Hawker-Siddeley Trident

Development


Original specification


In April 1956, BEA's chief executive Anthony Milward stated that the Corporation "would rather do without [jet airliners]".^{[Vous devez être inscrit et connecté pour voir ce lien][Vous devez être inscrit et connecté pour voir ce lien]}

Nevertheless, in July 1956, BEA announced what it called "outline requirements" for a short-haul "second generation jet airliner".

The new type would work alongside BEA's turboprop airliners, carry a payload of some 20,000 lb (9,000 kg) or some 70 passengers over up to 1,000 miles (1,600 km), weigh about 100,000 lb (46,000 kg), use 6,000 ft (1,800 m) runways, cruise at the very high speed of 610 to 620 mph (975 to 990 km/h) and have "more than two engines".

^{[Vous devez être inscrit et connecté pour voir ce lien][Vous devez être inscrit et connecté pour voir ce lien]} While not an express requirement, commentators ever since have taken these figures to constitute a definite call to industry.^{[Vous devez être inscrit et connecté pour voir ce lien]}

Four companies prepared projects to match the BEA views. [Vous devez être inscrit et connecté pour voir ce lien] proposed the four-engined (but ultimately three-engined) Bristol 200.

[Vous devez être inscrit et connecté pour voir ce lien] also proposed the four-engined Avro 740 which later became a three-engined design; the company eventually shelved its proposal and joined forces with Bristol and Hawker Siddeley. [Vous devez être inscrit et connecté pour voir ce lien] proposed a four-engined aircraft closely related to the future [Vous devez être inscrit et connecté pour voir ce lien] and designated the VC11.

The de Havilland company considered three possible contenders for the specification. Two were four-engined developments of the [Vous devez être inscrit et connecté pour voir ce lien]: the D.H.119 and the D.H.120, the latter also intended for offer to [Vous devez être inscrit et connecté pour voir ce lien].

The third, the D.H.121, was announced in May 1957, had three engines, and was the contender which eventually proceeded to bid for BEA's attention.

In February 1958, BEA announced that the D.H.121 had come closest to its requirements and that it would order 24 with options on 12 more.
It took a further six months for the British government to approve a formal BEA order for the D.H.121; the government had favoured the Hawker Siddeley Bristol 200 for industrial policy reasons.

The D.H.121 was to be the world's first [Vous devez être inscrit et connecté pour voir ce lien] airliner.

Its designers felt this configuration offered a trade-off between cruising economy and take-off safety in case of an engine
failure; moreover, the BEA specification had called for "more than two engines".

Each of the three engines would drive its own hydraulic system, offering triple redundancy in case of any of the other two
systems (or both of them) failing. The engines were to be 13,790 lb_f (61.34 kN) [Vous devez être inscrit et connecté pour voir ce lien].

The D.H.121 was to have a [Vous devez être inscrit et connecté pour voir ce lien] of 123,000 lb (55,900 kg) or optionally, up to 150,000 lb or 63,000 kg), a range of 2,070 miles (3330 km), and seating for 111 in a two-class layout (or for over 140 in a high-density single-class layout
as typical from the 1960s onwards on inclusive-tour [Vous devez être inscrit et connecté pour voir ce lien] flights).

The design initially included a [Vous devez être inscrit et connecté pour voir ce lien] tail layout similar to that of the [Vous devez être inscrit et connecté pour voir ce lien].

The engines were clustered at the rear, with the centre engine situated in the extreme rear of the fuselage fed by air ducted through a large oval intake at the front of the fin, a configuration similar to the later [Vous devez être inscrit et connecté pour voir ce lien] design.

In time, the design settled on a variable-incidence T-tail ^{[Vous devez être inscrit et connecté pour voir ce lien]} with the centre engine situated in the tailcone, beneath the fin.

From the outset, the D.H.121 was planned to employ [Vous devez être inscrit et connecté pour voir ce lien] which were very advanced for the period.

They were intended to offer the capability of automatic approaches and landings within a year or two of the airliner's service entry.

The avionics were also to have triplicated components for reliability, and also to allow "majority 2:1 voting" in guiding the aircraft during automatic approaches and landings.

The bulky size of the period's avionics required them to be housed in a large hold beneath the flightdeck floor; its size dictated a distinctive nose [Vous devez être inscrit et connecté pour voir ce lien] design: offset by 2 ft (60 cm) to the port side and retracting sideways to stow across the D.H.121's longitudinal axis beneath the forward passenger vestibule.

Revised specification

Through 1958, BEA management increasingly felt that the D.H.121's payload and range capacity would be too great and pleaded with de Havilland to reduce the design to fit its revised requirements. BEA's concern was due to three factors: a short-lived airline recession in the late 1950s; the imminent arrival into service of the turboprop [Vous devez être inscrit et connecté pour voir ce lien]
which duplicated the D.H.121's general payload and range area, and the growing trend to higher-density seating.

At the time, many reputable airlines were reducing their short/medium range seat pitches from the then-customary minimum of 36 in (90 cm) to 34 in (87 cm) or even less, while emergent inclusive-tour charter airlines installed their seat rows at yet shorter pitches.

Although de Havilland stated that they generally concurred with these BEA views, upper management also stated that they had worked "under terms more onerous than anything D.H. had previously undertaken".

^{[Vous devez être inscrit et connecté pour voir ce lien]}
Industry observers at the time felt that the British aircraft industry had again stumbled "into the pitfall of having designed exclusively for one customer an aeroplane that has potentially a much wider scope": a sentiment which would be echoed throughout the Trident's subsequent progress.

It was, however, noted that de Havilland had not yet secured a formal and final BEA order and that its competitor Bristol was actively promoting their 200 project, which was significantly smaller than the D.H.121.

At the time [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] were also downsizing their [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] projects and it was felt that the original large D.H.121 would have to compete against the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] some four years after their entry into service, whereas a cut-back design would be more competitive against the then-projected 75-100 seat, four-engined DC-9.

The result of BEA's and de Havillands' concerns that the D.H.121 "had been allowed to grow too large" was a wholesale downsizing.

Significantly, this involved changing the powerplant from the initial Medway engine to the 40 percent less powerful 9,850 lb_f (43.8 kN) [Vous devez être inscrit et connecté pour voir ce lien] 505.

The gross weight was cut by about a third to 105,000 pounds (48,000 kilograms), range was cut by more than half to 930 miles (1500 kilometres), and mixed-class seating was cut by about a quarter to 75 or 80 (97 in a single-class layout).

Wing span was reduced by approximately 17 ft (5 m), wing area by 30 percent and overall length by 13 ft (3,9 m).

The revised design retained some features of the original larger one, notably the [Vous devez être inscrit et connecté pour voir ce lien]
diameter.

It had a smaller flightdeck and single-axis, two-wheel, four-tyre main undercarriage legs in place of the four-wheel bogies of its larger predecessor.

^{[Vous devez être inscrit et connecté pour voir ce lien]} Fuller details, including particulars of the pioneering avionics fit, were announced to the public in early 1960.^{[Vous devez être inscrit et connecté pour voir ce lien][Vous devez être inscrit et connecté pour voir ce lien]}

It was this aircraft which BEA ultimately ordered on 24 August 1959, initially in 24 examples with 12 options.

The future airliner's name, Trident, was announced at the [Vous devez être inscrit et connecté pour voir ce lien] in September 1960, reflecting its then-unique three-jet, triple-hydraulic layout.

British aircraft industry consolidation

While the D.H.121 emerged in the late 1950s, British government policy on the aircraft and [Vous devez être inscrit et connecté pour voir ce lien] industries posed a requirement that the then-many companies should merge to form a few large groups.

De Havilland had accordingly consorted with [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] to manufacture and market the D.H.121 under the corporate name of [Vous devez être inscrit et connecté pour voir ce lien], after [Vous devez être inscrit et connecté pour voir ce lien]'s defunct pre-[Vous devez être inscrit et connecté pour voir ce lien] employer.