MadSci Network: Engineering

Re: What chemicals can be used to create

Date: Mon Aug 21 13:44:46 2000
Posted By: Joseph Weeks, President, Thermal Products, Inc.
Area of science: Engineering
ID: 965749944.Eg

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: or

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.

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