The P-51 D in Aces High II
Arguably the best plane in the game that is non-perked, though it is a rather difficult title to judge. It is at least within the top 10 if not the top 5. It combines good firepower, unparalleled views, excellent speed and the class of the field range. At most altitudes the P-51 is as fast or faster than any other plane within a couple of mph, typically it is the slightly faster plane. The P-51 D offers a 6 x 50 cal gun package which is perfect for the types of flying it deals with. The view from the bubble canopy is such that it enhances your situational awareness many-fold and allows you to easily track and position targets. The P-51 D is such a complete aircraft both offensive and defensively that it has all the tools it needs to be a dominant aircraft.
Firepower
You basically have 2 options, a 6 x gun package, or a 4 x gun package. The guns are U.S. .50's and so are great all around weapons. If you are used to heavily armed planes that carry upwards of 8 mg's or their equivalent in fire power, then you will notice the .50's actually take a small bit of time to do real damage. The 4 x gun option makes you a bit lighter, though it isn't very noticeable, or helpful. They might let you out turn closely matched planes, but your really not much of a turn fighter anyway. The 6 x gun option lets you get more lead on your target, over a shorter amount of time and is better for snap shots. Convergence is a matter of personal preference, and what your used to, though I set mine to point convergence.
Along with the guns, you can carry 6 x HVAR 5" rockets, and either drop tanks or bombs up to 1000 lbs in size. This is worse than some, but better than a lot. If you are going to go out and do some fighting, consider taking the rockets to let you hit tanks, GV's, etc.
For drop tanks, you can carry 2 x 75 gallon drop tanks. The only time you are going to NEED the drop tanks is if you plan on making long, full 2 way flights escorting bombers, or something else that would require large amounts of fuel. You can use the drop tanks to lessen the amount of internal fuel you carry, letting you shed weight in a hurry if you need to.
For bombs you can carry 2 x 100lb bombs, 2 x 250 lb bombs, 2 x 500 lb bombs, or 2 x 1000 lb bombs. The 1000 lb bombs are going to be your best choice if you are going for maximum bomb load, but keep in mind that there are others that can carry more, and that the real heavy lifting is what the bombers are for. If you want something that can take out tanks without needing direct or very close hits, then the 500 lb bombs would be a good choice as they can take out a tank, or any airfield structure other than a hanger, and won't slow you down a whole lot. The 250 lb bombs are good enough to knock out town buildings, light airfield structures, and light armored vehicles, but for tanks, your going to need a very close, or direct hit.
The 100 lb bombs are pretty much useless, I wouldn't consider taking them unless you knew there would be a swarm of jeeps along the way.
Maneuverability
I find that the P-51's maneuverability is like the rest of the plane good all around , without being great in any one area.
It's good in a dive, if not quite up to par with the likes of a P-47. I've taken a P-51 up to 500 IAS in a dive while in combat, but I've gotten up to 520 or so and still recovered. But generally, you shouldn't try to dive to such speeds unless its a last resort against a poor diver (109's for example).
Good high speed turn rate, in the top 1/3rd. And its good slow too, I've been out turned by one in a spitfire while slow. But don't push your luck, try to use your advantage over most planes: speed.
Climb rate is good, if not stellar. You can pull around 3500 on the deck, deteriorating the higher you get.
Roll rate is decent, but trying to use it against a 190 or a spit 16 will get you killed.
Fighting in the P-51D
The P-51 D is an excellent aircraft in the main arena. Where many other aircraft offer a combination of a few positive characteristics, the P-51 tends to offer any number of great attributes. The P-51 almost allows a pilot to be sloppy and still get, and land, kills, a trait which few other aircraft have.
The P-51 likes to have altitude, come in at least at the top part of the fight though it is not necessary to come in at the absolute top of the pile. You want to carry your full cruise speed and have finished your climbing away from the fight. One of the few negative characteristics of the P-51 is a poor climb and acceleration rate at lower levels. You really want to take care of those before getting to a fight. Once there, a BnZ or slashing style of attack is usually best as this helps maintain your speed and altitude.
High speed turning fights are not a problem either, the P-51 has excellent high speed maneuverability and using 1 notch of maneuvering flaps will give incredible high speed turn rates. Be careful using the flaps though, more than 1 or 2 notches will quickly bleed away your speed and the P-51 has difficulty regaining that lost energy through acceleration. The best times to use the flaps tends to be at the top of loops or by briefly using a single notch to get your nose into position for a deflection shot. The P-51 is not a sustained turner though, it becomes more and more dependent on flaps to maintain performance as speed decreases. Over-use of the maneuvering flaps can quickly spell disaster.
The firepower of the P-51 D is excellent, though you should consider taking the 6 gun option vs. the 4 guns. The 4 guns will make you lighter for a turn fight but that is not the strength of the P-51 against most opponents anyway. The six gun option really improves your ability to make snap, or deflection, shots. Remember that these are US .50s mounted in the wings too, so the maximum range for attempting shots is typically much further than for cannons. On fairly steady targets a D 650 shot is not very difficult, while on a non-maneuvering target the range could be extended to slightly over D 800. Don't expect to inflict serious damage at these ranges though every hit you can make helps. Sometimes long range hits can damage planes enough to make your job easier in the long run while other times you may get lucky at actually get kills at long ranges. Some have their convergence set long on the P-51 and set in a pattern, not a single focused point, to exploit the long range shot potential. With 3 closely spaced guns in each wing the convergence pattern is not as important to focus to a single point. Deflection, and merging front quarter shots with .50's are not a bad idea, lay out a pattern of fire and hope the enemy flies through it.
One of the greatest assets of the P-51 D is vastly under-appreciated though, the views from the cockpit. The bubble canopy with no rear fuselage to obstruct your vision is absolutely the best. It works for you both offensively and defensively since you can more easily keep track of aircraft to your front or aft. I'd say the views probably double the average pilots situational awareness and makes keeping track of the situation much easier.
Of course, the P-51 loves speed at all altitudes. At low level the P-51 is among the fastest aircraft while at high altitudes it is probably the fastest non-perk ride. A good lower altitude for the P-51 D is around 13.5 K where it can pull 410 mph on cruise. At sea level it makes 354 mph, while WEP will increase that to 367 mph. All are within a couple of mph of the fastest planes in the game though be careful, there are a couple of aircraft that can eventually catch you at certain altitudes. Also, remember that acceleration in the P-51 is not great so don't get caught slow or someone will probably catch you quickly. Save your WEP and only use it in combat since that extra horsepower and speed might be the difference between escape and being caught.
The final notes have to do with loading up on fuel. Full internal fuel is almost never necessary in a P-51. The range even with only 25% internal fuel is impressive. Typical scenario is to load 50% internal and drop tanks. While on the runway, drop one of the drop tanks and only take off with one. The plane will level easily with only 1 drop tank (it's not terribly unbalanced). Use the drop tank to climb to altitude and cruise to the area of the fight, then drop it. You should easily run out of ammunition before you even get close to running out of fuel. You never want to fight with more than 75% internal as the plane is a little unstable with all that fuel on board.
Fighting against the P-51D
The P-51 D is a tough plane to beat in the hands of a smart pilot. An altitude advantage is going to help but unless you have equal speed you are going to have difficulties catching up to a P-51. The same goes for escaping, if you have one on your tail there are only a couple of aircraft that can manage to extend away. The situational awareness provided by the excellent cockpit views is going to make sneaking up on a P-51 D difficult from most angles.
Luckily, lots of average or worse pilots fly the P-51 D and make lots of mistakes that open the door to kill it. All too often they allow themselves to get slow, low, or sometimes both. This really sets them up poorly for escape and should allow you to pounce on them. Also, lots of people take the P-51 D for granted as some super-plane when it can't actually completely cover up for flying poorly. For some reason P-51s don't tend to be overly aggressive, they are often seen floating high over the fight while not engaging unless they have absolute domination in numbers or position. P-51s are also usually the first people to dive away at high speed to sea-level at the first sign of trouble, a tactic that got them the nickname "RunStang". With the addition of the 190D9 and La7 the Runstang tactic became very risky as both of these aircraft would eventually catch-up to a P-51 trying to runstang and deal with it, something that made P-51 pilots rather unhappy.
Offensively a good idea is to try and force the P-51 into a turning fight to bleed off speed. A high speed turning fight is not good since the P-51 is going to be among the best planes at that, but if you can extend his turns or make them defensive then you can slowly bleed energy out of him. The P-51 will have little choice other than to trade altitude for speed in order to defend your attacks.
The P-51 is not great as a turner when slow, and it has troubles replacing lost E without trading altitude. Take snapshots, longer ranged shots, or high deflection whenever possible. The P-51 D is not terribly strong and often takes radiator or engine damage. Damage like that is forcing the P-51s hand since he knows he has a limited amount of time remaining before he is effectively helpless. Most P-51s will run when something like this has occurred, so best to make it difficult for him to run and continue to force him defensive. A side note is on WEP, P-51s really need it in acceleration and dogfighting, without it they suffer a noticeable performance penalty. The WEP is short on a P-51 D, only 5 minutes, and often impatient pilots will expend at least half of that trying to get better climb or to build speed prior to the fight. If you can run him out of his remaining WEP then your fight will be easier.
Defensively you can be in real trouble against a P-51 D. A smart pilot will continue to BnZ you from high above with little chance you can return fire. Try and force him to pull high G maneuvers for each gun solution on each of his passes, this will slowly bleed energy out of him. Typically you can achieve this by making sweeping turns and increasing the rate and Gs as his pass on you starts to develop. You need to leave your initial turns light and use it as time to build E, not expend it, but as he closes then tighten up the turn and make him have to work hard to pull enough lead on you for a shot. If he doesn't BnZ you, then try to get into a increasing altitude defensive spiral. Pull just enough Gs to defeat his gun solution while fighting slightly nose high in a spiral climb. The P-51 will quickly find his poor climb rate and average low speed handling are not well suited to this style of fight. If he doesn't then you have likely been able to sucker him and can out-class him badly if you are in a fair turning aircraft. Against a good energy fighter you can probably extend at this point and build up an E margin to return to the attack with.
Be careful of P-51s though, they tend to work in packs and while one person is making his pass there is another getting ready to make another, and thus they may be able to continue to keep you defensive. In these cases your best option may be to try and dive away, picking up as much speed as you can control and drag the P-51s to other friendlies. P-51s don't like the feeling of being low and if they realize they will be under bogie aircraft they will often break off pursuit. If they don't then at least you should have some help in dealing with them.