The purpose of a wind tunnel is to simulate flight, but in the
conventional tunnel the models of fullscale aircraft are
attached to supports so that aerodynamic forces can be measured.
The models are not free. A plane's maneuverability cannot be
gauged completely with these restrictions on motion. Since full-
scale aircraft are expensive to build, test fly, and modify-to
say nothing of the possible loss of test pilots-Langley
engineers decided to build a free-flight wind tunnel. The basic
idea was to let a model glide in a wind tunnel that is actually
tilted at the aircraft's glide angle. Thus the unpowered model,
nose tilted down at its glide angle, remains stationary and
horizontal in the rising airstream of the tilted tunnel, much
like a hawk or buzzard hovers in air currents. Maneuverability
and flight performance are tested as a "pilot" outside the wind
tunnel manipulates the model's control surfaces via electrical
signals sent through thin wires trailing behind the model. Two
of these tillable free-fligh