|MadSci Network: Physics|
In the "wingless wonder" example, the top part of the loop, where the straw was afixed is too disrupted to provide decent lift, however without the straw body any standard flight path, except straight down, would be impossible. There are 2 components here. First, is distributed weight, which affects stability. Second, is distributed lift, the "wing" or as generalized, the lifting body/surface. In your loop, as well as in the teacher's loop, the loop could easily break down into four simple sections-right, left, top and bottom-acting as four lifting surfaces. The air flow is faster down the center of the loop, due to bernoulli's therom and the laws of conservation. The volume flow rate ((m^3)/sec) must therefore be the same on the inside and outside of the loop. Due to the resultant three-dimensional effect of the "loop" design, the air flowing into the loop is actually streamlined or tunneled in, while the air outside the loop is relatively unaffected and slower. The result is a lower pressure and faster moving air flow over the inner surface of the bottom half of the loop vs. the underside/outside portion. This results in lift, the upward difference in pressure between the two surfaces. On the upper half of the loop, you have a more readily understood air flow, more like a traditional wing. This upper half is the second contibuting lift surface. It is the interplay between the lifting forces and gravity which lend to "flight." Focusing on straight-forward flight, you'll need the center of lift either at or in-front of the center of gravity. Only experimentation can find the best location for such a design. In your design you'd have to think a lot about this interplay, as your center of lift will tend to be behind your center of gravity and significantly impair flight. You would also need a fairly rigid and extremely light material, and you'd have to think really hard about where you put the wheels. In the end you'd be building a miniature, but very complex, ultra-light air craft. It could be done, but you'd be looking at an expensive life-long hobby :) Good luck! Ken
Try the links in the MadSci Library for more information on Physics.