Editing De Havilland Comet (section)

===Testing and prototypes===
[[File:Comet Prototype at Hatfield.jpg|thumb|upright=1.4|Comet 1 prototype (with square windows) at [[Hatfield Aerodrome]] in October 1949]]

As the Comet represented a new category of passenger aircraft, more rigorous testing was a development priority.<ref name=d17/> From 1947 to 1948, de Havilland conducted an extensive research and development phase, including the use of several stress test rigs at [[Hatfield Aerodrome]] for small components and large assemblies alike. Sections of pressurised fuselage were subjected to high-altitude flight conditions via a large [[pressure vessel|decompression chamber]] on-site{{Refn|The fuselage sections and nose simulated a flight up to {{cvt|70000|ft}} at a temperature of {{cvt|−70|°C|°F}}, with 2,000 applications of pressure at {{cvt|9|psi}}.<ref name=Birtles125>Birtles 1970, p. 125.</ref>|group=N}} and tested to failure.<ref name=d18/> Tracing fuselage failure points proved difficult with this method,<ref name=d18/> and de Havilland ultimately switched to conducting structural tests with a water tank that could be safely configured to increase pressures gradually.<ref name=Birtles125/><ref name=d18/><ref>{{Cite magazine |url=http://www.flightglobal.com/pdfarchive/view/1955/1955%20-%201835.html |title=Tank Test Mk 2. |magazine=Flight |publisher=Iliffe |date=30 December 1955 |pages=958–959 |access-date=26 April 2012 |archive-url=https://web.archive.org/web/20190131201738/https://www.flightglobal.com/pdfarchive/view/1955/1955%20-%201835.html |archive-date=31 January 2019}}</ref> The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to {{convert|2.75|psi|kPa}} overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service.<ref name=DaviesandBirtles>Davies and Birtles 1999, p. 30.</ref> The windows were also tested under a pressure of {{cvt|12|psi|kPa}}, {{cvt|4.75|psi|kPa}} above expected pressures at the normal service ceiling of {{cvt|36000|ft}}.<ref name=DaviesandBirtles/> One window frame survived {{cvt|100|psi|kPa}},<ref>{{Cite magazine|url=https://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200556.html |title=Comet Engineering |publisher=Iliffe |via=[[FlightGlobal]] Archive |magazine=[[Flight International|Flight]] |date=1 May 1953 |access-date=23 March 2019 |page=552 |archive-url=https://web.archive.org/web/20170202030058/https://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200556.html |archive-date=2 February 2017}}</ref> about 1,250 per cent over the maximum pressure it was expected to encounter in service.<ref name=DaviesandBirtles/>

The first prototype DH.106 Comet (carrying [[United Kingdom aircraft test serials|Class B markings]] G-5-1) was completed in 1949 and was initially used to conduct ground tests and brief early flights.<ref name=d18>Darling 2001, p. 18.</ref> The prototype's maiden flight, out of Hatfield Aerodrome, took place on 27 July 1949 and lasted 31 minutes.<ref>Dick and Patterson 2010, pp. 134–137.</ref><ref name=green174>Green and Swanborough April 1977, p. 174.</ref> At the controls was de Havilland chief test pilot [[John Cunningham (RAF officer)|John "Cats Eyes" Cunningham]], a famous night-fighter pilot of the Second World War, along with co-pilot Harold "Tubby" Waters, engineers John Wilson (electrics) and Frank Reynolds (hydraulics), and flight test observer [[Tony Fairbrother]].<ref>Prins 1998, p. 43.</ref>

The prototype was [[United Kingdom aircraft registration|registered]] G-ALVG just before it was publicly displayed at the 1949 [[Farnborough Airshow]] before the start of flight trials. A year later, the second prototype G-5-2 made its maiden flight. The second prototype was registered G-ALZK in July 1950 and it was used by the BOAC Comet Unit at [[Bournemouth Airport|Hurn]] from April 1951 to carry out 500 flying hours of crew training and route-proving.<ref>Swanborough 1962, p. 45.</ref> Australian airline [[Qantas]] also sent its own technical experts to observe the performance of the prototypes, seeking to quell internal uncertainty about its prospective Comet purchase.<ref>Gunn 1987, p. 268.</ref> Both prototypes could be externally distinguished from later Comets by the large single-wheeled main [[landing gear]], which was replaced on production models starting with G-ALYP by four-wheeled [[bogie#Bogie (aircraft)|bogies]].<ref name=Walker25/>