A lifting body airplane is a type of airplane consisting of a fuselage without conventional wings, whose shape alone supplies the lift normally created by wings. As the aircraft moves forward, air flows beneath the curved fuselage in the same way it would beneath a flying-wing, generating the lift required for flight. Because no distinct wing is present, a lifting body can be thought of as a fuselage with little or no conventional wing projecting from its sides, an arrangement that lets the body itself act as the lifting surface.
The efficiency of this lifting action is expressed by the lift coefficient, CL, a dimensionless quantity. Lifting body design often takes advantage of structure found on aeroplanes like the Short SC.7 Skyvan, whose fuselage shape produces almost as much lift as each of the attached wings contributes individually.
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Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is a lifting body fuselage?
A lifting body fuselage is a fuselage with little or no conventional wing in which. The aircraft has a thick, included fuselage and a delta wing planform. A lifting body fuselage is a fixed-wing aircraft or spacecraft configuration in which the body itself produces lift. In this arrangement the fuselage is designed so that it essentially acts as a wing. The vehicle relies for lift on the shape of its fuselage rather than on protruding conventional wings. The concept is that aerodynamic lift is obtained from the shape of the vehicle rather than from separate wings, so the fuselage without conventional wings becomes the primary lifting surface.
The configuration is characterised by an airfoil-contoured fuselage: the wide fuselage has an airfoil shape, giving the airplane a large fuselage with no distinct wings. Lifting-body aircraft have been described as wingless vehicles and any small surfaces that remain serve only for stabilising and steering effects, while propulsion is produced by jet engine or engines mounted on the body. Because the fuselage itself generates lift, the configuration eliminates the need for large conventional wings and allows the airplane to be controlled in both lateral and longitudinal directions.
Does a fuselage produce lift?
The fuselage of an airplane will generate lift if it is inclined to the flow. At low angles of attack the increment is modest. The C150 and C172 fuselage and engine together provide only about 5-7% of the total lift. At high angles of attack the fuselage produces positive lift at low speeds and can add noticeable increments to the overall force balance.
More pronounced gains appear when the fuselage is deliberately designed as an airfoil. Burnelli CBY-3 fuselage was airfoil designed to produce lift. Vincent Burnelli developed several aircraft between the 1920s and 1950 that used fuselage lift as a primary source. The Short SC.7 Skyvan produces a substantial amount of lift from its fuselage shape, and in slow flight the Skyvan fuselage produces almost as much lift as the wings.
Even on conventional jet configurations the wide fuselage becomes a contributor. The F-15 Eagle produces substantial lift from the wide fuselage, and the T33 fuselage provides all necessary lift at about 350 kts. The Boeing X-48 carries useful load in a fuselage producing lift, illustrating that any physical body moving through a fluid creates lift if it produces a net turning of the flow.
What is the fuselage lift coefficient?
The fuselage lift coefficient is a dimensionless quantity that aerodynamicists use to model how fuselage shape, inclination, and flow conditions affect lift. It equals the lift generated by the fuselage divided by one-half of the fluid density times the square of the velocity times a reference area. Because it is a dimensionless number, it isolates the pure influence of geometric and flow variables from absolute scale. The coefficient therefore links the local lift force directly to fluid density, flow speed, dynamic pressure, and a suitably chosen reference area.
What is the fuselage lift factor?
The fuselage lift factor is an imperceptible number that scales the pressure distribution over the aircraft structure obtained from aerodynamic loads acting on the body itself, distinct from the wing. Like the wing lift coefficient CL, this factor enters the lift equation that gathers information on factors that affect lift on the fuselage. The local lift L is expressed as L = CL x r x V2 x A, where CL is the lift coefficient, r is the density, V is the velocity, and A is the wing area. Because the fuselage is a blunt, low-aspect shape, its CL is far smaller than a wing's for the same angle of attack. At high angles of attack the inclined body adds noticeable lift. The load factor n equals L / W, so any fuselage lift directly reduces the share of weight that the wing must carry. During knife-edge flight, a sideways-attitude manoeuvre, the exposed side of the fuselage acts like a flat plate inclined to flow and generates a temporary lift force that contributes to the total aerodynamic force, making n deviate from 1. Thus the fuselage lift factor is simply the body's own CL, a small but measurable term in the overall lift budget of the aircraft.
