409
Federal Aviation Administration, DOT
§ 25.415
(2) The minimum forces specified in
§ 25.397(c).
(b) The control system must be de-
signed for pilot forces applied in the
same direction, using individual pilot
forces not less than 0.75 times those ob-
tained under § 25.395.
§ 25.405
Secondary control system.
Secondary controls, such as wheel
brake, spoiler, and tab controls, must
be designed for the maximum forces
that a pilot is likely to apply to those
controls. The following values may be
used:
P
ILOT
C
ONTROL
F
ORCE
L
IMITS
(S
ECONDARY
C
ONTROLS
)
Control
Limit pilot forces
Miscellaneous:
*Crank, wheel, or lever ..
((1 + R) / 3)
×
50 lbs., but not
less than 50 lbs. nor more
than 150 lbs. (R=radius). (Ap-
plicable to any angle within
20
°
of plane of control).
Twist ...............................
133 in.–lbs.
Push-pull ........................
To be chosen by applicant.
*Limited to flap, tab, stabilizer, spoiler, and landing gear op-
eration controls.
§ 25.407
Trim tab effects.
The effects of trim tabs on the con-
trol surface design conditions must be
accounted for only where the surface
loads are limited by maximum pilot ef-
fort. In these cases, the tabs are con-
sidered to be deflected in the direction
that would assist the pilot, and the de-
flections are—
(a) For elevator trim tabs, those re-
quired to trim the airplane at any
point within the positive portion of the
pertinent flight envelope in § 25.333(b),
except as limited by the stops; and
(b) For aileron and rudder trim tabs,
those required to trim the airplane in
the critical unsymmetrical power and
loading conditions, with appropriate
allowance for rigging tolerances.
§ 25.409
Tabs.
(a)
Trim tabs. Trim tabs must be de-
signed to withstand loads arising from
all likely combinations of tab setting,
primary control position, and airplane
speed (obtainable without exceeding
the flight load conditions prescribed
for the airplane as a whole), when the
effect of the tab is opposed by pilot ef-
fort forces up to those specified in
§ 25.397(b).
(b)
Balancing tabs. Balancing tabs
must be designed for deflections con-
sistent with the primary control sur-
face loading conditions.
(c)
Servo tabs. Servo tabs must be de-
signed for deflections consistent with
the primary control surface loading
conditions obtainable within the pilot
maneuvering effort, considering pos-
sible opposition from the trim tabs.
§ 25.415
Ground gust conditions.
(a) The control system must be de-
signed as follows for control surface
loads due to ground gusts and taxiing
downwind:
(1) The control system between the
stops nearest the surfaces and the
cockpit controls must be designed for
loads corresponding to the limit hinge
moments H of paragraph (a)(2) of this
section. These loads need not exceed—
(i) The loads corresponding to the
maximum pilot loads in § 25.397(c) for
each pilot alone; or
(ii) 0.75 times these maximum loads
for each pilot when the pilot forces are
applied in the same direction.
(2) The control system stops nearest
the surfaces, the control system locks,
and the parts of the systems (if any)
between these stops and locks and the
control surface horns, must be designed
for limit hinge moments H, in foot
pounds, obtained from the formula,
H=.0034KV
2
cS, where—
V=65 (wind speed in knots)
K=limit hinge moment factor for ground
gusts derived in paragraph (b) of this sec-
tion.
c=mean chord of the control surface aft of
the hinge line (ft);
S=area of the control surface aft of the hinge
line (sq ft);
(b) The limit hinge moment factor K
for ground gusts must be derived as fol-
lows:
Surface
K
Position of controls
(a) Aileron .....................
0.75 Control column locked
or lashed in mid-posi-
tion.
(b) ......do ......................
1
1
±
0.50
Ailerons at full throw.
(c) Elevator ...................
1
1
±
0.75
(c) Elevator full down.
(d) ......do ......................
1
1
±
0.75
(d) Elevator full up.
VerDate Mar<15>2010
10:12 Mar 18, 2014
Jkt 232046
PO 00000
Frm 00419
Fmt 8010
Sfmt 8010
Y:\SGML\232046.XXX
232046
pmangrum on DSK3VPTVN1PROD with CFR