breaking the sound barrier

With the development of jet-powered flight, a new series of record-breaking speed flights began as soon as the planes were available. The first achievement was to fly faster than the speed of sound (760 miles per hour [1,223kph1 at sea level, although that number falls as the altitude is increased until it is 659 miles per hour [1,060.Skph] at thirty-six thousand feet [10,973m]), designated Mach 1—meaning compared as a ratio to the speed of sound—after Ernst Mach, the nineteenth-century physicist who worked out some of the physics involved in “transonic” flight.

On October 14, 1947, Charles E. “Chuck” Yeager, a decorated American ace, became the first flyer to officially “break the sound barrier” by flying at Mach 1.015 (or 670 miles per hour [1,O78kph]) at forty-two thousand feet [12,801.5m]) in the experimental Bell X-1. Yeager named the airplane the Glamorous Glennis, after his wife. Pilots in Korea who took their aircraft near Mach 1 experienced a violent buffeting, and several lost their lives when their planes broke up. Yeager had encountered the same thing as he neared Mach 1, but once past it, he experienced an eerie quiet as he raced ahead of the noise and shock wave his airplane was creating.

The is very strong evidence that the sound barrier was first broken by pilots flying the Me 262 at the end of the Second World War.

In 1951 famed test pilot Bill Bridgeman flew a Douglas Skyrocket to Mach 1.88, demonstrating that several existing engines would be capable of taking an aircraft above Mach 1, and establishing Mach 2 as the next goal of the speed fliers. Meanwhile, research at NACA at Langley Field had reached an obstacle: airplane designs that were supposed to be able to break Mach 1 were falling consistently short. There had been speculation in the late 1940s that it might be impossible to break the sound barrier (that was why it was called a barrier), and the early tests of the Convair F-102 gave some credence to this fear.

Charles E. “Chuck” Yeager standing next to the Bell X-1, Glamorous Glennis, in which he broke the sound barrier in 1947. BELOW: Yeager set another record—Mach 2.44 (1,650mph) —in the Bell X-IA in December 1953, barely managing to land safely.

Then NACA aerodynamicist Richard Whitcomb reasoned that the smoothest airflow over an aircraft would be achieved if the cross-section of the craft increased smoothly from front to back. This would be a problem once the wings started to protrude from the plane. The solution was to pinch the fuselage in at the wings: the result was the classic “Coke bottle” design of supersonic aircraft. The revised design of the F-102 yielded a fighter that achieved speeds of Mach 1.2 with no other change in the plane.

Douglas D-558-2 Skyrocket High-Speed Research Aircraft

Jacqueline Cochran became the first woman aviator to break the sound barrier on May 18, 1953, flying a Canadian F-86E Sabre jet. Later that month an American F-100 Super Sabre became the first jet fighter to fly above Mach 1, and later that year test pilot A. Scott Crossfield flew a D-558-2 Douglas Skyrocket launched from a B-29 at Mach 2.01. Chuck Yeager ended the year with a record flight of 1,650 miles per hour (2,655kph)— Mach 2.44—though he was just barely able to regain control of the aircraft when it went hurtling earthward in a tailspin. In the years that followed, a corps of exceptional test pilots working at Boscombe Down in England and at Edwards Air Force Base in California became celebrated for “pushing the envelope” of flight.

In 1958 Major Howard C. Johnson, one of those pilots with the “right stuff,” set an altitude record (91,243 feet) and then a speed record (1,403 miles per hour, flying a Lockheed F1O4A Starfighter each time. The seven original Mercury astronauts were chosen from among this group of pilots. Speed flying took a quantum leap with the building of the North American X-15, designed by Harrison Storm. The X-15 was designed to fly as fast as Mach 7; when it was flown in July 1962 by Robert White at an altitude of fifty-nine miles above sea level, it was seen as a step toward putting an astronaut into space.

X-15A prior to launching from a B-52

The Underachiever X-Plane: The Stiletto

By:
Raul Colon
E-mail: rcolonfrias@yahoo.com
PO Box 29754
Rio Piedras, Puerto Rico 00929

One of the most striking looking aircraft ever conceived, the Douglas Company X-3 Stiletto, was also one of the most disappointing planes ever to fly. Intended primary as a research data collection aircraft, the X-3 did provide its handlers with some useful information, but not the amount of data the concept managers expected. The mission profile of this amazing looking aircraft was to research the effects of extreme temperatures on a titanium based airframes at supersonic speeds. The X-3 program was commenced in late November 1945 by the Douglas Corporation. The program was a direct response to the company’s long term goal of developing a high speed, high altitude interceptor for the newly formed U.S. Air Force. During the first three years of the program, Douglas engineers tackled a host of design and aerodynamics problems which delayed the production of an initial mock-up. After presenting their findings to the US Air Force, the Douglas Corporation was granted approval for construction in June 1949. The original Air Force order called for two research planes to be built during a period of three years, but in the end, only one sample was ever constructed.

As with many military related projects that started at this time, the development of this advance research plane was shrouded in secrecy. Its design alone was unprecedented in its complexity mainly because the design could only be met with a new type of structural construction material: aluminium and titanium alloys. What the designers were able to produce was nothing short of incredible. The X-3 plane was a slick and streamline design. It broke with the conventional, swept wing design that had dominated the new jet age. The X-3 had a 66’-9” length fuselage, its height was of 12’-6” and it possessed a long nose cone that provided extra space for testing equipment. At the end of the nose cone, there was an air data boom incorporated with the aircraft’s main data collection devices. The complete airframe weight it 16,086lb.The X-3 was the first aircraft to be fitted with thin and short wings. The complete wing span covered only 22’-8”, translating to a total wing area of just166sq ft. In fact, the X-3 wing design was so radical and proved to be so successful that it was extensively studied by brilliant American engineer, Kelly Johnson; who incorporated the X-3 wing configuration into its own F-104 Starfighter a decade later. The Stiletto was a single seat aircraft. The cockpit was pressurized and air conditioned. A necessity for the safety of the pilot since the aircraft was to be subjected to extreme temperatures. The safety of the pilot was a priority for the design team; they developed a space suit, with helmet; for the pilot to use. This suit was needed in case the pilot needed to eject from the aircraft at supersonic speeds. The whole airframe was made of aluminium composite, except for the underside of the tail boom, where the engine exhaust where located; that area was made of titanium alloys. The X-3 was covered with 850 pinholes designed to collect data on the effects of extreme temperatures. It was also fitted with 150 strain gauges designed to record air loads on the airframe. The power plant was the Westinghouse’s J34 WE17 turbojet engine capable of 4,860lb of thrust. Two were destined to be fitted on the X-3 giving the plane a maximum speed of 704mph. The engines gave the X-3 one of the faster recorded take-off speeds in history: 260mph. Being a research plane, the aircraft fuel capacity was very limited, if flying at top speed, the X-3 could only stay flying for one hour. Its operational range was also constrained by the lack of fuel capacity. It could only travel 500mi. Its operational ceiling was 38,000ft.

On the morning of October 15th, 1952, the X-3 took to the air for the first time, although the official recorded date for its maiden fly was October 18th. The Stiletto never set any speed records. In fact, its top speed was achieved on July 28th, 1953, when the aircraft was clocked at Mach 1.21, well short of the expected speed envelop designed for the aircraft. In all, Douglas flew the X-3 twenty times, with the US Air Force following with just six flights. The X-3 was unceremoniously transferred to the National Advisory Committee for Aeronautics were it flew for an additional twenty occasions until the plane was finally retired from active service in the summer of 1953. This marked the service end of one of the most visually stunning aircrafts ever to fly. Today, the lone X-3 sample is resting on the grounds of the US Air Force Museum at Wright-Patterson AFB in Ohio; a silent reminder of the early jet age.

Concept Aircrafts in US Inventory, Lan Pasquelleri, 1976
The Douglas Corporation: 1940-1950, Douglas 1980
Concept Aircrafts: Prototypes, X-Planes, and Experimental Aircraft, Edt Jim Winchester 2005

The next phase in speed flying came about because of the downing of a U-2 spy plane piloted by Francis Gary Powers over Russia in May 1960. The U-2 had been designed by Kelly Johnson at the “Skunk Works,” Lockheed’s secret plant in Burbank, California. The plane used a very high aspect-ratio (long, narrow wings) and a powerful Pratt & Whitney jet engine to fly very high and very fast over targets that it would then photograph. The Russians had found a way of hitting the plane with surface-to-air missiles and the ensuing scandal was one of the major crises of the Eisenhower administration.

U-2

The military turned to Lockheed again, and this time the Skunk Works, under the direction of Johnson and Ben Rich, produced an aircraft that was too fast even for missiles: the SR-71 Blackbird. The SR-71 began its life as the YF-12, a high-speed interceptor fighter—from certain angles, in fact, an SR-71 looks to be two aircraft melded together down the middle. The plane has been modified and improved many times since its introduction in 1964—new materials, new systems, and, most importantly, new fuels have allowed the aircraft to reach its potential speed of Mach 7- plus.

However, the world’s airplane speed record is held by William J. “Pete” Knight, who flew an X-15- 2A over Edwards Air Force Base at 4,535 mile or Mach 6.72—a record set on October 3, 1967. Aviation observers point out that several U.S. military aircraft (even some later models of the SR- 71) may be capable of greater speeds and that the USAF may well have established new records in secret since. In addition to high speed, designers of fighters are always on the lookout for high manoeuvrability. The newest experimental aircraft—one that may prove to be more agile than even a human-computer combination can control—is the X-29, a forward swept-wing that appears to be flying backward. This configuration creates hot spots on the skin of the aircraft that requires special heat-dissipative metals. It is feared that during some sharp turns at high speed pilots in this aircraft may be subject to G-forces that will kill them.

The Lockheed SR-71 Blackbird, developed by Clarence "Kelly” Johnson’s team at the Skunk Works, is the only aircraft capable of cruising at Mach 3 (its top speed is still classified) for extended periods (two or three hours). Its chief design element is the way it directs heat away from the cockpit, beginning with the remote placement of the engines.

New projects continue, but since the end of the cold war, the focus has changed from strategic capability to containment of smaller wars. This has created new requirements that will be met by aircraft designers around the world.