§3.217-1 Gust loads; horizontal tail surfaces (CAA policies which apply to § 3.217). The specified up gust and down gust load may be carried through the fuselage structure to the wing attachment points, assuming that the fuselage load factor is equal to that given by positive and negative gusts of 30 fps at Ve respectively. The angular inertia forces in general produce relieving loads and may be taken into account if desired. The attachments of concentrated mass items in the rear portion of the fuselage may be critically loaded by pitching acceleration forces. [Supp. 10, 16 F. R. 3287, Apr. 14, 1951]

§ 3.218 Unsymmetrical loads. The maximum horizontal tail surface loading (load per unit area), as determined by the preceding sections, shall be applied to the horizontal surfaces on one side of the plane of symmetry and the following percentage of that loading shall be applied on the opposite side:

%100-10 (n-1) where:

n is the specified positive maneuvering load factor.

In any case the above value shall not be greater than 80 percent.

VERTICAL TAIL SURFACES

§ 3.219 Maneuvering loads. At all speeds up to Vp:

(a) With the airplane in unaccelerated flight at zero yaw, a sudden displacement of the rudder control to the maximum deflection as limited by the control stops or pilot effort, whichever is critical, shall be assumed.

NOTE: The average loading of Figure 3-3 and the distribution of Figure 3-8 may be used.

(b) The airplane shall be assumed to be yawed to a sideslip angle of 15 degrees while the rudder control is maintained at full deflection (except as limited by pilot effort) in the direction tending to increase the sideslip.

NOTE: The average loading of Figure 3-3 and the distribution of Figure 3-7 may be used.

(c) The airplane shall be assumed to be yawed to a sideslip angle of 15 degrees while the rudder control is maintained in the neutral position (except as limited by pilot effort). The assumed sideslip angles may be reduced if it is shown that the value chosen for a particular speed

cannot be exceeded in the cases of steady slips, uncoordinated rolls from a steep bank, and sudden failure of the critical engine with delayed corrective action.

NOTE: The average loading of Figure 3-3 and the distribution of Figure 3-9 may be used.

§3.219-1 Vertical surface maneuvering loads (CAA policies which apply to §3.219). (a) The specified maneuvering loads may be applied to the vertical surfaces and carried through the fuselage structure to the wing attachment points, assuming the lateral inertia load factor along the fuselage structure as zero. The wing drag bracing through the fuselage should be analyzed for this condition since the wings will furnish a large part of the resisting angular inertia. Angular inertia forces on the fuselage may be included if desired.

(1) When the Figures 3-3, 3-7, 3-8, and 3-9 are used to compute the specified maneuvering loads on the vertical tail surfaces, it is not necessary to include the lg balancing load for unaccelerated flight which acts on the horizontal tail surfaces in considering the effects of the vertical tail loads on the fuselage.

(2) When rational methods are used, the maneuvering loads on the vertical tail surfaces and the lg horizontal balancing tail load should be applied simultaneously for the structural loading condition.

[Supp. 10, 16 F. R. 3287, Apr. 14, 1951, as amended by Supp. 21, 20 F. R. 6246, Aug. 26, 1955]

§3.220 Gust loads. (a) The airplane shall be assumed to encounter a gust of 30 feet per second nominal intensity, normal to the plane of symmetry while in unaccelerated flight at speed Vc.

(b) The gust loading shall be computed by the following formula:

W= design weight in pounds, S,

§ 3.222

vertical surface area in square feet.

(c) This loading applies only to that portion of the vertical surfaces having a well-defined leading edge.

NOTE: The average loading of Figure 3-6 and the distribution of Figure 3-9 may be used.

§3.220-1 Gust loads; vertical tail surfaces (CAA policies which apply to § 3.220). (a) The K factor specified in § 3.220 was derived from the K factor for vertical gusts (§ 3.188) on the assumption that the effective area of the airplane for lateral gusts is twice the vertical surface area. Substituting 2S, in place of S in the formula of § 3.188, we obtain:

(b) The specified gust loads may be applied to the vertical surfaces and carried through the fuselage structure to the wing attachment points as described in § 3.219-1.

[Supp. 10, 16 F. R. 3287, Apr. 14, 1951]

§3.221 Outboard fins. When outboard fins are carried on the horizontal tail surface, the tail surfaces shall be designed for the maximum horizontal surface load in combination with the corresponding loads induced on the vertical surfaces by end plate effects. Such induced effects need not be combined with other vertical surface loads. When outboard fins extend above and below the horizontal surface, the critical vertical surface loading (load per unit area) as determined by §§ 3.219 and 3.220 shall be applied:

(a) To the portion of the vertical surfaces above the horizontal surface, and 80 percent of that loading applied to the portion below the horizontal surface,

(b) To the portion of the vertical surfaces below the horizontal surface, and 80 percent of that loading applied to the portion above the horizontal surface.

AILERONS, WING FLAPS, TABS, ETC.

§ 3.222 Ailerons. (a) In the symmetrical flight conditions (see §§ 3.1833.189), the ailerons shall be designed for all loads to which they are subjected while in the neutral position.

Page 95

(b) In unsymmetrical flight conditions (see § 3.191 (a)), the ailerons shall be designed for the loads resulting from the following deflections except as limited by pilot effort:

(1) At speed Vp it shall be assumed that there occurs a sudden maximum displacement of the aileron control. (Suitable allowance may be made for control system deflections.)

(2) When Vc is greater than Vp, the aileron deflection at Vc shall be that required to produce a rate of roll not less than that obtained in condition (1).

(3) At speed Va the aileron deflection shall be that required to produce a rate of roll not less than one-third of that which would be obtained at the speed and aileron deflection specified in condition (1).

NOTE: For conventional ailerons, the deflections for conditions (2) and (3) may be computed from:

where:

81=total aileron deflection (sum of both aileron deflections) in condition (1).

82 total aileron deflection in condition (2).

83 total deflection in condition (3). In the equation for 83, the 0.5 factor is used instead of 0.33 to allow for wing torsional flexibility.

(c) The critical loading on the ailerons should occur in condition (2) if Va is less than 2Vc and the wing meets the torsional stiffness criteria. The normal force coefficient CN for the ailerons may be taken as 0.048, where 8 is the deflection of the individual aileron in degrees. The critical condition for wing torsional loads will depend upon the basic airfoil moment coefficient as well as the speed, and may be determined as follows:

(e) In lieu of the above rational conditions the average loading of Figure 3-3 and the distribution of Figure 3-10 may be used.

§3.223 Wing flaps. Wing flaps, their operating mechanism, and supporting structure shall be designed for critical loads occurring in the flap-extended flight conditions (see § 3.190) with the flaps extended to any position from fully retracted to fully extended; except that when an automatic flap load limiting device is employed these parts may be designed for critical combinations of air speed and flap position permitted by the device. (Also see §§ 3.338 and 3.339.) The effects of propeller slipstream corresponding to take-off power shall be taken into account at an airplane speed of not less than 1.4Vs where Vs is the computed stalling speed with flaps fully retracted at the design weight. For investigation of the slipstream condition, the airplane load factor may be assumed to be 1.0.

§ 3.223-1 Wing flap load distribution (CAA policies which apply to § 3.223). A trapezoidal chord load distribution with the leading edge twice the trailing edge loading is acceptable. (Note that these loadings apply in the up direction only; however, it is recommended that the supporting structure also be designed to withstand a down load equal to 25 percent of the up load.)

[Supp. 10, 16 F. R. 3288, Apr. 14, 1951]

§ 3.224 Tabs. Control surface tabs shall be designed for the most severe combination of air speed and tab defilection likely to be obtained within the limit V-n diagram (Fig. 3-1) for any usable loading condition of the airplane.

§ 3.224-1 Trim tab design (CAA policies which apply to § 3.224). (a) To provide ruggedness and for emergency use of tabs, it is recommended that trim tabs, their attachments and actuating mechanism be designed for loads corresponding to full tab deflection at speed Vc with main surface neutral; except that the tab deflection need not exceed that which would produce a hinge moment on the main surface corresponding to maximum pilot effort.

(b) A trapezoidal chord load distribution with the loading of the leading edge twice that of the trailing edge is acceptable.

Supp. 10. 16 F. R. 3288, Apr. 14, 1951]

§ 3.225 Special devices. The loading for special devices employing aerodynamic surfaces, such as slots and spoilers, shall be based on test data.

CONTROL SYSTEM LOADS

§ 3.231 Primary flight controls and systems. (a) Flight control systems and supporting structures shall be designed for loads corresponding to 125 percent of the computed hinge moments of the movable control surface in the conditions prescribed in §§ 3.211 to 3.225, subject to the following maxima and minima:

(1) The system limit loads need not exceed those which can be produced by the pilot and automatic devices operating the controls.

(2) The loads shall in any case be sufficient to provide a rugged system for service use, including consideration of jamming, ground gusts, taxying tail to wind, control inertia, and friction.

(b) Acceptable maximum and minimum pilot loads for elevator, aileron, and rudder controls are shown in Figure 3-11. These pilot loads shall be assumed to act at the appropriate control grips or pads in a manner simulating flight conditions and to be reacted at the attachments of the control system to the control surface horn.

§ 3.231-1 Hinge moments (CAA policies which apply to § 3.231 (a)). The 125 percent factor on computed hinge moments provided in § 3.231 (a) need be applied only to elevator, aileron and rudder systems. A factor as low as 1.0 may be used when hinge moments are based on test data; however, the exact reduction will depend to an extent upon the accuracy and reliability of the data. Small scale wind tunnel data are generally not reliable enough to warrant elimination of the factor. If accurate flight test data are used, the factor may be reduced to 1.0.

[Supp. 10, 16 F. R. 3288, Apr. 14, 1951]

§ 3.231-2 System limit loads (CAA policies which apply to § 3.231 (a) (1)). (a) When the autopilot is acting in conjunction with the human pilot, the autopilot effort need not be added to human pilot effort, but the autopilot effort should be used for design if it alone can produce greater control system loads than the human pilot.

(b) When the human pilot acts in opposition to the autopilot, that portion of

the system between them should be designed for the maximum effort of human pilot or autopilot, whichever is the lesser. [Supp. 10, 16 F. R. 3288, Apr. 14, 1951]

§ 3.231-3 Interconnected control systems on two-control airplanes (CAA policies which apply to § 3.231). (a) With respect to interconnected control systems such as in two control airplanes, the following is recommended in showing the "same level of safety" specified in § 3.10.

(1) If, in the case of two or more interconnected control systems, the control wheel or stick forces due to combined control system loads resulting from air loads on the control surfaces are less than the minimum prescribed in Figure 3-11 of this part, each control system from the interconnection to the control surface should be designed for minimum pilot effort on the control wheel or stick in order that sufficient ruggedness be incorporated into the system.

(2) If the control wheel or stick forces due to combined control system loads resulting from air loads on the control surfaces are in excess of the maximum forces prescribed in Figure 3-11 of this part, it is considered permissible to divide the maximum pilot effort loads in the control systems from the point of interconnection to the control surfaces in proportion to the control surface air loads. However, the load in each such control system should be increased 25 percent to allow for any error in the determination of the control surface loads, but in no case need the resulting loads in any one system exceed the total pilot effort, if the pilot effort were applied to that system alone. In any case, the minimum load in any one system should be no less than that specified in subparagraph (1) of this paragraph. [Supp. 10, 16 F. R. 3288, Apr. 14, 1951]

§3.232 Dual controls. When dual controls are provided, the systems shall be designed for the pilots operating in opposition, using individual pilot loads equal to 75 percent of those obtained in accordance with § 3.231, except that the individual pilot loads shall not be less than the minimum loads specified in Figure 3-11.

§3.233 Ground gust conditions. (a) The following ground gust conditions shall be investigated in cases where a deviation from the specific values for minimum control forces listed in Figure