Variable Diameter Downstream Propeller for CROF Noise Reduction
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Solution Overview
Problem
Contra-rotation open fan (CROF) aircraft engines face challenges in reducing takeoff noise due to Blade Vortex Interaction (BVI) noise, which requires cropping of downstream propeller blades, leading to decreased thrust, increased drag, and fuel consumption penalties, while current noise reduction methods incur significant weight and cost penalties.
Innovation Solution
A method and apparatus that control the length of downstream propeller blades in a CROF engine, allowing them to be retracted during takeoff and climb to reduce noise and extended during cruising to match the upstream propeller diameter, using a hydraulic actuator system and blade equalizer to maintain balance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the downstream propeller diameter is reduced (cropped) to reduce takeoff noise, then noise levels are reduced, but thrust and aerodynamic efficiency decrease
Solution Approach 1:
The patent applies variable geometry by making the downstream propeller diameter adjustable rather than fixed. The propeller can be cropped during takeoff to reduce noise, then extended during cruise to restore thrust and efficiency. This dynamic adjustment resolves the contradiction by allowing the system to optimize for noise during noisy phases and for thrust during high-performance phases.
Solution Approach 2:
The patent changes the physical parameter of propeller diameter from a static value to a variable value. By adjusting the diameter parameter according to flight conditions (smaller during takeoff, larger during cruise), the system can simultaneously address noise requirements and performance requirements that cannot be met with a fixed diameter.
2Object-affected harmful factors
If the downstream propeller diameter is reduced (cropped) to reduce takeoff noise, then noise levels are reduced, but fuel consumption increases
Solution Approach 1:
The variable diameter propeller dynamically adjusts its size based on flight phase. During takeoff, the reduced diameter lowers noise, and during cruise, the restored full diameter improves aerodynamic efficiency and reduces fuel consumption. This dynamic adaptation resolves the energy penalty by ensuring the propeller is optimally sized for each flight phase.
Solution Approach 2:
By changing the propeller diameter parameter from fixed to variable, the system can minimize fuel consumption during cruise by restoring the full diameter, while still meeting noise requirements during takeoff. This parameter flexibility eliminates the permanent fuel penalty associated with permanently cropped propellers.
3Productivity
If the downstream propeller pitch is increased to recover lost thrust from cropping, then thrust is recovered, but drag increases and off-design performance degrades
Solution Approach 1:
Instead of increasing pitch to compensate for cropping, the patent dynamically adjusts the diameter. This avoids the drag penalty associated with high-pitch configurations while still recovering thrust during cruise by restoring the full propeller diameter. The system uses diameter variation rather than pitch variation to manage thrust across different flight phases.
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
This approach effectively reduces noise during takeoff and climb while maintaining flight efficiency at cruising speed, minimizing fuel consumption and avoiding the weight and cost penalties associated with traditional noise reduction methods.
Implementation Method 1
using a hydraulic actuator system and blade equalizer to maintain balance and efficiency
Data Source
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AI summary
A method and apparatus for controlling a propeller of a contra-rotation open fan (CROF) engine of an aircraft. A diameter of the propeller is set to be at a first diameter during at least a portion of a first flight condition of the aircraft. The diameter of the propeller is set to be at a second diameter, different from the first diameter, during at least a portion of a second flight condition of the aircraft.