Low-Speed Limit

At low speeds, the maximum load factor is constrained by the aircraft maximum CL. The low-speed limit in a V-n diagram is established at the velocity at which the aircraft stalls in an acceleration flight load of n until it reaches the limit-load factor. At higher speeds, the maneuver-load factor may be restricted to the limit­load factor, as specified by the regulatory agencies.

Let VS1 be the stalling speed at 1 g. Then:

= (ovCm;) (!) or L=W=(0V S)Cim“

Let Vsn be the stalling speed at ng, where n is a number. Then:

nW = (0.5p V2„S)CLmax

Using Equations 5.1 and 5.2,

n X (0.5p VlS)CLmax = (0.5p V?„S)Clmax


n = Vl/Vl = until n reaches the limit-load factor (5.5)

VA is the speed at which the positive-stall and maximum-load factor limits are simul­taneously satisfied (i. e., VA = VSu/nlimit).

The negative side of the boundary can be estimated similarly.

Figure 5.3. Aircraft angles of attack in pitch-plane maneuvers

5.7.1 High-Speed Limit

VD is equal to the maximum design speed. It is limited by the maximum dynamic pressure that an airframe can withstand. At high altitude, VD may be limited by the onset of high-speed flutter.

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