National Aeronatics & Space Administration|
1979 - 1985 & 1986 - 1987
Quote from NASA Dryden:
Grumman F-14 Tomcats have been involved in two main projects at NASA Dryden.
NASA 991, an F-14 Navy Tomcat designated the F-14 (1X), the 1X signifying that it was Grumman's experimental testbed, was used at Dryden between 1979 and 1985 in extensive high-angle-of-attack and spin-control-and-recovery tests.
The NASA/Navy program, which included 212 total flights, acheived considerable improvement in the F-14 high-angle-of-attack flying qualities, improved departure and spin resistance, and contributed to substantial improvements in reducing "wing rock," (i.e., tilting from one side to another), at high angles of attack.
The Navy had been experiencing inadvertant spin entries caused by the F-14's aileron rudder interconnect. The NASA/Navy/Grumman team developed and tested 4 different configurations of the aileron rudder interconnect to address the spin problem. These problems prompted the Navy to ask the manufacturer, Grumman, and NASA to investigate the issue.
The tail control surfaces on F-14s are known as "rolling tails", in that the aircraft does not have ailerons on the wings to control roll. Roll control is instead provided at low speeds by wing-mounted spoilers and at high speeds by differential horizontal stabilizer deflection. This configuration also produces side force, or yaw, which contributed to the inadvertant spin entries. This large tail configuration is to aid in takeoff from aircraft carriers, by providing more pitch moment.
NASA 991 had numerous special additions for high-angle-of-attack and spin-recovery research. These included a battery-powered auxiliary power unit, a flight test nose boom, and a special spin recovery system, consisting of forward mounted, hydraulically actuated canards and an emergency spin chute.
NASA's F-14 was first flown by NASA research pilots, but was later flown by Grumman, and by Navy test pilots from Patuxent River Naval Air Station (NAS). The Navy test flights with the spin research vehicle constituted the first program that incorporated air combat maneuvering in its test flights at Dryden. The Navy brought F-14s from Point Mugu and Miramar NAS in San Diego to test the new spin control laws in combat situations. Although the new control laws proved valuable, the Navy did not incorporate them into production F-14s until the F-14D, nearly 15 years later.
Einar Enevoldson, the NASA test pilot on the project, developed a maneuvering technique to aid in testing these new spin control laws. This maneuvering technique was later adopted for use in F-18 High Angle-of-Attack Research Vehicle (HARV) spin tests.
Among the 212 flights completed for this research project, the F-14 also tested a flush air data system, for gathering data about air speed; provided an updated aeromodel, which is currently in use on Navy F-14 training simulators; created natural laminar flow baseline data for many of NASA's later laminar flow programs; and tested low altitude, asymetric thrust.
F-14s were later used in laminar flow studies in the Variable Sweep Transition Flight Experiment program (VSTFE) on NASA's F-14 #834.
NASA 991 was delivered back to the Navy on September 6, 1985.
NASA 834, an F-14 Navy Tomcat, was used at Dryden in 1986 and 1987 in a program known as the Variable-Sweep Transition Flight Experiment. This program explored laminar flow on variable sweep aircraft at high subsonic speeds.
Flight transition data applicable to swept wings at high subsonic speeds was needed to make valid assessments of the potential for natural laminar flow or laminar flow control for future tranports of various sizes operating at various cruise speeds. NASA initiated the VSTFE program to help establish a boundary-layer transition database for use in laminar-flow wing design.
An F-14 aircraft was chosen as the carrier vehicle for the VSTFE program primarily because of its variable-sweep capability, Mach and Reynolds number capability, availiability, and favorable wing pressure distribution.
The variable sweep outer-panels of the F-14 aircraft were modified with natural laminar flow gloves to provide not only smooth surfaces but also airfoils that can produce a wide range of pressure distributions for which transition location can be determined at various flight conditions and sweep angles.
Glove I, installed on the upper surface of the left wing, was a "cleanup" or smoothing of the basic F-14 wing, while glove II was designed to provide specific pressure distributions at Mach 0.7.
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