Abstract:

The failure of an engine in a multi-engine aeroplane, and the associated lateral-directional controllability issues, is a concern that permeates all aeroplane design phases, from conceptual studies, through development, testing, certification, and on to daily operations. Understanding aeroplane response in this scenario is crucial for sizing lateral and directional controls, fin and rudder surfaces, and the rudderdeflections needed for control, as all these parameters have a direct impact on take-off and landing performance.

The minimum control speed of an aeroplane is the minimum airspeed at which the application of the aerodynamic controls can overcome the imbalance of forces and moments caused by the failure of one or more engines. As the engine fails, the flight crew will adjust aeroplane controls to reach another balanced (trimmed) condition.

In this Data Item a mathematical procedure is developed for calculating the minimum control speed of a multi-engined aircraft with n operating engines and m inoperative engines. The application of this method is illustrated with a series of worked examples involving a range of aircraft that feature a different number of engines and have various propulsion forms.

This Data Item considers the effects of bank angle and weight on the minimum control speed of an aeroplane. Aircraft trim limitations are also considered. Additionally, airworthiness certification for, and testing to determine, minimum control speeds are discussed. Minimum control speeds represent a major concern for airworthiness certification, as lateral-directional control must be maintained during take-off, approach and landing in the event of an engine failure. Requirements then establish that operational speeds for take-off ( V₁ , V_R , V₂ ) and approach and landing ( V_APP , V_REF ) must be established in accordance with standards for minimum control speeds. This also leads to the need to determine (or verify) minimum control speeds in flight tests.

A proper understating of key aspects related to V_MC  is needed to achieve a balanced aeroplane design, which can fulfil all the applicable airworthiness requirements. Aircraft models and methods have been developed over the years to predict aeroplane response during conceptual and detailed design phases. A list of documents that address this aspect may be found in the bibliography at the end of this data item. However, these documents are general in nature and do not cover in full detail the specifics of minimum control speeds.

This Data Item collects relevant information on minimum control speeds considering the description of aircraft trim, the associated model equations and assumptions, and airworthiness and testing aspects. Examples are presented at the end of the document to provide the reader with further insight into how to estimate minimum control speeds.