Basic Fighter Maneuvers

Pursuit Curves

Pursuit curves were discussed previously in relation to missile trajec tories; they are equally relevant to fighter maneuvering. The three forms of pursuit—lead, pure, and lag—are technically defined by the orientation of the attacking aircraft's velocity vector ahead of, directly toward, or behind the target aircraft, respectively. Since the fighter pilot does not always have an indication of the precise direction of his velocity vector, his nose position is usually substituted as a reference. In maneuvering situations these two references (velocity vector and nose position) vary by the amount of the attacker's angle of attack and sideslip, which are generally not great enough to be of importance. So, what is called "pure pursuit," for instance, may actually involve a small amount of lag

Lead Pursuit

A lead-pursuit path is followed by positioning the aircraft's nose ahead of the target, or "bogey," fighter. As discussed in the gun-employment sec tion, the practical maximum lead when the attacker is maneuvering near the target's plane of turn is often limited by the attacker's over-the-nose visibility and the requirement that he maintain sight of the bogey. "Blind" lead turns may be appropriate under some circumstances, but they are inherently dangerous, both because of the possibility of a collision and because of the potential for losing sight of the bogey and allowing it to gain a more threatening position or to escape. Larger amounts of lead can often be generated by turning in a parallel plane with the target, so that sight may be maintained over the side of the attacker's nose.

The purpose of lead pursuit is primarily to increase closure on the target by use of geometry. The ideal lead angle for greatest closure depends on relative aircraft positions, relative speeds, and target maneuver. As with missiles, a proportional-navigation course usually maximizes closure, and can be estimated visually as the lead angle that causes the target to appear to remain stationary against the distant horizon. If the target's drift appears to be toward the attacker's nose, more lead is called for, and vice versa.

The lead-collision or lead-pursuit curve may even allow an attacker to close on a much faster target, particularly if that target turns toward the attacker at a rate that places the attacker at a large AOT.

Pure Pursuit

Holding the attacking aircraft's nose directly on the target also provides closure, unless the target has a significant speed advantage and AOT is very small. Although pure pursuit does not generate as much closure as lead pursuit under most conditions, neither does it cause AOT to increase as rapidly. In addition, pure pursuit presents the minimum frontal area of the attacking fighter to the target pilot, increasing the defender's visual problems.

Lag Pursuit

As long as the fighter has a speed advantage over its opponent and can achieve the same turn rate, stabilized lag pursuit is possible in the bogey's rear hemisphere. However, there are several very strict constraints on combinations of range, relative speed, turn radii, and relative fighter posi tions which must be met for stabilized lag pursuit. All these parameters are very difficult to meet in practice, even with a cooperative target, so lag pursuit is generally a temporary state of affairs. Nevertheless, this tactic does allow a fighter to maintain a speed advantage over a maneuvering target while remaining in its rear hemisphere.

Lag also may make it very difficult for the bogey pilot to maintain sight of the attacker, particularly when the attacker is on the cold side or near the bogey's six o'clock (i.e., dead astern); this forces the defender to turn harder or to reverse his turn direction. If the attacker is equipped with an off-boresight weapon, one that can be fired at a target that is not directly ahead, there may be a shot opportunity regardless of the bogey's maneuver. If the bogey pilot cannot safely reverse without giving his attacker a shot opportunity, the continued turn occupies his attention and forces him to be predictable, making him easy pickings for a second fighter.

Likewise, however, an attacker is also predictable and vulnerable while performing prolonged lag pursuit. When using this tactic a pilot should attempt to gain a position from which a shot opportunity will be presented with his available weapons if the bogey reverses. Unless the attacker is gun equipped, lag, particularly cold-side lag, at close range with the nose well off the bogey may allow the bogey to reverse with impunity, possibly gaining an offensive position. At the very least this condition does not make the bogey predictable. It also may result in a difficult position from which to disengage should disengagement be necessary. Additionally, sustained lag pursuit can be very taxing physically to the attacking pilot, since his greater speed requires a higher load factor than that of his opponent.

Stabilized lag pursuit with its many constraints may not offer the optimum offensive position for the attacker considering his weapons sys tem and relative maneuvering capabilities. It is usually desirable for the attacker to stabilize within the boundaries of his weapons envelope, possi bly only having to satisfy aiming requirements for a valid shot. If the attacker can reach such a position even temporarily, especially if he is out of the defender's field of vision, the bogey pilot is forced to react in order to regain sight.

Effective defense against lag pursuit involves simply changing the de fender's speed, turn direction, or G. For hot-side lag this generally means tightening the turn, sometimes with a gravity assist by turning nose-low. Cold-side lag is usually countered by a turn reversal, which places the attacker on the inside of the defender's turn in lead pursuit. Such a ma neuver results in a rapid decrease in range and may actually cause the attacker to fly out in front of the defender, reversing the roles. This reversal is often more effective when performed nose-high, causing a reduction in the defender's forward velocity and increasing closure. Reversals are quite effective against missiles-only fighters, as these fighters will often quickly pass through the min-range missile boundary unless the lag geometry is just right. For gun-equipped fighters, however, a bogey reversal usually results in at least a snapshot opportunity for the attacker.

Lag Displacement Rolls

In the lag-pursuit discussion one method was mentioned for achieving a lag position from a point inside the defender's turn at medium AOT (about 30° to 60° AOT), when the range is only slightly greater than that desired for lag. This method involves relaxing the turn and allowing the nose to drift behind the target, remaining essentially in the same maneuver plane as the target until approaching the desired lag position. When he sees this maneuver, the bogey pilot may assume that the attacker cannot match his turn performance and is about to overshoot. Such an assumption may induce the defender to reverse his turn direction to gain a position advan tage on the overshooting attacker—but this often presents the attacker with a gun-shot opportunity instead.

The displacement roll is similar to the lag roll, except that it is used in close-range, low-closure situations to reduce AOT and increase range, rather than to prevent an overshoot. This maneuver tends to "displace" the attacker's flight path from inside the bogey's turn toward or to the other side of the defender's flight path. In such nearly co-speed situations lag pursuit is not generally advantageous, so this tactic is primarily of value for positioning the attacker within a missile envelope. It allows the attacker to increase nose-tail separation with the defender (possibly to meet min-range constraints) without reducing speed. After completion of the displacement roll, the attacker will usually be in lag pursuit, requiring him to turn faster than the bogey to point at the target for a boresight missile shot. Essentially the displacement roll trades some angular advan tage for increased nose-tail separation and possibly reduced AOT.

Another variation of the lag roll is known as a barrel-roll attack. This maneuver is useful in making the transition from lead pursuit in the target's beam area or forward hemisphere to a rear-hemisphere position. Such a situation may develop when an attacker is performing lead pursuit against a bogey at fairly long range and the defender turns toward the attacker. At some point the attacker may realize that continued lead pursuit would result in passing the bogey at very high AOT (i.e., in his forward hemisphere). A barrel-roll attack is initiated with a wings-level pull-up and a roll toward the bogey, as with the lag roll. Since the range to the target is considerably greater, however, the climb established is con tinued for a longer time, resulting in a greater altitude advantage over the defender. Again the rolling pull is timed with the target's motion so the attacker arrives at a position well above the bogey, inverted, before passing slightly behind the defender. As the attacker approaches the overhead position his altitude advantage and gravity assist may provide the oppor tunity for him to pull hard down toward the target, remaining inside the horizontal boundaries of the bogey's turn, for a "high-side" (i.e., coming down from above and to one side) gun-firing pass. Or, depending on relative aircraft performance, available weapons, or bogey maneuvers, the attacker can delay and moderate his pull-down slightly to arrive at a lag-pursuit position.

Vertical and Oblique Turns

Since many fighters are unable to maintain corner speed at maximum G (i.e., they are power limited under these conditions), nose-low spirals often maximize turn performance for them. The optimum descent angle de pends on many factors, even for the same aircraft with the same power. These factors include weight, configuration, and altitude; greater weight, increased drag, and higher altitude usually require steeper descents.

The fighter pilot is concerned not only with optimizing absolute turn performance, however, but also with his performance relative to that of his opponent. Maximum performance is of little value if the aircraft is turning in the wrong direction. For instance, if a defender wishes only to maximize AOT for an attacker in the rear hemisphere, the defender generally should turn toward the attacker in the plane of the attack, assuming his aircraft is physically able to maneuver in this plane. This usually is accomplished in high-G situations by rolling to place the opponent near the vertical longitudinal plane (i.e., perpendicular to the wings) so that all the radial acceleration is working in the right direction. If both fighters are using the same technique this results in co-planar maneuvering.

Placement of the radial-acceleration vector, which for simplicity can be called the lift vector, may be compared with placement of the velocity vector in performing lead, pure, or lag pursuit. Since these two vectors define the maneuver plane, the velocity vector will follow where the lift vector pulls it. Placing the lift vector ahead of or behind the target in out-of-plane maneuvers is essentially lead or lag pursuit, respectively, and is used for the same reasons lead or lag pursuit are used, as demonstrated by the lag displacement rolls and yo-yos.

The effects of vertical and oblique maneuvers on an aircraft's energy state can also influence the outcome of an engagement. Possibly the best way to approach this concept is to determine the fighter's sustained-G capabilities (level, constant speed) at its given conditions of weight, power, configuration, and altitude. If a fighter is in a descending or climbing maneuver, this same load factor cannot be exceeded without loss of en ergy. For instance, in a nose-low oblique turn the rate of descent is equiva lent to negative specific excess power (Ps). (See the energy-maneuver ability discussion in the Appendix for an explanation of Ps.) If the pilot adjusts load factor to maintain constant speed, he is losing energy in proportion to his descent rate, but he is also increasing his turn rate. In order to maintain energy in such a maneuver he must reduce G and constantly accelerate, which would result in approximately the same turn rate in this oblique maneuver plane that he could achieve in a level, constant-speed turn at his altitude. However, if speed is allowed to in crease to a value higher than that best for sustained maneuvering, allow able G for maintaining energy will decrease further. Likewise, even un loaded dives at speeds higher than maximum level airspeed may reduce total energy, even if the aircraft continues to accelerate.

Long Range Discrimination Radar

The principle of discriminating against electromagnetic signatures of discrete systems has been, and will continue to be, paramount within the field of homeland security, and the defense-field, in totality. In as much, the study of electomagnetic signatures has brough about a sub-field of armed defense systems, identified as "electromagnetic warfare" (i.e., "EW"). There are numerous categories relegated to that of EW, such as "countermeasures," and "counter-countermeasures," etc. Whereupon the topic being discussed concerns itself primarily that of EW "countermeasures;" specifically, the topic of "Kalman filtering for systems with spatiotemporal dynamics."

Albeit the significance of LRDR is the multiple-simulataneous tracking of both position and velocity of aeronautic systems, implemented by and integrated radar system. To illustrate the last statement, "spatiotemporal dynamics" concerns itself with the convoluted relationship between "spatial resolution," and "temporal resolution." In a sense, the concept of spatial resolution within the context of LRDR is the ability to distinguish discrete electromagnetic signatures within a specific field of view, which in this case, is the field of view of the deployed LRDR system; temporal resolution is the ability of tracking that given EM system in real-time (i.e., the time latency is minimized when observing that given system). It is important to clarify the meaning of electromagnetic signatures in the context of LRDR. Specifically, electromagnetic signatures of the domain of the LRDR relate specific electromagnetic systems where these systems, by the advent of industrial processes, give rise to a specific electromagnetic signature that is explicitly associated with a certain class of an object. Meaning, each given discrete element within the set of possible aeronautic systems for which the given LRDR is tracking, for each given discrete element within that aeronautic set, there exists a unique electromagnetic signature. Albeit, that given EM signature must either be provided to LRDR operating personnel by the manufacturer who engineered the given EM system. Or, that given EM signature must be deduced through "observation." Wherein, an electromagnetic signature within the context of applied physics is the resonant frequency of a given topological structure; the identifier of a topological structure is used explicitly because properties of topologies do not change with scale.

Herein, LRDR personnel have databases of EM signatures for a plethora of aeronautic systems. Now, the operation of LRDR relative to EM signatures (i.e., the resonant frequency) of an aeronautic topology is that when LRDR is deployed, its field of view (i.e., the "FOV") for which these aeronautic systems are tracked (both within the dimension of space — spatial resolution, and the dimension of time — temporal resolution) produces a space for which electromagnetic vector fields produce a differential of electromagnetism between the environment for which the given aeronautic system traverses, as compared to when that given system is within and without the LRDR field of view. From here, the given electromagnetic signature can be calculated by measuring the difference of the EM signature of outside the FOV and inside the FOV to generate an EM signature for which the given system can be identified. Herein, the mechanisms for which this difference in electromagnetic signatures works, in the motivations for identifying aeronautic systems within an LRDR FOV is through the topic of "diffusion weighted imaging" (i.e., DWI).

Detailing the importance of DWI, the implementation of it relegates itself to the differences of EM "weightings" (i.e., DWI "b-values") whereupon the difference between those given b-values produces an identifying EM signature explicitly, and specifically associated with a given discreet element, where in this case is an aeronautical system, such as a fighter jet, or an unmanned aerial vehicle (i.e., a UAV). Therein, DWI oriented-systems must have two different b-values for which to classify a given object.