Editing Sound barrier (section)

===Early claims===
During WWII and immediately thereafter, a number of claims were made that the sound barrier had been broken in a dive. The majority of these purported events can be dismissed as instrumentation errors. The typical [[airspeed indicator]] (ASI) uses air pressure differences between two or more points on the aircraft, typically near the nose and at the side of the fuselage, to produce a speed figure. At high speed, the various compression effects that lead to the sound barrier also cause the ASI to go non-linear and produce inaccurately high or low readings, depending on the specifics of the installation. This effect became known as "Mach jump".<ref>Jordan, Corey C. [http://www.planesandpilotsofww2.webs.com/Welch2.html "The Amazing George Welch, Part Two, First Through the Sonic Wall"] {{Webarchive|url=https://web.archive.org/web/20120325044130/http://www.planesandpilotsofww2.webs.com/Welch2.html |date=2012-03-25 }}. ''Planes and Pilots Of World War Two'', 1998–2000. Retrieved: June 12, 2011.</ref> Before the introduction of [[machmeter|Mach meters]], accurate measurements of supersonic speeds could only be made remotely, normally using ground-based instruments. Many claims of supersonic speeds were found to be far below this speed when measured in this fashion.

In 1942, [[Republic Aviation]] issued a press release stating that Lts. [[Harold E. Comstock]] and Roger Dyar had exceeded the speed of sound during test dives in a [[Republic P-47 Thunderbolt]]. It is widely agreed that this was due to inaccurate ASI readings. In similar tests, the [[North American P-51 Mustang]] demonstrated limits at Mach 0.85, with every flight over Mach 0.84 causing the aircraft to be damaged by vibration.<ref>{{cite tech report |title= Compressibility Dive Tests on the North American P-51D Airplane, ('Mustang IV') AAF No.44-14134 |publisher=Wright Field |date=9 October 1944}}</ref>

[[File:spitfire mk11 pl965 arp.jpg|thumb|right|A Spitfire PR Mk XI (''[[United Kingdom military aircraft serials|PL965]]'') of the type used in the 1944 RAE Farnborough dive tests during which a highest Mach number of 0.92 was obtained]]

One of the highest recorded instrumented Mach numbers attained for a propeller aircraft is the Mach 0.891 for a [[Supermarine Spitfire#Speed and altitude records|Spitfire PR XI]], flown during dive tests at the [[Royal Aircraft Establishment|Royal Aircraft Establishment, Farnborough]] in April 1944. The Spitfire, a [[photo-reconnaissance]] variant, the Mark XI, fitted with an extended "rake type" multiple [[Pitot-static system|pitot system]], was flown by Squadron Leader J.&nbsp;R. Tobin to this speed, corresponding to a [[Position error|corrected]] [[true airspeed]] (TAS) of 606&nbsp;mph.<ref>[http://www.spitfireperformance.com/sd2011.jpg Spitfire – Typical high speed dive] {{Webarchive|url=https://web.archive.org/web/20150924104543/http://www.spitfireperformance.com/sd2011.jpg |date=2015-09-24 }}. spitfireperformance.com.</ref> In a subsequent flight, Squadron Leader Anthony Martindale achieved Mach 0.92, but it ended in a forced landing after over-revving damaged the engine.<ref>{{cite book |url=https://history.nasa.gov/SP-4704.pdf |title=NASA's First 50 Years: Historical Perspectives |publisher=U.S. Government Printing Office |editor=Dick, Steven J. |year=2010 |isbn=978-0-16-084965-7 |access-date=2017-07-12 |archive-date=2017-12-25 |archive-url=https://web.archive.org/web/20171225230740/https://history.nasa.gov/SP-4704.pdf |url-status=live }}</ref>

[[Hans Guido Mutke]] claimed to have broken the sound barrier on 9 April 1945 in the [[Messerschmitt Me 262]] jet aircraft. He states that his ASI pegged itself at {{convert|1100|km/h}}. Mutke reported not just transonic [[buffeting]], but the resumption of normal control once a certain speed was exceeded, then a resumption of severe buffeting once the Me 262 slowed again. He also reported engine flame-out.<ref>{{cite web |url=http://mach1.luftarchiv.de/first_flg.htm |archive-url=https://web.archive.org/web/20050206120808/http://mach1.luftarchiv.de/first_flg.htm |title=The Unknown Pilot |archive-date=6 February 2005 |first=Hans Guido |last=Mutke}}</ref>

This claim is widely disputed, even by pilots in his unit.<ref name=firstbroke>{{cite news |url=http://www.news24.com/xArchive/Archive/Nazi-era-pilot-says-he-broke-sound-barrier-first-20010612 |title=Nazi-era pilot says he broke sound barrier first |website=news24 |date=12 August 2001 |access-date=3 September 2015 |archive-date=20 March 2017 |archive-url=https://web.archive.org/web/20170320093135/http://www.news24.com/xArchive/Archive/Nazi-era-pilot-says-he-broke-sound-barrier-first-20010612 |url-status=live }}</ref> All of the effects he reported are known to occur on the Me 262 at much lower speeds, and the ASI reading is simply not reliable in the transonic. Further, a series of tests made by Karl Doetsch at the behest of Willy Messerschmitt found that the plane became uncontrollable above Mach 0.86, and at Mach 0.9 would nose over into a dive that could not be recovered from. Post-war tests by the RAF confirmed these results, with the slight modification that the maximum speed using new instruments was found to be Mach 0.84, rather than Mach 0.86.<ref>[http://www.aerospaceweb.org/question/history/q0198c.shtml "Me 262 and the Sound Barrier".] {{Webarchive|url=https://web.archive.org/web/20160305021742/http://www.aerospaceweb.org/question/history/q0198c.shtml |date=2016-03-05 }} ''aerospaceweb.org''. Retrieved: August 30, 2010.</ref>

In 1999, Mutke enlisted the help of Professor Otto Wagner of the [[Technical University of Munich|Munich Technical University]] to run computational tests to determine whether the aircraft could break the sound barrier. These tests do not rule out the possibility, but are lacking accurate data on the coefficient of drag that would be needed to make accurate simulations.<ref name=moor>{{cite news |url=http://www.spiegel.de/spiegel/print/d-18535490.html |first=Matthias |last=Schulz |title=Flammenritt über dem Moor |journal=Der Spiegel |date=19 February 2001 |access-date=3 September 2015 |archive-date=25 September 2015 |archive-url=https://web.archive.org/web/20150925003241/http://www.spiegel.de/spiegel/print/d-18535490.html |url-status=live }}</ref><ref>{{cite news |url=http://usatoday30.usatoday.com/news/world/2001-02-22-sound.htm |title=Pilot claims he broke sound barrier first |date=19 June 2001 |work=USA Today |access-date=2015-09-03 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304033151/http://usatoday30.usatoday.com/news/world/2001-02-22-sound.htm |url-status=live }}</ref> Wagner stated: "I don't want to exclude the possibility, but I can imagine he may also have been just below the speed of sound and felt the buffeting, but did not go above Mach-1."<ref name=firstbroke/>

One bit of evidence presented by Mutke is on page 13 of the "Me 262 A-1 Pilot's Handbook" issued by [[Air Force Materiel Command|Headquarters Air Materiel Command]], [[Wright-Patterson Air Force Base|Wright Field]], Dayton, Ohio as Report No. F-SU-1111-ND on January 10, 1946:
{{blockquote|Speeds of 950 km/h (590 mph) are reported to have been attained in a shallow dive 20° to 30° from the horizontal. No vertical dives were made. At speeds of 950 to 1,000 km/h (590 to 620 mph) the air flow around the aircraft reaches the speed of sound, and it is reported that the control surfaces no longer affect the direction of flight. The results vary with different airplanes: some wing over and dive while others dive gradually. It is also reported that once the speed of sound is exceeded, this condition disappears and normal control is restored.}}
The comments about restoration of flight control and cessation of buffeting above Mach 1 are very significant in a 1946 document. However, it is not clear where these terms came from, as it does not appear the US pilots carried out such tests.<ref name=moor/>

In his 1990 book ''Me-163'', former [[Messerschmitt Me 163|Messerschmitt Me 163 "Komet"]] pilot Mano Ziegler claims that his friend, test pilot [[Heini Dittmar]], broke the sound barrier while diving the rocket plane, and that several people on the ground heard the sonic booms. He claims that on 6 July 1944, Dittmar, flying Me 163B V18, bearing the {{lang|de|Stammkennzeichen}} alphabetic code VA+SP, was measured traveling at a speed of 1,130&nbsp;km/h (702&nbsp;mph).<ref>Käsmann, Ferdinand C. W. (1999) {{lang|de|Die schnellsten Jets der Welt}} (in German). Berlin: Aviatic-Verlag GmbH. pp. 17, 122. {{ISBN|3-925505-26-1}}.</ref> However, no evidence of such a flight exists in any of the materials from that period, which were captured by Allied forces and extensively studied.<ref>{{Skeptoid |id=4154 |number=154 |date=19 May 2009 |title=Was Chuck Yeager the First to Break the Sound Barrier? |access-date=22 June 2017}}</ref> Dittmar had been officially recorded at 1,004.5&nbsp;km/h (623.8&nbsp;mph) in level flight on 2 October 1941 in the prototype [[Messerschmitt Me 163#Me 163A|Me 163A V4]]. He reached this speed at less than full throttle, as he was concerned by the transonic buffeting. Dittmar himself does not make a claim that he broke the sound barrier on that flight and notes that the speed was recorded only on the AIS. He does, however, take credit for being the first pilot to "knock on the sound barrier".<ref name=firstbroke/>

There are a number of uncrewed vehicles that flew at supersonic speeds during this period. In 1933, Soviet designers working on [[ramjet]] concepts fired phosphorus-powered engines out of artillery guns to get them to operational speeds. It is possible that this produced supersonic performance as high as Mach 2,<ref>Durant, Frederick C. and George S. James. "Early Experiments with Ramjet Engines in Flight". ''First Steps Toward Space: Proceedings of the First and Second History Symposia of the International Academy of Astronautics at Belgrade, Yugoslavia, September 26, 1967''. Washington, DC: Smithsonian Institution Press, 1974.</ref> but this was not due solely to the engine itself. In contrast, the German [[V-2 rocket|V-2]] [[ballistic missile]] routinely broke the sound barrier in flight, for the first time on 3 October 1942. By September 1944, V-2s routinely achieved Mach 4 (1,200&nbsp;m/s, or 3044&nbsp;mph) during terminal descent.