Total Aircraft Drag

Total aircraft drag is the sum of all drags estimated in Sections 9.8 through 9.12, as follows for LRC and HSC:

At LRC,

C2

Cd — CDpmin + &Cdd + ПІК (9’30)

At HSC,

C2

( Merit )CD ‘ + CDw (9.31)

п AK

At takeoff and landing, additional drag exists, as explained in the next section.

9.11 Low-Speed Aircraft Drag at Takeoff and Landing

For safety in operation and aircraft structural integrity, aircraft speed at takeoff and landing must be kept as low as possible. At ground proximity, lower speed would provide longer reaction time for the pilot, easing the task of controlling an aircraft at a precise speed. Keeping an aircraft aloft at low speed is achieved by increas­ing lift through increasing wing camber and area using high-lift devices such as a flap and/or a slat. Deployment of a flap and slat increases drag; the extent depends on the type and degree of deflection. Of course, in this scenario, the undercarriage remains extended, which also would incur a substantial drag increase. At approach to landing, especially for military aircraft, it may require “washing out” of speed to slow down by using fuselage-mounted speed brakes (in the case of civil air­craft, this is accomplished by wing-mounted spoilers). Extension of all these items is known as a dirty configuration of the aircraft, as opposed to a clean configuration at cruise. Deployment of these devices is speed-limited in order to maintain structural integrity; that is, a certain speed for each type of device extension should not be exceeded.

After takeoff, at a safe altitude of 200 ft, pilots typically retract the undercar­riage, resulting in noticeable acceleration and gain in speed. At about an 800-ft alti­tude with appropriate speed gain, the pilot retracts the high-lift devices. The air­craft is then in the clean configuration, ready for an enroute climb to cruise altitude; therefore, this is sometimes known as enroute configuration or cruise configuration.

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