Longitudinal equilibrium solutions for a towed aircraft and tow cable

Abstract

A series of flight tests involving a modified F-106 fighter aircraft towed behind a C-141 cargo aircraft was completed at NASA's Dry den Flight Research Center in February 1998, under the title of the Eclipse Project.1 This paper presents a numerical approach used to compute tow cable shapes and altitude offsets in the vertical plane for the towed configuration as a function of trimmed flight condition. Each solution was generated in two distinct steps. First the trim condition of the towed aircraft was found using an existing aerodynamic database. Correction factors for this database were extracted from data measured during untowed steady-state test glides. The second step was numerical integration of the differential equations governing cable shape in the presence of distributed aerodynamic and gravitational loads. The aircraft trim condition from the first part of the solution provided the initial conditions needed for the second part. Computational results for nominal test conditions are compared with flight test measurements of aircraft altitude offset, angle of attack, pitch angle, cable pitch angle, and cable tension. Altitude offsets were measured using highly accurate differential GPS receivers. Families of computed cable shapes are presented as a function of elevator deflection and flight path angle.