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  The other branch of jet propulsion is the rocket. Rockets can be of the solid-fuel variety used mainly for assisting take-off; in which the propellant is in the form of a highly compressed powder. This is ignited and burns rapidly producing very hot gases which are discharged under great pressure at very high velocity. Once the charge is ignited, however, there is no control over the rate of combustion or the amount of thrust, and as a means of flight the bi-liquid fuel rocket is to be preferred. In this case, combustion takes place through the chemical reaction as the liquid propellant and an oxidizer mix in the combustion chamber.

  As the rocket carries its own oxygen with it, it is independent of the outside atmosphere and theoretically is therefore not limited in speed or altitude. Its main drawback is its present highly extravagant consumption of fuel, which is up to six times the rate of that of a ram-jet and from ten to twenty times as much as the turbo-jet fuel consumption. For instance, the German A.4, or V.2 as it was known in this country, consumed 9 tons of alcohol and liquid oxygen in 7.1 seconds. During that time, however, the V.2 had accelerated to a speed of over 3,500 m.p.h., and a height of 22 miles from which it continued to climb by its own momentum to an altitude of 68 miles before dropping to earth.

  The Germans also worked on a number of rocket-propelled fighters of which the Me163B, powered by an H.W.K. 509 Unit, was the first to see operational service in 1944. The Me 163B had sharply swept wooden wings and a high fin but no horizontal tail. The rocket unit burnt a mixture of concentrated hydrogen peroxide, and hydrazene hydrate mixed with alcohol, which were carried in separate tanks and pumped by a turbine to the combustion chamber. It developed a maximum thrust of 3,300 lb at the cost of a fuel consumption of 1,000 lb per minute, which gave a climb to 40,000 ft within 4 minutes, and a range after reaching that height of 22 miles which could be extended by gliding. Poor aerodynamic qualities restricted the top speed to 550 m.p.h. at 40,000 ft, or a Mach number of approximately 0.84.

  To get better endurance, the H.W.K. 509C was developed with a separate auxiliary combustion chamber. For cruising, the pilot switched over from the main combustion chamber, which gave a thrust of 3,740 lb, to the auxiliary which provided 660 lb thrust and therefore had a much lower fuel consumption.

  Attempts were also made to combine rockets with turbojets. The B.M.W. 003R, which was fitted into an Me 262, consisted of the B.M.W. 003 turbo-jet with a 180 lb rocket unti fared into the rear of the engine casing. Using 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

  Chuck Yeager was a US Army Air Corps test pilot. Yeager:

  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 the crystalline California air with the X-1 clutched to its underbelly. The bomber’s gear would come up and the prospect loomed of having to get into the driver’s seat of the X-1 “in the usual fashion,” as the unemotional post-flight reports described it. It was the worst part of the whole ride – suited more for a contortionist than a pilot.

  At altitude, engineer Jack Ridley and I would stroll back to the bomb bay, trying not to look through the gap between the mother ship and her tiny orange offspring, named Glamorous Glennis after my wife, who had happily suffered the standard deprivations as an Army Air Corps wife. It was cold and windy as I made my way to the small steel ladder mounted on slides that would descend to the X-1’s cabin door. I’d bounce on it a little and it would drop into position.

  Then the fun would start. I’d place my right hand up inside the door and hold on tight to the top of the frame inches away from all that sky. Then I’d slide in feet first with my left hand still holding the ladder behind my back. I’ll never forget that bad moment when I’d have to release my right hand and shift my weight from the ladder to the plane. This was the moment – half in and half out – when I always figured the X-1 would get inadvertently released (crack!) from the cable attachment point overhead. Once inside the plane, I’d have to bend around double to turn and slide into the pilot’s seat. But it wasn’t over. I’d still have to contend with the parachute (as much good as it would do in an emergency) and retrieve my helmet and oxygen mask from behind the seat – I’d stuffed my helmet and oxygen mask behind the seat of the X-1 before takeoff, two less items to worry about.

  When I’d settled, Ridley would lower the cabin door on a small cable and position it over the doorframe. He’d push from the outside and I’d latch from the inside and somehow, in the icy wind, with thinning oxygen and mounting anticipation, we’d get the X-1 ready for flight.

  The drop itself was the next big obstacle, and like entering the bird, it’s something that I never really got used to. During preflight checks, I’d practice neutralizing the controls and brace myself for the release. Cardenas would go through the countdown, finishing with an emphatic “Drop!” The X-1 would float from the B-29 and I’d get launched right up to the cockpit overhead, caressing the canopy with my helmet in the sudden swell of microgravity. My heart was in my mouth, stomach right behind it.

  The pilot’s reports I wrote afterward were devoid of these sensations – as a professional test pilot, you were expected to maintain a dispassionate tone. Consider these excerpts from the report following the eighth powered flight: “After pilot entry in the usual fashion at 7000 ft, the XS-1 was dropped from the B-29 at 20,000 ft and at 260 m.p.h. indicated airspeed . . . Immediately after the drop, all cylinders were started in rapid sequence, and with all four in operation it was noted that No. 1 and No. 3 had 210-psi chamber pressure, No. 2 and No. 4 having 220 psi, with approximately 290-psi LOX and fuel line pressure . . . The climb was made at .85 to .88 Mach until 40,000 ft was reached.”

  That flight, on Oct. 10, signalled enormous progress in the X-1 program. We thought it was only a matter of time before we’d push through the sound barrier. What would it be like? A pebble in the road of aviation we had merely to step over? Or an insurmountable Chinese Wall that would destroy the X-1 – and me with it? Naturally, thoughts at these moments turned to Glennis and my boys, who sacrificed plenty out in the desert in those brightly lit days of the late 1940s. I wanted to fly, wanted to take my shot at the speed of sound. And they were my own personal cheering section.

  As I stood looking at my carrot, my glasses and my rope on the morning of Oct. 14 – broken ribs secretly knifing at my side – I thought that this just might be the day. The eighth powered flight had gone exceedingly well. We had flown as fast or faster than anyone ever had before. And it looked as though we only had to step over the line to enter aviation’s new age. The day of the ninth powered flight began in the usual way. I fried the eggs while Glennis got ready to drive me over to the airfield. I’d had a bad night’s sleep – from the pain in my side, but also from the indecision about whether or not to fly the mission incapacitated. Tossing and turning, I decided to make up my mind in the air. If it became physically impossible to climb into the X-1, then I’d scrub the mission. If I could get into the pilot’s seat, I knew I could fly.

  As the team swarmed over the X-1, with cords from trouble lights dangling in the early morning gloom, and tools, racks, ladders and other gear surrounding the little ship, Ridley began the preflight coaching. “We got that Drene shampoo for the windshield,” he said, “so you shouldn’t have any trouble with the windscreen frosting over. Now remember, you play around with the stabilizer setting before you make your high-speed run. We know you’ll lose some elevator control, so find out where you get the most longitudinal control with the stabilizer. Try it a
t different settings and different speeds above .85 or .86 Mach.” Discussions continued over coffee. There was a heightened intensity, a new determination, on the part of everyone involved. This was it.

  This was the day. Would it end with another record shattered? Or with failure’s grim finality?

  After the X-1 was fueled, I returned to the ready room with Ridley to don my flight suit. Briefings continued, peppered by admonitions and warnings: “Under no circumstances are you to . . .,” “In the event of . . .,” “You’d better be sure to . . .” Their whole point was to make sure I didn’t take the X-1 over .96 Mach if I didn’t think the plane could handle it.

  Fear crouched in the deep recesses of the mind – present, accounted for, but well controlled. With the fueling and mating procedures completed, I walked back out to the B29 and stooped low to make a last-minute check of the X-1’s instrumentation. My helmet and oxygen mask were well secured behind the seat, I jogged to the boarding ladder and started climbing. Then there was the long wait as the B-29’s engines fired, the big bird began its takeoff roll and lumbered up to the drop altitude. I sat on a metal box inside the plane, ignoring my safety belt against the regulations. At 5000 ft, I nudged Ridley and said, “Let’s go.” We walked back to the bomb bay hatch and strode through. There was the little X-1, dangling in all that wind and cold and thinning air. Every move was torturous at this altitude. Getting into the X-1 on a good day was tiring enough. But I struggled through, wangled the hatch closed with the help of a 10-in piece of broomhandle I’d fashioned for the purpose (because of the limits imposed by my broken ribs) and continued checking the X-1’s pressurization, fuel delivery and controls.

  Richard Frost, Bell project engineer, was flying low chase that morning, and Lt. Bob Hoover was flying high chase well ahead of the B-29, both in Lockheed P-80s. In the standard routine, Frost would pull into a slight climb as I lighted the first chamber, aiming for Hoover’s P-80 about 10 miles ahead. I would try to pass Hoover at relatively close range as the fuel supply depleted, and he’d follow me down for an unpowered landing on the lakebed.