Inventing a way to shoot bullets through a propeller Matt 13 Sep 2006

16 comments Latest by M2 Ball

There was an interesting invention story on a WWI documentary I saw the other night. The problem back then: How do you let pilots shoot machine guns straight ahead without hitting the propeller blades right in front of them?

Dutchman Anthony Fokker, an aviation guru, eventually came up with a solution for the Germans: Connect the gun to the propeller via an interrupter gear so that gunfire is halted whenever the blade is directly in front of the gun’s muzzle. This way, bullets always went between the blades. Fokker said that once he was able to state the problem, the solution was obvious.

Fokker himself related: “The technical problem was to shoot between the propeller blades, which passed a given point 2400 times a minute, because the two-bladed propeller revolved 1200 times a minute. This meant that the pilot must not pull the trigger or fire the gun as long as one of the blades was directly in front of the muzzle. Once the problem was stated, its solution came to me in a flash.”

Three days later, Fokker had churned out an interrupter gear, which was the key to combining the machine gun and the plane. In essence, it allowed the plane to fire the gun, for as the pilot held down the trigger, the interrupter gear stopped the gun from firing every time the propeller blades passed before it. This amazing, yet simple, invention led to the time when Germany ruled the skies and Allied planes became known as “Fokker Fodder”.

16 comments so far (Jump to latest)

Michael 13 Sep 06

Awesome post.

Jeroen 13 Sep 06

Sry man…but who cares!

Matt Johnson 13 Sep 06

@Jeroen - *Laughs*

Good post, will help me clarify my presentation to a client later today.

Randy Peterman 13 Sep 06

Jeroen, It appears that you don’t comprehend the importance of this post. To clarify, there are probably lots of different applications, but the one that I see immediately is this: if you don’t have a clear understanding of the problem, its going to be difficult to work out a clear solution. And if you have a clear problem, followed by a clear solution, it makes it easier to get ahead of the competition who may not identify the problem as clearly and therefore not come up with a clear solution.

Joe Ruby 13 Sep 06

“This meant that the pilot must not pull the trigger or fire the gun as long as one of the blades was directly in front of the muzzle.”

You’d think the lag time between the trigger being pulled and the time when a bullet actually crossed the plane of the propellers would matter — if the propellers were spinning fast enough, and there was enough lag time, a bullet could very well not hit a propeller if the trigger was pulled while a propeller was directly in front of the muzzle. I would think the speed of the engine would vary too…

“Fokker” (heh heh heh, you said…)

John Dilworth 13 Sep 06

Great story, I’ve been dealing with this same issue lately —getting to a clear definition of a problem.

Unfortunately it seems that sometimes, just being able to define and state the problem clearly can take more work (and maybe it should) than developing the actual solution.

Mike 13 Sep 06

Awesome! This will help me greatly. I’ve been working on a way to shoot rubberbands at people as they walk past my cube. Problem is I keep hitting my water cup. I’ll just move the water cup! Brilliant!

Anonymous Coward 13 Sep 06

did you know that the bmw logo is actually a propeller turning in a blue sky …..after ww2 they wern’t able to make planes …..switched to cars. ……

Mike Swimm 13 Sep 06


Was this from the Nova Red Barron show? It was interesting. I was shocked that the Red Barron was killed just shy of his 26th birthday. Insane.

Russell Greenwood 13 Sep 06

One of my great-grandparent-relative-type people was an Australian test pilot for these things down here… he shot his own propellor off so many times and had to glide it on down…

those were the days.

James Head 14 Sep 06

It’s hardly that simple.

The time taken for the trigger / cock / bolt to slide through and fire the bullet, -and the time take for the bullet to move the 1 metre from the inside of the gun past the propellor blade.

Exactly how far does the propeller rotate in that amount of time?

Not an insurmountable problem, - but i think the description oversimplifies the engineering required..

It would be very interesting to see a 5000fps camera take a movie of that, (and watch it slowed down).

Robert McCall 14 Sep 06

I came across this some years ago. The point is that history is not just a collection of dry facts. It can teach us if we only look past the surface.

P.S.: Fokker’s efforts were spurred by the crude method of attaching steel wedges, by a French pilot, to the back of the propeller blades.

Yo 14 Sep 06

You would have to know the speed of the prop the size of the opening and the speed at which the bullet leaves the mussel of the gun. A typical 160 grain 30.06 mussel volocity is 3200 fps. There should be more than adequate space for the bullet to go through.

Michael 14 Sep 06

Read about this in Uncle John’s Bathroom Reader years ago.

joris 15 Sep 06

I think I remember an alternate solution that was employed during the first world war: armoured propellors. But to me the most elegant solution is to put the machine guns on the wing of the aircraft so you’d not have to worry about the properllor at all. Alternatively you could have mounted the gun on the undercarriage. It could be that this wasn’t technically feasible during WWI, but it wouldnt surprise me if people just simply hadn’t thought about these alternative solutions.

M2 Ball 29 Sep 06

Yo, you don’t know anything about ballisitics. I’ve never heard of a .30-06 load that approaches 3200 feet per second nor have I ever heard of a 160 grain bullet being used in the .30-06, or any .30 caliber rifle cartridge for that matter. The .30-06 in it’s military form used a 152 grain, flat base spitzer bullet at about 2800 feet per second. And the Germans at the time were using their 8x57mm Mauser cartridge firing a 198 grain bullet at about 2590 FPS.