How Does a Propeller Pull a Plane?

Step 1 of 5

A wing works by throwing air downward.

Air leaving the back of a wing is deflected down, and pushing air down pushes the wing up. That is all lift is, and it works whichever way the wing points.

Step 2 of 5

Turn it on its side and the push goes forward.

Mount the same shape vertically and spin it, and the air is thrown backward instead of downward. The aircraft is pushed forward by exactly the same rule.

Step 3 of 5

The blade is twisted along its length.

The far end of a blade covers a much longer circle each turn than the part near the hub. The two ends therefore meet the oncoming air at quite different angles. The blade is twisted so every part of it bites correctly at once.

Step 4 of 5

Tips cannot go too fast.

Approach the speed of sound at the tip and the blade starts losing far more than it gains. That limit is why propellers are the wrong tool for very fast aircraft.

Step 5 of 5

Big propellers can change their pitch.

Blades that rotate in their hub let the pilot pick a steep bite for climbing and a shallow one for cruising, in the same way a bicycle picks a gear.

A ship's propeller works on exactly the same principle in water, which is about eight hundred times denser and so needs far fewer turns.