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VFW 614: OLDIE USED FOR RESEARCH WORK

A late career for the VFW 614. The small twin-jet airliner out of German production, which took off for its first flight on July 14, 1971, was far ahead of its time, the airline industry not being ready for regional jets. The program was canceld after 19 aircraft were built. Today there are only five aircraft left.

In Germany, a VFW 614 has been in operation as a research aircraft with the German Aerospace Center (DLR). Another aircraft just enter a flight test program at DaimlerChrysler Aerospace Airgus in Bremen. The three aircraft which were operated by the German forces' flight department until just recently have been sold to an operator in Sweden.

For the industry and research community in Germany, the VFW 614 has become a vital tool in flight research. The aircraft operated by the DLR has accumulated approximately 1600 flying hours in aerospace research. DLR employs the aircraft as the Advanced Technologies Testing Aircraft System ATTAS.

ATTAS is a flying simulator and technology demonstrator which the DLR is primarily using in the research areas of flight control, flight guidance, flight characteristics and human-machine interface optimization. Along with its conventional mechanical flight control system the aircraft is fitted with a fly-by-wire flight control system on a second installation level.

While the right pilot workstation (the safety pilot's seat) is still equipped with the conventional control column, the left side ist equipped with a sidestick. The set-up of this aircraft is a unique platform for the evaluation of new technologies in realistic flight conditions. While the mechanical flight control system remained untouched for take-off, landing and safe flight operations, the research position with fly-by-wire system can be adapted very well to the various research experiments. In the past decade, the DLR has used this aircraft in a number of national and international projects.

In 1999, a comprehensive flight evaluation of new vision systems for approaches in bad visibility could be completed. First, the so called Synthetic Vision System (SVS) was evaluated. The project was a cooperation with the Technical University of Darmstad and, on the industry side, with VDO Luftfahrtgeräte and Dasa.

SVS is an entirely synthetic vision system. The system uses exact position data, for example derived from differential GPS. Based on stored terrain data, SVS then generates an artificial outside vision on the cockpit displays in real-time.

Another system is the so called EVS (Enhanced Vision System). Here the pilot gets an enhanced outside vision displayed in a head-up display. The picture is generated from data which come from forward looking infrared and millimeter-wave radar sensors. The HUD-picture is overlayed by the major flight data such as speed and altitude. This allows a quasi-visual landing approach which is independent from ground-based infrastructure.

ATTAS will be used this year for another project which focuses on the pilot integration into the flight loop. In the frame of the DLR research project EPIAS (Enhanced Pilot Information by Using Active Sidestick), the researchers plan to evaluate an active sidestick which has been developed together with the Technical University of Braunschweig.

Sidesticks are common technology in aviation since fly-by-wire flight control systems have been introduced. Since control inputs are not related via mechanical links from the cockpit, the need for the traditional control column has really vanished. A little grip with sensors that sense the inputs is enough. Such a system is standard on all of today's Airbus aircraft.

However, the problem of these so called passive sidesticks is that the pilots do not get a feedback from the aircraft. The movement of the passive stick is limited by dampers and springs and is de-coupled from the aircraft otherwise. Also the pilot and copilot sticks can not be coupled in such systems and there is no feedback from autopilot actions. Such a system also requires flight envelope protection to protect the aircraft from wrong control inputs.

Active sidesticks are to overcome these problems and are designed to put the pilot back in the loop. Such systems are fitted with a motor or actuating system which generate realistic stick forces depending on the aircraft's situation. However, today's active sidestick designs require complex mechanics with a motor, a transmission and a coupling.

This is not the case with the magnetic sidestick (MAGSI) that DLR is developing. MAGSI features a stick with a permanent magneto in the gimbal that rests between two poles with spools. The computer-generated regulation of the voltage in the spools allows the creation of a very realistic aircraft feel. In the safety-relevant case that the stickforce actuator looses its electricity, MAGSI automatically turns into a passive system. Acceptable stick forces are generated just by the sticks permanent magneto trying to align with the two poles. Such a magnetic system would be much lighter than any of today's systems.

Along with human-machine interface issues, ATTAS is mainly used to evaluate flight control systems and their associated control laws. Today, electronic flight control systems have reached a high technological and safety standard, based on 20 years of experience. The development of a any new flight control system for airliners is very cost-intensive. Due to this the goal of future research must focus on generating more efficient and such cost efficient development processes for the design of such systems.

In the frame of the European Commission's project REAL (Robust and Efficient Autopilot Control Laws Design) the DLR is planning the design of an automatic landing system with the focus being on the development process. The goal is to re-design the system in a short period of time for use with the ATTAS. At the end of the project, the control laws are to be verified in-flight with ATTAS.

In this program, DLR can use its experiences from a program that was conducted in the mid-nineties in cooperation with Dasa Airbus (DA). Back then, Dasa utilized the ATTAS in the SAFIR project (Small Airliner Flight Control Law Investigation and Refinement) to research and verify control laws for a 100-seat (or less) airliner with an electronic flight control system.

Dasa wanted to develop an electronic flight control system (EFCS) which would allow lower production and development costs in a later application, along with shorter development times and a higher dispatch reliability.

Still, Dasa did not want to question the traditional competence of its French Airbus partner, who is normally responsible for the flight control system of Airbus aircraft. The main goal, says DA's vice president development, Dr. Wolfgang Schneider, is to keep up the systems capability of Dasa and to gain competence for entire aircraft systems. The goal to acquire a certification for this EFCS required Dasa to find its own technology demonstrator since, if done with ATTAS, would have blocked DLR's research jet for years. With quite an effort, Dasa reactivated a stored VFW 614 which had been used over 16 years as a training object for new aerospace technicians.

Meanwhile the new EFCS has accomplished its first flight. The technology demonstrator took off in August of 1999 with its new high-tech interior. At the core of the EFCS is a primary flight control computer from Bodenseewerk Gerätetechnik with and integrated modular avionics architecture, the first safety-relevant application of such a technology in an airliner.

In the frame of the integration of the fly-by-wire system, one of the wing hydraulic systems was taken out and replaced with smart actuators for aileron and spoilers. The control units of the new actuators are right on the actuators. Also, rudder and elevator actuators have been replaced. A hydraulic power package was integrated decentrally in the aircraft tail.

The flight-evaluation of the EFCS is scheduled to last until mid-2000, then using the full control laws of the system: "We will then see this as a verification that the new technology can be employed in production aircraft", says Wolfgang Scheider.

From page 84 of FLUG REVUE 4/2000