SEA TRIALS of the first US Navy Northrop Grumman F-14 equipped with a digital flight-control system (DFCS) are due to begin at the end of this month.

The sea-trial phase is the last major test of the DFCS, which is expected to improve the F-14's safety levels, enhance shipboard recovery and improve its dog-fighting performance.

The system is expected to be retrofitted in all F-14A/Bs and Ds. The first aircraft to be equipped with the GEC-Marconi Avionics system are scheduled for initial operational clearance in June 1998.

The digital control system is derived from the fly-by-wire computers developed for the Eurofighter EF2000, and is being produced for the USN under an April 1996 production contract.

The award followed a successful initial proof-of-concept phase, conducted from July to December 1995, covering 21 sorties and 36.5h of test flying.

The upgrade was originally begun in 1992, although the final go-ahead was prompted in early 1996 by a spate of F-14 crashes, none of which, ironically, was directly connected with flight-control issues.

The DFCS initiative tackles several long-running F-14 flight-control problems. These include wing rock, roll reversal, and a susceptibility to flat spins and abrupt control-induced departures.

In addition, in power-approach conditions, the aircraft has suffered from significant adverse side-slip, non-linear roll response and a lightly dampened Dutch-roll characteristic. New control laws in the DFCS include Dutch-roll damping, a stick-to-rudder interconnect, automatic spin resistance and a spin-resistance function.

The Navy says that the new software "-greatly improves departure resistance. While attempting [spins], the aircraft rarely departs with the system and, when it does, the departures are generally benign, with recovery from forward stick alone and just occasionally differential rudder."

The aircraft now makes an "easy recovery" from inertia-coupled departures, which have been responsible for several F-14 crashes. Peak yaw rates entering the spin before the DFCS were up to 135í/s compared to "only 45í/s with the new system".

The system also produces tactical benefits. "Air-to-air tracking is improved, you can keep the gun sight on the target for longer, and roll response is improved", according to the Navy.

Approach-flying qualities have also improved, with modified spoiler-control producing reduced adverse side-slip and better capture of the runway centre line.

Source: Flight International