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Aviation History
1984
1984 - 1003.PDF
PROPULSION Supersonic Pegasus trials continue SHOEBURYNESS Rolls-Royce's latest series of plenum chamber burning (PCB) trials at the Ministry of Defence's Proof and Experimental Establishment, Shoeburyness, are proving that vectored thrust is still a front-runner for a late 1990s supersonic Stovl fighter, reports Julian Moxon. The Harrier, tethered to a 140-ton Goliath crane, "went dynamic" in January, after static tests demonstrated that hot gas reingestion, water intake, and cross-lighting were not significant problems. If funding continues, the old 1960's vintage Pegasus 2 engine, distinctive by the loud whine from its two-stage fan, will be exchanged for an up- to-date Pegasus 11 producing 21,5001b of thrust—almost double that of the Pegasus 2. This would be boosted to around 40,0001b with PCB. Given an early go-ahead, the new combination could be running in three years and flying in four in a McDonnell Douglas-built demonstrator. The Pegasus ll's PCB system would be smaller and lighter than that currently being tested, because of the modern engine's much higher fan pressure-ratio. Rolls- Royce has already carried out full-scale tests of a lightweight plenum chamber burner. A variable-area nozzle based on that used in the RB.199 would also be tested. The current programme is aimed at gathering data for all of the technological elements necessary for integrating the engine and airframe. The idea of canting the front nozzles inwards by a few degrees to prevent hot gases being sucked in the intake and dras tically reducing power has been proved, and is being tried along with other flow-control devices, including AV-8B- type dams on the underbelly. Lower fuselage temper atures, while significant, have been found "acceptable", and would be further reduced by careful use of plenum chamber burning. A super sonic Harrier would, for example, only land vertically, take-off being achieved after a short run (as it is today), enabling much higher pay- loads to be carried. Landing of 'LIGHT International, 16 June 1984 a supersonic Stovl aircraft remains a problem area since, with the engines now avail able, the manoeuvre requires the use of full PCB. The way round this is to use an engine producing more dry thrust, which would mean a cooler exhaust. Rolls-Royce is now developing the high-pressure section of such an engine under its Advanced Core Military Engine (Acme) programme. This incorpor- Water is used to help flow visualisation. The Shoeburyness trials have also helped identify suitable landing pad materials. Below: The inward-canted plenum chamber burning nozzles of the Shoeburyness Harrier are clearly seen from this angle. Nozzle size would be reduced in future work using a modern, high-thrust Pegasus. Note flow control dome on underbelly, similar to but larger than those used on the Harrier A V-8B ates the best technology avail able with respect to a late 1990's powerplant. The Acme work is also relevant to advanced, conventional fighter engines. Rolls-Royce is also inter ested in two other concepts for supersonic Stovl fighters. It has recently completed a study for the US Navy, based on the tandem fan principle originally proposed by Vought, and could, if neces sary, put together such an engine for testing at Shoe buryness. The main problem with the tandem fan idea (in which the core drives two fans separated by a long shaft, the front fan air being directed either down, or rearwards) is in the design of a suitable valve to control the airflow. This has to fit a near-circular duct and handle very high aerodynamic forces. The ejector lift system proposed by General Dynam ics has also been studied by Rolls-Royce, which claims that the Pegasus, with its higher fan pressure ratio, would be more suited to the concept than the General Electric F110 around which the model aircraft now being windtunnel tested at Nasa Ames is currently configured. Funding for the Shoe buryness trials is mostly by the MoD, only ten per cent being supplied by Rolls- Royce. This is not, however, a highly expensive programme —it has absorbed just over £1 million since it started in 1982. Much use is being made of existing equipment culled from earlier PCB work, and from the Olympus/Concorde programme. A state-of-the- art data acquisition system presents the full thermo dynamic cycle of the engine in 30sec, and can produce the figures for 144 engine tran sients in a few minutes. • A more powerful version of the existing Pegasus is being developed under Rolls- Royce's XG15 programme. The engine will have 15 per cent more thrust, obtained with a higher pressure ratio fan, a more advanced com bustion chamber, and low- and high-pressure turbines capable of operating at higher temperature. The XG15 improvements will be demon strated by early 1986. 1551
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