Flight Geometry and ACM

INTRODUCTION

Have you ever flown a duel in your favourite flight sim' only to have been out turned by an opponent with apparent ease? Have you ever watched helplessly as a bandit pulled his nose onto you for a guns tracking solution and left you wondering "How the heck did he do that?"

When it happens, don't you just hate knowing that you were out turned, while not being able to put your finger on the exact reason why? You might put it down to better energy management, or to a bad entry speed on that last manoeuvre. If you knew exactly why it happened, you could do something about it.

In this article I will explain what may be the greatest cause of "gun deaths" among flight sim' pilots, yet remains much less known or understood than its importance would seem to justify. I can't guarantee that reading this article will prevent you from being out turned again, but you will at least know why, what you may have done wrong and what you should do about it next time.

FACTORS

The effect of Geometry to influence our perception of being out turned is generally underestimated. Simple geometrical considerations can give the appearance of being out turned by a bandit who may only have a few degrees advantage. It may mean that you can come out of a manoeuvre, almost neutral in angles, only to find yourself being gunned in a single turn. This may happen even though you are sure that you have pulled around as tightly as possible. So how can such a dramatic advantage be achieved? Let's look at an example.

TURN CIRCLES

Many pilots think of a one circle fight as though there really was only one circle. That somehow, they have the exact same flight path as the bandit and that the only thing that will work is to out turn their opponent. Take a look at this situation in FIG 1. Here pilot A needs to gain another 60 degrees. Pilot B still has a few defensive options, but this situation is quite unlikely in a dogfight, it is far more likely that there will be some miss-alignment in the circles.

Now look at the situation shown in FIG 2. Here your flight path is off set from that of the bandit and the situation is very different. Even though pilot B still has at least a 60 degree lead on pilot A he is in big trouble. Pilot A will get the snap shot and the kill simply because the turn circles are off centre. Pilot B will think that he has been out turned, when in fact he may even have been gaining angles. He will think that this is so because it will look that way in padlock view! This kind of geometry is difficult to spot in a fight for two reasons. Firstly, because it will appear to pilot B as though he has been out turned. Secondly you will notice that these circles overlap in less than one full turn, so that once you have fallen into this situation, it may be over before you have time to understand what is happening.

THE POSITION PRINCIPLE

This is a very important observation. Many flight sim' pilots think in terms of energy and angles alone. This example shows how important geometry is in achieving a gun shot. Because an opportunity for a shot has been achieved by virtue of the position of the aircraft, I have named this simple but effective type of advantage, the "Position Principle". You can see from the diagrams just how deadly this type of positional advantage can be. The position principle may be more precisely stated: "The pilot who already has an angular advantage can win the opportunity for a shot by altering the position of his turn circle." An exposition of the position principle was first published in a Falcon3 article I wrote for "Enemy Lock On" magazine (Volume1 Issue3) and later in the "Official EF2000 Strategy Guide" where I wrote the chapters on A2A Combat, Aircraft Performance and Quick Combat, along with a great deal more of that fine SimTec publication.

So how can you tell when you have this type of advantage? You will be able to recognise such an advantage when you have it, by the aspect of the enemy aircraft. When you have the sort of positional advantage shown, you will be looking and shooting less at the rear of the enemy aircraft and more at the plan form. In effect you will be shooting into your opponent's canopy. This presents not only a bigger target, but is more difficult to evade by defensive jinks and breaks.

This position is shown in FIG 3. Here you can see what this will look like in the forward view. You will note that instead of looking up your opponent's tail pipe, you are looking at his plan form, you are as much above as behind your opponent. While I have chosen to illustrate with modern aircraft and a HUD, the idea translates readily to aircraft of any era.

From the perspective of the defending pilot, the loss of this type of advantage is more difficult to spot. If you find yourself in such a position you may see your opponent's nose pulling onto you and it will look just as if you are being out turned! Even worse, in the previous example, it will appear to you as though the bandit has gained a full 60 degrees in less than one circle. The bandit's nose will appear to whip around as the bandit crosses the intersection point of your respective flight paths. The fact that it will just appear to you as though you are being dramatically out turned, will delay your correct reaction, when you may only have a few very short seconds to react. The fact is that once you are in this type of bad situation it is often too late already.

This situation will be even more difficult to recognise especially in the heat of a dogfight. The big clue that your circles are off centre is that the bandit has his nose pointing at you in something other than the rear view. If you are flying a sim' with a padlock view, the bandit will be nose on, while still some degrees off your six. You may be staring down your opponent's gun barrel with the back of your seat nowhere in sight.

This situation is far more common than many flight sim' pilots realise. Think back over your recent experience. I am confident that the sort of high aspect shot that I have been describing is one that you will recall from some not too distant virtual engagement. Indeed gun shots from this aspect are by far the most common. This type of advantage is so valuable because it is not a one off, it will recur every cycle. Against a pilot who has not learned to recognise this, the position principle will result in several snap shot opportunities, any one of which may result in a good guns kill and the end of the fight. This type of advantage is effective in sim's like Air Warrior, Warbirds, EF2000, Su-27 and very many more. Indeed understanding the importance of the position principle will give you the ability to use geometry and not just "G for brains" and that is what ACM is all about.

DISPELLING A FALLACY

The real trick is knowing how to get your self into the position of pilot A in FIG2. Before I go on though I would just like to point out that you may already be thinking that you can engineer this situation artificially simply by reducing your turn radius. Well, you would be right of course, but there is a slight snag. There are two ways to reduce your turn radius. You can reduce your throttle in order to go slower, or you can pull more G. Assuming that both pilots are already at or below corner velocity, as one would expect after the first few seconds of a turning engagement, they will already be pulling their G limit. So that only leaves, the idea of going slower and that is a very bad idea. Trying to cut the corner by reducing the turn radius by reducing your airspeed is a big mistake! Why? Because it will have a far more dramatic effect in reducing your turn rate! This is a common mistake and in a sustained turning fight where both pilots have bled their energy to their sustained level you should stay as fast as possible to maximise your turn rate.

You will notice on the diagram that this situation is shown by the large red arrow. You will notice how small changes in speed can increase the turn rate, while the turn radius stays constant.

Such a downwards spiral manoeuvre is known as the Lufbery and is given a more complete treatment in another Combat Corner. Of course it also depends to some degree upon what flight sim', or flight model, you happen to be flying. In some simulations that model flaps there is an upside. If the reduction in speed is accompanied by an increase in the load factor, as will occur when flaps are lowered, this method will work. Air Warrior for instance is a classic example, however the advantage may be only short lived. Use of the flaps in a low energy situation will only result in a temporary advantage eventually leading to lower speeds and deeper problems. Generally trying to cut speed to tighten the turn radius for a snap shot is a waste of time unless you are confident of a kill.

Go to Part II

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