|MadSci Network: Engineering|
A flying backpack is a great idea, just difficult to produce. Lets examine the problem a bit. In order to fly you need to overcome the forces of gravity on you. Lets say that you and your backpack weight 150 pounds. Either your backpack must generate 150 pounds of upwards thrust for the entire time you are airborne, or you must counteract the effects of gravity by decreasing your density to that of the surrounding air, allowing you to float around in the sea of air that we live in. Lets consider first the latter approach. A balloon is the answer for quietly flying around. A balloon is a large, lightweight container which contains either hot air or a lighter than air gas. Although we don't feel it most of the time, air weighs about 30 grams per mole (since it is mostly nitrogen) and occupies about 24 liters at room temperature. So the density of air is about 1.25 grams per liter. If we filled a balloon with helium which weighs 4 grams per mole, the density would be about 0.167 grams per liter. So each liter of helium contained within our balloon provides you with 1.25-0.167=1.08 of lifting force. So, since your weight with the backpack is about 150 pounds or 68039 grams, you only need a balloon with a volume of 62805 liters to lift you quietly off the ground. That is only about 2217 cubic feet, or a sphere a little more than 16 feet across. The second alternative is to use a backpack which generates thrust equal to your weight. The jet packs or rocket belts which people have used for flying around are actually small rocket engines which use concentrated hydrogen peroxide as the fuel. When the hydrogen peroxide passes over a catalyst, it is converted to oxygen and steam which is forced through a nozzle to produce downward thrust. Unfortunately the packs only carry enough fuel for about 40 seconds of flight. You can read more about the rocket belts at: http://www.madsci.org/posts/archives/may97/861712872.Ch.r.html or http://www.the-strange.com/jetpack.html Now, if someone could actually invent an antigravity paint, so that you could directly counteract the forces of gravity, you would really have a hot invention. Unfortunately no substance or particle has ever been observed which is repelled by gravity.
Try the links in the MadSci Library for more information on Engineering.