aviation resources Federal Aviation Regulations

Sec. 25.415 - Ground gust conditions.

(a) The control system must be designed 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 ²cS, where --

V=65 (wind speed in knots)

K=limit hinge moment factor for ground gusts derived in paragraph (b) of this section.

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 follows:

------------------------------------------------------------------------
               Surface                     K       Position of controls
------------------------------------------------------------------------
(a) Aileron..........................      0.75  Control column locked
                                                  or lashed in mid-
                                                  position.
(b) ......do.........................     \1\ 1  Ailerons at full throw.
                                       ±0.
                                             50
(c) Elevator.........................     \1\ 1  (c) Elevator full down.
                                       ±0.
                                             75
(d) ......do.........................     \1\ 1  (d) Elevator full up.
                                       ±0.
                                             75
(e) Rudder...........................      0.75  (e) Rudder in neutral.
(f) ......do.........................      0.75  (f) Rudder at full
                                                  throw.
------------------------------------------------------------------------
\1\ A positive value of K indicates a moment tending to depress the
  surface, while a negative value of K indicates a moment tending to
  raise the surface.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-72, 55 FR 29776, July 20, 1990; Amdt. 25-91, 62 FR 40705, July 29, 1997]