Aircraft Nacelle Inner Cowl Segmented Nozzle Area Control
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Solution Overview
Problem
Existing aircraft nacelle designs face challenges in varying nozzle area efficiently, leading to reduced engine efficiency, noise, and increased weight due to complex activation mechanisms and potential air leakage, particularly when using movable inner flow surfaces.
Innovation Solution
An aircraft nacelle with a translatable aft portion of the inner cowl that adjusts the nozzle area by sliding in a forward-to-aft direction via actuators, allowing for a more compact and lightweight design with minimized leakage paths, using different materials for high-temperature resistance and reducing the need for heavy, robust components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If movable inner flow surfaces are used to vary nozzle area, then engine efficiency and noise performance are improved, but the nacelle weight increases due to heavy movable surfaces and robust activation mechanisms
Solution Approach 1:
The inner cowl is divided into a forward stationary portion and a rear movable portion. Only the rear portion that actually varies the nozzle area is made movable, while the forward portion remains fixed. This segmentation reduces the weight of movable components and simplifies the activation mechanism compared to making the entire inner cowl movable.
Solution Approach 2:
Instead of moving the entire inner cowl forward to vary nozzle area, the invention inverts the approach by keeping the forward portion stationary and only moving the rear portion backward. This inversion reduces the travel distance and weight of movable components while achieving the same nozzle area variation effect.
2Area of stationary object
If movable inner flow surfaces are positioned forward of trailing edges to limit nacelle size, then nozzle area can be varied, but air leakage paths increase at joints of movable surfaces
Solution Approach 1:
The inner cowl is segmented into forward and rear portions with a longitudinal seam. The rear portion is made movable while the forward portion remains stationary, allowing the movable section to be positioned optimally near the trailing edges to minimize leakage paths while still achieving the desired nozzle area variation.
Solution Approach 2:
Different portions of the inner cowl are given different properties: the forward portion is stationary and structurally robust, while the rear portion is movable and aerodynamically optimized. This local differentiation allows each section to be designed for its specific function, minimizing leakage at joints while maintaining nozzle area control.
3Temperature
If high-temperature materials are used in the nacelle, then thermal resistance is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
High-temperature resistant materials are applied locally only to the rear portion of the inner cowl that is exposed to high-temperature exhaust gases, while the forward portion uses standard materials. This localized application of special materials provides necessary thermal protection without unnecessarily complicating the manufacturing of the entire nacelle structure.
Solution Approach 2:
The nacelle employs composite material construction, combining high-temperature resistant materials in the rear section with standard aluminum or composite materials in the forward section. This composite approach provides thermal protection where needed while maintaining ease of manufacture and cost-effectiveness for the overall structure.
Data Source
AI summary
An aircraft nacelle comprising an outer cowl and an inner cowl located inward of the outer cowl with an air flow path formed therebetween. The inner cowl may comprise a forward portion and an aft portion slidable in a forward-to-aft direction via one or more actuators. When translated aftward, the aft portion may decrease the area of the nacelle's fan duct nozzle. The greatest radial distance between the inner cowl and a center axis of the nacelle may occur at or forward of a location in which the forward and aft portions overlap each other. The forward portion may be comprised of a different material than the aft portion.