Helicopters

To flail

to move energetically in an uncontrolled way

Curve

a line that bends continuously and has no straight parts

Flat

level and smooth, with no curved, high, or hollow parts

To harness

to control something, usually in order to use its power

Dense

having parts that are close together so that it is difficult to go or see through

Lift

the force on the wing of a bird or aircraft that keeps it in the air as it moves forward

Blade

the flat part on a knife or similar tool or weapon, with a very thin edge used for cutting / a wide, flat part on a tool or machine, used to push backwater or air

To hover

to stay in one place in the air, usually by moving the wings quickly:

Upside down

having the part that is usually at the top turned to be at the bottom

To spin

to (cause to) turn around and around, especially fast

Sizeable

large

Congested

too blocked or crowded and causing difficulties

Vital

necessary for the successor continued existence of something; extremely important