Editing De Havilland Comet (section)

==Design==

===Overview===
[[File:Museum of Flight DH Comet interior.jpg|thumb|upright|[[Dan-Air]] Comet 4C cabin at the [[National Museum of Flight]]]]

The Comet was an all-metal [[Cantilever wing|low-wing cantilever]] monoplane powered by four jet engines; it had a four-place [[Cockpit (aviation)|cockpit]] occupied by two pilots, a flight engineer, and a navigator.<ref name=francis99/> The clean, low-drag design of the aircraft featured many design elements that were fairly uncommon at the time, including a swept-wing leading edge, integral wing fuel tanks, and four-wheel bogie main undercarriage units designed by de Havilland.<ref name=francis99>Francis 1950, p. 99.</ref> Two pairs of turbojet engines (on the Comet 1s, Halford H.2 Ghosts, subsequently known as de Havilland Ghost 50 Mk1s) were buried in the wings.<ref name=francis100-101>Francis 1950, pp. 100–101.</ref>

The original Comet was the approximate length of, but not as wide as, the later [[Boeing 737|Boeing 737-100]], and carried fewer people in a significantly more-spacious environment. BOAC installed 36 reclining "slumberseats" with {{cvt|45|in|mm}} centres on its first Comets, allowing for greater leg room in front and behind;<ref>Hill 2002, p. 27.</ref> [[Air France]] had 11 rows of seats with four seats to a row installed on its Comets.<ref name=popmech149>Cookman, Aubery O. Jr. [https://books.google.com/books?id=6NkDAAAAMBAJ&pg=PA149 "Commute by Jet."] ''Popular Mechanics'', 93(4), April 1950, pp. 149–152.</ref> Large picture window views and table seating accommodations for a row of passengers afforded a feeling of comfort and luxury unusual for transportation of the period.<ref>Smith 2010. 30(4), pp. 489, 506.</ref> Amenities included a [[galley (kitchen)|galley]] that could serve hot and cold food and drinks, a [[bar (counter)|bar]], and separate men's and women's toilets.<ref name=francis98>Francis 1950, p. 98.</ref> Provisions for emergency situations included several [[lifeboat (shipboard)|life raft]]s stored in the wings near the engines, and individual [[personal flotation device|life vest]]s were stowed under each seat.<ref name=francis99/>

One of the most striking aspects of Comet travel was the quiet, "vibration-free flying" as touted by BOAC.<ref name=walker69>Walker 2000, p. 69.</ref>{{refn|BOAC flight crew revelled in standing a pen on end and pointing that out to passengers; invariably, the pen remained upright throughout the entire flight.<ref>Windsor-Liscombe, Rhodri. [http://pi.library.yorku.ca/ojs/index.php/topia/article/view/2680/1885 "Usual Culture: The Jet."] ''Topia: Canadian Journal of Cultural Studies (Toronto: York University)'', Number 11, Spring 2004. Retrieved 26 April 2012.</ref> |group=N}} For passengers used to propeller-driven airliners, smooth and quiet jet flight was a novel experience.<ref name=francis100>Francis 1950, p. 100.</ref>

===Avionics and systems===
[[File:De Havilland DH106 Comet 4 G-APDB Cockpit.JPG|left|thumb|The flight deck of a Comet 4]]

For ease of training and fleet conversion, de Havilland designed the Comet's flight deck layout with a degree of similarity to the [[Lockheed Constellation]], an aircraft that was popular at the time with key customers such as BOAC.<ref name=d18/> The cockpit included full dual-controls for the captain and first officer, and a flight engineer controlled several key systems, including fuel, air conditioning and electrical systems.<ref>Darling 2001, pp. 35–36.</ref> The navigator occupied a dedicated station, with a table across from the flight engineer.<ref name=d36>Darling 2001, p. 36.</ref>

Several of the Comet's avionics systems were new to civil aviation. One such feature was irreversible, powered [[aircraft flight control system|flight controls]], which increased the pilot's ease of control and the safety of the aircraft by preventing aerodynamic forces from changing the directed positions and placement of the aircraft's [[flight control surfaces|control surfaces]].<ref>Abzug and Larrabee 2002, pp. 80–81.</ref> Many of the control surfaces, such as the elevators, were equipped with a complex gearing system as a safeguard against accidentally over-stressing the surfaces or airframe at higher speed ranges.<ref>Darling 2001, p. 2.</ref>

The Comet had a total of four [[hydraulic system]]s: two primaries, one secondary, and a final emergency system for basic functions such as lowering the undercarriage.<ref>Darling 2001, pp. 16–17.</ref> The undercarriage could also be lowered by a combination of gravity and a hand-pump.<ref>Darling 2001, p. 40.</ref> Power was syphoned from all four engines for the hydraulics, cabin [[air conditioning]], and the [[de-icing system]]; these systems had operational [[redundancy (engineering)|redundancy]] in that they could keep working even if only a single engine was active.<ref name=d17>Darling 2001, p. 17.</ref> The majority of hydraulic components were centred in a single avionics bay.<ref>Darling 2001, p. 45.</ref> A pressurised refuelling system, developed by [[Cobham plc|Flight Refuelling Ltd]], allowed the Comet's fuel tanks to be refuelled at a far greater rate than by other methods.<ref>[http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200887.html "F.R. equipment speeds refuelling."] ''Flight,'' 11 May 1951. Retrieved 26 April 2012.</ref>

[[File:DeHavillandCometCockpit.jpg|thumb|The Comet 4 navigator's station]]
The cockpit was significantly altered for the Comet 4's introduction, on which an improved layout focusing on the onboard navigational suite was introduced.<ref name=d40>Darling 2001, pp. 40–41.</ref> An [[EKCO]] E160 [[radar]] unit was installed in the Comet 4's [[nose cone]], providing search functions as well as ground and cloud-mapping capabilities,<ref name=d36/> and a radar interface was built into the Comet 4 cockpit along with redesigned instruments.<ref name=d40/>

[[Sud Aviation|Sud-Est]]'s design bureau, while working on the [[Sud Aviation Caravelle]] in 1953, licensed several design features from de Havilland, building on previous collaborations on earlier licensed designs, including the [[De Havilland Vampire|DH 100 Vampire]];{{refn|The Sud-Est SE 530/532/535 Mistral (FB 53) was a single-seat fighter-bomber version of the de Havilland Vampire jet fighter, used by ''[[French Air Force|L'Armée de l'Air]]''.<ref>Watkins 1996, pp. 181–182.</ref>|group=N}} the nose and cockpit layout of the Comet 1 was grafted onto the Caravelle.<ref>Motem 1990, p. 143.</ref> In 1969, when the Comet 4's design was modified by [[Hawker Siddeley]] to become the basis for the Nimrod, the cockpit layout was completely redesigned and bore little resemblance to its predecessors except for the control yoke.<ref>Darling 2001, p. 96.</ref>

===Fuselage===
Diverse geographic destinations and cabin pressurisation alike on the Comet demanded the use of a high proportion of alloys, plastics, and other materials new to civil aviation across the aircraft to meet certification requirements.<ref name=engineering>[http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200555.html "Comet Engineering: The Performance of Airframe, Engines, and Equipment in Operational Service."] ''[[Flight International]],'' 1 May 1953, p. 551. Retrieved 26 April 2012.</ref> The Comet's high cabin pressure and high operating speeds were unprecedented in commercial aviation, making its fuselage design an experimental process.<ref name=engineering/> At its introduction, Comet airframes would be subjected to an intense, high-speed operating schedule which included simultaneous extreme heat from desert airfields and frosty cold from the kerosene-filled fuel tanks, still cold from cruising at high altitude.<ref name=engineering/>

[[File:De Havilland Comet RAF Museum Cosford (1).jpg|thumb|left|A Comet 1's fuselage and [[de Havilland Ghost]] engine intakes]]
The Comet's thin metal skin was composed of advanced new alloys{{refn|Fuselage alloys detailed in Directorate of Technical Development 564/L.73 and DTD 746C/L90.|group=N}} and was both riveted and chemically bonded, which saved weight and reduced the risk of [[Fatigue (material)|fatigue cracks]] spreading from the rivets.<ref>[http://www.rafmuseum.org.uk/online-exhibitions/comet/comet2.cfm "Comet Enters Service."] {{webarchive |url=https://web.archive.org/web/20090922200849/http://www.rafmuseum.org.uk/online-exhibitions/comet/comet2.cfm |date=22 September 2009}} ''[[Royal Air Force Museum Cosford]]''. Retrieved 1 November 2010.</ref> The chemical bonding process was accomplished using a new [[adhesive]], [[Redux (adhesive)|Redux]], which was liberally used in the construction of the wings and the fuselage of the Comet; it also had the advantage of simplifying the manufacturing process.<ref>Moss, C. J. [http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200269.html "Metal to Metal Bonding – For Aircraft Structures: Claims of the Redux Process."] ''Flight International'', 8 February 1951, p. 169. Retrieved 26 April 2012.</ref>

When several of the fuselage alloys were discovered to be vulnerable to weakening via metal fatigue, a detailed routine inspection process was introduced. As well as thorough visual inspections of the outer skin, mandatory structural sampling was routinely conducted by both civil and military Comet operators. The need to inspect areas not easily viewable by the naked eye led to the introduction of widespread [[radiography]] examination in aviation; this also had the advantage of detecting cracks and flaws too small to be seen otherwise.<ref>Jefford 2001, pp. 123–125.</ref>

Operationally, the design of the cargo holds led to considerable difficulty for the ground crew, especially [[baggage handler]]s at the airports. The cargo hold had its doors located directly underneath the aircraft, so each item of baggage or cargo had to be loaded vertically upward from the top of the baggage truck, then slid along the hold floor to be stacked inside. The individual pieces of luggage and cargo also had to be retrieved in a similarly slow manner at the arriving airport.<ref>Birtles 1970, p. 132.</ref><ref>Jones 2010, p. 67.</ref>

{{Anchor|Engines}}

===Propulsion===

The Comet was powered by two pairs of turbojet engines buried in the wings close to the fuselage. Chief designer Bishop chose the Comet's embedded-engine configuration because it avoided the drag of [[podded engine]]s and allowed for a smaller [[vertical stabilizer|fin and rudder]] since the hazards of asymmetric thrust were reduced.<ref name=francis101-102>Francis 1950, pp. 101–102.</ref> The engines were outfitted with [[sound baffle|baffle]]s to reduce noise emissions, and extensive [[soundproofing]] was also implemented to improve passenger conditions.<ref>Darling 2001, pp. 35, 46.</ref>

[[File:De Havilland Comet pic 1 REJS.jpg|thumb|The Comet 4's enlarged [[Rolls-Royce Avon]] engine intakes]]
Placing the engines within the wings had the advantage of a reduction in the risk of [[foreign object damage]], which could seriously damage jet engines. The low-mounted engines and good placement of service panels also made aircraft maintenance easier to perform.<ref name=Withuhn88/> The Comet's buried-engine configuration increased its structural weight and complexity. Armour had to be placed around the engine cells to contain debris from any serious engine failures; also, placing the engines inside the wing required a more complicated wing structure.<ref name=francis103>Francis 1950, p. 103.</ref>

The Comet 1 featured {{cvt|5050|lbf|kN}} de Havilland Ghost 50 Mk1 turbojet engines.<ref name=francis100-101/><ref>[http://www.rafmuseum.org.uk/online-exhibitions/comet/comet3.cfm "Ghost engine."] {{webarchive|url=https://web.archive.org/web/20100204110840/http://www.rafmuseum.org.uk/online-exhibitions/comet/comet3.cfm |date=4 February 2010}} ''Royal Air Force Museum Cosford''. Retrieved 1 November 2010.</ref> Two [[hydrogen peroxide]]-powered [[de Havilland Sprite]] booster rockets were originally intended to be installed to [[RATO|boost]] [[takeoff]] under [[hot and high]] altitude conditions from airports such as Khartoum and Nairobi.<ref name=popmech149/><ref name=francis98-102>Francis 1950, pp. 98–102.</ref> These were tested on 30 flights, but the Ghosts alone were considered powerful enough and some airlines concluded that rocket motors were impractical.<ref name=Birtles125/> Sprite fittings were retained on production aircraft.<ref>Gunn 1987, p. 269.</ref> Comet 1s subsequently received more powerful {{cvt|5700|lbf|kN}} Ghost DGT3 series engines.<ref name=walker190/>

From the Comet 2 onward, the Ghost engines were replaced by the newer and more powerful {{cvt|7000|lbf|kN}} Rolls-Royce Avon AJ.65 engines. To achieve optimum efficiency with the new powerplants, the air intakes were enlarged to increase mass air flow.<ref name=d33/> Upgraded Avon engines were introduced on the Comet 3,<ref name=d33/> and the Avon-powered Comet 4 was highly praised for its takeoff performance from high-altitude locations such as Mexico City where it was operated by [[Mexicana de Aviación (1921–2010)|Mexicana de Aviacion]], a major scheduled passenger air carrier.<ref>[https://www.timetableimages.com/ttimages/mx/mx60/mx60-5.jpg En route] Time Table Images</ref><ref>[https://books.google.com/books?id=qiEDAAAAMBAJ&pg=RA1-PA52 "Comet Gets Stronger Engines."] ''Popular Science'', 160(6), June 1952, p. 142.</ref>