# Man's physical universe

372 FORMS OF KNERGY

Flaps and Slots Permit Landings with Smaller Wings Than Would

Otherwise Be Possible.

In order to obtain a relatively low landing speed, a relatively large

wing area is required, but such a large wing area causes too much drag

at high speeds. Flaps on the trailing (rear) edge of a wing airfoil change

the camber of an airfoil and thus give it the greater lifting power and

slower speed required for landing.

Sometimes slots are provided in the leading edge of the wing airfoil.

These slots make it possible to increase the angle of attack from T up

to 30° or more without going into a stall and thus increase the lifting

power of an airplane at slow speeds. When the airplane is nosed up

into a high angle of attack, the air, instead of flowing over the leading

edge, flows up through the slot and over the thick part of the wing,

which gives the airfoil a high lift characteristic. Fixed slots, i.e.,

those which remain open at all times, work automatically to prevent

stalls. Some of the modern small airplanes are stall-proof.

The Direction of Flight of an Airplane Is

as the Rudder, the Elevators, and the Ailerons.

Controlled by Such Airfoils

There are three axes of motion of an aircraft — the vertical, the

longitudinal, and the lateral — about which the airplane may be rotated,

one, two, or all three at a time.

1. The vertical axis. Rotation about the Z-axis, called the yaw,

changes the direction in which the nose is pointing from left to right

and vice versa. Deflection of the tail rudder causes the airplane to

turn just as that of the rudder on a boat turns the boat.

The plane is turned to the left or right by pushing on the rudder bars

with the left or right foot, respectively.

2, The longittidinal axis. Rotation about the X-axis causes one

wing to lift as the other wing is lowered, and the plane is said to roll.

The rolling does for an airplane what banking a turn does for

automobiles.

The airplane is caused to rotate about its longitudinal axis by moving

the stick to either side; the airplane will roll in the same direction that

the stick is moved.

The rolling of the airplane is controlled by the ailerons. The ailerons

are identical to flaps in their action except that as one aileron moves

down the one on the opposite wing moves up.

When making turns an airplane is banked in order to prevent skidding

sidewise. If one overbanks the airplane, it will slip toward the

Thus when one wishes to make a right turn, the right

center of turn.

rudder bar is pushed with the right foot and the stick is moved to the

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