Machine Guns And Propellers

Stickers · Wed Jul 16, 2008 2:54 pm

I was just wondering if someone with some technical knowledge could answer this...

In lots of World War 1 aircraft, the machine guns shoot through the radius of the propeller, as in the picture below.

View Large View Medium
Click here for bigger photo!

Photo © Gavin Conroy

View Large View Medium
Click here for bigger photo!

Photo © Gavin Conroy

How did this actually happen. Was there some sort of timing device on the engine that was linked to the fire rate of the guns? Perhaps someone could elaborate on exactly how this worked as it seems quite advanced for the time. I know also that there are one or two WW2 fighters whose canon or machine gun also fired through the prop. If there was such a timing device, would it not have impeded engine power and made the aircraft unpredictable at a moment in which one needed it to be completely responsive and 100% predictable?

Anyone have any knowledge on this?

Thanks
Stickers listen

SoBe · Wed Jul 16, 2008 2:59 pm

It is an interrupter gear.

http://en.wikipedia.org/wiki/Interrupter_gear

gordonsmall · Wed Jul 16, 2008 3:01 pm

Quoting Stickers (Thread starter):
Anyone have any knowledge on this?

All you'll ever need to know ............

http://en.wikipedia.org/wiki/Interrupter_gear

TSS · Wed Jul 16, 2008 3:03 pm

Actually there was a timing device that affected the gun, not the engine. I'm sure others will post with a whole lot more detail, but with a two-bladed propellor it isn't that hard to synchronize/interrupt bullet bursts with a propellor blade swinging past the line of fire.

CosmicCruiser · Wed Jul 16, 2008 3:10 pm

IIRC, the French were the first to put the machine gun right in front of the pilot (better aiming) but hadn't figured out the prop problem so they just reinforced the back of the prop and let the bullets bounce off. The earlier planes with the gun on the top wing were difficult to aim and shoot. I haven't looked this up but remembering an old "Wings" docu on Dicov it was a German that figured out the interrupt cam.

Jetlagged · Wed Jul 16, 2008 3:37 pm

Quoting TSS (Reply 3):
Actually there was a timing device that affected the gun, not the engine. I'm sure others will post with a whole lot more detail, but with a two-bladed propellor it isn't that hard to synchronize/interrupt bullet bursts with a propellor blade swinging past the line of fire.

It's always the gun which is affected. Fokker's original synchronisation gear meant the gun fired once per cam revolution, so rate of fire was proportional to engine rpm. Later designs worked faster so more firing impulses could be made between blades.

[Edited 2008-07-16 08:50:42]

Analog · Wed Jul 16, 2008 3:47 pm

In WWII there were designs that had the gun in the center of the propeller (the P-39 comes to mind.)

Quoting Stickers (Thread starter):
If there was such a timing device, would it not have impeded engine power and made the aircraft unpredictable at a moment in which one needed it to be completely responsive and 100% predictable?

Are you talking about the reverse thrust from the gun? [Gets out the back of an envelope]... A gun firing a 10g bullet at 800m/sec and 10 rounds/sec delivers 80kgm/s of momentum, which would slow an 800kg aircraft (heavy WWI fighter) down by 0.1m/s, or 0.36km/h. Not much, especially considering that one could only fire for a few seconds.

SlamClick · Wed Jul 16, 2008 5:41 pm

Ahh, progress, in just another twenty years we get:

That is a 37mm cannon firing through the propeller hub as installed on the Bell P-39 Airacobra
And of course we have the business end of the P-38 or the F-7F which one might see as very effective in the manufacture of aluminum confetti.

KELPkid · Wed Jul 16, 2008 6:28 pm

Quoting SlamClick (Reply 7):
That is a 37mm cannon firing through the propeller hub as installed on the Bell P-39 Airacobra
And of course we have the business end of the P-38 or the F-7F which one might see as very effective in the manufacture of aluminum confetti.

Didn't the Messerschmidt Bf.109 (sometimes reffered to as the Me.109) also fire cannon shells through the prop hub? A more interesting feat in the Messershmidt, considering that the Daimler inverted V-12 was actually up front in it (in the Airacobra, the prop was driven by a driveshaft, as the engine was aft of the cockpit...).

KELPkid · Wed Jul 16, 2008 6:32 pm

Quoting SlamClick (Reply 7):
That is a 37mm cannon firing through the propeller hub as installed on the Bell P-39 Airacobra
And of course we have the business end of the P-38 or the F-7F which one might see as very effective in the manufacture of aluminum confetti.

Hehehe. If Combat Flight Simulator 3 is any sort of indication as to reality, getting the guns on just about anything with the Lightning, air or ground, means it's usually over with quickly, especially if you have cannon rounds left and add them to the burst... Wink

Gotta be sparing, though with the cannon, IIRC, there's only 150 cannon rounds with the magazine fully loaded.

MD11Engineer · Wed Jul 16, 2008 7:03 pm

Quoting CosmicCruiser (Reply 4):
I haven't looked this up but remembering an old "Wings" docu on Dicov it was a German that figured out the interrupt cam.

The bloke was Anthony Fokker, a Dutch aircraft manufacturer selling his planes to the Germans (The Netherlands were neutralin WW1 and not invaded, but, since the Boer Wars sympathizing with the Germans)

Quoting KELPkid (Reply 8):
Quoting SlamClick (Reply 7):
That is a 37mm cannon firing through the propeller hub as installed on the Bell P-39 Airacobra
And of course we have the business end of the P-38 or the F-7F which one might see as very effective in the manufacture of aluminum confetti.

Didn't the Messerschmidt Bf.109 (sometimes referred to as the Me.109) also fire cannon shells through the prop hub? A more interesting feat in the Messershmidt, considering that the Daimler inverted V-12 was actually up front in it (in the Airacobra, the prop was driven by a driveshaft, as the engine was aft of the cockpit...).

The P-39 had the engine behind the pilot, with a drive shaft going forward beneath the pilot's seat. In front was a gear box, which allowed the cannon barrel to be routed through the prop hub.
The Bf 109 was similar in as far as the crankshaft of the Daimler Benz V12 engine was below the propellor hub, again requiring a reducer gear between the crankshaft and the prop. This allowed the cannon to be mounted in between the two banks of cylinders on to of the engine.

Jan

Stickers · Wed Jul 16, 2008 10:51 pm

Quoting Analog (Reply 6):
Are you talking about the reverse thrust from the gun?

Interesting stats Analog, thanks. But no, i wasn't talking about the reverse thrust of the gun, i was wondering if the Interuptor/synchroniser (as i have now learnt - thanks everyone) actually makes a noticable difference to the power as it slows or speeds up the prop. But as i have read the wiki entry, i understand that the Gun was synchronised to the engine, and the engine isn't slowed or sped up to match the gun.

SlamClick · Wed Jul 16, 2008 11:03 pm

Quoting Stickers (Reply 11):
But as i have read the wiki entry, i understand that the Gun was synchronised to the engine, and the engine isn't slowed or sped up to match the gun.

You read correctly.

Actually it is very easy to interrupt the firing of a gun. It is impossible to speed or slow a great whirling, reciprocating mass of airplane engine and propeller INSTANTLY which would virtually be necessary if you wanted to syncronize it with a gun firing at a constant rate. Add to that, the fact that the LeRhone rotary, a common engine of WW the first, had a crankshaft that bolted to the airframe and an engine and prop that rotated together. Try speeding that up and slowing it down.

Some airplanes did not have throttles. They climbed by leaving the ignition ON and descended by turning it off. Pretty crude stuff. The synchronized machine gun was major military secret of its day.

You could take a theoretical rate of fire of 600 rounds per minute for ease of math, and calculate what kind of revolution rate would be needed for a two-bladed propeller. I don't know much about WW I airplanes but would guess that no more than about 1200 RPM for the big fat-bladed props.

Stickers · Wed Jul 16, 2008 11:34 pm

Quoting SlamClick (Reply 12):
a crankshaft that bolted to the airframe and an engine and prop that rotated together.

Thats amazing. Did a quick search and came accross this short video clip

http://www.youtube.com/watch?v=De6gF0AalZ8

Imagine that at full speed. definitly not an easy thing to synchronise. boggled

Must have been pretty slow to respond, and no such thing as a subtle increase or decrease in speed. eyepopping

CosmicCruiser · Wed Jul 16, 2008 11:42 pm

Quoting SlamClick (Reply 12):
They climbed by leaving the ignition ON and descended by turning it off. Pretty crude stuff.

True statement. And also they had to be vewy, vewy careful in the descent because with ignition off for long periods of time fuel accumulated in the intake and the possibility of an engine fire was great.

SlamClick · Wed Jul 16, 2008 11:52 pm

Quoting CosmicCruiser (Reply 14):
vewy, vewy careful in the descent because with ignition off for long periods of time fuel accumulated in the intake and the possibility of an engine fire was great.

On the workbench of the blacksmith shop on the ranch where I grew up was a carburetor (you Brits feel free to add a superfluous "t") with the float chamber burst outward. I'd love to know the story! All I can picture is some kind of intake manifold fire but...

I've played with the mixture control to kill an engine in flight and bring it back to life smoothly but can't imagine doing that with ignition. As David Hobbs says: "Ker-Blammo"

MD11Engineer · Thu Jul 17, 2008 5:21 am

Quoting CosmicCruiser (Reply 14):
Quoting SlamClick (Reply 12):
They climbed by leaving the ignition ON and descended by turning it off. Pretty crude stuff.

True statement. And also they had to be vewy, vewy careful in the descent because with ignition off for long periods of time fuel accumulated in the intake and the possibility of an engine fire was great.

Not just this, the engines were also lubricated by adding castor oil to the fuel, in asimilar way as today's two stroke engines. Leaving them at windmilling speeds for too long couldseize up the engine due to lack of lubricant.

Quoting SlamClick (Reply 12):
Actually it is very easy to interrupt the firing of a gun.

You just need an additional sear, controlled by a cam driven by the prop, stopping the gun for the short time it takes for a prop blade to pass through.

The French used a different method first on their Moranes: They added steel deflectors to the back of the prop, which would deflect the bullets, which else would hit the prop blades, sideways.

Jan

Analog · Thu Jul 17, 2008 6:32 am

It seems to this [non-mechanical] engineer that interrupting the firing of a gun asynchronously would be mechanically... how to say it... stressful on something, probably parts of the gun itself.

Were WWI engines/props constant speed or close to it, say +/- 20%)? If so, why not synchronize the firing to the prop? Power loss?

Quoting MD11Engineer (Reply 16):
Not just this, the engines were also lubricated by adding castor oil to the fuel,

Bunch of wanna-be terrorists. Or commie assasins. Smile

ThirtyEcho · Thu Jul 17, 2008 8:43 am

The technology of the interrupter gear was well known even prior to WWI; it was derived, in whole, from the motion picture projector. I know this from long experience in the movie industry.

In fact, the gear that synchronizes the shutter with film frame advancement in a projector is still called an interrupter gear. It was an easy step from this to synchronizing a prop (shutter) with a bullet (film frame).

tdscanuck · Thu Jul 17, 2008 8:46 am

Quoting Analog (Reply 17):
It seems to this [non-mechanical] engineer that interrupting the firing of a gun asynchronously would be mechanically... how to say it... stressful on something, probably parts of the gun itself.

I doubt it's any more stressful than the the firing of the gun itself. There's a lot of shock loading going on there already.

Quoting Analog (Reply 17):
Were WWI engines/props constant speed or close to it, say +/- 20%)? If so, why not synchronize the firing to the prop? Power loss?

I think the WWI props were mostly fixed pitch, which means variable speed.

Tom.

CosmicCruiser · Thu Jul 17, 2008 12:52 pm

Quoting Tdscanuck (Reply 19):
think the WWI props were mostly fixed pitch, which means variable speed.

Like SlamClick said earlier the rotary engines were either on or off, no throttle. That's why in the old WWI movies you would here the cutting in and out when landing. That's the only way they had to control speed on app. See my previous post on engine fires as well.

MD11Engineer · Thu Jul 17, 2008 12:55 pm

Quoting ThirtyEcho (Reply 18):
In fact, the gear that synchronizes the shutter with film frame advancement in a projector is still called an interrupter gear. It was an easy step from this to synchronizing a prop (shutter) with a bullet (film frame).

But it works differently. In movie projectors you generally use a maltese cross gear to move the film forward, while the shutter is simply a segmented plate rotated into the light beam while the film is moving.

The machine gun interuptor uses an additional sear, similar to e.g. the safety sear on a FN FAL or the full auto sear on an AK-47, which operates additionally to the trigger operated sear and is actuated by a cam plate attched to the prop shaft. You can pull the trigger as long as you like to, but if the interuptor sear is not freed, the firing pin will not go forward and fire the round.

Jan

ThirtyEcho · Fri Jul 18, 2008 9:47 am

Quoting MD11Engineer (Reply 21):
In movie projectors you generally use a maltese cross gear to move the film forward

Quite true, now, but in turn-of-the-century projectors the most common drive that moved the film was the claw drive. That is just what it was, a claw that engaged the sprocket hole and pulled the film down.

Without the shutter turning, the claw would not engage anything. In the case of a machine gun, the firing pin would not operate without the prop turning.

Stickers · Fri Jul 18, 2008 5:21 pm

Interestingly enough, as soon as jet engines came out, the guns returned to the Fuselage.

View Large View Medium
Click here for bigger photo!

Photo © Kamil Macniak - Epgd Spotters

In fact this tend continues to today. One of the sites i was reading as i studied the synchroniser (I forget which one) spoke of the advantages of a wing mounted gun. With the overwhelming evidence to the contrary (basically every fighter using fuselage mounted guns,) was the only advantage in WW2 era planes, the absence of the synchroniser?

Jetlagged · Fri Jul 18, 2008 8:59 pm

Quoting Stickers (Reply 23):
One of the sites i was reading as i studied the synchroniser (I forget which one) spoke of the advantages of a wing mounted gun.

Wikipedia says something like that. It's not really an advantage, more that the wing structure was strong enough to take gun recoil loads so the disadvantage of needing a synchroniser was avoided. Twin engined fighters mostly had nose mounted guns (the Beaufighter had light machine guns in the wings as well as nose mounted cannon).

rwessel · Fri Jul 18, 2008 11:14 pm

Quoting Stickers (Reply 23):
With the overwhelming evidence to the contrary (basically every fighter using fuselage mounted guns,) was the only advantage in WW2 era planes,

That's simply not true. Examples of WW2 fighters that had wing mounted guns include the P-51, F4F, F4U, Spitfire, Hurricane...

ex52tech · Sat Jul 19, 2008 10:06 pm

Quoting MD11Engineer (Reply 10):
The Bf 109 was similar in as far as the crankshaft of the Daimler Benz V12 engine was below the propeller hub, again requiring a reducer gear between the crankshaft and the prop. This allowed the cannon to be mounted in between the two banks of cylinders on to of the engine.

I hate to be a stickler for details here, but......the Daimler Benz 601 or 605 engine in the ME-109 (Bf 109) was inverted in its installation. Yes it did have a reduction gear box for the propeller, so they had room to mount a 30mm cannon to the bottom of the engine, it lined up with the back of the reduction gearbox, and could then fire through the propeller hub.

They inverted the engine because the fuselage had to be wider where it joined the wing out of necessity, so in inverting the V-12 it allowed them to narrow the upper fuselage and lower drag. The engine was fuel injected so it didn't know it was upside down. Still it must have been hard, even with a dry sump oil system to keep oil from getting on top of the pistons. With a radial you have a few cylinders to worry about, with an inverted V-12 you have 12.

ptrjong · Mon Jul 21, 2008 1:50 am

Quoting MD11Engineer (Reply 10):
The bloke was Anthony Fokker, a Dutch aircraft manufacturer selling his planes to the Germans (The Netherlands were neutralin WW1 and not invaded, but, since the Boer Wars sympathizing with the Germans)

It's true that there were some anti-British feelings in the Netherlands because of the Boer wars, but it's not like the Dutch Fokker factory sold planes to the Germans.

Fokker simply started his aviation career in Germany and founded his company there before the war broke out. During the war he assumed the German nationality to please the authorities. According to legend he refused to personally test his interrupter gear over the front, by the way.

Fokker was a gifted pilot and businesmann, but hardly an aircraft designer himself, and the Wikipedia article says he didn't really invent the interrupter gear, either.

After WWI Fokker fled Germany for the Netherlands, taking some trains with planes and parts with him, and from then on Fokker was a Dutch company, though still employing quite a few Germans.

Another Dutch designer, Koolhoven, worked in Britain during WWI, by the way.

Peter

Stickers · Mon Jul 21, 2008 9:59 pm

Quoting Rwessel (Reply 25):

Quoting Stickers (Reply 23):
With the overwhelming evidence to the contrary (basically every fighter using fuselage mounted guns,) was the only advantage in WW2 era planes,

That's simply not true. Examples of WW2 fighters that had wing mounted guns include the P-51, F4F, F4U, Spitfire, Hurricane...

Sorry, i might have been a bit ambiguous here. I meant that just about every (jet) fighter since WW2 had fuselage mounted guns and therefore was assuming that this was overwhelming evidence that fuselage mounted guns had some significant advantage over wing mounted ones, and i was wondering if that advantage had more to it than just the absence of a synchroniser.

Stickers

MD11Engineer · Tue Jul 22, 2008 4:49 am

Quoting Stickers (Reply 28):
Sorry, i might have been a bit ambiguous here. I meant that just about every (jet) fighter since WW2 had fuselage mounted guns and therefore was assuming that this was overwhelming evidence that fuselage mounted guns had some significant advantage over wing mounted ones, and i was wondering if that advantage had more to it than just the absence of a synchroniser.

Stickers

One reason might be that with higher speeds the wings became thinner, so that it became more difficult to store the gun's ammunition in the wings. Since the nose was now free of a rotating prop (eliminating the need for interupter gear), the guns moved into the fuselage, where the is more space.
Also, it iseasier to align the guns for instinctive shooting.
The wingmounted guns had to be zeroed to converge at a point ahead of the plane. The exact location of this point was a reason for many arguments during WW2, both among allied fighter pilots and German ones. Generally the authorities preferred an aligning point 300 - 500 yards ahead of the aircraft due to new pilots often shooting from a longer distance, while the experienced fighter aces prefered a much closer range (who went really close in to make a kill, so theywanted to have the guns zeroed at that shorter range).

Jan

rwessel · Tue Jul 22, 2008 6:52 am

Quoting Stickers (Reply 28):
I meant that just about every (jet) fighter since WW2 had fuselage mounted guns and therefore was assuming that this was overwhelming evidence that fuselage mounted guns had some significant advantage over wing mounted ones, and i was wondering if that advantage had more to it than just the absence of a synchroniser.

Well, fuselage mounted guns typically fired straight ahead, while wing mounted guns were often set to converge at some point ahead of the aircraft, the former was preferred, and was one of the reasons the P-38 was considered a good gun platform.

An additional disadvantage of fuselage mounting was that the front end of a typical single engine, propeller driven, fighter was already a darn crowded place, and it would be difficult to mount a significant number or size of guns in that area without either increasing the cross section (which would have been bad for performance), or seriously lengthening the nose. Burying them in the wing, OTOH, does (almost) nothing but displace some fuel. Even fighters that started out with only nose mounted guns (like the Bf-109) often grew wing mounted ones as time went on, because there was simply no room in the nose to add them.

As for jets, I think the (near) central mounting has more to do with weight management plus a desire to keep the gun somewhere close to the centerline or ease of shooting. Which is easier because you don’t have a big engine trying to occupy the same space. But given the growth of radars, many fighters have the gun in a wing root, rather than in the fuselage itself. Consider the F-15 where the gun (cannon) is in the strake.

Stickers · Thu Jul 24, 2008 7:32 pm

Another possibility is that gun technology itself has developed significantly and there is no longer a need for multiple guns or barrels, so its eay to stick just one in the fuselage, and as mentioned keep the balance and the firing line natural.
Thanks for all the info.

Stickers

3MilesToWRO · Fri Jul 25, 2008 11:30 am

Quoting Stickers (Reply 31):
Another possibility is that gun technology itself has developed significantly and there is no longer a need for multiple guns or barrels

It's not the gun technology. It's the rocket technology that developed Smile

Starlionblue · Fri Jul 25, 2008 12:05 pm

Quoting 3MilesToWRO (Reply 32):

It's not the gun technology. It's the rocket technology that developed

Missile, not rocket. And in any case gun aiming systems are much more advanced than 50 years ago.

LY744 · Fri Jul 25, 2008 3:48 pm

Quoting Starlionblue (Reply 33):
And in any case gun aiming systems are much more advanced than 50 years ago.

That's debatable. Although faster, more accurate, and somewhat easier to use, today's radar-ranged sights still use the same principles as the gyro sights of 65+ years ago.

LY744.

XT6Wagon · Sat Jul 26, 2008 12:37 am

Quoting Stickers (Reply 23):
In fact this tend continues to today. One of the sites i was reading as i studied the synchroniser (I forget which one) spoke of the advantages of a wing mounted gun. With the overwhelming evidence to the contrary (basically every fighter using fuselage mounted guns,) was the only advantage in WW2 era planes, the absence of the synchroniser?

As stated before you "need" to aim the wing guns so they all converge on some spot in the distance. Some pilots liked wing guns more though as they were better against light targets with minimal armor/redundancy since it would only take a few bullets to get the job done... and Wing mounted guns fire off a "fan" making for more area covered during firing. However Fuselage guns are easier to put onto target, have less structural issues, and more volume for ammunition, making most designers prefer them. The interupter gears also cut your firepower by quite a bit unless your machinegun has an insane ROF. Design issues also arrise from the interupter gear since you can find nasty jamming issues if your MG isn't all that well designed/built.

Quoting Analog (Reply 6):
Are you talking about the reverse thrust from the gun? [Gets out the back of an envelope]... A gun firing a 10g bullet at 800m/sec and 10 rounds/sec delivers 80kgm/s of momentum, which would slow an 800kg aircraft (heavy WWI fighter) down by 0.1m/s, or 0.36km/h. Not much, especially considering that one could only fire for a few seconds.

Run the math on the A=10's GAU-8 at full ROF. I know this is just about as far from a WWI fighter's MG as possible, but it should show that a gun CAN have a noticable affect on a aircraft when firing.

Starlionblue · Sat Jul 26, 2008 2:27 am

Quoting LY744 (Reply 34):
Quoting Starlionblue (Reply 33):
And in any case gun aiming systems are much more advanced than 50 years ago.

That's debatable. Although faster, more accurate, and somewhat easier to use, today's radar-ranged sights still use the same principles as the gyro sights of 65+ years ago.

Sure. But they're "faster, more accurate, and somewhat easier to use". Wink

Not to mention the control systems are smaller.

baroque · Sat Jul 26, 2008 1:15 pm

Quoting Starlionblue (Reply 36):
Quoting LY744 (Reply 34):
Quoting Starlionblue (Reply 33):
And in any case gun aiming systems are much more advanced than 50 years ago.

That's debatable. Although faster, more accurate, and somewhat easier to use, today's radar-ranged sights still use the same principles as the gyro sights of 65+ years ago.

Sure. But they're "faster, more accurate, and somewhat easier to use". Not to mention the control systems are smaller.

It would also be the case that the radar at least thinks it knows where the target actually IS together with its velocity????

LY744 · Sat Jul 26, 2008 2:32 pm

Quoting Baroque (Reply 37):
It would also be the case that the radar at least thinks it knows where the target actually IS together with its velocity????

In the WWII style sights, instead of radar they used the wingspan and angular size of the target, to compute exactly the same parameters.

LY744.

Analog · Sat Jul 26, 2008 6:53 pm

Quoting XT6Wagon (Reply 35):

Run the math on the A=10's GAU-8 at full ROF. I know this is just about as far from a WWI fighter's MG as possible, but it should show that a gun CAN have a noticable affect on a aircraft when firing.

GAU-8
Projectile mass: ~600g (average of API & HEI rounds)
Velocity: ~1100m/s
ROF: 65 rounds/s

One second burst: 42,000kgm/s. For a 20,000kg aircraft that changes its speed by about 2m/s, or about 7kph. This means it produces about 40kN of force. My calc's do sync with the wikipedia article on the GAU-8 (it says 45kN). A 1-2 second burst (typical use, right?) would lower the A-10's speed by 10-15kph. I guess it's best not to fire when just above stall speed. Smile

Firing all 1200 rounds (or so) in one burst would slow the aircraft down by almost 130kph, not trivial. Of course that gives the pilot/autopilot plenty of time to adjust the engine thrust to compensate.

baroque · Sun Jul 27, 2008 1:20 pm

Quoting LY744 (Reply 38):
Quoting Baroque (Reply 37):
It would also be the case that the radar at least thinks it knows where the target actually IS together with its velocity????

In the WWII style sights, instead of radar they used the wingspan and angular size of the target, to compute exactly the same parameters.

A bit late for profound thoughts on this, but the sights gave an estimate of range to the target but not of said target's velocity? And velocity has to be speed in terms of X, Y and Z. Not to mention that the measures of the plane with the sights velocity were what shall be say a bit on the hazy side!

And the differences were not just because measurements were in analogue terms, but many of the parameters now available simply were not available.

LY744 · Sun Jul 27, 2008 3:08 pm

Quoting Baroque (Reply 40):
A bit late for profound thoughts on this, but the sights gave an estimate of range to the target but not of said target's velocity?

They did estimate velocity, hence computing the lead required for the shot. By 'tracking' the target on the sight (using the wingspan-angular size device) for some given amount of time you gave the mechanical computer a chance to calculate the target's 3D velocity. If the target decided to maneuver while you were in the middle of aiming or shooting then you were out of luck, but that holds true today with radar as well.

LY744.

baroque · Sun Jul 27, 2008 6:05 pm

Quoting LY744 (Reply 41):
Quoting Baroque (Reply 40):
A bit late for profound thoughts on this, but the sights gave an estimate of range to the target but not of said target's velocity?

They did estimate velocity, hence computing the lead required for the shot. By 'tracking' the target on the sight (using the wingspan-angular size device) for some given amount of time you gave the mechanical computer a chance to calculate the target's 3D velocity. If the target decided to maneuver while you were in the middle of aiming or shooting then you were out of luck, but that holds true today with radar as well.

Aha, we are sort of in agreement, but I would think the prediction part of the WWII sight was not quite the best.

Even less able to argue after a goodly few (more) hours working!! chat

Now it is Monday here!! Not that that makes any difference.

LY744 · Sun Jul 27, 2008 6:14 pm

Quoting Baroque (Reply 42):
but I would think the prediction part of the WWII sight was not quite the best.

The prediction part is the worst part of any gunsight. Wink

LY744.

sprout5199 · Mon Jul 28, 2008 1:51 am

Quoting LY744 (Reply 41):
They did estimate velocity, hence computing the lead required for the shot.

I either read or heard on some TV show that the best "gunners" in WWII were farm boys who hunted fowl. Leading the other aircraft was natural to them, as they were used to doing it to birds on the fly.

Dan in Jupiter

Starlionblue · Mon Jul 28, 2008 4:35 am

Quoting Sprout5199 (Reply 44):

I either read or heard on some TV show that the best "gunners" in WWII were farm boys who hunted fowl. Leading the other aircraft was natural to them, as they were used to doing it to birds on the fly.

Now that's what I call fowl play!

XT6Wagon · Mon Jul 28, 2008 4:39 am

Quoting Analog (Reply 39):
Firing all 1200 rounds (or so) in one burst would slow the aircraft down by almost 130kph, not trivial. Of course that gives the pilot/autopilot plenty of time to adjust the engine thrust to compensate.

Thanks for the math

I believe that the GAU-8 is incapible of long bursts at full rate due to thermal issues. I am somewhat suprised that they even have the full rate allowed on the gun since 1/2 rate is still a hell of alot of lead.

Analog · Mon Jul 28, 2008 6:56 am

Quoting XT6Wagon (Reply 46):
I believe that the GAU-8 is incapible of long bursts at full rate due to thermal issues. I am somewhat suprised that they even have the full rate allowed on the gun since 1/2 rate is still a hell of alot of lead.

My data is Wikipedia-based, so grain of salt, yada yada...

Anyways, the initial full-rate was 4200 rpm (or a slower 2100 rpm). Now it's 3900rpm, limited to 1-2 seconds and 21000 rounds per set of barrels.

However, quoting WikiGospel: "Technically, however, there is no tech order limitation on the duration the gun may be continuously fired; therefore the pilot could, in theory, hold the trigger down and expend all rounds in the magazine one burst, with no damage or ill effects."

My general point is that firing the gun shouldn't significantly lower the aircraft's speed, be it a modern or WWI aircraft.

Now if one could put 6 GAU-8s on an A-10 things might be different...

Who is online

Popular Searches On Airliners.net