Twin Electromechanical Actuators (EMA) are employed in a load sharing arrangement to open and close an air stair door.
An existing rotor-wing aircraft was to be outfitted with a new air stair concept for executive transport. Operation of the air stair/ramp must be completed in both a powered and manual mode function. Manual mode allows the air crew members to open or close the air stair/ramp in a no-power operation.
Twin actuators are used in the airframe design. Under powered operation, the twin actuators must match speed and equally share mechanical load so as not to ‘rack’ or distort the air stair/ramp during transition and ramp mating to the aircraft fuselage. Each EMA was sized to both carry the maximum mechanical loads and function at the very high operational velocities in the unpowered mode. Special consideration was also given to actuator sizing from additional loads generated by the main rotor down wash air stream. Vibration levels generated by the aircraft environment and rotor beat frequencies were also used to properly size the EMAs to satisfy the very high MTBFs demanded with this application.
Ingenium Aerospace engineers accomplished the load sharing/speed match of the twin actuators in a novel control theory that was incorporated into the Circuit Card Assembly (CCA). At one end of stroke, the EMAs must also mechanically latch, hold and lock the air stair/ramp once the air stair/ramp is closed and unpowered. Status of EMA position as well as integral lock status is reported to the crew annunciator panel via status signals generated within the EMAs. A visual indication of actuator and latch position was added to the design to show status when no power is applied to the aircraft.
An electromechanical clutch and electromechanical brake were used within the mechanical drive train. This design concept allowed the EMA to be manual back driven with minimal amount of external force. Dynamic, mechanical overtravel stops are included in the EMA and are used to respond to excessive travel whether generated from manual force or aerodynamic loading. Other design considerations for this actuator design solution included the acoustic noise level, electromagnetic interference (EMI), and lightning strike requirements.
Results & Outcome
Actuators have entered Qualification and Environmental tests regimen. Initial test results have matched closely to analysis and predictions.