nitric acid as its propellant, the rocket gave a thrust of 275 lb for 3 minutes. Another project was to fit the Me 262 with an auxiliary H.W.K. rocket unit in the tail.
In the United States, initial research into the question of rocket propulsion was carried out by the Aerojet Engineering Corporation, founded in 1942. Within two years they had developed a solid-fuel Jato (jet assisted take-off) rocket. This consisted of a single cylindrical chamber inside which the solid propellant and oxidizer were moulded into a cartridge. The cartridge was fired electrically, producing a thrust of 1,000 lb for 14 seconds. Used on the Lockheed F.80, two Jato rocket units reduced take-off from 3,000 ft to 1,200 ft.
The first American rocket engine designed for straightforward aircraft propulsion was that developed by Reaction Motors. This was the unit used in the world’s first supersonic aircraft, the Bell X-1. It consisted of four cylindrical combustion chambers, each with a separate igniter so that they could be used individually or together. The chambers, expansion nozzles, and fuel system were supported within a frame of chrome-molybdenum steel, the whole unit weighing 210 lb. The fuel, a mixture of ethyl-alcohol and water, was circulated through cooling ducts in the exhaust nozzles and round the combustion chambers. Both the fuel and liquid oxygen were injected separately under pressure into the front of the combustion chamber, where the chemical reaction produced a jet velocity of 6,182 ft per second and a thrust of 1,500 lb from each chamber, or a total maximum thrust of 6,000 lb.
America’s first aircraft designed on the rocket-cum-turbo-jet principle was the Republic XF.9 in which provision was made for the installation of four rocket units in farings above and below the exhaust, to give extra power at take-off and for climbing. The XF.91 was powered by a General Electric J.47 turbo-jet engine equipped with reheat.
The Douglas D-588-II Skyrocket which reached Mach 1.03 in straight and level flight at 26,000 ft in July 1949, and attained Mach 2.0 at 72,000 ft (about 1,324 m.p.h.) on 11 June 1951, was originally designed to use both rocket and turbo-jet. Built to fly at 1,820 m.p.h. at 75,000 ft, it was at first equipped with a Westinghouse J.34 turbo-jet engine supplied with 250 gallons of ordinary aviation petrol giving a 30minute endurance, and the Reaction Motors rocket unit.
This was the same as that used in the Bell X-1 but it had only one-third the amount of propellant (3,000 lb) so that the total rocket endurance by using the chambers individually was about 3 minutes. At maximum power, the endurance was less than one minute so to save fuel, Jato rocket units were also used for take-off.
Later, the turbo-jet engine was abandoned because it failed to give the performance anticipated, and the space saved was devoted to increasing the supply of propellant for a new Reaction Motors L.R.8-R.M.6 rocket engine which incorporated certain small modifications on the 6,000 lb C.4 which was used in the Bell X-I. To enable sufficient altitude to be reached for the high-speed run, a B.29 Superfortress was used as a mother aircraft to carry the Skyrocket, fitted to the bomb-bays, to 35,000 ft.
A considerable quantity of fuel was lost by evaporation before the Skyrocket was launched, and in future the mother aircraft will no doubt carry rocket fuel so that it can top up the tank. As it was, by the time the pilot, William Bridgeman, had reached his altitude only 5% of the fuel supply was left. This gave him an endurance of about 3 minutes powered flight for his record breaking run during which he maintained a speed of over 1,000 m.p.h. for about 10 seconds.
Breaking the sound barrier
The joke was on me.
It was just after sunup on the morning of Oct. 14, 1947, and as I walked into the hanger at Muroc Army Air Base in the California high desert, the XS-1 team presented me with a big raw carrot, a pair of glasses and a length of rope. The gifts were a whimsical allusion to a disagreement I’d had the previous evening with a horse. The horse won. I broke two ribs. And now, as iridescent fingers of sunlight gripped the eastern mountain rims, we made ready to take a stab at cracking the sound barrier – up until that point aviation’s biggest hurdle.
The Bell XS-1 No. 1 streaked past the speed of sound that morning without too much fanfare – broken ribs notwithstanding. And when the Mach indicator stuttered off the scale barely 5 minutes after the drop from our mother B-29, America entered the second great age of aviation development. We’d fly higher and faster in the XS-1 No. 1 in later months and years. Its sister ships would acquit themselves ably as the newly formed U.S. Air Force continued to “investigate the effects of higher Mach numbers.” And Edwards Air Force Base, formerly known as Muroc Army Air Base, would witness remarkable strides in supersonic and even transatmospheric flight.
But with the XS-1, later shortened to X-1, we were flying through uncharted territory, the “ugh-known” as we liked to call it. And as ominous as it seemed to us then, that was the whole point. America was at war with Germany and Japan in December 1943 when a conference was called at the fledgling National Advisory Committee for Aeronautics (NACA, NASA’s forerunner) in Washington. The subject was how to provide aerospace companies with better information on high-speed flight in order to improve aircraft design. A full-scale, high-speed aircraft was proposed that would help investigate compressability and control problems, power-plant issues and the effects of higher Mach and Reynolds numbers. It was thought that a full-scale airplane with a trained pilot at the controls would yield more accurate data than could be obtained in a wind tunnel. And, following the English experience with early air-breathing jet propulsion, the notion of using a conventional jet powerplant was advanced.
Discussions continued through 1944, but winning the war was first on everyone’s agenda. It wasn’t until March of 1945, with the war drawing to a close, that the project picked up momentum. Researchers concluded, however, that jet engines of the period weren’t powerful enough to achieve the required speeds.
Rocket propulsion was explored – specifically, a turbo-pump-equipped rocket made by Reaction Motors Inc. Delivering 6000 pounds of thrust, the acid-aniline-fueled engine was believed to be capable of boosting an airplane to the fringes of the known performance envelope. Ultimately, the Reaction Motors turbo pump became stalled in development, so another 4-chamber Reaction Motors engine, this one fueled by liquid oxygen and diluted ethyl alcohol, was slated for installation. A pressure system using nitrogen gas provided a basis for fuel delivery. This fallback meant the X-1 could carry only half the fuel originally anticipated, but at least the project could move ahead.
With an engine in place, Larry Bell of Bell Aircraft Corp. and chief design engineer Robert J. Woods could proceed on the design of the X-1. It was to be unlike any other airplane designed up to that day. The Germans had experimented with rocket planes in the waning days of the war. The ME-163, with its HWK 509C engine, was credited with a top speed of around 600 mph. (The ME-262, with two jet engines, was clocked at 527 mph.) But the Bell X-1 would be far superior – with a clean, aerodynamic profile that whispered “power” even while dormant on the tarmac. The nose was shaped like a .50-cal. bullet, and its high-strength-aluminum fuselage stood a mere 10.85 ft high and 30.9 ft long. Wingspan was 28 ft and wing area was 130 sq ft. Launch weight was 12,250 pounds. Landing configuration was close to 7000 pounds. Packed inside the X-1’s diminutive frame were two steel propellant tanks, 12 nitrogen spheres for fuel and cabin pressurization, three pressure regulators, retractable landing gear, the wing carry-through structure, the Reaction Motors engine, more than 500 pounds of special flight test instrumentation, and a pressurized pilot’s cockpit. Performance penalties, fuel limits and safety concerns dictated an air launch by a specially modified B-29. (However, I did make a successful ground takeoff on Jan. 5, 1949.) The Army Air Technical Service awarded the contract for the XS-1 No. 1 (serial No. 46–062) to Bell on March 16, 1945, the first of six in the X-1 series. XS-1 No. 2 (serial No. 46063) was later flight-tested by NACA and was modifed to become the X-1E Mach 2+ research plane. The X-1 No. 3 (serial No. 46–064) had a turbo-pump- driven, low-pressure fuel-feed system. It was destroyed in an explosion on the ground in 1951. The X-1A, X-1B and X-1D were also test-flown. The A and D were also lost to propulsion system explosions.
You get the idea that designing, maintaining – and particularly flying – these research tools was not without hazard. But despite the risks, the first X-1 flew like a dream. Its smooth, precise flight characteristics defined the plane’s personality. I remember pulling three slow rolls on the first unpowered flight in midsummer 1947. And as we embarked on the quest to explore aviation’s potential, fear – albeit subsurface – supplied a businesslike edge to the work. It lurked in the shadows of the psyche as the great B-29, piloted by Maj. Bob Cardenas, lumbered into
