The Design

Blade Design
The initial designs consisted of three different models, based on various ideas and initial technical analyses. Our first conceptual design consisted of a three blade system, which was modeled using SolidWorks. As seen below, at the end of each arm there is a "cup" blade which is used to capture the available wind. This design, as expected, was estimated to be too expensive and difficult to manufacture on a small scale for prototyping. 


Original Conceptual Design


The team then investigated ways in which to decrease the difficulty of manufacture and associated costs with the cupped blade design. Initially, it was formulated to create a skeleton system which would be made from a steel frame and wrapped in a lightweight material shell. This design, would decrease weight, and allow for a simple yet effective blade. However, the process of connecting the blade to the shaft of the turbine would be problematic due to the joint (whether welded or bolted) being a weak point of design. 


Design #2 - Lightweight Skeleton Cup


An alternative design, would be to elongate a cup design which would essentially create a vertical trough. The troughs were free to rotate, in order to capture the wind from any direction, and would cup the wind for maximum potential energy. The vertical blades would then be connected around a shaft into a center hub. Issues with this design were found to be the significant manufacturing time as well as a poor connection to the central hub. 


Design #3 - Vertical Trough


The third blade design proved to be the most simple to manufacture and in design. A simple creased triangle (the crease angle was to be determined later), where the spine was connected directly to the back of the crease via angle-iron. The most significant advantage of the third design is the ability to not only catch the wind but the ability to "cut" the wind as it rotates around the shaft, therefore decreasing drag.The design was later evolved into our current and final design - the "Kite" design.


Final Kite Blade/Hub Design


The "Kite" Design is a combination of both the initial cup and the last folded triangle. This design not only will cut through the wind as it rotates around and therefore decreases overall drag, but it also will effectively catch the wind due to its closed in end. When technical analysis was completed on the blade, it was seen that a stagnation zone occurs in the pocket of the blade, but it still catches and utilizes the majority of significant wind power. 


In order to further optimize the blade, the team performed an angle optimization in order to define the best possible angle on the blade. As seen below, the reasoning used for an almost 45 degree angle is that it provides not only a substantial ability to catch the wind, but it also has minimal drag. 
Various Draft Angles



The ultimate goals were to maximize the front wind force (aka the capability to capture as much wind as possible) and to minimize the "back" wind force, or drag. 
Front Wind Force versus Wind Velocity for Varying Draft Angle Profiles


Back Wind Force versus Wind Velocity for Varying Draft Angle Profiles

Blade Optimization for Draft Angle


Below is an image of the final blade with a draft angle of roughly 45 degrees.




Final Kite Blade/Hub Design

Center Hub
The center hub was used to connect the blade spine to the actual rotating shaft. This hub was made from two 5" OD cylinders of aluminum alloy and each was milled to have three 90 degree channels. It's purpose, is to securely hold the spine and support the blades as the unit rotates. 1/4-20 threaded bolts are used to securely fasten the two pieces together and hold the spine in place.  A model can be seen below of the final hub. 






Here is the final design, with a mock base if mounted on a rooftop.