X-38 Aerodynamics During
Rapid Pitch Up
Jason M. Merret and Michael B. Bragg
University of Illinois, Urbana, Illinois, 61801
ABSTRACT
A series of experiments were conducted on the
extreme high-angle-of-attack aerodynamics of a model of the X-38 reentry
vehicle. These tests were conducted at the University of Illinois low-speed
wind tunnel. The 4.7% scale model was constructed in three parts using stereolithography
and was sting mounted with a 6-component strain gauge balance to measure
the forces and moments. The model positioning system allowed the model to
vary in angle of attack from –7o to 95o in three separate
angle of attack ranges. The effects of Reynolds number, transition, and flow
control were all investigated. Reynolds number, based on body length, was
varied from 1.0 x 106 to 1.5 x 106. In addition to
the force measurement, pressure data were collected using 99 taps on the
body. Surface oil flow visualization was used to define the surface flowfield.
The forces and moments collected in the analysis revealed a sharp change
in the side force at extremely high angles of attack. Although the position
and shape of the spike varied with Reynolds number and boundary-layer state,
the change was always apparent. The single strake case demonstrated that
the clean and tripped side force change was not insignificant. The dual strake
case demonstrated that the phenomena could be controlled by controlling the
separation on the side of the forebody.