Flight Research: Problems Encountered and What They Should Teach Us (Milton O. Thompson, NASA SP-2000-4522)

J. D. Hunley's foreword says this text began as 'an untitled rough draft' in Milton Thompson's papers, written around 1974 and never edited, so it runs in the present tense. Thompson flew the X-15 and the lifting bodies for the research center at Edwards. The draft sorts the problems those programs met into aerodynamic, environmental and hardware kinds. On the HL-10's first flight the airflow separated at the junction of the tip fin and fuselage, and the pilot lost nearly all pitch and roll control. The X-15 carried subsystems that were new and pushed the state of the art, and most of its trouble came from them.

The HL-10 section turns on two wind-tunnel results. The 16-inch model had measured elevon effectiveness about right. The full-scale tunnel used the actual flight vehicle at Reynolds numbers closer to flight conditions, and Thompson writes 'we had chosen to believe the full-scale wind-tunnel results.' The vehicle recovered by itself that time.

Early in the draft he counts over 5,000 research flights, three aircraft lost and two pilots. Hunley supplies a history of the center from 1946 to 1979 ahead of Thompson's text.