(a) The flight control systems and surfaces must be designed for the limit loads generated when the airplane is subjected to a horizontal 65-knot ground gust from any direction while taxiing and while parked. For airplanes equipped with control system gust locks, the taxiing condition must be evaluated with the controls locked and unlocked, and the parked condition must be evaluated with the controls locked.
(b) The control system and surface loads due to ground gust may be assumed to be static loads, and the hinge moments H must be computed from the formula:H = K (1/2) [rho]o V\2\ c S Where-- K = hinge moment factor for ground gusts derived in paragraph (c) of
this section;[rho]o = density of air at sea level;V = 65 knots relative to the aircraft;S = area of the control surface aft of the hinge line;c = mean aerodynamic chord of the control surface aft of the hinge line.
(c) The hinge moment factor K for ground gusts must be taken from the following table: ------------------------------------------------------------------------
(1) Aileron......................... 0.75 Control column locked
or lashed in mid-
position.(2) Aileron......................... * Sec. 25.427 Unsymmetrical loads.
(a) In designing the airplane for lateral gust, yaw maneuver and roll maneuver conditions, account must be taken of unsymmetrical loads on the empennage arising from effects such as slipstream and aerodynamic interference with the wing, vertical fin and other aerodynamic surfaces.
(b) The horizontal tail must be assumed to be subjected to unsymmetrical loading conditions determined as follows:
(1) 100 percent of the maximum loading from the symmetrical maneuver conditions of Sec. 25.331 and the vertical gust conditions of Sec. 25.341(a) acting separately on the surface on one side of the plane of symmetry; and
(2) 80 percent of these loadings acting on the other side.
(c) For empennage arrangements where the horizontal tail surfaces have dihedral angles greater than plus or minus 10 degrees, or are supported by the vertical tail surfaces, the surfaces and the supporting structure must be designed for gust velocities specified in Sec. 25.341(a) acting in any orientation at right angles to the flight path.
(d) Unsymmetrical loading on the empennage arising from buffet conditions of Sec. 25.305(e) must be taken into account. [Doc. No. 27902, 61 FR 5222, Feb. 9, 1996]