ENGINEERS from north Essex-based Fl�kt Woods have completed refurbishment work on what is believed to be the world's largest fans. The Colchester company won a contract to replace impellers as part of an upgrade of the giant S1MA wind tunnel at the ONERA aerospace research facility at Modane in France.

ENGINEERS from north Essex-based Fl�kt Woods have completed refurbishment work on what is believed to be the world's largest fans.

The Colchester company won a contract to replace impellers as part of an upgrade of the giant S1MA wind tunnel at the ONERA aerospace research facility at Modane in France.

Two counter-rotating fans, each 15 metres in diameter, enable scale models of proposed designs for aircraft or spacecraft to be tested for their aerodynamic behaviour at different wind speeds - up to the speed of sound - before the construction of full-sized prototypes.

Each impeller weighs 58 tonnes and requires 88 megaWatts of power, which is delivered - unusually - by a channelled waterfall 850 metres high.

Fl�kt Woods, which has built many of the largest fans in use around the world, including those used to ventilate a number of major road tunnels, won the contract with ONERA (Office National d'Etudes et de Recherches A�rospatiales) after demonstrating detailed solutions to overcome problems of wear and tear on the blades.

One suggestion included use of composites substitutes, which Fl�kt Woods calculated would offer significant advantages to metals due to the flexibility of selecting various combinations of glass, kevlar, carbon reinforcement and resin matrix.

However, because of the history of using metal and the cost implications of composites, the decision was taken to replace the existing steel fabricated blades with a new steel blade design, optimised to reduce peak stress level to half the previous level and using high strength steel in the blades construction, with double the original strength.

After nearly four years of extensive work, the project is now complete, with the supply and installation of new impellers. Energy savings of more than 10% have also been achieved as a result.