The Royal Aeronautical Society Aerodynamics Grouporganised a CEAS European Forum on High Lift andSeparation Control which was held at the Universityof Bath on 29-31 March 1995. This paper gives anidea of the scope of the Forum and of the mainconclusions that emerged and it is followed in thisspecial issue of The AeronauticalJournalby four papers that were invitedfor the Forum.

The process of designing the Boeing 777 high liftsystem is described. Particular attention is givento design constraints and examples are given of thetrade studies completed. The theoretical designtools and experimental test program are described. Asurvey of the high lift elements is presented andflight test results are compared withpredictions.

The aerodynamic performance of a multi-elementhigh-lift system has a critical influence on thedirect operating cost of a subsonic civil transportaircraft. A thorough understanding of theaerodynamic characteristics of these multi-elementaerofoils and wings allows aircraft companies todesign and build more competitive aircraft withhigh-lift systems that are less complex and lighterfor given high-lift performance or that haveimproved lift and drag characteristics for givensystem complexity and weight. Flight experiments onNASA Langley's B737-100 aircraft have been conductedto further enhance the understanding of the complexflows about multi-element high-lift systems atfull-scale flight conditions. In this paper, anoverview of the flight program is provided, followedby highlights of experimental results andcomputational analysis. Measurements includedsurface pressures on the slats, main element andflap elements using flush pressure ports andpressure belts, surface shear stresses using Prestontubes, off-surface velocity distributions usingboundary layer/wake rakes, aeroelastic deformationsof the flap elements using an optical positioningsystem, and boundary layer transition detectionusing hot-film anemometers and an infrared imagingsystem. Boundary layer transition measurements onthe slat using hot-film sensors are correlated withthe flow visualisation results from an infraredimaging technique. Extensive application of severalcomputational techniques and comparisons with flightmeasurements are shown for a limited number ofcases. This program has generated an extensive setof data, much of which are still being analysed.

Prior to the adoption of modern flybywire highauthority flight control systems, the usable lift orangle of attack was usually dictated by the wingstall and subsequent loss of control of theaircraft.

With the advent of the high authority FCS, with highlevels of integrity, the designer of modern combataircraft faces the possibility of providing goodlevels of aircraft control up to and well beyond theAoA at which maximum lift or loss of control wouldhave occurred in the past. Further, the use of suchcontrol systems has allowed maximum advantage to betaken of control configured vehicle technology toenhance the performance of the aircraft within theconventional angle of attack range.

This paper provides a review of the experience whichhas been gathered within BAe Military Aircraft,Warton, in the use and benefits of thesetechnologies with regard to the high AoA capabilityand impact on maximum usable lift. Examples aredrawn from the Tornado, Jaguar FBW and EAP aircraftprogrammes, all of which have employed flybywirecontrol, to some degree or other, combined withvarying degrees of CCV technology, leading to theiradoption on the Eurofighter 2000 programme.

In doing this, some of the engineering compromiseswhich the modern aircraft designer faces inachieving the customer required levels of aircraftperformance will be addressed, together with theoutcome which has satisfied these purposes in theparticular example considered. In particular, thepower of the modern FCS places an increased relianceon the knowledge of the aerodynamics of theaircraft, around which the FCS must be designed.This raises particular challenges in the increasedAoA ranges which associate with the maximum lift ofthese high performance configurations.

The paper concludes with an indication of thedevelopments in technology which are evolving andwhich will lead to further advances and increasedcapability combat aircraft in future years.

High-lift systems have to provide adequate low speedperformance in terms of takeoff and landing lengths,approach speed, climb rate and community noise. Evenif the performance of these systems has beencontinuously improved during the years, there arestill some possibilities for furtherimprovements.

ONERA has been involved for a long time in research onhigh-lift systems for transport aircraft. Thisresearch has provided valuable results in thefollowing areas:

• ● The knowledge of the dominant flow processesinvolved for 2D and 3D geometries. In particularthe stall mechanism, Reynolds and Mach numbereffects as well as sweep effects have been studiedby performing detailed experiments.

• ● The development of 2D analysis and designcodes which have been extensively calibrated withexperimental data and are used with confidence forpractical applications.

• ● The design and testing of various high-liftsystems which provide manufacturers with data fortheir own designs.

The paper summarises these activities and presents sometypical results. Future trends for research onhigh-lift systems at ONERA are also given.