Of all the air-to-air combat maneuvers employed by fighter pilots during the jet age, vectoring in forward flight, or VIFF-ing, remains something of an outlier. Practiced exclusively by Harrier jump-jet pilots, like the Sea Harrier FA2s and Harrier GR9s I flew, this is a form of thrust-vector control, or TVC, but is very different from that which is seen on jets like the F-22. The major difference is that Harrier VIFF is done with four nozzles that all move together, are centrally located on the jet’s fuselage, and can only move in one plane. With a pull of control stick next to the throttle, they can move up to 98.5 degrees deflection, with 81 degrees needed to hover.
Although it became something of a legendary trademark of the Harrier, VIFF-ing remains very much misunderstood. Many will even claim that it has no place at all in a dogfight situation, being little more than a unique ‘party trick.’ But the truth is different. Case in point, my experience of dissimilar air combat maneuvering, with my Royal Air Force Harrier GR9 attack jet up against an RAF Typhoon — a true thoroughbred in the air-to-air domain:
The Typhoon was up in the deep blue stuff. The driver had just gunned my playmate and was straightening his cravat. I needed to reef the nose up to get a shot off, but the combination of Harrier and the Bernoulli principle decided that this was someone else’s problem and the GR9’s nose was staying well below the threat fighter. I reached for the nozzle lever, yanked it back about 40 degrees and the nose rose perfectly to place the Sidewinder symbology over the Typhoon. Fox 2. About three triumphant seconds later I was windmilling earthward with no airspeed on the clock or control of any kind. Out of the fight. Good times.
As in this example, VIFF-ing comes into its own on the few occasions where the nozzle can gain an advantage. But it also provides more than a few ways of embarrassing yourself.
Many other aircraft with TVC use a multi-directional nozzle mounted at the back of the aircraft and can achieve maneuverability that isn’t dissimilar to witchcraft. Harrier VIFF is more a thing of yesteryear and is probably most relevant in guns combat where it can disrupt an attacker’s tracking or give them a massive ‘angle and closure’ problem — which can be enough to evade destruction.
Let’s get one thing straight. Most things in the military have a degree of utility. Most of them have absolutely no utility if used badly or at the wrong time. VIFF is one of those many things. VIFF has, however, and contrary to popular belief, been used in combat.
A Sea Harrier pilot of 800 Naval Air Squadron used nozzles to slow his descent while trying to get a Sidewinder lock on an Argentinian Pucara close support aircraft. It didn’t work out — but then again at least it was available in an aircraft that made it to the warzone. A whole heap of technologies, tactics, and even aircraft types don’t get that far.
You know who you are.
I have, in exercises — as well as losing a couple of hundred times — simulated successful shots from Sea Harrier FA2 against F-15, from Harrier GR9 against Typhoon, and from F/A-18E against F-22. In all three cases, the poorer air-to-air combatant won. I used VIFF to shoot the Typhoon. Does that mean that Harrier plus VIFF was in any way comparable to the Typhoon in an air-to-air engagement? Of course not. Not by a country mile, well, closer to a light year. However, it probably demonstrates that used correctly, VIFF can extend your envelope and if that little bit of extension improves lethality or survivability — well, you would be crazy not to use it. It also demonstrates that a ‘Hail Mary’ play involving the nozzles is a one-shot deal and things will not go your way in subsequent maneuvers if you don’t make it count!
VIFF cannot change the laws of physics (that would be absurd, it relies upon them) but it can make the enemy’s day a little harder and can also create the mother of all aerodynamic catastrophes for the user. It can enhance a Harrier’s performance, but the price you pay for changing thrust direction is energy decrease and instability. Instability is easy to understand — VIFF relies upon taking a sleek(ish) fighter with a tidy vector diagram and moving one of the really important parts.
So what was it? A pilot can VIFF by moving the nozzles using the nozzle lever and therefore change the direction of the thrust vector. It provides a nose-up pitch change, in return for energy loss. The Sea Harrier FA2 Aircrew Manual noted that dropping nozzle produced a trim change, but whether that was, down to using thrust to counterweight or a moment being generated between thrust axis and center of gravity (CoG), wasn’t actually explained. The answer is both but the relationship between thrust vector and CofG position varies with nozzle deflection. As early as 1961, though, aerodynamicists were examining whether or not vectored thrust could unload the wing. At about the same time, U.S. Marine Corps pilots were wondering what this natty little lever could achieve and whether or not an unloaded wing could be immediately loaded up again to greater effect.
Just think of an aircraft at the bottom of a loop. The lift vector can be drawn as a great arrow pointing up through the wing (or pilot’s head if you like) towards the center of the circle the aircraft is transcribing in the sky. The size of the arrow has a limit, based on the lift the wing can give at the aircraft’s current speed — and performance is also limited by the aircraft’s maximum g. Lift is opposed by weight, acting straight down. What if you could remove a little bit of that opposing force? Essentially removing weight with a little bit of thrust?
Same lift. Less weight. Better pitch.
That would be a great idea and would be similar to the effect at the top of the loop where weight and lift are both acting downwards, and higher pitch rates can be achieved. That’s how small-angle VIFF works. Momentarily. What is removing weight or augmenting lift is no longer pushing you along. What you gain in instantaneous pitch you pay for in reducing energy — and the maximum attainable g will reduce as the aircraft decelerates.
Now turn that loop on its side and add an enemy fighter. You have a turning fight and pitch is determining the rate and radius of turn. Lift vector placement is describing where you wish the aircraft to go — which we can probably all agree is quite important. Early recommendations for VIFF included 20 degrees of nozzle to be used for sustained turns and 60 degrees to be used for instantaneous turns. Sixty degrees was quite a snatch but definitely got the nose moving.
However, VIFF is weird and therefore places abnormal stresses on parts of the aircraft that might not be expecting them. Early and enduring VIFF limits were actually due to the high-pressure ducts leading from the Harrier’s Rolls-Royce Pegasus engine to the control vanes for V/STOL flight control. These were charged when nozzle was deflected and could only withstand so much — originally designed for very low speed they couldn’t withstand being charged at high speeds and powers. Therefore, limits on altitude, airspeed, and engine setting were laid down.
From an in-cockpit perspective, it really is — to start with — as simple as ‘take hand off throttle, grasp the nozzle lever, pull it a bit.’ There will be a positive, rapid, nose-up change and the aircraft will get a little more unstable and slow down. None of these effects will be particularly marked for the experienced aviator — but a newcomer to the game would find the experience both violent and disconcerting. The FA2 Aircrew Manual makes repeated recommendations to keep things simple ‘until experience is gained,’ which is probably wise — if somewhat open to interpretation.
When can we use small-angle VIFF? Things like nozzle biting. Taking small chunks out to get your nose gradually further around the circle — useful if you and an adversary are in a largely neutral turning fight and you want to chomp away at the problem, particularly if your circle and that of the adversary aren’t 100 percent aligned and a judicious bit of nozzle can bring your nose to bear. This is most effective when combined with any off-boresight capability the weapons system can give you.
Fighting slow is a race to the wall. First prize is taking a shot in the ass and VIFF can help you get slow, thereby taking second place — where you got to award the prize. VIFF is therefore a good thing. This fight is sometimes called a ‘scissors.’ Both jets attempting to fly as slowly as possible. A bit of nozzle can get your nose up to stop down-range travel at the same time as slowing you down. Win-win.
Some advocated flying the resulting scissors with some nozzle down as it charged the reaction control vanes and augmented aerodynamic control with jets in the wings, nose, and tail — meant for control in the hover. I personally found the slow-speed fight hard enough in any case — and as VIFF made the jet more unstable — I didn’t think being more unstable than ‘only just in control’ was a great place to be.
Other uses of small-angle VIFF would be when one really doesn’t care about losing energy — throwing in some nozzle to get onto a decent turning parameter if you are fast for any reason — or a really quick transition between instantaneous and sustained turning.
Detractors of VIFF point out that the other aircraft can actually win this simplistic competition if it simply decides not to fly slow — to light the afterburner, fly a loop, or just position out of plane. This would put it behind the now very slow Harrier wallowing around wondering what had happened. This is plausible if the bandit can add that much energy quickly enough. Both viewpoints are annoyingly correct in isolation. This brings us to a thorny issue. The school of thought that VIFF only ever caught people out once; and the opposing school of thought that you only need it to work once.
I would probably side with the latter view — but the debate is probably more a reflection on military pilots flying millions of peacetime hours for each hour of combat than it is a reflection on whether or not VIFF actually brings an advantage.
The fun uses of VIFF are the larger angles, right to the point of having the nozzles facing forward. Forward nozzle —98.5 degrees deflection — is a whole load of deceleration, and the Marine Corps originally envisaged it as a means to get slow really quickly to defeat helicopters.
The large deflections take some mastering and for me resulted in more than one complete departure from controlled flight — which was like being thrown through space in an asymmetric washing machine. These maneuvers included the 'braking stop barrel roll' whereby the nozzles are jammed all the way forward and a decelerating (and I mean decelerating) barrel roll ensures that all forward motion is killed and anyone behind you goes sailing past. Yes of course a jet can maneuver to avoid being thrown out in front — but again if it only works once, in combat, that will be the time that actually counts.
In the cockpit this means a momentary unload at the inverted point to guard against immediate departure and a smooth application of nozzle all the way forward. This leaves the pilot thrown forward, hanging in the straps and the jet begins to waffle a little as airspeed collapses. No time to dawdle though as the one-shot opportunity will only last a heartbeat. You needed to be nozzles aft, weapons ready the second the other jet flies past… which you track by craning your neck over the seat box and accepting a modicum of spit across your face from an oxygen mask that has about as much clue as to which way was up as you do.
Eventually, most jets run out of energy, and it is common for a slow-speed fight to essentially ‘fall out’ into a descending, accelerating turning fight. In this situation, with the nozzles fully forward, one can keep a very tight spiral going. If anything, an aileron roll pointing at terra firma — or the sea — with the enemy aircraft accelerating faster and therefore moving ahead and producing a shot opportunity. I used to practice that one by looping and taking all the nozzle in one go from the halfway point. Bullseye nose high to staring at the nadir symbol in one fell swoop, essentially a 'Bolt Flop,' named after the Marine Corps officer, but without the acceleration after the nose-down flop. Exciting stuff. Two jets doing this to each other was usually very good fun as it led to a canopy-to-canopy spiral at full power but with the thrust wondering why it was going in the wrong direction.
Is it dangerous? Well, yes to a certain extent. It is possible to make a closing bandit’s ‘angles, speed, closure’ problem so bad that you make it into a ‘closure, collision’ problem instead. For that reason, we didn’t allow peacetime use of last-ditch Braking Stop decelerations which would be used in wartime to counter a fighter closing from behind. There was, in the FA2, no altitude limit for VIFF in the Aircrew Manual but we didn’t do it below 8,000 feet because of how long a recovery from departure could take! The manual contained all the usual advice such as not to VIFF when you were already in pre-departure wing rock and noted that progressive nozzle made the aircraft unstable and hard to control. One nasty accident included VIFF-ing jets that ended up crashing into eastern England.
The summary, however, remains the same. All military aircrew should recognize the need to get the absolute maximum performance out of their aircraft. That’s all VIFF does in some niche circumstances, with some benefits and some gotchas — and it can be one hell of a ride!
Paul Tremelling joined the U.K. Royal Navy in 1996 and flew the Sea Harrier on 800, 801, and 899 Naval Air Squadrons. Qualifying as an Air Warfare Instructor, he transitioned to the Harrier GR9 and served on the Naval Strike Wing, where he became Senior Pilot. After a U.S. Navy exchange tour flying the F/A-18E, he returned to the Harrier and undertook operational missions in Afghanistan and off Libya.
Contact the editor: Tyler@thedrive.com