Basic Fighter Maneuvers - BFM Principles - Turn Performance

Turn Performance

Both turn rate, (degrees per second), and turn radius, (diameter of the turn), increase with speed, until the "corner speed" is reached. At this point, the growing turn radius begins to decrease the turn rate, so the aircraft will reach its best turn performance at its particular corner speed. The corner speed of an aircraft is the minimum speed at which it can pull the maximum sustainable g-force load, and varies with its structural design, weight, and thrust capabilities. It often falls in the area of 250 to 400 knots. This is the speed at which the fighter can achieve the fastest turn-around time without losing energy, flying the craft just at the edge of buffeting (the turbulence preceding a stall).

Instantaneous turn rate describes maximum g turns which cause a loss in energy, either in the form of speed or altitude. These turns are unsustainable, although to some degree the energy loss may be compensated for by increasing thrust, known as applying "excess specific power." This usually occurs during hard turns or even harder breaks. Only by turning the aircraft at its best "sustained turn rate" can the aircraft maintain its specific energy. However, situations in combat may require a change in energy, and energy may also be increased by pulling less than the maximum sustained g-force.