Thrust Vectoring In The Real World

Editor's Notes: This article appeared in the July 1994 issue of Code One Magazine. Subscribers to e-Code One get access to MATV video.

"One's ready."

"Two's ready."

"Three's ready."

"Turn in."

"Fight's on!"

This series of radio calls became a familiar prelude to some unique aerial combat encounters last November [1993] as some of USAF's best fighter pilots flew no-holds-barred fights in and against an F-16 like no other in the world—one with a thrust-vectoring engine nozzle. Their purpose: to test the tactical utility of thrust vectoring and post-stall maneuvering.

The multi-axis thrust-vectoring F-16 had already impressed a small group of Lockheed and USAF test pilots during its initial envelope expansion and development flight testing. In only four months, the airplane, previously limited to twenty-five degrees angle of attack, was cleared to perform such maneuvers as the Cobra, J-turn, and helicopter to unlimited AOAs. But whether this capability would have real tactical utility was left for the operational phase of the test program.

Critics of post-stall maneuvering argue that fighters should never get slow. They equate low speed, regardless of agility, with presenting an easy target. Proponents argue that vectoring offers a decided agility advantage as aerial encounters progress and combatants become slower. The debate has been mostly theoretical.

That's why the pilots from the 422nd Test and Evaluation Squadron at Nellis AFB were called in to fly the F-16/MATV. The 422nd tests and develops tactics for new equipment and systems for operational F-16, F-15, A-10, and F-4G squadrons. Typically, the squadron performs this operational testing after the folks at Edwards AFB (and a few other test sites) complete developmental testing.

The 422nd chose two of its top F-16 pilots, Maj. Jay Pearsall and Capt. Jim Henderson, to fly in and against the F-16/MATV. Pearsall has over 2,400 hours in the F-16. He has completed F-16 tours at Kunsan, Luke, and Spangdahlem. Besides completing several operational tours in the F-16, Henderson, who has 1,900 hours in the F-16, also served as an F-16 instructor pilot. Both pilots are graduates of the USAF's rigorous Fighter Weapons School.

Pearsall and Henderson participated in the early planning stages of the program and then flew the F-16/MATV soon after the envelope was cleared by the F-16 Combined Test Force at Edwards. The CTF consists of Lockheed, General Electric, and USAF test pilots, engineers, mechanics, and technicians. Thanks to these people and a great design team, the envelope expansion phase was so successful that no restrictions were placed on the aircraft for the operational phase.

However, the 422nd pilots were asked to keep the throttle at military power or higher when flying above the Category I limiter (above twenty-five degrees AOA). Doing so would keep the thrust and the resulting vectoring force high. (Throttle chops to idle were tested earlier in the flight test program and showed no problems other than reducing the vectoring force.) The altitude floor for the air-to-air engagements was raised from the normal 10,000 feet to 20,000 feet as an added safety precaution for an aircraft with a prototype system.

The 422nd pilots rotated between MATV and the bandit or aggressor aircraft, which were F-16 Block 32 aircraft from the 422nd Squadron. The pilots flew one-vs-one engagements first. The weapons simulated during the evaluation were the F-16's standard gun with increased range PGU-28 bullets, AIM-9Ms, and AIM-120s.

Throughout their evaluation, the 422nd pilots were encouraged to fight their best BFM (basic fighter maneuvers). Each engagement was no duck shoot. The goal was to get a no-kidding reality check on the usefulness of thrust vectoring.

The one-vs-one engagements started from offensive and defensive perches (positions in trail or in lead of the bandit) as well as from neutral or head-on passes. Initial speeds ranged from 435 knots down to 250 knots. The lower speeds were used to represent a fight that had already progressed through several turns.

The F-16 already possesses awesome maneuvering characteristics. But vectoring allowed the offensive pilot to get a quicker kill, and it helped eliminate some of the common mistakes of overshooting or getting stuck in lag (a situation in which the aircraft can't quite get its nose onto the bandit because of the AOA limiter).

The bandit was still able to shoot at the airplane, but the shots had a lower probability of kill because the F-16/MATV was more elusive than a standard F-16. In addition, the known ability of the F-16/MATV to use post-stall maneuvering caused the attacking pilot to feel somewhat defensive and thereby modify his tactics to guard against any real, or perceived, threat from the thrust-vectoring jet.

From a defensive position, thrust vectoring allowed the F-16/MATV to survive longer. The high-speed neutral one-vs-one engagements displayed the benefits of the F-16 limiter. The limiter allows the pilot to maintain the aircraft's energy in the turns by keeping the airplane out of the post-stall region, where drag is dramatically higher. If the MATV pilot employed post-stall maneuvering too early or at the wrong time, he would indeed slow down too fast and the bandit could gain an advantage. However, thrust vectoring allowed the F-16 to employ that portion of the flight envelope between the normal AOA limiter and the AOA for maximum lift (around thirty-five degrees AOA). As a result, the MATV pilot could take advantage of the F-16's maximum turn capability.

Thrust vectoring and post-stall maneuvering did improve the F-16's air-to-air capability as airspeeds decreased and as the one-vs-one neutral setups progressed to offensive or defensive positions. Of course, the neutral setups were against another F-16 with good vertical capability. Against a dissimilar aircraft without such a high thrust-to-weight ratio, the F-16/MATV would have a distinct advantage because it could exploit post-stall maneuvering earlier in the fight.

For the one-vs-two engagements, the 422nd sent Capt. Dave Dodson as a dedicated bandit. Dodson, with over 1,000 hours of F-16 flying time, has a background that makes him a most formidable adversary. It includes a tour flying nothing but air-to-air engagements in the F-15C and a tour as a dedicated F-5 and F-16 aggressor. Like Pearsall and Henderson, Dodson is also a graduate of the USAF Fighter Weapons School.

In the one-vs-two engagements, Dodson flew exclusively as an adversary against the F-16/MATV while Pearsall and Henderson switched between the adversary and the front seat of the F-16/MATV. The three pilots flew a total of sixty-two one-vs-two aerial engagements.

In these encounters, the bandits tried to send the wingman high to gain an advantage in the fight-along with trying everything else in the fighter tactics handbook. Their strategy was to attack the F-16/MATV from above while it countered an aggressive lead bandit. Employing this strategy successfully would support the critics' main argument against post-stall maneuvering. That is, any advantage offered by post-stall capability could be easily overcome by multiple bandits.

The actual results, however, may surprise these critics. The MATV aircraft was able to hold its own in these lopsided contests, and it was often impressively offensive. Post-stall maneuvering forced the bandits to modify their tactics and to reduce their mutual support to counter the thrust-vectoring opponent. Although the bandit wingman tried going high, the F-16/MATV would use its post-stall capability to get a shot at or, at least, threaten the high wingman before continuing to fight the lead bandit.

The evaluation also showed that the gun (with the increased-range PGU-28 bullets) was the weapon used most of the time because of the close ranges and short reaction times associated with the dogfights. Missiles were used only a portion of the time. And most of the missile shots were fired within the standard AOA envelopes for the missiles. (High-AOA missiles are in development. In fact, a specially instrumented AIM-9M was carried on the F-16/MATV's wingtip during several flights to gather vibration and loads data on the impact of the high-AOA environment on the missile itself.)

The pilots of the 422nd commented that while thrust vectoring would never be a substitute for a good understanding of basic air-to-air fighting skills, the capability significantly improves the airplane's lethality.

The F-16 would also benefit from the ability to carry air-to-air missile loadings presently limited to around fifteen degrees AOA (asymmetric missiles, for example) out to the maximum lift AOA of thirty-five degrees and beyond. This advantage, however, was not specifically addressed in the flight test program.

So it appears that the debate over thrust vectoring has moved from the chalkboard to the cockpit. Whether this capability, which is designed into the F-22 Air Superiority Fighter, will find its way into future versions of the F-16 remains to be seen. Those who have witnessed what this capability can do in the air, however, have been favorably impressed.

F-16 MATV In Retrospect

By James Sergeant

 The F-16 MATV demonstrated significant increases in air-to-air maneuver capability by expanding the usable F-16 flight envelope from the current 25 degrees AOA to beyond eighty degrees, including a record stabilized AOA of eighty-three degrees. This expansion included unrestricted dynamic maneuvering beyond 125 degrees AOA with no pilot restrictions required. And the MATV test team did all this in less than three months.

Pilots from the F-16 Combined Test Force at Edwards and from the 422nd Test and Evaluation Squadron at Nellis AFB, Nevada, completed more than 260 tactical engagements during the tactical phase of the testing.

Thrust vectoring proved to provide some distinct advantages in close-in aerial combat. However, two factors weighed against any retrofit of the F-16 fleet.

The first was technical. The advent of highly effective off-boresight missiles and helmet mounted targeting systems made the ability to point the nose of the aircraft less important.

The second was tactical. The MATV system proved most effective near the end of an aerial engagement when most energy (speed) was used up. And a slow fighter can be an easy target, especially when the engagement involves more than one adversary. Cobra maneuvers and J turns make for eye-watering displays at airshows, but they are not as effective for aerial encounters with an aerial adversary, until the very end of a close-in fight. But for the F-16, MATV could have provided a capability to remove the twenty-five degree AOA limiter, which would open the door to new BFM tactics.

Design requirements for the Advanced Tactical Fighter, what led to the F-22, did demand the extra agility thrust vectoring provides. Today, single axis thrust-vectoring plays a significant role in the agility of the Raptor.

In the late 1990s, the design team for the Joint Strike Fighter, what became the F-35, took a hard look at thrust vectoring for incorporation into the basic design for the non-STOVL variants. Although the technology would have provided an increased capability, the additional weight at the back end of the airplane and cost for the engine nozzles on a strike fighter that spends as much or more time in ground attack as it does in aerial engagements led to the thrust vectoring capability not earning its way into the final design.

James Sergeant was the lead flight test engineer for the F-16 MATV program and is now a lead flight test engineer for the F-35 program.