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equivalent the aerodynamic characteristics CN, CP (or C), and Co shall be determined as follows:

(a)

ni (W/S) CN= QL

(qL is dynamic pressure corresponding to VL; see §§ 4a.40 (c) and 4a.42.)

(b) Cc' value corresponding to CN1, or value equal to -.20 CN1, whichever is greater negatively.

(c) CP' most forward position of the center of pressure between CL-CN, and CL max.; when CN, exceeds CL max., the CP curve shall be extended accordingly.

(d) For biplane combinations the CP of the upper wing shall be assumed to be 2.5 percent of the chord forward of its nominal position.

(e) Cм'=moment coefficient necessary to give the required CP' in conjunction with CNI

§ 4a.80 Condition I (positive high angle of attack modified).

The smaller of the two values of Cc specified in § 4a.79 (b), and the most rearward CP position in the range specified in § 4a.79 (c) shall also be investigated when Condition I is critical for the rear spar (or its equivalent) or if any portion of the front spar (or its equivalent) is likely to be critical in tension. Only the wings and wing bracing need be investigated for this condition.

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(2) Cc actual value corresponding to CNIII.

(3) When Cc is positive or has a negative value smaller than 0.02 it may be assumed to be zero.

(4) См actual value corresponding to CNIII

(b) Positive low angle of attack, modified. If the moment coefficient of the airfoil section at zero lift has a positive value, or a negative value smaller than 0.06, the effects of displaced ailerons on the moment coefficient shall be accounted for in condition III for that portion of the span incorporating ailerons. To cover this point it will be satisfactory to combine 75 percent of the loads acting in condition III with the loads due to a moment coefficient of -0.08-CM111 acting over that portion only of the span incorporating ailerons. The design dynamic pressure for the additional moment forces shall be equal to 0.75qg. Only the wings and wing bracing need be investigated for this condition.

[CAR, May 31, 1938, as amended by Amdt. 48, 5 F. R. 1835, May 22, 1940]

§ 4a.83 Condition IV (negative low angle of attack).

The factors given in Table 4a-1 for this condition shall be used, with the following provisions:

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(b) Cc-actual value corresponding to CNIV.

(c) When Cc is positive or has a negative value smaller than 0.02 it may be assumed to be zero.

(d) С actual value corresponding to CNIV•

[CAR, May 31, 1938, as amended by Amdt. 48, 5 F. R. 1835, May 22, 1940]

§ 4a.84 Condition V (inverted flight).

The factors given in Table 4a-1 for this condition shall be used, with the following provisions:

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(b) Cc'=Cc max (positive) +0.01. (c) С actual value corresponding to CNYI

(d) The drag of nacelles and other items attached to the wings shall be conservatively estimated and properly included in the investigation of this condition.

(e) Only the wings and wing bracing need be investigated for this condition. [CAR, May 31, 1938, as amended by Amdt. 48, 5 F. R. 1835, May 22, 1940]

SYMMETRICAL FLIGHT CONDITIONS (FLAPS OR AUXILIARY DEVICES IN OPERATION)

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When flaps or other auxiliary high-lift devices are installed on the wings, the design conditions shall be suitably modified to account for their use in flight. The modifications shall be based on the intended use of such devices and the aerodynamic characteristics of the wing. The conditions as set forth in §§ 4a.874a.89, together with Table 4a-2, shall be considered as representing the minimum number of conditions required to cover a suitable range of symmetrical flight loadings in cases where the flaps are used only at relatively low air speeds.

§ 4a.87 Condition VII (positive gust, flaps deflected).

The factors given in Table 4a-2 for this condition shall be used, with the following provisions:

(a) The most critical deflection of the flap shall be investigated.

(b) The magnitude and distribution of normal, chord, and moment forces over the wing shall correspond to that which would be obtained in developing the specified limit gust load factor at the specified air speed.

[CAR, May 31, 1938, as amended by Amdt. 48, 5 F. R. 1835, May 22, 1940]

§ 4a.88 Condition VIII (negative gust, flaps deflected).

The factors given in Table 4a-2 for this condition shall be used, with the following provisions:

(a) The most critical deflection of the flap shall be investigated.

(b) The magnitude and distribution of normal, chord, and moment forces over the wing shall correspond to that which would be obtained in encountering the specified limit gust load factor at the specified air speed.

[CAR, May 31, 1938, as amended by Amdt. 48, 5 F. R. 1835, May 22, 1940]

§ 4a.89 Condition IX (dive, flaps deflected).

The factors given in Table 4a-2 for this condition shall be used, with the following provisions.

(a) The most critical deflection of the flap shall be investigated.

(b) The load factor and the magnitude and distribution of normal, chord and moment forces over the wing shall correspond to the angle of attack at which the greatest rearward chord loads are produced on the wing structure.

(c) Only the wings and wing bracing need be investigated for this condition. UNSYMMETRICAL FLIGHT CONDITIONS

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§ 4a.91 Condition I..

Condition I (§ 4a.79) shall be modified by assuming 100 percent of the air load acting on one wing and 40 percent on the other. For airplanes over 1,000 pounds standard weight the latter factor may be increased linearly with standard weight up to 80 percent at 25,000 pounds. [Amdt. 48, 5 F. R. 1834, May 22, 1940] § 4a.92 Condition III..

Condition III (§ 4a.82) shall be modified as described for condition I in § 4a.91.

[Amdt. 48, 5 F.R. 1835, May 22, 1940]

§ 4a.93 Condition V..

Condition V (§ 4a.84) shall be modified as described for condition I in § 4a.91.

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§ 4a.97

Unsymmetrical propeller thrust. The structure shall incorporate an ultimate factor of safety of 1.5 against failure due to loads caused by maximum (except take-off) power applied on one side of the plane of symmetry only, when power on the other side is off and the airplane is in unaccelerated rectilinear flight.

§ 4a.98 Wing tanks empty.

If fuel tanks are supported by the wing structure, such structure and its bracing shall also be investigated for conditions I, II, III, and IV with wing tanks empty. The design weight may be reduced by 0.9 pound per certified maximum (except take-off) horsepower.

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The limit load acting on the horizontal tail surface shall not be less than the maximum balancing load obtained from conditions I, II, III, IV, VII, and VIII set forth in §§ 4a.79, 4a.81, 4a.82, 4a.83, 4a.87 and 4a.88. In computing these loads for tail surface design the moments of fuselage and nacelles shall be suitably accounted for. The factors given in Table 4a-3 shall be used, with the following provisions:

(a) For conditions I, II, III, and IV, P (in Fig. 4a-4)=40 percent of net balancing load. (This means that the load on the fixed surface should be 140 percent of the net balancing load.) In any case P need not exceed that corresponding to a limit elevator control force of 150 pounds, applied by the pilot.

(b) For conditions VII and VIII, P may be assumed equal to zero. [Amdt. 48, 5 F. R. 1835, May 22, 1940]

§ 4a.117 Maneuvering (horizontal surfaces).

The factors and distributions specified in Table 4a-3 and Fig. 4a-5 for this condition shall be used, together with the following provisions:

(a) The limit unit loading in either direction need not exceed that corresponding to a 200-pound force on the elevator control (see Table 4a-6).

(b) The average limit unit loading shall not be less than 15 pounds per square foot (see Table 4a-3).

[Amdt. 48, 5 F. R. 1835, May 22, 1940]

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The total limit load acting down on the fixed surface (stabilizer) in the maneuvering condition (§ 4a.117) shall be applied in accordance with the load distribution of Fig. 4a-6, acting in either direction. The load acting on the movable surface in the maneuvering condition may be neglected in determining the damping loads.

§ 4a.119 Tab effects (horizontal surfaces).

When a tab is installed so that it can be used by the pilot as a trimming or assisting device, a limit up load over the tab corresponding to the dynamic pressure at VL and the maximum tab deflection shall be assumed to act in conjunction with the limit down load specified in § 4a.117, disregarding the provisions of § 4a.117 (a), applied over the remaining area. If the control force necessary to balance the resulting loads on the elevator and tab exceeds 200 pounds (Table 4a-6), the loadings over the areas not covered by the tab may be reduced until the control force is equal to this maximum limit value.

[Amdt. 48, 5 F. R. 1835, May 22, 1940]

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The factors given in Table 4a-4 and Fig. 4a-5 for this condition shall be used, with the following provisions:

(a) If the propeller axes are not in the plane of symmetry, the design speed shall not be less than the maximum speed in level flight with any engine inoperative.

(b) The limit unit loading in either direction need not exceed that corresponding to the maximum limit control force (Table 4a-6) except as modified by paragraph (c) of this section.

(c) In any case the average limit unit loading shall not be less than the minimum pressure specified in Table 4a-4 for this condition.

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w is in pounds per square foot,
U is in feet per second,

V is in miles per hour, and
m=slope of lift curve, CL per radian,
corrected for aspect ratio. The
aspect ratio shall not be taken
as less than 2.0 in any case.

(c) This condition applies only to that portion of the vertical surface which has a well-defined leading edge.

(d) The chord distribution extending over the fixed and movable surfaces shall simulate that for a symmetrical airfoil, except that the distribution in Fig. 4a-6 may be used where applicable.

§ 4a.123 Tab effects (vertical surfaces).

(a) When a tab is installed on the vertical movable tail surface so that it can be used by the pilot as a trimming device the limit unit loading over the entire vertical tail surfaces shall not be less than that corresponding to the maximum deflection of the tab together with simultaneous application of the following control force in a direction assisting the tab action:

(1) For airplanes with all propeller axes in the plane of symmetry, zero.

(2) For airplanes with propeller axes not in the plane of symmetry, 200 pounds.

(b) The factors specified in Table 4a-4 for this condition shall be used, with the following exception:

(1) If the propeller axes are not in the plane of symmetry, the design speed VL specified in Table 4a-4 may be reduced to the maximum speed in level flight with any engine inoperative. § 4a.124 Special cases faces).

(vertical sur

A special ruling shall be obtained from the Administrator when an automatic pilot is used on airplanes with propeller axes not in the plane of symmetry.

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The factors given in Table 4a-5 and Fig. 4a-7 for this condition shall be used, with the following provisions:

(a) If the propeller axes are not in the plane of symmetry, the design speed shall not be less than the maximum speed in level flight with any engine inoperative.

(b) The limit unit loading in either direction need not exceed that corresponding to the maximum control force (Table 4a-6) resisted by only one aileron, except as modified by paragraph (c) of this section.

(c) In any case the average limit unit loading shall not be less than the minimum pressure specified in Table 4a-5 for this condition.

§ 4a.126 Tab effects (ailerons).

(Applies only to airplanes with propeller axes not in the plane of symmetry.) When a tab is installed on one or both ailerons so that it can be used by the pilot to assist in moving the ailerons, the limit unit loading over both ailerons shall be of sufficient magnitude and in such direction as to hold the ailerons in equilibrium with the tab or tabs deflected to the maximum position. The factors specified in Table 4a-5 for this condition shall be used.

§ 4a.127

Flying conditions (ailerons).

The ailerons and their control system shall be capable of meeting all requirements specified in the basic symmetrical flying conditions so far as the latter produce symmetrical loads on the ailerons.

WING FLAPS AND TABS

§ 4a.128 Wing flaps.

Wing flaps shall be loaded in accordance with conditions VII and VIII (§§ 4a.87, 4a.88) and in addition shall be capable of developing an ultimate factor of safety of at least 1.5 with respect to any intermediate conditions which are more severe for any part of the flap or its operating mechanism. § 4a.129

Tabs.

The limit forces acting on controlsurface tabs shall be determined from the most severe combination of airplane speed and tab normal force coefficient likely to be obtained for any usable loading condition of the airplane and at speeds up to the design gliding speeds,

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All control systems shall be designed for limit loads 25 percent greater than those corresponding to the limit loads specified for the control surfaces to which they are attached, assuming the movable surface to be in that position which produces the greatest load in the control system, except that the maximum and minimum control force limits in Table 4a-6 shall apply as specified in this part. The factors of safety specified in Table 4a-6 shall be used.

CROSS REFERENCES: For multiplying factors of safety required in certain cases, see For §§ 4a.207-4a.216. operation requirements for control systems, see § 4a.271. § 4a.138 Control wires or push rods.

The forces in the control wires or push rods operating the movable surfaces shall be computed and their effect on the rest of the structure shall be investigated and allowed for in the design of such structure.

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In applying § 4a.137 the control force specified in Table 4a-6 and Fig. 4a-8 shall be assumed to act in a fore-and-aft direction and shall be applied at the grip of a control stick, or shall be equally divided between two diametrically opposite points on the rim of a control wheel.

§ 4a.140 Rudder systems.

In applying § 4a.137 the control force specified in Table 4a-6 shall be assumed to act in a direction which will produce the greatest load in the control system and shall be applied at the point of contact of the pilot's foot.

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