Why is a plane’s propeller at the front but a boat’s at the back? Because of how they move through the medium they travel in, the angle they need to move at, and the obstacles they encounter.
The propeller was obviously first used on a boat because they were invented long before planes were. The very first propeller was based on Archimedes’ screw, which was invented in about 200 BC. It was a straight screw that rotated in a spiral motion in a tube and could be used to raise water out of a river. It is called the Archimedes’ screw, but he may have simply recorded it, rather than invented it. The screw was used for irrigation for a few thousand years and it made agriculture possible in areas that don’t get a lot of rain. Then, possibly in 320 AD, a propeller was made based on the screw. The bamboo-copter was a child’s toy made in China. It has a propeller on one end that is attached to a thin bamboo stick. When the stick is spun between the hands, it makes the propeller rotate and the bamboo-copter flies up. It is the first helicopter. Leonardo da Vinci designed a helicopter in the 15th century, which may have been inspired by the Chinese bamboo helicopter.
A propeller was first used on a boat in the late 17th century. A modified Archimedes’ screw was made that could push a ship through the water. There were several more made in the early 18th century, but the main problem was that there were no engines with which to power the screws. This all changed with the advent of steam power during the Industrial Revolution and steam powered propeller ships soon displaced sailing ships. Then the electric engine arrived and it is rare to find a ship that doesn’t have a propeller. The first working propeller on an aircraft was flown in 1852. A three-bladed propeller was used to power an airship. Then, of course, the Wright brothers managed to fly the Wright Flyer in 1903, which had a propeller and an engine.
So, why does a plane have the propeller at the front and a ship has the propeller at the back? We should probably stop to consider that planes don’t have to have the propeller at the front and there are several examples of planes with the propeller at the back. The difference is that a propeller at the front pulls the plane through the air and a propeller at the back pushes the plane through the air. The first reason is due to the way they move. Planes travel through the air and they need to produce lift. The propeller on the front of the plane is like a set of mini wings. When they spin, they create lift, but in a forward direction rather than upwards. This provides the forward thrust of the plane, but it also helps in another way because the motion of the propeller forces air over the wings, which helps give them more lift. A propeller at the back of a plane can push it, but it doesn’t give more lift to the wings.
The angle of the craft is also a reason. When a plane flies, the nose needs to be slightly up and a propeller that is pulling the plane naturally keeps it at that angle. A boat in the water has the opposite problem. To be able to ride over waves and just stay above the water, a boat needs to be able to keep the nose higher than the back of the boat. If the propeller was at the front of the boat, it would be heavy and it would pull the front of the boat down, causing problems with every wave it encountered.
The last reason comes down to the risk of damaging the propeller. Planes are very unlikely to encounter anything while they are flying through the air and if they do hit another plane, they have far more to worry about than just damage to their propeller. A boat in the sea has far more chance of running into something while moving. The sea is full of animals, bits of wood, and a whole host of other things that could damage the propeller. By having it at the back, the boat hits the obstacle first and moves it out of the way, protecting the propeller. And this is what I learned today.
Photo by Thierry Fillieul: https://www.pexels.com/photo/gray-airplane-638698/
Sources
https://en.wikipedia.org/wiki/Bamboo-copter
https://en.wikipedia.org/wiki/Archimedes%27_screw
https://howthingsfly.si.edu/propulsion/propellers
[…] wings and this is where thrust comes in. With a plane, the thrust comes from the jet engine or the propeller. With a bird the thrust is produced by flapping the winds up and down, which drives the bird […]