Expert: Paul Soderman - 6/5/2009

Question
hello i am a tenth grader taking ap physics and for class we are making an airship. what it entails is a structure (no more than 4ft each way) that flies 40 ft in a strait line and remains neutrally buoyant. i was wondering if you could help me by giving me some pointers, equations for things like thrust, and anything that you think would help. even the slightest details would be appreciated. also we have to have an adjustable rudder and i was wondering where the best place for it would be. thank you
              Ben Snellings

Answer
Ben
This site will give you the basic equations for aerodynamics and thrust:

http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html

This link has information on airships including how to build your own:

http://www.myairship.com/

I would put the rudder in the tail aft of the propulsive device, just like a submarine.  You can also find information on helium or hot air on the web (google).  All you need is a gas lighter than normal air.  The lift is equal to the weight of air displaced by the airship.  If that equals total weight you have neutral buoyancy.

If you get stuck get back to me.
Paul