Flying fan

This fan will fly up at the height of a few meters, like a real helicopter, if you twist it in your hands.

Military transport aeroplanes or passenger planes operating on short distances are powered by similar propellers. While jet planes fly at high altitudes of 10-11 km where the air is thinner and resistance is smaller, turbo-prop planes have to fly at lower altitudes, e.g. 5 km, where the air is dense enough for the propellers.

Big wind turbines provide electricity. In Denmark more than 10% of electricity is produced by wind turbines. Contrary to popular belief, wind turbines are quite efficient. Their efficiency of transforming wind energy into electricity is around 15%. It seems that even a small turbine can provide enough electricity for a number of households. There are a lot of wind farms in mountainous regions of Spain and on plains of Germany.