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Federal Aviation Regulations

Sec. 23.335 — Design airspeeds.

Except as provided in paragraph (a)(4) of this section, the selected design airspeeds are equivalent airspeeds (EAS).

(a) Design cruising speed, V C.For V Cthe following apply:

(1) Where W/S′=wing loading at the design maximum takeoff weight, Vc(in knots) may not be less than—

(i) 33 √(W/S) (for normal, utility, and commuter category airplanes);

(ii) 36 √(W/S) (for acrobatic category airplanes).

(2) For values of W/S more than 20, the multiplying factors may be decreased linearly with W/S to a value of 28.6 where W/S =100.

(3) V Cneed not be more than 0.9 V Hat sea level.

(4) At altitudes where an M Dis established, a cruising speed M Climited by compressibility may be selected.

(b) Design dive speed V D.For V D,the following apply:

(1) V D/MDmay not be less than 1.25 V C/MC; and

(2) With V C min,the required minimum design cruising speed, V D(in knots) may not be less than—

(i) 1.40 V c min(for normal and commuter category airplanes);

(ii) 1.50 V C min(for utility category airplanes); and

(iii) 1.55 V C min(for acrobatic category airplanes).

(3) For values of W/S more than 20, the multiplying factors in paragraph (b)(2) of this section may be decreased linearly with W/S to a value of 1.35 where W/S =100.

(4) Compliance with paragraphs (b)(1) and (2) of this section need not be shown if V D /M Dis selected so that the minimum speed margin between V C /M Cand V D /M Dis the greater of the following:

(i) The speed increase resulting when, from the initial condition of stabilized flight at V C /M C,the airplane is assumed to be upset, flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up with a load factor of 1.5 (0.5 g. acceleration increment). At least 75 percent maximum continuous power for reciprocating engines, and maximum cruising power for turbines, or, if less, the power required for V C/ M Cfor both kinds of engines, must be assumed until the pullup is initiated, at which point power reduction and pilot-controlled drag devices may be used; and either—

(ii) Mach 0.05 for normal, utility, and acrobatic category airplanes (at altitudes where MDis established); or

(iii) Mach 0.07 for commuter category airplanes (at altitudes where MDis established) unless a rational analysis, including the effects of automatic systems, is used to determine a lower margin. If a rational analysis is used, the minimum speed margin must be enough to provide for atmospheric variations (such as horizontal gusts), and the penetration of jet streams or cold fronts), instrument errors, airframe production variations, and must not be less than Mach 0.05.

(c) Design maneuvering speed V A.For V A,the following applies:

(1) V Amay not be less than V Sn where—

(i) V Sis a computed stalling speed with flaps retracted at the design weight, normally based on the maximum airplane normal force coefficients, C NA ; and

(ii) n is the limit maneuvering load factor used in design

(2) The value of V Aneed not exceed the value of V Cused in design.

(d) Design speed for maximum gust intensity, V B. For VB, the following apply:

(1) VBmay not be less than the speed determined by the intersection of the line representing the maximum positive lift, CNMAX, and the line representing the rough air gust velocity on the gust V-n diagram, or VS1√ ng, whichever is less, where:

(i) ngthe positive airplane gust load factor due to gust, at speed VC(in accordance with §23.341), and at the particular weight under consideration; and

(ii) VS1is the stalling speed with the flaps retracted at the particular weight under consideration.

(2) VBneed not be greater than VC.

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as amended by Amdt. 23–7, 34 FR 13088, Aug. 13, 1969; Amdt. 23–16, 40 FR 2577, Jan. 14, 1975; Amdt. 23–34, 52 FR 1829, Jan. 15, 1987; Amdt. 23–24, 52 FR 34745, Sept. 14, 1987; Amdt. 23–48, 61 FR 5143, Feb. 9, 1996]

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