Laminar flow control by suction as applied to the x-21a airplane

Abstract

After many years of preparatory work in wind-tunnel testing and analysis, the X-21A, an 80,000-lb jet airplane with a laminar flow control wing, was designed and built by Northrop. Laminar flow control reduces wake drag on the wing by surface suction. The suction system consists of turbocompressor units that remove boundary-layer air from the wing surface by many fine slots in the skin. Laminar flow on the outer halves of the wing was established very early in the flight test program and, after eliminating spread of turbulent disturbances along the attachment (stagnation) line, essentially the whole possible area was made laminar with predicted suction quantities. The gain due to laminar flow control on the wing of a big, long-range transport airplane is expected to be 35% in range at the same pay load and a similar percentage in pay load at the same range.