Test rig takes on any gearbox

Citation

(2002), "Test rig takes on any gearbox", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 1. https://doi.org/10.1108/aeat.2002.12774aab.012

Test rig takes on any gearbox

Keywords: Gearboxes, Aircraft

Westland Transmissions Ltd in Yeovil has installed a new flexible transmissions test rig (FTTR), as part of a £9 million investment that is being used to test helicopters such as the Westland WAH-64 Apache and the EH101 and to develop future aircraft gearboxes. Powered and controlled by five motors and drives from ABB the FTTR is claimed to be the world's most advanced test rig (Plate 6).

As the gearbox is central to the distribution of engine power to the rotors and other power outputs in the aircraft, it goes through a rigorous test cycle before delivery. Historically, different gearboxes needed individual test rigs, but the FTTR can reportedly test different types of gearboxes, under practical conditions, for helicopter and aero-engine applications.

Working with the main contractor, RENK of Germany, ABB supplied AC variable speed drives and large induction motors to drive the engine inputs and to exert load onto the rotor and tail outputs of the test gearbox.

The FTTR utilises four identical 2,000kW AMB 560 induction motors in a symmetrical arrangement. Each motor can traverse up to 4 metres along the side of the test rig and elevate 300mm. The vertical motion is achieved with a slideway integrated into a custom designed motor housing.

To accommodate the demands of each aircraft type, the rig is equipped with a different pallet for each gearbox. The motors are coupled through drive gearboxes mounted on the pallet, which allow motor speed and efficiency to be optimised. The pallets are pushed into position on air casters and all input and output power connections are standardised. All services such as hydraulics, electricity, cooling water and oil are connected to the pallet by a docking plate.

The four motors are used to transmit power to, or absorb power from, the gearbox. On a three- engine gearbox, such as the EH101, three of the motors would be used to simulate engine power inputs and the fourth used to simulate tail rotor drive output load.

The main rotor load is simulated by an ABB uQ 800 motor rated at 5,250kW and powered by its associated ABB Variable Speed Drive. The motor is fitted above the test gearbox with shaft-down mounting. A tilt mechanism is employed for small adjustments in rotor shaft angle to suit the test gearbox.

Test rigs, especially in the aerospace industry, are subjected to high loads with vibration and oscillation problems. These tend to be acute requiring careful design of all the components. For this particular contract, the engineering was very specialised to allow for the degree of movement of the motors. ABB was able to supply the engineering expertise for this special configuration and was also able to provide full load combined tests at its Birr, Switzerland plant to meet the client's criteria (Plate 7).

Plate 6 Westland's FTTR has been designed to help develop the gearboxes of complex aircraft such as the WAH-64 Apache while minimising the costs traditionally associated with these tests

Plate 7 ABB supplied five induction motors with associated drives and control equipment for Westland's innovative FTTR. Test rigs in the helicopter industry are subjected to high levels of vibration and oscillation creating particular design demands

As only a new pallet is required for each new gearbox type, the cost of acquiring a new test rig has reportedly been reduced by 90 per cent.

The rig operates on a closed loop system, where the energy is re-circulated to significantly reduce mains demand and cost. The energy is re-circulated electrically by the variable speed drives using a common DC link. Each motor may be used to provide energy or as a generator to absorb energy. During testing mechanical torque is carefully applied to the gearbox input and output shafts in opposition to "wind up" the gearbox to simulate the loads and speeds imposed in flight conditions. Mechanical energy returning from the tested gearbox is re-converted into electrical energy and returned to the DC link of the Drives. The returned electrical energy is topped-up by the Drives Supply Rectifier to make up for any losses. Up to 6MW of power can be needed to test a gearbox; recycling the power is thought to reduce this demand to 1 MW. While 6MW represents over 50 per cent of the power consumption of the Westland site, this recycling brings power consumption down to a level where it can be supported by the local grid without restrictions on operation.

The FTTR is said to provide accurate simulation of aircraft operating conditions and set-up takes less than an hour. According to ABB, these factors, combined with the low running costs and high reliability, ensure that this rig is one of the most advanced in the world. Housed in a custom-built 2, 000m2 building, the 180-tonne FTTR is more than 8 metres high standing on a 780-tonne seismic concrete block supported by 25 giant springs to isolate vibration. It is easily operated from a test control room using a sophisticated PC-based control system, where critical parameters such as speed and torque are constantly displayed. Some £6 million of the total investment was spent on developing the FTTR. WTL decided to undertake the investment, to meet new programme demands and replace some of its existing rigs, which are nearly 30 years old.

Details available from: ABB Automation Ltd, Tel: +44 (0)161 445 5555; Fax: +44 (0)161 445 6066; Website: http:\\www.abb.com/ motors&drives