Method and system for controlling an emergency device

Control method for an emergency device of a helicopter, said helicopter comprising a rotor adapted to be rotated, said emergency device being adapted to supply additional emergency propulsive power to the helicopter,

• said method comprising the following steps:
• a step of measuring the rotation speed of the helicopter rotor,
• a step of calculating the derivative of the measured rotation speed,
• a step of detecting a drop in the rotation speed of the rotor at an instant t0 below the nominal rotation speed VNRnom of the helicopter rotor,
• a step of activating a timer to measure the duration Δt from the instant t0, the timer being activated as long as the rotation speed of the rotor is dropping,
• a step of measuring at an instant t0+Δt the rotation speed of the rotor VNR,
• a step of continuously verifying the following conditions:
• the rotation speed of the rotor is greater than a predetermined value, said arming speed,
• the derivative of the rotation speed is greater than a predetermined value, said arming derivative,
• the derivative of the rotation speed at instant t0+Δt is lower than or equal to:
• V
• DEC
• -
• V
• NR
• Δ
• 
• 
• t
• the derivative of the rotation speed at instant t0+Δt is greater than or equal to:
• V
• DEC
• -
• V
• NRnom
• Δ
• 
• 
• t
• with VDEC being the stall speed of the helicopter rotor, below which the helicopter is in stall due to the loss of lift of the helicopter,
• an activation step of the emergency device if the verified conditions are validated.