Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2002-08-23
2003-08-05
Carone, Michael J. (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S039000
Reexamination Certificate
active
06601795
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
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FEDERALLY SPONSORED RESEARCH
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REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX
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1. Background of the Invention—Field of Invention
The invention relates to air vehicles such as manned and unmanned aircraft, missiles, and bombs that fly in the air and, in particular, to air vehicles having scissors wings that improve their aerodynamic performance at a wide range of speed.
2. Background of the Invention—Description of Prior Art
The contradictory requirement of wing aspect ratio at high speed and low speed flying is a major obstacle preventing existing air vehicles from efficiently and effectively flying at both low speed and high speed up to supersonic speed.
The aspect ratio of a wing is defined as the square of the wingspan divided by the area of the wing. At transonic and supersonic flying, wings of low aspect ratio, such as delta wings and swept-back wings, are preferred for air vehicles because they have much less drag than wings of high aspect ratio. However, wings of high aspect ratio are preferred for air vehicles in the condition of low speed flying, take-off, and landing because they have higher lift-to-drag (L/D) ratio than wings of low aspect ratio. This contradictory requirement of aspect ratio for flying at high speed and low speed makes existing supersonic aircraft with wings of low aspect ratio inefficient in the flying conditions of low speed flying, take-off, and landing.
Concorde, the supersonic passenger aircraft having a pair of delta wings, needs a long take-off run to reach its 400 kilometers/hour (250 miles/hour) take-off speed that is higher than the take-off speed of most subsonic aircraft like Boeing 747. In addition, the low lift-to-drag ratio (L/D) of its delta wings demands high engine thrust to take-off and fly at low speed, making Concord a noisy aircraft around airports. The requirement of high engine thrust at low speed also makes Concorde consume a lot of fuel to climb to its cruise altitude, contributing to the high operating cost of the aircraft.
Although modern fighter aircraft with wings of low aspect ratio have excellent take-off and landing performance, it is mainly achieved by high thrust-to-weight ratio and low wing loading, which are too costly and inefficient for non-fighter aircraft. In other words, at an expense of high fuel consumption, fighter aircraft mainly rely on high engine thrust and big wings to achieve short take-off and landing.
In addition, the “area rule” of transonic and supersonic flying adds another problem to aircraft with wings of low aspect ratio. In order to conform to the “area rule” to have low transonic and supersonic drag, aircraft with wings of low aspect ratio usually need to have a fuselage with an indentation, or “wasp waist”, around the place where wings are installed. This “wasp waist” increases the cost to manufacturer the aircraft and reduces the spaces for payload such as passengers and cargo.
One attempt to make aircraft efficiently flying at both low and high speed is variable sweep wings. The concepts of aircraft with variable sweep wings are shown in U.S. Pat. No. 3,053,484 issued to W. J. Alford, Jr. et al, U.S. Pat. No. 3,405,280 issued to F. G. Willox et al, U.S. Pat. No. 3,405,891 issued to R. Jacquart et al, and U.S. Pat. No. 3,447,761 issued to P. C. Whitener et al. Existing aircraft like Boeing B-1B bomber have adopted variable sweep wings. According to the configuration, at take-off, landing, and low speed flying, the sweepback angle of the wings is small, making the wings somewhat similar to a pair of straight wings. At high speed flying, the wings are swept back so that the sweepback angle is big, making the wings similar to a pair of swept-back wings.
Variable sweep wings have structure and control disadvantages. The pivotally mounted left and right wings generate huge bending moments on the left and right pivot points at wing roots. In order to transfer the bending moments as well as ensure the smooth swiveling of the wings, the pivot points must be structurally strong and thus structurally heavy. These heavy pivot points and the additional control system for swiveling the wings make an aircraft structurally inefficient. In addition, the swiveling of the wings changes the center of lift and center of gravity of the aircraft, requesting large horizontal stabilizers to balance the aircraft. Some aircraft even have a system that can quickly transfer fuel from one place to another place in the aircraft to facilitate the balancing of the aircraft when the wings are swiveling. The shift of center of lift and center of gravity make the aircraft difficult to control, and the large horizontal stabilizers and fuel transfer system also add weight to the aircraft.
Oblique wing is another attempt to optimize both high speed and low speed performance by modifying the wing configuration of an air vehicle during flight. This concept is shown in U.S. Pat. Nos. 3,971,535 and 3,737,121, both issued to R. T. Jones, and U.S. Pat. No. 5,154,370 issued to J. W. Cox et al. The basic idea of oblique wing is to have a main wing pivotally installed on the fuselage or fuselages of an aircraft. The pivotal attachment allow the main wing to be yawed relative to the fuselage or fuselages for high speed flight, and to be positioned at right angles with respect to the fuselage or fuselages during take-off, landing, and low speed flight.
Oblique wing configuration has inherent stability and control disadvantages. One problem is the coupling of roll and pitch movement of the aircraft. For example, suppose the wing is yawed to an angle so that the right side of the wing becomes a swept-forward wing, the left side of the wing becomes a swept-back wing, and the aircraft uses ailerons or flaperons to achieve roll control. When the pilot of the aircraft wants to bank the aircraft to the left, the aircraft will make an unexpected nose-up movement while banking to the left. On the country, when the pilot wants to bank to the right, the aircraft will make an unexpected nose-down movement while banking to the right. The reason of this problem is that the ailerons or flaperons on the left and right wings are not located along the same transverse axis thus generate pitch movement moments when they are adjusted to roll the aircraft. Another problem is that the aerodynamic lift generated by the oblique wing is not evenly distributed along the long axis of the wing when the wing is at a high yaw angle from perpendicular to fuselage. This causes a roll moment on the aircraft. In order to solve this problem, both U.S. Pat. Nos. 3,971,535 and 3,737,121 issued to R. T. Jones invent the wing to be upwardly curved at both ends of the wing. The upward curved ends make the swept-forward part of the oblique wing has a higher angle-of-attack than the swept-back part of the wing. By constructing the wing to a specific upward curvedness, the aircraft can fly at a certain speed with the wing yawed at a certain angle without generating the unexpected roll moment. However, this fixed upward curvedness cannot eliminate the roll moment at a wide variety of flying conditions, limiting the flexibility of an oblique wing aircraft.
U.S. Pat. No. 4,998,689 issued to R. R. Woodcock and U.S. Pat. No. 3,155,344 issued to R. Vogt show a concept of “two-position wing”. The “two-position wing” is rotatably mounted on the fuselage of an aircraft and consists of two sets of wings, one set is a pair of supersonic wings and another is a pair of subsonic wings. At low speed flying, take-off, and landing, the “two-position wing” is at a position that the pair of subsonic wings is used and the pair of supersonic wings is attached to the fuselage. At supersonic flying, the “two-position wing” rotates 90 degrees to another position so that the pair of supersonic wings generates lift but the pair of subsonic wings is attached to the fuselage.
This concept has two disadvantages. First, both the supersonic and subsonic wings have to have their airf
Carone Michael J.
Matz Daniel
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