|Click Here for Video Link|
|The prototype, nearing completion. Much prettier than last year's plane (TOM) if I do say so myself.|
This year's plane differs in a number of ways from last year. First, after last year, there's a larger core team who generally know how to do what needs to be done. Our president, Josh Nieman, has really taken that core and pushed us to put those abilities to the best use possible, and it payed off: we flew before the paper was due, and incorporated some flight data into the paper, compared to last year when we flew about two months after the paper due date. Thanks to that, we're now able to spend the next month or so remaining before competition fine-tuning our configuration and building the competition plane, instead of desperately working to get one flyable plane.
Another change from last year is our use this year of a molded fuselage, rather than a built up fuselage. What that means is that previously, our fuselage was built from discrete panels of carbon-fiber honeycomb, connected at the joints with carbon fiber strips. This required very complex build-ups, and was costly in terms of time and materials. An image of this process in action can be seen below--yes, this was infact every clamp in the shop in use at once.
|First, we would build up the sides.|
|We would bend the skin-hinges to shape the front and back of the fuselage.|
|Finally, we would add internal bulkheads and other structure.|
|First core. Pretty, but unfortunately the wrong airfoil on the root section|
|Second core. Produced in only about 10 hours. Correct wing section, but not pretty--didn't go together right.|
|Me with the third and final fuselage mold core after layup and waxing|
We also completed the connections on the plane. If you'll recall, a few moths ago I a diagram that showed the types of connections the plane was planned to use. If you don't, here's that post linked, and the diagram in question is reproduced below.
|Connections used on aircraft|
|Aircraft disassembled in preparation for packing|
Other than the landing gear, you'll note that the plane above very much resembles the diagram above. I'm very proud of how the connections have moved from concept, to design, to execution this year without severe changes. Minor tweaks have been made to materials and some geometry, but the concept and designs are largely reflected in the aircraft as built, which is much more than I can say about last year's aircraft.
On the theme of dramatic images, some more from testing the connections. I made a test version of the wing spar connections before the prototype was built, and tested how well it stood up to shear and moment loads by cantilevering it over the edge of a workbench with weights on it. The image below shows the connection taking 24 pounds of shear load, and a applied moment of 12 pound-feet, equal to our plane in a 5 g turn with margin. As you can see clearly, the connections had no issues with even this overload.
We also added the wing locking connection recently. These wing locks prevent the wing from pulling off of the fuselage along the axis of the spar and alignment pins. In flight, these forces along the wing (known as "spanwise forces" in jargon) are fairly minimal, however, the connections we've designed are capable of taking fairly significant forces without issue, as demonstrated below.
|Should have seen the one that got away....|
In this image, the entire weight of the fuselage, batteries, motor, and the other wing are being applied to the port wing locks without issue. This ensures we have plenty of margin, and gives us a lot of resilience to damage. The overall size of the plane is also fairly visible in this image. I stand 6 feet, so you can get an idea of what a job we're doing getting these wings to fit into a conventional carry-on suitcase. We do it, though.
I'd love to close this piece with a flight video from one of the two more recent times at the field, with the plane cruising around like a champ, but as I mentioned, I don't think they're on the web yet and I don't have the files to upload myself. Instead, I'm going to point to several videos from last year showing our biplane from three years ago doing flips with the hugely over-sized motor from last year's plane.