Turn radius

Turn radius is how much room a level turn needs. It depends on just two things: bank angle and speed (V in knots). When you bank, part of the lift points sideways and pulls the aircraft around the turn; a steeper bank (bigger tan φ, where φ is the bank angle) pulls harder and tightens the turn.

r = V² / (11.26 · tan φ) (r in feet)

• The constant 11.26 folds in gravity and the knot→ft/s conversion, so V is in knots and r in feet. If a speed is given in mph, convert first (1 kt ≈ 1.15 mph).
• Radius grows with V²: double the speed and the turn needs four times the room at the same bank.
• At a fixed bank, slowing down tightens the turn (smaller radius); steepening the bank (more tan φ) also tightens it.

Turn rate (degrees per second) is the companion measure, ω = 1091 · tan φ / V; see the turn-rate lesson.

Note: 11.26 is derived standard turn geometry, not a value printed in the CARs/TC AIM/TP 1102.

Trap: forgetting to square V, or reaching for sin φ instead of tan φ.

Practice