[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR25.335]
[Page 366-367]
TITLE 14--AERONAUTICS AND SPACE
CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES--Table of Contents
Subpart C--Structure
Sec. 25.335 Design airspeeds.
The selected design airspeeds are equivalent airspeeds (EAS).
Estimated values of VS0 and VS1
must be conservative.
(a) Design cruising speed, VC. For VC, the
following apply:
(1) The minimum value of VC must be sufficiently greater
than VB to provide for inadvertent speed increases likely to
occur as a result of severe atmospheric turbulence.
(2) Except as provided in Sec. 25.335(d)(2), VC may not
be less than VB + 1.32 U REF (with UREF
as specified in Sec. 25.341(a)(5)(i)). However VC need not
exceed the maximum speed in level flight at maximum continuous power for
the corresponding altitude.
(3) At altitudes where VD is limited by Mach number,
VC may be limited to a selected Mach number.
(b) Design dive speed, VD. VD must be selected
so that VC/MC is not greater than 0.8
VD/MD, or so that the minimum speed margin between
VC/MC and VD/MD is the
greater of the following values:
(1) From an initial condition of stabilized flight at VC/
MC, the airplane is upset, flown for 20 seconds along a
flight path 7.5 deg. below the initial path, and then pulled up at a
load factor of 1.5g (0.5g acceleration increment). The speed increase
occurring in this maneuver may be calculated if reliable or conservative
aerodynamic data is used. Power as specified in Sec. 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 probability
basis. The margin at altitude where MC is limited by
compressibility effects must not less than 0.07M unless a lower margin
is determined using a rational analysis that includes the effects of any
automatic systems. In any
[[Page 367]]
case, the margin may not be reduced to less than 0.05M.
(c) Design maneuvering speed VA. For VA, the
following apply:
(1) VA may not be less than VS1
[radic]n where--
(i) n is the limit positive maneuvering load factor at
VC; and
(ii) VS1 is the stalling speed with flaps
retracted.
(2) VA and VS must be evaluated at the design
weight and altitude under consideration.
(3) VA need not be more than VC or the speed
at which the positive CN!max curve intersects the positive
maneuver load factor line, whichever is less.
(d) Design speed for maximum gust intensity, VB.
(1) VB may not be less than
[GRAPHIC] [TIFF OMITTED] TR09FE96.016
where--
VS1=the 1-g stalling speed based on CNAmax with
the flaps retracted at the particular weight under consideration;
Vc=design cruise speed (knots equivalent airspeed);
Uref=the reference gust velocity (feet per second equivalent
airspeed) from Sec. 25.341(a)(5)(i);
w=average wing loading (pounds per square foot) at the particular weight
under consideration.
[GRAPHIC] [TIFF OMITTED] TR09FE96.017
[rho]=density of air (slugs/ft\3\);
c=mean geometric chord of the wing (feet);
g=acceleration due to gravity (ft/sec\2\);
a=slope of the airplane normal force coefficient curve, CNA
per radian;
(2) At altitudes where VC is limited by Mach number--
(i) VB may be chosen to provide an optimum margin between
low and high speed buffet boundaries; and,
(ii) VB need not be greater than VC.
(e) Design flap speeds, VF. For VF, the
following apply:
(1) The design flap speed for each flap position (established in
accordance with Sec. 25.697(a)) must be sufficiently greater than the
operating speed recommended 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 programmed or allowed
by the device may be used.
(3) VF may not be less than--
(i) 1.6 VS1 with the flaps in takeoff position
at maximum takeoff weight;
(ii) 1.8 VS1 with the flaps in approach
position at maximum landing weight, and
(iii) 1.8 VS0 with the flaps in landing
position at maximum landing weight.
(f) Design drag device speeds, VDD. The selected design
speed for each drag device must be sufficiently greater than the speed
recommended for the operation of the device to allow for probable
variations in speed control. For drag devices intended for use in high
speed descents, VDD may not be less than VD. When
an automatic drag device 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]