What are the strengths and weaknesses of biplane vs monoplane design?

As an aircraft scales up, its weight goes up as the cube of the scale, while the wing area goes up only as the square. Double an airplane size in all dimensions and it will be 8 times the mass but only will have 4 times the wing area (and accordingly 4 times the lift at a given speed).

Early planes did not fly fast, and since they are quite large compared with birds, would need proportionally longer wings that a scaled bird has. Structurally, a very long and thin wing (like those on sailplane) are heavy and fragile. So it made sense to cut the wing in two chunks and stack those on top of one another: the wings became stubbier and thus easier to build, cross- bracing would ensure rigidity, while the shorter span would improve maneuverability.

As planes started flying faster, the need of very large wing reduced (on the other hand, it required longer takeoff and landing runs, as those would be done at a higher speed) and flaps were added to increase the area for the take off and landing phases. Material were changed (wood and fabric were replaced with metallic alloys and more recently composites) allowing a wing to be made larger without too much weight, and the need for a biplane configuration went away.

For the record, the first aircraft to fly across the English channel in 1909 (Louis Bleriot) was a monoplane. Deperdussin was also producing monoplane aircraft before the first world war, so it was not all the planes of that time that were biplanes.

Actually, there WERE airplanes with only one wing back in the early days of aviation. Louis Bleriot was the first to cross the English Channel in a powered, heavier than air craft in 1909, using a single wing aircraft of his own design. Santos DuMont, the "father of aviation" in Brazil also built and flew monoplane aircraft

The MAIN reason for two wings was that with the stick-and-fabric structure technology of the day, a biplane could carry a heavier load, and the structure could be made stronger due to cross-bracing between the two wings. Single wing airplanes (monoplanes) didn't become popular until after the end of WWI, when metal frames and wing structures became more common.

Biplanes were used initially because the wing layout allowed the wings to be braced against each other and also allowed greater wing area within a smaller span, span being the difficulty with building strong wings.

Once stronger materials, such as duralumin and monococque construction were developed, monoplanes are aerodynamically far cleaner and more efficient

Hi the reason was about the wing design as a biplane used a very simple aerophile shape. the later monoplane uses a much detailed shape. this is what R.J Mitchel discovered when designing the super marine wings which they used in the design which became the spitfire.

Probably better wing design thus more lift less drag made for the change.

Neither me or my memom knows. I hope someone knows