Tốc độ V (V-Speeds)

Là Gì V-Speeds?

V-speeds are a system of standardized reference airspeeds used in aviation to define critical speed boundaries across all phases of flight. The "V" stands for velocity (from the French "vitesse"). These speeds are not arbitrary — they are calculated for each specific aircraft type, weight, altitude, temperature, and configuration based on flight test data and regulatory requirements. V-speeds are published in the aircraft's flight manual and displayed on airspeed indicators as colored arcs and markings.

Cách Hoạt Động

The most critical V-speeds for transport category aircraft include:

• V1 (Decision Speed): The maximum speed at which a takeoff can be safely rejected. Above V1, the crew must continue the takeoff even if an engine fails, because insufficient runway remains to stop. V1 is the go/no-go boundary.
• VR (Rotation Speed): The speed at which the pilot pulls back on the controls to raise the nose. The aircraft is designed to lift off shortly after rotation.
• V2 (Takeoff Safety Speed): The minimum speed that must be maintained after engine failure during the initial climb. Guarantees obstacle clearance on one engine.
• VS (Stall Speed): The minimum airspeed in a specific configuration at which the aircraft maintains controlled flight. VS0 is stall speed in landing configuration; VS1 is in a specific clean configuration. Directly related to stall characteristics.
• VFE (Maximum Flap Extension Speed): The highest speed at which flaps may be extended without structural damage.
• VMO/MMO (Maximum Operating Speed): VMO in knots and Mach number MMO — the redline speed beyond which the aircraft must not be flown.
• VREF (Reference Landing Speed): Typically 1.3 × VS0, the target speed over the threshold during landing.

V-speeds shift with weight, altitude, temperature, and flap setting. Heavier aircraft have higher V1, VR, and V2 speeds because more lift is needed and the flight envelope boundaries change accordingly.

Ý Nghĩa Trong Hàng Không

V-speeds are the operational backbone of every commercial takeoff. Before departure, crews enter actual weight, runway, temperature, and pressure altitude into the flight management computer, which calculates and displays the specific V-speeds for that flight. These speeds are then verbally confirmed during taxi and called out during the takeoff roll. A rejected takeoff above V1 has led to multiple accidents from runway overruns — the commitment to continue must be absolute once V1 is reached.

Tác Động Thực Tế

The Spanair Flight 5022 crash in Madrid (2008) occurred partly because flaps were not extended, causing VR to be lower than the actual stall speed in the contaminated configuration — the aircraft stalled during rotation. Air France Flight 358 (2005) overran the runway at Toronto after landing at excessive speed, 33 knots above VREF. Understanding and respecting V-speeds is so fundamental that they are among the first concepts taught in pilot training programs worldwide.