Test flights
First engine test runs of prototype G-5-1 were made on 2nd April
1949 with roll out on 25th July after a complex program of engine
tests. This Comet was marked with the manufacture's Class B markings it was
otherwise unpainted.
Two days later the Comet made it's historic maiden flight which lasted 31
minutes. Crew: piloted by de Havilland Chief Test Pilot John Cunningham, John
Wilson as co-pilot and the flight test observer was Tony Fairbrother.
In
Class B Markings -G-5-1
Fairbrother was quoted as saying (Aeroplane Monthly 8/89) that,
"The Comet must have been one of the all-time technical achievements. I
don't think it is too much to say that the world changed from the moment its
wheels left the ground". This was undoubtedly true.
Rapid Progress
Less than three years was to elapse from the finalization of the detailed
design specification to it's historic first flight! Exactly one year later G-5-2
the second prototype was ready and development flying accelerated rapidly.
First public view of the Comet was at the 1949 Farnborough Air Show. Early
indications were that the Comet met most of its design specifications. It could
cruise at 490 mph. (788 Km/h) at 40,000ft (12,200 m) and, with an all-up weight
of 105,000 lb. (47,600 Kg), could carry 36 passengers over 2,600 miles (4,180
Km). There was some flexibility too - with a modest range reduction up to 48
passengers could be accommodated.
The 1949 SBAC show at Farnborough, Hampshire was described as, "The
finest show ever held". Also present was the Bristol Brabazon which made
its maiden flight on the 4th September - four days earlier - the largest of the
Types (III) recommended by the Brabazon
. Other civilian transports on display were - the Handley Page Hermes V
prototype which, powered by four Bristol Theseus turboprops was the fastest
turboprop transport at the show (351 mph); another prototype was the Vickers
Type 630 Viscount which was powered by four Rolls-Royce Dart turboprops. The
Viscount was slightly smaller than the Hermes.
Rocket assistance?
G-5-1, later given the civilian registration G-ALVG, continued test flights
primarily concerned with range and fuel consumption assessment. On the results
of these tests depended much. In the final analysis these figures were critical
to the success of pure-jet transports in general and to Comet sales potential in
particular. There were still many people in the industry who thought that
pure-jet transports would never be economically viable. In the event the
prototype G-5-1 performed superbly and without difficulty met its design
specification.
Difficulties keeping the all-up-weight (AUW) down had resulted in proposals
to improve takeoff performance and/or range. Rocket assistance on take-off was
tested as was in-flight refueling!
Peter Bois
[quotes in red]
de Havilland Test Pilot Peter Bois, who joined the Company in 1950, recalled
a number of experimental 'Sprite' assisted test flights made between May 1951
and May 1952. These tests were carried out on G-ALVG (ex G-5-1) in which two
5,000lb thrust Sprites rocket motors had been installed, one located each side
of the fuselage between the jet pipes of the Ghost engines. They gave a 55
second burn and effectively gave an (approximate) 50% increase in the total
available thrust. The technique used was to fire them on reaching 'decision
speed' and this would have allowed a, quote, "very worthwhile
increase in the Comets maximum AUW in high temperature/altitude
conditions."
The 'Sprite' option was not adopted for a number of reasons. The fuel used in
the Sprite was hydrogen peroxide which required a catalyst to release the
hydrogen which burned in oxygen - which was also released in the catalytic
reaction. Initially the catalyst used was potassium permanganate, quote, "this
was effective but unfortunately dyed everything in sight a delicate shade of
violet!"
Things improved somewhat when platinum mesh was
used as the catalyst instead of permanganate - the drawback was however that
platinum was much more expensive. In practice though the particular problems
associated with handling peroxide were not significantly greater than those
encountered with high-octane fuel. Peter, "they were different. An
electric spark in the vicinity of permanganate was of no consequence but even a
small impurity in the fuel tank could make it explode".
Large
quantities of water needed to be always available on hand ready to dilute
accidental spills.
Soon it was decided that the expense of bringing Sprites into regular use
would be difficult to justify. Factors to consider were the cost of the
peroxide, peroxide fuel availability problems, and the fact that ground crews at
all prospective Comet destinations would need special training were taken into
account. There was another unexpected problem though. Peter Bois, "peroxide
fumes rapidly turned the handling crew into platinum blondes and they were
greatly relieved when the project was dropped!"
Sprite Demonstrated
However before the project was cancelled the public were treated to
demonstrations of Sprite rocket assisted takeoffs at the SBAC show at
Farnborough in September 1952.
In flight refueling was tested too. On 14th December 1950 John
Cunningham and Peter Bois made a one and a half hour flight in 'VG to assess the
difficulties. The problem during the tests was that the tanker aircraft was a
converted Lincoln which had a cruising speed considerably less than that of the
Comet.
Peter Bois comments,
It should be explained that the Comet was fitted with a dummy probe so that, for
the test, the tanker's supply hose was empty. "This increased the
difficulty of coupling considerably as there was no weight to stabilize the
hose. It needed all John's considerable skill to make the connection and neither
of us felt we would have enjoyed being paying passengers in the cabin while the
struggle was in progress."
As it happened BOAC pilots said that
they were not prepared to be responsible for flying their aircraft so close to
another as a matter of routine on scheduled services. Fair comment!
Flights
Over the next months a whole series of test flights were undertaken setting
records all the way. In October 1949 a round trip to Castel Benito, Libya
achieving an average speed of 448 mph. Endurance tests were completed around the
British Isles and in February 1950 the first pressurization flight to 40,000ft
was undertaken (with a cabin pressure of 8.25 P.S. equivalent to an altitude of
8,000 ft.). Trials during the first year went smoothly with very few problems.
In March 1950 another record was set during a return trip to Rome - the
London - Rome leg at an average of 447 mph and the return at average speed of
453 mph. In the first 11 months of testing 324 flying hours were completed.
Tropical trials took place at Eastleigh, Nairobi in April and May 1950 where
the availability of a high altitude runway in high ambient air temperatures was
ideal for the testing purposes. By contrast Khartoum provided higher
temperatures but at a lower altitude. No great problems were encountered during
any of these trials.
John Cunningham, when asked to recall how he felt about the
Comet as a flying machine, is quoted as saying, "It felt wonderful,
right from the start. The smoothness and comfort were absolutely marvelous. It
was my pleasure and enjoyment to help put it all together".
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