Minimum control speeds

Minimum control speeds are typically established by flight tests[1][2][3] as part of an aircraft certification process.

[7] The rudder, and to a certain extent the ailerons via the use of bank angle, are the only aerodynamic controls available to the pilot to counteract the asymmetrical thrust yawing moment[citation needed].

[8] The minimum control speed is the airspeed below which the force the rudder or ailerons can apply to the aircraft is not large enough to counteract the asymmetrical thrust at a maximum power setting.

[4][5] Most test pilot schools use multiple, more specific minimum control speeds, as VMC will change depending on the stage of flight.

[4][5] A high VMCA therefore results in higher takeoff speeds, and so longer runways are required, which is undesirable for airport operators.

Any factor that has influence on the balance of forces and on the yawing and rolling moments after engine failure might also affect VMCs.

[13]: 13  The longitudinal centre of gravity affects the VMCA as well: the further from the tail it is, the lower the minimum control speed, because the rudder will be able to provide a larger yawing moment, and so it is easier to counteract the imbalance in thrust.

There may be less power available to maintain flight overall, but the minimum safe control speeds remain the same as they would be for an aircraft being flown at 50% thrust on all four engines.

If an engine fails during taxiing or takeoff, the thrust yawing moment will force the aircraft to one side on the runway.

[13]: 21  The airspeed at which the aircraft, after engine failure, deviates 9.1 m from the runway centerline, despite using maximum rudder but without the use of nose wheel steering, is the minimum control speed on the ground (VMCG).

Due to the inherent risks of operating at or close to VMCA with asymmetric thrust, and the desire to simulate and practice these manoeuvres in pilot training and certification VSSE may be defined.

[4] This speed is selected to reduce the accident potential from loss of control due to simulated engine failures at inordinately slow airspeed.

The most important forces and moments acting on the aircraft while using the rudder to counteract the asymmetrical thrust and while keeping the wings level. Notice a sideslip cannot be avoided when the yawing moment is being counteracted.
Fig. 1. Overview of all existing minimum control speeds V MC for all multi-engine aircraft types. In this article, V MC(A) is used rather than V MC for air minimum control speeds.
The effect of bank angle on V MCA and sideslip when the left engine (No. 1) is inoperative and the other is at maximum thrust. The bank angle for zero sideslip is used for sizing the vertical tail and also during flight-testing to determine V MCA in-flight.