Aircraft Energy - maneuverability

There are five main things a pilot must remain aware of when contemplating aerial engagement, of which, getting sight of your opponent and keeping sight of them are the most important. Other major factors influence a dog fights are, thrust-to-weight ratio, wing loading, and the "corner speed" (the maximum/minimum speed at which the aircraft can attain the best turning performance). Apart from this, variable limitations must also be considered, such as turn radius, turn rate, and the specific energy of the aircraft.  The concept of energy awareness during air combat is not new. Wise use and conservation of energy during combat will increase your chances of victory.

When an aircraft is flying, it has both kinetic energy and potential energy. These energies can be easily converted to each other by initiating a dive, or by pulling the aircraft’s nose up.
 
Kinetic Energy: - Kinetic energy is related to airspeed. High levels of kinetic energy, or speed, are needed to perform many combat maneuvers.
 
Potential Energy: - Potential energy is related to altitude and the force of gravity on your aircraft.

If you have low speed (kinetic energy) but high altitude (potential energy), you can dive and pick up speed needed to perform a series of combat maneuvers. Conversely, if you have high speed but low altitude, you can convert this speed (kinetic energy) into altitude (potential energy) by climbing.

This combination of airspeed and altitude is often referred to as your energy state. The aircraft's ability to climb, dive, and accelerate to change this state is called energy maneuverability.
The level of energy of an aircraft is a function of the following primary flight parameters and of their rate of change (trend):
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• Airspeed and speed trend
• Altitude and vertical speed (or flight path angle)
• Aircraft configuration (i.e., drag caused by speed brakes, slats/flaps and/or landing gear)
• Thrust level

One of the tasks of the pilot is to control and monitor the energy level of the aircraft (using all available cues) in order to:

• Maintain the aircraft at the appropriate energy level throughout the flight phase
— Keep flight path, speed, thrust and configuration; or,

• Recover the aircraft from a low-energy or high-energy situation, i.e., from:
— Being too slow and/or too low; or,
— Being too fast and/or too high.
Controlling the aircraft energy level consists in continuously controlling each parameter: airspeed, thrust, configuration and flight path, and in transiently trading one parameter for another.
So what does this mean to you in combat situations? To illustrate this concept, consider the following examples.
 
Example 1. You're at low altitude, down in the weeds, approaching an enemy aircraft at the same altitude head-on. You're flying considerably faster than your opponent. In a tight turning fight, the slower plane will have the advantage, but you're thinking in three dimensions. So as you approach, you pull up into a steep climb and your opponent pulls up after you. This is called a zoom maneuver.
Since you possess more kinetic energy (you're flying faster), you're able to climb higher and gain the advantage. He'll run out of airspeed first and be forced to dive to regain it. You can then pitch back and dive to get on his tail.

Example 2. You're following an enemy aircraft flying at the same speed as you, but you're at a higher altitude. As your enemy twists and turns in an effort to escape, he'll lose speed (kinetic energy). If you follow him through those turns, you'll lose speed, too. But, because you're at a higher altitude, you'll have more potential energy, so you can dive to pick up speed, catch the enemy, and maneuver into a good firing position.
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What these examples mean to you, a fighter pilot, is that you must constantly keep an eye on your speed and altitude during combat. A heavy-handed pilot who twists and turns the aircraft around without paying attention to energy losses will soon be unable to maneuver. Once lost, energy is hard to regain; then your only hope is to dive hard and regain some speed (assuming, of course, you've left yourself enough altitude to perform this maneuver.) The lesson here is to avoid low altitude and low speed conditions. If you don't, you're a sitting duck for air-to-air or surface-to-air fire. Also, in this type of fight, it's easy to depart the flight envelope and stall. At low altitude, a stall generally translates into a smoking hole in the ground.

Specific energy of an Aircraft (energy per unit mass) He

Aircraft-specific energy represents the combined kinetic and potential energy of the vehicle at any given time. It is the total energy of the vehicle (relative to the Earth's surface) per unit weight of the vehicle and being independent of the mass of the vehicle provides a powerful tool for the design of optimal trajectories. A zero value of aircraft-specific energy is at the Earth's surface and increases as speed and altitude increases. The specific energy is computed by the total energy (as defined above relative the Earth's surface) divided by the mass of the vehicle. It is a key element in performance of aircraft and rockets.
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In aviation, the term "energy" does not refer to the fuel nor the thrust it produces. Instead, thrust is referred to as "power." Energy is the state of the fighter's mass at any given time, and is the result of the power. Energy comes in two forms, which are kinetic and potential. Kinetic energy is a function of the fighter's mass and speed, while potential energy is a function of its mass, gravity and altitude. The combined potential and kinetic energy is called the total energy, or "energy package." Because the energy package is the combination of mass, speed and altitude, a fighter flying at low altitude but a high speed may have the same total energy as a fighter of equal mass, but flying at a low speed and high altitude.
 
An aircrafts specific energy (energy per unit weight) is total energy divided by its weight; thus
 
He= (mgh+ 1/2mV2)/ W = h= (V2/2g)
 
An aircraft flying at 400ft/s & at an altitude of 7500 ft has an energy height of 9984.5ft. this means that it could  theoretically(if the aircraft was only subjected to gravity) reach a maximum altitude of 9984.5 ft by trading all of its KE for PE or it could achieve a velocity of 802ft/s at zero altitude by trading its potential energy for KE. However this neither takes into account any energy dissipitated by the aircrafts drag nor any energy input from the aircrafts thrust. The rate of change per unit time of energy height is called specific power Ps, which has unit of velocity
 
Specific excess energy (Ps)
 
The specific excess energy is proportional to the ratio of net motive forces compared to the weight of the plane and proportional to velocity.  The net motive force is found by calculating the engine's ability to move the plane after accounting for friction and other aerodynamic issues that slow down the plane.
 
Ps= (Thrust-Drag) Velocity/ Weight
 
Specific excess power represents the power available to an aircraft for use in maneuvers. This can be substituted for the specific power used, P. However, it should be noted that when Ps = 0 the aircraft can still climb, but its forward speed will reduce. Similarly the aircraft can accelerate, but only by descending at the same time.
 
 
The ratio (T-D)/W is similar to T/W, the Thrust-to-weight ratio, which is also used as a figure of merit for airplanes and rockets. By normalizing the motive forces to the weight of the plane, it is clear how efficient the plane is. A very large engine may be able to generate a huge thrust but could be so heavy that it would not even lift itself. The ratio is unity (T-D)/W = 1 when the engine is only powerful enough to keep the plane at constant speed in a 90 degree ascending trajectory.
 
The difference between the T/W and (T-D)/W are that T/W does not include the effects of friction and other aerodynamic losses. When a plane is moving very slowly, these losses are small and can be ignored. However, T/W does not accurately describe the performance of the plane at its normal operating conditions. By including drag in the formula, the aerodynamics of the plane are also summarized in the Ps value
 
Energy maneuverability theory can be used to provide specific excess power and turn capability of an aircraft throughout its operating envelope. The various maneuvers comprising a complete mission can then be optimized from this data and a convenient graphical method employed to analyze the mission performance.
 
The combat segment of a mission profile may specify n umbers of maximum maneuver turns or alternatively numbers of turns at a particular altitude, Mach number and power setting. A maximum maneuver turn is the maximum sustainable turn rate at a particular energy level. At any energy level the maximum turn rate occurs at the load factor (g’s) for which the Maximum energy rate is equal to zero (Ps = 0). Any further increase in turn rate results in negative Ps such that an aircraft experiences a loss of altitude or Mach number or both. However instantaneous turns at negative values of Ps are valid maneuvers. The ability of an aircraft to persist in combat can be conveniently quantified by computing the number of 360 degree turns that can be executed at a given radius from base. The number of such turns possible will depend on the aircraft energy level and the fuel available for combat.
 
The ability of an aircraft to change its energy in three-dimensional maneuvering flight is determined by its Ps. Given two fighters engaged in combat, the fighter with the higher PS will be able to out maneuver the other.
 
Air-to-air combat is frequently initiated at high speed, but is then characterized by a loss of energy and a reduction in air speed as aircraft jostle for supremacy. Therefore, the low speed Ps characteristics of combat aircraft are vitally important.
 
In designing a new fighter, it is necessary to have a Ps higher than that of the expected threat. In analyzing an existing fighter, it is useful to know the region of the flight envelope where it has a higher PS than that of a potential threat. Then, air combat should only be attempted at these values of height and Velocity. 

Energy Maneuverability
 
Energy Maneuverability is the analysis of maneuverability (the ability to perform a change, or a combination of changes, in direction, altitude, and airspeed) expressed in terms of energy and energy rate. Thus, energy maneuverability is not directly concerned with fuel consumption. However, use of appropriate energy maneuverability tactics can result in reduced fuel consumption also.
 
Generally, the fighter that is able to maintain a higher energy package will have the advantage. However, a high energy-package alone does not improve maneuverability, because optimum turn performance typically occurs within a range near a certain speed, called the "corner speed." Also, increasing the mass of the aircraft would increase its energy package, but angular momentum would hamper maneuverability, causing the heavier aircraft to turn wider circles. Instead, the fighter's useful energy is calculated by dividing its energy package by its weight, determining its specific energy (total energy per unit-weight). A fighter with less mass will generally be more maneuverable than a fighter with more mass, even if energy packages are equal, because the lighter aircraft has more specific-energy.
 
"Specific power," on the other hand, is the thrust divided by weight, and the fighter's ability to generate excess specific-power aids the craft in maintaining its specific energy longer when forced to turn at an energy-depleting rate. Typically, the fighter with higher energy (energy fighter) will make an "energy move" like an "out-of-plane maneuver," to maintain the energy-advantage, while the fighter at an energy-disadvantage (angles fighter) will make an "angles move" such as a break turn, trying to use the opponent's energy to their own advantage.
 
In combat, a pilot is faced with a variety of limiting factors. Some limitations are constant, such as gravity, structural integrity, and thrust-to-weight ratio. Other limitations vary with speed and altitude, such as turn radius, turn rate, and the specific energy of the aircraft. The fighter pilot uses maneuvers to turn these limitations into tactical advantages. A faster, heavier aircraft may not be able to evade a more maneuverable aircraft in a turning battle, but can often choose to break off the fight and escape by diving or using its thrust to provide a speed advantage. A lighter, more maneuverable aircraft cannot usually choose to escape, but must use its smaller turning radius at higher speeds to evade the attacker's guns, and to try to circle around behind the attacker.
 
Basic Fighter Maneuvers are a constant series of trade-offs between these limitations to conserve the specific energy state of the aircraft. Even if there is no great difference between the energy states of combating aircraft, there will be as soon as the attacker accelerates to catch up with the defender. However, potential energy can easily be traded for kinetic energy, so an aircraft with an altitude advantage can easily turn the potential energy into speed. Instead of applying thrust, a pilot may use gravity to provide a sudden increase in speed, by diving, at a cost in the potential energy that was stored in the form of altitude. Similarly, by climbing the pilot can use gravity to provide a decrease in speed, conserving the aircraft's kinetic energy by changing it into altitude. This can help an attacker to prevent an overshoot, while keeping the energy available in case one does occur.
 
While an actual air combat encounter lasts only a few minutes, considerable preparation must precede the encounter. A prerequisite for a successful or at least neutral encounter is knowledge of the maneuvering capability of both the friendly and adversary aircraft. Prior to any encounter a pilot must compare his energy maneuverability with that of a potential adversary. Armed with this knowledge the pilot can then develop tactics which favor his aircraft and which may force his adversary to fly in a regime where the adversary aircraft has less capability.
 
Defensive
 
The prime objective for the pilot on the defensive is that of remaining out of the adversary's cone of fire. The pilot can accomplish this either by turning faster or by turning inside of his opponent. This is where the pilot's knowledge of his maneuvering capability relative to his adversary is required. If the defensive pilot has too much energy, his maneuvering capability is seriously hampered, both in terms of altitude and airspeed. On the other hand, if the defensive piot remains at too low an energy level maneuvering performance is again hampered and, even worse, the pilot will probably not be given an opportunity to regain lost energy. The defensive combat role is generally characterized by a series of energy loss maneuvers, because maximum maneuvering performance occurs at corner velocity, the point of maximum energy loss.
 
While gaining energy would be useful for increasing maneuvering potential. the adversary would most certainly welcome the defensive pilot's mistake of unloading just for the sake of energy gain. On defense the pilot will either force an overshoot by losing energy faster than the adversary, or increase the adversary's bearing angle to a point where an energy gain maneuver might be accomplished.
 
As one would expect, during close-in combat the energy levels of both aircraft are reasonably close together, with the defender setting the pace. If the attacker possesses too much energy, he is leaving himself open to a disastrous overshoot. If the attacker does not possess enough energy, the target will soon out-turn the attacker.
 
Neutral
 
The neutral situation is a near standoff where neither airplane can easily gain a positional advantage. To break the stalemate one pilot must either capitalize on the other's mistake or utilize his maneuvering capability to change the situation. In this situation discretion may be the better part of valor, and the pilot may choose to unload and gain energy for separation. On the other hand the pilot may choose to exercise a vertical plane maneuver (trading airspeed for altitude) like a yo-yo, to reduce bearing by decreasing his effective turn radius in his adversary', turning plane. As was the case for the defensive airplane, the pilot can be provided valuable information about the energy consequences of each maneuver to assist in his decision making.

Offensive
 
To perform offensive, aggressive combat, positional advantage must be achieved and maintained. The pilot must manage his energy if he is to maintain his positional advantage. On the offensive, the chief objective of energy management is to maintain the proper use of energy gain-energy loses maneuvers relative to the adversary. In an offensive engagement (other than a hit and run) with excessive energy, the adversary will attempt to force an overshoot or force the attacked to lose too much energy. So, for the pilot on the offensive energy management is necessary for achieving and maintaining good positional advantage for subsequent tracking tasks.
 
Energy Mismanagement

The door swings both ways, of course, and available energy can be mismanaged. In an all-engines-out scenario, mismanagement occurs when potential energy is converted to kinetic energy at an insufficient rate: Airspeed is reduced to less than Velocity Gradient as the pilot inappropriately increases AoA and pitches up too much, increasing induced drag. Doing so is an energy-depletion maneuver. In extreme cases, energy mismanagement results in a precipitous decrease in kinetic energy, leading to exceeding critical AoA, stalling and loss of control.
Energy mismanagement also occurs when potential energy is converted to kinetic energy at too fast a rate. This can happen when a pilot inappropriately pitches down too much, resulting in a rapid decrease in altitude and increase in airspeed greater than velocity gradient. In this situation, limited and valuable potential energy is needlessly wasted at too rapid a rate

Energy fighting 
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Energy fighting is, along with Boom and Zoom and turn-fighting, one of the major fighting styles in aerial combat. Where Turn fighting relies on angles and speed, and Boom and Zoom relies on speed and altitude, Energy fighting relies on gaining an energy advantage through maneuvers over the opposition. As such, it aims to drain the opposition of speed and\or altitude and set him up for a well aimed deflection shot. Compared to Boom and Zoom, Energy fighting is closer in, relies less on an initial altitude advantage, more on initial acceleration, and involves short zoom climbs and short dives

Basic principles

Energy is a combination of speed and altitude. As such, for optimum result it's recommended to keep your energy up, meaning that you should maintain both speed and altitude. Fortunately, this isn't a very hard thing to do, as most energy fighters tend to have good power to weight ratios and as a result of that, good rates of climb; therefore, it's important to use these qualities and climb at the beginning of the match.

The modus operandi of the energy fighter should be as follows:

1.Assess target's energy state
2.Maneuver against the target
3.Drain the target of energy
4.Set up the target for the kill
 
Assessing Energy

This is arguably the most important step in any situation. As you rely on draining the opponent's energy, it's absolutely vital that you can make a reasonable assessment of the energy state of the opponent. Speed and altitude dictate the amount of energy an opponent has, and the type of aircraft will clue you in to the amount of energy that he can generate. Another good indication of energy states is the rate of closure. Assuming you are at the same altitude as your opponent, low closure rate indicates that your energy levels are closer to each other, whereas a high closure rate means that your energy states are dissimilar. Generally, a level flying opponent below you presents a good target. As his altitude lower than yours, you (most likely) will have a significant energy advantage to work with unless the opponent is flying at a much greater speed. As stated earlier, an energy advantage is generally good; however, given the fact many energy fighters lock up at high speeds, try to keep it smaller then you would in a dedicated boom and zoomer.

Maneuver against the target

After the target's energy level has been determined, it's time to commence the attack. The Trick here is to not stick around, but extend, (gain distance and preferably altitude) and set yourself up for another pass. This way, you drain the target of his speed, while keeping your own up. This kind of approach has 2 advantages. The first being that by making repeated passes, you are forcing the target to evade by either turning or by diving, which causes him to lose altitude, and thus energy. Consistent turning means you can cut into his turning circle for a deflection shot.
It's important to resist the temptation of sitting on his tail, this makes you predictable, and you lose your (hard gained) advantage. If he dives away, you are offered with an opportunity. On one hand, you have won the engagement (he has bugged out). Leaving you high and dry, and for the time being he will not be a threat to you. This means you can pursue higher threat targets, or, if no major threat is in the area, you can reengage him. Depending on his altitude, it may be prudent to waste some energy in order to remain in optimum control of your aircraft.
When you are forced to fly defensively, the same principle of gaining an energy advantage applies. The first step is to maneuver against his attack. This has the dual purpose of making a deflection shot difficult, and secondly you want him to bleed his energy. The exact move you make very much depends on the situation, but generally, a gentle break turn can work. When you detect his dive, begin a simple, gentle, flat horizontal turn. As he comes closer, you gradually sharpen the turn, tempting him to roll and pull his stick, meaning he will (due to his higher speed) increase his G load and therefore start losing speed. The result usually is that he will not be able to make the deflection shot and will have lost energy in his attempt to shoot at you (if he takes the shot and he misses, that's even better). When he zoom climbs away, get back your lost energy by increasing the throttle and maneuvering as little as possible, and if possible, set yourself at an unfavorable angle. This needs to be repeated until parity has been established. It's important to keep in mind, that climbing, while leveling the field, is potentially problematic as your speed generally drops, therefore it can render you more vulnerable. When flying defensively, it’s extremely important you plan ahead and figure out how to turn the tables on your attacker. A successful defense leads to a strong attack.

Draining the Target of energy

When you have maneuvered yourself into a good position, it’s time to begin the hardest part, which is to drain his energy, and, in doing so, make him slow and predictable. As speed and altitude are vital, a good energy fighter forces his opponent to move in such a way he has to waste both to stay alive. Although this is closely related to what has been said above. There are 2 considerations that are good to keep in mind. The first is that while many options are up to the pilots, the plane imposes certain limits on his actions. As such, it's good to assess the strengths and weaknesses of the plane in question.
 
 
Info Sources / References

War thunder.com
Aircraft performance (Reference text)
NASA Technical Note
David.T.Johnson
Wikipedia
And many more…………………………..