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A subsonic aircraft is an aircraft with a maximum speed less than the speed of sound (Mach 1). The term technically describes an aircraft that flies below its critical Mach number, typically around Mach 0.8. All current civil aircraft, including airliners, helicopters, future passenger drones, personal air vehicles and airships, as well as many military types, are subsonic.
Although high speeds are usually desirable in an aircraft, supersonic flight requires much bigger engines, higher fuel consumption and more advanced materials than subsonic flight. A subsonic type therefore costs far less than the equivalent supersonic design, has greater range and causes less harm to the environment.
The less harsh subsonic environment also allows a much wider range of aircraft types, such as balloons, airships and rotorcraft, allowing them to fill a much wider range of roles.
Subsonic flight is characterised aerodynamically by incompressible flow, where dynamic pressure changes due to motion through the air cause the air to flow away from areas of high dynamic pressure to areas of lower dynamic pressure, leaving the static pressure and density of the surrounding air constant. At high subsonic speeds, compressibility effects begin to appear. [1]
The propeller is one of the most efficient sources of thrust available and is common on subsonic aeroplanes and airships. Sometimes it is enclosed in the form of a ducted fan. At higher subsonic speeds and at high altitudes, such as attained by most airliners, the turbojet or turbofan becomes necessary. Pure jets such as the turbojet and ramjet are inefficient at subsonic speeds and not often used.
The span and area of a wing are both important to the lift characteristics. They are related by the aspect ratio, which is the ratio of the span, measured from tip to tip, to the average chord, measured from leading edge to trailing edge.
The aerodynamic efficiency of a wing is described by its lift/drag ratio, with a wing giving high lift for little drag being the most efficient. A higher aspect ratio gives a higher lift/drag ratio and so is more efficient. [2]
The drag of a wing consists of two components: the induced drag, which is related to the production of lift, and the profile drag, largely due to skin friction which is contributed to by the whole wing area. [3] It is therefore desirable for a wing to have the least area compatible with the desired lift characteristics. This is best achieved with a high aspect ratio, and high-performance types often have this kind of wing.
But other considerations such as light weight, structural stiffness, manoeuvrability, ground handling and so on often benefit from a shorter span and, consequently a less efficient wing. Small, low-altitude general aviation planes typically have aspect ratios of six or seven; airliners of 12 or more; and high-performance sailplanes of 30 or more.
At speeds above the critical Mach number, the airflow begins to become transonic, with local airflow in some places causing small sonic shock waves to form. This soon leads to the shock stall, causing a rapid increase in drag. [4] The wings of fast subsonic craft such as jet airliners tend to be swept in order to delay the onset of these shock waves.
In theory, induced drag is at its minimum when the span wise distribution of lift is elliptical. A number of factors influence induced drag, however, and as a practical matter a wing of elliptical planform, like that of the Supermarine Spitfire fighter of World War II, is not necessarily the most efficient. The wings of jet airliners, which are highly optimized for efficiency, are far from elliptical in shape.
The ratio of tip chord to root chord is called the taper ratio. Taper has the desirable effect of reducing the root bending stress by shifting the lift inboard, but it has been argued by some noted designers, including John Thorp and Karl Bergey, that an untapered rectangular planform is best for aeroplanes of less than 6,000 pounds gross weight.
In aeronautics, the chord is an imaginary straight line joining the leading edge and trailing edge of an aerofoil. The chord length is the distance between the trailing edge and the point where the chord intersects the leading edge. The point on the leading edge used to define the chord may be the surface point of minimum radius. For a turbine aerofoil the chord may be defined by the line between points where the front and rear of a 2-dimensional blade section would touch a flat surface when laid convex-side up.
A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ).
A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.
A supersonic transport (SST) or a supersonic airliner is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 and it was last flown in 1999 by NASA. Concorde's last commercial flight was in October 2003, with a November 26, 2003 ferry flight being its last airborne operation. Following the permanent cessation of flying by Concorde, there are no remaining SSTs in commercial service. Several companies have each proposed a supersonic business jet, which may bring supersonic transport back again.
A swept wing is a wing that angles either backward or occasionally forward from its root rather than in a straight sideways direction.
In aeronautics, wave drag is a component of the aerodynamic drag on aircraft wings and fuselage, propeller blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects, and tends to present itself as a sudden and dramatic increase in drag as the vehicle increases speed to the critical Mach number. It is the sudden and dramatic rise of wave drag that leads to the concept of a sound barrier.
The Lockheed L-2000 was Lockheed Corporation's entry in a government-funded competition to build the United States' first supersonic airliner in the 1960s. The L-2000 lost the contract to the Boeing 2707, but that competing design was ultimately canceled for political, environmental and economic reasons.
In aeronautics, the aspect ratio of a wing is the ratio of its span to its mean chord. It is equal to the square of the wingspan divided by the wing area. Thus, a long, narrow wing has a high aspect ratio, whereas a short, wide wing has a low aspect ratio.
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars with airfoil wings that redirect air to cause a downforce. It is symbolized as , and the lift-induced drag coefficient as .
In aerodynamics, the critical Mach number of an aircraft is the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it. At the lower critical Mach number, airflow around the entire aircraft is subsonic. Supersonic aircraft such as Concorde and combat aircraft also have an upper critical Mach number at which the airflow around the entire aircraft is supersonic.
A supercritical aerofoil is an airfoil designed primarily to delay the onset of wave drag in the transonic speed range.
A supersonic aircraft is an aircraft capable of supersonic flight, that is, flying faster than the speed of sound. Supersonic aircraft were developed in the second half of the twentieth century. Supersonic aircraft have been used for research and military purposes, but only two supersonic aircraft, the Tupolev Tu-144 and the Concorde, ever entered service for civil use as airliners. Fighter jets are the most common example of supersonic aircraft.
An elliptical wing is a wing planform whose leading and trailing edges each approximate two segments of an ellipse. It is not to be confused with annular wings, which may be elliptically shaped.
In aerodynamics, pitch-up is an uncommanded nose-upwards rotation of an aircraft. It is an undesirable characteristic that has been observed mostly in experimental swept-wing aircraft at high subsonic Mach numbers or high angle of attack.
The wing configuration of a fixed-wing aircraft is its arrangement of lifting and related surfaces.
In aeronautics, a trapezoidal wing is a straight-edged and tapered wing planform. It may have any aspect ratio and may or may not be swept.
A supersonic airfoil is a cross-section geometry designed to generate lift efficiently at supersonic speeds. The need for such a design arises when an aircraft is required to operate consistently in the supersonic flight regime.
An airbreathing jet engine is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air, which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle. Compression may be provided by a gas turbine, as in the original turbojet and newer turbofan, or arise solely from the ram pressure of the vehicle's velocity, as with the ramjet and pulsejet.
The crescent wing is a fixed-wing aircraft configuration in which a swept wing has a greater sweep angle on the inboard section than the outboard, giving the wing a crescent shape.
In aeronautics, the thickness-to-chord ratio, sometimes simply chord ratio or thickness ratio, compares the maximum vertical thickness of a wing to its chord. It is a key measure of the performance of a wing planform when it is operating at transonic speeds.