Editing Biplane (section)

=== Advantages and disadvantages ===
[[File:Antonov an2 ha-mkf arp.jpg|thumb|Soviet [[Antonov An-2]] biplane from the 1940s]]
The primary advantage of the biplane over a [[monoplane]] is its ability to combine greater stiffness with lower weight. Stiffness requires structural depth and where early monoplanes had to have this provided with external bracing, the biplane naturally has a deep structure and is therefore easier to make both light and strong. Rigging wires on non-cantilevered monoplanes are at a much sharper angle, thus providing less tension to ensure stiffness of the outer wing. On a biplane, since the angles are closer to the ideal of being in direct line with the forces being opposed, the overall structure can then be made stiffer. Because of the reduced stiffness, wire braced monoplanes often had multiple sets of flying and landing wires where a biplane could easily be built with one bay, with one set of landing and flying wires. The extra drag from the wires was not enough to offset the aerodynamic disadvantages from having two airfoils interfering with each other however. Strut braced monoplanes were tried but none of them were successful, not least due to the drag from the number of struts used.{{facts|date=August 2021}}

The structural forces acting on the spars of a biplane wing tend to be lower as they are divided between four spars rather than two, so the wing can use less material to obtain the same overall strength and is therefore lighter. A given area of wing also tends to be shorter, reducing bending moments on the spars, which then allow them to be more lightly built as well.<ref>Berriman, 1913, p.26</ref> The biplane does however need extra struts to maintain the gap between the wings, which add both weight and drag.

The low power supplied by the engines available in the first years of aviation limited aeroplanes to fairly low speeds. This required an even lower [[Stall (fluid dynamics)|stalling]] speed, which in turn required a low [[wing loading]], combining both large wing area with light weight. Obtaining a large enough wing area without the wings being long, and thus dangerously flexible was more readily accomplished with a biplane.{{facts|date=August 2021}}

The smaller biplane wing allows greater [[Aerobatics|maneuverability]]. Following World War I, this helped extend the era of the biplane and, despite the performance disadvantages, most [[fighter aircraft]] were biplanes as late as the mid-1930s. Specialist sports [[aerobatics|aerobatic]] biplanes are still made in small numbers.{{facts|date=August 2021}}

Biplanes suffer aerodynamic interference between the two planes when the high pressure air under the top wing and the low pressure air above the lower wing cancel each other out.{{dubious|date=August 2021}} This means that a biplane does not in practice obtain twice the lift of the similarly-sized monoplane. The farther apart the wings are spaced the less the interference, but the spacing struts must be longer, and the gap must be extremely large to reduce it appreciably.

As engine power and speeds rose late in [[World War I]], thick cantilever wings with inherently lower drag and higher wing loading became practical, which in turn made monoplanes more attractive as it helped solve the structural problems associated with monoplanes, but offered little improvement for biplanes.{{facts|date=August 2021}}