I want to fly. Is it better to use compressed air to power a propeller or just use the air as a jet?

Question

I want to use compressed air to power a small personal aircraft. How would I compare the two methods? What are the important considerations in each method?

Assume I want to do vertical takeoffs... like a harrier... then I can use wings to glide later.

Answer 1

You have to look at lift vs weight ratio.  With current componets available you will be heavier than what output you could get from your power source.  While compressed air can provide power, it usually takes lots of it to provide power over any length of time.  Look at an air tool, it can drain a 60 gallon tank in a couple of minutes and that is a small device.  Your best bet is to use a gasoline engine to power your take-offs.

Answer 2

You would have to do a lot of aerodynamic type calculations involving lift and drag and thrust.  For a given amount of airflow and pressure you could figure the thrust you could get directly, but that would depend on the design of the nozzle.

Then you would have to calculate how big a propeller you could drive with a turbine that worked with the same pressure and flow, and how much lift you could get from the propeller.  That would depend on the design of the propeller and the air turbine.

I don't believe either method is practical because you would have to have an enormous amount of airflow, which means a huge tank and compressor, and something to drive the compressor.  You would have to lift all this into the air along with your person.  Or else you would have to be tethered by a long hose to the apparatus on the ground.

Answer 3

"AirHogs" (toys) off-the-shelf, use the air to power a propeller.  Doing so, with an inter-heater may allow more power by absorbing heat from the ambient.  

Jetting the air out may cause it to cool more, so that your aircraft spits out liquid air with out much thrust.

You may also wish to consider the *weight* (mass) of each method.  The prop (and engine, and interheat) may weigh more.

Answer 4

Compressed air holds very little energy compared to gasoline or jet fuel. Any possible aircraft would run out of fuel in a few minutes.