Team Wharton B
Team Wharton B designed a framed parachute in order to maximize the time the tennis ball spent in the air after they dropped it.
When they dropped it from the second story of Hicks, it had a drop time of 4.84 ± .02 seconds.
We started brainstorming ideas when we got our materials. Initially, we discussed making a triangular glider or kite, with the three dowels joined at the one end (braced by the plastic container and flared out at the other, then covered with the opened plastic bag. We hoped that a glider would look and act like a paper airplane, falling slowly by catching air currents as it moved forward, instead of just falling. However, we ran into problems when we considered that a glider would need horizontal motion to get started--we would have to throw it, not drop it. Without a
horizontal impetus, it seemed likely to fall nose-down, very fast. We discussed compensating for this by distributing the weight of the tennis ball further back, to pull the back of the glider down and keep it horizontal. This, however, would have required a lot of trial-and-error adjustments to distribute the weight correctly, possibly damaging our materials in the process, or possibly not working at all.
Ultimately, we decided that the glider was too risky to attempt, and settled on a parachute design instead, with a wooden frame to keep the parachute open as wide as possible and to hold the tennis ball. After considering several possible configurations the dowels for the frame, we settled on an H-shape, to maximize the surface area. We then decided to open the sides of the plastic bag and pleat the edges. Pleated and attached to the frame, the bag would poof out when dropped, catching as much air as possible. The tennis ball would hang underneath the apparatus, stabilizing it and keeping it from overturning. We initially discussed cutting the tennis ball up to distribute its weight farther out to the sides of the frame, but decided that it wouldn't really gain us anything. At this point, we intended to use the red drawstring from the plastic bag as string, and to supplement it with twisted tape. During the building process, we decided that the drawstring would be better used reinforcing the frame, and that it was simpler and more effective to fold the tape instead of twisting it.
After we settled on the design, construction began! Our first order of business was to cut open the plastic trash bag and reinforce it with tape in a grid pattern. This kept the plastic from sticking to itself, strengthened the parachute, and encouraged it to open and fill rapidly and completely when dropped. At the same time, other team members cut the bottom piece of the plastic container in half, for use in reinforcing the frame's joints. Our greatest worry at this point was that the frame might twist, making the parachute unbalanced. The plastic semi-circles would make it more structurally sound.
Next, two team members lashed the three wooden dowels into the H pattern, taping the joints as tightly as possible to keep them from moving. Other team members removed the red drawstrings from the plastic bag and pleated the edges until it fit the dimensions of the frame at the sides. The greatest challenge here was to pleat the bag evenly, so that it wouldn't be bunched up on one side and stretched out on the other. If that happened, the parachute would catch air unevenly and tilt. We solved this problem by dividing each edge into sections and then pleating each section to the same length. We then fastened the pleats with two layers of tape, one on each side.
Then they modified the plastic braces to fit properly and attached them. Next they attached the red draw-strings from the trash bag to the wooden frame to give it another two sides, adding stability and strength. Finally, they attached the pleated trash bag to the frame and suspended the tennis ball from the whole thing using folded over tape as string.
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