Hello PF! I have a project/competition in freshman college Aerospace that calls for a plane that can stay in the air for as long a time as possible while going as far as possible. The requirements don't explicitly say we need rubber bands as a propulsion but pretty much prohibit everything but. The plane will be fairly large and it must be launched into the air via throwing it. My teammates and I are wondering if a rubber band propulsion system would be more helpful or detrimental to the flight. I argue the later, saying that after the coiled rubber bands expend their stored energy the propeller will become nothing but air resistance and cause the plane to slow down faster. Essentially, the air resistance will produce more negative ΔV than the rubber bands with the propeller will produce positive ΔV. Not to mention that having no propulsion system will make the craft lighter. Therefore, such a plane will fly farther and stay in the air longer without a propulsion system. My team mate argues that the propeller will produce more ΔV than the air resistance will produce negatively. So who do you think is the correct one? The design of our plane will be akin to a sailplane (like the DG-800). Alternatively, is there any other propulsion system we might use? I thought of magnetism but I am not sure how to implement that. The requirements for the project are... - no electricity whatsoever - no metal ouside of an inch from the main propulsion unit. - 2 Kg mass limit - limit of 2 propellers - must carry a payload of unknown weight - cannot use any explosive or potentially hazardous systems or mass-ejection systems - cannot use anything to artificially lighten the plane like a balloon of helium - $50 worth of materials limit Sorry if I posted in the wrong spot. The idea was that the main question was about just the plane and was not specific to the class.