One-vs-One Maneuvering: Dissimilar Aircraft

Dissimilar fighters are fighters that have some performance characteris tics which differ from those of the opponent by more than about 10 percent. The performance measures of most interest are turn performance (both instantaneous and sustained) and energy performance (climb, accel eration, and speed). Of course there are many other ways in which fighters may differ (e.g., roll and pitch performance, size, pilot visibility limits, combat endurance, and radar capabilities). The influence of some of these factors is also discussed when appropriate.

Instantaneous turn performance is deter mined primarily by the ratio of aerodynamic lift to aircraft weight at low speeds (i.e., below corner velocity) and by the ratio of structural strength to aircraft weight at high speeds. Except in cases of extreme disparity in structural strength between fighters (i.e., on the order of a 50 percent advantage in maximum structural G for one aircraft), this limit is not usually as important in air combat as the aerodynamic limit. When a fighter pilot finds himself in a serious defensive situation, and to some extent when he is very near a lethal offensive position, he will use what ever G is required to save himself or to get the shot. A few popped rivets or some wrinkled skin is a small price to pay for the pilot's life or for a downed enemy aircraft. Since World War I there have been very few instances when a pilot has actually pulled the wings off his own fighter. Limits of struc tural strength must be adhered to in peacetime, however, since over stresses result in additional maintenance time, expense, and lost training. Therefore, ways must be found of winning within the design limits of the aircraft.

The relative low-speed instantaneous-turn-performance capabilities of two fighters can be determined by comparing their velocity-load factor (V-n) diagrams (see the Appendix). The aircraft with the greatest usable G capability at a given speed has superior instantaneous turn performance (i.e., faster turn rate and smaller radius) at that speed. This G capability reflects the maximum lift-to-weight ratio of the fighter, which depends to a great extent on the ratio of aircraft weight to total wing area, commonly called the "wing loading." As explained in the Appendix, wing loading alone can be misleading in this regard if one fighter has a more efficient wing for producing lift, possibly as a result of maneuvering slats or flaps. The way in which wing loading is calculated provides a further complica tion, as illustrated in Figure 4-1. The wing loading of the F-14 fighter shown here might be stated conventionally as 97 Ibs/sq ft, based on the shaded area in the left-hand silhouette. The very broad fuselage of this aircraft, however, provides a large proportion of the total lift, particularly at very high AOA, so a more realistic value of wing loading (54 Ibs/sq ft) might be based on the area shaded in the right-hand silhouette.

Because of these complications it will be necessary to make some assumptions to simplify maneuver discussions. Therefore, the term low wing loaded is assumed to denote superior instantaneous turn perform ance and slower minimum speed.

Sustained turn performance is a little more complex. The Appendix explains that sustairied-G capability is the result of a fighter's thrust-to weight ratio (T/W) in combination with its aerodynamic efficiency, which may be expressed as its lift-to-drag ratio (L/D) at the particular maneuver ing conditions. But G alone does not make turn performance, as turn rate and radius are also dependent on airspeed. Lower airspeed at a given G level improves both turn rate and turn radius. All else being equal, low-wing loaded aircraft tend to achieve their best sustained G at a lower speed, and therefore they often have a sustained-turn advantage. It is possible, how ever, for a high-wing-loaded fighter to have better sustained turn rate at a higher airspeed by sustaining much greater G, which, in the case of aerody namically similar aircraft, could be achieved with greater T/W. Sustained turn radius, however, is such a strong function of airspeed that the low wing-loaded fighter nearly always has the advantage here, regardless of T/W. In this chapter a low-wing-loaded fighter is assumed, unless otherwise stated, to have an equal or better sustained turn rate and a tighter sustained turn radius than its high-wing-loaded opponent.

A fighter's aerodynamic efficiency, in particular its lift-to-drag ratio, is also vitally important to energy performance, especially at high G or high speed. In order to simplify this discussion, however, the term high T/W infers greater climb rate, faster acceleration, and higher maximum speed capability relative to the opponent.

Obviously fighter performance can be a complex subject, and the num bers alone don't always tell the whole story. Development of effective tactics against dissimilar aircraft is, however, highly dependent on inti mate knowledge of all aspects of relative fighter performance and design, as well as total familiarity by the pilot with his own aircraft and weapons system. Comparison testing, in which enemy aircraft are flown against friendly fighters, is undeniably the best method of gathering this crucial information.

Low Wing Loading versus High Thrust-to-Weight

Encounters between a low-wing-loaded fighter and an enemy fighter with greater T/W are quite common. In this case each fighter has performance advantages and disadvantages relative to its opponent. The engagement strategy is for the pilot to exploit the opponent's most serious weaknesses while taking full advantage of his own fighter's greatest strengths.

The low-wing-loaded fighter's greatest performance advantages are assumed to be good instantaneous turn performance, slow minimum speed, and a tight sustained turn radius. In some cases this aircraft also might have a significant sustained-turn-rate advantage. Its weaknesses include inferior climb and acceleration performance under low-G condi tions, and slower "top-end" speed.

These characteristics are ideally suited to the use of angles tactics as described in the last chapter. One of the problems of the pilot of a low wing-loaded fighter is how to get close to an opponent who has greater speed capability. This may be accomplished with geometry by use of pure and lead pursuit. High and low yo-yos and barrel-roll attacks also may be useful. Since the high-T/W opponent has better climb capability and vertical potential, the pilot of the low-wing-loaded fighter should attempt to constrain the fight to the horizontal plane as much as possible. Nose-to nose turns make best use of a turn-radius advantage, and lead turns can be devastating because of instantaneous-turn superiority. A flat scissors should be lethal to the high-T/W fighter since it suffers from both a turn-performance and a minimum-speed disadvantage. The low-wing loaded aircraft might also have some advantage in a rolling scissors be cause of better slow-speed controllability, but usually not so great an advantage as in the flat scissors. In cases where the high-T/W enemy has a sustained-turn-rate advantage, the rolling scissors generally should be avoided.

On the other hand, the pilot of a high-T/W fighter should concentrate on energy tactics when he is engaging a low-wing-loaded opponent. Lag pur suit and vertical/oblique maneuvers are necessary ingredients. Nose-to tail geometry is usually preferable because of the assumed disparity in turn radii.

The defensive spiral might be handy if the pilot of the high-T/W fighter finds himself at a serious disadvantage, A high-wing-loaded aircraft often can generate much greater induced drag than a low-wing-loaded adversary, which may lead to a rapid vertical overshoot and subsequent position advantage for the high-T/W fighter. If this advantage cannot be capitalized on quickly, however, the low-wing-loaded bogey may use its superior low-speed turn performance to shallow out its spiral and regain the upper hand as the maneuver continues.

The Angles Fight: Guns Only

The angles tactics recommended in the similar-aircraft guns-only scenario are almost all relevant to the low-wing-loaded fighter in this case. There are a few slight differences in detail, however. For instance, in the similar aircraft case each fighter attempted to gain an energy advantage over the other by climbing or accelerating before the first pass. In this case the bogey's higher T/W may allow it to win this preengagement race and achieve a speed and/or height advantage. To reduce this factor to a mini mum, the pilot of the angles fighter might choose to cruise at an altitude well above that at which bogeys might be expected, so that his initial height advantage may offset the bogey's preengagement performance and provide the low-T/W fighter with an energy advantage, or at least make it nearly equal in energy to the high-T/W fighter at the beginning of the fight. Since the low-wing-loaded fighter is likely to have lower maximum speed capability, some height advantage is desirable at the pass to help ensure energy parity. Practical considerations such as visibility and weapons system performance, however, may prevent use of this technique.

Another consideration is the performance superiority of the low-wing loaded fighter at slow speeds. For example, its best climb speed, best sustained-turn speeds, and minimum vertical-maneuvering speed all are probably lower than those of its high-wing-loaded adversary. This slow speed efficiency improves relative performance in nose-to-nose turn situa tions. The angles fighter also may have some sustained-turn-rate advan tage, which would enable it to make angular gains in nose-to-tail turns with little relative energy sacrifice, but this process would be very slow and is definitely inferior to the nose-to-nose technique.

In approaching the initial pass, the angles fighter should attempt to generate some flight-path separation for a lead turn, as shown in Figure 3-1. Turn-performance superiority should provide the low-wing-loaded fighter with some angular advantage at the pass. If the bogey continues straight ahead or turns away from the attack to set up a nose-to-nose condition, the angles fighter should continue in the original turn direction. Should the bogey turn toward the attack, however, a turn reversal is called for, as depicted in Figure 3-1. Since the pilot of the low-wing-loaded fighter does not have to optimize his turn performance to gain an advantage on the opponent, best sustained-turn-rate speed, rather than corner velocity, is normally the best engagement airspeed. Because energy is so critical for this fighter, the pilot should maneuver only as hard as necessary. Quite often small angular gains can be made in nose-to-nose situations simply by using level sustained turns.

Throughout the fight, the pilot of the angles fighter can be somewhat less concerned with overshoots than he would be in the case of similar fighters, since the bogey's larger turn radius and higher speed make it more difficult for its pilot to gain advantage after an overshoot by the angles fighter. Gross vertical overshoots still should be avoided, however, since they may allow the bogey at least a temporary advantage, and possibly a snapshot, after one turn of a rolling scissors. Minimum vertical maneuvering speed should be observed whenever the angles fighter is in close proximity with the bogey to guard against zoom maneuvers. Greed is the angles fighter pilot's greatest enemy. He should avoid trying to grab angles faster than his aircraft's performance permits. Once further angular gains can no longer be made at speeds greater than that required for vertical maneuvering, the high-wing-loaded fighter must have bled its speed down to or below that of the angles fighter, so the bogey should have little vertical potential remaining. In this case the pilot of the angles fighter can safely bleed to slower speeds and finish off his opponent.

Whenever he is engaging in a zooming contest, the angles fighter pilot must take care not to allow his speed to bleed below that required for control in level flight (i.e., power-on stall speed). Once the nose is parked near vertical, it is all too easy to let the airspeed fall below this value, even to zero, in an attempt to get a few more feet of altitude out of the zoom. If this is allowed to happen, the nose of the airplane will soon become an "earth seeker," falling to a near-vertical nose-down attitude. Even if the pilot can maintain control during this maneuver, he will have very little G available with which to fend off an attack by the higher bogey, which now has been placed astutely in the rear quarter.

Should a vertical overshoot occur, however, and the angles fighter pilot find himself level with or below the bogey in the spiral, decelerating tactics should not be attempted. Instead, the low-wing-loaded fighter pilot can continue the spiral to defeat any guns solution while slowly pulling out of the dive at full power and maximum lift. The turn-performance advantage of the low-wing-loaded fighter should allow the pilot to shallow his dive angle more quickly, causing the high-wing-loaded bogey to overshoot vertically, again becoming defensive.

The Energy Flight: Guns Only

The preceding scenarios of angles tactics should make the task of the energy fighter pilot evident. The pilot of the high-T/W fighter must avoid getting shot until he can build a large energy margin, allowing him to zoom well above his opponent and position for a high-to-low gun attack. A steep approach to a high-side gun pass helps the high-wing-loaded fighter com pensate for his turn-performance deficiency. Roll rate can be substituted for turn rate to accomplish much of the heading change required in man euvering to a gun-firing envelope, and in a steep diving attitude the energy fighter has to oppose less gravity than it would when performing a level turn. It should be noted, however, that while the guns approach may be a steep dive, the firing pass itself usually is more successful if it can be shallowed somewhat, as discussed later. Even with these advantages, however, the pilot of the energy fighter should not expect a lengthy track ing gun shot against a well-flown low-wing-loaded fighter with a substan tial instantaneous-turn advantage, since this bogey nearly always can generate enough turn performance to keep the energy fighter out of steady tracking parameters. The major exceptions to this rule occur when the bogey pilot loses sight of his attacker or the bogey is near stall speed at tree-top altitudes. Although the energy fighter pilot can work at creating these conditions, a lethal snapshot opportunity often will be achieved first.

Obviously, an energy fighter must have a substantial altitude advantage over its opponent immediately preceding an effective high-side or over head gun pass. The exact amount of this required advantage depends on many factors, but in general the altitude advantage should be about equiva lent to the minimum instantaneous turn radius of the energy fighter. That is, a fighter that can generate a minimum horizontal turn radius of 2,000 ft at engagement altitude and optimum speed (i.e., below corner speed) would require about a 2,000-ft altitude advantage for an effective overhead or steep high-side gun attack. A well-flown angles fighter can be expected to deny such an altitude advantage, if possible, whenever the energy fighter is near guns range. The bogey pilot may do this by zooming with the energy fighter or by saving enough airspeed to allow a vertical pull-up, if neces sary, to meet the diving attacker nearly head-on.

Engaging with an Initial Energy Advantage

Depending on relative performance, the energy fighter pilot may be able to assure the desired energy advantage at the first pass by attaining a speed that is well above the maximum capability of the low-T/W bogey. This is common when a supersonic fighter engages a bogey that is limited to subsonic speeds. Just how much excess speed is required can be estimated using an altitude Mach (H-M) diagram or Equation 3 in the Appendix before the engage ment. Assuming an engagement altitude, the bogey's maximum attain able energy level can be located on the chart. Adding the desired energy (altitude) advantage to the bogey's energy level determines the approxi mate energy level required of the high-T/W fighter. The speed at which this desired energy level intersects the engagement altitude represents the necessary airspeed of the energy fighter.

The speed advantage necessary to provide a given zoom-altitude advan tage is highly dependent on the bogey's airspeed. For example, a 2,000-ft zoom advantage over a bogey traveling at 100 knots true airspeed (KTAS) would require the energy fighter to have about 130 knots of excess airspeed (230 KTAS total). But with the bogey at 500 KTAS, the energy fighter would need about 540 KTAS (only a 40-knot advantage). Although faster bogeys require less speed advantage for the energy fighter to attain a given zoom-altitude margin, this phenomenon is offset to a large degree because faster fighters generally need more altitude margin. The figures given here are only gross estimates, since they do not consider possible energy changes during the zoom maneuver.

In this scenario the energy fighter has a substantial speed advantage approaching the pass (time "1") as well as slightly greater altitude. Together this speed and altitude advantage form the high-T/W fighter's desired energy margin. The purpose of the height advantage in this case is not only to provide extra energy margin, but also to induce the bogey pilot into a sharply nose-high maneuver. Allowing some vertical separation (i.e., passing almost directly over the bogey) gives the bogey room for a lead turn, but the pilot must turn almost purely in the vertical to take advan tage of it. Too much separation here may provide the low-wing-loaded opponent a reasonable snapshot at the pass, while too little vertical advan tage offers him little incentive to zoom. An altitude advantage at the pass equal to about one-quarter of the bogey's best turn radius is usually a good compromise.