Wind Effects and Crab Corrections -Cont.

CHAPTER FOUR

T-34C CONTACT

direction as its path over the ground or, to put it another way, the path of the aircraft through the

air and its path over the ground coincide. However, you will notice the aircraft does not always

follow a course over the ground in the same direction the nose is pointed.

You have been or will be, at one time or another, flying parallel to a road or section line. The

longitudinal axis of the aircraft is aligned perfectly with this road or section line and you are

flying a straight and level course. Suddenly, you realize that the aircraft is getting closer to the

road or has actually crossed it, without any turn having been made. This would indicate to you

that the air in which you are flying is moving in a direction which has caused the aircraft to cross

the road at some angle.

Suppose you were flying along straight and level and the wind was blowing 30 knots from a

direction 90 to your left. At the end of one hour, the body of air in which you were flying would

have moved 30 miles to your right. Since the aircraft was in the body of air, and moving with it,

you and the aircraft would also have drifted 30 miles to your right in one hour. Of course, in

relation to the air mass itself, you would have moved forward only, but in relation to the ground,

you would have moved forward and 30 miles sideways. This effect of the movement of the air

on the track of the aircraft is known as drift. The difference between the actual heading of the

aircraft and its track over the ground is called the angle of drift. Drift must be compensated for,

in order to cause the aircraft to maintain a desired track over the ground. The proper way to

correct the drift when you are flying in straight and level flight and wish to follow a desired

ground track, is to make a shallow balanced turn into the wind. When you seem to have the

drifting effect neutralized or stopped, return to straight and level flight. The aircraft is now

pointed into the wind slightly. This causes the aircraft to fly into the wind at the rate that the

wind is trying to move it sideways. Since the effect of drift has now been neutralized, the

aircraft will fly a straight and selected ground track. The nose of the aircraft, however, is not

pointed in the direction of the ground track. This is known as drift correction, and is usually

referred to as "crabbing" because the aircraft is moving sideways in relation to the ground.

(Figure 4-9).

4-16

FUNDAMENTAL FLIGHT CONCEPTS