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Aviation History
1965
1965 - 0158.PDF
92 FLIGHT International, 21 January 28 P PITCH FURNISHING AND FINISHING Problems In Passenger Seat Design . . . factor should be increased; in fact, in Australia the requirement has been increased to 12g. Seat structures, when tested, must withstand this acceleration without ultimate failure and after failure considerable deformation should have taken place, implying a measure of shock absorption in a crash. Some manufacturers are now applying the acceleration to their seats dynamically so as to investigate the actual amount of energy absorption which can be provided. Secondly, the design must be free of any feature which would injure a passenger when thrown against it during a crash. It is highly desirable that all structural members at the seat extremities, and embellishments such as meal trays, should be adequately padded to give at least some measure of protection to passengers' heads, legs and arms. Another major consideration in any design is the provision of an adequate standard of comfort. This, of course, varies according to the category of seat, but there are certain basic dimensions necessary for a reasonable seated position. These are shown in Figl. Airline travellers will agree that the most important parameter is the width between arm-rests, and in any particular aircraft layout this is fixed by the fuselage cross-section, the number of seats across the aircraft and the width of gangway required—usually a minimum of 15in. It is normally possible to provide a seating width of about 17in, but this is often reduced because of the necessity for providing six-abreast seating. Tourist Type To provide comfort at a pitch as low as 28in the seat cannot be considered solely in terms of the passenger using it; consideration must also be given to any restriction caused to the passenger seated immediately behind. To avoid restriction, the passenger's legs must be allowed the maximum amount of freedom and clearance, and to achieve this the base may be constructed in Short Type 720 ultra-light economy-class seat for high- density short-range work Fig I (upper left) Rasic dimensions for an adequate standard of comfort Fig 2 (left) Achieving freedom for the passenger's legs either of two ways—by using a high rear beam in a twin-beam construction, or by employing a single-beam construction. Both are illustrated in Fig 2. In the single-beam construction the interference caused is at a minimum, but the space available beneath the seat for stowage of hand baggage is greatly reduced and under high vertical crash accelerations the position of the main structural member could prove lethal. Because of the geometry of its construction the back- support structure must be cantilevered from the beam, with unavoidable weight penalties. The twin-beam construction favoured by Shorts is probably lighter than the single beam. It also eliminates the possibility of fatalities under high vertical accelerations as well as leaving ample space beneath the seat for stowage. The main disadvantage is that the leg attachment to the rear beam may, in certain athwartships positions, cause some obstruction to the comfortable positioning of the feet. The single beam form of construction also has this disadvantage to a lesser degree. Access to very closely pitched seats is often difficult—which means that for tourist units the designer usually incorporates tip-up seats. In addition, because of the very limited room available, seat-back recline is not really practicable, so no particular purpose is served by providing a head-rest at the top of the seat-back. An advantage in omitting the head-rest is that the seat-back may be made short enough to allow freedom of visibility for the passenger, and the air- craft interior is thus given a more spacious appearance. General-purpose Type For longer flights, and where it is desirable to provide a higher standard of comfort, the general-purpose type of seat is employed. The usual requirement is for these seats to incorporate recline through an angle of about 15°, the pitch of 32in to 34in allowing more leg-room for the occupant. In addition, air- lines often prefer the unit to be capable of forward- or aft-facing installation to facilitate cabin layout. As with the tourist seat, single, and double-beam structures are produced to meet this requirement—both types have their adher- ents and the advantages and disadvantages are mainly as previously described. However, as there is not the same necessity to provide leg room beneath the seat, the double-beam versions usually have the rear beam in a somewhat lower position to facilitate recline. This also makes it possible to reverse the legs to suit forward- and aft-facing installations. Recline on modern seat designs is invariably controlled by a hydraulic mechanism which provides smooth and positive action
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