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FAA Federal Aviation Regulations (FARS, 14 CFR)

FARs   >   Part 23   >   Section 335 - Design airspeeds

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

(a) Design cruising speed, VC. For VC the 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) VC need not be more than 0.9 VH at sea level.

(4) At altitudes where an MD is established, a cruising speed MC limited by compressibility may be selected.

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

(1) VD/MD may not be less than 1.25 VC/MC; and

(2) With VC min, the required minimum design cruising speed, VD (in knots) may not be less than --

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

(ii) 1.50 VC min (for utility category airplanes); and

(iii) 1.55 VC 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 VD/MD is selected so that the minimum speed margin between VC/MC and VD/MD is the greater of the following:

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(i) The speed increase resulting when, from the initial condition of stabilized flight at VC/MC, 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 VC/MC for 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 MD is established); or

(iii) Mach 0.07 for commuter category airplanes (at altitudes where MD is 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.

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

(1) VA may not be less than VS√ n where --

(i) VS is a computed stalling speed with flaps retracted at the design weight, normally based on the maximum airplane normal force coefficients, CNA; and

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

(2) The value of VA need not exceed the value of VC used in design.

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

(1) VB may 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) ng the 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) VS1 is the stalling speed with the flaps retracted at the particular weight under consideration.

(2) VB need 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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