Instantaneous Turn / Sustained Turn
by TC aka Tequila Chaser

You can classify turns into (2) categories which are Instantaneous or Sustained.

Instantaneous Turn / Instantaneous Turn Rate - where a plane pulls max G's (near 6 right before blackout) to turn quickly for a short period of time, turn rate varies with speed , usually bested at the corner speed/ corner velocity of a given aircraft. A turn that quickly expels speed and possibly alt, while an instantaneous turn is by definition unsustainable, most times to be no more than a 180 degree turn or change in direction. While usually bested at the corner speed of the given aircraft, this turn can be performed at higher or lower speeds with less benefit.

Sustained Turn / Sustained Turn Rate - where a plane maximizes it’s smallest turn radius, g - load, and speed to acquire the best possible turn rate and continuously sustains the turn for long periods of time, without giving up alt, speed, or degrees of turn.

As the above definitions have defined, the difference between the two is the period of time you're able to maintain the rate of turn. While you can achieve a high instantaneous G-load by pulling back hard on the stick, you will not be able to maintain that high rate of turn for very long because that high G-load will increase drag and slow the aircraft, in return this will reduce the maximum G obtainable. Conversely, a lower G-load produces less drag. Eventually you'll reach a point where thrust will be sufficient to overcome the drag being produced. This will allow you to maintain the current G-load and speed. This is called sustained turn rate.

You will find that most Aces high pilots rely solely on an aircrafts sustained turn rate performance speed and basically ignore the instantaneous turning ability when choosing their ride. This is usually because an aircraft with a high sustained turning rate will be easier to fly in combat. To ignore instantaneous turn rates would be a really bad judgment call on your part. A superior instantaneous turn rate can be useful for defensive maneuvering, but when used effectively, it can be deadly in an offensive capacity. This advantage can allow you to come to a guns solution faster, but the downside is that if your sustained turn rate is inferior, unless you make the kill immediately, you're in for trouble. It is at exactly this point that you'll understand why a superior sustained-turning-rate aircraft is easier to fly.