The UK Defence Research Agency (DRA) and Calspan, a US-based flight-test support company, are to develop the DRA's British Aerospace Harrier Vectored-thrust Aircraft Advanced Control (VAAC) tests into a flight-control development aircraft for the Joint Strike Fighter (JSF) project, it was revealed at the 41st Society of Experimental Test Pilots meeting in Beverly Hills, California, on 25-26 September.

The proposed conversion will build on research work being conducted by the DRA into flight- control technology for the UK's future short take-off and vertical landing (STOVL) recovery requirements. This will also include tests of new head-up-display guidance symbology and helmet-mounted displays for vertical shipboard landing in bad weather or night.

The two-seat Harrier is fitted with a digital fly-by-wire flight-control system connected to a standard flight-control system which allows a safety pilot to follow inputs from the front cockpit. Unlike other in-flight simulators such as those operated by Calspan, the control gains of the VAAC digital flight-control software can be adjusted, allowing the aircraft to be reconfigured in flight.

The aircraft is now in Phase II of a flight-test programme designed to reduce pilot workload, increase safety and provide carefree handling for future STOVL aircraft. Phase I, which ran from 1990-4, covered the approach and vertical-landing task with digital-control authority in the pitch axis only. This phase achieved a large workload reduction by demonstrating a unified approach to the automation of thrust vectoring.

Phase II began with initial clearance flights after modification of the VAAC Harrier by Cranfield University in the UK to include full digital control of the lateral and directional axes. A key aspect of the latest configuration is an independent monitor which disconnects automatically the controls of the rear cockpit and hands authority back to the safety pilot if it detects a problem. Most of the recent flying has been proving the system, which acts if it detects exceedences of the flight envelope, irregularities in control or a system failure.

The bulk of the clearance work was finished in August with the discovery that "-so far the monitor is not too restrictive", according to the test team. The current phase of flying will complete the flight-qualification evaluation and give Harrier and non-Harrier pilots a chance to assess the preferred flight-control methods. Options include whether to adopt automatic thrust vectoring, and whether to maintain manual height control with the left or right hand.

Source: Flight International