Propellor hub-firing machine guns.

[HoHun]

Hi Welch,

>How many bullets would fire through a propeller at a time I wonder?

With a rate of fire of 13 rounds per second and an engine rpm of 2600 at a reduction ratio of 1:1.685, about two blades would pass by between each shot from one machine gun of the Me 109G.

I don't know if both machine guns were individually triggered or combined. From the looks of the Me 109E synchronizer cover, it looks as if it had two independend sensors.

Regards,

Henning (HoHun)

[xtberia]

Originally Posted by HoHun

Hi Xtberia,

>In any case, what I was actually trying to figure out as to how the machine guns could have been synchronized to fire through the propellor without hitting the blades, in the process.

Interrupter gear - Wikipedia, the free encyclopedia

Note that typically for Wikipedia articles, it features some good stuff (the diagram of a WW1 era interrupter gear) mixed with some deliberate spin-doctoring.

("German and Soviet fighter types in particular were slow to abandon fuselage-mounted guns" - the truth is that everyone else "was slow to" adopt electrical synchronization that made synchronization rock. Naturally every air force wanted their guns as close to the centreline as possible to do away with convergence/divergence issues, it's just that it was a technological challenge to develop a reliable, fast-firing, high-firepower, synchronization-compatible gun that would fit neatly into the nose or wing roots of an aircraft.)

Regards,

Henning (HoHun)

Thanks Henning. Great article.

[xtberia]

Originally Posted by HoHun

Hi Xtberia,

>In any case, what I was actually trying to figure out as to how the machine guns could have been synchronized to fire through the propellor without hitting the blades, in the process.

Interrupter gear - Wikipedia, the free encyclopedia

Note that typically for Wikipedia articles, it features some good stuff (the diagram of a WW1 era interrupter gear) mixed with some deliberate spin-doctoring.

("German and Soviet fighter types in particular were slow to abandon fuselage-mounted guns" - the truth is that everyone else "was slow to" adopt electrical synchronization that made synchronization rock. Naturally every air force wanted their guns as close to the centreline as possible to do away with convergence/divergence issues, it's just that it was a technological challenge to develop a reliable, fast-firing, high-firepower, synchronization-compatible gun that would fit neatly into the nose or wing roots of an aircraft.)

Regards,

Henning (HoHun)

Thanks Henning. Great article.

[HoHun]

Hi xtberia,

Here is another sectional drawing, showing the pneumatical (or is it electric-pneumatical?) system of a British inter-war fighter:

Vickers-Gun-interuptor-deta

Regards,

Henning (HoHun)

[Tony Williams]

Originally Posted by HoHun

Here is another sectional drawing, showing the pneumatical (or is it electric-pneumatical?) system of a British inter-war fighter:

Neither electric nor pneumatic, I would assume: I believe that the RAF retained the hydrosonic CC gear (Constantinescu-Colley) from late WW1 until they stopped using synchro guns. This was not hydraulic, by the way, although the transmission media did consist of liquid-filled tubes. Basically, there was a mini loudspeaker at the prop end and a microphone at the gun solenoid. The signal was sent in the form of a sound wave (the speed of sound in a liquid is much faster than in air).

Incidentally, it is misleading (although common) to call such systems "interrupter gear", which implies that the MG was firing on automatic and was stopped from firing by the synchro gear whenever a prop blade was in the way. Only the very first designs worked that way. For the rest, the MGs were converted to semi-auto fire and each shot was fired individually by the synchro gear as soon as the gun was ready to fire and the prop was out of the way.

Losses in rate of fire depended on the synchro system and on the gun mechanism. The best was the German electric system, which lost only around 10% of the RoF. The worst was the US .50 BMG which lost around 40%. Most were around 25%.

[HoHun]

Hi Tony,

>This was not hydraulic, by the way, although the transmission media did consist of liquid-filled tubes.

Highly interesting - quite advanced technology for WW1 in my opinion!

I guess I was confused by the remark on "Petty Air Release Valves", a term I couldn't translate but which had a certain pneumatical ring to it

>Incidentally, it is misleading (although common) to call such systems "interrupter gear", which implies that the MG was firing on automatic and was stopped from firing by the synchro gear whenever a prop blade was in the way.

Roger that, it's an inaccurate term of historical origin.

By the way, do you have any information on the system used by the Russians, for example on the Lavochkin La-5?

Regards,

Henning (HoHun)

[Tony Williams]

Hi Henning,

Originally Posted by HoHun

By the way, do you have any information on the system used by the Russians, for example on the Lavochkin La-5?

Sorry I don't. Getting info on guns is very easy compared with finding anything out about the synchro systems. The only thing I know about the Russian system is that the 12.7mm UBS dropped 24% in RoF, from 1,050 to 800 rpm (which still made it about as fast as a .50 M2 Browning unsynchronised...).