The Royal Aeronautical Society Aerodynamics Group organised a CEAS European Forum on High Lift and Separation Control which was held at the University of Bath on 29-31 March 1995. This paper gives an idea of the scope of the Forum and of the main conclusions that emerged and it is followed in this special issue of The Aeronautical Journalby four papers that were invited for the Forum.

The process of designing the Boeing 777 high lift system is described. Particular attention is given to design constraints and examples are given of the trade studies completed. The theoretical design tools and experimental test program are described. A survey of the high lift elements is presented and flight test results are compared with predictions.

The aerodynamic performance of a multi-element high-lift system has a critical influence on the direct operating cost of a subsonic civil transport aircraft. A thorough understanding of the aerodynamic characteristics of these multi-element aerofoils and wings allows aircraft companies to design and build more competitive aircraft with high-lift systems that are less complex and lighter for given high-lift performance or that have improved lift and drag characteristics for given system complexity and weight. Flight experiments on NASA Langley's B737-100 aircraft have been conducted to further enhance the understanding of the complex flows about multi-element high-lift systems at full-scale flight conditions. In this paper, an overview of the flight program is provided, followed by highlights of experimental results and computational analysis. Measurements included surface pressures on the slats, main element and flap elements using flush pressure ports and pressure belts, surface shear stresses using Preston tubes, off-surface velocity distributions using boundary layer/wake rakes, aeroelastic deformations of the flap elements using an optical positioning system, and boundary layer transition detection using hot-film anemometers and an infrared imaging system. Boundary layer transition measurements on the slat using hot-film sensors are correlated with the flow visualisation results from an infrared imaging technique. Extensive application of several computational techniques and comparisons with flight measurements are shown for a limited number of cases. This program has generated an extensive set of data, much of which are still being analysed.

Prior to the adoption of modern flybywire high authority flight control systems, the usable lift or angle of attack was usually dictated by the wing stall and subsequent loss of control of the aircraft.

With the advent of the high authority FCS, with high levels of integrity, the designer of modern combat aircraft faces the possibility of providing good levels of aircraft control up to and well beyond the AoA at which maximum lift or loss of control would have occurred in the past. Further, the use of such control systems has allowed maximum advantage to be taken of control configured vehicle technology to enhance the performance of the aircraft within the conventional angle of attack range.

This paper provides a review of the experience which has been gathered within BAe Military Aircraft, Warton, in the use and benefits of these technologies with regard to the high AoA capability and impact on maximum usable lift. Examples are drawn from the Tornado, Jaguar FBW and EAP aircraft programmes, all of which have employed flybywire control, to some degree or other, combined with varying degrees of CCV technology, leading to their adoption on the Eurofighter 2000 programme.

In doing this, some of the engineering compromises which the modern aircraft designer faces in achieving the customer required levels of aircraft performance will be addressed, together with the outcome which has satisfied these purposes in the particular example considered. In particular, the power of the modern FCS places an increased reliance on the knowledge of the aerodynamics of the aircraft, around which the FCS must be designed. This raises particular challenges in the increased AoA ranges which associate with the maximum lift of these high performance configurations.

The paper concludes with an indication of the developments in technology which are evolving and which will lead to further advances and increased capability combat aircraft in future years.

High-lift systems have to provide adequate low speed performance in terms of takeoff and landing lengths, approach speed, climb rate and community noise. Even if the performance of these systems has been continuously improved during the years, there are still some possibilities for further improvements.

ONERA has been involved for a long time in research on high-lift systems for transport aircraft. This research has provided valuable results in the following areas:

• ● The knowledge of the dominant flow processes involved for 2D and 3D geometries. In particular the stall mechanism, Reynolds and Mach number effects as well as sweep effects have been studied by performing detailed experiments.

• ● The development of 2D analysis and design codes which have been extensively calibrated with experimental data and are used with confidence for practical applications.

• ● The design and testing of various high-lift systems which provide manufacturers with data for their own designs.

The paper summarises these activities and presents some typical results. Future trends for research on high-lift systems at ONERA are also given.