Ducted Fan Fluidic Thrust Vectoring for Stealth VTOL
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Solution Overview
Problem
Current UAVs require runways for takeoff and landing or specialized systems, limiting their versatility, and typical VTOL aircraft with open rotor disks have high radar cross-sections, making them detectable.
Innovation Solution
A ducted fan assembly with an active flow control system that includes injection zones to manage airflow and thrust vectors, allowing for vertical takeoff and landing, hover, and low observable characteristics by reducing radar reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If open rotor disks are used for VTOL operations, then vertical takeoff and landing capability is achieved, but radar cross-section increases making the aircraft detectable
Solution Approach 1:
The rotor system is segmented into multiple independent ducted fans rather than a single open rotor disk. Each ducted fan operates independently within its own duct structure, allowing the system to achieve VTOL capability through distributed thrust while reducing radar cross-section through the ducted configuration and segmentation of the rotor elements
Solution Approach 2:
Ducts are introduced as intermediary structures between the rotor blades and the external environment. These ducts enclose the rotating blades, preventing direct radar interaction with the rotor elements while still allowing thrust generation. The ducts act as mediators that maintain VTOL capability while providing low observable characteristics
2Device complexity
If conventional ducted fans with fixed thrust vectors are used, then simple structure is maintained, but maneuverability and control flexibility are limited
Solution Approach 1:
The ducted fan system incorporates dynamic control capabilities where the thrust vector of each ducted fan can be actively adjusted during operation. The diffuser geometry and flow control elements are designed to allow dynamic modification of thrust direction and magnitude, enabling maneuverability control without requiring complex mechanical articulation of the entire duct assembly
Solution Approach 2:
Flow control elements within the ducts utilize pneumatic principles to adjust thrust vectors. By controlling airflow patterns within the duct and diffuser regions, the system can modify thrust direction and magnitude through fluid dynamic effects rather than mechanical movement, maintaining structural simplicity while achieving thrust vector control
3Power
If diffusers with large diffuser angles are used to increase thrust, then thrust magnitude is improved, but flow separation occurs reducing efficiency
Solution Approach 1:
The diffuser angle and geometry are optimized to balance thrust generation with flow attachment. Rather than using excessively large diffuser angles that would cause severe flow separation, the design employs carefully calculated diffuser angles that maintain attached flow while still providing sufficient pressure recovery and thrust augmentation. Flow control elements further adjust local flow parameters to prevent separation
4Adaptability or versatility
If active flow control systems with multiple injection zones are implemented, then thrust vectoring capability is enhanced, but system complexity increases
Solution Approach 1:
The active flow control system implements injection zones at specific local positions within the duct where they are most effective for thrust vectoring. Rather than distributing injection uniformly throughout the duct, the system places injection zones at strategically selected locations that maximize thrust control authority while minimizing the number of injection elements required, thus reducing overall system complexity
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
Enables UAVs to operate without runways and specialized systems, while minimizing radar detectability through controlled airflow and thrust vectoring, enhancing stealth and operational flexibility.
Implementation Method 1
A fan is disposed within the duct between the inlet and the expanding diffuser. The fan is configured to rotate relative to the duct about a fan axis to generate an airflow therethrough.
Implementation Method 2
The expanding diffuser has a diffuser angle configured to create flow separation when the airflow is uninfluenced by the active flow control system such that the airflow has a thrust vector having a first direction that is substantially parallel to the fan axis.
Implementation Method 3
each injection zone including an injector configured to inject pressurized air toward the outlet. Injection of pressurized air in a first injection zone of the plurality of injection zones asymmetrically reduces the flow separation between the airflow and the expanding diffuser downstream of the first injection zone such that the thrust vector of the airflow has a second direction that has a non-zero angle relative to the first direction.
Data Source
AI summary
A ducted fan assembly includes a duct having an inlet, an inner surface, an expanding diffuser and an outlet. A fan disposed within the duct between the inlet and the expanding diffuser is configured to rotate about a fan axis to generate airflow. An active flow control system includes a plurality of injection zones circumferentially distributed about the inner surface. The expanding diffuser has a diffuser angle configured to create flow separation when the airflow is uninfluenced by the active flow control system such that the airflow has a thrust vector with a first direction that is substantially parallel to the fan axis. Injection of pressurized air from one of the injection zones asymmetrically reduces the flow separation between the airflow and the expanding diffuser downstream of that injection zone such that the thrust vector of the airflow has a second direction that is not parallel to the first direction.