Ask the Mechanic - Biplanes

 Ask the mechanic.

Why did most old aircraft have upper and lower wings, while others had one?
The wings of old aircraft were of very shallow construction and made from cotton stretched over a wooden frame. This made it difficult to get a single wing that had sufficient strength to take the flight and ground loads. The biplane solved this problem by forming a box structure with struts and bracing wires that made it strong and light. Biplanes also had a lower take-off and landing speed, and generated more lift and less drag than an equivalent monoplane design.
How was the alignment of the wings checked?
After assembly, the biplane was supported in the level attitude and the cables between the fuselage and the upper wing centre-section were checked for alignment with the fuselage. The wings were also checked for the ‘stagger’ – that is, the fore-aft distance between leading edges of the upper and lower wings. Another check ensured that both wings would meet the air at the same angle – known as the ‘angle of incidence.’
Why is one wing further back than the other?
Every wing has an area of low pressure above its curved surface and an area of relatively high pressure below the wing – the difference giving the ‘lift’ to the wing. If a second wing is mounted too close to the first then there will be interference between the low-pressure area on the lower wing and the high-pressure area of the upper wing. The designers usually put the upper wing ahead of the lower wing. A notable exception is the 1932 Beech Staggerwing. It has the lower wing ahead of the upper wing, known as ‘negative stagger.’ This improves the pilot’s visibility and also allows the use of a retractable undercarriage.
Why did biplanes go out of style?
Metal structures were strong and light, even if more expensive. As aircraft speeds increased and streamlining became important, the penalty of the drag from the biplanes’ struts and wires was significant. An additional hazard when flying in winter conditions was the serious icing penalties of biplanes. The inter-war period gave rise to scheduled passenger flights where maintaining a schedule was paramount. A huge biplane with a pair of massive wings, struts and wires was unable to handle the winter conditions with safety. This gave rise to the new generation of fighters and transports designed as streamlined monoplanes constructed of metal.
How come the Museum’s Waco Cabin has a smaller lower wing?
To retain the benefit of the box structure, Waco built the lower wing smaller to save weight and drag. This configuration is known as a sesquiplane. This model also has no bracing wires. Instead, a single strut is used between the fuselage and the lower wing to take the compression and tension loads.
What were the last biplanes used in the Canadian military?
The majority of basic training biplanes, such as the Tiger Moth and Fleet Finch were retired by 1945. The Grumman Goblin, a Canadian-built stop-gap fighter, was retired in 1942, while the Supermarine Walrus flying boat and the Fairey Albacore torpedo bomber did not see extensive service in Canada.