2.250 -T 2.251 2.252 2.253 2.254 2.2540 Design Weight. For transport category airplanes, the design weight used in the water landing conditions shall not be less than the maximum landing weight, or 87 percent of the maximum take-off weight for which certification is desired, whichever is greater. Landing With Inclined Reactions (Float Seaplanes). The vertical component of the limit load factor shall be 4.20 except that it need not exceed a value given by the following formula: n=3.0+0.133 (W/S). metric: 3.0+.0272 (W/S) where W/S-kg/m.2 The propeller axis (or equivalent reference line) shall be assumed to be horizontal and the resultant water reaction to be acting in the plane of symmetry and passing through the center of gravity of the airplane but inclined so that its horizontal component is equal to one quarter of its vertical component. The forces representing the weights of and in the airplane shall be assumed to act in a direction parallel to the water reaction. Landing With Vertical Reactions (Float Seaplanes). The limit load factor shall be 4.33 acting vertically, except that it need not exceed a value given by the following formula: n=3.0+0.133 (W/S). metric: 3+.0272 (W/S) where W/S=kg/m.2 The propeller axis (or equivalent reference line) shall be assumed to be horizontal, and the resultant water reaction to be vertical, and passing through the center of gravity of the airplane. Landing With Side Load (Float Seaplanes). The vertical component of the limit load factor shall be 4.0. The propeller axis (or equivalent reference line) shall be assumed to be horizontal and the resultant water reaction shall be assumed to be in the vertical plane which passes through the center of gravity of the airplane and is perpendicular to the propeller axis. The vertical load shall be applied through the keel or keels of the float or floats and evenly divided between the floats when twin floats are used. A side load equal to one fourth of the vertical load shall be applied along a line approximately halfway between the bottom of the keel and the level of the water line at rest. When twin floats are used, the entire side load specified shall be applied to the float on the side from which the water reaction originates. The factor of safety shall be 1.50. Boat Seaplanes Local Bottom Pressures (a) Maximum Local Pressure. The maximum value of the limit local pressure shall be determined from the following equation: P 2.2541 where: P-pressure, pounds per square inch (kg/cm.2) (To be calculated on the basis of wind tunnel The factor of safety shall be 1.5. (b) Variation in Local Pressure. The local pressures to be applied to the hull bottom shall vary in accordance with Fig. 2-5. No variation from keel to chine (beamwise) shall be assumed, except when the chine flare indicates the advisability of higher pressures of the chine. (c) Application of Local Pressure. The local pressure determined from 2.2540 and Fig. 2-5 shall be applied over a local area in such a manner as to cause the maximum local loads in the hull bottom structure. Distributed Bottom Pressures (a) For the purpose of designing frames, keels, and chine structure, the limit pressures obtained from 2.2540 and Fig. 2. 2542 2-5 shall be reduced to one half the "local" values and simultaneously applied over the entire hull bottom. The loads so obtained shall be carried into the side-wall structure of the hull proper, but need not be transmitted in a fore-and-aft direction as shear and bending loads. The factor of safety shall be 1.5. (b) Unsymmetrical Loading. Each floor meinber or frame shall be designed for a load on one side of the hull center line equal to the most critical symmetrical loading, combined with a load on the other side of the hull center line equal to one half of the most critical symmetrical loading. Step Loading Condition (a) Application of Load. The resultant water load shall be applied vertically in the plane of symmetry so as to pass through the center of gravity of the airplane. (b) Acceleration. The limit acceleration shall be 4.33. (c) Hull Shear and Bending Loads. The hull shear and bending loads shall be computed from the inertia loads produced by the vertical water load. To avoid excessive local shear loads and bending moments near the point of water load application, the water load may be distributed over the hull bottom, using pressures not less than those specified in 2.2541. The factor of safety shall be 1.5. 2. 2543 Pow Loading Condition 2. 2544 2. 2545 (a) Application of Load. The resultant water load shall be applied in the plane of symmetry at a point one tenth of the distance from the bow to the step and shall be directed upward and rearward at an angle of 30° from the vertical. (b) Magnitude of Load. The magnitude of the limit resultant water load shall be determined from the following equation: ng the step landing load factor We = an effective weight which is assumed equal to one half the design weight of the airplane. (c) Hull Shear and Bending Loads. The hull shear and bending loads shall be determined by proper consideration of the inertia loads which resist the linear and angular accelerations involved. To avoid excessive local shear loads, the water reaction may be distributed over the hull bottom, using pressure not less than those specified in 2.2541. The factor of safety shall be 1.5. Stern Loading Condition (a) Application of Load. The resultant water load shall be applied vertically in the plane of symmetry and shall be distributed over the hull bottom from the second step forward with an intensity equal to the pressure specified in 2.254. (b) Magnitude of Load. The limit resultant load shall equal three quarters of the design weight of the airplane. (c) Hull Shear and Bending Loads. The hull shear and bending loads shall be determined by assuming the hull structure to be supported at the wing attachment fittings and neglecting internal inertia loads. This condition need not be applied to the fittings or to the portion of the hull ahead of the rear attachment fittings. The factor of safety shall be 1.5. Side Loading Condition (a) Application of Load. The resultant water load shall be applied in a vertical plane through the center of gravity. The vertical component shall be assumed to act in the plane of symmetry and the horizontal component at a point halfway between the bottom of the keel and the load waterline at design weight (at rest). (b) Magnitude of Load. The limit vertical component of acceleration shall be 3.25 and the side component shall be equal to 15 percent of the vertical component. 2.255 2.2550 2.256 (c) Hull Shear and Bending Loads. The hull shear and bending loads shall be determined by proper consideration of the inertia loads or by introducing couples at the wing attachment points. To avoid excessive local shear loads, the water reaction may be distributed over the hull bottom, using pressures not less than those specified by 2.2541. The factor of safety shall be 1.5. Seaplane Float Loads. Each main float of a float seaplane shall be capable of carrying the following loads when supported at the attachment fittings as installed on the airplane. The factor of safety shall be 1.5. (a) A limit load, acting upward applied at the bow end of the float and of magnitude equal to one half of that portion of the airplane gross weight normally supported by the particular float. (b) The limit load specified in paragraph (a) above, acting upward at the stern. (c) A limit load, acting upward, applied at the step and of magnitude equal to 1.33 times that portion of the airplane design weight normally supported by the particular float. Seaplane Float Bottom Loads. Main seaplane float bottoms shall be designed to withstand the following loads. The factor of safety shall be 1.5. (a) A limit load of at least 5.53 pounds per square inch (.3888 kg/cm.2) over that portion of the bottom lying between the first step and a section at 25 percent of the distance from the step to the bow. (b) A limit load of at least 2.67 pounds per square inch (.1877 kg/cm.2) over that portion of the bottom lying between the section at 25 percent of the distance from the step to the bow and a section at 75 percent of the distance from the step to the bow. (c) A limit load of at least 2.67 pounds per square inch (.1877 kg/cm.2) over that portion of the bottom lying between the first and second steps. If only one step is used, this load shall extend over that portion of the bottom lying between the step and a section at 50 percent of the distance from the step to the stern. Wing Tip Float Loads. Wing tip floats and their attachment, including the wing structure, shall be analyzed for each of the following conditions, using a factor of safety of 1.5. (a) A limit load acting vertically up at the completely submerged center of buoyancy and equal to three times the completely submerged displacement. (b) A limit load inclined upward at 45° to the rear and acting through the completely submerged center of buoyancy and equal to three times the completely submerged displacement. 2.2560 2.257 2.3 2.30 2.301 2.3011 2. 3012 2. 302 (c) A limit load acting parallel to the water surface. (laterally) applied at the center of area of the side view and equal to one and one-half times the completely submerged displacement. The primary wing structure shall incorporate sufficient extra strength to insure that failure of wing-tip float attachment members occurs before the wing structure is damaged. Sea-Wing Loads (Sponsons). Sea-wing design loads shall be based on suitable test data. DETAIL DESIGN REQUIREMENTS General. The airplane shall be designed to comply with the basic flight and strength requirements of 2.1 and 2.2, and the flutter and vibration prevention requirements of 2.33. In addition, certain design features which have been found to be essential to the airworthiness of an airplane are hereinafter specified and shall be observed. The structure and all mechanisms essential to the safe operation of the airplane shall not incorporate design details which experience has shown to be unreliable or otherwise unsatisfactory. The suitability of all questionable design features shall be established by tests. Minimum tests required to prove the strength and proper functioning of particular parts are specified hereinafter. Materials. The reliability of all materials used in the airplane structure shall be established on the basis of experience or tests. All materials used in the airplane structure shall conform to specifications which will insure their uniform quality. Strength Properties and Design Values. Material strength properties shall be based on a sufficient number of tests to establish design values on a statistical basis. The design values shall be so chosen that the probability of any structure being understrength because of material variations is extremely remote. Variability Factor. For parts of the primary structure whose strength is subject to appreciable variability due to uncertainties in manufacturing processes and inspection methods, the factor of safety shall be increased sufficiently to make the probability of any part being understrength from this cause extremely remote. Minimum variability factors are as follows, and shall be considered as multiplying factors on top of any other required factors: Castings. Where external visual inspection only is to be employed, the variability factor shall be 2.0. For 100 percent X-ray inspection which has been properly correlated with strength tests to establish acceptance criteria, the variability factor may be reduced to 1.25. Fabrication Methods. The methods of fabrication employed in constructing the primary structure shall be such as to produce a uniformly sound structure which shall also be reliable with respect to maintenance of the original |