Design manoeuvring speed (Va)
Va (design manoeuvring speed): max speed for full control deflection without structural damage (TP 1102, Load Factors; TP 13014 Q22).
- Below Va: wing stalls before load factor reaches airframe limit (PHAK); one full single-axis deflection or gust won't overstress airframe.
Va = Vs1g × √(limit load factor)
- Vs1g: wings-level (1 g) stall speed.
- Limit load factor: set by certification category.
| Category | Limit load factor |
|---|---|
| Normal | 3.8 g |
| Utility (mild acrobatics, incl. spins) | 4.4 g |
| Acrobatic | 6.0 g |
- Va falls with weight: lighter aircraft, lower Vs1g.
Structural loads (PHAK):
| Load | Meaning |
|---|---|
| Limit load | Force that permanently bends structure without breaking |
| Ultimate load | Force where structure breaks |
- Regs require structure to survive 1.5 × limit load before failure ("factor of safety").
Below vs above Va:
| Speed | Result |
|---|---|
| Below Va | Wing stalls first, sheds load before limit |
| Above Va | Full abrupt control deflection or gust can exceed limit load: bends or breaks airframe |
Va protects against: one full deflection, on one axis, once.
- No protection against rapid, repeated, or multi-axis inputs: can damage structure at any speed, incl. below Va (PHAK).
Turbulence (TP 1102, Load Factors, turbulence):
- Moderate or extreme: slow to Va. Speed least likely to permit structural damage, with margin above stall for abrupt control movements.
- Never-exceed speeds set for smooth air only.
Trap: Va is not fixed for the type; it drops with weight, so a numeric answer needs weight given.
References
- PHAK ch.5 Aerodynamics of Flight
- TP 1102 (Flight Training Manual), Load Factors, design manoeuvring speed (line 575)
- TP 13014 Q22 (sample exam), key 22-(2)