§23.333 Flight envelope.

(a) General. Compliance with the strength requirements of this subpart must be shown at any combination of airspeed and load factor on and within the boundaries of a flight envelope (similar to the one in paragraph (d) of this section) that represents the envelope of the flight loading conditions specified by the maneuvering and gust criteria of paragraphs (b) and (c) of this section respectively. (b) Maneuvering envelope. Except where limited by maximum (static) lift coefficients, the airplane is assumed to be subjected to symmetrical maneuvers resulting in the following limit load factors: (1) The positive maneuvering load factor specified in Sec. 23.337 at speeds up to VD; (2) The negative maneuvering load factor specified in Sec. 23.337 at VC; and (3) Factors varying linearly with speed from the specified value at VC to 0.0 at VD for the normal [and commuter category,] and -1.0 at VD for the acrobatic and utility categories. (c) Gust envelope. (1) The airplane is assumed to be subjected to symmetrical vertical gusts in level flight. The resulting limit load factors must correspond to the conditions determined as follows: (i) Positive (up) and negative (down) gusts of 50 f.p.s. at VC must be considered at altitudes between sea level and 20,000 feet. The gust velocity may be reduced linearly from 50 f.p.s. at 20,000 feet to 25 f.p.s. at 50,000 feet. (ii) Positive and negative gusts of 25 f.p.s. at VD must be considered at altitudes between sea level and 20,000 feet. The gust velocity may be reduced linearly from 25 f.p.s. at 20,000 feet to 12.5 f.p.s. at 50,000 feet. [(iii) In addition, for commuter category airplanes, positive (up) and negative (down) rough air gusts of 66 f.p.s. at VB must be considered at altitudes between sea level and 20,000 feet. The gust velocity may be reduced linearly from 66 f.p.s. at 20,000 feet to 38 f.p.s. at 50,000 feet.] (2) The following assumptions must be made: (i) The shape of the gust is-- where-- s = Distance penetrated into gust (ft.); = Mean geometric chord of wing (ft.); and Ude = Derived gust velocity referred to in subparagraph (1) of this section. (ii) Gust load factors vary linearly with speed between VC and VD. [(d) Flight envelope. ] Note: Point G need not be investigated when the supplementary condition specified in Sec. 23.369 is investigated.