MATLAB Project: Airfoil Generator

I'm taking a class in aerodynamics this semester, and I know we will be working a lot with airfoils. So for fun I decided to write a MATLAB GUI to display any NACA series airfoil. Currently it only works with the 4-series airfoils, but soon I will expand it to work with 5, 6, 7,  8 series airfoils as well.

The program takes inputs of the NACA airfoil number, desired chord length, angle of incidence (AOI), and the wing length. The program then plots each individual airfoil, and lofts the two together in an isometric view. The 'export airfoils' button doesn't work right now, but soon it will export XY coordinates for the airfoils to a text file, so they can be loaded into SolidWorks or another CAD program to make a 3-D model of the wing. 

Download the files to run the program here.

Mini Project: Tooling/Fixturing for Tensegrity Rods

Part of my job as an engineering education developer includes designing and manufacturing the parts needed for the activities. One of the activities I helped create was on the structural design principle of tensegrity. Tensegrity is a way to build structures that are lightweight and strong. They rely on flexible tensile elements such as strings, ropes, or cables; as well as on stiff compressional elements such as rods. Tensegrity structures are pre-stressed and self stabilizing, and none of the compressional members touch. They are suspended in a web of tensional elements, a phenomenon referred to as "floating compression" by artist Kenneth Snelson. 

The activity itself is like a board game to teach students the entrepreneurial aspects of engineering. The activity centers around building a mini tensegrity tower. These towers use wooden dowels with notches cut in either end; rubber bands fit in these notches and hold the rods together in a simple tensegrity structure. The problem is that the balance and symmetry of the tower depends on the quality of the rods. All the rods must be made to a high standard, or else the tensegrity towers become very asymmetrical and unstable. This is because with different length rods, the rubber bands are stretched to different lengths and therefore exert different restoring forces. The imbalance of restorative forces within the structure causes the structure to shift in order to find a new equilibrium. This throws everything off. 

To make the towers as balanced as possible, a manufacturing method was needed to produce the rods very quickly and precisely. I decided to make a simple vise to hold the rods. The vise is clamped into the vise of a mill, which can be used to machine the notches on one end. Then, the inner vise can be flipped upside down to machine the other side of the rods. 

There were a few caveats to this approach; the length of the rods compared to the size of the vise made it difficult to clamp into the mill's vise jaws. Additionally, the length of the dowels sticking out of the vise made it difficult to machine cleanly without using extra clamps to restrict the motion. All in all, however, it worked pretty well and I think these towers will perform much better.

Project: Drafting Bars

Engineers convey ideas through drawings and sketches. When sketching rectangular objects in orthographic or isometric views, it is necessary to be able to draw parallel lines. Additionally, for isometric views, the lines are offset 30˚ from the horizontal. I wanted to make a tool that would help me draw parallel lines and 30˚ angles to be able to make sketches quicker and more accurately.

My initial conceptual idea was to have two bars connected by two rods to form a parallelogram linkage. This way, one bar could 'follow' the original line, while the other [parallel] bar could be extended and a parallel line could be traced along the edge of the bar at any desired distance. 

Making the 30˚ angle was more tricky. My original thought was to have different sized rods that could be swapped out to make different angles, but I thought there was probably a simpler and more elegant way to do it. I eventually decided to add extra holes as alternate positions for the rods. In their alternate positions the rods are no longer parallel, and thus the angle between the bars can change. The freedom of motion of the bars is limited by their interference, and so by adjusting the geometries of the parts, a 30˚ can be obtained when the bars are touching each other. 

The last element of the design was how all the pieces fit together. I decided to use knurled brass knobs that threaded into a nut. The nut head fits into a channel, and the shank of the nut slides in a slot. The rod end fits around the nut, and the length of the rod is contained within a pocket in the bar. Tightening the knob presses the bar against the rod to lock it in place. If the knob is unscrewed completely, the rod end can be moved to a different hole to get the 30˚ angle.

This is the first version of the design. I'm still not sure what materials to use for the different parts. I really like the look of knurled brass knobs and rods, but I'll need to make sure they are strong enough. I originally planned to use 304 Stainless Steel for the bars for longevity and cost, but the locking function depends on the the ability of the bar to deflect under the force of the knob and press against the rod.