The F-14s’ spin issue made it difficult for them to engage in a dogfight successfully
A line of post-Vietnam fighters began with the Grumman F-14 Tomcat and included the F-15 Eagle, F-16 Fighting Falcon, and F-18 Hornet.
These aircraft, known as “teen fighters,” were built to be maneuverable in air-to-air combat.
Since the F-14s tended to diverge from a controlled flight at the high angles of attack that typically occur in close-range engagements, this caused challenges for its ability to engage successfully in a dogfight. After being introduced to the fleet for the first time in October 1972, the Navy’s F-14s started to suffer from out-of-control mishaps. It became out that the aircraft’s analog automatic flight-control system had a straightforward control-law architecture that, under specific flight conditions, induced departures from the desired flight path. A number of aircraft and crews were lost as a result of the control system’s failure to give the pilots complete control authority (flight-control-surface deflections) for recovering from spins and other departures.
According to Ruby Calzada on NASA.gov, a collaborative NASA/Navy/Grumman program used NASA 991—a U.S. Navy Tomcat with serial number 157991 that was actually designated “F-14 (1X)” and served as Grumman’s experimental testbed—at Dryden Flight Research Center between 1979 and 1985 to address this issue. The F-14’s handling at high angles of attack, spin resistance, “wing rocking” (i.e., tilting from side to side), and aircraft recovery when it deviated from the controlled flight were all examined (e.g., entered a spin).
As seen in the photos, NASA 991 was equipped with a number of unique modifications for high-angle-of-attack and spin-recovery research. These modifications included a battery-powered auxiliary power unit, a flight test nose boom, and a unique spin recovery system that included forward-mounted, hydraulically actuated canards and an emergency spin chute. The NASA/Navy/Grumman team successfully limited departures and provided recoveries from spins by developing new control laws with an aileron/rudder interconnect (ARI).
The F-14 with the new control laws proved to be “very responsive and maneuverable above 30 degrees angle-of-attack, with no abrupt departure or spin tendencies.”
Among the 212 flights completed for this research project, Calzada claims that the F-14 tested a flush air data system for gathering information about airspeed, provided an updated aero model, which was used on Navy F-14 training simulators, created baseline data for natural laminar flow for many of NASA’s later laminar flow programs, and tested low altitude, asymmetric thrust.
Despite the program’s undeniable success, the Navy delayed implementing the new control regulations in its F-14s due to a lack of resources. Mishaps with the Tomcats kept happening as a result. Finally, the Navy hired GEC Marconi Avionics of the UK to implement the control laws into a digital flight-control system with minimal changes. This system was installed in fleet F-14Ds aboard the USS Kitty Hawk and USS Roosevelt in March 1999, reducing the risk of uncontrollable flight and significantly enhancing the safety of powered approaches to carrier landings. The NASA Exceptional Service Medal had already been awarded to Dryden research pilot Einar Enevoldson in 1980 for his work as a project pilot on the F-14 stall and spin resistance tests.
Instead, the Variable-Sweep Transition Flight Experiment at Dryden in 1986 and 1987 employed NASA 834, another U.S. Navy F-14 Tomcat (VSTFE). This program investigated high subsonic laminar flow on variable-sweep aircraft. Because of its variable-sweep capability, Mach and Reynolds number capability, availability, and advantageous wing pressure distribution, an F-14 aircraft was selected as the carrier vehicle for the VSTFE program.
Natural laminar flow gloves were added to the F-14’s variable-sweep outer panels so that they would not only have smooth surfaces but also airfoils with a wide variety of pressure distributions whose transition points could be identified under different flight situations and sweep angles. Glove II was created to produce specific pressure distributions at Mach 0.7, whereas Glove I was designed to “clean up” or smooth the basic F-14 wing (seen mounted on the upper surface of the left wing in the image above).
A research program on the NASA 848 F-16XL, a laminar flow experiment that uses a wing-mounted panel with millions of tiny laser-cut holes to pull out turbulent boundary layer air with a suction pump, continues laminar flow research at Dryden.
Source: NASA; Photo by NASA
