Hybrid Aircraft Propeller Start Sequence Under Torque Limits
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Solution Overview
Problem
Hybrid-electric propulsion systems face challenges in coordinating the operation of electric motors and thermal engines to respect propeller placard speed and torque limits during start-up and shutdown sequences, particularly when the thermal engine idle speed is high, risking propeller torque encroachment.
Innovation Solution
A method and system that coordinates the operation of electric motors and thermal engines by transitioning the propeller drive from electric motor to thermal engine, controlling the pitch of propeller blades, and managing engine oil systems to respect propeller speed and torque limits, using a hybrid electric propulsion system with a thermal engine, an electric motor, a gearbox, and a propulsion unit with propeller blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thermal engine is run at high idle speed to ensure self-sustaining operation, then the engine can maintain stable operation and power accessories, but the propeller torque encroaches upon the propeller torque limit in feather configuration
Solution Approach 1:
The patent divides the propeller drive function into two separate power sources: the electric motor handles propeller rotation and unfeathering, while the thermal engine provides auxiliary power for accessories and systems. This segmentation allows the thermal engine to operate at high idle speed without directly driving the propeller, thus avoiding torque limit encroachment while maintaining engine reliability
Solution Approach 2:
The electric motor acts as an intermediary that decouples the thermal engine from direct propeller drive during ground operations. The electric motor drives the propeller independently, allowing the thermal engine to run at high idle to power accessories without transmitting torque to the propeller, thereby resolving the contradiction between engine reliability and propeller torque limits
2Ease of operation
If the electric motor drives the propeller at high speed to enable unfeathering, then the propeller can transition from feathered to unfeathered mode, but the propeller may exceed the placard speed range
Solution Approach 1:
The patent implements dynamic control of the electric motor during propeller unfeathering, where the motor speed and torque are continuously adjusted based on real-time propeller blade angle and rotational speed feedback. This dynamic control ensures the propeller transitions smoothly through the feathered, intermediate, and unfeathered positions without exceeding placard speed limits, resolving the contradiction between ease of unfeathering and speed control
3Reliability
If the thermal engine and electric motor operate simultaneously to drive the propeller, then the system can provide redundant power and maintain operation under varying conditions, but the coordination complexity increases
Solution Approach 1:
The patent employs preliminary action by pre-programming the controller with specific operational sequences for different flight phases. During ground operations, the controller automatically selects electric motor-only propeller drive with thermal engine providing accessory power. During flight, it transitions to thermal engine primary drive with electric motor available for assistance. This pre-planned coordination reduces real-time control complexity while maintaining system redundancy and reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system ensures propeller operation within safe speed and torque limits, avoiding excessive torque on the propeller and enabling efficient start-up and shutdown sequences while maintaining accessory operation, such as electrical and hydraulic systems.
Implementation Method 1
driving the propeller from a static state to a target rotational speed within a predetermined range of speeds using the electric motor
Implementation Method 2
starting the thermal engine; and transitioning the driving of the propeller using the electric motor to driving the propeller using the thermal engine
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A method of and system for operating a hybrid electric propulsion system (20) for an aircraft in a start sequence is provided. The hybrid electric propulsion system (20) includes a thermal engine (22), an electric motor (24), a gearbox (36), an electric power storage unit (26), and a propulsion unit (28) having a propeller (40) having propeller blades (40A). The method includes: driving the propeller (40) from a static state to a target rotational speed within a predetermined range of speeds using the electric motor (24); transitioning the propeller blades (40A) from a feathered mode to an unfeathered mode while the propeller (40) is being driven at the target rotational speed solely by the electric motor (24); starting the thermal engine (22); and transitioning the driving of the propeller (40) using the electric motor (24) to driving the propeller (40) using the thermal engine (22).