Comparative analysis of effects of hover control concept on V/STOL aircraft size.

Abstract

The design of a minimum size V/STOL aircraft to meet given mission requirements is directly influenced by the hover control concept selected and the control power requirements. Parametric studies were conducted on a lift-plus-lift-cruise variable sweep V/STOL fighter aircraft to indicate the aircraft weight penalty and control effectiveness associated with various hover control arrangements. These studies evaluated the effectiveness of three basic control systems: 1) engine bleed, 2) thrust modulation, 3) combined bleed and thrust modulation. Engine bleed systems included bleeding lift engines only, bleeding lift cruise engines only, or bleeding all engines. Both continuous and demand bleed systems were studied. Twenty control arrangements were evaluated for the normal power hover flight condition. Using unique digital computer models, aircraft size, engine size, and control effectiveness were parametrically determined as a function of percent engine bleed, vertical lift-to-weight ratio at takeoff, and hover control power requirements. Data was obtained for both singleaxis and simultaneous three-axis hover control power maneuver requirements. Comparison of the effectiveness of each control arrangement clearly indicated the most efficient system, i.e., one yielding a minimum size vehicle meeting both mission and hover control power requirements.