Solar UAV Wing Tip Tails for Drag Reduction and Mass Relief
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Solution Overview
Problem
High-altitude, long-endurance solar-powered UAVs face challenges in achieving stability and minimizing structural mass while maintaining aerodynamic efficiency, particularly at higher speeds, due to inherent pitch-down moments and torsional loads on the wing, which require significant structural mass to manage.
Innovation Solution
Incorporating canted down wing tips with additional trailing 'tip tails' positioned in the upwash field of the mainplane tip vortices, which provide torsional relief, reduce the mass of the mainplane, and enhance lift and thrust, while allowing for a smaller and lighter central tailplane or eliminating it in 'flying wing' designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If significant structural mass is added to the mainplane to cope with torsional loads and pitch-down moments, then strength and stability are improved, but weight increases
Solution Approach 1:
The invention divides the stabilizing function into two parts: the canted down tips handle induced drag reduction, while the separate tip tails provide torsional relief and pitch stability. This segmentation allows each component to be optimized for its specific function with minimal mass, rather than requiring the entire mainplane structure to be massively reinforced.
Solution Approach 2:
The tip tails act as intermediary elements that mediate between the mainplane and the aerodynamic loads. By positioning them in the upwash field, they provide leverage and mechanical advantage, allowing small tip tail structures to counterbalance large torsional moments on the mainplane without requiring proportional reinforcement of the mainplane structure.
2Loss of energy
If canted down tips are used to reduce induced drag, then aerodynamic efficiency is improved, but tip vortex upwash positioning becomes critical for tip tail effectiveness
Solution Approach 1:
The invention changes the geometric parameters of the wing tips by canting them downward at a specific angle. This parameter change serves dual purposes: it reduces induced drag by modifying the vortex structure, and simultaneously positions the upwash field at the optimal location for the tip tails, creating a synergistic effect rather than a trade-off.
3Force
If tip tails are positioned in the upwash field, then lift and thrust are enhanced, but positioning precision requirements increase
Solution Approach 1:
The canted down tips automatically generate and position the upwash field in the optimal location. The system is self-configuring: the tip geometry creates the flow pattern that then benefits the tip tails. This self-service mechanism reduces the need for external precision positioning, as the aerodynamic field itself provides the positioning reference.
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
The solution reduces structural mass, increases operating speed for a given mass, enhances lift and thrust, and provides stability and gust alleviation, leading to improved aerodynamic efficiency and reduced drag, enabling perpetual flight with minimized weight and increased operational capabilities.
Implementation Method 1
positioned aft with respect to the respective said tip, preferably to be subject to the upwash field of the respective mainplane tip vortex
Implementation Method 2
preferably to be subject to the upwash field of the respective mainplane tip vortex
Implementation Method 3
the power generated by the photovoltaic cells is used to drive the motors
Data Source
Figure 1~3
AI summary
An aircraft, particularly a solar powered, high altitude, long endurance, unmanned aerial vehicle, is equipped with a combination of canted down, raked back wing tips 7 and trailing "tip tails" 10 carried on booms 9 from the tip regions of the mainplane 4. Each tip tail is positioned to be subject to the upwash field of the respective wing tip vortex, at least in the cruise condition of the aircraft. The wing tip form can achieve a reduction in induced drag and help to relieve wing root bending moment while the tip tails can act through their connections to the mainplane to provide torsional relief to the latter, particularly under lower incidence/higher speed conditions. In the higher incidence/lower speed cruise condition, however, the presence of the tip tails in the upwash fields of the wing tip vortices means that they can generate lift with a component in the forward direction of flight and hence contribute to the thrust requirements of the aircraft.