US Patent 9387934 Method and a rotary wing aircraft having three engines

An aircraft (1) having a rotary wing (2) and at least one main gearbox (5) for driving rotation of said rotary wing (2), said aircraft (1) having a first main engine (11) and a second main engine (12) driving said main gearbox (5), said aircraft (1) being provided with a main regulation system (15) regulating the first main engine (11) and the second main engine (12) in application of a setpoint that is variable. A secondary engine (21) is also capable of driving said main gearbox (5), said aircraft (1) having a secondary regulation system (25) that regulates the secondary engine (21) in application of a setpoint that is constant and that is independent of said main regulation system (15).