percent and 40 percent, respectively, of the limit side and/or drag load factors corresponding with the most severe condition resulting from consideration of the prescribed taxiing and ground handling conditions except that, for the braked roll conditions of § 4b.235 (b) (1) and (2) (ii), the drag loads on each inflated tire shall not be less than those at each tire for the symmetrical load distribution with no deflated tires. For one and two deflated tires the vertical load factor at the center of gravity shall be 60 percent and 50 percent, respectively, of the factor with no deflated tires except that it shall not be less than 1 g. Pivoting need not be considered.

(3) Towing conditions. For one deflated tire and for two deflated tires, the towing load, Frow, shall be 60 percent and 50 percent, respectively, of the load prescribed.

NOTE: In determining the total load on a gear unit with respect to the provisions of paragraphs (b) and (c) of this section, the transverse shift in the load centroid, due to unsymmetrical load distribution on the wheels, is normally neglected.

[Amdt. 4b-6, 22 F.R. 5564, July 16, 1957, as amended by Amdt. 4b-8, 23 F.R. 2590, Apr. 19, 1958; Amdt. 4b-11, 24 F.R. 7069, Sept. 1, 1959]

The structure of hull and float type seaplanes shall be designed for water loads developed during take-off and landing with the seaplane in any attitude likely to occur in normal operation at appropriate forward and sinking velocities under the most severe sea conditions likely to be encountered. Unless a more rational analysis of the water loads is performed, the requirements of §§ 4b.251 through 4b.258 shall apply. [Amdt. 4b-6, 17 F. R. 1090, Feb. 5, 1952] § 4b.250-1 Water loads; alternate standards (FAA policies which apply to §§ 4b.10 and 4b.250). ANC-3 provides a level of safety equivalent to, and may be applied in lieu of, § 4b.250.

[Supp. 16, 16 F. R. 1630, Feb. 16, 1951, as amended by Supp. 20, 17 F. R. 10102, Nov. 7, 1952]

§ 4b.251 Design weights and center of gravity positions.

(a) Design weights. The water load requirements shall be complied with at

all operating weights up to the design landing weight except that for the takeoff condition prescribed in § 4b.255 the design take-off weight shall be used.

(b) Center of gravity positions. The critical center of gravity positions within the limits for which certification is sought shall be considered to obtain maximum design loads for each part of the seaplane structure.

[Amdt. 4b-6, 17 F. R. 1090, Feb. 5, 1952] § 4b.252 Application of loads.

(a) The seaplane as a whole shall be assumed to be subjected to the loads corresponding with the load factors specified in § 4b.253, except as otherwise prescribed. In applying the loads resulting from the load factors prescribed in § 4b.253, it shall be permissible to distribute the loads over the hull bottom in order to avoid excessive local shear loads and bending moments at the location of water load application, using pressures not less than those prescribed in § 4b.256 (b).

(b) For twin float seaplanes, each float shall be treated as an equivalent hull on a fictitious seaplane having a weight equal to one-half the weight of the twin float seaplane.

(c) Except in the take-off condition of § 4b.255, the aerodynamic lift on the seaplane during the impact shall be assumed to be 23 of the weight of the seaplane

[Amdt. 4b-6, 17 F. R. 1090, Feb. 5, 1952]

8 angle of dead rise at the longitudinal station at which the load factor is being determined (see fig. 4b-15a);

W seaplane design landing weight in pounds;

K1 empirical hull station weighing factor. (See fig. 4b-15b.) For a twin float seaplane, in recognition of the effect of flexibility of the attachment of the floats to the seaplane, it shall be acceptable to reduce the factor K, at the bow and stern to 0.8 of the value shown in figure 4b-15b. This reduction shall not apply to the float design but only to the design of the carry-through and seaplane structure;

T=ratio of distance, measured parallel to hull reference axis, from the center of gravity of the seaplane to the hull longitudinal station at which the load factor is being computed to the radius of gyration in pitch of the seaplane, the hull reference axis being a straight line, in the plane of symmetry, tangential to the keel at the main step.

[Amdt. 4b-6, 17 F.R. 1090, Feb. 5, 1952]

§ 4b.254 Hull and main float landing conditions.

The

(a) Symmetrical step landing. limit water reaction load factor shall be in accordance with § 4b.253. The resultant water load shall be applied at the keel through the center of gravity perpendicularly to the keel line.

(b) Symmetrical bow landing. The limit water reaction load factor shall be in accordance with § 4b.253. The resultant water load shall be applied at the keel 5 of the longitudinal distance from the bow to the step, and shall be directed perpendicularly to the keel line.

(c) Symmetrical stern landing. The limit water reaction load factor shall be in accordance with § 4b.253. The resultant water load shall be applied at the keel at a point 85 percent of the longitudinal distance from the step to the stern post, and shall be directed perpendicularly to the keel line.

(d) Unsymmetrical landing; hull type and single float seaplanes. Unsymmetrical step, bow, and stern landing conditions shall be investigated. The loading for each condition shall consist of an upward component and a side component equal, respectively, to 0.75 and 0.25 tan 6 times the resultant load in the corresponding symmetrical landing condition. (See paragraphs (a), (b), and (c) of this section.) The point of application and direction of the upward component of the load shall be the same as that in the symmetrical condition, and the point of application of the

side component shall be at the same longitudinal station as the upward component but directed inward perpendicularly to the plane of symmetry at a point midway between the keel and chine lines.

(e) Unsymmetrical landing; twin float seaplanes. The unsymmetrical loading shall consist of an upward load at the step of each float of 0.75 and a side load of 0.25 tan ẞ at one float times the step landing load obtained in accordance with § 4b.253. The side load shall be directed inboard perpendicularly to the plane of symmetry midway between the keel and chine lines of the float at the same longitudinal station as the upward load.

[Amdt. 4b-6, 17 F. R. 1091, Feb. 5, 1952]

§ 4b.255 Hull and main float take-offcondition.

The provisions of this section shall apply to the design of the wing and its attachment to the hull or main float. The aerodynamic wing lift shall be assumed to be zero. A downward inertia load shall be applied and shall correspond with the following load factor: CTO V11* n= tan 2/38W1/3

where:

n

Cro

inertia load factor;

2

empirical seaplane operations factor equal to 0.003;

seaplane stalling speed (mph) at the

design take-off weight with the

flaps extended in the appropriate take-off position;

angle of dead rise at the main step (degrees);

W seaplane design take-off weight in pounds.

[Amdt. 4b-6, 17 F. R. 1091, Feb. 5, 1952] § 4b.256 Hull and main float bottom pressures.

The provisions of this section shall apply to the design of the hull and main float structure, including frames and bulkheads, stringers, and bottom plating. In the absence of more rational data, the pressures and distributions shall be as follows:

(a) Local pressures. The following pressure distributions are applicable for the design of the bottom plating and stringers and their attachments to the supporting structure. The area over which these pressures are applied shall be such as to simulate pressures occurring during high localized impacts on the

Flared Bottom

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