Editing Concorde (section)

==Design==
[[File:ConcordeCockpitSinsheim.jpg|thumb|Concorde flight deck layout]]

===General features===
Concorde is an [[Delta wing#ogival delta|ogival delta]] winged aircraft with four [[Rolls-Royce/Snecma Olympus 593|Olympus]] engines based on those employed in the RAF's [[Avro Vulcan]] [[strategic bomber]]. It has an unusual [[tailless aircraft|tailless configuration]] for a commercial aircraft, as does the [[Tupolev Tu-144]]. Concorde was the first airliner to have a [[fly-by-wire]] flight-control system (in this case, analogue); the [[avionics]] system Concorde used was unique because it was the first commercial aircraft to employ [[Hybrid integrated circuit|hybrid circuits]].<ref name='elecflybywire' /> The principal designer for the project was Pierre Satre, with [[Archibald Russell|Sir Archibald Russell]] as his deputy.<ref>{{cite news |first=Peter |last=Masefield |title=Obituary: Sir Archibald Russell |work=The Independent |date=1 July 1995 |location=UK}}</ref>

Concorde pioneered the following technologies:

For high speed and optimisation of flight:
* [[Double delta]] ([[ogee]]/ogival) shaped wings<ref name= 'deltawing' />
* Variable engine air [[intake ramp]] system controlled by [[digital computer]]s<ref name=nova>{{cite web |url=https://www.pbs.org/wgbh/nova/transcripts/3203_concorde.html |title=NOVA transcript: Supersonic Dream |publisher=PBS |date=18 January 2005 |quote=Jock Lowe (Concorde Chief Pilot): We did some research which showed that the Concorde passengers actually didn't know how much the fare was. When we asked them to guess how much it was, they guessed that it was higher than it actually was, so we just started to charge them what they thought they were paying anyway. |access-date=26 August 2017 |archive-date=5 April 2011 |archive-url=https://web.archive.org/web/20110405035636/http://www.pbs.org/wgbh/nova/transcripts/3203_concorde.html |url-status=live}}</ref>
* [[Supercruise]] capability<ref>{{cite web|url=http://www.janes.com/transport/news/jae/jae000725_1_n.shtml |title=Rolls-Royce Snecma Olympus |publisher=Janes |date=25 July 2000 |url-status=dead |archive-url=https://web.archive.org/web/20100806140324/http://www.janes.com/transport/news/jae/jae000725_1_n.shtml |archive-date=6 August 2010}}</ref>

For weight-saving and enhanced performance:
* [[Mach number|Mach]] 2.02 (~{{convert|2154|km/h|mph|disp=or|abbr=on}}) cruising speed{{sfn|Frawley|2003|p=14}} for optimum fuel consumption (supersonic drag minimum and turbojet engines are more efficient at higher speed);<ref>{{cite web |url=http://ocw.mit.edu/ans7870/16/16.unified/propulsionS04/UnifiedPropulsion8/UnifiedPropulsion8.htm |title=Unified propulsion 8 |publisher=MIT |access-date=8 December 2010 |archive-date=18 June 2012 |archive-url=http://webarchive.loc.gov/all/20120618175121/http://ocw.mit.edu/ans7870/16/16.unified/propulsionS04/UnifiedPropulsion8/UnifiedPropulsion8.htm |url-status=live}}</ref> fuel consumption at {{convert|2|Mach|altitude_ft=60000|sigfig=3}} and at altitude of {{convert|60000|ft}} was {{convert|4800|gal/h|L/h}}.<ref>Allen, Roy, Concorde The Magnificent, Airliner Classics, July 2012, p. 65</ref>
* Mainly aluminium construction using a high-temperature alloy similar to that developed for aero-engine pistons.<ref>The Development of Piston Aero Engines, Bill Gunston 1999, 2nd ed., Patrick Stephens Limited, {{ISBN|1 85260 599 5}}, p. 58</ref> This material gave low weight and allowed conventional manufacture (higher speeds would have ruled out aluminium)<ref>{{cite journal |url=http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A6424111AH&q=Concorde+aluminium+construction&uid=789267644&setcookie=yes |archive-url=https://web.archive.org/web/20120822230903/http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A6424111AH&q=Concorde+aluminium+construction&uid=789267644&setcookie=yes |url-status=dead |archive-date=22 August 2012 |title=''Concorde''&nbsp;– Choice of a light alloy for the construction of the first supersonic commercial aircraft |journal=Revue de l'Aluminium |issue=316 |date=March 1964 |pages=111–19}}</ref>
* Full-regime [[autopilot]] and [[autothrottle]]<ref>{{cite journal |title=The Concorde Automatic Flight Control System: A description of the automatic flight control system for the Anglo/French SST and its development to date |first=B.S. |last=Wolfe |journal=Aircraft Engineering and Aerospace Technology |year=1967 |volume=39 |issue=5 |page=40 |issn=0002-2667 |doi=10.1108/eb034268}}</ref> allowing "hands off" control of the aircraft from climb out to landing
* Fully electrically controlled analogue [[Aircraft flight control system#Fly-by-wire control systems|fly-by-wire]] flight controls systems<ref name='elecflybywire'>{{cite book |url=https://books.google.com/books?id=DbUhEnlI3OkC&pg=PA211 |title=Advances in aircraft flight control |editor=Mark B. Tischler |author=Favre, C. |year=1996 |isbn=978-0-7484-0479-7 |page=219 |publisher=CRC Press |access-date=28 November 2020 |archive-date=14 April 2021 |archive-url=https://web.archive.org/web/20210414103603/https://books.google.com/books?id=DbUhEnlI3OkC&pg=PA211 |url-status=live}}</ref>
* High-pressure hydraulic system using {{cvt|28|MPa}} for lighter hydraulic components.<ref>{{cite journal |url=http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A7716749AH&q=Concorde+hydraulic&uid=788858323&setcookie=yes |title=Concorde has designed-in reliability |author=Schefer, L.J. |journal=Hydraulics and Pneumatics|volume=29|date=1976 |pages=51–55|url-status=dead|archive-url=https://web.archive.org/web/20120823182306/http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A7716749AH&q=Concorde+hydraulic&uid=788858323&setcookie=yes|archive-date=23 August 2012}}</ref> 
* [[Air data computer]] (ADC) for the automated monitoring and transmission of aerodynamic measurements (total pressure, [[static pressure]], [[angle of attack]], side-slip).{{sfn|Owen|2001|p=101}}
* Fully electrically controlled analogue [[brake-by-wire]] system<ref>{{cite journal |doi=10.1108/eb035278 |title=Aircraft Stopping Systems |journal=Aircraft Engineering and Aerospace Technology |year=1975 |volume=47 |issue=10 |issn=0002-2667 |page=18}}</ref>
* No [[auxiliary power unit]], as Concorde would only visit large airports where [[Ground support equipment#Air start unit|ground air start carts]] were available.{{sfn|Owen|2001|p=206}}

===Powerplant===
[[File:Concorde.highup.arp.750pix.jpg|thumb|The four powerplants mounted in two nacelles under the wings.]]
[[File:Concorde Ramp.jpg|thumb|Twin air intake assembly for each nacelle.]] 
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[[File:Rolls-Royce-Snecma Olympus - Musée Safran.jpg|thumb|Engines and twin exhaust system for each nacelle.]]
{{Main|Rolls-Royce/Snecma Olympus 593}}

A symposium titled "Supersonic-Transport Implications" was hosted by the [[Royal Aeronautical Society]] on 8 December 1960. Various views were put forward on the likely type of powerplant for a supersonic transport, such as podded or buried installation and turbojet or ducted-fan engines.<ref>{{cite magazine |title=Supersonic – Transport Implications |magazine=Flight International |date=23 December 1960 |page=971 |url=https://www.flightglobal.com/pdfarchive/view/1960/1960%20-%203039.html |via=FlightGlobal Archive |archive-url= https://web.archive.org/web/20171222052952/https://www.flightglobal.com/pdfarchive/view/1960/1960%20-%203039.html |archive-date=22 December 2017}}</ref><ref>{{cite magazine |magazine=Flight International |date=30 December 1960 |page=1024 |url=https://www.flightglobal.com/pdfarchive/view/1960/1960%20-%203108.html?search=supersonic%20transport%20implications |title=Supersonic – Transport Implications |via=FlightGlobal Archive |access-date=26 February 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170226132358/https://www.flightglobal.com/pdfarchive/view/1960/1960%20-%203108.html |archive-date=26 February 2017}}</ref> Concorde needed to fly long distances to be economically viable; this required high efficiency from the powerplant. [[Turbofan]] engines were rejected due to their larger cross-section producing excessive drag (but would be studied for future SSTs). Olympus turbojet technology was already available for development to meet the design requirements.<ref>{{cite web|url=http://papers.sae.org/760891/Olympus |title=SAE International – mobility engineering |website=Papers.sae.org|access-date=21 December 2017|url-status=dead|archive-url=https://web.archive.org/web/20170801033212/http://papers.sae.org/760891/Olympus/ |archive-date=1 August 2017}}</ref> Rolls-Royce proposed developing the RB.169 to power Concorde during its initial design phase,<ref>{{cite magazine |title=Aero Engines 1962 |magazine=Flight International |date=28 June 1962 |page=1018 |url=http://www.flightglobal.com/pdfarchive/view/1962/1962%20-%201020.html |access-date=29 December 2013 |archive-url=https://web.archive.org/web/20131231002631/http://www.flightglobal.com/pdfarchive/view/1962/1962%20-%201020.html |archive-date=31 December 2013 |url-status=live}}</ref> but developing a wholly-new engine for a single aircraft would have been extremely costly,<ref>{{cite journal |last1=Parker |first1=R. |title=Aircraft engines: a proud heritage and an exciting future |journal=The Aeronautical Journal |date=2016 |volume=120 |issue=1223 |pages=131–69 |doi=10.1017/aer.2015.6 |s2cid=18375144}}</ref> so the existing BSEL [[Rolls-Royce Olympus variants#Bristol Olympus (BOl) 22R (Mk. 320)|Olympus Mk 320]] turbojet engine, which was already flying in the [[BAC TSR-2]] supersonic strike bomber prototype, was chosen instead.{{sfn|Owen|2001|p=50}}

Boundary layer management in the podded installation was put forward as simpler with only an inlet cone, however, Dr. Seddon of the RAE favoured a more integrated buried installation. One concern of placing two or more engines behind a single intake was that an intake failure could lead to a double or triple engine failure. While a ducted fan over the turbojet would reduce noise, its larger cross-section also incurred more drag.<ref>{{cite book |last=Birtles |first=Philip |title=Concorde |pages=62–63 |place=Vergennes, Vermont |publisher=Plymouth Press |year=2000 |isbn=1-882663-44-6}}</ref> Acoustics specialists were confident that a turbojet's noise could be reduced and SNECMA made advances in silencer design during the programme.<ref>{{citation |magazine=Flight International |url=https://www.flightglobal.com/pdfarchive/view/1971/1971%20-%200616.html |year=1971 |title=Noise and Environment |page=xxi |via=FlightGlobal Archive |access-date=26 February 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170226212746/https://www.flightglobal.com/pdfarchive/view/1971/1971%20-%200616.html |archive-date=26 February 2017}}</ref> The Olympus Mk.622 with reduced jet velocity was proposed to reduce the noise<ref>{{cite magazine |magazine=Flight International |url=https://www.flightglobal.com/pdfarchive/view/1974/1974%20-%200593.html |title=Up to date with Rolls-Royce Bristol |date=11 April 1974 |page=463 |via=FlightGlobal Archive |access-date=26 February 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170226132427/https://www.flightglobal.com/pdfarchive/view/1974/1974%20-%200593.html |archive-date=26 February 2017}}</ref> but was not pursued. By 1974, the spade silencers which projected into the exhaust were reported to be ineffective but "entry-into-service aircraft are likely to meet their noise guarantees".<ref>{{citation |magazine=Flight International |url=https://www.flightglobal.com/pdfarchive/view/1974/1974%20-%201690.html |title=Commercial Aircraft of the World |via=FlightGlobal Archive |page=546 |date= 24 October 1974 |access-date=26 February 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170226132353/https://www.flightglobal.com/pdfarchive/view/1974/1974%20-%201690.html |archive-date=26 February 2017}}</ref>

The powerplant configuration selected for Concorde highlighted airfield noise, boundary layer management and interactions between adjacent engines and the requirement that the powerplant, at Mach 2, tolerate pushovers, sideslips, pull-ups and throttle slamming without surging.{{sfn|Talbot|2013|p=131}} Extensive development testing with design changes and changes to intake and engine control laws addressed most of the issues except airfield noise and the interaction between adjacent powerplants at speeds above Mach 1.6 which meant Concorde "had to be certified aerodynamically as a twin-engined aircraft above Mach 1.6".{{sfn|Talbot|2013|p=48}}

Situated behind the wing leading edge, the engine intake had a wing boundary layer ahead of it. Two-thirds were diverted and the remaining third which entered the intake did not adversely affect the intake efficiency{{sfn|Talbot|2013|p=21}} except during pushovers when the boundary layer thickened and caused surging. Wind tunnel testing helped define leading-edge modifications ahead of the intakes which solved the problem.<ref>{{cite journal |title=Concorde Airframe Design and Development |author=D. Collard |date=April 1999 |journal=Swiss Association of Aeronautical Sciences |publisher=ETH-Zentrum |issue=8092 |place=Zürich |page=6}}<br/>* {{cite journal |author=Collard, D. |title=Concorde Airframe Design and Development |journal=SAE Transactions |series=SAE Technical Paper Series |volume=100 |pages=2620–41 |id=912162 |year=1991 |doi=10.4271/912162 |jstor=44548119}}</ref> Each engine had its own intake and the [[nacelle]]s were paired with a splitter plate between them to minimise the chance of one powerplant influencing the other. Only above {{convert|1.6|Mach}} was an engine surge likely to affect the adjacent engine.{{sfn|Talbot|2013|p=48}}

The air intake design for Concorde's engines was especially critical.<ref>{{cite conference |conference=Aerospace Technology Conference and Exposition |url=https://www.sae.org/publications/technical-papers/content/912180/ |title=Concorde Propulsion{{snd}}Did we get it right? The Rolls-Royce/Snecma Olympus 593 Engine reviewed |publisher=SAE International |author=Ganley, G. A. |date=September 1991 |doi=10.4271/912180 |series=SAE Technical Paper Series |access-date=27 August 2018 |archive-date=27 August 2018 |archive-url=https://web.archive.org/web/20180827142352/https://www.sae.org/publications/technical-papers/content/912180/ |url-status=live}}</ref> The intakes had to slow down supersonic inlet air to subsonic speeds with high-pressure recovery to ensure efficient operation at cruising speed while providing low distortion levels (to prevent engine surge) and maintaining high efficiency for all likely ambient temperatures in cruise. They had to provide adequate subsonic performance for diversion cruise and low engine-face distortion at take-off. They also had to provide an alternative path for excess intake of air during engine throttling or shutdowns.<ref>{{cite journal |title=Design and Development of an Air Intake for a Supersonic Transport Aircraft |author1=I. H. Rettie |author2=W. G. E. Lewis |journal=Journal of Aircraft |volume=5 |issue=6 |pages=513–21 |date=November–December 1968 |doi=10.2514/3.43977}}</ref> The variable intake features required to meet all these requirements consisted of front and rear ramps, a dump door, an auxiliary inlet and a ramp bleed to the exhaust nozzle.{{sfn|Talbot|2013|loc=plate 4}}

As well as supplying air to the engine, the intake also supplied air through the ramp bleed to the propelling nozzle. The nozzle ejector (or aerodynamic) design, with variable exit area and secondary flow from the intake, contributed to good expansion efficiency from take-off to cruise.<ref>"An experiment on aerodynamic nozzles at M=2" Reid, Ministry of Aviation, R. & M. No. 3382, p. 4.</ref> Concorde's Air Intake Control Units (AICUs) made use of a digital processor for intake control. It was the first use of a digital processor with full authority control of an essential system in a passenger aircraft. It was developed by BAC's Electronics and Space Systems division after the analogue AICUs (developed by [[Ultra Electronics]]) fitted to the prototype aircraft were found to lack sufficient accuracy.<ref>{{cite journal|last1=Page|first1=N.|last2=Dale|first2=R. S.|last3=Nelson|first3=N.|title=Engine intake-control|journal=Flight|date=8 May 1975|pages=742–743|url=https://www.flightglobal.com/FlightPDFArchive/1975/1975%20-%200828.PDF|access-date=19 January 2016|archive-date=26 January 2016|archive-url=https://web.archive.org/web/20160126153712/https://www.flightglobal.com/FlightPDFArchive/1975/1975%20-%200828.PDF|url-status=live}}</ref> Ultra Electronics also developed Concorde's thrust-by-wire engine control system.<ref>{{cite web |url=http://www.flightglobal.com/pdfarchive/view/1976/1976%20-%201835.html |title=1976 &#124; 1835 &#124; Flight Archive |publisher=Flightglobal.com |date=4 September 1976 |access-date=15 June 2013 |archive-date=3 September 2015 |archive-url=https://web.archive.org/web/20150903215336/https://www.flightglobal.com/pdfarchive/view/1976/1976%20-%201835.html |url-status=live}}</ref>

Engine failure causes problems on conventional [[subsonic aircraft]]; not only does the aircraft lose thrust on that side but the engine creates drag, causing the aircraft to yaw and bank in the direction of the failed engine. If this had happened to Concorde at supersonic speeds, it theoretically could have caused a catastrophic failure of the airframe. Although computer simulations predicted considerable problems, in practice Concorde could shut down both engines on the same side of the aircraft at Mach 2 without difficulties.<ref>{{cite web |url=https://www.flightglobal.com/news/articles/concorde-special-the-test-pilot-john-cochrane-172657/ |title=Concorde Special&nbsp;– The test pilot&nbsp;– John Cochrane |work=[[Flight International]] |date=21 October 2003 |access-date=2 April 2018 |archive-date=2 April 2018 |archive-url=https://web.archive.org/web/20180402225635/https://www.flightglobal.com/news/articles/concorde-special-the-test-pilot-john-cochrane-172657/ |url-status=live}}</ref> During an engine failure the required air intake is virtually zero. So, on Concorde, engine failure was countered by the opening of the auxiliary spill door and the full extension of the ramps, which deflected the air downwards past the engine, gaining lift and minimising drag. Concorde pilots were routinely trained to handle double-engine failure.<ref>{{cite news |url=http://www.highbeam.com/doc/1G1-63710463.html |archive-url=https://web.archive.org/web/20120207015537/http://www.highbeam.com/doc/1G1-63710463.html |url-status=dead |archive-date=7 February 2012 |title=How a Concorde pilot would handle a nightmare failure |newspaper=Birmingham Post |first=Peter |last=Woodman |date=27 July 2000}}</ref> Concorde used [[reheat]] (afterburners) only at take-off and to pass through the [[transonic]] speed range, between Mach 0.95 and 1.7.<ref>{{cite conference |url=http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A9110958AH&q=Rolls-Royce%2FSnecma+Olympus+593&uid=788858323&setcookie=yes |url-status=dead |archive-date=21 September 2011 |archive-url=https://web.archive.org/web/20110921053303/http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A9110958AH&q=Rolls-Royce%2FSnecma+Olympus+593&uid=788858323&setcookie=yes |title=The Rolls Royce/SNECMA Olympus 593 engine operational experience and the lessons learned |conference=European Symposium on the Future of High Speed Air Transport, Strasbourg, France; 6–8 Nov 1989 |author=Ganley, G. |author2=Laviec, G. |year=1990 |pages=73–80 |access-date=30 June 2011}}</ref>

===Heating problems===
Kinetic heating from the high speed boundary layer caused the skin to heat up during supersonic flight.<ref name="harpur176">{{cite journal |url=https://arc.aiaa.org/doi/abs/10.2514/3.43926?journalCode=ja |title=Concorde Structural Development |last1=Harpur |first1=N. F. |journal=J. Aircraft |date=22 May 2012 |volume=5 |number=2 |page=176 |via=Aerospace Research Council |doi=10.2514/3.43926}}</ref> Every surface, such as windows and panels, was warm to the touch by the end of the flight.<ref>Dalton, Alastair. [http://www.scotsman.com/news/transport/supersonic-the-enduring-allure-of-concorde-1-2415088 "Supersonic: The enduring allure of Concorde"] {{Webarchive|url=https://web.archive.org/web/20120728231129/http://www.scotsman.com/news/transport/supersonic-the-enduring-allure-of-concorde-1-2415088 |date=28 July 2012}}. Scotsman.com, 17 July 2012.</ref> Apart from the engine bay, the hottest part of any supersonic aircraft's structure is the [[nose cone|nose]], due to [[aerodynamic heating]]. [[Hiduminium]] R.R. 58, an aluminium alloy, was used throughout the aircraft because it was relatively cheap and easy to work with. The highest temperature it could sustain over the life of the aircraft was {{convert|127|°C|°F|abbr=on}}, which limited the top speed to Mach 2.02.<ref>{{cite journal |doi=10.2307/3951418 |title=When the SST Is Too Slow… |journal=Science News |first=Jonathan |last=Eberhart |volume=91 |issue=22 |date=3 June 1967 |pages=528–29 |jstor=3951418}}</ref> Concorde went through two cycles of cooling and heating during a flight, first cooling down as it gained altitude at subsonic speed, then heating up accelerating to cruise speed, finally cooling again when descending and slowing down before heating again in low altitude air before landing. This had to be factored into the metallurgical and [[fatigue (material)|fatigue]] modelling. A test rig was built that repeatedly heated up a full-size section of the wing, and then cooled it, and periodically samples of metal were taken for testing.<ref>{{cite journal |doi=10.1108/eb034143 |title=The Concorde takes shape: Test programme and construction proceeding according to schedule |journal=Aircraft Engineering and Aerospace Technology |page=38 |year=1966 |volume=38 |issue=4 |issn=0002-2667}}</ref><ref>{{cite journal |bibcode=1972NASSP.309..631N |volume=309 |title=Fatigue Tests on Big Structure Assemblies of Concorde Aircraft |page=631 |year=1972 |author=N'guyen, V.P. |author2=J.P. Perrais |journal=Advanced Approaches to Fatigue Evaluation. NASA SP-309}}</ref> The airframe was designed for a life of 45,000 flying hours.<ref>{{cite web|url=http://www.flightglobal.com/pdfarchive/view/1967/1967%20-%202250.html|title=Concorde – 1967–2250 – Flight Archive|work=flightglobal.com|access-date=11 July 2013|archive-date=7 April 2014|archive-url=https://web.archive.org/web/20140407090353/http://www.flightglobal.com/pdfarchive/view/1967/1967%20-%202250.html|url-status=live}}</ref>

[[File:Concorde - airframe temperatures.svg|thumb|Concorde skin temperatures. They depended on the balance of heat transfer from the boundary layer, heat picked up from solar radiation, heat radiated back from the surface to the atmosphere, and heat transferred to the internal structure.<ref name="harpur176" />]]
As the fuselage heated up it [[Thermal expansion|expanded]] by as much as {{cvt|300|mm}}. The most obvious manifestation of this was a gap that opened up on the flight deck between the [[flight engineer]]'s console and the bulkhead. On some aircraft that conducted a retiring supersonic flight, the flight engineers placed their caps in this expanded gap, wedging the cap when the airframe shrank again.<ref>{{cite news |url= http://www.seattlepi.com/business/147276_pilot07.html |first= James |last= Wallace |title= Those who flew the Concorde will miss it |work= Seattle Post Intelligencer |date= 7 November 2003 |access-date= 25 April 2010 |archive-date= 16 March 2020 |archive-url= https://web.archive.org/web/20200316023128/https://www.seattlepi.com/business/article/Those-who-flew-the-Concorde-will-miss-it-1129118.php |url-status= live}}</ref> To keep the cabin cool, Concorde used the fuel as a [[Thermal energy storage|heat sink]] for the heat from the air conditioning.<ref>{{cite journal |title= Introduction to Concorde: A brief review of the Concorde and its prospects |journal=Aircraft Engineering and Aerospace Technology |author=Gedge, G.T. |author2=M.I. Prod |volume= 40 |issue= 3 |year=1993}}</ref> The same method also cooled the hydraulics. During supersonic flight a visor was used to keep high temperature air from flowing over the cockpit skin.{{sfn|Owen|2001|p=14}}

Concorde had [[aircraft livery|livery]] restrictions; the majority of the surface had to be covered with a [[Anti-flash white|highly reflective white]] paint to avoid overheating the aluminium structure due to heating effects. The white finish reduced the skin temperature by {{convert|6|to|11|C-change|F-change}}.<ref>{{cite web |url=http://www.flightglobal.com/pdfarchive/view/1967/1967%20-%200821.html |title=1967 &#124; 0821 &#124; Flight Archive |publisher=Flightglobal.com |access-date=15 June 2013 |archive-date=3 September 2015 |archive-url=https://web.archive.org/web/20150903215336/https://www.flightglobal.com/pdfarchive/view/1967/1967%20-%200821.html |url-status=live}}</ref> In 1996, Air France briefly painted F-BTSD in a predominantly blue livery, with the exception of the wings, in a promotional deal with [[Pepsi]].<ref>{{cite web|url=http://www.highbeam.com/doc/1P2-4794332.html |title=Is this the colour of the new millennium? |work=The Independent |date=3 April 1996 |location=UK |url-status=dead |archive-url=https://web.archive.org/web/20130516143325/http://www.highbeam.com/doc/1P2-4794332.html |archive-date=16 May 2013}}</ref> In this paint scheme, Air France was advised to remain at {{convert|2|Mach|altitude_ft=60000|sigfig=3}} for no more than 20 minutes at a time, but there was no restriction at speeds under Mach 1.7. F-BTSD was used because it was not scheduled for any long flights that required extended Mach 2 operations.<ref>{{cite news |title=Azul contra rojo |work=El Mundo |date=5 April 1996 |first=Cristina |last=Frade}}</ref>

===Structural issues===
[[File:Concorde fuel trim.svg|thumb|upright|Fuel pitch trim]]

Due to its high speeds, large forces were applied to the aircraft during turns, causing distortion of the aircraft's structure. There were concerns over maintaining precise control at supersonic speeds. Both of these issues were resolved by ratio changes between the inboard and outboard [[elevon]] deflections, varying at differing speeds including supersonic. Only the innermost elevons, attached to the stiffest area of the wings, were used at higher speeds.{{sfn|Owen|2001|p=78}} The narrow fuselage flexed,<ref name="nova" /> which was apparent to rear passengers looking along the length of the cabin.<ref name="popular">Kocivar, Ben. [https://books.google.com/books?id=lpiMSzja6W4C&lpg=PA142 "Aboard the Concorde SST."] {{Webarchive|url=https://web.archive.org/web/20210225182355/https://books.google.com/books?id=lpiMSzja6W4C&lpg=PA142 |date=25 February 2021}} ''Popular Science'', October 1973, p. 117.</ref>

When any aircraft passes the [[critical mach]] of its airframe, the [[Center of pressure (fluid mechanics)|centre of pressure]] shifts rearwards. This causes a pitch-down moment on the aircraft if the centre of gravity remains where it was. The wings were designed to reduce this, but there was still a shift of about {{convert|2|m}}. This could have been countered by the use of [[Trim tab|trim controls]], but at such high speeds, this would have increased drag which would have been unacceptable. Instead, the distribution of fuel along the aircraft was shifted during acceleration and deceleration to move the centre of gravity, effectively acting as an auxiliary trim control.<ref name='fueltrim'>{{cite journal |doi=10.1108/eb035344 |title=Flight Refuelling Limited and Concorde: The fuel system aboard is largely their work |journal=Aircraft Engineering and Aerospace Technology |volume=48 |issue=9 |date=September 1976 |issn=0002-2667 |pages=20–21}}</ref>

===Range===
To fly non-stop across the Atlantic Ocean, Concorde required the greatest supersonic [[Range (aeronautics)|range]] of any aircraft.<ref>{{cite web|title=Celebrating Concorde|url=http://www.britishairways.com/en-gb/information/about-ba/history-and-heritage/celebrating-concorde|publisher=British Airways|access-date=19 January 2016|archive-date=20 January 2016|archive-url=https://web.archive.org/web/20160120063601/http://www.britishairways.com/en-gb/information/about-ba/history-and-heritage/celebrating-concorde|url-status=live}}</ref> This was achieved by a combination of powerplants which were efficient at twice the speed of sound, a slender fuselage with high [[fineness ratio]], and a complex wing shape for a high [[lift-to-drag ratio]]. Only a modest payload could be carried and the aircraft was trimmed without using deflected control surfaces, to avoid the drag that would incur.<ref name='deltawing' /><ref name='fueltrim' />

Nevertheless, soon after Concorde began flying, a Concorde "B" model was designed with slightly larger fuel capacity and slightly larger wings with [[leading edge slats]] to improve aerodynamic performance at all speeds, with the objective of expanding the range to reach markets in new regions.<ref>{{cite web |url=http://www.concordesst.com/concordeb.html |title=Concorde SST: Concorde B |work=concordesst.com |access-date=13 September 2012 |archive-date=8 June 2007 |archive-url=https://web.archive.org/web/20070608082935/http://www.concordesst.com/concordeb.html |url-status=live}}</ref> It would have higher thrust engines with noise reducing features and no environmentally-objectionable [[afterburner]]. Preliminary design studies showed that an engine with a 25% gain in efficiency over the Rolls-Royce/Snecma Olympus 593 could be produced.<ref>{{cite journal |url=http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=N9222540AH&q=Concorde+engines&uid=788858323&setcookie=yes |archive-url=https://web.archive.org/web/20110921055740/http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=N9222540AH&q=Concorde+engines&uid=788858323&setcookie=yes |url-status=dead |archive-date=21 September 2011 |title=Propulsion challenges and opportunities for high-speed transport aircraft |journal=Aeropropulsion |date=1987 |author=Strack, William |pages=437–52 |access-date=30 June 2011}}</ref> This would have given {{convert|500|mi|0|abbr=on}} additional range and a greater payload, making new commercial routes possible. This was cancelled due in part to poor sales of Concorde, but also to the rising cost of aviation fuel in the 1970s.<ref>{{cite web |url=https://news.google.com/newspapers?id=Q-0cAAAAIBAJ&pg=6914,3256355 |title=Fuel costs kill Second Generation of Concordes |first=Alison |last=Smale |work=Sarasota Herald-Tribune |date=22 September 1979 |access-date=28 November 2020 |archive-date=14 April 2021 |archive-url=https://web.archive.org/web/20210414125209/https://news.google.com/newspapers?id=Q-0cAAAAIBAJ&pg=6914,3256355 |url-status=live}}</ref>

===Radiation concerns===
{{multiple image
| direction         = vertical
| width             = 220
| image1            = ConcordeFuselageSinsheim.jpg
| image_caption1          = External view of Concorde's [[fuselage]]
| image2            = Concorde passenger cabin.jpg
| image_caption2          = [[British Airways]] Concorde interior, after refurbishment during time out of service following the 2000 Air France Concorde crash. The narrow fuselage permitted only a 4-abreast seating with limited headroom.
<!-- Please do not add more images here as it disrupts the spacing -->}}

Concorde's high cruising altitude meant people on board received almost twice the [[flux]] of extraterrestrial [[ionising radiation]] as those travelling on a conventional long-haul flight.<ref>{{cite web |url=http://www.britishairways.com/travel/healthcosmic/public/en_gb#4 |title=How much radiation might I be exposed to? |publisher=British Airways |access-date=11 January 2010 |archive-date=3 July 2009 |archive-url=https://web.archive.org/web/20090703115818/http://www.britishairways.com/travel/healthcosmic/public/en_gb#4 |url-status=live}}</ref><ref name='concradi'>{{cite journal |doi=10.1108/eb035011 |url=http://www.emeraldinsight.com/Insight/viewContentItem.do;jsessionid=E0A02B0587619C9A40D5736FCE7B3F02?contentType=Article&hdAction=lnkpdf |title=Electronic safety test replaces radioactive test source |author=Guerin, D.W. |journal=Aircraft Engineering and Aerospace Technology |year=1973 |volume=45 |issue=4 |issn=0002-2667 |page=10}}{{Dead link|date=December 2021 |bot=InternetArchiveBot |fix-attempted=yes}}</ref> Upon Concorde's introduction, it was speculated that this exposure during supersonic travels would increase the likelihood of skin cancer.<ref>{{cite news |url=https://news.google.com/newspapers?id=GfUNAAAAIBAJ&pg=2948,4208 |title=Skin cancer danger linked to stratospheric jet planes |newspaper=St. Petersburg Times |date=1 April 1975}}{{Dead link|date=December 2021 |bot=InternetArchiveBot |fix-attempted=yes}}</ref> Due to the proportionally reduced flight time, the overall [[equivalent dose]] would normally be less than a conventional flight over the same distance.<ref>{{cite web |url=http://www.britishairways.com/travel/healthcosmic/public/en_gb |title=Cosmic radiation |publisher=British Airways |access-date=11 January 2010 |archive-date=3 July 2009 |archive-url=https://web.archive.org/web/20090703115818/http://www.britishairways.com/travel/healthcosmic/public/en_gb |url-status=live}}</ref> Unusual [[Solar variation|solar activity]] might lead to an increase in incident radiation.<ref>{{cite journal |last=Arctowski |first=Henryk |year=1940 |title=On Solar Faculae and Solar Constant Variations |pmid=16588370 |volume=26 |issue=6 |pmc=1078196 |pages=406–11 |doi=10.1073/pnas.26.6.406 |url=http://www.pnas.org/cgi/reprint/26/6/406.pdf |archive-url=https://web.archive.org/web/20150903215336/http://www.pnas.org/cgi/reprint/26/6/406.pdf |archive-date=3 September 2015 |url-status=live |journal=Proceedings of the National Academy of Sciences|bibcode=1940PNAS...26..406A|doi-access=free}}</ref> To prevent incidents of excessive radiation exposure, the flight deck had a radiometer and an instrument to measure the rate of increase or decrease of radiation.<!--<ref name='concradi' />--> If the radiation level became too high, Concorde would descend below {{convert|47000|ft|m}}.<ref name='concradi'/>

===Cabin pressurisation===
[[Aircraft cabin|Airliner cabins]] were usually maintained at a pressure equivalent to {{convert|6000|-|8,000|ft}} elevation. Concorde's [[Cabin pressurization|pressurisation]] was set to an altitude at the lower end of this range, {{convert|6000|ft|m}}.<ref>{{cite journal |doi=10.1093/occmed/17.2.47 |title=Human Factors in the Concorde |journal=Occupational Medicine |last=Hepburn |first=A.N. |volume=17 |issue=2 |year=1967 |pages=47–51 |pmid=5648731}}</ref> Concorde's maximum cruising altitude was {{convert|60000|ft|m}}; subsonic airliners typically cruise below {{convert|44000|ft|m}}.{{sfn|Schrader|1989|p=64}}

A sudden [[Uncontrolled decompression|reduction in cabin pressure]] is hazardous to all passengers and crew.<ref>{{cite book |title=Flight Training Handbook |url=https://books.google.com/books?id=ioRTAAAAMAAJ |year=1980 |publisher=U.S. Dept. of Transportation, [[Federal Aviation Administration]], Flight Standards Service, 1980 |page=250 |access-date=15 March 2016 |archive-date=24 June 2016 |archive-url=https://web.archive.org/web/20160624192910/https://books.google.com/books?id=ioRTAAAAMAAJ |url-status=live}}</ref> Above {{convert|50000|ft|m}}, a sudden cabin depressurisation would leave a "[[time of useful consciousness]]" up to 10–15 seconds for a conditioned athlete.<ref>{{cite web |url=http://www.theairlinepilots.com/medical/decompressionandhypoxia.htm |title=Cabin Decompression and Hypoxia |first=Mark |last=Wolff |publisher=PIA Air Safety Publication |date=6 January 2006 |access-date=29 January 2010 |archive-date=16 March 2020 |archive-url=https://web.archive.org/web/20200316023131/https://www.theairlinepilots.com/forumarchive/aeromedical/decompressionandhypoxia.php |url-status=dead}}</ref> At Concorde's altitude, the air density is very low; a breach of cabin integrity would result in a loss of pressure severe enough that the plastic [[emergency oxygen system|emergency oxygen masks]] installed on other passenger jets would not be effective and passengers would soon suffer from [[Hypoxia (medical)|hypoxia]] despite quickly donning them. Concorde was equipped with smaller windows to reduce the rate of loss in the event of a breach,{{sfn|Nunn|1993|p=341}} a reserve air supply system to augment cabin air pressure, and a rapid descent procedure to bring the aircraft to a safe altitude. The FAA enforces minimum emergency descent rates for aircraft and noting Concorde's higher operating altitude, concluded that the best response to pressure loss would be a rapid descent.<ref>{{cite web |url=http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument |title=Interim Policy on High Altitude Cabin Decompression&nbsp;– Relevant Past Practice |first=Steve |last=Happenny |publisher=Federal Aviation Administration |date=24 March 2006 |access-date=22 March 2010 |archive-date=22 October 2011 |archive-url=https://web.archive.org/web/20111022084743/http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument |url-status=live}}</ref> [[Continuous positive airway pressure]] would have delivered pressurised oxygen directly to the pilots through masks.{{sfn|Nunn|1993|p=341}}

===Flight characteristics===
[[File:Concorde at Baginton - geograph.org.uk - 156846.jpg|thumb|alt=A BA Concorde, wheels and nose-cone lowered as if for landing, with a crowd of spectators in the foreground|Concorde performing a low-level fly-by at an air show in August 1981]]

While subsonic commercial jets took eight hours to fly from Paris to New York (seven hours from New York to Paris), the average supersonic flight time on the transatlantic routes was just under 3.5 hours. Concorde had a maximum cruising altitude of {{convert|18300|m|ft|sigfig=3}} and an average cruise speed of {{convert|2.02|Mach|altitude_ft=60000|sigfig=3}}, more than twice the speed of conventional aircraft.{{sfn|Schrader|1989|p=64}}

With no other civil traffic operating at its cruising altitude of about {{convert|56000|ft|m|abbr=on}}, Concorde had exclusive use of dedicated oceanic airways, or "tracks", separate from the [[North Atlantic Tracks]], the routes used by other aircraft to cross the Atlantic. Due to the significantly less variable nature of high altitude winds compared to those at standard cruising altitudes, these dedicated SST tracks had fixed co-ordinates, unlike the standard routes at lower altitudes, whose co-ordinates are replotted twice daily based on forecast weather patterns ([[jetstream]]s).{{sfn|Orlebar|2004|p=84}} Concorde would also be cleared in a {{convert|15000|ft|m|adj=on|sigfig=3}} block, allowing for a slow climb from {{convert|45000|to|60000|ft|m|abbr=on}} during the oceanic crossing as the fuel load gradually decreased.<ref>[[Shanwick Oceanic Control|Prestwick Oceanic Area Control Centre]]: Manual of Air Traffic Services (Part 2). [[National Air Traffic Services|NATS]]</ref> In regular service, Concorde employed an efficient ''cruise-climb'' flight profile following take-off.{{sfn|Orlebar|2004|p=92}}

The delta-shaped wings required Concorde to adopt a higher [[angle of attack]] at low speeds than conventional aircraft, but it allowed the formation of large low-pressure vortices over the entire upper wing surface, maintaining lift.{{sfn|Orlebar|2004|p=44}} The normal landing speed was {{convert|170|mph|km/h|0}}.{{sfn|Schrader|1989|p=84}} Because of this high angle, during a landing approach Concorde was on the backside of the [[Parasitic drag|drag force]] curve, where raising the nose would increase the rate of descent; the aircraft was thus largely flown on the throttle and was fitted with an autothrottle to reduce the pilot's workload.{{sfn|Orlebar|2004|p=110}}

{{blockquote|text=The only thing that tells you that you're moving is that occasionally when you're flying over the subsonic aeroplanes you can see all these 747s 20,000 feet below you almost appearing to go backwards, I mean you are going 800 miles an hour or thereabouts faster than they are. The aeroplane was an absolute delight to fly, it handled beautifully. And remember we are talking about an aeroplane that was being designed in the late 1950s&nbsp;– mid-1960s. I think it's absolutely amazing and here we are, now in the 21st century, and it remains unique.|sign=John Hutchinson, Concorde Captain|source='The World's Greatest Airliner' (2003)<ref>{{cite AV media|url=https://www.youtube.com/watch?v=9uMm16fUwoQ| archive-url=https://web.archive.org/web/20140624220847/http://www.youtube.com/watch?v=9uMm16fUwoQ| archive-date=2014-06-24 | url-status=dead|title=Concorde – The World's Greatest Airliner Part 3/4|date=19 January 2013|work=YouTube}}</ref>}}

===Brakes and undercarriage===
{{multiple image
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 |image1= Train d'atterrissage Concorde Musee du Bourget P1020039.JPG
 |image_caption1= Concorde main undercarriage
 |image2= Concorde tail gear.JPG
 |image_caption2= Tail bumper of Concorde G-BOAG at the [[Museum of Flight]] in Seattle
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}}

Because of the way Concorde's delta-wing generated lift, the undercarriage had to be unusually strong and tall to allow for the angle of attack at low speed. At [[Rotation (aviation)|rotation]], Concorde would rise to a high angle of attack, about 18 degrees. Prior to rotation, the wing generated almost no lift, unlike typical aircraft wings. Combined with the high airspeed at rotation ({{convert|199|knot|disp=or}} [[indicated airspeed]]), this increased the stresses on the main undercarriage in a way that was initially unexpected during the development and required a major redesign.<ref>{{cite web |url=http://www.iasa.com.au/folders/Safety_Issues/others/concordespacer.html |title=The real story of Flight 4590: Special Investigation |publisher=iasa.com.au |date=13 May 2001 |first=David |last=Rose |access-date=26 June 2007 |archive-url=https://web.archive.org/web/20100207121508/http://www.iasa.com.au/folders/Safety_Issues/others/concordespacer.html |archive-date=7 February 2010 |url-status=dead}}</ref> Due to the high angle needed at rotation, a small set of wheels was added aft to prevent [[tailstrike]]s. The main undercarriage units swing towards each other to be stowed but due to their great height also needed to contract in length telescopically before swinging to clear each other when stowed.<ref>Brooklands Museum</ref>

The four main wheel tyres<!-- please leave British spelling of "tyres" on British/French aircraft ---> on each [[bogie]] unit are inflated to {{convert|232|psi|kPa|abbr=on}}. The twin-wheel nose undercarriage retracts forwards and its tyres are inflated to a pressure of {{convert|191|psi|kPa|abbr=on}}, and the wheel assembly carries a spray deflector to prevent standing water from being thrown up into the engine intakes. The tyres are rated to a maximum speed on the runway of {{convert|250|mph|km/h|abbr=on}}.<ref>After the Paris accident in 2000 Concorde was fitted with improved tyres uprated to {{cvt|290|mph}}.</ref>

The high take-off speed of {{convert|250|mph|km/h}} required Concorde to have upgraded brakes. Like most airliners, Concorde has [[anti-lock braking system|anti-skid braking]]&nbsp;to prevent the tyres from losing traction when the brakes are applied. The brakes, developed by [[Dunlop Rubber|Dunlop]], were the first carbon-based brakes used on an airliner.<ref>{{cite journal |title=Design and Engineering of Carbon Brakes |author=Stimson, I.L. |author2=R. Fisher |volume=294 |issue=1411 |date=January 1980 |pages=583–90 |journal=Philosophical Transactions of the Royal Society of London |jstor=36383 |bibcode=1980RSPTA.294..583S |doi=10.1098/rsta.1980.0068|s2cid=122300832}}</ref> The use of carbon over equivalent steel brakes provided a weight-saving of {{convert|1200|lb|kg|abbr=on}}.{{sfn|Owen|2001|p=118}} Each wheel has multiple discs which are cooled by electric fans. Wheel sensors include brake overload, brake temperature, and tyre deflation. After a typical landing at Heathrow, brake temperatures were around {{convert|300|-|400|°C|°F|abbr=on|sigfig=2}}. Landing Concorde required a minimum of {{convert|6000|ft|m|abbr=out}} runway length; the shortest runway Concorde ever landed on carrying commercial passengers was [[Cardiff Airport]].<ref>{{cite news|title=Concorde takes off from Cardiff|url=http://news.bbc.co.uk/1/hi/wales/3118506.stm|publisher=BBC|access-date=19 January 2016|date=18 September 2003|archive-date=23 July 2004|archive-url=https://web.archive.org/web/20040723172418/http://news.bbc.co.uk/1/hi/wales/3118506.stm|url-status=live}}</ref> Concorde G-AXDN (101) made its final landing at [[Duxford Aerodrome]] on 20 August 1977, which had a runway length of just {{convert|6000|ft|m|abbr=out}} at the time.<ref>{{Citation |title=Concorde 101 {{!}} On board with a Test Engineer | date=27 April 2022 |url=https://www.youtube.com/watch?v=nh3ty6wp6qQ |language=en |access-date=27 April 2022}}</ref><ref>{{Cite web |title=Concorde G-AXDN (101) |url=https://www.heritageconcorde.com/g-axdn-101 |access-date=27 April 2022 |website=heritage-concorde |language=en}}</ref> This was the last aircraft to land at Duxford before the runway was shortened later that year.<ref>{{Cite news |date=25 August 1977 |title=Concorde lands safely at Duxford |work=Saffron Walden Weekly News |url=https://www.newspapers.com/article/saffron-walden-weekly-news-concorde-land/136696156/ |via=[[Newspapers.com]]}}</ref>

===Droop nose===
{{Main|Droop nose (aeronautics)}}

Concorde's drooping nose, developed by [[Marshall Aerospace|Marshall's of Cambridge]],<ref name="Concorde nose">{{cite web |url=http://www.flightglobal.com/pdfarchive/view/1971/1971%20-%201503.html |title=Droop nose |work=Flight International |date=12 August 1971 |pages=257–258 |access-date=20 November 2011 |archive-date=4 February 2012 |archive-url=https://web.archive.org/web/20120204172010/http://www.flightglobal.com/pdfarchive/view/1971/1971%20-%201503.html |url-status=dead}}</ref> enabled the aircraft to switch from being streamlined to reduce drag and achieve optimal aerodynamic efficiency during flight, to not obstructing the pilot's view during taxi, take-off, and landing operations. Due to the high angle of attack, the long pointed nose obstructed the view and necessitated the ability to droop. The droop nose was accompanied by a moving visor that retracted into the nose prior to being lowered. When the nose was raised to horizontal, the visor would rise in front of the cockpit windscreen for aerodynamic streamlining.<ref name="Concorde nose" />

[[File:Concorde landing Farnborough Fitzgerald.jpg|thumb|left|alt=a BAC-liveried aircraft a few feet above a runway, with wheels down |Concorde landing at [[Farnborough Aerodrome|Farnborough]] in September 1974, with dropping nose lowered]]
A controller in the cockpit allowed the visor to be retracted and the nose to be lowered to 5° below the standard horizontal position for taxiing and take-off. Following take-off and after clearing the airport, the nose and visor were raised. Prior to landing, the visor was again retracted and the nose lowered to 12.5° below horizontal for maximal visibility. Upon landing the nose was raised to the 5° position to avoid the possibility of damage due to collision with ground vehicles, and then raised fully before engine shutdown to prevent pooling of internal condensation within the [[radome]] seeping down into the aircraft's [[Pitot tube|pitot]]/[[Air data computer|ADC]] system probes.<ref name="Concorde nose" />

The US [[Federal Aviation Administration]] had objected to the restrictive visibility of the visor used on the first two prototype Concordes, which had been designed before a suitable high-temperature window glass had become available, and thus requiring alteration before the FAA would permit Concorde to serve US airports. This led to the redesigned visor used in the production and the four pre-production aircraft (101, 102, 201, and 202).{{sfn|Owen|2001|p=84}} The nose window and visor glass, needed to endure temperatures in excess of {{convert|100|°C|°F|abbr=on|sigfig=2}} at supersonic flight, were developed by [[Triplex Safety Glass|Triplex]].<ref>[http://www.flightglobal.com/pdfarchive/view/1968/1968%20-%202105.html "Triplex in Concorde: The story behind the film"] {{Webarchive|url=https://web.archive.org/web/20120204172615/http://www.flightglobal.com/pdfarchive/view/1968/1968%20-%202105.html |date=4 February 2012}}. Flightglobal.com, 1968. Retrieved 7 June 2011.</ref>
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