Man has long desired to conquer the skies due to his incapacity to take flight like birds and reach unimaginable speeds possible while in flight. This desire had led man to creating machines that mimicked flight, leading to the development of aviation and air transportation. With human flight now made possible through aviation, the desire to reach the speed that exceeds the speed of sound had fueled research even further to understand how it could be attained through aircrafts, automobiles and artillery. For years, several attempts have been done to reach this speed of sound or break the so-called “sound barrier”. In aerodynamics, the “sound barrier” pertains to the transition point wherein the object moves from transonic speeds to the speed of sound.
The very concept of the “sound barrier” has been a topic of immense debate between scientists, engineers and experts; especially in breaking the limits it sets in enabling speeds beyond measure or the speed of sound. The term “sound barrier” had been coined by British aerodynamicist William Frank Hilton in 1935, who was known for his high-speed experiments conducted in the National Physical Laboratory in England. Hilton, who at that time was preparing for his presentation for the NPL show day, stated that he had been so concentrated in understanding the High-Speed Tunnel when he had taken the curve of CD (drag coefficient) against V/a (Mach number), he noticed‘the resistance of a wing shoots up like a barrier against higher speeds up to the point it reaches the speed of sound’. Hilton’s declaration of the presence of a “sound/sonic barrier” had been misinterpreted by the British media and led to an uproar to the possibility of an actual “sound barrier”. While the idea in itself caught the attention of the public given the notion that human flight is still restricted in speed, the “sound barrier” was seen as a myth. Nonetheless, the idea of a “sound barrier” had been considered by scientists as the barrier between the transonic and supersonic speed phases. The Russians even claimed that there is a “sonic wall” that acts similar to the sound barrier .
Engineers, at the period, had agreed that while the idea of the sound barrier is plausible, there is still no concrete means on how much drag coefficient is required once reaching the transonic plane and how airplanes could thrust towards the speed of sound. Further challenges were also seen in the design of early aircrafts in the 1930s. Airplanes would be able to reach supersonic speeds and varies depending on the aircraft type. The Stearman and the North American T-6 Texan aircraft had been reported to reach supersonic speeds upon making turns; however, studies show that passengers would experience shockwaves and turbulences that may destroy the aircraft. Aircrafts also show propeller troubles once they reach the supersonic plane. Scientists concluded that the weight of the engine, the right type of propellers and power output would have to be taken into consideration if planes would be developed for high-speed flights . Studies continued to show further challenges to the possibility of aircrafts in piercing the sonic/sound barrier, noting that propulsion would determine if the plane could traverse from the transonic plane towards the speed of line without reaching difficulties . Myths pertaining to the plane’s stability upon reaching Mach 1 had also raised skepticism in research as some believe that the command interface of the plane may freeze upon reaching the sound barrier and cause damages. Pilots have also been skeptical in accepting the idea of a “sound barrier” once they reach the transition plane or the barrier found within 1000 km/h (620mph). Initial tests were done throughout the period to prove that a “sound barrier” did not exists such as the flight of Mk XI Spitfire flown by English pilot Tony Martindale in 1944, wherein the plane reached Mach 0.9 and landed without a propeller or gearbox .
While the challenges showcased the uncertain aspects of the sound barrier, the United States and the European countries such as Germany and Russia had attempted to develop their own means on breaking the sound barrier with the breakthrough in the development of the turbojet and the jet engine. Aerodynamicists had continued to study the complexities of the sound barrier and the transonic region to locate solutions to counter compression and propulsion problems given the reported successes in breaking this barrier. On October 23, 1934, the Italian plane Macchi-Castoldi MC.72 had reported a record of 440.69 miles per hour (mph) despite being a seaplane. The record had been broken by a German landplane, the Messerschmitt 209R, on April 26, 1939 when it reached a speed of 469.22 mph (Mach 0.6). The records remained untarnished for both planes until engineer John Stack proposed a study on shock waves and attendant flow separations that would aid in understanding the compressibility issue and develop a more powerful plane. Stack would continue to coordinate with the National Advisory Committee for Aerodynamics to work on his concept .
In the case of United Kingdom, the Ministry of Aviation had begun a secret plan in 1942 with Miles Aircraft to create the first aircraft capable of breaking the sound barrier through the Miles M.52 aircraft. The aircraft has the capacity of reaching speeds of up to 1,000 mph and attain an altitude of 36,000 ft. in a record of 1 minute and 30 seconds. The project had been cancelled due to several concerns over its design (which consisted a conical nose and sharp thin wings) and engine (which would trigger the control system while transferring from transonic to subsonic speeds) . In the case of the United States, its first attempt to create a plane capable of reaching high speed was in 1943 when the US Army and the NACA, including John Stack, conceptualized the plane powered by a rocket engine after the German interceptor, the Me-163. The proposed US plane would attempt to fly supersonically rather than begin in transonic speeds in order to prove that the sound barrier exists. The NACA and the Army continued to argue regarding the designs of the plane, however, the opinions of both parties had been applied with the development of the X-1 .
It was only in October 14, 1947 when the sound barrier is officially broken through the partnership of the British Air Ministry, the United States NACA and the Bell Aircraft Company to create the Bell X-1. Since all parties had argued over the design of the plane for the US proposed plane, the conceptualization of X-1 had been conceived when Robert J. Woods of Bell Aircraft met with the members of the NACA on November 30, 1944. Woods was only set to meet Ezra Kotcher at that time to chat, however, Kotcher had shared the problem regarding the non-military high speed airplane they are trying to conceptualize. Woods had agreed with the request for his company to design and build the plane, enabling the creation of the X-1. A drop-body concept had been applied with the design of the plane; wings were mounted on bomb-shaped bodies, dropped from an altitude of 30,000 feet. Research showcased that it was capable of reaching the required velocity to reach the speed of sound. While the data still lacked some estimates, the NACA had utilized the data acquired from the tests to design the plane. NACA Chief of the Flight Research Section Robert Gilruth had proposed a wing-flow method in 1944 to develop a wing that would be added to the plane in a perpendicular angle to enable the plane to gain enough speed up to Mach 0.81. The NACA was satisfied with the tests conducted with the wing-flow method and upon the rocket-model testing, the NACA used the data to finalize the designs of the Bell X-1. On October 14, US Air Force Captain Charles “Chuck” Yeager had been selected to pilot the X-1 (which he named Glamorous Glennis) and flew it through the sound barrier with speeds up to Mach 1.06 (807.2 mph). The success of the program had given the team the 1947 Collier Trophy on December 17, 1948 awarded by President Harry Truman. The X-1 was seen as a landmark to the field of aeronautics and broke the misconception on the sound barrier .
While man had been able to conquer the skies and reach unimaginable speeds that have the capacity to break the sound barrier, aerodynamicists and experts continue to refine and discover alternative means to replicate this feat in other fields. On the one hand, the original concept of the sound barrier had been mistaken as a myth by many considering the impossibility of having such barrier exist in the sky that would hinder human flight. However, studies debunked these skepticism and misconception and proved that there is a way to break this barrier and reach supersonic speeds that originally was deemed impossible for man to achieve. With the sound barrier continuously broken, it is unclear if the sound barrier still exists. Nonetheless, whether or not it still exists or not, the sound barrier enables man to understand the complexities that still exists when it comes to the limits of aviation, the perception on speed, and if there is a possibility it could be broken through means of automobiles and artillery.
Works Cited
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Anderson, John. "Research in Supersonic Flight and the Breaking of the Sound Barrier." Mack, Pamela. From Engineering Science to Big Science. Washington, D.C.: National Aeronautics and Space Administration , 1998. 59-90. Print.
Hansen, James. The Bird is on the Wing: Aerodynamics and the Progress of the American Airplane. Texas: Texas A&M University Press, 2004. Print.
Krehl, Peter. History of Shock Waves, Explosions and Impact: A Chronological and Biographical Reference. Berlin: Springer, 2008. Print.
"Miles on Supersonic Flight." Flight 3 (1946): 355. Document. 3 February 2014. <http://www.flightglobal.com/pdfarchive/view/1946/1946%20-%201965.html>.
Moret, Robin. Through the Sound Barrier, A Historical and Technical Survey. Toulouse: École Nationale Supérieure de l'Aéronautique et de l'Espace, 2000. Print.
von Karman, Theodore. Aerodynamics: Selected Topics in the Light of their Historical Development. New York: Dover Publications, 2004. Print.
