Figure 3-7 Proper Crab Directions

CHAPTER THREE

T-6A CONTACT

311.

WIND EFFECTS AND CRAB CORRECTIONS

The path of aircraft travel over the ground will be determined not only by the direction in which

it is headed, but also by the direction and velocity of the air mass movement (i.e. the winds) in

which the aircraft is flying. In perfectly still air, the nose of the aircraft points exactly in the

same 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.

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

left and at 90 to the direction your aircraft was pointed. 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 that

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. The

effect of the movement of air on the track of the aircraft is known as drift. The difference

between the actual heading of the aircraft and its actual track over the ground is called the angle

of drift. Drift must be compensated for in order for the aircraft to maintain a desired track over

the ground. The heading compensation to correct for drift is called crab.

The proper way to correct for drift when you are flying in straight and level flight is to make a

shallow balanced turn into the wind. When you have the drifting effect neutralized or stopped,

return to straight and level flight. This causes the aircraft to fly into the wind at the rate the wind

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

fly straight down the selected ground track. With the nose now angled off your ground track, you

have now applied a drift correction and are "crabbing into the wind." Figure 3-7- shows proper

crab angles into the wind to fly the given rectangular ground track. Notice that on the top and

bottom sides of the rectangle, the aircraft experiences pure headwind or tailwind. No crab is

necessary; only the actual ground speed is affected flying perfectly into or with the wind.

Figure 3-7 Proper Crab Directions

3-10

FUNDAMENTAL CONCEPTS