Are the (built-in) guns on fighter jets fixed, or can they be elevated up and down or panned right and left for aiming?
In other words are fighter jet guns aimed by pointing the whole aircraft at the target or can they be aimed independently?
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They are fixed, and many attempts were made over the years to have an aiming capability - and all failed. That should tell you something.
The earliest aereal combats used indeed handguns which were pointed at the adversary by the pilot. But it soon became obvious that only the rapid fire of a machine-gun will give the pilot a realistic chance of hitting a fast-moving target. To learn what has to be considered when aiming at aircraft I recommend to watch this B-29 gunnery instruction movie on YouTube.
During the Italo-Turkish war of 1911 and 1912, the Italians used aircraft in war for the first time. Since the Ottoman Empire had no air force yet, the Turks engaged European aviators who flew their own aircraft, taking a handgun along to shoot at the Italians.
The same was tried in the opening months of WW I, but it soon became obvious that only a machine gun was effective. Before gun synchronisation was invented, pusher designs were fielded, some of which carried a dedicated gunner in a seat ahead of the cockpit.
Vickers F.B.5 "Gun Bus" (picture source)
Of course, the much smaller and nimbler Fokker single-seaters with gun synchronisation made such designs soon obsolete.
When Great Britain prepared for WW II, the firing power of bomber turrets impressed the Generals so much that they ordered several dedicated fighters with a gun turret mounted right aft of the cockpit. The resulting Bouton-Paul Defiant was again too slow and easily outmanoeuvred by the single-seaters, and the Blackburn Roc and the Hawker Hotspur were even worse. The Defiant's only successful role was as an early night fighter; when attacked by day it could only join others in a Lufbery circle to defend against being shot down itself.
Bouton-Paul Defiant F. Mk.I (picture source). Note the retractable belly-mounted antenna masts which gave the gunner a free field of fire in the upper hemisphere.
Another attempt was made by the MiG design bureau in the 1950s. In a dogfight the pursuer needs to get inside the circle of its opponent in order to score a hit with a fixed machine gun. The Russians thought: Why not pivot the gun into the circle, so the pursuer can fly the same circle as its opponent and still shoot at it? A MiG-17 was modified accordingly, but flight testing soon revealed that the recoil from the machine gun would push the nose of the fighter down and outside of the circle when the gun was not aligned with the longitudinal axis of the fighter, so this idea was dropped very soon.
Now I need to mention that rarely are the guns completely aligned with the longitudinal axis; instead, they point slightly up to compensate for the ballistic bullet drop at the expected distance of the target. Also, wing-mounted guns point slightly inward, again to ensure the bullet path is straight ahead when it catches up with the target, a procedure called gun harmonisation. This also means that interceptors will have their guns pointing up slightly more than those of air-supremacy fighters. One particular case involved the MiG-15: Being designed to fight large B-29 formations, the guns were badly aligned for fighting the F-86 Sabre during the Korea War. The MiG-15 armament consisted of two 23mm guns and one 37mm gun with very different ballistics. In order to ensure that the path of all bullets would meet at the right distance for fighting bombers, the 23mm guns pointed more up, and when used against the much smaller F-86, the Russian and Chinese pilots opened fire at a shorter distance so that the 23mm bullets would fly over the target while the 37mm bullets went below it. This was a major reason for the poor kill ratio of the MiG-15 vs. the F-86 despite the MiG's better performance.
Gun harmonisation on a jacked-up P-47 (picture source)
Modern high-off-boresight missiles with helmet-mounted cueing (or sight-controlled missile targeting) have turned that longtime dream of shooting at what the pilot is looking into reality, and the gun is carried largely as a low-priority weapon of last resort.
The guns of modern fighter jets are fixed to the airframe—they can't be moved in any direction; the pilot has to maneuver the aircraft to bring the guns to bear. The image shows the mounting of General Electric M61A1 Vulcan cannon in an F-16.
Photo copyright (c) Meindert de Vreeze. Source: designer.home.xs4all
Gun installation in F-16.
The pilot aims the guns using an optical representation in the Heads-Up Display (HUD). Some of the aircraft use the Lead Computing Optical Sight where:
... a prediction angle is continually computed and displayed on the Heads Up Display (HUD) as a reticle offset from a fixed reference on the gunsight. ... (which) accounts for ballistic curvature, own motion, and predicted target motion.
Basically, it shows where the shells will pass through at a certain distance. Some aircraft use Enhanced Envelope Gun Sight (EEGS). It basically shows a pair of lines which the cannon shells will follow- the lines moves as the aircraft maneuvers, showing the effect of the maneuver on the flight path (of the shell). The correct 'solution' exists when the wingtips of the target touches the funnel lines.
EEGS; image from simhq.com
They are fixed. The pilot must maneuver the aircraft such that the trajectory of the bullets will impact his selected target.
Here is a picture of the HUD on a F/A-18 during a gun run on a ground target. Note the circular symbol which indicates where the bullets will hit. (Screenshot of JetStream Episode 8)
I was a light attack pilot in the 1980s and flew off the USS Nimitz. I don't want to give anyone the idea that air-to-air warfare is something that can be scripted. It is highly complex, like chess, constantly changing, where deception and trickery often win the engagement over technology and a high performance airframe.
Consider this: A light single prop aircraft, maybe something like the Douglas A-1 Skyraider, can be a formidable threat when attacking a carrier with even a small bomb hung under the wing. It is slow with a tight turn radius, can fly very low, and has a very small heat signature. All these things can be used to its advantage.
I can add a few things of interest. The guns on the attack and fighter jets were fixed in angle, and aligned above boresight. I know this to be the case for the F-14. This was so that when you were tracking a target in a high-g turn the gun would be pointing ahead of the turn, instead of behind your adversary in the turn. On the other hand the A-7E had its cannon boresighted, because it was aligned for strafing.
Having a gun aligned above boresight can have its problems. I was on a war-at-sea strike against a destroyer and was intercepted by an F-14 at around 50 miles out. I was cruising the wave tops at around 650 knots. The F-14 stayed in a position above and behind and did not engage me as I flew in on my attack. Later we met back at the ship and he told me that, at such a low altitude, he would have to go inverted to get his forward pointing gun on me to get a kill. He said this was something he was not willing to do, and so he waited for a better opportunity. Perhaps I would pop up coming in to the target for my to delivery.
Which brings me to the more interesting consideration. The tactics of air combat maneuvering (ACM) have evolved over the years. When I began ACM training (1980) in the A-4 Skyhawk we were taught that you needed to gain a 6-o'clock position in the fight, and be tracking your target for at least six seconds to have a successful kill.
Later in the mid-1980s things had changed and we were being taught the snapshot. Israeli experience showed that most dogfights quickly degrade in to "furballs" with many-to-many engagements. If you track a target for six seconds in such an engagement you will be dead. Essentially, there is always someone finding themselves at your 6 o'clock. So we were taught to attempt to position yourself outside the furball and blow through the fight without engaging any particular target too long, taking shots of opportunity. These shots typically had to be taken with large angles and lots of closure. Picture someone crossing your canopy from left to right in a high-g turn. You would use "Kentucky windage" and take your shot so the opposing aircraft ended up flying through the 20 mm cannon shells you fired at 6000 rounds per minute. So much for "aiming."
One final comment. The F-4 Phantom was designed without an air-to-air cannon and carried only missiles. On the F-14's, for example these weapons were close in missiles, e.g. the AIM-9, and longer range (over the horizon), e.g. the Phoenix and Sparrow missiles. There was no gun on the F-4, because prior to Vietnam it was thought that aerial dog fights were a thing of the past with the advancing technology. This of course turned out to be a mistake, and gun pods were mounted on F-4's to give them a close-in capability, while at the same time sacrificing performance. The number of missiles carried on one aircraft are expended rapidly against a large number of targets, and then one is reduced to battling it out close-in.
The internal cannon on a jet fighter is s permanent fixture in the aircraft, hard mounted to the airframe and cannot be swiveled independent of the flight path.
To the second question, yes, aiming the gun involves pointing the aircraft's flight vector at the target or at a lead impact point in front of the target. The pilot, in essence is riding a very large flying gun and many of the same shooting techniques i.e. breathing work, trigger press, leading are very similar to that found while handling and discharging a firearm, particularly a shotgun, at a moving target.
As mentioned above firing symbology and sighting arrangements vary from plane to plane. Some common ones are the Lead Computed Optical Sight (LCOS) or Enhanced Envelope Gun Sight (EEGS) but all use either pre ranged hit points or a lead computed pipper - 'death dot' in fighter jock speak - with ranging cues.
It is possible, either now or in the near future, with position tracking helmet mounted cueing systems that flight control software can be developed for air to air use which allows the pilot to point the nose of the jet - and the gun - simply by looking at it. The technology already exists to slave FCRs, IRSTs, gimballed FLIRs and weapon seeker heads to the HMCS, allowing for use of both radar guided missiles high off-bore sight IR air to air missiles as well as with ground munitions based on simply looking, designating and shooting.
A few points why 'aimable' cannons/turrets wouldn't be feasible:
Fixed wing - No, Rotary Wing - yes. As they have previously stated the guns are attached to the airframe. They do have revolving barrels, lots of rounds (that they go through at a very fast rate) but everything is aimed by the pilot. We are good, but not that good yet. It will be interesting looking aircraft when we can do that though. Interesting question.
About the helmets in the F-15, 16, and 18. That could be interesting as well. However, currently in the helo community they are used to point say the M197 gun at the target. I think in fixed wing, they may be used to point the aircraft.
This still proves what has already been posted though. There is no way to point the weapon system without pointing the aircraft for fixed wing.
The Saab JA 37 Viggen fighter jet actually had a system (automatsiktning) that would aim the entire aircraft instead of letting the pilot do it. It would make small adjustments to yaw etc. to make the cannon hit. (the cannon was still fixed though)
It was mainly used in frontal attack or long range rear attacks. It was very successful in frontal attacks.
The pilot would engage with radar lock and the computer would control pitch and jaw. The pilot controlled roll to keep the plane flying clean.
There were at least MiG-15SU and MiG-17SP experimental fighters with a moving gun carriage V-1-25-Sh-3 with 2 Sh-3-23 guns mounted on it. Pilot could remotely adjust guns in combat (11 grad up or 7 - down), thus reducing time needed to get in firing position against maneuvering enemy. The system had no guidance of course.
Although I have no idea if this device was ever put in production, I believe in later aircraft designs stakes were made on missiles as primary weapon, leaving guns secondary role.
Guns are fixed in all modern fighter aircraft, and can only be aimed by aiming the entire aircraft. This is normally done with the aid of a Lead Computing Optical Sight (LCOSS). There are three components to an air-to-air gun solution, that must be taken into consideration by the engineers designing the gunsight mechanics, and well understood by the pilot utilizing the system.
Lead for Target Motion or Velocity Lead (Lm). This is the same thing as is utilized by a skeet shooter. You must aim the barrel of the gun where the target will be when the bullets get there, not where it is now. You cannot just point the gun at the target. You must point it some angle in front of the target in the direction the target is moving in your field of view. Lm always lies in the target's plane of motion. This requires that the system know the time of flight (TOF) of the bullets, and the Line-of-sight rate (LOS) of the target (how fast is it drifting across the inertial background in your field of view. If the target is moving at 20 degrees per second, and, based on the range, the TOF is 1.5 seconds, then you must aim 30 degrees in front pf the target, along it's projected velocity vector. Fighter pilots use a radar lock on to determine the range and TOF, and gunsights assume a Default range(in the F-4 it was 1000 feet) when there is no radar lock. The target LOS is determined by the gunsight by assuming that if the pilot is "tracking" the target, the shooter aircraft turn rate must be identical to the target's LOS. When the pilot is not tracking the target (as in a highly dynamic close range, high angle shot (called a snap shot), the pilot must understand this effect in order to turn on the gun with an additional lead angle to compensate for the target's relative motion in the windscreen. Effectively he pulls the trigger when the target, moving towards the gunsight aiming reference, appears to be about to cross that aiming reference about a second or two in the future.
Lead for Target Acceleration or Acceleration Lead (La). If the target was at zero Gs, (in ballistic free fall), there would be no need for La. Only Lead for target motion and Drag shift would be required. La is required when the target is turning away from the ballistic path that the gunsight would be predicting without La. La always lies in the target's plane of acceleration (the plane the target aircraft is accelerating in (normally defined by where the lift vector or rudder points). The gunsight assumes that the target Plane of motion is the same as the shooter plane of motion, and that the the target G-load is the same as the shooter G-Load. The solution is based on the assumption that the target is accelerating or pulling Gs towards the shooter, and that the shooter, to match the target's turn rate, is pulling the same amount of Gs in the same direction. This is normally close to accurate when the target is at low angle off relative to the shooter, but is not accurate at higher angle off.
The last component is the correction for what is called Drag Shift. Bullets slow down after they leave the muzzle. This slowing causes the bullets to drift aft of their original line of fire (Line of departure or LOD). Imagine the top turret on a B-17 firing forward and upwards at a head-on approaching target. If the bullets maintained a constant velocity after they left the muzzle, all that would be necessary s to point the guns where the target will be one TOF from trigger squeeze (La), and correct for 1 G target acceleration (La). But the bullets slow down. That means it will take a slight bit longer to get out there, and the target will drift further aft in that small amount of time. Therefore, the gunner must aim slightly lower in elevation (less lead), to compensate for that. Imagine a high pressure water hose, forwards and upwards out of the sunroof of your SUV at 80 mph. The stream of water will appear to curve and bend backwards relative to the vehicle, the further it is from the nozzle. If you were trying to hit a drone flying 15 feet above you and 15 feet in front of you, you would have to aim in front of him to compensate for the apparent rearwards drift of the stream of water. This correction is required whenever the gun firing line is not aligned with the shooter aircraft velocity vector through the air. For a fighter, since guns are must be in lead, this means it reduces the the lead required by a small amount in the plane of target motion.
The relative contribution to the total gunsight solution from these three components, generally, is as follows:
Lead for target motion: 70-85%
Lead for target acceleration: 10-25%
Drag Shift: 5-10%
Pilots can aim by looking at their targets-even in High G situations.
These days, fighter pilots' helmets are nearly as complex as their airplanes. And with good reason: If the helmets can't tell where the pilot is looking, many of the airplane's systems, including weapon targeting, are useless.
The folks at San Jose, California, who have designed advanced U.S. military helmets for the F-15, F-16, and F/A-18, make their living at the nexus between man and machine. VSI's flagship program is the Joint Helmet Mounted Cueing System. It uses a magnetic field in the cockpit to sense the orientation of the helmet, then feeds information on the current line-of-sight to the aircraft's flight computer. VSI's helmet has an accuracy of about four milliradians, an angular measure commonly used in the world of shooting and targeting. One milliradian equates to one one-thousandth the distance to the target. So if the target is 1,000 feet away, you'd be accurate to within a foot.
Determining where a pilot is looking by tracking eye movement is a much taller order. "You would not believe some of the human factor issues you have to overcome to have a successful eye tracker," says Louis Taddeo, VSI marketing director. "Although we have research projects into eye tracking, it is a very difficult task both from a technical [standpoint] and the physiology."
So for now, VSI uses helmet position to achieve that four-milliradian accuracy. Pilots need only turn their heads to aim their weapons, even during high-G maneuvers, freeing their hands for other tasks.