The Spitfire Mk IX in Aces High II
The Spitfire Mk IX has a wonderful combination of characteristics that have earned it a great deal of respect. It simply does almost everything well and has few obvious weaknesses, making it an obvious choice for newer players. That is not to say that it is a newbie aircraft though, it offers great growth potential and even some veteran pilots fly the Spit IX quite extensively. The Spitfire can actually be quite a creative aircraft to fly and adopts well to many styles with great success.
 Engine Power
The Spit IX is generally seen as a power upgrade over the Spit V, which is generally true. The Spitfire IX is still a bit slow though at lower altitudes mostly because of the selection of the model we have in the game. At sea-level it is capable of only 310mph (319mph with WEP), clearly below average, but there is a pretty constant improvement of about 4.5mph/1,000ft of altitude gain up to 15K (~376mph at 15K). There is a bit of a dead-zone between 16-20K but then speed jumps up again until you can cruise at over 405mph at 27K. Generally most people aim to climb their Spitfires just a bit to get better transit speeds (8-15K). Climb rate is very good, around 3,800ft/min up to 14K, making low-mid altitude climb times quite short. There is a drop in climb over 14K though you can maintain over 3,000ft/min right up through 25K with WEP. WEP is very important though only lasts 5 minutes. It adds about 9mph to your speed at any altitude and roughly 300ft/min of climb so you should save it for when you really need it (i.e. combat). Acceleration is solid at lower altitudes, placing it in the top 1/3 of aircraft, and even better with altitude (top 10). Fuel range is good at 35 minutes with all internal fuel contained in a single tank making it easy to gauge how much fuel you have remaining. The option exists to extend with duration by 21 minutes with the addition of a single drop tank. This option is highly recommended for transit and so you can take less than full internal fuel but still have the desired range.
 Aces High II Performance Charts
The only choice of armament is four .303s with 350 rounds/gun and a pair of Hispano 20mm cannons with 120 rounds/gun. The .303s are spread far out on the wings. If you set convergence in close, where the guns are more effective, you will be way out of convergence at longer ranges. If you set convergence farther out, where convergence is less of an issue, the .303s are less powerful. Regardless, even under the best circumstances, the .303s matter little compared to the Hispanos. At only 120 rounds per gun, there is only about 9 seconds of trigger time. But 9 seconds from a pair of Hispanos is no small amount of firepower. There's enough here to take out several enemies. Fire the 20s in short bursts to conserve ammo and if you get someone completely outmaneuvered, fill them up with .303s for a little extra fun.
Excellent. The Spit IX is quite small and quite light with a low wing loading, which gives it a high level of maneuverability. The Spit IX is slightly less maneuverable than the Spit V but the extra engine power allows many maneuvers to be held just a little longer so it's a trade off. Anything you can't out-run you should be able to out-turn, except the N1K which will give you problems at lower altitudes (under 10K). Most faster aircraft will have nowhere near the turn potential that you do at medium or lower speeds and none have anywhere near the stability under heavy maneuvering. Speeds over 350mph don't really suit the Spit IX though there is little or no danger at very high speeds. It may not even be possible to compress a Spitfire without a very large dive under power as it is still controllable even after the speedometer markings have been exceeded. Structural failure is rare in a Spitfire except under the most unbelievablely extreme maneuvers. Even more impressive than the high speed handling is low speed handling which remains quite responsive even under 100mph. Stall speed without flaps is around 85mph and with flaps it is even lower. The Spits all retain energy unlike any other aicraft though so hard maneuvering can tend to be sustained longer with less energy loss. Roll rate is about average but gets somewhat heavy at higher speeds. The main dangers in turn-fights for the Spit IX come from a small group of aircraft that are very dedicated turners though, the FM2, F4F-4, Zero, N1K, Spit V, and Hurricane. If you can take almost any other aircraft into a turn fight under 250mph you should easily beat them.
 Fighting in the Spitfire Mk IX
Most aircraft require that they be flown in a "style" in order to be the most successful but the Spit IX can be flown almost recklessly and still do alright. Typically it is used as a TnB fighter though it is at least as equally impressive when used in a BnZ role. Being on the receiving end of a BnZ Spit IX is a simply scary situation that needs to be avoided.
Offensively you should try and always store some energy in speed/altitude for any part of the initial combat. Too many high speed monsters will simply try and run away from you if you can't do a decent job of cornering them and slowing them down a bit. Charging into the middle of a pack of slow enemies is also quite common although typically that will end up as a race to see how many enemy you can shoot down before you are a casualty. High altitude climbs (over 15K) are not required though they seem to be pretty typical for people who aren't confident in their maneuvering/energy management skills. Try and always remember that you may need your last bit of energy in altitude or speed for your own escape. While the Spit IX accelerates pretty well, it also reaches top speed much lower than other typical aircraft you are bound to encounter. A little room to dive and run is advisable rather than fighting only a couple of 100ft off the deck. Try and time your shot opportunities so you only pull enough lead to get your Hispanos on target at relatively short ranges. Long range shooting is alright but you don't have a lot of cannon ammunition so you should really pick your opportunities. Snapshots and high deflection should be as easy in the Spit as in any aircraft in the game with good results if the cannons are hitting. Never accept Head-Ons unless there are few options - the Spitfire can deal out the damage but not really absorb it. A key to good Spitfire fights is to get a decent merge or to slow the fight down against faster opponents. If you can, try and get the fight slower by climbing rather than diving and you may find you easily nail any of the faster aircraft as they struggle to match you. Also, remember about lag style turns, they can help a Spit force an enemy to maintain his harder turn and bleed speed until such time as the Spit can simply pull in behind a helpless enemy.
Defensively, you need to take care of a Spitfire because they tend to be a little fragile. Don't give up any easy hits and maneuvers like scissors tend not to be all that safe unless you can ensure the enemy doesn't get even a brief snapshot. A single fuel tank and easily punctured radiator can leave a Spit in real trouble from even minor hits. As the Spit is pretty slow at lower altitudes you will usually find enemies trying to catch you from behind. The Spit is an excellent break-turn aircraft and should be able to slip away from most of these attacks. You should always endeavor to make a higher energy (speed) opponent slow down though unless he is in a superior turner (in that case, try and break away and run as he is likely slower than you). Most pilots will constantly try and pull enough lead on your Spit to take a shot but you should in most cases be able to keep them from getting angle while they find themselves slowing rapidly.
 Fighting against the Spitfire Mk IX
The Spit IX is probably among the most dangerous planes to encounter as it can put up a fight in so many ways and win. At high altitudes it's the best maneuvering and among some of the fastest planes. Down low it is a great turner with good climb and acceleration if not for a bit of a lack of top end speed. You are also bound to see lots of Spitfires, both above and below you so you need to know how to identify them quickly and build a plan on how to deal with them.
Typically it is a good idea to identify a Spit IX from the other Spit models though the dangers are pretty much the same. A Spit V is more likely to get into an extended turn-fight though where a Spit IX may fly in a number of styles. The Spit V has a darker overall paint scheme while the Seafire is more grey. The chances of encountering a Spit I are very low. The Spit IX is more likely to use climb/acceleration to defeat you though they all retain some excellent handling at the top of any low speed maneuver.
Offensively, try and slash the Spitfire and not slow down. You can't afford to remain anywhere near the front of a Spit for any period of time as it has the firepower to quickly reduce you to flames even in the toughest aircraft. You must try and maintain your energy through use of smart maneuvering. If you try and play energy games with the Spit you are most likely going to lose unless you know exactly what you are doing. The Spit has very good climb/acceleration and will match any energy you can gain with at least as much. Try and just land hits though, the Spit can be easily disabled by hitting the engine, radiator, or fuel and that might take only a single .50 cal in a lucky place. Almost remain careful of the "Spit-reversal" where a Spit appears to turn 180 degrees without loss of energy. The power, low wingloading, and wing design allow this ability and it can cause great problem unless you can force the Spitfire to have to maintain a high G turn. Always place a floor on your combat altitude and leave enough room to enter a dive in a faster plane in order to accelerate to a higher speed than the Spitfire is capable as an escape option.
Defensively the Spit can be almost impossible to shake from your tail. If you are in one of the clearly superior turners you can maybe avoid him and sucker him into a turn-fight but he may be able to leave at almost any time he wishes. Scissors are not always all that effective either, you have to be very careful. The problem is not in generating the overshoot as most Spit pilots are super aggressive and pull lead constantly (thus causing really bad overshoots frequently). The issue is, once slow from scissors the Spit is still super maneuverable and will simply turn at 100mph and wail on you. The best Spit defense is to always maintain some separation so he can't shoot you and when you get close always have superior energy. Co-Alt/Co-E Spits are simply no fun to face.
A wildcard in this discussion though should include mention of the fact that most Spit pilots you will encounter are very new and use the Spit quite poorly. Even so, they are very dangerous as the Spit allows a pilot to make a lot of mistakes and still win. Be on the lookout though because new pilots tend to fall for maneuvers quite easily and can be defeated. A veteran Spit pilot though can simply be impossible to shake and will let you flail around avoiding him until you run out of options. Then he will pounce and put you in your parachute.
 External Links
Soda's Aircraft Evaluations