Andrew Doyle/BIRMINGHAM

A LOW COST FIBREBOARD used in the production of kitchen worktops, can be used as a substitute for high density aerospace foam, in the production of patterns for composite components, says UK aerospace engineers involved in the design of a jet-powered supersonic car (SSC), in which an attempt to break the world land-speed record will be made.

The UK-based Thrust SSC team needed to build large patterns for the production of the composite forward-body section of the Rolls-Royce Spey-powered car, but found the cost of aerospace foam prohibitive.

"Our carbonfibre sponsor, Cytec Aerospace, suggested we look to the marine industry for ideas," says Mike Horne, responsible for Thrust SSC's bodywork. "A boat builder in Cornwall explained that they had had some success with MDF [medium-density fibreboard]."

The team discovered that the patterns could be machined from 25mm-thick sheets of MDF joined together with epoxy glue, instead of solid blocks of aerospace foam. The patterns are used to form a "female" copy of the part, for use as a mould. The composite component is then vacuum-formed inside the mould, using pre-impregnated (prepreg) carbonfibre. An epoxy resin is released from the prepregs during curing in an autoclave, hardening the component.

Richard Noble, the man behind the Thrust SSC project, estimates that the required quantity of aerospace foam would have cost around £30,000 ($46,000), while the MDF board is worth £3,000-4,000.

According to Norman Kench, of Birmingham, UK-based Survirn Engineering, which machined the patterns for Thrust SSC, MDF costs around 10% less to machine, because the material can be outputted faster and less wear is applied to machine tools.

"At a time when aerospace [manufacturing] costs are being driven down, it must make sense to consider cutting composite patterns in MDF which Survirn has found is easy to cut, saves machine time and costs one-sixth as much as the expensive foams," says Noble.

Although MDF may be suited to the production of "one-off" or prototype composite parts, manufacturers believe that it is unlikely to be used for mass-produced parts. They say that MDF patterns are less suitable for re-use than aerospace foam, as they are more likely to degrade and change dimensionally.

Testing of the Thrust SSC, will start in the UK in mid-1996, before transferring to the Black Rock Desert, Nevada, USA. Royal Air Force Panavia Tornado pilot Andy Green will attempt to take the car through the sound barrier - Mach 1, calculated at 745mph (1,200km/h) for the intended site - in November 1996.

The car will initially be fitted with two 89kN (20,000lb)-thrust Spey 202s, although 111kN Spey 205s are available for when transonic testing is complete. The vehicle is designed to travel at speeds over 850mph.

Source: Flight International