Hawker-Siddeley Trident

The Minister of Supply, however, stated of the Airco consortium that "this is not quite what [he] had in mind".

By late 1959, he had forced de Havilland to merge into the Hawker Siddeley group which until recently had promoted its competing Hawker Siddeley Bristol 200 project and publicly deprecated the D.H.121 project.

The complex merger was completed by April 1960. Until its very eve, Airco executives intensively explored alternatives to the merger, such as the possibility that Boeing may drop its 727 project and instead manufacture Airco D.H.121s in the USA.

This involved two Airco visits to Boeing and a return visit by Boeing executives and engineers.

British commentators have tended to interpret this episode as involving the acquisition of sensitive proprietary data on the D.H.121 by a direct competitor.

Bristol 200

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After the de Havilland takeover by Hawker Siddeley, Airco was disbanded. Hunting was marshalled into the competing newly-formed [Vous devez être inscrit et connecté pour voir ce lien] ([Vous devez être inscrit et connecté pour voir ce lien]).

Their departure removed any putative possibility of the Hunting 107 (later the [Vous devez être inscrit et connecté pour voir ce lien]) being marketed alongside the D.H.121 as a complementary, smaller member of the same airliner family.

Fairey Aviation, partially incorporated into [Vous devez être inscrit et connecté pour voir ce lien], also left the D.H.121 project.

^{[Vous devez être inscrit et connecté pour voir ce lien]} With the move to Hawker Siddeley Aviation, the designation eventually changed to the HS 121.

By 1960, the cumulative delays to the D.H.121 programme from changes to BEA's requirements and British aircraft industry mergers had amounted to between two and three years.

Nevertheless, for a year the D.H.121 was the first and only firm contender in a market segment so far unoccupied by an American or other product: that for a short/medium range, medium capacity jet airliner.

Design

The Trident was a [Vous devez être inscrit et connecté pour voir ce lien] of all-metal construction with a [Vous devez être inscrit et connecté pour voir ce lien] and a low-mounted [Vous devez être inscrit et connecté pour voir ce lien] with a quarter-chord sweepback of 35 degrees.

It had three rear-mounted engines: two in side-fuselage pods, and the third in the fuselage tailcone, aspirating through an [Vous devez être inscrit et connecté pour voir ce lien].


One version had a fourth "boost" engine aspirated through a separate intake duct above the main S-duct.

All versions were powered by versions of the [Vous devez être inscrit et connecté pour voir ce lien], while the boost engine was also by Rolls-Royce: the RB162, originally intended as a lift engine for [Vous devez être inscrit et connecté pour voir ce lien] applications.

RB-162

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The Trident was one of the fastest subsonic commercial airliners, regularly cruising at over 610 mph (965 km/h).

At introduction into service its standard cruise Mach Number was 0.88/ 380kts IAS, probably the highest of any of its contemporaries.

Designed for high speed, the wing produced relatively limited lift at lower speeds.

This, and the aircraft's low power-to-weight ratio, called for prolonged takeoff runs.

Nevertheless, the Trident fulfilled BEA's 6,000 ft (1,800 m) field length criterion and its relatively staid airfield performance was deemed adequate before the arrival into service of the Boeing 727 and later jet airliners built to 4500 ft (1360 m) field
length criteria.^{[Vous devez être inscrit et connecté pour voir ce lien]}

2E

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The Trident was routinely able to descend at rates of up to 4500 fpm (23 m/sec) in regular service. In emergency descents it was permissible to use reverse thrust of up to 10,000 rpm.

Below 280 kt IAS, it was also possible to extend the main landing gear for use as an emergency airbrake.

The Trident's first version, Trident 1C, had the unusual capability of using reverse thrust prior to touchdown.

The throttles could be closed in the flare and reverse idle set to open the reverser buckets.

At pilot discretion, up to full reverse thrust could then be used prior to touchdown.

This was helpful to reduce hydroplaning and give a very short landing run on wet or slippery runways, while preserving wheel brake efficiency and keeping wheel brake temperatures low.

Avionics fit

The Trident had a complex, sophisticated and comprehensive avionics fit which was successful in service.

This comprised a completely automatic [Vous devez être inscrit et connecté pour voir ce lien] developed by Hawker Siddeley and [Vous devez être inscrit et connecté pour voir ce lien].
It was capable of guiding the aircraft automatically during airfield approach, flare, touchdown and even roll-out from the landing runway.

The system was intended to offer autoland by 1970.

In the event, it enabled the Trident to perform the first automatic landing by a civil airliner in scheduled passenger service as early as 10 June 1965 and the first genuinely "blind" landing in scheduled passenger service as early as 4 November 1966.

The ability to land in fog solved a major problem at [Vous devez être inscrit et connecté pour voir ce lien] and other British airports.

Delays were commonplace when Category 1 (Cat 1 = 200 ft (61 m) decision height and 600 metre runway visual range
RVR) [Vous devez être inscrit et connecté pour voir ce lien] (ILS) was in use.

The Trident with its autoland system pioneered the use of lower landing minima starting with Cat 2 (100 ft decision height
and 400 metres RVR) and going on to "zero-zero" (Cat 3B) operations.

Because the Trident fleet could operate safely to airfields equipped with suitable ILS installations, it could operate as scheduled irrespective of weather, while other aircraft were forced to divert.

The Trident's advanced avionics displayed the aircraft's momentary position relative to the ground on a moving map display on the centre instrument panel.

This electro-mechanical device also recorded the aircraft's track using a stylus plotting on a motor-driven paper map.
Positional information was derived from a [Vous devez être inscrit et connecté pour voir ce lien] navigation system which read groundspeed and drift data which, alongside heading data, drove the stylus.

The Trident was the first airliner fitted with a quick access flight data recorder.

This sampled 13 variables, converted them into a digital format and stored them on magnetic tape for ground analysis.

Operational history

Hawker Siddeley Aviation, by this time, the parent of de Havilland, needed additional customers for the Trident, so entered into discussions with [Vous devez être inscrit et connecté pour voir ce lien] (AA) in 1960.

They demanded an aircraft with a longer range, which meant that the original DH121 design would have fulfilled American's requirements almost perfectly.

To fill AA's needs, design began on a new Trident 1A, powered with uprated [Vous devez être inscrit et connecté pour voir ce lien] 510s of 10,700 lb_f (47.6 kN) [Vous devez être inscrit et connecté pour voir ce lien], and a larger wing with more fuel, raising gross [Vous devez être inscrit et connecté pour voir ce lien] to 120,000 lb (54,000 kg) and range to 1,800 miles (2900 km).

American Airlines eventually declined the aircraft in favour of the Boeing 727, an aircraft which filled the original DH121 specifications almost exactly.

In fact, de Havilland had invited a group of engineers from Boeing to see the DH121 design and development program in its early stages, partly because Boeing was looking to develop a similar medium-range version of its [Vous devez être inscrit et connecté pour voir ce lien] design.