Ian Sheppard/LONDON

Boeing has started to produce F-15 ailerons based on a new structural design concept which was pioneered by BFGoodrich's Tolo division.

The Grid-Lock process reduces such assemblies down to two machined parts bonded together. The design replaces the multi-piece, honeycomb panel construction on the fighter, which has been plagued by ingress of moisture. This can lead to corrosion and disbonding as early as one year after its entry into service, after having to withstand in-flight temperatures of over 150íC and vibration levels of around 168dB, says Tolo.

To cope with the moisture the new structure has vents and drains, rather than being sealed. For acoustic damping, integral skin stiffeners are featured between each rib of the structure.

The key to Grid-Lock is in its advanced machine tools which allow it to produce aluminium structures with metal removal rates up to 131cm3/kW/min (6in3/ hp/min) down to wall thicknesses of 0.5mm with 0.015mm accuracy and 0.008mm repeatability.

In late 1997 Tolo installed a high-speed Flexible Machining Center (FMC), produced by UK firm Marwin Production Systems, which Tolo believes is "one-of-a-kind". The FMC has spindle speeds of up to 40,000RPM and feed rates of over 3m a minute, and automatically loads or unloads parts up to 1.22 x 2.13m under 4min.

A similar machine has now been installed at Boeing's Philadelphia production plant, says Tolo. Terry Rogers, F-15 programme manager with Irvine, California-based Tolo, says Boeing is incorporating Grid-Lock ailerons on its next F-15 upgrade, known as E210, which is due to be flown next April. Other Grid-Lock features will include the horizontal aileron fairings, vertical stabiliser and wing flaps.

Tolo is also pushing the technology towards new applications, having already undertaken a first civil application for rigid cargo bulkheads for FedEx McDonnell Douglas DC-10s. It has licensed Grid-Lock to Cyclone Aviation of Israel, which produced some original F-15 ailerons for Boeing and is now looking at applying the technique to the Israel Aircraft Industries' Galaxy business jet.

Canada's Spar Aerospace is the only other licensee, and is starting to apply the technique to building satellite structures. Rogers says Tolo is"-discussing licensing with several other companies". The US Government is also looking at a redesign of the "ruddervator boom" used by Boeing KC-135 tankers for refuelling, he adds.

Source: Flight International