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Aviation History
1946
1946 - 0185.PDF
JANUARY 31ST, I94L F LI G HT 105 Westland Cabin Atmosphere Control Review of Components and Install lations for Typical Cabin Interior Conditioning Scheme TO the potential ordinary passenger of the modernairliner there is something psychologically forbiddingabout the idea of pressurising. It seems to connote inflation, and the idea of being blown up is naturallysomewhat repulsive. It is, therefore, desirable that the term '' pressurising '' be relegated purely to the technicalfield for specific use—and that we should, instead, adopt the term "atmosphere control": after all, the latter isboth more descriptive and more accurate for, although pressurisation per se is only part of the general aspirativeproblem, the term has come to be used as an overall title for the whole field. Westland Aircraft, Ltd., have specialised in cabin atmo-sphere control for some time and have amassed a greater fund of data on the subject than prob-ably any other commercial concern. They have an M.A.P. contract to actas consultants on comfort and safety provisions as well as on the operationalside of cabin atmosphere control and, in fact, are consulted by most Britishfirms interested in this branch of aeronautical design. The laboratoriesat Yeovil are fairly extensive and in their comprehensive range of testequipment include a decompression tank sufficiently large to take a 12ft.dia. fuselage test section. Almost lotal evacuation can be attained, alsolefrigeration to somewhere in the region of —65 deg. F. Humidifyingand drying equipment is also available and, at a later date, means of artificial excitation of thetest fuselage will be embodied to show the effects of vibra- tion on the aspirative problem in order more accuratelyto simulate actual dynamic flight conditions. Perhaps the best way of "giving a general overall picture VALVE DIAPHRAGM Recirculating fan,blades and central Non-return and spill valve, showing masking sleeve andvalve diaphragm with control linkage. and reasonable appreciation of the problem would be todeal with a typical system as installed, say, in a high-speed luxury passenger aircraft designed to operate at 25,000ft.,which altitude by general consensus of opinion, appears to be the average* optimum economicheight for the new British aircraft coming along. This figure of 25,000ft. has beenagreed upon in connection with a dif- ferential pressure of 5^ lb./sq. in. togive a cabin interior pressure equiva- Jent to atmospheric at 8,000ft. How-ever, this can be regarded as some- thing of an interim measure as it wouldpatently be better to maintain ground level conditions in the cabin irrespec-tive of the height at which the aircraft flies. It has been held by some that theapplication of pressure should be de- layed until the aircraft reaches 8,000ft.and, as additional height is gained, the 8,000ft pressure should be maintained in the cabin. Oneof the main drawbacks to this scheme is that the aircraft must not be allowed to gain or lose height too quicklybelow 8,000ft., as discomfort is caused to sitting passengers at rates of descent in excess of 250 ft./min., whilst for with two banks ofrectifying vanes. ENGINEER'S PANEL QU "^ SPILL AND NON RETURNVALVE SAEETY AND VENTILATING VALVE Diagrammatic section through cabin, showing disposition c* conditioning equipment components and airflow paths in atypical installation.
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