Synchronising of weapons fired through the prop arc....

[TwoDeadDogs]

Hi all
Could anyone give a decent description of how this was achieved and how reliable the systems were.
regards
TDD

[spekesoftly]

Achieved using an 'interrupter gear', which only allowed the guns to fire when the prop was out of the way.

A 'Google' search on 'Interrupter Gear' shows plenty of info, here's (http://www.spartacus.schoolnet.co.uk/FWWsynchronizing.htm) one example that gives a reasonable description towards the bottom of the page.

[Genghis the Engineer]

Very early in WW1 the propellers were armoured, and guns fired through them, accepting that a certain proportion would hit the prop. I have to say, it's not an idea that appeals to me much, but apparently worked.

During the early part of the war, the quality of ammnition improved enormously, one consequence of this was that the time between the pin hitting the bullet casing, and firing became far more consistent, the other is that so did muzzle velocities. It was this that made interruptor gear feasible. This was properly appreciated I believe by a Dutchman named "Fokker" (no relation to a German of similar name who designed aeroplanes) about 1916, who designed the initial interruptor gear.

I think that it was then pretty reliable, apart from the inevitable risk of guns jamming, which was endemic in the period.

G

[Tim Inder]

I thought it WAS the same Antony Fokker chap who designed aeroplanes for the Germans. He was Dutch, wasn't he?

[JDK]

Um,
Same Fokkers, Genghis.

Anthony Fokker, the Dutchman, took his skill to the Germans because the allies weren't interested. At the end of the war, he took a trainload of D.VIIs back to Holland.

He was responsible for the interupter gear on the Fokker Eindekker after examining Garros' lash up and reconing he could do better. As to if he designed it, I don't know.

The British gear was called (something like) 'Consteninescu' and was a pressure system. If you didn't pump it up you could still perforate your prop!

HTH
Cheers
James K

[Dr Illitout]

AHHHHHH Gladiators. Glad you mentioned them. The picture of one I saw had the gun barrels mounted in groves on the fuselage, but they seemed to be too far aft to me. It looked as if the bullets had to travel all the way along the fuselage, through the engine AND then through the prop!. Didn't look right to me!!!. Can any one enlighten me?.

[Genghis the Engineer]

Okay, I've looked it up this time.

First interrupter gear was patented by Franz Schneider in July 1913, he was at the time working as a designer for Nieuport. Details were published in the German magazine "Flugsport" 2 months before the outbreak of WW1, despite which the Allies failed to notice, and the German authorities refused to loan a machine gun so that he could test the design. This used a mechanical timing device.

An improved version was patented in January 1914 by Armand Deperdussin, from gaol, where he was serving a prison sentence for fraud. This used an electrical interrupter.

In February 1914, the Italian company Nieuport Macchi patented another mechanical version, with full design drawings.

Then in April 1914 Raymond Saulnier patented a fully working version (although apparently most of the design work was done by Morane-Saulnier's Chief Draftsman Luis Peyret), and finally got to test it in 1915 at the workshops of the Hotchkiss Machine Gun Co. (near the Eiffel Tower). This synchronised with engine speeds of 1200rpm. However, it was impractical because of the unreliablility of French ammunition at the time (hence the preferred option of the Saulnier deflector plates, which were basically steel wedges on the back of the blarde).

At some point around then a couple of Russians called Poplavko and Smylsov-Dibovsky did something similar.

The first aerial trials of the deflectors were flown early in the war by Roland Garros, a test pilot flying for Morane-Saulnier. He first tried with an M-S type G, which broke up on the ground, then an M-S type L, which apparently worked quite well and was tested in action, until a storm destroyed the aircraft on the ground. They built him another one, with which he shot down three German 2-seaters in April 1915.


Then finally, three designers working for Fokker managed to get an interruptor to work, they were Heber, Leimberger and Lubbe. They tested it with a modified Parabellum machine gun on a Fokker Mk.5k (which was a copy of an M-S type G). They also invented the padded headrest, positioned to improve the pilot's steadiness and aim.

This mechanism went into service in June 1915 in the Fokker E1, a modified version of which (with three guns) was flown by Immelmann.

The allies ignored all this for a while, putting guns just about everywhere else on the aircraft except for firing through the propeller disk. Eventually however they realised that they had to do something, and the first Allied aircraft with an interruptor gear was a Bristol Scout with a Vickers-Challenger machine gun arrangement, which entered the French theatre on 25 March 1916. The Nieuport 17 with a synchronised gun appeared at about the same time in French service. By the end of that year, the Sopwith Pup and Spad S.7 were also in serviced with single synchronised guns.


Then it got complicated.

Where would I be without my library?

G

[CoodaShooda]

The one that always got me was the Fw 190/Ta 152 with the cannons in the wing roots firing through the propellor. A complex approach to concentrating fire power.

[Milt]

Holes Shot Through the Props

Extract from memoirs.

Then there was the two week visit to the Advanced Flying Training School at Uranquinty, near Wagga, in NSW. Wirraways were in abundance and the tempo of the base was all bustle. The war was at its peak and air crews were in much demand. We were wide eyed watching all of the flying activity which seemed to go on night and day. How impressive were those Wirraways with their big radial engines. We were able to sit in the Wirraway cockpits under strict supervision and wonder how on earth one could manage to ever learn how to make sense of all of those dials and levers and things. Some aircraft even had guns fitted in front of the pilot's cockpit. These fired through the prop. There was an interrupter mechanism which was supposed to stop the guns from firing rounds through the propellor blades but there was ample evidence that this did not always work properly. Many blades had neat holes through them.

Probably, in order to balance the three bladed assembly, blades with holes in them would be assembled together. Whilst examining one of these holy blades and observing how carefully the surface of each hole had been smoothed out and polished I found that my right index finger would just fit through one of these holes. So there I was showing my mates the first two joints of my finger wriggling through the other side of this particular prop. Imagine my embarrassment when I found that my finger had swelled up and I couldn't pull my finger out again. The more I tried the more desperate I became and the more it swelled. Initially it was all a big joke and there were many suggestions made as to how to overcome the problem. An airman even climbed into the cockpit making out that he had to do an engine run and that the war would not wait for me to pull my finger out.

Eventually, it was realised that it was a serious situation and claiming that the finger would have to be cut off someone called the hospital. An ambulance arrived and a doctor made his way through the assembled crowd and made derogatory remarks about the Air Training Corps and one stupid cadet in particular. He pondered how to handle the problem and ordered the crowd to get lost. He managed to come up with some soap which he proceeded to work into the hole around the now very sore finger. Then he found a piece of string which he wound around the finger starting at its tip. On reaching the surface of the blade he had me pull on the finger as he slowly unwound the string. The finger came out easier than it had gone in. I felt like bolting away and hiding.

A later visit to Bankstown with the ATC provided the opportunity to see an Aerocobra fighter start up and take off. Wow! Here was a real live fighter. The Aerocobra had an engine behind the cockpit and a long hollow shaft to the prop though which a 20 mm cannon could fire. We were most impressed, even when the Aerocobra taxied and turned so that it blew dust and dirt all over us.

[teeteringhead]

On the subject of Fokker and interrupter gear, I seem to remember a (highly romanticised/artificial??) story in a magazine in my youth, which claimed he was inspired by his (Dutch) childhood pastime of throwing stones at moving windmill blades.......

Thanks CoodaShooda (next post) I remember having that book as a kid, must have been where I saw it .... one of the things that got me into flying I guess.....

[CoodaShooda]

Quentin Reynolds in "They Fought for the Sky" recounts the story that Fokker was called to Berlin to examine Garros's deflector plate set-up after Garros was captured and was ordered to copy it for the GAF.

During the train journey back to his factory, he discounted Garros's concept as unviable, thought of his experiences throwing stones at the windmill blades, where the stones more often missed than hit - despite the slow speed of the blades - and came up with the idea of having the propellor fire the gun.

He had the concept of a cam based mechanical system nutted out by the time he got home. HIs staff then developed the system.

Given the work being carried out in the field by others, it is possible the story was circulated by Fokker at the time to gain credit for the achievement. Then again, perhaps he was not aware of the other systems at the time and the story is true.

[Genghis the Engineer]

Well, he was the bloke who made it work effectively, I think he deserves the credit for that. (Or at-least he employed the people who did.)

After all, there were many people who discussed how to make a flying machine work, but it was Wilbur and Orville who get the credit, since they actually made it work. Equally, we're very polite about Leonardo's efforts, but Sikorsky gets the credit for a working helicopter.

The fact is, nothing is ever one person's work in this game. RJ Mitchell didn't design the Spitfire without a team of talented people beneath him, and the experience of numerous other designs to draw upon - but he still deserves the credit.

G

[RatherBeFlying]

was of Goofy the WWI biplane ace watching the prop arc diminish from a full circle to nothing accompanied by the sound track of a circular saw cutting through wood:uhoh:

[FBS]

Fokker was a good pilot and a brilliant salesman and self-promoter. He was very good at claiming credit for things and his biography is a classic in this respect. He apparently knew of the earlier patents and found an ideal way of getting his company a lead in the business.

There is evidence that Immelmann had interupter gear faliure. Photos of the wreckage of his EIII show one blade appearing to be shot off.

I used to have a WW1 pilot's diary and he had a failure. Then, of course, you have to hope that you shoot off both blades ond not just one!

FBS