During WWI, airplanes were still a very new technology. Planes that could fly for extended periods of time were only a few years old, and people were still trying to figure out how they would work in combat.
One of the most logical steps was to add a big gun to the front of a plane so it could shoot down other planes. Machine guns were a logical complement to aircraft, but there was one problem: how to stop the gun from hitting the big propeller in the front.
Machine guns were mounted on the top of the fuselage, directly in front of the pilot, but that position placed the gun directly behind the propeller. The gun had to be designed to fire through the propeller without hitting it, which was not an easy task.
The solution was timing, as is demonstrated in glorious slow-motion in a new video from The Slow Mo Guys. Watch the video above.
While the video above is a joy to watch, it doesn’t touch on the real innovation behind what makes it work, an invention called the synchronisation gear, which restricted the machine gun so it could only fire in between the propellers.
There are many different types of synchronisation gear, but the simplest involves an irregular-shaped disk that triggers the gun to fire once per revolution, at a specific point. This produces a high rate of fire without the risk of hitting the propeller.
In the slow motion video, you’ll notice how there’s actually a quite a bit of time for a gun to fire between the blades, but in real life the margin of error wasn’t quite that wide. On a plane that’s actually flying, the propeller would be spinning roughly 5 times as fast, which makes the precision of the synchronisation gear all the more important.
This article was originally written for and published by Popular Mechanics USA.