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Aviation History
1953
1953 - 1573.PDF
FLIGHT, 4 December 1953 HIGH-ALTITUDE COCKPIT COMFORT 727 WATER 40 #/MIN RAM-* AIR PILOT VENTILATOR PRESS SUIT COCKPIT extremely dangerous. (In the early days of such systems the fog was thought to be smoke, and many pilots baled out, assuming their aircraft to be on fire.) Inside fog occurred most frequently when the aircraft passed through clouds at relatively low alti tudes. It could be avoided in modern fighters if the pilot selected high cockpit-temperature on his auto matic temperature-control. A further problem with these cockpit condition ing systems arose if exhaust smoke from missiles entered the engine intake and passed thence into die cockpit. Since the pilot breathed mainly oxygen the effect was to be considered mainly in relation to cockpit visibility and body absorption. Air con tamination through oil leaks in the engine compressor was considered unlikely, since, if such a leak occurred on a modern engine, it would almost certainly indi cate engine failure, and contaminated air would no longer reach the cockpit. Mr. Lemke finally dealt with the services other than cockpit conditioning and ancillary drive tur bines, which were also operated through air bled from the engine compressor. These systems included anti-icing, windscreen demisting, windscreen rain clearance, fuel-tank pres surization and cockpit canopy seals. Air bled for anti-icing would amount to 80-90 lb/min. It would not be required above 20,000ft, at high speed, or for long periods, because the aircraft could rapidly climb beyond icing regions. Since the fighter's windshield and canopy were thick and strong to resist pressurization and high-speed-airflow loads, they had an appreciable temperature-lag. While cruising at high altitude their temperature dropped; if brought rapidly to low altitude they would tiien invariably mist up, due to condensation. The most common method of obviating this was to blow hot air over them. This required about 4 lb/min of compressor-bled air. Other methods (principally electrical) were, however, available and preferable. Compromises could be made in the extent of demisting provided both in the area demisted and intensity of demisting. Since rain formed an untransparent layer of water over the windscreen some method of clearing it was desirable. Repellents were efficient but short-lived. Windscreen wipers were too weak to stand up to high-speed airflow. It had been found, however, that jets of air directed at almost sonic speed across the wind screen would divert rain drops from it. Direct bleed air was too hot for this purpose, however, and flow from the A.T.M. limited and too slow. Pressure-regulators would also be required to cope with varying engine-bleed conditions during low power approach and full-power take-off. Mr. Lemke now suggested a modified air-conditioning and ancillary-drive system (illustrated in Fig. 2) aimed at reducing to the minimum the aircraft-performance penalty caused by engine FLOW CONTROL 1 */MIN RAM AIR ENGINE COMPRESSOR HEAT EX. I ENGINE TURBINE ENGINE THRUST BLEED AIR 20-30 J/MIN 80-90 t/MIN ATM ACCESSORY DRIVE 40 HI/MI N FWD ELECTRONICS OVERBOARD AFT ELECTRONICS ANTI-ICING TAIL WING ENGINE DUCT 1-2 */MIN MISC ATM COMPARTMENT ENGINE ACCESSORY COMPARTMENT 3000 pi. COMP CANOPY SEAL FUEL TANK PRESSURIZATI MISC TANK PRESS. OVERBOARD Fig. 2. The lecturer's suggestion for a simplified system reducing the load in engine compressor bleeding. compressor bleeding, and at lessening the weight of the refrigera tion and power systems. He suggested the following modifica tions : diat the electronic equipment be cooled by ram air, which would itself be cooled by means of water evaporation when ram air temperature exceeded 100 deg F; use of electronic equipment, allowing higher component temperature; and intake pressure-drop low enough to permit cooling at high altitude. The pilot should be cooled by a ventilated pressure-suit and the cockpit allowed to seek its own temperature level. Finally, maximum cockpit differential pressure should be reduced to 1.5 lb sq/in (a maxi mum cabin altitude of 40,000ft) this pressure being maintained by air discharged from the pilot's suit. The pilot would use a pressure-breathing oxygen system. The above conditions could be achieved with ram cooling flow over the electronic equipment of approximately 40 lb/min. Dur ing high-speed flight water injection would cool ram air to 100 deg F. This would be automatically controlled and the ram cooling airflow adjusted by a flow control valve to allow for altitude. The small amount of engine bleed air required for the pilot's ventilated pressure suit would be cooled by passing it through a heat-exchanger located in the cooling ram air duct ahead of the electronic equipment. Mr. Lemke ended by stressing that in his opinion the principal lines of progress in the field of air conditioning and cooling, lay in the development of self-cooling electronic equipment and in the introduction of ventilated pressure suits for pilots. AIRCREW at ALTITUDE THE physiological effects of high altitude were discussed in another lecture at the S.A.E. meeting. Bearing the title Taking Man to Higher Altitudes, this paper was by Mr. A. M. Mayo, head of the equip ment and interiors engineering section of Douglas Aircraft. He began by saying that, in the endeavour to reach higher altitude, both the physical stresses and the physio logical load on the human pilot had tended to increase. But the total efficiency of the man-machine combination depended on die individual efficiency of die two parts and excessive reduction of the man's efficiency by an accumula tion of a number of relatively light stresses became a very serious factor. Flying in reduced pressures above those altitudes where the mere addition of oxygen was sufficient for the pilot's needs brought certain effects beyond simple hypoxia*: for instance, "bends" and "chokes," and excessive swelling due to evaporation of liquids widiin the body. Simple compression of outside air to produce suitable cockpit atmosphere became inadequate above 70,000ft. In the ozonosphere, simple pressurization could produce ' ' < ' .5 1.5 DISTANCE IN MILES 2.0 * Oxygen deficiency at high altitude, a condition normally Jh . between visual sighting of an obstacle and initiation of avoiding lCeJ, V±f L2T 0LTLrjeTll°Jt mZ action"!: hZ graphicaUy shoJ. TL is but one of the problems of high speed inhaled; the term anoxia, often regarded as synonymous, actually implies a complete lack of oxygen—ED. flight.
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