ACM stands for Aerial Combat Maneuvers.
In this page I will try to collect some simple but useful information for the new recruits.
Here you'll find a short explanation of the basic fighting maneuvers.
I've also added some RealPlayer videos made by Lemsko from Aces High (http://www.lemsko.de)
Remember that this is only the "abc" of fight maneuvers, and that the real combat is far more complex and unpredictable.
These are not to be intended as "rules", either.
You will soon experience (usually going down in flames...) that each player develops his own approach to the fight, and that each plane type is better suitable for some tactics, while it won't for some others.

Finally, a brief digression about the two main ways to fight: Angle-fighting and  E-fighting.

Last, but not least, we'll talk about SA: situational awareness.
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There are three types of pursuit commonly referred to in tighter combat: Pure, Lead and Lag.

Pure pursuit is when the nose of your aircraft is pointed directly at the target.

Use Pure pursuit to shoot the target at close range.
Flying Pure pursuit all the way to the target will increase AOT (Angle of Tail) and force you to fly past the target (overshoot).
 

In a turning fight use Lead pursuitto get closer to the target.

Fly with your nose ahead of the target, thus flying a tighter circle and gaining ground.
Use Lead pursuit when you are flying the same speed or a little slower than your target. Once you get close enough, drop back to Pure pursuit and fire your guns. Or, at a longer range, you can fire while in Lead pursuit. Watch your tracers to see if they are hitting home. Caution: using a Lead pursuit from too far away can position you in the enemys gun sights!
 

Lag pursuitis flown by putting your nose behind the target's tail.

    SEE THE VIDEO

Use Lag pursuit when you are flying faster than the target. Flying Lead or Pure pursuit would result in an overshoot. lfyour speed is too greatyou may still overshoot, but there are other maneuvers for that situation. Hold your Lag pursuit until your airspeed bleeds off,then pull into Pure or Lead pursuit, as necessary, and smoke the devil.
 

Use a 'High yo-yo' when you have a high AOT (Angle Of Tail, 30°-60°) and are roughly at the same speed as your target.

Roll a little toward level so you can pull 'out of plane', raising your nose and slowing.
Then perform a low G, rolling maneuver back into the target. When you see the Bogey, keep lag or lead pursuit as necessary.
Finally, saddle up and fire.
The maneuver can also be performed in the opposite way, diving under the target's path, then attacking from below. In this case it is named "Low yo-yo" (obvious...).
The name yo-yo comes from the man who perfected the maneuver, a Chinese pilot named Yo-Yo Noritake.
 

You can use a Lag Roll when in danger of overshooting the target.

You must have a low AOT (Angle Of Tail), and be flying much faster than the target.
Roll yourwings level and pull your nose up to bleed off speed. Then perform a maximum rate roll away from the target.
You should be able to see the target as you go inverted by looking up. Complete your roll as you pull into Lag pursuit.
The trick is to slow your aircraft enough to get into Lag pursuit.
 

A Break turn is a hard break away from an enemy on yourtail.

Usually the bogey comes suddenly behind you at high speed. A hard turn towards the same side he's coming (to increase quickly the AOT) can keep you away from his crosshairs long enough to think your move (at least will make it harder for him to aim!). If you are lucky (= the bogey is not too experienced), he may eventually overshoot.
The maneuver should be performed when the bogey is quite close: with the wrong timing, you may find yourself standing exactly in front of his crosshairs. No good.
 

A Scissor is a series of jinks put together, jink left, jink right, and so on.

With this useful defensive maneuver you will try to make the bogey overshoot and become the prey.
The trick is to slow down (thus letting the bogey come closer and closer - dangerous!) reducing engine power and rolling the opposite way the bogey does. This requires great calm and timing. The bogey must be quite close, or you'll simply give him a nice oportunity to kill you. You must fly always looking at the bogey behind you: in the exact moment he starts to roll one way, you must roll the opposite way. If it all goes well (practice...) the bogey will prolly give up the attack, or he will overshoot you. Then it is YOUR time to hunt!
So, looking from the attacker side, the target will roll opposite your rolls as soon as you start them. Keep this in mind and resist to follow all his turns. If you don't manage to prevent his moves, break off before it is too late.
Notice that this maneuver requires also a good plane response at mid/low speeds: you should always keep in mind the performance of the planes involved in the maneuver. Planes that stall easily at low speeds (and are also hard to recover from stall - Corsair, Spit...) should pay great attention if they choose to use this maneuver. Expecially if the attacker flies a plane with good lo-speed handling, (Zero, 109...).

The Split-S is a maneuver that allows to reverse direction very quickly, while gaining speed (but losing alt).

The pilot must perform a quick 180° roll, followed by a 90° dive. He keeps pulling back unless he finds himself flying level again, but in the opposite direction and at an higher speed.
It's a common evasive maneuver, but can be used as offensive as well.
Be sure to have enough room beneath you! Each plane has its own minimum alt to perform this maneuver safely.

The Immelman turn (developed by Max Immelman during WWI) also allows to reverse direction very quickly, while gaining alt (but losing speed).

The pilot must perform a steep 90° dive. He keeps pulling back unless he finds himself flying level upside-down (and rolls 180°)  in the opposite direction and at an higher alt (and lower speed).
This maneuver requires a certain amount of speed, depending on the plane type.
 

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Angle-fighting vs. E-fighting

Angle fighting is probably the more instinctive approach to a dogfight. Not necessary the best, or the right one.
In its simpliest form, the opponents try to gain each other's six circling as tight as they can.
The guy who turns tighter, usually wins.
Things are not so simple in a real fight, tho - and in a "virtual" fight as well
(such fights - contrary to the common belief - were not so usual in WWII).
Many things must be kept in mind:
- each different plane has a different turn radius: for example, a Spit can easily out-turn a FW190
- the turn radius changes at different speeds (make a try with the Zeke!)
- each plane type has got its own optimal speed, where the turn radius is minimum
- flaps and rudder can help reducing the turn radius (but add lots of drag)
- turn-fighting bleeds speed very quickly: this can be deadly in planes with poor low-speed performance (ex. the Corsair)
- turn-fighting bleeds alt. very quickly: this can be deadly in planes with poor climbing performance (ex. Corsair, Spitfire)

E-fighting is a totally different approach.
"E" stands for "ENERGY". Energy can be "stored" in two different ways: SPEED and ALT.
The two kinds are in some measure interchangeable: if you are slow but high, your alt-e can be coverted in speed-e by diving.
If you are fast and low, your speed-e can be converted in alt-e by climbing (obviously, due to drag, some E will be lost anyway).
The main goal for the pilot is to gain "E" and to try keeping it high enough to allow him a wider choice of maneuvers.
Each maneuver has an "E" cost that must be kept in mind. The "E" fighter should avoid - if possible - maneuvers with great loss of "E": a flat turn, for example. When you find yourself out of speed and low, you're dead.
In its simpliest form, E-fighting resolves in a vertical game: mainly dives and climbs. The pilot starts the fight at high alt., finds his target (lower and with a lower "E"), waits for the right time, drops on him, shoots, AVOIDS TO FOLLOW HIS TURNS and quickly climbs again to a safe alt.
Then he restarts the sequence. Maybe he will need to repeat the maneuver many times before the bogey will go down (if he will...).
This technique, better known as "Boom and Zoom" (BnZ), requires great patience, timing and self-control.
Maybe many players won't like it too much, as it is less spectacular than the close turn-fight, and requires a lot of practice to give good results.
It is more similar to what happened in the real war, tho. This technique was massively introduced when the US pilots had to counter the devilish Zero. They soon realized that they had poor chances to survive in a turning fight, so they developed this new approach that maximized the US fighter's main advantage: engine power = SPEED.

To use this technique, the pilot needs:
- "E" - mainly alt.
- engine power: the best planes for e-fighting are the FW190, the Corsair and the Mustang.
- fire power: the pilot has little time to shoot (he's - should be! - always very fast), so he needs big (or many) bullets.

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Situational Awareness

SA measures the pilot's knowledge of what is goin' on. Don't take it for granted and understimate it. It seems a simple and obvious concept, but you will soon realize that this is the hardest thing to learn. The best pilots have high SA, and they had to practice a lot to get it. And this is true both for the real fighter pilots and the "armchair pilots". You may perform perfect aerobatics and have a perfect aim, but they count nothing if you lack SA.

SA - about yourself
You must always know (as the experience grows you will "feel") your own situation: speed, alt, heading, ammo, fuel, damage.
You cannot take the right decision if you miss to know one of those vital info.
Always remember what you are flying: each plane has its own pluses and minuses.

SA - about the enemy
You must always know where the bogeys are (and how many they are!): being the first to spot the enemy gives a great advantage.
As quickly as possible, try to understand which plane they are flying, in order to choose the best tactic to use.
Never fly straight and level, always turn "your" head in all directions: never noticed the silk foulards often used by WWII pilots? It wasn't for fashion purposes, but to protect the neck's skin from continuous friction while the head was turning in all directions.
And assume that if you don't see the bogeys, they are most likely BEHIND you (possibly a little lower, in your blind spot) and ready to pull the trigger.
Try to understand how far they are, their direction, alt. and speed. You cannot allow them to come too close at a better alt. and speed, right?
Usually, is a matter of seconds.
Once you spot the bogeys and choose the ones that are a danger for you, or may be good targets, keep your eyes on them. ALWAYS.
This involves that you should be able to fly looking somewhere else than straight in front of you (often looking back, actually). It is not easy, at the beginning, but practicing will help a lot. More or less like riding a bicycle without hands...

SA - about your wingmen
Team flying is the hardest to learn - but most rewarding - way of flying. It doesn't happen so often to fly SF or FC with the full rosters, but it's surely a great experience. Expecially in a "no-boxed" game, it is very important to recognize as fast as possible your teamsters, in order to:
1. not kill them (hehe)
2. stay close to them
3. help them when they're in trouble
(it's a nice sensation when you can call a "your 6 is clear!" to your wingman - or when he calls it at you!)
 
 

Finally,
theory apart, the most important thing is to fly. Flying is the only true way to learn, expecially if you fly against humans. Possibly, fly with (or against) expert pilots, and watch them. Try to steal their "secrets". Each good pilot has a different ace, a favourite maneuver that gives him that "plus" that will make you end in the drink. And most of them will be glad to help you learning some secrets of good flying.