A handicap for Comet 1 operators was limited range – insufficient for North or South Atlantic routes.
This was partially overcome with the arrival of the Rolls-Royce axial-flow engine – the Avon. These were more compact and more powerful than the Ghost.
Development work had begun with the R.A.29 before the Comets first flight. It was a development of a military engine – the Avon 100 series. The 200 series made its first flight on 16th February 1952 installed in a modified Mk.1 (G-ALYT). Now called the Avon 501 its rating was 6500 lb.st. This Comet – now designated 2X – was later fitted with the slightly more powerful version, the Avon 502 (at 6600 lb.st.).
The 2X became an engine development test bed in order to speed up certification of the Comet 2. Gradually certifiable engine over-haul life was increased and by February 1954 the 502 was approved by the ARB for a test-bed thrust of 7150lb.
BOAC ordered 12 Comet 2s. Air France initially ordered three but later in December 1953, added another three. A number of other airlines were also interested.
The Mk.2 thus evolved: Four Avon 503s were fitted all were rated at 7300 lb.st. The installation of the Avon necessitated enlarging the engine air intake ducts – which gave the Mk.2 a distinctive appearance.
These modified ducts were first seen, along with the revised leading edge, on G-AMXA, the first Series 2 production Comet, in January ‘54. Fuselage length had increased by 3ft (0.91m) to give 96ft 1 inch (29.28m). The span remained the same as was height. Wing area was marginally up at 2027 sq.ft. Gross weight: 120,000lbs (54545Kg) and range, would give a practical stage-length of 2200 – 2400 miles (3520-3840Km) with usual airline reserves.
RAF Comet 2
The Comet 2 now had genuine South Atlantic (but not North Atlantic) capability.
Extensive test flights with G-AMXA confirmed true long-range capability. In January 1954, en route for tropical trials, ‘XA set a new point to point record between Hatfield and Khartoum of 6hrs. 22min. 7.2 seconds for the computed distance of 3064.1 miles (4902Km) at an average of 481.1 mph.
Onboard were13 persons. Crew members John Cunningham and Peter Buggé of de Havilland with Capt. A.M.A. Majendie and Capt. H.J. Field from the Corporation, along with representatives from the ARB and Rolls-Royce.
‘XA demonstrated that, even with less favourable weather conditions, impressive stage lengths could be flown on normal tankage. This was to bode well for Transport Command.
The tropical trials in Khartoum were followed by high altitude work from the Jan Smuts Airport at Johannesburg which, with an above sea-level altitude of 5,559ft (1694m), enabled high-altitude take-offs and other testing.
The whole series of African tests was scheduled to last only two weeks because the bulk of testing had been completed the previous May (1953) with the Avon 2X – which was also flown to Khartoum and Entebbe for tropical trials.
Parameters evaluated: normal and engine-out take-offs, accelerate-stop distances would be measured with those for all-engine and engine-out climbs as well as baulked landings. Cruise control techniques were evaluated on various inter-stage flights.
On the South African route Jan Smuts, Johannesburg was the highest airfield. Later BOAC decided to operate via Nairobi – at 5,380ft (1,640m). More importantly, it had a runway only 7,980ft (2,432m) in length.
Figures produced by the company illustrate the relationship of Altitude / Temperature / AUW / Runway length –
So at Nairobi the Mk.2 would have to be operating with a low AUW to be sure to get airborne especially at high ambient temperature.
To get round this problem it was decided to schedule Nairobi via Entebbe – a short stage-length of only 317 st. miles (507Km) and so the fuel load, and consequently AUW, could be kept low. It was thought that 216 Sqd. would probably have to make similar arrangements if faced with high-altitude/short runways on overseas routes.
Once the tropical trials had been completed the bulk of the work for ARB Certification had also been completed. A total of eighteen Comet 2s were eventually completed – though three of these did not fly.
Eventually it was decided that all Comet 2s – then on the production line – would be allocated to the services. 10 were destined for RAF. 216 Sqd.. They would be fully ARB Certified, have full cabin pressurization and so would be able to carry troops and other passengers. In addition there would be three unmodified aircraft for other duties (reconnaissance) with RAF Signals Sqd. These would only be capable of limited pressurization. ‘Other duties’ a euphemism meaning for use in ‘under cover’ operations. Finally there would be three unmodified incomplete aircraft for fleet reserve.
External modifications were necessary and 2Es featured enlarged intakes at the outer positions.
Two Comet 2s were destined to serve ‘over and above the call of duty’. They became development test-beds for the Comet 4 program.
Mk.2s G-AMXD, and G-AMXK were both modified by having the outboard Avon engines replaced with the latest more powerful variant – the 524. These Mk.2s were designated the 2Es
2Es were used to evaluate the RA29 engine which was destined for Comet 4. It was necessary to build up the certified overhaul life of the engine. The ARB required a minimum life between major overhauls of 1000 hours per engine. Each stage of development had to be authorized – progress was thus: an engine would be certified for, say, 200 hours initially but with ARB approval given for extension up to 500 hours operation. Once proved at the higher figure the certification would extend the ‘extension’. And so on.
Each engine was returned to RR for stripping down and wear analysis as they reached successively higher accumulated hours. The first two engines were returned after 250 hours. The third was returned after 350 hours and the forth after 450. 600 hours was the next target and so on.
Between September ‘57 and early in 1958 the certified life of 524 was extended from 200 hours to 750 hours – in fact by May 1958 some 7000 hours had been accumulated. Rolls-Royce were confident that by the time the Mk.4 was due to enter service 1500 hours would be achieved but, in the meantime, the ARB had approved an extension to 1000 hours for one 524s in each 2E.
The ‘Comet Flight’s’ objective was speed Avon development while the crew training program got underway.
It was decided to provide the Corporation with two 2E’s – the first being delivered on 26th August 1957. It was flown from Hatfield by Capt. A. P. W. Cane who was to reform the ‘Comet Flight’ – it had been suspended in 1954. The Corporation decided to purchase ‘XK outright. ‘XD remained the property of the Ministry of Supply.
The ‘Flight’s’ team comprised three complete crews and two extras. Ten captains and four engineering officers attended technical courses at Hatfield and Rolls-Royce at Derby.
Deputy of the ‘Flight’ was T. B. Stoney while H.J. Field had responsibility for performance assessment; Eng./Off. J. Kingston handled engineering and radio matters were in the hands of R. J. Dolman.
BOAC’s plan called for the accumulation of 3500 hours before the end of May 1958 so ‘Flight’ they were putting in six flights a week each averaging 11½ hours! As more crews became available development accelerated.
The 2E performed excellently and the Corporations targets achieved.
By January 1958 their 2Es had achieved 1500 hours on proving flights. Also revised were Comet Mk.1 jet holding patterns, climb and descent procedures, cruising techniques, and the 2Es were later used extensively during the evaluation of the Decca/Dectra navigation system.
This system was planned for the transatlantic Mk.4s. There had been much rivalry between the British Decca system and the less sophisticated Vortac system from the USA. The American Loran C – similar to Dectra – was not yet up and running and so the choice was relatively simple.
The MoS 2E G-AMXD equipped with Dectra had been giving a series of demonstrations in an attempt to convince airlines and CAA of its merit. Dectra equipped 2Es were operated on the North Atlantic routes and provided accurate en route tracking and lateral separation.
The Ministry of Supply 2E ‘XD was returned in May 1958. In June BOAC switched their own aircraft ‘XK to transatlantic proving flights to gain valuable operational experience on the North Atlantic route. Schedule jet services were planned from the autumn.
This program ran in three phases:-
Eleven daily return flights to Gander routed west-bound via Keflavic.
Eight three day trips, the first day to Gander, the second day flights from Gander to Goose, Stephenville, Sydney, Moncton and return to Gander, third day back to London.
Eight further trips beginning as on day one of Phase 2 to Gander but then on day two
practicing approach and let-down procedures at Baltimore, Montreal, Boston and New York.
This series of transatlantic flights added 423 hours to BOAC experience.
G-AMXD was re-registered as XN453 and joined the RAE, Farnborough for ‘radio development’ work. G-AMXK was modified to test auto-pilot and automatic landing systems for Smiths Industries (destined for use in the DH 121 ‘Trident’) and later – in 1966 – it found itself at Blind Landing Experimental Unit (BLEU) as XV144. It was used for spares for XN453 when it retired in 1970.