Patent GB-774550-A (GB)
Title: Improvements in silencing equipment for the engine testing of jet-engined aircraft when stationary on the ground
IPC: B64F1/26
Filed: 1954-09-14
Abstract: 774,550. Silencing equipment for testing jet engines. REEVES, H. Q. A. Sept. 14, 1955 [Sept. 14, 1954], No. 26584/54. Class 7 (2). [Also in Group X] For testing the jet engines of an aircraft when stationary on the ground, an open-topped pen is provided by at least one door and walls which entirely surround the aircraft, the doors allowing the aircraft to be backed into position in the pen, and the wall opposite the doors being provided with at least one opening 15 through which the inlet section of an exhaustgas muffler, located outside the pen, can be brought into the pen for alignment with the jet pipe of the aircraft. As shown, the back wall 11 of the pen is shaped to an obtuse angle and has a flattened apex 14 in which the opening 15 is formed, the two sliding doors 12 being L-shaped so as to contribute to the enclosed area of the pen and being mounted on trucks 39 running on rails 40. The walls may be of brick, concrete or asbestos or steel sheeting lined on the inside with soundabsorbent material; breeze blocks may be built into the inner face of the walls so that panels of the lining material may be secured thereto. The floor of the pen is of concrete with a non-absorbent finish and has a soundabsorbing section underneath the aircraft and/ or underneath the air gap between the jetpipe 17 of the aircraft and the muffler 16 such section or sections being formed by a loadbearing grid 45, Fig. 4, of cast-iron or fabricated steel flush with the adjacent parts of the floor and covering an air space divided horizontally by a sound-absorbing layer comprising rock wool or fibre-glass disposed between a thin perforated sheet 46 of galvanized steel and a thicker perforated metal sheet 48; an air space 49 below the sound-absorbing layer receives and drains away rain. Low walls 36, of brick or concrete, at the front end of and extending partly across the pen prevent dirt and dust being blown by the wind into the pen when the doors 12 are open. For the purpose of silencing the noise emanating from the airgap between the jet-pipe 17 and muffler 16 the pen is provided with a roof 20 built up to cover the tail of the aircraft and side walls 21 having sliding doors 22 which are shaped to seal with a part of the aircraft when the doors are closed ; also a vertically sliding shutter, or shutters is or are provided on the doors 22, and inflatable rubber segments are attached thereto to ensure a sound-proof joint. The compartment 23 formed by the roof 20 and walls 21 is lined with sound-absorbing material, and, further, has screening walls 24. Openings 26 in the back wall 11 allow for the entry of cooling air required for the muffler 16, this air passing through passages 27 which are bent, curved or baffled to provide an acoustic filter effect; the passages are covered by roofing 28 and fitted with acoustic splitter panels of known type. The opening 15 is sealed with packing 19 of suitable acoustic design. Side doors give access to lobbies 43 and allow for the entry of personnel into the pen. Suitable wheel tracks or guides 31 and chock retaining fittings 32 are fixed to the floor, the track for the nose-wheel of the aircraft having a mechanically, electrically or hydraulicallyoperated height-adjusting platform 37 housed in a pit 38 so that by raising or lowering the nose wheel the height of the jet-pipe exit can be varied to secure correct alignment with the muffler 16. Instead of wheel chocks, other gear may be provided to prevent lifting of the tail of the aircraft during running of the engine. The muffler may be rigidly supported in a horizontal position, or made adjustable in height or tilt by mechanical or hydraulic means.