Why do older planes have double levels of wings ?

In layman terms, a plane needs wingspan in order to increase the surface area of which the force lift can act on it. This is because of only one major reason- their engines weren't strong enough.This thus meant that aeroplanes could only fly slowly. read more

Engines of earlier planes did not have a lot of power, so two wings were used although there were many single, or monoplane, winged aircraft at the time. Although some had more, like the Fokker Tri-plane. The wings provided extra lift and manuverability. Also, powered flight was in its infancy, aeronautical engineering was a new field. read more

Etrich Taube in flight. Note the truss below the wing and the many wires keeping it in shape (picture source). The shorter wingspan of a biplane also reduces the load on the wings. Biplanes tend to have a lot of lift (for their size) because of the large wing area, but also a lot of drag, so they're quite inefficient overall. read more

Simply put, planes have wings to generate the necessary amount of ‘lift’ to fly it in the air. An airplane’s wings are designed according to the Bernoulli’s theorem. read more