Mathematics

(Steady ) subsonic flow problems arc mainly of elliptic type in both the inviscid and viscous pans, which means that functions and all denvatives arc continuous. Only the invtscid Euler equations allow for discontinuities normal to the path (stream) line. Methods are on the develop­ment level as available for subsonic aircraft. Similar to subsonic aircraft technology, extremely complex flow separation is not yet really understood

5.3.2 Tasks

At take-off. it is necessary to

• improve lift

• maintain control

• improve L/D by reduction of drag; whereas at landing it is required to

• improve lift

• increase drag, possibly by drag control devices

• guarantee handling qualities, especially when using partially separated flow