Spar (wing)

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Side view of different designs of wing spars.
a : Box spar
b : I-spar ( double T-beam )
c : C-spar (U-profile).
The straps are shown in gray. They absorb the normal forces from the bending moments. The shear bar is shown in black and absorbs the shear and lateral forces .

A spar or wing spar is the supporting component of an aircraft wing (wing). The bar-shaped beam is from a static view of a cantilever - carrier . Its task is to absorb the transverse forces and bending moments resulting from lift , air currents and inertial forces .


The spar is often designed as a composite cross-section, consisting of the upper and lower chord , which absorb the normal forces from the bending moments, and the web in between, which dissipates shear and lateral forces.

The spar must be sufficiently rigid to prevent impermissible deformation of the sash. Due to the deformations, aircraft wings are calculated according to higher order theory.

With the exception of the box spar, spars consist of open cross-sections in the manner of a solid wall beam . Open cross-sections have a low torsional and warping stiffness . In order to be able to absorb all torsional moments , wings with open spars are usually given an additional, closed profile, the torsion nose .

Depending on the aircraft type and construction, aircraft wings are equipped with several spars or with a main and secondary spar (auxiliary spar). These wings are called Mehrholmer.


In aircraft of metal construction, spars are riveted together from sheet metal or milled from solid (worked out of a block of material).

In the case of wood-built aircraft, the spar is made of plywood . The push bar is made of locked plywood .

In plastic aircraft, spars are made of fiber-plastic composites . With this design, the belts are made from a unidirectional layer . The fabric of the push bar is inserted at a 45 ° angle, the so-called AWV45 . In the case of wings made of plastic, the closed wing shell takes on the role of the torsion nose .

Further areas of application

Spars are also used in rotor blades , e.g. B. by wind turbines and helicopters , as well as in tail units (z. B. the vertical stabilizer ).

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