System and method for propeller response enhancement during transition from ground to flight configuration for a turbopropeller engine

1. An electronic control system for a turbopropeller engine having a gas turbine and a propeller assembly coupled to the gas turbine, the electronic control system comprising:

a propeller control unit configured to control propeller operation based on a pilot input request, via generation of an actuator driving quantity for an actuation assembly designed to adjust a pitch angle of propeller blades of the propeller assembly; and

an electronic processing unit configured to, in response to a takeoff input request to transition from a ground operating mode to a flight operating mode and preceding a validation of the takeoff input request:

cause, prior to engagement of a mechanical lock and during engine acceleration to takeoff power, pressurized oil from a ground gallery of the pitch actuation assembly to start emptying so as to increase the pitch angle of the propeller blades towards a minimum flight pitch; and

cause, prior to takeoff and to transition from the ground operating mode to the flight operating mode, engagement of the mechanical lock, the mechanical lock, when engaged, prevents the pitch angle from falling below the minimum flight pitch while in the flight operating mode.

2. The electronic control system according to claim 1 , wherein the electronic processing unit is configured to cause pressurized oil from the ground gallery of the pitch actuation assembly to start emptying so as to increase the pitch angle of the propeller blades towards the minimum flight pitch in a time period following the takeoff input request and preceding the validation of the takeoff input request, and wherein the electronic processing unit is configured to cause engagement of the mechanical lock after the validation of the takeoff input request.

3. The electronic control system according to claim 1 , wherein the takeoff input request is determined by actuation of an operator-manipulated input device towards a takeoff position.

4. The electronic control system according to claim 1 , wherein the propeller control unit is configured to implement a pitch-angle closed control loop, the pitch-angle closed control loop comprising:

a first reference generator, configured to determine a value of a reference pitch angle; and

a first regulator, configured to generate a first control quantity based on an error between the reference pitch angle and a measured pitch angle, and

wherein the first reference generator is configured to increase the reference pitch angle from a minimum ground value to a value not lower than a minimum flight value before engagement of the mechanical lock.

5. The electronic control system according to claim 4 , wherein the electronic processing unit is configured to implement a propeller-speed closed control loop, the propeller-speed closed control loop comprising:

a second reference generator, configured to determine a value of a reference propeller speed;

a second regulator, configured to generate a second control quantity based on an error between the value of the reference propeller speed and a measured value of a propeller speed; and

a priority selection stage, coupled to the first and second regulators to receive the generated first and second control quantities, and in implementing the priority selection stage, the electronic processing unit is configured to:

implement a priority selection scheme to select one of the generated first or second control quantities; and

provide, at its output, the actuator driving quantity that is supplied to the actuation assembly of the turbopropeller engine to control the pitch angle of the propeller blades, in order to regulate the measured value of the propeller speed.

6. The electronic control system according to claim 5 , wherein in implementing the priority selection scheme, the electronic processing unit is further configured to:

select one of the first or second control quantities generated by the pitch-angle closed control loop during the ground operating mode and the transition from the ground operating mode to the flight operating mode.

7. The electronic control system according to claim 4 , wherein the first reference generator comprises:

a scheduler configured to receive a signal indicative of an input power request and a further signal indicative of engagement, or disengagement, of the mechanical lock, and to determine a first reference value for the pitch angle; and

a rate limiter, which is coupled to the output of the scheduler to receive the first reference value and is configured to implement a rate-limitation thereof, thereby generating a second reference value for the pitch angle, to be supplied as the reference pitch angle in at least one operating condition.

8. The electronic control system according to claim 7 , wherein the rate limiter is automatically tuned according with environmental and/or engine conditions, including altitude and temperature, in order to ensure a monotonic propeller speed increase during the transition from the ground operating mode to the flight operating mode.

9. A turbopropeller engine for an aircraft, comprising:

a gas turbine; a propeller assembly, coupled to the gas turbine via a gearbox assembly; and

an electronic control system comprising:

a propeller control unit configured to control propeller operation based on a pilot input request, via generation of a driving quantity for an actuation assembly designed to adjust a pitch angle of propeller blades of the propeller assembly; and

an electronic processing unit configured to:

receive a takeoff input request to transition from a ground operating mode to a flight operating mode;

perform a takeoff validation to validate the takeoff input request is an intentional command; and

cause pressurized oil from a ground gallery of the actuation assembly to start being emptied so as to increase the pitch angle of the propeller blades towards a minimum flight pitch before the takeoff input request is validated during the takeoff validation.

10. The turbopropeller engine of claim 9 , wherein the electronic processing unit is further configured to:

cause, after the takeoff input request is validated, engagement of a mechanical lock to further increase the pitch angle of the propeller blades towards the minimum flight pitch so as to continue emptying pressurized oil from the ground gallery of the pitch actuation assembly.

11. A control method for a turbopropeller engine having a gas turbine and a propeller assembly coupled to the gas turbine, the method comprising:

receiving a takeoff input request to transition from a ground operating mode to a flight operating mode, and preceding a validation of the takeoff input request after receiving the takeoff input request:

increasing, prior to engagement of a mechanical lock and during engine acceleration to takeoff power, a pitch angle of propeller blades of the propeller assembly towards a minimum flight pitch; and

engaging, prior to takeoff and to transition from the ground operating mode to the flight operating mode, the mechanical lock, the mechanical lock, when engaged, prevents the pitch angle from falling below the minimum flight pitch while in the flight operating mode.

12. The control method according to claim 11 , further comprising:

performing the validation of the takeoff input request; and

wherein the increasing the pitch angle of the propeller blades towards the minimum flight pitch occurs in a time period following the takeoff input request and preceding the validation of the takeoff input request, and wherein the engaging of the mechanical lock occurs after the validation of the takeoff input request.

13. The control method according to claim 11 , wherein the increasing of the pitch angle of propeller blades of the propeller assembly towards the minimum flight pitch comprises:

implementing a pitch-angle closed control loop, comprising:

determining a value of a reference pitch angle; and

generating a control quantity based on an error between the reference pitch angle and a measured pitch angle, and

wherein the determining comprises increasing the reference pitch angle from a minimum ground value to a value not lower than a minimum flight value before the mechanical lock engagement.

14. The control method according to claim 13 , wherein increasing of the pitch angle of propeller blades of the propeller assembly towards the minimum flight pitch comprises:

implementing a propeller-speed closed control loop, comprising:

determining a value of a reference propeller speed;

generating a further control quantity based on an error between the reference propeller speed and a measured propeller speed; and

implementing a priority selection scheme between the generated control quantities to provide an actuator driving quantity that is supplied to an actuation assembly of the turbopropeller engine to control the pitch angle of the propeller blades.

15. The control method according to claim 14 , wherein implementing the priority selection scheme comprises selecting the control quantity generated by the pitch-angle closed control loop during the ground operating mode and the transition from the ground operating mode to the flight operating mode.

16. The control method according to claim 13 , wherein determining the value of the reference pitch angle comprises:

determining a first reference value for the pitch angle based on a signal indicative of an input power request and a further signal indicative of the engagement or disengagement of the mechanical lock; and

implementing a rate-limitation of the first reference value, thereby generating a second reference value for the pitch angle, to be supplied as said reference pitch angle.

17. The control method according to claim 16 , wherein implementing the rate-limitation comprises automatically tuning the rate-limitation according with environmental and/or engine conditions, including altitude and temperature, in order to ensure a monotonic propeller speed increase during the transition from the ground operating mode to the flight operating mode.