An interplane strut is an aircraft airframe component designed to transmit lift and landing loads between wing (mainplane) panels on biplanes and other aircraft with multi-wing designs. They also maintain the correct angle of incidence for the connected wing panels and are often braced with wires. Very early aircraft used interplane struts made from bamboo, while later designs employed streamlined struts made either from spruce or ash; woods chosen for their strength and light weight. More modern or higher performance aerobatic biplanes often feature metal interplane struts.
The most common configuration is for two struts to be placed in parallel, one behind the other. These struts will usually be braced by "incidence wires" running diagonally between them, and more than one of these strut pairs may be placed along the span of the wing, creating multiple "bays" (see below). Other common arrangements include N-struts, where the diagonal bracing wires are replaced by an extra wooden or metal member running diagonally from the top of one strut to the bottom of the other in a pair; V-struts, where the struts from the upper wing converge to a single point on the lower wing (commonly used when the lower wing has a considerably smaller chord than the upper wing); and the I-strut, where the pair of struts is replaced by a single, thicker strut. Some biplane wings are braced with struts forming a Warren truss.
The compartments created by adding interplane struts are known as "bays"; this relates to only one side of the aircraft's wing panels. For example, the de Havilland Tiger Moth is a single-bay biplane where the Bristol F.2 Fighter is a two-bay biplane.
V-strut on a Nieuport 10
N-strut on a Boeing-Stearman Model 75
I-strut on an Antonov An-2
Struts arranged in a Warren truss on a Fiat C.R.42
- Taylor, 1990. p. 71.
- Taylor, 1990. p. 76
- Taylor, John W.R. The Lore of Flight, London: Universal Books Ltd., 1990. ISBN 0-9509620-1-5.