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, 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
(i) 33 √(W/S) (for normal, utility, and
commuter category airplanes);
(ii) 36 √(W/S) (for acrobatic category
(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:
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
(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
(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.
(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;
(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
(2) VB need not be greater
[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]