European Air War 

Energy Management Basics

Before debating the relative merits and applications of maneuvers like barrel rolls, yo-yos and so forth, pilots must first understand the underlying principle behind all such maneuvers: energy management. Energy Management basically means utilizing the laws of physics governing flight to achieve maximum performance from an aircraft.
There are two types of energy: kinetic energy and potential energy. In terms of air combat, kinetic energy equates to speed. The faster the aircraft is moving, the more kinetic energy it possesses. For all practical purposes, combat pilots treat kinetic energy like money. As we will see below, maneuvering an aircraft expends kinetic energy. In simplest terms, combat pilots try to stockpile kinetic energy, then "spend" it during combat to "buy" maneuvers.
In terms of air combat, potential energy equates to altitude. Where kinetic energy operates as "cash" to buy maneuvers, potential energy acts like "credit." Kinetic and potential energies are interchangeable. A climbing aircraft slows down (thus reducing kinetic energy) but increases altitude (thus increasing potential energy). A diving aircraft accelerates (thus increasing kinetic energy) while losing altitude (thus reducing potential energy). A slow moving aircraft at high altitude possesses a "line of maneuvering credit" based on its altitude. By diving, and thus cashing in the potential energy "credit" for kinetic energy "cash," the aircraft obtains maneuvering energy.
Total energy status indicates the combination of an aircraft's kinetic energy (speed) and potential energy (altitude) at any given time. Using energy management techniques, the pilot attempts to maintain the highest total energy status at all times by utilizing the laws of physics and exchanging speed and altitude. If the aircraft needs to slow down, it should climb as much as possible and store that speed as altitude. When an aircraft has speed it can maneuver. When an aircraft has altitude it can exchange altitude for speed and subsequently maneuver. When an aircraft has neither speed nor altitude, it is little more than a target.
If you want a quick comparison of how the various aircraft in EAW compare with one another statistically, see the Aircraft & Armament section. Numerical aircraft ratings like climb, turning ability and roll rate, though important, are only snapshot comparison indicators, and are not entirely representative of an aircraft's performance characteristics over a broad range of speeds and altitudes. Once the latter are taken into consideration, aircraft performance can be displayed graphically as a "flight envelope." The best combat pilots learn how to push the envelope of their aircraft, and deny the enemy the opportunity to do the same.
Obviously, no combat pilot whips out a slide rule during a dogfight and begins solving formulas. Understanding the relationship between angle of attack (AOA), lift, and turn performance, however, separates veteran combat pilots from their eager young protégés. The next two sections detail the interrelationships of these factors, but some technical jargon is required. Before diving into those points, the following table is offered as a very generic guide to the various plane matchups you will encounter in the game. The table states which tactics, energy-based or angles-based, are applicable in a given one-on-one dogfight, assuming both aircraft begin at the same altitude and speed, with neither pilot at a positional advantage. In other words, this is a table that has no correlation to the real world, where pilots must evaluate all of these factors to determine whether energy or angles tactics are the best choice. This table offers a starting point to make that decision, based ONLY on comparisons of airframe capabilities.

1 = Allied, 2 = Axis
Converting Energy Into Maneuverability
Every aircraft in EAW has maneuvering characteristics which determine how well that particular plane converts energy into maneuverability. Two of the most important characteristics are turn rate and turn radius. The turn rate indicates how many degrees an aircraft can turn per a given unit of time, such as "10 degrees per second." Turn radius indicates how large the radius of the circle the aircraft is circumscribing will be, such as "5,000 feet." Ideally, a fighter design should possess a high turn rate with a low turn radius. Unfortunately, there are problems achieving that goal.
If you've read the manual, you've probably read about the "four forces" of flight. Briefly, gravity is just the weight of the aircraft. Lift is the force generated by the wings which offsets weight and makes the aircraft airborne and is measured as "G forces." Thrust is the propulsion generated by the engines which creates speed. Drag is the amount of resistance the aircraft feels while moving forward which decreases speed. The relationship between these forces is critical to air combat.
In basic terms, turn rate is dependent upon lift and airspeed: increasing the G load increases the turn rate while increasing speed reduces the turn rate. Turn radius increases exponentially as speed increases, but increasing G load reduces the turn radius. These relationships mean that high G loads at low speed offer the best turn rate and turn radius. Unfortunately, there's a problem achieving that. To understand this problem, we must examine where G loads come from.
We measure the lift the wings produce in terms of Earth's gravity, or G loads. A lift of 2g, therefore, is a force twice the strength of Earth's gravity. In this context, "lift" and "G load" are synonymous. Lift is based on several items, such as the current speed, the size and shape of the wing, and the angle of attack. AOA is the angle at which the wing meets the airflow. Increasing AOA increases the amount of lift (and drag) the wings generate up to a point. When AOA increases too far, airflow over the wing is disrupted and the wing stalls. Stalling an aircraft has nothing to do with speed, attitude, or G load. A stall occurs when the wing exceeds its critical AOA. Every wing developed to this point in time has a "critical" or "stall" AOA. Upon reaching stall AOA, lift dissipates. The wing generates the maximum lift possible just before reaching stall AOA. The actual amount of lift the wing generates at this point is primarily dependent upon the speed and altitude of the aircraft. For example, an aircraft at 10 degree AOA would generate more lift at 300 knots than at 100 knots.
You can stall the aircraft by exceeding stall AOA regardless of the aircraft's speed. The amount of AOA required to stall does not change regardless of airspeed; however, the amount of G forces experienced when you reach stall AOA varies significantly with airspeed. The faster the aircraft is moving when it reaches stall AOA, the more G forces are exerted on the airframe. Every aircraft has a maximum G load. Exceeding that G load damages or possibly even destroys the aircraft. You must observe this structural limit of your aircraft regardless of available airspeed and AOA or you will find yourself walking home, or worse.

Instantaneous versus Sustained Performance

So, at any given time we can look at an aircraft's speed and AOA and determine the amount of G forces being generated. Using the G load and speed we can further determine the aircraft's current turn rate and turn radius. And we've determined that the best turning characteristics occur when you keep speed low and G load high. Now the problems appear. In simple terms, pulling G uses up energy.
First, the relationship between lift and drag comes back into play. Keeping G high means generating lots of lift. Unfortunately, generating lift also generates drag. Drag slows the aircraft down, thus in turn reducing the amount of lift available. Pilots call this vicious cycle "bleeding speed". In a high-g turn, every aircraft will bleed speed and slow down. When speed drops, available G drops and turn performance suffers. The laws of physics prevent the aircraft from maintaining high G load at low speed.
Therefore, we have two types of turn performance: instantaneous and sustained. Instantaneous turn performance is a transitory value. It describes how much lift the aircraft can generate immediately after beginning a turn. Since speed begins to decay immediately, the amount of lift being generated also drops quickly. Instantaneous turn performance is the best performance the aircraft can manage for a fraction of a second before drag begins eroding speed away. Sustained turn performance is a "steady state" value. Remember, while drag is trying to reduce airspeed, the engine's thrust is trying to maintain airspeed. Speed drops so available G load also drops. Since G load drops, the amount of generated drag also drops. Eventually, thrust and drag reach equilibrium.
Second, lift is a "bounded" quantity compared to speed; speed can increase much more than lift because of the aircraft's structural limit. Above that structural limit lift remains constant at the maximum value while speed is (in this context) unbounded. Referring back to the turn rate and turn radius relationships, we see that if we keep G load constant, but increase speed, then turn performance begins to suffer quickly. That's where the concept of corner speed comes in. "Corner speed" is the minimum velocity required to produce the maximum G limit at maximum AOA. Above corner speed, the aircraft's velocity is "too high" for the amount of G being generated, causing turn rate to decrease and turn radius to increase.
Please note a very important point: "turn performance at corner speed" and "sustained turn performance" are not necessarily related items. Corner speed occurs at maximum possible G load with minimum speed. " Sustained turn performance" occurs at maximum sustainable G load and airspeed. Corner speed provides the best performance but cannot be maintained for any length of time in most aircraft unless the pilot practices good energy management.

This material was included in the original 1998 release of European Air War by Microprose.

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