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Aviation History
1951
1951 - 0163.PDF
PLIGHT, 25 January 1951 105 (Left) This photograph shows the connection between mask and pressure-waistcoat, and also shows how the hood of the cold-weather blouse can be worn over the flying helmet to afford added protection to the face and neck. (Right) Detail of newly-developed flying helmet with modified ea The new vizor is shown in the partly raised position, when*if*would serve as qi efficient sunshield. f •• Flioht •• photooravh*. Witness for Duty . . to evacuate the chambers down to a pressure-equivalent of 40,000ft (5.55in Hg or 2.72 Ib/sq in) in approximately four minutes, but it takes considerably longer to attain the maxi- mum depression of 0.75in Hg which is equivalent to an altitude of about 76,000ft Control valves permit a variety of conditions to be simulated: for example, high-speed climbs and descents through any required ranges of altitudes; stabilized altitude conditions; gradual decompression; rapid decompression; explosive decompression; and so forth. The last-mentioned condition is simulated in an ingeniously simple manner. In the bulkhead dividing the two chambers is a doorway and an observation port; the doorway is, of course, closed, and the normal £in-thick armoured-plate glass of the port is replaced by a diaphragm of special paper. The test speci- mens, human or otherwise, are accommodated in one chamber, which is evacuated down to the equivalent altitude of the aircraft's pressure cabin; the complementary chamber thereafter continues to be evacuated until it reaches the equivalent altitude at which the aircraft is assumed to be flying, whereupon the paper diaphragm fractures, and the test specimens are consonantly subjected to virtually instantaneous decompression. Along each wall of the chambers are bench seats and tables, oxygen supply points and regulators, intercomm sockets and, above, a line of observation windows, 15in in diameter and glazed with armoured-plate glass. In the larger chamber is an X-ray seat station, and an ingenious optical system—devised at the Institute—pierces the end- wall of the chamber and permits the subject to be X-rayed by means of the radiographic unit outside the chamber. It will be appreciated that before designing equipment suitable for operation in given conditions, it is necessary for the physiological effects of operation at those conditions to be established. In many instances, a good deal of data exist, but even so, the research staff of the, Institute are frequently required to act as guinea-pigs. There is no question of " you will volunteer "; it is simply that the man or men chiefly concerned with a particular piece of research naturally use themselves as means of gathering data. There is a great deal to be said for this, cold-bloodedly heroic though it might appear and, on occasion, undoubtedly is; reduced to essentials, it is simply confirmation that an ounce of experience is worth a ton of theory. In the photograph on page 104 are shown a couple of medical officers in the small low-pressure chamber, each wearing the new-type pressure-waistcoats and oxygen- masks developed in conjunction with the RA.E. and M.O.S. They are close-fitting garments of two-layer rubberized- fabric with a zipp front. At the right breast is a light-alloy junction-box into which the oxygen lead from the source of supply is connected, and from which the flexible trunk up to the mask is taken; the junction-box is open to the inter-wall volume of the waistcoat. An exhaust valve is embodied in the oxygen mask, and opens at a fraction above the pressure-value of the system supply: thus the wearer breathes "through" the waistcoat. A moment's consideration will suffice to, show that the pressure waistcoat provides a local ambient pressure around the lungs to give a state of working balance comparable with that normally enjoyed. Clothing and- specialized items of personal equipment naturally claim a large measure of attention in the work of the I.A.M. A new type of flying helmet has been devised, and an ex- ceedingly comfortable piece of headgear it is. Service pilots will be glad to know that the bulky and cumbersome insert earphones have given way to compact little units which are housed in snugly comfortable noise-excluders of astonishing effici- ency. The oxygen mask and microphone have been given a good measure of attention and excellent point—the microphone is con- by a short cord to a junction-box carried onxfhe lower left side of the helmet, the long tercommunication lead being taken from the junction-box. Work is also going ahead on a vizor to take the place of goggles. Carried on a shock-absorbing headband, the vizor takes the form of a curved piece of transparent Perspex, dyed to a neutral grey. A friction-clamp butterfly-nut permits the vizor to be locked at any required position between the fully down and the fully up (out of use), and the neutral darkening of the Perspex is such that it provides utility as an anti-glare sunshield without destroying colour- definition. Whilst on the subject of headgear, it is worth mentioning that the Institute views with some reserve the plastic-basin "crash-hats" issued to American fighter pilots. The view is taken that such helmets, by virtue of their weight—and it is exceedingly difficult to make them really light—can impose an unwarranted load on the wearer's neck during high-g manoeuvres; that protection for the head against bumping the canopy is better left to the efficient design of seat and harness; and that protection from getting hit by a canopy during its jettison is also better left to the sense of the pilot to duck his head when freeing the canopy. On the other hand, if loss of the hood is unpremeditated, the Demonstration of new flotation jacket, illustrating the fact that partial inflation does not distend the wearer's harness.
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