The optimum climb rate

Beginners pitch up the nose and think they can climb like a rocket. The steeper, the faster.

There is actually an optimum angle for climbing - not too low, not too fast - and it varies by plane type, upgrade status and altitude.

I'll tell you two general rules of thumb here:

(1)

Save for jets and biplanes, the optimum climb rate for a fighter is at about 250-280 kph speed for most planes and at about 220-250 kph speed for turnfighters with low wing loading (weight divided by wing area) such as Ki-43, A6M or most Spitfires.

(2)

A much better rule of thumb is to look at the climb angle instead of the speed, since you may inititally be faster anyway. Switch to the "F4" view with the "F4" key. There you see a head up display as used in 1970's and newer military aircraft. It indicates your angle of climb, similar to an artificial horizon.

For good climbers (propeller monoplane fighters) such as fully upgraded P-63, Fw 190D-9, Spitfire LF Mk IX etc use this:

Initially climb at 25-30°, drop to about 20° at about 3,500-4,000 m and drop to 15° (or even later on 10°) at unusually high altitudes (fitting to rule (1)).

For most (propeller monoplane) fighters try to climb at 20° at first and drop to 15° at about 3,500 m.

Bombers (propeller) should usually climb at about 10°, some good climbers (Do 217, Il-4 etc) at 15° up to about 5,000 m at least. At very high altitudes (above 7,000 m) as little as 5° may be most useful.

Jets; climb at about 10-15°.

Remember; climbing slows you down, and slow planes are easy targets. Switch to level flight or even gain speed  by dropping about 300 m before you engage in combat with a fighter who's aware of your presence! Do this in time or you'll be shot down before you can make good use of your energy!

500 m ~ 1,500 ft  (accurately: 1,640 ft)

"Energy"

You probably heard about "energy" and "energy fighting" in War Thunder. The latter means a style in air combat with which the pilot strives to keep his energy high at all times, avoiding any large expense of energy. Good "energy fighters" are planes which by virtue of a low drag lose little energy at high speed (or are at least the least weak in energy fighting compared to turnfighting and boom and zoom tactics).

Energy is not something spiritual here; it's about physics.

Potential energy is the energy of altitude:

mass * local gravitational field * altitude difference = potential energy

Higher is better.

Kinetic energy is the energy of speed:

0.5 * mass * velocity * velocity = kinetic energy

Again, usually more is better. 

You see velocity twice (or squared) in the kinetic energy formula, but only once in the potential energy formula. This is important for the comparison between fast and slow fighters.

The kinetic energy difference between 800 kph and 900 kph is much greater than between 200 kph and 300 kph even though the speed difference is the same.

900^2 - 800^2 = 170,000

300^2 - 200^2 = 50,000

Meanwhile, the potential energy difference betwen 8,000 m and 9,000 m is the very same as between 2,000 m and 3,000 m. The faster you are, the more potential energy gain (altitude gain) can you get by sacrificing some (such as 100 kph) of your speed.

At battle rating 2.0-5.0 you can assume to be safe if all reds are either far away or a least 2.5 km below yourself. At battle rating 6.0-9.0 you can assume such only if all reds are either *really* far away or at least 4 km below yourself. 

The increased speed of the red fighters flying below you enables them to climb up to you within seconds.

Now about energy retention and building up energy:

The drag caused by movign a plane through a fluid (the air) approximately grows squared with its speed: The drag is quadrupled if you double your speed.

You need engine power to make up for this drag, and only what little engine power is left after maintaining your speed this way can be used to gather altitude (potential energy). To maintain a high kinetic energy thus requries a lot of constant effort by your engine.

Meanwhile, maintaining a high altitude is about as easy as maintaining a low altitude. Your engine power drops at higher altitudes and the drag drops in thinner air as well, but as a rule of thumb to maintain a certain high potential energy is as easy as to maintain a certain low potential energy.

The path towards energy superiority over your adversary at the beginning of air combat is thus not to accelerate to a high speed (built up kinetic energy), but to climb (build up potential energy).

Be aware: You're losing energy whenever you are flying faster than the top speed your plane can maintain at that altitude. The very high drag at that high speed bleeds your energy.

For reasons of manoeuvrability you should stop the climbing well before engaging a red fighter at about equal or lower altitude, though; build up speed again (even by dropping by 200-300 m) in time, for your plane is less manoueuvrable at its optimum climb speed (measured as IAS) than at a moderately higher speed.

One last note: Kinetic energy depends on your indicated air speed (the IAS). The other method of measuring speed measures the speed over ground and is useful only for navigational purposes ("how far did I fly in the last ten minutes?").

The turnfighter's fate

Turnfighter planes such as Ki-43, Yak-1B, A6M, I-153 or early Spitfires can be used to great effect by skilled players, and make it much easier to score some kills than boom and zoomer or energy fighters. All you need to do for *some* success is to fly into the red furball, turn towards some red plane, exploit your plane's turning rate to keep the sights ahead of the red plane('s lead indicator) and keep pressing the trigger.

Combined with a little skill this is an easy method for scoring more kills than planes lost; most players are stupid enough to join such furballs or fighters even with planes unsuitable for turnfighting - and end up as easy fodder.

There is a fairly low glass ceiling concerning the kill/death ratio with turnfighting, though: While occasionally one may end up even with a 15:0 kills match, I myself never succeeded to exceed a k/d ratio of about 6:1 with turnfighters (A6M, Ki-43-III) by much unless they were suitable for BnZ (Sptifire IX) as well. The reason is the turnfighter's fate:

To turnfight means to bleed energy. A warship that turns by 90° loses half its speed, and then sustains this low speed even during further circling. It's quite the same with aircraft; one ends up typically at 200-280 kph in propeller planes during sustained turns (in AB), and likely even loses altitude until there's none left to spend. A turnfighter in such a position is despite his (predictable) turning an easy target for new red fighters who join the fray with superior energy. Maybe the first one does only slight damage, the second probably misses - but sooner or later the turnfighter will be shot down by new opponents in such a situation. Once locked in a turnfight with more than one enemy a turnfighter cannot break off and run, climb, enter a fight at his own conditions again. He's locked into the fight as long as not all reds are dead or blues outnumber the reds, absorbing their attention.

It's thus quite easy to reach a good kill ratio with a turnfighter and turnfighting skill, but exceedingly hard to reach really high kill ratios. I doubt anyone in War Thunder has a kill ratio in excess of 10:1 in any specialized turnfighter plane spanning more than ten matches. That's reserved for fine BnZ or energy fighting planes (and exceptions such as the B7A2).

The foundations of a really high kill:death ratio

I know some guys who are really good at head-on-head (frontal) clashes; they can kill a plane this way, seconds later another, yet another, yet another and then after killing the fifth they burn out.

That's an impressive streak, but it's still "only" a kill/death ratio of 5:1.

Can you imagine players to average more than this in head-on-head fights?

6:1?

8:1?

10:1?

I cannot. In fact, those impressive players I just wrote about have an average of 2:1 or 3:1 in head-on engagements.

Such a tactic doesn't seem to be very helpful if you strive for a really high kill ratio of maybe 10:1 or 15:1. Even an impressive five-kill streak at the expense of a single plane would be a setback in the quest for such high kill ratios.

This is no bashing of head-on engagements; it was an example for a fundamental, even mathematical, insight: 

(I) Avoid engagements and tactics that yield a worse kill ratio than the one you're aspiring to reach.

It's even more troublesome than this sounded whenever you're trying to reach a very high kill ratio.

Imagine a player with a kill ratio of 50:1. This player wants to improve his kill ratio to 100:1*.

Now imagine how much a lost aircraft means to him, and how much one more kill means to him.

One more kill is near-meaningless to him compared to the loss of a single plane!

Even worse, every match with a single lost plane is a bad match for him, since he's not going to score 100 or even only 50 kills in that match as a compensation.

(II) The quest for really high kill ratios is not about being great at killing planes. It's about being great at survival.

This is what makes very high kill ratios so difficult to achieve and difficult to maintain: It requires A LOT of ambition, focus on the goal, self-discipline and patience.

One golden rule exists that embodies all this: The Golden rule of the least risky target.

Imagine yourself flying at superior altitude, looking at red planes below yourself. Do you attack? Which one do you attack?

You should most likely kill one that pursues the objective if you want to win, but if your ambition is to maximize kill/death ratio, you better obey a simple rule:

(III) ALWAYS attack the least risky target only. Wait instead of attacking if you estimate the odds to be worse than the kill ratio you're trying to achieve.

*: I actually only reached these heights for a single aircraft type, ever - I had a score of 165:1 with the Ki-45ko once.

Book: Spitfire vs Bf 109

There are plenty of Osprey's book series uploaded at Scribd. The topics of the various books series include fighter aces, aircraft and tanks among many other topics. It's a treasure trove.