Definition
A mathematical relationship used to calculate the increase in stall speed during a banked turn. The stall speed in a level turn equals the wings-level stall speed multiplied by the square root of the load factor imposed by that turn. For example, in a 60° bank level turn the load factor is 2 Gs, so the stall speed increases by a factor of √2 (approximately 1.41), meaning a 60-knot stall speed rises to about 85 knots.
Plain English
It's a quick math rule that tells you how much faster your airplane will stall when you bank it into a turn. Take the G-load the turn pulls, find its square root, and multiply your normal stall speed by that number. The steeper the bank, the higher the stall speed.
Context Anchor
Seen in steep-turn training when explaining why an airplane can stall at a higher airspeed during a steep bank than it does in straight-and-level flight.
Derivation
A square root is the number that, multiplied by itself, gives the original number. The square root of 4 is 2 because 2 × 2 = 4. Stall speed rises with the square root of load factor (rather than load factor itself) because lift varies with the square of airspeed -- so to double the lift you only need to fly about 1.41 times faster, not twice as fast.
Why Pilots Care
Pilots apply this factor to choose a safe entry speed that keeps adequate margin above stall during steep turns.
Grounding Statement
As the turn gets steeper, the wing must support more force, and the stall speed rises by the square root of that added load factor.
Intuition Check
Do not read load factor as baggage or cargo weight; here it means how many times the airplane's weight the wing is effectively supporting. Also, the square root is not half the load factor; it is the number that multiplies by itself to make the load factor.
Example Sentence 1
Before entering the steep turn, the instructor reminded the student that stall speed increases by the square root of the load factor, so a 2-G turn raises a 60-knot stall to about 85 knots.
Example Sentence 2
Knowing the square root of the load factor lets the pilot calculate the minimum airspeed needed to avoid an accelerated stall in the steep turn.