, and can be deflected relative to the trailing edge of first wing
13
and second wing
16
, respectively, to generate increased or decreased lift. Because of their distance from a centerline
11
of aircraft
8
, the increased or decreased lift generated by deflecting aileron
15
or aileron
18
can readily cause aircraft
8
to rotate about centerline
11
, i.e., a roll maneuver. For example, deflecting aileron
15
downward generates increased lift, and deflecting aileron
18
upward generates decreased lift, which together can cause aircraft
8
to roll in the direction of arrow
12
. In general, aileron
15
and aileron
18
can be deflected simultaneously, albeit in opposite directions, or individually to cause aircraft
8
to roll in either direction. Note, aileron
15
and aileron
18
can also be used in making turns, especially coordinated turns. In addition, rudder
19
can be deflected to turn aircraft
8
either left or right, i.e., a yaw maneuver. Rudder
19
, however, can also be used during roll maneuvers, as discussed below.
FIG. 2
is a plot illustrating the relation between the coefficient of drag and the coefficient of lift for first wing
13
and second wing
16
based on the deflection of aileron
15
and aileron
18
, respectively. Note, the coefficient of lift and the coefficient of drag are converted to actual lift and drag forces by multiplying the coefficients by the area of the surface and the square of the velocity. When aircraft
8
is flying level, aileron
15
and aileron
18
are typically set so that first wing
13
and second wing
16
have substantially equally coefficients of lift and drag, represented by point
15
U and point
18
U, respectively, allowing aircraft
8
to be balanced in roll moment and yaw moment. When aircraft
8
is to execute a roll maneuver, however, the coefficient of lift and the coefficient of drag for first wing
13
and second wing
16
change, due to the deflection of aileron
15
and aileron
18
, respectively. For example, when aircraft
8
is to roll in the direction of arrow
12
in
FIG. 1
, aileron
15
deflects downward, causing the coefficient of lift to increase and a consequent increase in the coefficient of drag, represented by point
15
DD, and aileron
18
deflects upward, causing the coefficient of lift to decrease and a consequent decrease in the coefficient of drag, represented by point
18
DU. The increased lift generated by the deflection of aileron
15
and the decreased lift generated as a consequence of the deflection of aileron
18
cause aircraft
8
to roll in the direction of arrow
12
. However, the increased drag generated as a consequence of the deflection of aileron
15
and the decreased drag generated as a consequence of the deflection of aileron
18
produce a moment that causes aircraft
8
to yaw in the direction of first wing
13
, i.e., away from the roll, termed “adverse yaw.”
Typically, an adverse yaw moment is not problem because aircraft have control surfaces, such as rudders or differential drag flaps, to compensate for the induced yaw moment. Rudder
19
of aircraft
8
, for example, may be deflected to compensate for an induced yaw moment. But in aircraft that have no such control surfaces, or prefer not to use them due to radar cross section concerns, compensating for either adverse yaw moment or its opposite, i.e., proverse yaw moment, during a roll maneuver becomes more difficult.
SUMMARY OF THE INVENTION
The present invention provides a system and method that substantially reduces or eliminates at least some of the disadvantages and problems associated with previously developed aircraft control surfaces. Accordingly, in certain embodiments, the present invention provides a system and method that compensate for yaw moment during at least certain roll maneuvers of an aircraft without the use of a rudder or differential drag flaps.
In particular embodiments, a system in accordance with the present invention includes an airframe, a first airfoil, and a second airfoil. The first airfoil is coupled to a first side of the airframe, and the second airfoil is coupled to a second side of the airframe, at least a portion of the first airfoil and at least a portion of the second airfoil being controllably deflectable to facilitate roll maneuvers of the aircraft. The deflectable portion of the first airfoil is deflectable to generate increased lift and a consequent increased drag for at least a portion of the first airfoil, and the deflectable portion of the second airfoil is deflectable to generate negative lift and a consequent increased drag for at least a portion of the second airfoil during at least one roll maneuver, the increased lift of the first airfoil and the decreased lift of the second airfoil causing the aircraft to roll, and the increased drag of the second airfoil producing a yaw moment that counteracts the yaw moment produced by the increased drag of the first airfoil such that the roll maneuver does not substantially change the yaw moment of the aircraft.
In other embodiments, a method in accordance with the present invention includes deflecting at least a portion of a first airfoil to generate increased lift and a consequent increased drag for at least a portion of the airfoil to facilitate a roll maneuver and deflecting at least a portion of a second airfoil to generate negative lift and a consequent increased drag for at least a portion of the airfoil to facilitate the roll maneuver. The increased lift of the first airfoil and the decreased lift of the second airfoil generate a roll moment causing the aircraft to roll, and the increased drag of the second airfoil produces a yaw moment that counteracts the yaw moment produced by the increased drag of the first airfoil such that the roll maneuver does not substantially change the yaw moment of the aircraft.
The present invention has several technical features and advantages. For example, in particular embodiments, the invention allows an aircraft to perform a roll maneuver without substantially changing the yaw moment of the aircraft, which allows the aircraft to perform a roll maneuver without substantial adverse yaw. This ability may be particularly useful in making coordinated turns in aircraft where the design emphasis is on low radar cross section, because the use of rudders or differential drag flaps to compensate for adverse yaw increases radar cross section. As another example, in certain embodiments, the invention allows an aircraft to perform a roll maneuver without experiencing a substantial change in net lift, which prevents the aircraft from losing altitude during the maneuver. As an additional example, in some embodiments, the invention allows an aircraft to perform a roll maneuver without substantially changing the pitch moment of the aircraft, which prevents the aircraft from changing its longitudinal orientation during the maneuver. As a further example, in certain embodiments, the invention allows an aircraft to produce a yaw moment without substantially changing the roll moment. This could allow a pilot to line up the aircraft with the runway
Baker & Botts L.L.P.
Holzen Stephen A.
Northrop Grumman Corporation
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