APU-Powered Boundary Layer Fan for Aircraft Drag Reduction
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Solution Overview
Problem
Existing aircraft designs face challenges in reducing drag caused by the fuselage boundary layer, as known solutions require large, heavy thrust-producing engines that are not retrofittable and introduce system penalties, leading to negative tradeoffs in fuel consumption and operating costs.
Innovation Solution
The use of a fan powered by an auxiliary power unit (APU) to ingest and accelerate the fuselage boundary layer, which is lighter and more compact, leveraging electrical energy to reduce drag without generating thrust, and is retrofittable to existing aircraft designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large thrust-producing engine is installed at the rear of the fuselage to ingest and accelerate the boundary layer, then drag reduction is achieved, but the device becomes heavy and complex, and structural modifications are required
Solution Approach 1:
The invention extracts the boundary layer acceleration function from a large thrust-producing engine and implements it using a smaller fan powered by an auxiliary power unit. This separates the drag reduction function from thrust production, allowing the use of lighter equipment that doesn't require major structural modifications to the aircraft.
Solution Approach 2:
The auxiliary power unit, which serves multiple functions including powering onboard systems, is made to also drive the boundary layer ingestion fan. This multi-functional use eliminates the need for dedicated thrust-producing engines for boundary layer control, reducing overall system weight and complexity.
2Object-affected harmful factors
If a large thrust-producing engine is installed at the rear of the fuselage to ingest and accelerate the boundary layer, then drag reduction is achieved, but significant structural modifications are required, reducing adaptability
Solution Approach 1:
The boundary layer ingestion system is extracted from the main engine system and implemented as a separate, smaller fan unit powered by the auxiliary power unit. This modular approach allows installation on existing aircraft without major structural modifications, significantly improving retrofittability while maintaining drag reduction effectiveness.
3Weight of moving object
If a fan powered by APU is used to accelerate the boundary layer, then device weight and complexity are reduced, but the energy source must be sufficient to power the fan
Solution Approach 1:
The auxiliary power unit, which already consumes energy to power onboard systems, is made to also drive the boundary layer ingestion fan. This multi-functional use means the additional energy consumption for boundary layer control is offset by the existing operational requirements of the APU, making the energy tradeoff acceptable while maintaining significant weight savings.
Solution Approach 2:
The energy that would otherwise be wasted in the drag wake is converted into useful work by using the APU to power the fan. The fan accelerates the boundary layer, reducing drag and converting what would be energy loss into a beneficial aerodynamic effect, while the energy source (APU) is already required for other onboard functions.
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 solution effectively reduces drag by accelerating the fuselage boundary layer without increasing fuel consumption or operating costs, as the fan's energy requirements are less than the energy dissipated in the drag wake, and it does not produce a net velocity gain relative to the free stream velocity.
Implementation Method 1
Air traveling over the fuselage of an aircraft creates a boundary layer along the fuselage where the velocity of the air reduces below the free stream velocity
Implementation Method 2
The rotation of the fan blades is to accelerate a fuselage boundary layer traveling rearward along the outer skin from a first velocity to a second velocity greater than the first velocity
Implementation Method 3
The fan drive is configured to rotate the fan blades in response to a supply of electrical energy provided to the fan drive from the APU
Data Source
AI summary
Methods and apparatus for accelerating an aircraft fuselage boundary layer via a fan powered by an APU of the aircraft are disclosed. An example aircraft includes a fuselage, an APU, and a fan. The fuselage includes an outer skin. The APU is located within the fuselage. The fan includes a plurality of fan blades arranged circumferentially about the APU and projecting radially outward from the outer skin. The fan further includes a fan drive operatively coupled to the APU. The fan drive is configured to rotate the fan blades in response to a supply of electrical energy provided to the fan drive from the APU. The rotation of the fan blades accelerates a fuselage boundary layer traveling rearward along the outer skin from a first velocity to a second velocity greater than the first velocity.