Section 31.43 Section 31.43 14 CFR Ch. I (1-1-19 Edition) Fitting factor. (a) A fitting factor of at least 1.15 must be used in the analysis of each fitting the strength of which is not proven by limit and ultimate load tests in which the actual stress conditions are simulated in the fitting and surrounding structure. This factor applies to all parts of the fitting, the means of attachment, and the bearing on the members joined. (b) Each part with an integral fitting must be treated as a fitting up to the point where the section properties become typical of the member. (c) The fitting factor need not be used if the joint design is made in accordance with approved practices and is based on comprehensive test data. Section 31.45 Fuel cells. If fuel cells are used, the fuel cells, their attachments, and related supporting structure must be shown by tests to be capable of withstanding, without detrimental distortion or failure, any inertia loads to which the installation may be subjected, including the drop tests prescribed in Section 31.27(c). In the tests, the fuel cells must be loaded to the weight and pressure equivalent to the full fuel quantity condition. [Amdt. 31-3, 41 FR 55474, Dec. 20, 1976] Section 31.46 Pressurized fuel systems. For pressurized fuel systems, each element and its connecting fittings and lines must be tested to an ultimate pressure of at least twice the maximum pressure to which the system will be subjected in normal operation. No part of the system may fail or malfunction during the test. The test configuration must be representative of the normal fuel system installation and balloon configuration. [Amdt. 31-3, 41 FR 55474, Dec. 20, 1976] spaschal on DSK3GDR082PROD with CFR Section 31.47 Burners. (a) If a burner is used to provide the lifting means, the system must be designed and installed so as not to create a fire hazard. (b) There must be shielding to protect parts adjacent to the burner flame, and the occupants, from heat effects. (c) There must be controls, instruments, or other equipment essential to the safe control and operation of the heater. They must be shown to be able to perform their intended functions during normal and emergency operation. (d) The burner system (including the burner unit, controls, fuel lines, fuel cells, regulators, control valves, and other related elements) must be substantiated by an endurance test of at least 40 hours. Each element of the system must be installed and tested to simulate actual balloon installation and use. (1) The test program for the main blast valve operation of the burner must include: (i) Five hours at the maximum fuel pressure for which approval is sought, with a burn time for each one minute cycle of three to ten seconds. The burn time must be established so that each burner is subjected to the maximum thermal shock for temperature affected elements; (ii) Seven and one-half hours at an intermediate fuel pressure, with a burn time for each one minute cycle of three to ten seconds. An intermediate fuel pressure is 40 to 60 percent of the range between the maximum fuel pressure referenced in paragraph (d)(1)(i) of this section and minimum fuel pressure referenced in paragraph (d)(1)(iii); (iii) Six hours and fifteen minutes at the minimum fuel pressure for which approval is sought, with a burn time for each one minute cycle of three to ten seconds; (iv) Fifteen minutes of operation on vapor, with a burn time for each one minute cycle of at least 30 seconds; and (v) Fifteen hours of normal flight operation. (2) The test program for the secondary or backup operation of the burner must include six hours of operation with a burn time for each five minute cycle of one minute at an intermediate fuel pressure. (e) The test must also include at least three flameouts and restarts. 694 VerDate Sep<11>2014 12:50 Apr 30, 2019 Jkt 247046 PO 00000 Frm 00704 Fmt 8010 Sfmt 8010 Y:\SGML\247046.XXX 247046