A question on the P38 guns...

[Hazard69]

Was just wondering why is it that the P38s nose mounted 50cals fire one at a time as opposed to simultaneously or more likely alternately (i.e. 1 & 3 fire and then 2 & 4 fire, like a pony's do).

I'm sure HTC's mimicking reality, but I'm curious as to why the manufacturer would limit the aircraft lethality that way? I mean it'd sure be way more lethal if it was spouting out twice as much lead in the same time. Heating/ventilation issues? Stability problems? What?

Also, I am not sure but I seem to recall some variant had 6 or 8 50 cals installed instead of the 20mm. Is that accurate, and was it a common enough configuration? Might have avoided any need for different convergences if all the guns were of the same variety.

And finally, also why are all 4 the 50cals of varying lengths? Just so they could all be accommodated in the nose cone or some other aerodynamic reason?

Enquiring cadets would like to know!

  Hazardus

[tunnelrat]

This is just a hypothesis, but the guns may have been arrayed in such a fashion due to their close proximity with one another.



The receiver sections, firing mechanisms, and ammunition feeds are much bulkier than the protruding barrels let on.  So, perhaps they were staggered internally for space/serviceability considerations?

[Shuffler]

They were staggered for space and feed belts. They each have to be fed and have their corresponding belt box.



There were some other setups including a 23mm and even a 30mm canon. There was also a mix of 50s and 30s. Those were tested and some used but the main setup in action was 4 50s and a 20mm.

[Hazard69]

This is just a hypothesis, but the guns may have been arrayed in such a fashion due to their close proximity with one another.

(Image removed from quote.)

The receiver sections, firing mechanisms, and ammunition feeds are much bulkier than the protruding barrels let on.  So, perhaps they were staggered internally for space/serviceability considerations?

That's a nice cutaway. I can see why they'd have to stagger them to accommodate the ammo belts.  

Now, any ideas as to why they had to stagger the firing sequence too? 

  Hazardus

[FLS]

I don't recall the firing sequence but I assume you're looking at the tracers and only every 5th round is a tracer in each gun. It makes sense to stagger the tracer rounds instead of sending them out in groups.

[Hazard69]

I don't recall the firing sequence but I assume you're looking at the tracers and only every 5th round is a tracer in each gun. It makes sense to stagger the tracer rounds instead of sending them out in groups.

No not the tracers, Im looking at the muzzle flashes. In a pony as u fire the quad guns, u can see them firing two at a time, whereas in a P38, u can see the flashes on one gun after another.

  Hazardus

[tmetal]

might be an attempt to create a more constant stream of lead with less spacing between bullets? or maybe all 4 .50s firing at the same time created a harmonic vibration that would escalate and eventually cause damage to the plane.

just my semi-educated guesses

[tunnelrat]

No not the tracers, Im looking at the muzzle flashes. In a pony as u fire the quad guns, u can see them firing two at a time, whereas in a P38, u can see the flashes on one gun after another.

  Hazardus

Well, check the ammo.... and time firing (just the .50 cals) all the way down.

They should fire @ 850 RPM.....  that will give you the true indicator of firing sequence...

Now, assuming this is historically accurate (and that is in no way meant to insinuate that it is anything but), if the guns are firing in sequence it may be due to the inherent inaccuracy of the average pilot of the day... to allow the greatest chance for SOME hits...

My other hypothesis would be as tmetal said... though maybe not harmonic vibration so much as the 4x force of simultaneous discharge being too much for the air frame and/or avionics to handle.



Some other food for thought... here is a pic of a P-38 firing:



In that pic, all guns fire at once (and it appears that they are all tracers).

Now, the other tidbit to keep in mind is that there is a difference between delaying the guns firing, and the guns firing sequential but each at the cyclic (or whatever was the standard) rate.


If all 4 guns empty in 35 seconds (or thereabouts) - and assuming that a total of 2,000 .50 BMG rounds are thrown downrange, then it is good to go.

If it take appreciably longer, then there is some delay being introduced into the firing sequence that does not jive with what I have read about the P-38 (however I have nothing that proves to me whether or not what I have read is legitimate)

But I love talking about the P-38 hehe

[FLS]

Keep in mind that pictures are deceptive because of the length of time the shutter is open.

[Hazard69]

Well, check the ammo.... and time firing (just the .50 cals) all the way down.

Heheh, funny you should say that. I tried something like that just yesterday. Offline, I emptied the P38s 50cals with the 200rpg loadout. It took 46 seconds by my count. Then took out a P51 and fired off the secondaries with 267rpg and they emptied in about 47seconds. (Will recheck today once I get back home). That makes it seem as though the pony is firing almost 270 rounds more in almost the same duration.

Weird?

Yes Im leaning towards the instability/fatigue/vibration issue as a reason too, since the only real difference seems to be that the pony's guns are wing mounted as opposed to the 38s being nose mounted.

Keep in mind that pictures are deceptive because of the length of time the shutter is open.

Yes, I doubt they had a secret 38 variant with lasers installed.   Or do tracers actually extend so far out?  

Judging from the smoke, seems like a stationary aircraft, probably testing convergence? Looks like its hitting a target off in the distance?

  Hazardus

[Captain Virgil Hilts]

Given the fact that the cyclic rate of an M2 Browning 50 caliber heavy machine gun cannot be that closely controlled, you could see pretty much any firing rhythm in those weapons on a P-38, or any aircraft that was not firing them through a propeller with interrupter gear. The actual rate of fire in rounds per minute will vary such that even if they start out firing in sequence, they will only continue to do so for a relatively short period of time. The manufacturing tolerances of both the weapons and the ammunition is too wide for that level of control. Especially considering that dispersion is built in to machine gun ammunition.

[Mongoose]

Given the fact that the cyclic rate of an M2 Browning 50 caliber heavy machine gun cannot be that closely controlled, you could see pretty much any firing rhythm in those weapons on a P-38, or any aircraft that was not firing them through a propeller with interrupter gear. The actual rate of fire in rounds per minute will vary such that even if they start out firing in sequence, they will only continue to do so for a relatively short period of time. The manufacturing tolerances of both the weapons and the ammunition is too wide for that level of control. Especially considering that dispersion is built in to machine gun ammunition.

I remember reading a story a P-38 pilot wrote about one of his missions.  No, I don't remember where, it was a long time ago.

He said that when he pulled the trigger, all the guns fired at once, then settled into a rhythm.  I don't know how accurate the story, or my memory, is.   

[Slash27]

They were staggered for space and feed belts. They each have to be fed and have their corresponding belt box.



There were some other setups including a 23mm and even a 30mm canon. There was also a mix of 50s and 30s. Those were tested and some used but the main setup in action was 4 50s and a 20mm.

Too bad they didn't go with the 2 20mm/4 .50 cal set up.

[Captain Virgil Hilts]

No, a better version would have been four 20MM cannons with 200-225 rounds each. A C hog, with no convergence to deal with.

The parts were available to create an incredible performer out of the P-38, even better than the best version built. The G series V-1710 Allison was a "bolt in" swap. Combined with the "K" model (Hamilton Standard high activity paddle props) conversion that Lockheed did about 9 months before the G series engines were built, it would have produced a true monster. A P-38 with as much as 4500HP driving two Hamilton Standard 13 foot diameter 4 blade props would have been a real climber. Throw in the four 20MM cannons and you'd have a serious ride. You'd just have to be damned careful about not getting into compression, because it could have been easily done in level flight. Imagine this P-38 http://www.456fis.org/P-38K.htm taken to the next level, the G series engines with 2250HP http://www.thunderboats.org/history/history0323.html (almost 400HP each more than the F-15 Allisons in the P-38K) with 4 blade Hamilton Standard props. A seriously sexy beast for a P-38 fan.

[Denniss]

But they would have had to import 20mm guns from the UK as the home-made Hispano copies were really bad (unreliable, jamming).