Synchronized guns

[MANDOBLE]

I'm not an expert, but afaik, gun syncronization is done by the propeller position, not by any kind of timer. So, during each propeller revolution, the gun is, at least, locked once and unlocked once for firing. Suppose a gun able of 800 rounds per minute synchronized with a propeller doing 1200 rpm. Why this gun should loose 40-50% of its ROF? This is the case of the 190 Mg151/20 compared to the same gun in 109G10 with gondolas.

[RAM]

Because the gun must fire when there is no paddle in the way of the round...and with a ROF of 800 firing through the disc of the propeller some rounds will SURELY hit the prop.

The measure to evade it is a mechanical swich, so when a paddle is in the way of the round the gun wont fire. The mechanism was first applied in Fokker Eindeckers of WWI. The net result is a lower RoF some 25-35% less than the usual.

The outboard 190 cannons fire at the same RoF than the nose gun in Me109.

[funked]

nm

[This message has been edited by funked (edited 06-13-2000).]

[Pongo]

The RPMs of the prop are not that relevent. Imagine a solid disk in place of the propeller. Now measure how much of the area of that disk is taken up by the blades of the propeller. That % is about how much synchronizing reduces the rof of guns.

[funked]

What Pongo said.

That approach will give you the minimum possible ROF reduction, the "ideal" ROF.

However each firing is a discrete event, and there is some conservatism in the design of the synchronizing mechanism, so the real ROF reduction will be even larger.

Haven't been bored enough yet to check the Aces High ROF vs. the propeller dimensions and synchronizing instructions in my Fw 190A-8 manual, but I'm guessing HTC used the "ideal" ROF because it is simple to calculate.  

[Graywolf]

 

Originally posted by funked:
What Pongo said.

That approach will give you the minimum possible ROF reduction, the "ideal" ROF.

However each firing is a discrete event, and there is some conservatism in the design of the synchronizing mechanism, so the real ROF reduction will be even larger.

The RPM is relevent. Picture the scenario where the prop is rotating at the same RPM as the ROF of the gun, the prop will always be in the same orientation for each attempt to fire. The result would be either firing all the time (normal ROF) or not firing at all...OK, that's a bit odd and extreme, but I believe in real life (at least on planes without a constant speed prop) there were certain RPMs that resulted in smoother firing than others. These were often selected for combat even though they might not be quite optimum for performance.

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Graywolfe <tim@flibble.org>

[MANDOBLE]

That is the point Graywolf. RPM is relevant. In the case of 190 inner guns and machine guns, I suppose each weapon was synchronized individually. So, at some points, left gun cant fire, but right one can. The situation where all the blades are obsuring all the guns over'n over each time the guns can fire is remote. So, IMO, some gun can fire per each propeler revolution if RPM of the propeller is greater or equal to the MROF of the guns. There will be situations where all the guns can fire all the time with maximun ROF.
In the case you describes, RPM = MROF, when a gun fires first time (first time syncrhonization mechaninsm unlock that gun to fire), the gun will keep synchronized with the blades all the time while RPM = MROF, so, maximum ROF will be achieved.

[Nashwan]

It helps if you consider the alternative name for synchronization: interuptor gear. Sometimes the prop gets in the way and you have to stop the gun firing.
 

In the case you describes, RPM = MROF, when a gun fires first time (first time syncrhonization mechaninsm unlock that gun to fire), the gun will keep synchronized with the blades all the time while RPM = MROF, so, maximum ROF will be achieved.

I don't think this perfect situation could ever be reached. The revs would have to be very precise to get to that situation.
BTW, what is the rpm of a Fw190 prop at full power etc. Just an approximation will do.

[Pongo]

I am just sermising.
but with 4 weapons to sycronize, that have 2 different rates of fire and three blades that are narrower at the point where they block the cowl guns then the wing root guns and a variable pitch propeller that can cut down the cross section of the blade...
how in the hell could you hope to manage the kind of optimization that you are describing...(course they were germans....)
Each gun has a switch that will interupt it if the interupter contact for it is triggered. And they will all be triggered simutaniosly(sp).
In examining my 1/48th scale 190D9.. I note that any time one of the guns is interupted they all would be by the other two blades...If the firing cycle was waiting to take a shot for each gun.
I think my approximation above is pretty accurate.

[Sorrow[S=A]]

currently the sync rate is the ROF -10%.

It is certainly not -35% or anything close to that.