344
14 CFR Ch. I (1–1–14 Edition)
Pt. 23, App. F
I
w
=rotational mass moment of inertia of roll-
ing assembly (in slug feet);
V
H
=linear velocity of airplane parallel to
ground at instant of contact (assumed to
be 1.2
V
S0
, in feet per second);
V
c
=peripheral speed of tire, if prerotation is
used (in feet per second) (there must be a
positive means of pre-rotation before
pre-rotation may be considered);
n=equals effective coefficient of friction (0.80
may be used);
F
Vmax
=maximum vertical force on wheel
(pounds)=
n
j
W
e,
where
W
e
and
n
j
are de-
fined in § 23.725;
t
s
=time interval between ground contact and
attainment of maximum vertical force
on wheel (seconds). (However, if the
value of
F
Vmax,
from the above equation
exceeds 0.8
F
Vmax,
the latter value must be
used for
F
Hmax
.)
(b) The equation assumes a linear vari-
ation of load factor with time until the peak
load is reached and under this assumption,
the equation determines the drag force at
the time that the wheel peripheral velocity
at radius
r
e
equals the airplane velocity.
Most shock absorbers do not exactly follow a
linear variation of load factor with time.
Therefore, rational or conservative allow-
ances must be made to compensate for these
variations. On most landing gears, the time
for wheel spin-up will be less than the time
required to develop maximum vertical load
factor for the specified rate of descent and
forward velocity. For exceptionally large
wheels, a wheel peripheral velocity equal to
the ground speed may not have been attained
at the time of maximum vertical gear load.
However, as stated above, the drag spin-up
load need not exceed 0.8 of the maximum
vertical loads.
(c) Dynamic spring-back of the landing
gear and adjacent structure at the instant
just after the wheels come up to speed may
result in dynamic forward acting loads of
considerable magnitude. This effect must be
determined, in the level landing condition,
by assuming that the wheel spin-up loads
calculated by the methods of this appendix
are reversed. Dynamic spring-back is likely
to become critical for landing gear units
having wheels of large mass or high landing
speeds.
[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23–45, 58 FR 42167, Aug. 6,
1993]
A
PPENDIX
E
TO
P
ART
23 [R
ESERVED
]
A
PPENDIX
F
TO
P
ART
23—T
EST
P
ROCEDURE
P
ART
I—A
CCEPTABLE
T
EST
P
ROCEDURE
FOR
S
ELF
-E
XTINGUISHING
M
ATERIALS FOR
S
HOW
-
ING
C
OMPLIANCE
W
ITH
§§ 23.853, 23.855,
AND
23.1359
Acceptable test procedure for self-extin-
guishing materials for showing compliance
with §§ 23.853, 23.855 and 23.1359.
(a)
Conditioning. Specimens must be condi-
tioned to 70 degrees F, plus or minus 5 de-
grees, and at 50 percent plus or minus 5 per-
cent relative humidity until moisture equi-
librium is reached or for 24 hours. Only one
specimen at a time may be removed from the
conditioning environment immediately be-
fore subjecting it to the flame.
(b)
Specimen configuration. Except as pro-
vided for materials used in electrical wire
and cable insulation and in small parts, ma-
terials must be tested either as a section cut
from a fabricated part as installed in the air-
plane or as a specimen simulating a cut sec-
tion, such as: a specimen cut from a flat
sheet of the material or a model of the fab-
ricated part. The specimen may be cut from
any location in a fabricated part; however,
fabricated units, such as sandwich panels,
may not be separated for a test. The speci-
men thickness must be no thicker than the
minimum thickness to be qualified for use in
the airplane, except that: (1) Thick foam
parts, such as seat cushions, must be tested
in
1
⁄
2
inch thickness; (2) when showing com-
pliance with § 23.853(d)(3)(v) for materials
used in small parts that must be tested, the
materials must be tested in no more than
1
⁄
8
inch thickness; (3) when showing compliance
with § 23.1359(c) for materials used in elec-
trical wire and cable insulation, the wire and
cable specimens must be the same size as
used in the airplane. In the case of fabrics,
both the warp and fill direction of the weave
must be tested to determine the most crit-
ical flammability conditions. When per-
forming the tests prescribed in paragraphs
(d) and (e) of this appendix, the specimen
must be mounted in a metal frame so that (1)
in the vertical tests of paragraph (d) of this
appendix, the two long edges and the upper
edge are held securely; (2) in the horizontal
test of paragraph (e) of this appendix, the
two long edges and the edge away from the
flame are held securely; (3) the exposed area
of the specimen is at least 2 inches wide and
12 inches long, unless the actual size used in
the airplane is smaller; and (4) the edge to
which the burner flame is applied must not
consist of the finished or protected edge of
the specimen but must be representative of
the actual cross section of the material or
part installed in the airplane. When per-
forming the test prescribed in paragraph (f)
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