An integrated system for transport aircraft cabin interior design and certification by analysis

Abstract

Every cabin configuration, in all types of aircraft (Transport, General Aviation and Rotorcraft), need to be certified as per the existing Code of Federal Regulation governing that particular type of aircraft. The current practice used to comply with Federal Aviation Regulations (FAR’s) related to aircraft seats and cabin interiors is to conduct full-scale system sled tests. This approach can be expensive and the test results are sensitive to changes in test conditions, such as the sled pulse, dummy calibration, seat belt elongation, etc., resulting in scatter in the results. With the development of the more robust codes for the analytical tools, it should be possible to successfully capture the test conditions by one of these tools and to obtain results which compare favorably with the actual tests results. For Part 25 category of transport aircrafts, 14CFR 25.562 states: “Each seat type design which approved for crew or passenger occupancy during takeoff and landing must successfully complete dynamic tests or be demonstrated by rational analysis based on dynamic tests of a similar type seat, in accordance with each of the following emergency landing conditions” and then the conditions are stated. When these federal regulations were enacted, the ability of analytical tools was limited and there did not exist enough data to show that certification could be performed using analysis. The objectives of this research are to identify the conditions under which a Part 25 type aircraft could be certified by analysis for compliance with the 14 CFR 25.562 regulation, and also to identify the validation criteria when using analytical tools. The validation criteria for the analytical model have been developed based on the scatter that is seen in actual testing. The underlying premise is that the analytical modeling of the testing should be allowed to predict the injury criteria within the same band of scatter as the actual tests. The study develops a validated model and this model is shown to be robust in predicting the protection/injury criteria that the tested configurations offer. Using these validated models, a full factorial design of experiment (DOE) analysis was performed to determine the effect the factors have on the dynamic response of the seat-dummy-restraint-cabin systems. In this study, the factors chosen were the seat cushion type, thickness of the cushion and the rigidity of the seat for the 14 CFR 25.562 Test -1 condition (up test) and the studied response was the resulting lumbar load. For 14 CFR 25.562 Test -2 condition (down test), the studied factors were the seat set back distance, seat belt type, type of bulkhead and the coefficient of friction of the impact surface, while the studied response was the resulting Head injury criteria (HIC) based on the impact of the dummy head with the frontal structure. Guidelines were developed in this study pertaining to the circumstance under which analytical tools could be considered as a valid replacement for the certification testing. Based on the sensitivity study, a new integrated analytical system methodology has been developed that would help the aerospace cabin interior designers in developing crashworthy cabin interiors. A graphical user interface was developed which would help the cabin interior designers to optimize their design by selecting component that would help in minimizing the injury criteria studied. This would reduce the time it takes to design these configurations and would reduce the cost of certification while improving the safety of the flying public.