title-14-part-25-sec25-335

236

14 CFR Ch. I (1–1–24 Edition)

§ 25.335

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–86, 61 FR 5220, Feb. 9, 1996]

§ 25.335

Design airspeeds.

The selected design airspeeds are

equivalent airspeeds (EAS). Estimated
values of

and

must be conserv-

ative.

(a)

Design cruising speed, V

. For

the following apply:

(1) The minimum value of

must be

sufficiently greater than

to provide

for inadvertent speed increases likely
to occur as a result of severe atmos-
pheric turbulence.

(2) Except as provided in § 25.335(d)(2),

may not be less than V

+ 1.32 U

REF

(with U

REF

as specified in

§ 25.341(a)(5)(i)). However V

need not

exceed the maximum speed in level
flight at maximum continuous power
for the corresponding altitude.

(3) At altitudes where

is limited

by Mach number,

may be limited to

a selected Mach number.

(b)

Design dive speed, V

must be

selected so that

is not greater

than 0.8

or so that the minimum

speed margin between

and

is the greater of the following values:

(1) From an initial condition of sta-

bilized flight at

the airplane is

upset, flown for 20 seconds along a
flight path 7.5

below the initial path,

and then pulled up at a load factor of
1.5

g (0.5g acceleration increment). The

speed increase occurring in this maneu-
ver may be calculated if reliable or
conservative aerodynamic data is used.
Power as specified in § 25.175(b)(1)(iv) is
assumed until the pullup is initiated,
at which time power reduction and the
use of pilot controlled drag devices
may be assumed;

(2) The minimum speed margin must

be enough to provide for atmospheric
variations (such as horizontal gusts,
and penetration of jet streams and cold
fronts) and for instrument errors and
airframe production variations. These
factors may be considered on a prob-
ability basis. The margin at altitude
where M

is limited by compressibility

effects must not less than 0.07M unless
a lower margin is determined using a
rational analysis that includes the ef-
fects of any automatic systems. In any

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237

Federal Aviation Administration, DOT

§ 25.337

case, the margin may not be reduced to
less than 0.05M.

(c)

Design maneuvering speed V

. For

, the following apply:

(1) V

may not be less than V

√

where—

(i)

n is the limit positive maneu-

vering load factor at

; and

(ii)

is the stalling speed with flaps

retracted.

(2)

and

must be evaluated at

the design weight and altitude under
consideration.

(3)

need not be more than

the speed at which the positive

N max

curve intersects the positive maneuver
load factor line, whichever is less.

(d)

Design speed for maximum gust in-

tensity, V

(1) V

may not be less than

K U

V a

ref

1 2

498

⎡
⎣

⎢

⎤
⎦

⎥

where—

= the 1-g stalling speed based on C

NAmax

with the flaps retracted at the particular
weight under consideration;

= design cruise speed (knots equivalent

airspeed);

ref

= the reference gust velocity (feet per

second equivalent airspeed) from
§ 25.341(a)(5)(i);

w = average wing loading (pounds per square

foot) at the particular weight under con-
sideration.

cag

5 3

= density of air (slugs/ft

);

c = mean geometric chord of the wing (feet);
g = acceleration due to gravity (ft/sec

);

a = slope of the airplane normal force coeffi-

cient curve, C

per radian;

(2) At altitudes where V

is limited

by Mach number—

(i) V

may be chosen to provide an

optimum margin between low and high
speed buffet boundaries; and,

(ii) V

need not be greater than V

(e)

Design flap speeds, V

. For

, the

following apply:

(1) The design flap speed for each flap

position (established in accordance
with § 25.697(a)) must be sufficiently

greater than the operating speed rec-
ommended for the corresponding stage
of flight (including balked landings) to
allow for probable variations in control
of airspeed and for transition from one
flap position to another.

(2) If an automatic flap positioning or

load limiting device is used, the speeds
and corresponding flap positions pro-
grammed or allowed by the device may
be used.

(3)

may not be less than—

(i) 1.6

with the flaps in takeoff po-

sition at maximum takeoff weight;

(ii) 1.8

with the flaps in approach

position at maximum landing weight,
and

(iii) 1.8

with the flaps in landing

position at maximum landing weight.

(f)

Design drag device speeds, V

. The

selected design speed for each drag de-
vice must be sufficiently greater than
the speed recommended for the oper-
ation of the device to allow for prob-
able variations in speed control. For
drag devices intended for use in high
speed descents,

may not be less

than

. When an automatic drag de-

vice positioning or load limiting means
is used, the speeds and corresponding
drag device positions programmed or
allowed by the automatic means must
be used for design.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5672, Apr. 8,
1970; Amdt. 25–86, 61 FR 5220, Feb. 9, 1996;
Amdt. 25–91, 62 FR 40704, July 29, 1997]

§ 25.337

Limit maneuvering load fac-

tors.

(a) Except where limited by max-

imum (static) lift coefficients, the air-
plane is assumed to be subjected to
symmetrical maneuvers resulting in
the limit maneuvering load factors pre-
scribed in this section. Pitching veloci-
ties appropriate to the corresponding
pull-up and steady turn maneuvers
must be taken into account.

(b) The positive limit maneuvering

load factor

n for any speed up to Vn

may not be less than 2.1 + 24,000/ (

W +

10,000) except that

n may not be less

than 2.5 and need not be greater than
3.8—where

W is the design maximum

takeoff weight.

load factor—

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