FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1938
1938 - 1273.PDF
MAY 5. 1938. FLIGHT. 447 )EVELOPMENT An American Engineer Records the Progress Made in the United States : Prof. J. E. Younger's R.Ae.S. Lecture The Lockheed XC-35 experimental monoplane with which the flight tests were made. It is equipped to operate at 30,000ft. thought the possibility of this happening very small. Referring to the fact that most artists' sketches of proposed stratosphere aeroplanes showed circular windows, Prof. Younger said there did not appear to be any obvious reason why round windows should be used. Narrow, rectangular windows arranged longitudinally in long narrow strips were most desirable from a structural and practical standpoint. He thought that individual windows might be six inches high and twelve inches long. After investigations into the bursting strength of laminated plate-glass windows, it was recommended that a modulus of rupture of 4,500 Ib./sq. in. should be adopted. Another problem was that of designing suitable doors for a pressure cabin. The type adopted in the XC-35 was held in place by 14 bolts actuated simultaneously by a handle on a master cam. The handle could be turned through approxi- mately 90 deg. before the cam, which operated in a slot, made proper contact for withdrawing the bolts. The object of this was that during the process of turning through 90 deg. a disc on the inside of the door rotated, thus bringing air holes in the disc and the valve seat into line, and thus releasing the air from the cabin. After a number of trials it was found that air leakage between the disc and its seat could be prevented by using glazed leather -^in thick soaked in oil and held in place by a pad of sponge rubber. There was a certain amount of disagreement concerning whether doors should open inwards or outwards. Prof. Younger thought that the logical answer was that there should be two doors, one opening inwards and one opening outwards. The outward opening door required fairly intricate operated mechanism which might be deranged in case of a crash, while -OUTSIDE WALL OF DOOR -LOCKING BOLT INSIDE WALL OF DOOR -RUBBER FLAP -AIR PRESSURE HOLDS FLAP AIR-TIGHT WOODEN BLOCK AROUND DOOR FRAME, GLUED IN PLACE -DOOR FRAME -FUSELAGE SKIN Airtight seal of cabin door. the inwardly opening door would require no mechanism for its operation and need only be held in place loosely against a gasket of soft rubber by small spring clips. Glass windows could be sealed in the same manner, but it was advisable to separate thf glass from the metal structure and the clips must not press heavily in order that distortional stresses should not be transmitted from the structure to the glass. He recom- mended that soft rubber should be used, as this allowed a more even distribution of stress in the glass. Control Glands.—Here the principal problem was that of her- metically sealing the exits of control wires, tubes, etc., through the walls of the cabin. Two types of motion were involved, rotation and sliding. The sealing of a gland for a torsion shaft was very simple and one of the illustrations shows the simple gland used in the laboratory in connection with the supercharger vaive control. Another illustration shows a gland which had proved satisfactory for either rotation or sliding, even at very low temperatures and when sprayed by a water mist so as to cover the gland completely with ice. Other ways of constructing such glands were obvious and the lecturer illustrated a bellows arrangement. This gland, by the way, was designed for use in the investigations but was not constructed as the other designs mentioned were simple, light and safe. Safety Valves.—The tendency to flutter of the ordinary spring operated valve suggested that a special device would have to be developed. However, a simple type of spring loaded valve, shown diammetrically in an illustration, was constructed and to everyone's surprise proved entirely satisfactory This valve was, of course, an outwardly opening one. It was necessary to have also an inwardly opening one in order to make sure that the pressure on the inside of the cabin could never become less than that on the outside, since otherwise the cabin walls might be crushed inward. The in- wardly opening safety valve was of very simple type and consisted of a soft sponge rubber flap hung like a curtain on the inside of the cabin over several small holes in the side wall. . Discharge Valves - - Apart from the safety valves, it is, of course, necessary to have a valve which discharges the pressure air from the cabin. Such a valve should maintain a constant pressure inside of the cabin regardless of the barometric pressure on the out- side and should be free from any possibility of freezing. The simple valve shown in an illustration fulfilled these two con- ditions satisfactorily for fairly high differential pressures but at low differential pressures the spring effect of the sylphon bellows caused a variation of about half pound per sq. in., when the differential pressure was changed from pbout one pound per sq. in. to 51b. per sq. in. This valve had the dis- advantage that it would not close readily when the pressure in the cabin was reduced. For instance, if the pressure was 5 lb. per sq. in. in the cabin and the supercharged air supply was cut off suddenly, the discharge valve would allow the pressure to drop to 3 or 4 lb. per sq. in. before it closed. An electrically operated valve is shown in another illustra- tion. Such a valve was installed in the XC-35 and gave fair service but considerable refinement was still necessary. Regulation of the quantity of air flowing into the cabin was necessary. If the supercharging unit was separate from the main aero engines, the regulation could be effected by regu- lating the speed of the supercharger. This would not be pos- sible if the supercharger were operated by the aero engines, and in that case it would be necessary either to regulate the
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
