Airborne Distance

From Figure 7.20, since 0n is a small angle, the total airborne distance, sA, is given by

This assumes the flare to be a circular arc having a radius of R. If VA is the approach velocity, this velocity is assumed to remain constant throughout the flare. The acceleration toward the center of curvature, a„, will therefore be

R

However,

T ur – w

L— W = —a„

Thus,

h

g(UW-l)

If CLa denotes the lift coefficient during the steady approach then, during the flare,

The flare radius can therefore be expressed as

FAR Part 25 requires that VA exceed the stalling speed in the landing configuration by 30%. Thus,

Thus the ratio CJCLa can vary anywhere, from just above 1 to 1.69 or higher. \ typical value of this ratio for jet transports is 1.2. Using this value, but keeping in mind that it can be higher, the total airborne distance, in meters, becomes

15.2

“ T~ +

tfD

A jet transport approaches typically at a speed of 125 kt at an angle of 3°. Thus,

sA — 290 + 55

= 350 m (1155 ft.)

After touchdown, an approximately 2-sec delay is allowed while the pilot changes from the landing to the braking configuration. During this period the airplane continues to roll at the speed VA. Actually, practice has shown that the speed decreases during the flare by approximately 5 kt typically. Denoting this portion by a subscript “tran” for transition,

Stran=2(FA)

= 130 m (427 ft)