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VECTOR TO TARGET SHORT LANDINGS

Almost 10 years after its maiden flight in October 1990 the X-31 is poised to take off again in August for a new test programme. The test-bed built by Dasa and Rockwell International (now Boeing) was shipped from Palmdale, California to the US Navy's Patuxent River test site on the east coast of the USA on 10 April in a C-5 Galaxy. Final preparation of the VECTOR campaign will take place shortly.

VECTOR stands for Vectoring Extremely short take-off and landing Control and Tailless Operational Research, and is being used to research extremely short take-off and landing capability and also the aerodynamic characteristics of tailless flight using integrated thrust-vector control. However, it will not be possible to test all aspects of the technology in the air, since, now that Sweden has pulled out of the programme, the available resources have shrunk to little more than $50 million (DM105 million).

Until recently the US Navy's Air Systems Command and the German Federal Office of Defence Technology and Procurement (BWB) had hoped that the Scandinavians would take part in the study, which contributed to a programme delay. Formal definition studies for the planned trials have actually been under way since February 1998, and the memorandum of understanding between Germany and the USA was concluded in April 1999. However, official contracts with Boeing and Dasa were only signed, respectively, in December 1999 and April 2000.

The VECTOR programme which has now been given the go-ahead will run to February 2002. As a first step, check-out flights will be performed by a US Navy pilot and another pilot from WTD 61, the German armed forces establishment for flight test and evaluation. The Advanced Air Data System (AADS) developed in Germany will then be installed. This advanced air data sensor should provide accurate data even at high angles of attack. Above all, however, it is to be inserted straight into the nose and is expected to result in a lower radar cross-section during operational use. 11 tiny Nord-Micro pressure gauges will record the data which is converted straight into digital data and then passed to the airborne computer.

After that, calibration of the AADS will run in parallel to the first ESTOL flight tests. Approaches with an angle of attack of 40* will be tested, subsequently rising to 70*, although at first these will only be simulated at a safe altitude. During these trials, the VECTOR partners expect the approach speed to be reduced from 295 km/h (159 kt) to less than 180 km/h (97 kt), which should make significantly shorter stopping distances possible.

The results of the trials will be of especial interest to the US Navy, since they open up the possibility of reducing the head wind components over the aircraft carrier deck that are required for take-off and landing, i.e. so that the ship no longer needs to sail at full speed against the wind. An increase in landing weight should also be feasible, enabling expensive, unused guided missiles to be brought back instead of having to be jettisoned. All in all, the wear and tear on the aircraft should be lower.

Before the X-31 can try out short landings for real, further modification of the aircraft is necessary. In particular, a highly accurate navigation system based on differential GPS and an inertial platform must be installed. Since with a high angle of attack the pilot cannot see the landing strip until the very last moment, the approach will have to be automated, and a new set of symbology will certainly be needed in the cockpit. These tests are scheduled to take place in the fourth quarter of 2001.

Before that researchers will have to make do with theoretical studies of the effects of reducing the vertical tail surface or doing away with it altogether. This modification is of interest because of the likely resulting reduction in radar cross-section, but there are no funds available for a practical trial. Nevertheless, all the participants should obtain useful results from the VECTOR programme which can be applied to future applications. And the X-31 will be able to better still further the record it has already set as the most frequently flown X aircraft (to date it has flown 580 times).

From page 54 of FLUG REVUE 7/2000