Power Systems Engineering is a class at Haines High School taught my Mark Fontenot. It focuses on all aspects of the engineering process, including system design, 3D modeling and drafting, construction, and testing. This page details the work of that class during the 2012-2013 school year. The main project, which this page will focus on, was the development of a Vertical-Axis wind turbine (VAWT). This project is still being completed, so this page will change as more work is done. Below you can see a step by step guide to the process of designing and building the VAWT.
We started by designing project concepts individually. Using a a 3D modelling program, we had to model a system, completely with wings, shaft, power transmission, etc. Then, as a class, we incorporated different aspects of all of the different designs to arrive at a one single design. This was still just a rough design, but it set a few parameters to work within, such as the number of blades (4), the idea of using a pulley system transmission, and overall dimensions. From here, we started to refine the design. We split into a few different groups. One would design the power transmission, one would design the shaft and connecting assembly, and one would design the wings themselves.
This aspect required a fair amount of research. We had to pick a profile for the airfoil (a crosssection of the wing) that would provide the right amont of lift for the turbine to start and continue to spin. Preset wing profiles designed by NACA are available online. This have known, measured performance, so we could skip some college level aerodynamic physics. Once we picked out a profile, we digitized it and created a 3D Model of the wing. Structurally, the wing would be made of 1/4in plywood ribs, cut into the shape of the profile, connected by aluminium tubes that run the length of the wing. Small hardwood stringers would run through notches cut into the ribs, and the leading and trailing edges would also be cut out of hardwood. A sheet of 1/8in ply would cover this frame, and then be fiberglassed over. The wings would end up being 2 meters long, yet only 2 cm thick and 17cm wide.
The base consists of 4 concrete blocks, connected by angle iron, as seen in the picture to the right. We tried to calculate a rough estimate of the maximum torque and force that might be applied to the turbine, to figure out the the size/weight of concrete we would need. This required a bit of work, done by Patrick, to figure out. We had to assume a maximum windspeed of 30mpmh, then assume the turbine, at best, catch the full force of the wind. While this is not true, according to Betz rule, we wanted to overestimate in any case (having our turbine fall over wouldn't look very good). After applying some physics formulas and trig, we got a weight which was split up among the blocks. This ended up being x pounds of concrete, or 4 1ft x 1ft blocks.
Although we started out with a basic design for the structure, it ended up being completely redesigned during the construction process. We decided to try and reuse materials, to save time, money, and the planet! So we built the structure around a 17in truck rim. We constructed a H shape out of angle iron around this, which then attached to pillow block bearings to support a steel shaft. The top end of this connects to a steel pipe with two four way hubs, at the top and the bottom. Pipes screw into this and connect ot the wings, as seen in the picture to the right. A pulley at the bottom of the shaft will turn a DC motor (being used as a generator). We also designed a covering for this to protect it from the elements.
The wings were constructed out of high-grade, 1/4in plywood. Using the profile designed before, we cut out 50 of them on the bandsaw, then used a beltsander to get them exact. The next step was to drill holes for aluminium tubes that would connect the ribs within the wings. This took longer than it should have, but we finally got them all drilled. Within each wing were two ribs made out of 1/4in aluminium. These would be the attachment points to the structure. We designed a system using washers that would allow use the adjust the angle each wing was at. This would effect how well the turbine would start, so we didn't want to be stuck with a single angle. The next step was assembly. Using a full scale blueprint (designed by Eli), we laid the parts out and glued them together. See the timelapse to the right for details. We then skinned them with 1/8in plywood. We weren't sure the best way to do this, and ended up messing one up and having to redo it. We used the high tech tool of a iron to steam the wood so it would bend, and then epoxied it to the ribs underneath.
Constructing the concrete base just involved pouring some concrete, with angle iron embedded. We then moved it up to the roof with the help of Turner Construction. Construction of the structure was done for the most part by Zack, who welded angle iron in numerous different ways.