How Things Work: Thrust Vectoring
In a tight spot, you need zoom to maneuver.
- By Jim Mathews
- Air & Space magazine, July 2008
NASA's F/A-18 (left) and X-31 are among the airplanes used to gather data for thrust-vectoring.
NASA Dryden Flight Research Center
Remember the scene in the movie Top Gun when Navy pilot Pete “Maverick” Mitchell gets the upper hand on his instructors by slowing down, pulling up the nose of his F-14 Tomcat, and watching his opponent fly right by? The idea was to get a quick, unexpected position behind the bad guy, putting Maverick (played by Tom Cruise) and his trusty sidekick Goose into place to win the Engagement.
Real fighter pilots will tell you that what Maverick does is a showoff move that bleeds off so much energy that you’re vulnerable to getting shot down yourself. What a pilot really needs is a way to quickly get in the right position to fire at the enemy. Today’s most maneuverable fighters use thrust vectoring, which can make a jet turn faster and more tightly.
Powered by Pratt & Whitney F119 turbofans, each with 35,000 pounds of thrust, the F-22A—the Air Force’s newest fighter—sports a nozzle that can direct exhaust thrust up or down as much as 24 degrees.
The advantage to pilots is superior low-speed and high angle-of-attack maneuverability, compared to conventional-thrust aircraft, says Second Lieutenant Aaron Hoke, a propulsion engineer on the U.S. Air Force team that manages the Lockheed Martin F-22A Raptor program at Wright-Patterson Air Force Base in Ohio.
“Our [one-on-one] tactics have changed to incorporate the ‘post-stall’ regime, where other aircraft cannot operate,” explains Captain John “Rocks” Wagemann, who flies the F-22A in the First Fighter Wing at Langley Air Force Base in Virginia. Thrust vectoring enables the pilots to fly up and over in a very tight arc, Wagemann says, and “gives us the nose authority to turn the jet while the wings are stalled, similar to a controlled flat spin.”
Thanks to advanced computers and flight control systems, pilots don’t have to think about choosing vectoring or executing specific steps to perform a maneuver. They simply point the airplane where they want, and the onboard systems automatically coordinate the right combination of flaps, rudder, elevator, and nozzle angle. “The F119’s vectoring nozzle is integrated into the F-22 flight control system” so that “the pilot doesn’t control the nozzle independently,” says Chris Flynn, Pratt & Whitney’s F119 director.
Flaps in the engine nozzle point up or down to “steer” the jet exhaust, making the airplane more responsive and maneuverable. In a two-engine airplane like the F-22, directing the exhaust from both engines upward points the nose up, while reversing the direction points the nose down. The F119 engines are designed to vector in the same direction and by the same amount. The nozzle is said to be “two dimensional” when the shape of the throat is rectangular.
Flight tests of thrust-vectoring designs began in the early 1990s with airplanes like NASA’s modified F/A-18 and F-15, the Rockwell/MBB X-31, and a modified Air Force F-16. In 1994, the X-31 demonstrator was fitted with what German program managers called a “poor man’s thrust vectoring nozzle”—three paddle-like vanes that pushed into the exhaust stream—and the results were spectacular. Without thrust vectoring, the X-31 lost twice as often as it won against the F/A-18 in mock combat; with it, the X-31 didn’t lose once in 129 matches.
Theorists say air combat could be changed by the introduction of some maneuvers unique to thrust vectoring. A high angle-of-attack descending spiral is one. At a high angle of attack, a rudder loses its effectiveness, and being able to rely on thrust vectoring would let a pilot enter what’s essentially a controlled flat spin, yawing the airplane around to aim at a target without worrying about the rudder. The pilot also gets extra maneuverability at high altitudes, says Wagemann, “where the air density is so low that the flight control surfaces become significantly degraded.” Then there’s the super-tight J-turn, or even a modified hammerhead, in which an airplane appears to briefly fly backward.
One common misconception about thrust vectoring involves the flashy cobra maneuver, also known as Pugachev’s cobra, after Russian pilot Viktor Pugachev, who first wowed crowds with it in a Sukhoi Su-27 at the 1989 Paris Air Show. The maneuver is not an example of thrust vectoring. If the pilot is skilled enough, he can do the cobra in nearly any type of U.S. jet fighter. In essence, the pilot abruptly pulls the control yoke full aft while flying around 300 knots—about 345 mph—and thus pitches the nose up dramatically so the airplane is nearly standing on its tail. Just as abruptly, the pilot pushes the stick forward, dropping the nose back down. When the maneuver is flown correctly, with little change in altitude, the effect is like the striking of a cobra’s head.
Right now, the F-22A and the Russian Sukhoi Su-37 and Su-30MKI (flying with the Indian air force) are the only fighter aircraft with two-dimensional thrust vectoring nozzles.
More sophisticated designs, which have yet to fly beyond the testing stage, feature nozzle flaps that can move 17 to 20 degrees in nearly any direction, resulting in maneuvers around both the pitch and yaw axes. Both major U.S. fighter engine makers, Pratt & Whitney and General Electric, tested multi-axis vectored nozzles about a decade ago for an Air Force demonstration program.
Until thrust vectoring becomes more widespread, few will enjoy that extra edge—and that’s just fine with U.S. pilots. “Thrust vectoring provides such a significant advantage in the visual maneuvering arena that I rarely find myself in a defensive position,” says Wagemann. “When we start defensive, for training, you are almost always able to transition to offensive without getting shot.”
Comments (15)
I can not see risking a 200 million dollar fighter in a close in visual engagement. I thought dog fighting was obsolete, again. The more expensive the figher and less that will be built. This then promotes more conservative tactics that put the aircraft less at risk. That may be why so few aircraft have employed thrust vectoring and why more effort is being spent on stealth and longer range air to air missles.
Posted by Brian Cavanagh on May 18,2008 | 07:46 AM
You could have talked a little more about the Russian fighters holding thrust vectoring.
Posted by Marcelo Augusto on May 25,2008 | 10:40 PM
In response to Brian,
Dogfighting will never be obsolete. That's the hard lesson that the military learned when introducing the F-4 phantom over Vietnam. The "experts" went so far as to influence the military to not put guns on the aircraft. They thought the advent of missiles would make dogfighting obsolete, but the pilots without dogfighting training didn't know how to position themselves correctly to fire the missiles, so the missile kill rate was much lower than expected. Furthermore, once they are out of missiles, they aren't as good at evading the enemy because they don't know how to dogfight.
The F-22 is the perfect blend of technology and tradition, able to take the enemy out from miles away, but still more capable in dogfighting than any other fighter on earth. Dogfighting may never become obsolete, but the one thing for certain is that technology will always play a crucial role in how dogfighting is carried out.
You're right - you don't want to risk a $200 million aircraft, which is why you fire missiles first. But in case you need to get up close and personal, the F22 has teeth that bite there, too.
Posted by Kel Jackson on June 14,2008 | 09:25 PM
For Marcelo:
Ah, I would have, but magazines only have just so much space. I could have talked not only about the Russians but the Indians, who have taken Russian MiG technology and run with it...particularly in thrust-vectoring.
Posted by Jim Mathews on June 15,2008 | 04:53 PM
Well, I litteraly thought you did a great job on this article. But as far as reality is concerned about creation of jets. The Germans were the first to accomplish this. That is...in WWII before the battle of Berlin in 1942, the Germans created the first jet-born fighter which I don't exactly remember the name of. Furthermore, these guys know exactly what thrust vectoring is; and if they see something wrong with the models. They are quick to judge the schematics or blueprints that went into creating an aircraft capable of thrust vectoring. Then also, you mentioned about the early flight tests of thrust vectoring NASA performed on the aircrafts that German managers called the "poor man’s thrust vectoring nozzle." I thought the reason they said this was because the response timing took slightly too long to position the pilots during a dogfight in order to gain the upperhand. Then again, I could be wrong.
Posted by David Smith on June 26,2008 | 11:08 AM
For David,
The aircraft was the X-31 demonstrator, and it was the "poor man's" thrust-vectoring nozzle because it used three paddles to deflect into the jet efflux rather than a full-up nozzle. It still worked like a champ, though!
And yes, it was the Germans who came up with the first operational jet fighter, the Me 262. But they also built half a dozen others as prototypes and experimental aircraft, and it was only economic collapse and poor tactical employment that kept the 262...plus a follow-on jet fighter and a little-known jet bomber called the Ar 234 (I think...someone correct me on the designation if I've recalled it incorrectly)...from having a bigger effect on the course of the war.
Posted by Jim Mathews on July 5,2008 | 03:01 PM
I think Kel Jackson is right about why the F-22 needs to be as effective at close range as it is at greater ranges.
If the pilot of the F-22 shoots down six adversaries, he may still need to shot down some more planes without going home to re-arm. So the F-22 have to be able to get in some good shots with the AIM-9 or the cannon. So dogfighting will never become obsolete as it will be nessecary when the plane runs out of BVR-missiles, and you would take even greater risks with the 200 million dollar plane if it can't engage in close in fights.
About those german WW2 jets; there was several designs from Henschel that did not make it into production for various reasons, not only jets. There was a small production run of planes that used the DB-601A (those planes were used to defend the Henschel factory) that outperformed all contemporary british and german fighters at the time of the Battle of Britain. Fortunely the Luftwaffe were content with the Bf-109....
Henschels jet fighter easely outmanouvered all other german fighters, but they "lost" the contract to the more elegant (and inferior) Me-262. Henschels jets were ready for massproduction much earlier as well.
Posted by freddan on July 12,2008 | 12:19 PM
For Jim - good article, but you can't do a Cobra in a military aircraft as easily as you state.
Doing this in an F-16 will cause it to depart controlled flight, according to its stability characteristics (AIAA Journal of Aircraft 1973) - but happy to be corrected by any Viper driver!
Northrop (& Eidetics) did a lot of work on fighter high-alpha handling during the 70s & 80s, resulting in the F-20's "shark" nose; the basic design premise behind this seems to have been carried on for the F-22 & F-35.
They did consider thrust vectoring (particularly for the ND-102) but considered that the additional weight at the back end (aft CG implications) and moving parts in very hot gas flow would be a major maintenance problem.
Obviously Lockheed's design team thought otherwise for the F-22, but you'll always get differing design philosophies between different fighter houses. ;-)
Posted by Mike Kim on July 19,2008 | 04:19 PM
In response to Kel Jackson -
I think it's a mistake to rely on the experience of the Vietnam war, in the issue of relevance of dog-fights.
Fifth generation air to air missiles don't need to be stationed exactly "behind" the target in order to lock on it, and be shot. The "cone" of the IR/radar/optics of the missile is very wide, and it can be lunched without "seeing" the target at all. I'm talking about missiles such as the Python 5. Not mentioning future developments..
The fighting aircraft can carry about 4 air to air missiles - I think that by the time they run out, the fight will be over, and no "god-fight skills" will be needed.
Fighters usually don't fly alone with significant quantity inferiority.
Posted by Joseph on October 17,2008 | 09:29 AM
The 3 panal system used on the X-31, doesn't sound like the poor mans thrust vectoring, it indicates 3D thrust vectoring for both pitch and yaw, while the F-22 has 2D thrust vectoring for pitch.
Using 3 panels is how 3D thrust vectoring works, all 3 panals move. It allows for extreme maneuverability.
I think the German programmers misunderstood what it was they were looking at.
Posted by Salman on February 13,2009 | 07:23 AM
I have reason to believe that all the noise out there regarding the rear of the F-22 is wrong, and deliberately so.
Those triangles that stick out the back of the engine cowlings are nothing more than exhaust vector controls. The mount on the V-shaped cutout that you see on all the engine tests. Everything else is a deception. I even found that the museum's copy of the jet is deceptively modified, so that the engine areas have an extra metal frame put over them that shrinks the engine area, which in reality, would prevent maintenance because the engines slide in and out from behind the aircraft.
Those triangles are exhaust vector control panels. If all four vector controls were activated at the same time, a pyramid would form that could shut-off the engines completely, if not almost completely.
These are the vector controls that allow the aircraft to rotate in place. Without these, the F-22 is merely a smart version of the SST-- which had no lateral controls other than up or down thrusting one bank of engines.
As for you F-22 modelers out there?-- keep trying, because the designs I've seen use the center vector control as a single piece, when in reality, there are two vector panels on the inside, back to back, and one each on the outsides of the engines.
Anyway, just wanted to show what my son and I figured out over this last weekend.
Vasco
Posted by Vasco de Sena on February 23,2009 | 01:04 PM
I thought it was a good article!
Posted by David Hobson on August 5,2010 | 04:35 AM
The noise above is mostly misleading. 1st tech facts, then uses facts:
Tech Facts: 3D TV effectively replaces the dangerous, 100-years old, stall-spin sensitive, Conventional Flight Control [CFC]as proved first in 1987, in Israel by first ever design, lab and proof-of-concept flight tests of 3D jet steered, Stealth-Tailless air vehicle, including the 1st post-stall COBRA Maneuver.
[Refers: Aviation Week, May 18, 1987; U.S. Patent 5,782,431; USAF "TAILLESS VECTORED FIGHTERS"; "Vectored Propulsion, Supermaneverability & Robot Aircraft", Springer 1990; Video link on FB Wall: "THE NEW ERA IN AVIATION"; "Future Jet Technologies" (2011), Int'l J. Turbo and Jet Engines, Degruyter, 28, No. 1]
The 1987 proof-of-concept opened the gate to many air, sea & land applications: (a) flight where CFC fails; [Cf. F-22, SU-MKI-30], including the Herbst & helicopter maneuvers; (b) maxim flight safety in mil & civil domains [Aerospace America 1996, six AIAA papers, etc.]; (c) enhanced stealth capabilities;(d) reduced vertical tail/tailless designs [X-36, X-45, X-47B, X-44MANTA,RQ-170, X-48; (e) saving fuel
In fact, all advanced air vehicles, manned and unmanned will be jet steered w or w/o CFC. So we are in a revolution, just entering the jet-steering era.
3D-TV Uses with benefits over CFC: 1. Unmatched Air-to-ground efficiency, 2. Unmatched WVR engag. by min sum of times; shortest time 4 AA missile 2 destroy target by rapidly pointing nose to target under any condition [shorter path to destroy target prior to its launching], or for guns. 3. max safety in case all hydraulics stop, except those of engines/3D-TV; 4. Uses in military cargo to prevent catastrophic failures. 5. uses in sea water-jet Littorial Combat Ships, patrol boats, attack boats[Hamina Class, Dvora MK III, LCS 1 & 2.
Cf. President Lincoln: "It is better to remain silent and may be considered a fool, than open your mouth and remove any doubt".
Posted by Benjamin Gal-Or on June 23,2011 | 02:02 AM
To Joseph:
Well, what you said is ok if you're fighting Iraq, North Korea or another 3rd world nation. How about when you're fighting against China or Russia, which might have even more fighters than you and have 90 percent the capability of our jets with ten to twenty times the number? It's likely those planes will have counter measures, stealth, advance avionics, and long-range missiles. Before you know it you will have guns blazing. Chances are it'd be an aerial melee, so what will happen to the fighter without dogfighting capability? Dogfighting will never grow obsolete and in the advent of stealth it just become a lot more important.
Posted by Tarl on April 13,2012 | 03:12 AM
What I'm curious about,(layman)is which is superior, 3D , manually controlled as in current SUs or CPU'd 2D as in the f-22. Where would yaw be effective in ACM and why didn't we use it seeing we've tested it quite a while ago? I've read at one site that the PAK-50 is or was considering a 2D version as well. Bottem line, which is better?
Posted by Dan Kuyek on April 24,2012 | 07:06 PM