Is it possible to build a flight-capable aircraft powered by compressed gas?
In aircraft design, the main problem is energy density of the energy source. Even with the phenomenally high energy density of kerosene fuels (&gt;42 MJ/kg), the fuel still represents a sizable chunk of the weight of an aircraft. For example, fueling an Airbus A330 will double its weight!
According to Wikipedia, compressed air has a practical energy density of about 0.1MJ/kg. There is no way you can offset the enormous amount of compressed air required by downsizing your engines. You would go from 110.000 kg of fuel to over 400 million kg of compressed air.
A more relatable example would be a Cessna 172. It can carry 212 litres of fuel, or about 150kg. On top of that, it can carry about 190kg of useful payload. If we instead use compressed gas, we would need over 60.000kg of compressed gas to get the same range.