Variable Sweep Aircraft Lifting Surface Design
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Solution Overview
Problem
Aircraft lifting surfaces, such as horizontal and vertical tail planes, experience reduced lift curve slope due to interference with the fuselage, particularly pronounced in commercial aircraft with varying rear fuselage cross-sections, leading to suboptimal performance and increased aerodynamic drag.
Innovation Solution
A lifting surface with a variable sweep angle along its span, where the inboard section has a different sweep angle than the outboard section, optimized to match local Mach number conditions, allowing for reduced sweep angles inboard to increase lift curve slope and delay compressibility effects, thus enhancing aerodynamic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant sweep angle is used along the span of the lifting surface, then the structural design is simplified, but the aerodynamic performance is suboptimal due to fuselage interference effects
Solution Approach 1:
The lifting surface employs different sweep angle characteristics in different spanwise regions: the inboard section has a first sweep angle characteristic while the outboard section has a second sweep angle characteristic. This local differentiation allows each section to be optimized for its specific flow conditions, with the inboard section addressing fuselage interference effects and the outboard section maintaining overall aerodynamic efficiency.
2Object-affected harmful factors
If the sweep angle is increased to delay compressibility effects, then compressibility effects are delayed, but the lift curve slope is reduced
Solution Approach 1:
By applying different sweep angle characteristics to different spanwise sections, the patent locally optimizes each region: the inboard section uses a sweep angle designed to delay compressibility effects, while the outboard section uses a sweep angle optimized for maintaining lift curve slope, thereby resolving the contradiction between these two competing requirements.
Solution Approach 2:
The lifting surface is divided into at least two spanwise sections (inboard and outboard) with different sweep angle characteristics. This segmentation allows independent optimization of each section's sweep angle to address different aerodynamic requirements without compromising the overall performance.
3Weight of moving object
If the lifting surface size is reduced to decrease weight, then structural weight is reduced, but aerodynamic performance deteriorates
Solution Approach 1:
The differentiated sweep angle characteristics enable more efficient aerodynamic performance from a reduced-sized lifting surface by optimizing each spanwise section for its specific flow conditions, thereby maintaining required performance levels with less structural weight.
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 design optimization increases the lift curve slope of lifting surfaces, reducing size requirements and delaying adverse compressibility effects, thereby improving aerodynamic efficiency and reducing structural weight while maintaining acceptable in-flight performance.
Implementation Method 1
The local Mach number distribution along the span of the lifting surface due to the interference with the fuselage (lower Mach numbers in the inboard part than in the outboard part) allows a reduction of the sweep angle in the inboard part that increases the lift curve slope of the lifting surface.
Implementation Method 2
the sweep angle in the inboard part (which is variable along its span) is lower than the constant sweep angle α1 in the outboard part. The local Mach number distribution along the span of the lifting surface due to the interference with the fuselage (lower Mach numbers in the inboard part than in the outboard part) allows a reduction of the sweep angle in the inboard part that increases the lift curve slope of the lifting surface.
Data Source
AI summary
An aircraft lifting surface attached to the rear or frontal end of the aircraft fuselage with a variable sweep angle α in an inboard part and with a constant sweep angle α1 in an outboard part. The aircraft lifting surface can be for example a horizontal tail plane or a vertical tail plane attached to the rear end fuselage or a canard attached to the frontal end fuselage.