Turning and G

What a Turn Really Is

A wing makes its lift straight out of its upper surface, roughly at right angles to the span. Hold the wings level and all of that lift points straight up, fighting gravity and nothing else. Now roll the aeroplane over so one wing is high and one is low, and that same lift tilts with it. Part of it still points up. Part now points sideways, towards the lower wing.

That sideways part is the entire mechanism of the turn. It is a horizontal pull, and a horizontal pull is exactly what is needed to drag the aeroplane out of a straight line and around a curve. The aeroplane does not turn because the tail swung the nose round, the way a rudder turns a boat. It turns because it is banked, and the tilted lift is towing it sideways through the sky.

This is why a well-flown turn feels like nothing at all from inside. There is no sense of being flung outwards, because the aeroplane is not being pushed against anything, it is falling around the curve with the sideways lift providing precisely the pull required. A ball on the floor of the cabin stays dead centre. The drinks stay level in the glass. The turn is, in the most literal sense, a controlled sideways fall.

The Cost Has a Number

Here is the bill. When the lift is tilted to one side, the upward part of it, the part actually holding the aeroplane up, is smaller than the whole. So the wing has to make more total lift just to keep that upward part equal to the weight, and the steeper the bank, the more it must make. That extra lift is load, measured in g, where one g is the normal weight of the aeroplane and two g is twice that. The numbers climb faster than intuition expects.

Thirty degrees of bank

About 1.15 g. A gentle everyday turn, the wing carrying around fifteen per cent more than in level flight.

Forty-five degrees of bank

About 1.4 g. A firm turn, the wing now carrying nearly half as much again as the plain weight.

Sixty degrees of bank

Exactly 2 g. The aeroplane and everyone in it now weigh double, and the wing must lift all of it.

Seventy-five degrees of bank

Nearly 4 g. Steep enough that many light aircraft cannot hold height in the turn at all.

Why a Hard Turn Slows You Down

All that extra lift does not come free, and the wing charges for it in drag. Making more lift always drags more air along with it, so a hard turn is draggy in direct proportion to how hard it is. At two g the aeroplane is dragging as though it had suddenly become much heavier, because as far as the wing is concerned it has.

With the throttle left where it was, something has to give, and what gives is speed. Roll into a steep turn without adding power and the airspeed sags, sometimes alarmingly, as the extra drag eats into it. Roll into it while climbing and the climb simply stops. This is why an aeroplane racing against the clock cannot afford to throw in hard turns for nothing: each one is a quiet payment of energy, made whether the pilot noticed sending it or not.

Fighter pilots have a blunt way of putting it. They talk about turning as spending and about energy as money, because a hard sustained turn drains speed and height the way an open tap drains a tank. Win the turn but arrive slow and low and you may have lost the fight. The whole art is turning only as hard as the moment is actually worth.

The Turn That Bites

The dangerous part of turning is what it does to the stall. A wing lets go at its critical angle, and in a turn the wing is already working harder and sitting at a higher angle to carry the extra load. It is closer to the edge before the pilot does anything at all. Pull a shade too eagerly to tighten the turn and the wing reaches its critical angle while the aeroplane is flying far above its usual stalling speed.

This is the accelerated stall, and the arithmetic behind it is worth carrying. The speed at which the wing quits rises with the square root of the load. At two g the stall speed goes up by about forty per cent, and at four g it doubles outright. A turn hard enough to pull four g has doubled the speed at which the aeroplane will let go, which is how a wing that stalls at sixty knots in level flight can stall at a hundred and twenty in a hard one.

Worse, if the turn is uncoordinated, one wing can stall before the other. The aeroplane does not sink gently, it drops a wing and rolls towards the ground, and a pilot who hauls back on reflex can flick it into a spin. This is why the classic stall and spin happens in a turn, low down, exactly where there is no height left to recover in. The turn that bites is never the gentle one. It is the eager one, tightened a fraction too far by a pilot whose attention was somewhere else.

Rate Against Radius

There are two different ways to be good at turning, and they pull against each other. Rate is how quickly you swing the nose around, measured in degrees per second. Radius is how tight a circle you carve through the air. You might assume they are the same thing, but they are not, and a fast aeroplane and a slow one, each turning as hard as it can, will trace very different fights.

Fly faster and, for a given bank, your rate falls but you cover more ground, so the circle grows: high speed favours a big, fast-sweeping arc. Fly slower and the circle shrinks but you travel around it more slowly. Somewhere in between sits corner speed, the sweet spot where an aeroplane turns at its best possible rate and its tightest possible radius at once, without either running out of lift or overstressing the airframe. Every fighter pilot knows the corner speed of their aeroplane by heart.

You feel the difference across the games without being taught the theory. Drone Race is a radius problem: the gates are fixed in space and the tightest line through them wins, so you trade speed for a smaller circle. Dogfight is a rate problem: getting your nose onto the other aeroplane first is what matters, and the pilot who manages energy to stay near corner speed is the one who ends up behind the other rather than in front of it.