V-speeds are standardised defined speeds in the AFM (CS-23.45 ff, ICAO Annex 8). Every PPL student must know them for their aircraft.
Stall and minimum speeds
| Symbol | Meaning |
|---|---|
| Vs | Stall speed (general) |
| Vs0 | Stall speed in landing configuration (full flaps, gear down) |
| Vs1 | Stall speed in specified configuration (usually clean — flaps up, gear up) |
| Vmc | Minimum control speed (multi-engine) |
Climb speeds
| Symbol | Meaning | Use |
|---|---|---|
| Vx | Best climb gradient speed — altitude per horizontal distance | Obstacle clearance; also stated as: the speed at which a given altitude is reached within the minimum distance |
| Vy | Best rate of climb speed — altitude per time | Cruise climb, reaching cruise altitude; also: the speed at which a given altitude is reached in the shortest time |
Note: Vx < Vy in piston aircraft. At Vx climb is steepest; at Vy you climb fastest in time.
Application: reach altitude in shortest time
To reach a specified altitude in the shortest possible time, the pilot must:
- Flap position 0 (fully retracted) — flap drag impairs climb performance,
- Vy as the speed — best rate of climb,
- Full power and proper mixture setting.
Flap and gear limits
| Symbol | Meaning |
|---|---|
| Vfe | Max flap extension speed |
| Vle | Max speed with gear extended |
| Vlo | Max speed for gear operation |
Structural limits
| Symbol | Meaning |
|---|---|
| Vno | Max structural cruising (Normal Operating; start of yellow arc) |
| Vne | Never exceed (red line) |
| Va | Manoeuvring speed — at full control deflection the wing stalls before structural limit load. Decreases with lower mass. |
Va — important
In turbulence: reduce speed to Va or below — protects against structural overload from gusty vertical winds. Consult the AFM for Va at current mass (some types provide tables/diagrams).
TAS, IAS and Vs at altitude / hot weather
In a climb at constant IAS (indicated airspeed — the cockpit reading), TAS (true airspeed) increases. Reason:
- The pitot probe measures dynamic pressure ½ρv², and the airspeed indicator (ASI) is calibrated for sea-level standard density (ρ₀ = 1.225 kg/m³).
- At altitude ρ < ρ₀ → for the same dynamic pressure (IAS), true speed (TAS) is higher.
- Rule of thumb: +2 % TAS per 1000 ft of pressure altitude above ISA standard.
Vs and air density (stall speed at altitude / heat)
The stall speed in TAS depends on air density:
Vs(TAS) = √(2 × W / (ρ × S × CLmax))
- With decreasing air density (higher pressure altitude, higher temperature, lower pressure), Vs(TAS) increases — and vice versa.
- Example: on a hot summer day (high density altitude) the TAS stall speed is noticeably higher than at ISA.
BUT: Vs in IAS (indicated in cockpit) remains approximately constant — the wing "feels" the same dynamic pressure (½ρv²) at the same IAS regardless of altitude. Therefore:
→ On a hot summer day, the approach is flown with the normal IAS reading (AFM Vref) — no extra speed margin needed for heat. The true ground speed will be higher automatically, but stall safety (measured at angle of attack) is the same.
Consequence: the pilot always flies by IAS (not by feel), and AFM IAS values are valid at any altitude and temperature.