V-speeds are simply, important speeds for aircraft. While commercial pilots are well aware of V-speeds, these are also translated for general aviation aircraft, with different coloured arcs on the airspeed indicator. The sequence of V-speeds on take off are especially popular questions for CPL and ATPL performance exams, but even if you are flying a single engine, general aviation aircraft, understanding what these speeds are, and the sequence they follow, will make you more mindful of your own take off speed sequence.
Minimum Control Ground – Is the starting point, on the ground, it is the minimum speed that must be maintained on a multi engine aeroplane, in the case of one engine failing, while the other engine/s are on take off power. This speed allows the aeroplane to be controlled in the ground run using only the aerodynamic controls such as ailerons and rudder. Below this speed, the aeroplane will not be aerodynamically controllable in an engine-out situation, and could cause a runway excursion.
Take Off Decision Speed – Determines whether the take off will be aborted or continued in the case of an engine failure during the take-off ground run. This speed is not fixed, and is subject to various conditions, with the most significant being the mass of the aircraft. However, once V1 has been determined for a particular flight, then it must be adhered to in the case of an engine failure. If an engine fails below V1, the take off must be aborted, and the aircraft must be brought to a complete stop in the accelerate-stop distance available (ASDA). Only in an emergency situation may the stopway be used, normally it is not included in the ASDA. If an engine fails and our speed is already higher than V1, then we must continue with the take off. V1 must never be lower than VMCG.
Rotation Speed – At this point the aircraft has sufficient speed for the pilot to commence applying back pressure to the control column, which will cause the load on the nose-wheel to diminish, and eventually lift off the runway surface. V1 may be equal to VR, but not higher.
Lift-off Speed – The aircraft becomes airborne at this speed. All wheels are lifted off the ground.
Stall Speed – Important to all aircraft that reach the airborne stage, this is the minimum speed in steady flight that the aircraft can be controlled. Below this speed, airflow over the wings is insufficient to maintain lift, and insufficient over the aerodynamic control surfaces for them to be effective in pitch or roll.
Minimum Control Air – Similar to VMCG, except we are now talking about minimum control speed in the air. This means that above this speed, directional control can safely be maintained with one engine inoperative (the critical engine in the case of a twin engine aeroplane), whilst the remaining engine/s are at take off power, and a maximum 5 degree bank towards the good engine. Especially when you have only two engines, the failure of one (the critical engine is worse), will result in unfriendly (adverse) yaw which will take you away from the direction you want to go. As airflow over control surfaces is essential for them to work properly, and counter the adverse yaw, this is the minimum speed which will provide sufficient airflow to give you the rudder authority you need. Below this speed, any rudder input will be insufficient to counter the yaw.
Take Off Safety Speed – If an engine fails above V1 and we continue the take off, then this is the safe speed that we will be able to climb at with one engine inoperative.