Performance, flight mechanics and load factor
Overview
Performance, flight mechanics and load factor tests the relationship between lift, weight, turns and the V-n diagram.
Core rules
- Load factor n = L/W. In level flight n = 1; in a level turn n = 1/cos φ.
- Bank 60° gives n = 2; bank 75° gives n ≈ 3.9.
- The V-n diagram plots speed against load factor. The stall line follows V_S√n; the gust and manoeuvre lines bound the envelope.
- V_A (manoeuvring speed) is the speed at which full deflection is safe at limit load; V_A falls as weight falls.
- Climb performance depends on excess thrust (best angle, V_X) or excess power (best rate, V_Y).
- Takeoff and landing distances increase with density altitude, weight, tailwind and upslope.
Worked example
A 1,200 kg aircraft in a 60° level turn: n = 1/cos 60° = 2, so lift = 2 × 11,772 = 23,544 N. Stall speed rises by √2 to 1.41 V_S, and the turn can be sustained only if thrust covers the extra induced drag.
Traps
- V_A is not a fixed number - it decreases with weight.
- Load factor in a level turn depends on bank, not on speed.
- Gust loads can exceed manoeuvre loads at high speed.