Welcome back to the latest PoTP, literally and figuratively! Today I will be be talking about the Comet, the worlds first jetliner.
The Comet 4, the last of the breed. It can be identified by the circular windows and the fact that it hasn’t broken up in mid air yet. (I kid)
Specifications from Wikipedia
Comet 1 Comet 2 Comet 3 Comet 4
Cockpit crew 4 (2 pilots, flight engineer and radio operator/navigator)
Passengers 36–44 58–76 56–81
Length 93 ft (28 m) 96 ft 1 in (29.29 m) 111 ft 6 in (33.99 m)
Wingspan 115 ft (35 m)
Tail height 29 ft 6 in (8.99 m)
Wing area 2,015 sq ft (187.2 m2) 2,121 sq ft (197.0 m2)
Aspect ratio 6.56 6.24
Airfoil NACA 63A116 mod root, NACA 63A112 mod tip
Maximum takeoff weight (MTOW) 110,000 lb (50,000 kg) 120,000 lb (54,000 kg) 150,000 lb (68,000 kg) 156,000 lb (71,000 kg)
Operating range (typical performance) 1,500 mi (1,300 nmi; 2,400 km) 2,600 mi (2,300 nmi; 4,200 km) 2,700 mi (2,300 nmi; 4,300 km) 3,225 mi (2,802 nmi; 5,190 km)
Cruising speed 740 km/h (400 kn; 460 mph) 790 km/h (430 kn; 490 mph) 840 km/h (450 kn; 520 mph)
Cruise altitude 42,000 ft (13,000 m) 45,000 ft (14,000 m) 42,000 ft (13,000 m)
Powerplants (x 4) Halford H.2 Ghost 50 turbojets: 5,000 lbf (22,000 N) Rolls-Royce Avon Mk 503/504 turbojets: 7,000 lbf (31,000 N) Rolls-Royce Avon Mk 502/521 turbojets: 10,000 lbf (44,000 N)Rolls-Royce Avon Mk 524 turbojets: 10,500 lbf (47,000 N)
The de Havilland Comet went down in history as a failure, most things considered. It fell out of the sky, the Comet 1 only flying 2/3 years from 1952-1954 before being replaced by the Comet 4. The 1 suffered from pressurisation problems that caused metal fatigue to set in around the square windows, dooming multiple flights. The 707 which came out later, never faced these problems and went on to be a success, making it the poster child of jet aviation, unlike the Comet which is mostly referred to as the “First Jet Airliner”, but no more. What caused this?
On the 23rd of December, 1942, the Brabazon Committee was formed. Led by John-Moore Brabazon, it served to investigate the needs of the British aviation needs after World War II. Of most interest was the Type IV, a jet-powered 100 seat design added after Geoffrey de Havilland (sound familiar?) insisted that it be put in. Geoffery owned de Havilland, the aircraft company that made the Mosquito, the Trident, the BAe 146, and the Comet.
In 1946 after WWII, a design team was formed to further this concept. It was originally planned to be a 24-seat aircraft, later changed to 36 seats at the behest of BOAC, who had been the first to order the Comet with 10 aircraft. The original Halford H.1 Goblin engines were also changed to the Rolls-Royce Avons, also used in the Hawker Hunter fighter.
Throughout 1947 to 1948, de Havilland conducted extensive research and development towards the new jet, including several large stress test rigs and a water tank to test pressurisation. The plane was tested for metal fatigue in this tank, with the entire forward fuselage being tested to 19kPa and running through 16000 cycles. The windows were tested as well, being subjected to 83kPa, with one even managing 690kPa, 1250% over what it was expected to withstand in service.
In 1949, the Comet 1 was complete. On the 27th of July 1949, prototype DH106 Comet G-5-1 took to the skies, with a first flight lasting 31 minutes. Powered by Halford H.2 Ghosts and special single-wheeled MLG, the prototype looked different to most production Comet 1s.
The Comet itself was a low-wing cantilever monoplane, powered by 4 jet engines hidden inside the wings. It was around the length of the original 737, but seated fewer people in a much more comfortable environment. BOAC had fitted the entire plane with 36 reclining seats, each boasting 45-inch centers for room never seen before. The experience was new to most people, having come from the noise of propeller-driven airliners.
The first production aircraft, registered G-ALYP or “Yoke Peter” first flew on the 9th of Jan 1951. On the 2nd of May 1952, Yoke Peter took off on the worlds first jetliner flight with proper fare-paying passengers, from London to Johannesburg.
However, all was not well for Yoke Peter. On the 10th of Jan 1954, it broke up in mid air and crashed, with the loss of all 35 on board. With no witnesses, a bunch of partial radio transmissions, and no clues to what could have happened, no-one knew what had happened to the first Comet. BOAC voluntarily grounded its entire Comet fleet pending the results of the investigation. The conclusion that the committee came to was that fire was to blame, and changes were made to the Comets to protect the engines and wings from fire damage that would lead to another hull loss. All was alright, until the 8th of April 1954…
…where G-ALYY, named “Yoke Yoke” crashed in the Mediterranean near Naples with all 21 on board perishing in the crash. After this incident, the Comets Certificate of Airworthiness was revoked and production suspended. The BOAC fleet was also permanently grounded, cocooned and stored.
In the investigation, G-ALYU, an identical Comet 1, was donated to help further examination of what happened. It was thrown into the water tank, and 3057 flight cycles later, it burst open. Stress on the square window corners were much higher than expected, causing stress 2 to 3 times larger than across the rest of the fuselage. Further tests resulted in the same burst due to metal fatigue, suggesting that the problem was not just due to a few offending frames.
The tear in the fuselage caused by metal fatigue. Now imagine this happening at 42000 feet!
After the problems were identified, all Comet 1s were withdrawn from service, with some undergoing modifications such as a stronger skin and the square windows replaced by oval ones. de Havilland also went back to the drawing board, coming up with the Comet 4.
It was not only stretched from the earlier Comet 2, but also had extra fuel tanks, visible on the outer leading edge of the wing. The Comet 4C could also seat 119 in a special high-density seating configuration, or what we would now call Business Class. It also had the more powerful Rolls-Royce Avons, allowing it to gain more range, a higher cruising speed and a higher MTOW. Unfortunately, it was too little too late for the Comet and BOAC began withdrawing most of them by 1959. If the Comet 4 had been the first variant produced, it would have trounced the 707 and the DC-8, beating both of them to service. (Comet 1 first flight: 1949 | 707 first flight: 1957 | DC-8 first flight: 1958)
The lessons learnt from the Comet also helped the 707 and the DC-8. Most of the data gained from the crash of the two Comets went to the US, where it helped Boeing and Douglas not to make the same mistakes as dH did with the Comet 1. The 707 was also beaten across the Atlantic by the Comet 4. Many modern ideas of fatigue testing, fuselage design, and even the deep-sea salvage techniques needed to retrieve the wreckage of the crashed Comets also formed the basis of many ideas used to this very day. Subsequent fuselage thickness was also much thicker and windows no longer square for all planes afterwards, a design change mandated from the Comet.
The de Havilland Comet - so much wasted potential, but a much needed sacrifice in the pursuit of progress.
I hope you enjoyed reading this as much as I did researching about the Comet!
As always, have a great weekend and see you in Part 8!