Thrust For The Future

Sharing the same development programme, the Tay 61O and 620 engines, both with a maximum thrust of 13,8001b, were produced for the Gulfstream G-IV and Fokker 100 aircraft respectively and achieved certification by the United Kingdom Civil Aviation Authority (CAA) in the middle of 1986. Another model, the Tay 650, will produce 14,5001b thrust and power higher weight versions of the Fokker 100. It will also equip the re-engined British Aerospace 1-11.

The next growth step is the Tay 670, producing 16,000lb thrust and embodying a larger fan. This engine will offer the same Stage 3 noise compliance as the other models as well as increased aircraft performance and engine efficiency. The tightening of noise regulations both in the United States and Europe will probably lead to the phasing out of older, noisy aircraft and the Tay 670 is being considered for re-engining the DC-9 and Boeing 727-200 and 737-200. It will also be suitable for growth versions of existing aircraft in the 100 to 120 seat range. Such an engine could enter service about 3½ years after the programme is launched.

In the Tay the higher efficiency realised by the engine is largely due to the improved fan design first introduced on the RB211-535. In an engine of this type the fan produces some three-quarters of the thrust and has to satisfy the basic requirements of a suitable diameter, aerofoil shape and rotational speed, together with the achievement of stress levels consistent with adequate fatigue life.

The wide chord fan of the 535E4 has demonstrated enhanced bypass stage efficiency, resulting in a specific fuel consumption (SFC) improvement of over 4% at maximum cruise compared to the narrow chord fan with on the 535C. Also, as each wide chord blade has more effective area than the narrow chord snubbed blade and an optimum space/chord ratio has been maintained, only 22 blades are required compared to 33 in the earlier engine.

However, for small diameter wide chord fans there is no weight advantage to be gained by a fabricated construction. The fan on the Tay, which is only 111. 8cm in diameter compared to the 188. 2cm diameter of the 535E4 fan, is therefore of solid construction.

This fan has the advantage that the smaller number of increased chord blades, matched to the number of stators in the compressor, leads to a significant change in noise transmission losses through the rotor, as compared with a conventional narrow chord fan. A reduction of 2 EPNdB at approach power is a typically achieved figure. The wide chord blade also has increased integrity and resistance to foreign object damage and bird ingestion.

Reliability of the Tay is assured by incorporating the core and external gearbox of the well proven Spey, together with an advanced LP system tailored to complement these by maintaining core inlet and outlet conditions similar to those of the original engine.

The latest technology is used to ensure that the cold bypass air and the hot exhaust from the turbines are combined in a new low loss forced mixer to give high propulsive efficiency with low sound generation. The lightweight bypass duct is also produced in carbon fibre-reinforced composite material, a 25% weight saving having been achieved over the more conventional titanium alloys.

First test run of the Tay engine took place in August 1984 and it achieved certification less than two years later. Production deliveries of the 61O series began towards the end of 1986 to Gulfstream and the G-IV achieved flight certification in April of the following year, entering service in June 1987.

The 13,8001b thrust Tay 620 for the Fokker 100 obtained certification in 1986, enabling the aircraft to be certificated the following year. First production delivery of the Fokker 100 took place in February 1988 to Swissair which has ordered eight with six options. Other airlines and agencies that have selected this aircraft include KLM, USAir, Wardair and International Lease Finance Corporation (ILFC) and Guinness Peat Aviation (GPA).

Of great importance to the operators is ease of maintenance and, in line with current practice, the Tay is built in seven modules: fan, IP compressor, gearbox, intermediate case, combustion and HP turbine, HP compressor and LP turbine. Line maintenance checks of the engine have been scheduled to coincide with aircraft checks for both improved efficiency and economy. To extend the on-wing life of the engine beyond the anticipated hot end mid life inspection of 10,000 hours and full overhaul of 20,000 hours, condition monitoring facilities available include borescope access ports for internal visual inspection, magnetic chip detectors in the oil return lines and engine mounted vibration pick ups. Removal and installation of the engine is achieved with minimum down time and engine change can be carried out by three men within three hours, with satisfactory operation ensured by ground running for a maximum of 15 minutes.

Development of the engine continues with the Tay 650 which represents the first stage in a programme matched to the airframe manufacturers’ requirements. In comparison to the Tay 620, the 650 gives a 9% increase in maximum takeoff thrust and a 15% increase in maximum continuous climb and cruise thrust. A small increase has been made in the fan diameter (113. 8cm compared to 111. 8cm) as well as other improvements throughout the engine, including a new HP turbine system and additional borescope access.

Further development is envisaged in the Tay 670 which would have a fan increased to 188. 9cm to give a maximum takeoff thrust of around 18,000lb. This engine would have a weight of 1,518kg compared to 1,409kg for the other versions.