Air International 1988-12
D.Brown - Variable Stability: A valued flight test tool
This variable-stability Lockheed NT-33A has been employed since 1958 on a variety of flying qualities research programmes and aircraft simulations, it was used to evaluate flying qualities of the F-15, YF-16, YF-17 and F/A-18 before their respective first flights, and the AFTI/F-16 was also simulated. The NT-33A has a fully programmable Head-Up Display and associated sensors to examine the interaction of display characteristics and flying qualities. In 1977, a joint US Navy/US Air Force programme known as Display Evaluation Flight Test (DEFT) started using this research capability. The aircraft is currently in use at the USN and USAF Test Pilot Schools.
The Convair NC-131H TIFS, owned by the USAF, has been used in a variety of aircraft programmes since 1969, typically to assess large aircraft handling qualities. It is at present configured as an Avionics Systems Test Training Aircraft, used for radar and FLIR testing at the USAF Test Pilot School.
The Convair NC-131H Total In-Flight Simulator incorporates a sophisticated computerised flight control system that embraces the conventional ailerons, rudder and elevators as well as the side-force generators (vertical surfaces at mid-span) and direct-lift flaps.
The first Calspan variable-stability Learjet flies over the Navy Test Pilot School at Patuxent River. The Calspan Learjet 23 is used to demonstrate the effect of changing damping ratios, dutch roll and other characteristics.
The Learjet N101VS flown by the author for AIR INTERNATIONAL has a Variable Stability System which can have a large number of stability and control characteristics programmed into it. Characteristics can be selected either singly or in combinations to give many configurations, a large number of which can be demonstrated during a single flight.
The cockpit of the Learjet N101VS has a conventional yoke on the left for use by the safety pilot, and a fighter-type stick on the right for the evaluation or test pilot. The central console has a configuration control system (CCS) panel under transparent cover.
The Learjet's configuration control system panel includes a finger-touch keyboard (lower right corner) to enter the selected configuration.
Three indicators on the main panel of the Learjet show the limits for pitch, roll and yaw. If the limits are exceeded, the VSS will automatically trip out.