Acceleration

The three primary factors affecting acceleration are altitude, attitude, and airspeed.

4.6.5.3.1. Effects of Altitude

The lower the density altitude the more effective the acceleration will be because of increased thrust.

4.6.5.3.2. Effects of Attitude

The total energy gained during an acceleration maneuver is a trade off between airspeed gained and altitude lost. Aircraft attitude determines the effect of gravity on an acceleration maneuver. If the aircraft velocity vector is above the horizon, acceleration effectiveness is reduced. If the aircraft velocity vector is below the horizon, effectiveness is enhanced. Aircraft G loading effects induced drag and acceleration effectiveness. The fastest airspeed gain occurs in an unloaded (0 G), nose-low acceleration. The end result of this maneuver is a large altitude loss and very nose-low attitude that may be unacceptable in an aerial engagement. If altitude is a factor, select AB and fly a 0.7 to 0.9 G, slightly nose-low extension maneuver. While airspeed gain will not be as rapid as at 0 G, altitude loss is minimized and you will not bury the nose. The point to remember is that the closer you are to 0 G, the faster you will accelerate, but you will bury the nose more and lose more altitude. This is especially important in an attempt to separate from an opponent, because if the nose is buried in a very nose-low, unloaded acceleration, the resulting high G pullout may provide the bandit a chance to affect a lead pursuit course or "arc you" during the ground avoidance turn. In any case, however, attempt to get the nose below the h orizon before establishing the "optimum G" for an acceleration. Rarely will a nose-high acceleration be effective.

4.6.5.3.3. Effects of Airspeed

Acceleration is a trade off between thrust and drag. Thrust increases at a greater rate than parasite drag with velocity increases over the speed range of 100 KCAS to 450 KCAS (or 0.95 mach whic hever comes first) due to the ram air effects on the engine. Above 450 KCAS, acceleration rates decrease as drag becomes dominant (both parasite drag and compressibi lity drag). As a rule of thumb, the best acceleration rates occur in the speed range from 300 to 400 KCAS.

Figure 4.18 Effect of Bank Angle on Separation

Often, the purpose of an acceleration m aneuver is to separate from an adversary—get beyond his maximum missile range. In this case, the object is to fly a straight line over the ground to prevent the adversary from arcing. As bank angle increases from wings level to 90°, the corresponding "optimum" acceleration G decreases (to maintain a straight line flight path). At 0.9 G and 90° of bank, the aircraft is turning laterally as though it was in a 30° (rejoin) level turn (Figure 4.18). To reduce the potential for arcing, reduce G to 0 when approaching 90° of bank.

4.6.6. Lead Turns

A lead turn is the most efficient BFM maneuver. A lead turn is nothing more than an attempt to decrease angle-off prior to passing the opponent's 3/9 line. It can be done in any plane (horizontal, vertical or combination of both). The classic lead turn is accomplished by the pilot offsetting his flight path one turn diameter from his adversary. He observes where his opponent is going and predicts where he will be at some point in the future. He then initiates a turn to arrive at a point in space with reduced aspect and angle-off (Figure 4.19). Plan to lead turn to a position about one turn radius behind the defender.

Figure 4.19 Lead Turn

The size of your turn circle, turn rate capability, and the defender's airspeed will determine the point you initiate the lead turn. Considerable judgment is required to properly initiate and execute a lead turn so as to arrive within the intended weapons parameters. It is important to stress that a lead turn requires the initiation of the turn forward of the defender's 3/9 line. (Remember turning room for one is also turning room for the other and the tighter turning fighter has the advantage.) The point to start the turn is based on the question "Can I make that corner?" When the answer is "Yes," start the turn. You may also notice the proper lead point as where LOS movement increases. The lead turn oppo rtunity normally begins inside the bandit’s turn circle, and just as the LOS rate changes as you enter a bandit’s circle from a 9,000 foot perch setup, the LOS rate will increase in a high aspect pass as you enter the bandit’s turn circle, except that the change in LOS rate is not as apparent. This LOS rate is that caused by the relative motion between the fighter and the bandit, not the apparent LOS rate caused by fighter maneuvering. During the turn, G should be adjusted as required to keep the adversary moving slightly forward along the horizon (horizontal turn). The objective is to roll out behind the adversary. The more turning room acquired, the longer the range for lead turn initiation and the lower the G -loading required to complete the maneuver. Conversely, if the maneuver is initiated at short range with little or no offset, a high-G turn will be required to complete the maneuver. The uprange distance at which a lead turn is initiated will govern the roll-out range at the target's six (Figure 4.20). Lead turns against a target that maneuvers prior to passing your 3/9 line will not produce a dead six position, but should still result in some turn advantage. Bandit LOS rate aft on the canopy and aspect less than 180 are the visual cues for a lead turn and work for both horizontal and vertical conversions. these cues only take into a ccount positional advantages, not energy differences. Once LOS movement becomes apparent, put the lift vector in lead of the bandit and use enough G to keep the turn rate as close to the LOS rate as possible, or allow the LOS to drift slightly forward. If you pull to exceed the bandit’s LOS rate (bandit moving forward on the canopy) you may be turning belly up to the bandit and risk becoming defensive, unless the conditions permit a no-respect lead turn. A bandit who turns to pass 180 aspect with you will not allow a lead turn. If you were to try to lead turn a bandit 180° out prior to passing him, and without seeing the proper cues, you could allow yourself to be lead turned unless you are in a no respect lead turn situation.

Figure 4.20 Lead Turn to Weapons Parameters

A lead turn may be attempted without turning room simply by initiating a turn prior to passing the opponent's 3/9 line. This is commonly referred to as a "no respect" lead turn and should only be done if you can definitely out perform the defender or if you are positive the bandit has not detected you. If the opponent continues on his present course, the attacker will roll out with decreased angle-off, but will still have a small aspect angle problem (Figure 4.21). This lead turn may be easily countered by pulling away from the direction the attacker is turning and continuing to build angle-off (Figure 4.22). If the attacker initiates the turn well outside the defender's turning circle, the defender can slow his forward vector (throttle, speed brakes, out-of-plane) and allow the attacker to fly in front of the former defender's 3/9 line (Figure 4.23).

Figure 4.21 Lead Turn Without Turning Room

Lead turns can be accomplished in any plane. Assuming airspeed is in the "corner plateau" region, lead turns going down will require slightly less offset than lead turns going up. A lead turn down or a split-S is useful because it preserves airspeed. This is especially important if the adversary has a predictable flight path due to a low energy state. The adversary must try to deny the lead turn with a turn degraded by the effects of gravity. If the attacker achieves offset above his adversary, but is hesitant to commit to a nose-low slice, he may lead turn in the horizontal. This is done by pulling to a lead point in a plane above the bandit's flight path. Although not as efficient (there is still an aspect problem to be solved) as a turn done in a plane with the bandit, it preserves nose position (the vertical HCA between the attacker and defender) and prevents a vertical overshoot should the bandit counter the lead turn by pulling up and into the attacker. A lead turn up is effective because it allows visual contact with the defender while possibly placing the attacker in the defender's blind zone. A lead turn coming from low to high takes great advantage of radial G during the terminal portion of the turn (when the attacker's lift vector is below the horizon). The lead turn in the vertical should be avoided if over the top airspeed is not achieved (minimum of 250 KCAS level) or a significant energy advantage does not already exist (ascending aircraft does not have vertical maneuvering potential). Lateral offset should be achieved as necessary to maintain a tally during the maneuver.

4.6.6.1. No-Respect Lead Turn (Lead Turn Without Turning Room)

A no-respect lead turn can be accomplished against a bandit that does not see the fighter or a turn deficient bandit (Figure 4.21). If the bandit does not see the fighter, the end result is an unobserved conversion turn. A turn deficient bandit has a either very large turn radius and/or a very slow turn rate generally because of two reasons-either the bandit is extremely fast or extremely slow. For example a bandit traveling at Mach 1.3 will have a very large turn radius compared to a fighter near corner velocity. The fighter at corner velocity can begin a lead turn well ahead of the bandit’s 3-9 line, giving up angles and even going belly up to the bandit. But because of the bandit’s high airspeed and the inability to perhaps bleed it down quickly, he cannot take advantage of the angles the fighter is giving up. A second example is a very slow bandit coming down from over the top. If a bandit goes vertical and is coming down slow on airspeed, a fighter may lead turn the bandit and even go belly up to the bandit prior to the 3-9 line because the bandit is too slow to bring his aircraft to point at the fighter lead turning in front of him. The above two examples are extreme cases where a bandit cannot stop a fighter from lead turning in front of him because of an airspeed related performance limit.

4.6.6.2. Counters

The counter to a lead turn is to r emove the offset prior to the lead point, i.e., take your share of turning room by beginning your own lead turn. Against aircraft with inferior turn performance, if the pilot plans and initiates a lead turn at the proper range, he will automatically negate any turn his opponent attempts (Figure 4.24). The opponent with an inferior turn performance will initiate a lead turn sooner than you wish to initiate yours. The inferior turning aircraft will also strive for more lateral offset than you need for your own turn. This can be easily countered by turning to deny his lead turn and initiating your own lead turn at the proper point for your turn capability. This will quickly develop into a lagging contest won by the aircraft generating the best sustained turn rate.

Figure 4.24 Denying Lead Turn Versus Inferior Performer

Against an aircraft with superior turn performance, or if you have gotten slow and have less turning capability, a defending pilot should fly directly at his opponent, eliminating all offset and denying any chance for a lead turn. It is important that he make the turn to point at his opponent prior to the point where the opponent transitions inside the defender's turn circle. The sooner this is accomplished, the less severe the maneuvering required to deny the lead turn (Figure 4.25).

4.6.7. Energy Versus Position

Energy is the potential to maneuver. However, too much energy can be a dangerous thing. Excessive speed can lead to severely degraded turn performance, minimum time in weapons parameters, and reduced station time. The key to the fighter pilot is the determination of how much energy he needs and how much he is willing to expend for a given positional advantage. BFM allows the achievement of weapons parameters with minimum energy expenditure in as little time as possible. This concept of efficient maneuvering is important because in a tactical situation, it will dictate how much BFM is to be employed in a given engagement. How much predictable time can the F-16 pilot afford on one attack with regard to the entire tactical environment? How much energy or future maneuvering potential can be expended for a given positional advantage? Will that position be sufficient for the kill or will it just prolong the maneuvering, requiring more time and energy? All these questions must be asked and evaluated to determine the trade off for a given situation. Obviously, high energy bleed off for position is justified to achieve firing parameters against a Flogger attacking the home drome, while the same P s expenditure may be unwise in an outnumbered sweep vs sweep scenario deep in enemy airspace. Energy and position must continually be balanced by the fighter pilot. BFM is a tool the F-16 pilot uses to achieve this balance—always trading energy for position and using position to employ ordnance, remaining cognizant of his own need for survival.