Air Combat Manoeuvers (ACM) - Page 1/1

Created on 2004-12-10

Title: Air Combat Manoeuvers (ACM)
By: Leon 'BadBoy' Smith
Date: Unknown Publish Date 5240
Flashback: Orig. Multipage Version
Hard Copy: Printer Friendly


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.


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.


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.


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.


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.

Flight Geometry and ACM: Part II

Realism in instruments! The ME262 Panel From Fighter Duel II


Ok so how can you get the sort of geometrical advantage that pilot A has in FIG 2. Well almost any out of plane manoeuvre will do it. For example a lesser known advantage of performing a largish high Yo-Yo is to create just this kind of geometrical advantage. Take a look at Fig 4.

In this example pilot A and B start with the flight path as shown in FIG1. Pilot B can close the 60 degrees by using a high Yo-Yo to alter the geometry of his flight path. He knows that getting the outside circle will lead to a snap shot. The effect of the high Yo-Yo is to cut across the circle and create the situation shown in FIG5 some moments later. Pilot B now has a shot, even though he may not have gained any angles.

In this example you have seen that a pilot with some sixty degrees to gain achieved a snap shot simply by altering his flight path. Don't get too excited though because the defence is fairly simple. In order to avoid this kind of trap Pilot A can simply do a high Yo-Yo of his own. Of course he may not realise the danger, but good pilots do this instinctively without knowing exactly why. However there are many good pilots out there who will still be caught like this through ignorance. The important thing to remember is not to try this if you are in the position of Pilot A. If you do, the whole thing will work in reverse, and Pilot B will get the snap shot on the following flight path intersection. You will in effect have been the architect of your own demise. Similarly this is the main reason for becoming stuck in a lufbery with a bandit just off your six. It can be very dangerous to attempt a vertical manoeuvre in defence since going high or low may give this type of geometrical advantage to the bandit. Take

You will see that pilot A has attempted to use a vertical move in defence. He has now allowed pilot B to use the geometry of his flight path to get a snap shot. Pilot B has achieved this by pulling up early, instead of driving to his opponent's six, and thus created an off-set in the turn circles. In this example you can see that Pilot B is almost 90 degrees off, but pilot A has handed him an easy kill. This is the fate of so many pilots who try to use the vertical in defence. Remember also that low vertical manoeuvres are as bad as high ones. The Split-S would result in the same situation as shown, but with the circles drawn downwards instead. This type of mistake leads to more "Position Principle" kills than almost any other. Very often the unwary victim will die at the very top or bottom of their loop, as the positional advantage is greatest. I know that many flight sim' pilots have been on the receiving end of this type of mistake, now you know why.

I'm not saying that a vertical move will always get you killed, far from it. The situation in figure 4 does require a certain amount of turning room. Very often that turning room will not exist, you need to be aware of the bandit's range as well as his position, the closer you are the more likely it is that you will survive. This is something you need to develop a feel for.


Another major factor in achieving this kind of kill is weapons effectiveness. In some simulations, lethality is a vital consideration. Because of the variety in the effectiveness of weapons, deflection shots like those I have described are either easy or hard to kill from! However in many simulations, deflection shots as a result of the geometry described here, will always be advantageous or even deadly. Even in those simulations where deflection shots are more difficult these considerations will still be of some importance. In "Art of the Kill" Bonanni talks about passing up the deflection shot by not turning early and instead driving for the elbow. Real pilots do that because deflection shots are difficult to get in real life and the price you pay for missing is an overshoot, the reward, only another difficult snap shot. As a flight sim' pilot with more lives than a cat, I will take those difficult shots.

Weapons effectiveness is modelled very differently from sim' to sim'. Indeed some simulations even use different modelling for different modes of play. Generally though Guns are becoming much more realistic in modern sim's. In any case the degree to which you apply these principles will depend upon the extent to which you are able to use deflection shots in the simulation you are flying at the time. It will also depend to some extent upon your own gunnery skill, more so in sim's with realistic hit bubbles, less so in sim's with larger hit bubbles. For Air Warrior, Su-27, Warbirds and EF2000 these methods work very well.


I will explain how this kind of geometrical advantage can be gained from a merge. Many engagements begin this way, so it might seem strange to deal with this last, however you will appreciate the theory having now understood the position principle. In this example I envisage a situation where you have been denied the separation for a lead turn and are about to pass a bandit in a head on merge. In this example one pilot enters the merge above corner velocity and will therefore use the Immelmann. The other pilot is in a low energy state and will therefore perform a low slice. If you were to guess that the pilot with the higher energy state should win, you would be correct, but let's see why.

In FIG7, time 1 shows the merge, time 2 shows the pilot on the left going into an Immelmann and rising vertically out of the paper at you while the other pilot goes into a low slice. Time 3 shows the high pilot adjusting his flight path and following in the same direction as the low pilot. Normally this would be a bad thing to do because the high pilot has given away his turning room. However this is exactly what will get the high pilot the outside circle. The large amount of vertical separation in this example will prevent the low pilot from taking advantage of the turning room. At time 4 the high pilot has managed to gain the outside circle and with only a small angular advantage will still be able to make a kill from this geometry. He will in effect now be in the same position as pilot B in FIG 5. This will work in most sim's and even if you are unable to get an outright kill, you will get another high aspect snap shot every 360 degrees.


What I hope I have done in this work is to explain how you can appear to be out turning a bandit without actually having a turn rate advantage. You are able to do this by using geometry! If you depend upon turn rate alone you are going to finish too many missions under the silk watching your opponent doing victory rolls. Turn rate alone is the tool of the pilot with "G" for brains, while geometry is the weapon of the ACE. One of the biggest barriers to good ACM for new flight sim' pilots is achieving the three dimensional awareness that can make the use of geometry possible. That means being able to visualise this kind of geometrical pattern in the space around your aircraft during combat. I hope you now see how important this geometry is. If so you will have already taken those first big steps to becoming a great flight sim' ACE!


Explaining more fully how to use geometry to your advantage deserves a more complete treatment. Because the nuances of application for each of the many manoeuvres that can lead to a positional advantage require a much larger and detailed work, I intend to elaborate in the future. It is too early to say where any further exposition will appear, so keep your eyes open for books or articles with my name in the credits.

Check Six!

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