Question

Can a human fly with wings? In order for a 70?? person to hover in the air by beating two wings at 1??, how large does each wing have to be? Assume that the up-stroke and the down-stroke motions take the same amount of time, and that the amplitude of wing beat equals the distance of free fall (i.e. “hovering”). Treat the wings as horizontal in the entire down-stroke. Ignore the air resistance during the up-stroke. Also assume that the lifting force is completely provided by a constant force of air resistance during the down- stroke. Estimate the area of each wing that is facing down during the down-stroke.

Answer 1

Solution:

Among the living animal species, true flight is confined to insects, birds and bats. Man has to use machines to be able to flight. We should first know the essential elements necessary for flight. These are-

1) a light weight high strength structure 2) wings and feathers for generating lift and forward thrust 3) flight muscles to provide the power 4) a fast response flight control and navigation system.

The basic aerodynamic requirements for sustained flight are:

1) Enough lift to balance body weight, and

2) Enough forward thrust to balance backward body drag.

The estimates and calculations provide information and sometimes explanations to wing shape, overall weight and musculature.

The amount of lift(L) and drag(D) generated by the motion of a wing through the air depend upon the five main factors:

1) shape of the wings

2) angle between the surface of wing and direction of air stream

3) area of the wing(S)

4) density of the air and its kinematic viscosity

5) velocity of the air stream relative to the wing(V)

The relationship between these factors can be :

where & are non dimensional coefficients which depends upon properties of the airfoil section and Reynolds number.

Power required for flight is given by the expression as-

Where

Power for hovering flight:

The above equation cannot hold for V=0, which is the case of hovering flight. To get an estimate of the power required for hovering we can use simple momentum or actuator disc theory

For the hovering condition V=0 and is negligible. The induced velocity is

and the induced power for hovering is

  

In terms of aspect ratio and wing area.

By understanding this mechanics we can easily conclude about the requirements for human flight.