Short SC.1

Development

During the 1940s, various nations became interested in developing viable aircraft capable of conducting vertical take-offs and landings (VTOL). During the 1950s, Britain had developed and flight tested the purpose-built Rolls-Royce Thrust Measuring Rig, a crude but pioneering VTOL aircraft that successfully flew as envisioned, demonstrating the viability of the concept as well as providing useful date to build upon. However, while the Thrust Measuring Rig had provided valued insight into the design specifics of VTOL aircraft, such as the requirement for a capable auto-stabilisation system, it suffered from some deficiencies that undermined its value as a platform for further detailed research, such as control lag and a lack of aerodynamic surfaces. There was a need present for an aircraft that would exploit the experienced gained from the Thrust Measuring Rig, and to explore areas that the earlier aircraft was not capable of.

The SC.1 has its origins within a submission by Short Brothers to meet a Ministry of Supply (MoS) request for tender (ER.143T) for a vertical take-off research aircraft, which had been issued in September 1953. On 15 October 1954, the proposed design was accepted by the ministry and a contract was promptly placed for a pair of aircraft to conform with the requirements of Specification ER.143D. As envisioned, the aircraft was to be used for a series of flight tests to investigate its behaviour during the transition between vertical and horizontal flight modes, to determine the optimum and minimum level of assistance required from the auto-stabiliser during the transition process, to uncover likely operational issues, and to develop related support aids and equipment for the pilot to develop an all-weather approach and landing system.

As per the issued order, Short constructed two prototypes, designated XG900 and XG905.

Design

The Short SC.1 was a single-seat low wing tailless delta wing aircraft of approximately 8,000 lb all-up weight (max. 7,700 lb for vertical flight). It was powered by a total of four vertically mounted, lightweight Rolls-Royce RB108 lift engines that provided a total vertical thrust of 8,600 lb, along with a single RB.108 cruise engine in the rear of the aircraft to provide thrust for forward flight. The lift engines were mounted vertically in side-by-side pairs in a central bay so that their resultant thrust line passed close to the centre of gravity of the aircraft. These pairs of engines could be swivelled about transverse axes; they were therefore able to produce vectored thrust for acceleration/deceleration along the aircraft's longitudinal axis.

During conventional flight, the lift engines would be inactive; shortly prior to entering vertical flight, compressed air provided by the single cruise engine would be used to accelerate the startup of the lift engines. Considerable attention was paid during development to the design of the air intake for the engines, while involved a set of 7 variable hinged grills which open in a forward-facing position to increase airflow to the lift engines; flow into the engines had to be relatively consistent and stable to avoid issues such as engine surges and vibration. Initially, the series of scuttles were fitted to the exit nozzles of the lift engines to maintain a low-pressure environment beneath the engines and ensure that that the turbine blades rotated in the correct direction; due to the effectiveness of the intake and engine refinements, the scuttles became unnecessary.

The cockpit of the SC.1 had a mainly conventional nature, while having to accommodate a large number of systems and their controls, providing for a complex environment that a pilot would have to closely monitor. For its role as a research aircraft, it was furnished with a comprehensive recording system; this suite was refined during the testing process in order to capture newly determined quantities and to deal with unsatisfactorily low accuracy of some types of information, such as the electronic recording of temperatures.

The common throttle lever for the four vertical lift engines was the only additional primary control input present; it was operated in a similar manner to that of the Collective pitch level of a rotorcraft. The type possessed two means of exercising attitude control over the aircraft; aerodynamic surfaces which were used during conventional flight, and air jet nozzles during hovers and vertical flight. Bleed air was extracted from the four lift engines (using approximately 10 per cent of the intake air mass/thrust) to power variable nose, tail and wing tip air jet nozzles, which acted to provide pitch, roll and yaw control at low speeds during which there would be insufficient airflow over the aerodynamic surfaces for conventional controls to be effective.

The SC.1 was also equipped with the first "fly-by-wire" control system to be fitted to a VTOL-capable aircraft. This electrically-signalled control system, which also comprised the auto-stabiliser, not only transferred signals from cockpit controls such as the position of the stick, but also monitors feedback signals from the servos to provide stability of the systems itself. A total of three modes of control for the aerodynamic surfaces and/or the nozzle controls were permitted by the system:

1. Aerodynamic surfaces and air-jet nozzles controlled electrically via three independent servo-motors (with "three-way parallel" or "triplex" fail-safe operation) in conjunction with three autostabilizer control systems ("full fly-by-wire")
2. Hybrid-mode, in which the nozzles were controlled by servo/autostabilizer and the aerodynamic surfaces were linked directly to the manual controls
3. Direct mode, in which all controls were linked to the control stick

Modes 1 and 2 were selected on the ground; whenever the autostabilizer was in use, the pilot had an emergency override lever available with which to revert to direct control mode in flight. The outputs from the three control systems were compared and a "majority rule" enforced, ensuring that a failure in a single system was overridden by the other two (presumably correct) systems. Any failure in a "fly-by-wire" pathway was indicated to the pilot as a warning, which he could either choose to ignore or respond to by switching to direct (manual) control.

In common with other VTOL aircraft, the Short SC.1 suffered from vertical thrust loss due to the ground effect. Research into this performed on scale models suggested that for the SC.1 these losses would be between 15 per cent and 20 per cent at undercarriage height. Fuel tanks were located along the wing leading edges and in "bag" tanks fitted between the main wing spars. The SC.1 was fitted with a tricycle undercarriage arrangement; while non-retracting, the landing gear could be set between two alternative positions, suited to either conventional and vertical landings. The fixed undercarriage legs were designed specifically for vertical flight; each leg carried a pair of head-resistant castoring wheels, while the rear undercarriage was also fitted with disc brakes. Long-stroke oleos were used to cushion vertical landings. The robust gear was able to withstand a descent rate of 18 ft (5.5m) per second.

Testing

Constructed at Short's Belfast factory in Northern Ireland, the first SC.1 prototype, XG900, first undertook initial engine runs at this facility. After being transported by sea to England, XG900, which was initially fitted only with the propulsion engine, was delivered to the Royal Aircraft Establishment (RAE) at Boscombe Down to begin the flight test programme. On 2 April 1957, the prototype conducted the type's maiden flight, which was also its first conventional takeoff and landing (CTOL) flight.

Just over a year later, on 26 May 1958, the second prototype made the first tethered vertical flight. Initial flights of the type were performed while attached to a specially-devised gantry, which accommodated only a limited amount of freedom, up to 15ft vertically and 10ft off-centre in any direction, vertical velocity was also restricted to less than 10ft/second; progressive arresting of the aircraft occurred beyond these limitation. It would take off from a grid platform positioned 6ft above the ground itself in order to circumvent the ground effect phenomenon; considerable effort on the part of Shorts had been made during development of a suitable platform to eliminate the negative impact of ground effect and was redesigned several times. The gantry facility was used for ab initio training and familiarisation purposes for the first 8 pilots to fly the SC.1.

On 25 October of that year, the type performed the first 'free' vertical flight. On 6 April 1960, the first in-flight transition between vertical and horizontal flight was successfully conducted. While successful at transitioning between the two modes, the Short SC.1 had a reputation as being somewhat ungainly as an aircraft.

The SC.1 was publicly displayed at the Farnborough Airshow in 1958 and 1960; it also appeared at the Paris Air Show in 1961, at which it performed a demonstration flight. On 2 October 1963, the second test aircraft crashed in Belfast, killing the pilot, J.R. Green; the cause was later determined to have been a control malfunction. Following the accident, the aircraft was rebuilt and returned to flight for further testing, both continued flying until 1967. By 1965, a total of different 14 pilots had flown the type.

As a result of ground suitability tests, it was determined that conventional runway concrete, pavement, and even grass strips would be adequate for vertical takeoff and landing of the SC.1; however, debris that may be forced out from imperfect surfaces would pose a risk to personnel but not to the aircraft itself. The test programme also allowed experience upon the maintenance and serviceability of a VTOL aircraft to be acquired, even though these were not primary objectives of the design nor the research effort; throughout the programme, an overall average of 2.6 flights were performed per week. While numerous errors with the auto-stabiliser were reported during flights, no fault ever occurred that endangered the aircraft or had any affect upon its control.

Testing found the significance and difficulty in measuring actual engine thrust, leading to further tests using improved intakes and instrumentation, Ultimately, the engines proved to be far less problematic that may have been expected considering the experimental nature of the aircraft and its powerplants; the triplex auto-stabiliser was also discovered to be easy to locate reported faults upon, in part due to the system's self-checking nature. According to a Ministry of Aviation report, the SC.1 was determined to have been an effective research vehicle when operated within the limits imposed by its small size and restricted capacity; it was found that a larger aircraft would be necessary for more extensive instrument flight and guidance equipment assessment flights however.

The SC.1 flew for over ten years, during which it provided a great deal of data that served to influence later design concepts such as the "puffer jet" controls on the Hawker Siddeley P.1127, the precursor of the Hawker Siddeley Harrier. The flight testing work relating to vertical takeoff and landing techniques and technologies also proved to be invaluable, and helped further Britain's lead in the field. The Short SC.1 was ultimately rendered obsolete by the emerging Harrier which, amongst other things, proved that it was unnecessary to carry an additional four engines solely for the purposes of lift-off and landing.

Aircraft on display

The first SC-1 (XG900) became a part of the Science Museum's aircraft collection at South Kensington, London. It had been used until 1971 for VTOL research.

The second SC-1 (XG905) was also preserved and is on static display at the Flight Experience exhibit at the Ulster Folk and Transport Museum, Cultra, Northern Ireland.

Operators

Specifications

Data from Shorts Aircraft since 1900, Ministry of Aviation

General characteristics

Performance