Pretty sure this is the right forum for this.

 

Say you have something cone-shaped. The large end of the cone has some sort of propeller in it that causes it to pull air into the cone. This also means that the air will be pushed out the back as new air is pulled into the cone. Now, let's just throw some figures out.

 

Say the large opening is a circle with a 10-inch diameter. The propeller is producing 10 pounds of thrust. The small opening in the cone is a circle with a 1-inch diameter. Am I correct in assuming that the air coming out of the cone is at 100 pounds of thrust?

 

Now, that makes it seem very easy to make a lot of power. Knowing what I do know, there must be a cap to the amount of power created before the air can't be compressed to create that much thrust. So, what would the limit likely be? Also, what other factors affect the amount of power? Would things like the length (or technically height, but it's horizontal in this scenario) affect it?

 

Thanks for whatever you might tell me.

I`m unclear as to why, but a few years ago I actualy did the thing you posted about, I wanted an air pump as my fish tank pump was broken, needless to say, it didn`t work as expected, I even made all the seals air tight. I used a 4" PC fan and built the cone out of cardboard. when taken down to a 5mm tube there wasn`t even enough prussure to make little bubbles on the surface of water