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Aviation History
1958
1958 - 0186.PDF
196 FLIGHT, 14 February 1958 MORE ABOUT THE X-15 NORTH AMERICAN AVIATION'S MILE-A-SECOND RESEARCH AIRCRAFT, THREE OF WHICH ARE TO FLY NEXT YEAR SUPERFICIAL examination of aviation today might lead anobserver to suppose that the science of flight had come to aparting of the ways with, on the one hand, unmanned ballistic missiles and space vehicles achieving unprecedentedspeeds, ranges and altitudes, and, on the other, winged piloted aeroplanes ploughing their way much more slowly through theearth's atmosphere. It is a sine qua non that the two types of travel will soon be linked; and the logical means of accomplishingthis are either to put a man in a ballistic vehicle or to make a winged aeroplane capable of travelling very much faster and atmuch greater altitude than has so far been achieved. The most important "fastest and highest" aeroplane—in the Western world,at least—is the X-15, and it is now possible to add much to what was said about this project in our issue of January 24. At present the fastest and highest aeroplane is the Bell X-2,which on different missions has established a controllable speed of approximately 2,260 m.p.h. and an altitude (by no means thelimit of the trajectory which it could achieve) of 126,200ft. The X-2, the design of which has already been revealed in some detail,is a relatively conventional low-wing monoplane, powered by a single throttleable Curtiss-Wright rocket motor of 12,000 lb thrustwith turbopump feed from tankage sufficient to give a full-thrust endurance of approximately five minutes. Like the earlier Bell rocket-powered aircraft, the X-2 wasdeveloped for the co-operative research aircraft programme managed jointly by the National Advisory Committee for Aero-nautics, the U.S.A.F. Air Research and Development Command and the U.S. Navy Bureau of Aeronautics. Early in 1952 theN.A.C.A. began a long-term research investigation into flight at extreme speeds and altitudes. The study was directed particularlyat piloted flight, and embraced aerodynamic problems (or rather, owing to the vastly increased mean free path of the air molecules,the problems of slip-flow and super aerodynamics) together with stability and control, structural, propulsion and physiologicalinvestigations. On July 9,1954, the N.A.C.A., U.S.A.F. and Navy held their first meeting with a view to the design and manufactureof an aeroplane capable of investigating the new field. With the designation X-15, a competition for the aircraft was launched inDecember of that year, and twelve months later the prime con- tractor was named as North American Aviation, with ReactionMotors responsible for the powerplant. As we stated on January 24, financial appropriations have beenmade for three X-15s. The first is due to start air-launched flight testing in about eleven months' time and all three should be estab-lished in their respective research programmes before the end of next year. It is appropriate to describe these aircraft in somedetail before outlining the work which they are intended to do. As the illustrations indicate, the X-15 will have a mid-mountedwing (not low-mounted as we suggested three weeks ago). Remark- ably enough, in view of the thermal problems which will beencountered, the cockpit is raised well above the fuselage profile and is mounted in the nose. Otherwise the design is roughlywhat one would expect for a Mach number of five or more, design performance figures being given in the table of data beneath thethree-view drawing. Most of the X-15's manifold peculiarities can be seen in the simplified cut-away sketch opposite. It must the emphasized that the features shown are unusual only by reason of the fact that this is the first hypersonic aeroplane to reach an advanced stage of design; ten years hence such designs should be commonplace. Aerodynamically there are few surprises. The nose is blunterthan might be expected (the included angle at the entry is some 45 deg), but beyond the atmosphere this is of no consequenceand ballistic-missile research has shown that the optimum re-entry nose is actually a blunt one. At least one of the X-15s will be £\ J North American X-15 (provisional drawing). One single-chamber ReactionMotors rocket engine rated at 60,000 Ib at sea level (about 70,000 Ib outside the atmosphere). Wing span, 22ft; overall length, 50ft; height across fin tips, 13ft 6in;tailplane span, 15ft; body diameter, 4ft; launching weight, about 33,000 Ib; design Mach number, ranging from 5.5 to at least 7; peak altitude, at least 100 miles(possibly as great as 300); range, at least 450 nautical miles. stressed to carry an instrumented boom on its nose, but this will,of course, be useless except within the denser regions of the atmosphere up to about 100,000ft altitude. It was originally thought that most of the area of each wingwould have constant thickness across any given chord line, but it now seems certain that the profile will have a leading-edge radiusof around 0.25in (greater than that of the F-104) followed by a smooth curve, possibly of an elliptic form, to a perfectly squaretrailing edge with a thickness ranging from O.375in at the tip to 2.125in at the root. The most surprising surface is the verticaltail which, although it retains the simple wedge section prophesied in our previous article, has a trailing-edge thickness of no less than12in. The upper half is pivoted to provide yaw control within the atmosphere and the total wedge angle at its extremity is no lessthan 20 deg. Aerodynamic stability is also provided by the small fixed ventral fin, which is jettisoned before landing, and by theslab-type powered tailplanes which have an anhedral angle of 15 deg. For roll control a small aileron is mounted at mid-spanon each wing. For non-aerodynamic control at altitudes of from 50 to over 100 miles (where aerodynamic surfaces would have no effect) reaction jets are provided at the points shown in one of the draw-
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