Stall speed vs bank angle
Bank into a turn and the wings must both hold up the weight and pull the aircraft around, so they make more lift than level flight, more than 1 g. That extra loading is the load factor, and stall speed rises with its square root (TP 1102):
- Load factor:
n = 1 / cos φ(φ = bank angle). The steeper the bank, the more lift leans sideways instead of straight up, so you need more total lift to hold the weight up. - Stall speed:
Vs(φ) = Vs1g · √n, where Vs1g is the wings-level (1 g) stall speed and Vs(φ) the stall speed at bank angle φ. A wing always stalls at the same angle of attack, and lift grows with the square of airspeed (lift ∝ V², V = airspeed), so making n times the lift needs only √n times the speed.
| Bank φ | Load factor n | Stall speed × |
|---|---|---|
| 30° | 1.15 | 1.07 |
| 45° | 1.41 | 1.19 |
| 60° | 2.00 | 1.41 |
At 60° the load factor is 2 g, so stall speed is √2 ≈ 1.41× the wings-level value.
These are indicated stall speeds. A wing stalls at the same IAS at any altitude, because it always stalls at the same dynamic pressure, even though the true speed at the stall gets higher as you climb.
V-speeds are indicated airspeed. If a stall speed is quoted in mph (older ASIs), convert to knots first (1 kt ≈ 1.15 mph) before scaling by √n.
Trap: use the square root. Multiplying by n itself makes the rise look bigger than it really is.
References
- TP 1102 (Flight Training Manual)