Compression lift
Encyclopedia
In aerodynamics
, compression lift refers to an aircraft
that uses shock wave
s generated by its own supersonic
flight to generate lift
. This can lead to dramatic improvements in lift for supersonic
/hypersonic
aircraft, which often fly at high altitudes and thus suffer from decreased lift due to the thin air. Clarence A. Syvertson
and Alfred J. Eggers
discovered this phenomenon 1956 as they analyzed abnormalities at the reentry of nuclear warheads.
The basic concept of compression lift is well known; "planing" boats reduce drag by "surfing" on their own bow wake in exactly the same fashion. Using this effect in aircraft is more difficult, however, because the "wake" does not generate until supersonic speeds, and is highly angled. Aircraft have to be carefully shaped to take full advantage of this effect. In addition the angle of the shock wave
s varies greatly with speed, making it even more difficult to design a craft that gains significant lift over a wide range of speeds.
To date the only potential production aircraft that used compression lift has been the XB-70 in the 1960s, although with the cancellation of the program after only two prototypes had been built, it ended up being a testbed only. The compression lift decreased the induced drag of the XB-70 about 30%. Designs using compression lift, waverider
s, remain an interesting possibility for hypersonic
vehicle designs, although only testbed models have been flown.
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
, compression lift refers to an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
that uses shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
s generated by its own supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
flight to generate lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
. This can lead to dramatic improvements in lift for supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
/hypersonic
Hypersonic
In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...
aircraft, which often fly at high altitudes and thus suffer from decreased lift due to the thin air. Clarence A. Syvertson
Syvertson
Clarence A. "Sy" Syvertson is the retired Center Director of the Ames Research Center of the National Aeronautics and Space Administration, located at Moffett Field, California....
and Alfred J. Eggers
Alfred J. Eggers
Alfred J. Eggers, Jr. was NASA's Assistant Administrator for Policy and devoted efforts to determine the influence of aviation technology in world peace and lectured widely....
discovered this phenomenon 1956 as they analyzed abnormalities at the reentry of nuclear warheads.
The basic concept of compression lift is well known; "planing" boats reduce drag by "surfing" on their own bow wake in exactly the same fashion. Using this effect in aircraft is more difficult, however, because the "wake" does not generate until supersonic speeds, and is highly angled. Aircraft have to be carefully shaped to take full advantage of this effect. In addition the angle of the shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
s varies greatly with speed, making it even more difficult to design a craft that gains significant lift over a wide range of speeds.
To date the only potential production aircraft that used compression lift has been the XB-70 in the 1960s, although with the cancellation of the program after only two prototypes had been built, it ended up being a testbed only. The compression lift decreased the induced drag of the XB-70 about 30%. Designs using compression lift, waverider
Waverider
A waverider is a hypersonic aircraft design that improves its supersonic lift-to-drag ratio by using the shock waves being generated by its own flight as a lifting surface. To date the only aircraft to use the technique is the Mach 3 supersonic XB-70 Valkyrie, which was waverider-like with its...
s, remain an interesting possibility for hypersonic
Hypersonic
In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...
vehicle designs, although only testbed models have been flown.