Turn rate & radius
Level turn: rate (heading change, °/s) and radius (room needed) depend only on bank angle and speed (V in knots). Not weight, wing area or power. Banked lift's sideways part pulls the aircraft around.
| Change (other held fixed) | Rate | Radius |
|---|---|---|
| Speed up | Falls (longer arc; divides by V) | Larger, grows with V² (TP 1102 l.2169-2171) |
| Slow down | Rises | Smaller |
| Steeper bank (more tan φ) | Rises | Smaller |
| Smallest radius + greatest rate | Lowest possible airspeed for that bank | Same |
- Speed: major factor in radius (PHAK ch.5).
- Radius = V² / (11.26 x tan bank), V in kt, radius in ft.
Rate-one (standard-rate) turn:
- 3 °/s, shown by the turn needle held on the standard rate index on the dial (not the ball, not the bank scale)
- 360° in 2 min; 90° in 30 s; 30° in 10 s (heading change / 3 = seconds)
- Instrument turns use the bank that gives this rate, normally 30° or less
Rate-one bank (rule of thumb):
bank (deg) = IAS/10 + K (TP 1102 l.5569)
| IAS unit | K |
|---|---|
| Knots | +7 |
| Statute mph | +5 |
- Example: 120 kt gives 120/10 + 7 = 19°
- Bank for a constant rate is proportional to airspeed (TP 1102 l.5557)
- Estimate before rolling in; set it on the attitude indicator right away, not by chasing the turn needle
- Approximate: roll to that bank, then trim against the turn needle or turn coordinator until it settles on the rate-one index
Trap: swapping rate with radius: rate divides by V, radius grows with V² (double speed = 4x radius, not 2x). Also +7 with mph or +5 with knots: one constant per unit.
References
- TP 1102 (Flight Training Manual)
- TP 1102 Instrument Flying, Suggested rules of thumb, p.158
- TP 1102 Instrument Flying: Turns
- PHAK ch.5 Aerodynamics of Flight