4.6. Principles/Concepts Of Basic Fighter Maneuvers (BFM)
The maneuvers required during a BFM engagement are nothing more than a combination of those learned during AHC. The primary objective of BFM is to maneuver your aircraft into weapons parameters to employ ordnance. To accomplish this you may first need to maneuver so as to keep a bandit from employing ordnance against you. The required maneuvers are not pre-staged to arrive at the end game solution, but are combined as necessary based upon continual reassessment of the situation. The entire process of observing, predicting, and maneuvering is repeated until either a kill or disengagement has been achieved. In order to successfully execute BFM, a pilot must understand his geometric relationship to the target and how it affects his ability to employ his weapons. The spatial relationship of two aircraft can be analyzed from three perspectives: positional geometry, attack geometry, and the weapon envelope.
4.6.1. Positional Geometry
When discussing one aircraft's position relative to another, range, aspect angle, and angle-off (heading crossing angle [HCA]) are used to describe angular relationships. These three factors dictate which aircraft enjoys a positional advantage, and how much of an advantage it is (Figure 4.1). Range is the distance between two aircraft. Aspect angle describes the relative position of the attacker to the target, without regard to the attacker's heading. It is defined as the angle measured from the tail of the target to the position of the attacker. Angle-off is primarily concerned with the relative headings of two aircraft. Angle-off is defined as the angular distance between the longitudinal axes of the attacker and the defender. Whenever the attacker is pointing at the defender, the aspect angle and angle-off will be the same.
Figure 4.1 Angular Relationships
4.6.2. Attack Geometry
There are three available attack pursuit courses: lead, lag, and pure (Figure 4.2). The attacker's nose position or his lift vector will determine the pursuit course being flown. If the attacker is in the defender's plane of turn, the position of the attacker's nose determines the pursuit course. With his nose pointed in front of the defender (such as in the case of a gunshot), he is in lead pursuit. If he points behind the defender, he is in lag pursuit. If he points at his adversary, he is in pure pursuit. Note that an initial lead pursuit attacker could be driven into a lag pursuit course if he has insufficient turn rate available to maintain lead (Figure 4.3).
Figure 4.3 Insufficient Turn Rate To Maintain Lead (Resulting in Lag)
When the attacker is out of the defender's plane of turn, his pursuit course is determined by where his present lift vector (the top of his canopy) will position his nose as he enters the defender's plane of turn. For example, if forced out-of-plane by a defender's hard turn, an attacker may have his nose pointed behind the defender during the reposition. After gaining sufficient turning room, if the attacker pulls far enough in front of the bandit to arrive back in-plane with his nose in front on the defender, then he is in lead pursuit. The same holds true for pure or lag pursuit (Figure 4.4). Whether to establish a lead, lag, or pure pursuit course will depend on the relative position of the attacker with respect to the defender's turn circle (TC). The key at point C is to be sure you will enter the defender's turn circle aft of his wingline with the ability to establish an in-plane, lead pursuit course at point D.
Figure 4.4 Out-of-plane Maneuvering
4.6.3. Weapons Envelope
The vulnerable cone of a defender is defined using range, aspect, angle-off, and pursuit course to approximate the employment envelope for a specific type of ordnance. BFM is used when nece ssary to decrease range, aspect, and angle-off, or until an attacker is within the bandit's vulnerable cone for the ordnance he plans to employ.
4.6.4. Turning Room
In order to discuss how BFM can solve range, aspect, and angle-off, a concept called turning room and turning circles is used. Turning room is the separation between the two aircraft that can be used to accelerate, to decrease range, or turn and decrease aspect angle and angle-off. A turn circle is defined by aerodynamics and is based on a certain size (the diameter) and how quickly an aircraft can move its nose (turn rate). The determinant of whether an aircraft is (at any instant in time) "inside" or "outside" of a defender's turn circle is the relationship between the attacker's aspect angle and range and the defender's turn radius/rate. If the defender is turning at a rate that will allow him to continue to i ncrease aspect angle, the attacker is outside the defender's turn circle (Figure 4.5). At the instant the defender can no longer increase aspect angle, the attacker has "arrived" inside the defender's turn circle.
AAT "B" AND "C" ATTACKER ISINSIDE TURNING CIRCLE
OUTSIDE TURNING CIRCLE MCM0405
Figure 4.5 Outside/Inside The Turn Circle
The attacker's nose position (i.e., lead or lag) relative to the defender's current position and flight path does not strictly determine whether the attacker is inside or outside the defender's turn circle (Figure 4.6).
Figure 4.6 Lag Pursuit Outside/Inside the Turn Circle
As the defender bleeds off energy and airspeed, while performing his defensive turn, his turn radius will decrease. His turn rate will also decrease, once the defender slows below his corner velocity (discussed later). This relationship often results in a characteristic "fishhook" appearance to the defender's turn (Figure 4.7). The attacker may start inside the turn circle, but end up outside as the defender tightens his turn or slows below corner velocitydepending on the defender's ability to maintain the turn rate and how the attacker maneuvers. It is very important to note that turning room can be acquired in either the lateral or vertical planes or a co mbination of both. Another important note is turning room can be used by either aircraft.
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Figure 4.7 Fishhook Turn
Lateral turning room is in the bandit's plane of motion. The bandit's turn direction (into or away from the attacker) will affect how much turning room is available. If the attacker is inside the bandit's turn circle, he must have a turn rate and radius capability that will allow him to "make the corner" the bandit presents. The disadvantage of lateral turning room inside the bandit's turn is that it frequently requires high energy bleed rates to generate the turn rate required to make the corner and stay in the bandit's plane of motion. If the defender turns away from the attacker, turning room increases. If the attacker is on the belly-side of the defender's turn, part of his geometry problem is being solved initially since the bandit is rotating his vulnerable cone towards the attacker. Vertical turning room is acquired out of the bandit's plane of turn. If the bandit is in a vertical turn, this turning room may be located in a horizontal plane. If the bandit is in the horizontal, then turning room will be available either above or below his plane of motion. Range and closure will govern the amount of turning room that can be generated. Energy can be gained while maneuvering for turning room below. If the pilot elects to go for turning room above the bandit, he must have the airspeed to drive above the bandit while retaining sufficient energy to continue his attack. The attacker must remember his turning room is also the bandit's turning room. If the attacker does not have the energy to use the turning room, then he must deny the bandit the use of it. Turning room required is based on an aircraft's turn performance and turn geometry; therefore, a more maneuverable aircraft will not require as much turning room as a less maneuverable one. Turning room is normally established as you transition inside the defender's turn circle. Trying to establish vertical or lateral turning room outside the turn circle can result in the attacker becoming the defender. The same thing can happen while trying to build turning room starting from inside a defender's turn circle if you subsequently maneuver outside of his turn circle. The bandit may have the capability to force a role reversal similar to an overshoot. The attacker can recognize that he is inside or will transition inside the defender's turn circle by observing the defender. If the defender's present rate of turn will not bring his nose on the attacker and the attacker sees line of sight (LOS) movement by the defender, then the attacker is inside, or will transition inside, the defender's turn circle (Figure 4.8). Another visual cue is the defender's aspect angle remains constant or begins to decrease. As you can see from Figure 4.8, both attackers A and B begin outside the bandit's turn circle and transition inside. The position relative to the defender's 3/9 line has nothing to do with being inside or outside the defender's turn circle. The defender's ability to point at the attacker will determine whether the attacker is inside, will transition inside, or is outside of the turning circle. There are a myriad of things that determine the aspect and angle-off when transitioning into the defender's turn circle, i.e., range, V, defender's turn capability, and the aspect and angle-off when beginning the attack. The aspect and angle-off the attacker perceives at the transition will determine the initial pursuit course he elects. The actual aspect and angle-off as well as the turning room and relative energy states will dictate weapons envelope and the degree of BFM necessary to achieve a kill.