A-20 and A-22 defensive gun firing arcs
- Thread starter elbmc1969
- Start date
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Trying to type out the lower gun arcs confused the hell out of myself so I just did a diagram. I hope it's clear enough.
Vickers 'K' armed Maryland
Vickers 'K' armed Boston
Vickers 'K' armed Maryland
Upper gun elevation:
+3 degrees to +60 degrees
Upper gun traverse:
40 degrees to starb (at this point only -10 degrees depression is possible)
30 degrees to port (at this point only -10 degrees depression is possible)
Lower gun:
Vickers 'K' armed Boston
Upper gun elevation:
+3 degrees to +43 degrees
Upper gun traverse:
85 degrees to port or starb
Lower gun:
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- Thread starter
- #3
Thanks very much! Where did you find this information?
Question on the Maryland: as the gun traverses to it's maximum, the depression is "only" -10°. However, the general elevation listed it +30 to +60, so -10 is better. I assume the +3 limit is when you're firing back over the fuselage. Any idea about depression limits across the rest of the traverse?
- Thread starter
- #5
Do you have the title, document #, etc. so that I can see if there are any related documents?
Air Fighting Development Unit
Report No. 29
Tactical Trials - Maryland Aircraft
I would bet there is more in-depth information from the A&AEE (they usually have actual diagrams of fields of fire, further pertinent info, etc.) but I have nothing on the Maryland from them.
Report No. 29
Tactical Trials - Maryland Aircraft
I would bet there is more in-depth information from the A&AEE (they usually have actual diagrams of fields of fire, further pertinent info, etc.) but I have nothing on the Maryland from them.
Greg Boeser
1st Sergeant
Interesting that the traverse isn't symmetrical.
- Thread starter
- #8
The mounting was off-center.
Incidentally, I just realized that the crash of the DB-7 on January 23, 1939, with Captain Maurice Chemidlin of the French Air Force aboard, which set off a firestorm among isolationists, happened in our neighborhood!
- Thread starter
- #9
Greg Boeser
1st Sergeant
That pivot arm is similar to the waist gun mounts on B-26s.
MiTasol
2nd Lieutenant
I think you will find that the arrowed pivot link was able to move through a 180 degree arc. That photo has the Browning MG so the ammo box on far side of the gun could limit travel that way. Note the cocking handle is just below that plate which would surely get in the way and skin knuckles when usede
Likewise the Vickers K ammo drum would limit travel one way if mounted on its side like they often were.
- Thread starter
- #12
, I had considered that, but if you pivot it to the other side you hit the expanding part of the beam that supports the gun mount. That beam slips up against the side of the fuselage keep it out of the gunner's way when not in use and when the gunner is seated for takeoff or a landing, etc. It's possible, but it looks like it would end up as a very awkward position. If the pivot link is in the center of its swing, so that it is sticking straight out, the gunner has to slide forward to a fairly awkward position. It also raises the question of why you wouldn't use that center position all the time. After all, it would provide a wider field of fire in azimuth because you would clear a little bit more of the sloped edges of the hatch, and it would provide more travel on the side with the ammo box. It would also possibly allow slightly more depression.
I believe that the pivot arm was used for stowing the gun against the fuselage.
Overall, a center position seems as though it would have so many advantages that it would be considerably preferable, so I'm not sure why they couldn't manage it, unless it was simply a problem with the stowed position of the gun.
A note on a different point: the armor protection for the lower gunner is quite good. Since he is prone, he presents a very small frontal area to enemy fire. The gun shield mounted above the gun (shown flipped down in its storage position in the photo) provides near total protection for his shoulders and head, while the plate mounted under the barrel protects his lower torso very effectively. This is much more protection than almost any rear gunner that I've seen in an upper position. They generally have armor above the gun in a conventional gunshield arrangement, especially lower torso, and anything from the hips down. How large a frontal area is exposed to fire and how much weight it requires to offer adequate bulletproof protection. In this case, I suspect that the armor plates are positioned at distances from the pintle calculated to balance quite neatly.
The lower Gunner has one huge problem: visibility. He simply can't see out to the sides to spot enemy fighters closing in from below on the flanks. He's depending on the upper rear gunner to be able to keep watch in all directions to a sufficient depression. Of course, if the upper gutter with little things like firing at attacking enemy interceptors, he's not going to be keeping an eye out at all! This is one of the few nice things I can say about the gondola positions used in some of the German bombers. At least they had windows on the sides!
I believe that the pivot arm was used for stowing the gun against the fuselage.
Overall, a center position seems as though it would have so many advantages that it would be considerably preferable, so I'm not sure why they couldn't manage it, unless it was simply a problem with the stowed position of the gun.
A note on a different point: the armor protection for the lower gunner is quite good. Since he is prone, he presents a very small frontal area to enemy fire. The gun shield mounted above the gun (shown flipped down in its storage position in the photo) provides near total protection for his shoulders and head, while the plate mounted under the barrel protects his lower torso very effectively. This is much more protection than almost any rear gunner that I've seen in an upper position. They generally have armor above the gun in a conventional gunshield arrangement, especially lower torso, and anything from the hips down. How large a frontal area is exposed to fire and how much weight it requires to offer adequate bulletproof protection. In this case, I suspect that the armor plates are positioned at distances from the pintle calculated to balance quite neatly.
The lower Gunner has one huge problem: visibility. He simply can't see out to the sides to spot enemy fighters closing in from below on the flanks. He's depending on the upper rear gunner to be able to keep watch in all directions to a sufficient depression. Of course, if the upper gutter with little things like firing at attacking enemy interceptors, he's not going to be keeping an eye out at all! This is one of the few nice things I can say about the gondola positions used in some of the German bombers. At least they had windows on the sides!
- Thread starter
- #13
Well, I was completely wrong about this. The short arm pivots out to center the gun in the hatch. As I mentioned that gives just a bit larger arc of fire all around.
MiTasol suggested that the short arm ("short pivot link") could move through a 180 degree arc, but the book on the A-20 that I found, with extensive photos and other documentation, show that it pivots no more than 90 degrees.
MiTasol
2nd Lieutenant
The A-20C/Boston III installation showing Vickers GO installation.
The installation is much more complex than the photo elbmc1969 posted first suggests as the stowage moves in two directions. Unfortunately no text accompanies the diagrams but in the equipment at crew stations section it does give some information which totally supports the comment that the gun is only used when the gun support arm (what I called pivot link) is locked fore and aft.
Source 01-40AD-2 = AP 2023 Vol 1, A-20C, Boston III, E&M (1942-01-08)
If I get a chance I will rescan pages 428 & 9 as they are difficult to read tho, from memory, I scanned them at 4 or 5 settings and chose the clearest.
The installation is much more complex than the photo elbmc1969 posted first suggests as the stowage moves in two directions. Unfortunately no text accompanies the diagrams but in the equipment at crew stations section it does give some information which totally supports the comment that the gun is only used when the gun support arm (what I called pivot link) is locked fore and aft.
Source 01-40AD-2 = AP 2023 Vol 1, A-20C, Boston III, E&M (1942-01-08)
If I get a chance I will rescan pages 428 & 9 as they are difficult to read tho, from memory, I scanned them at 4 or 5 settings and chose the clearest.
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varsity07840
Airman 1st Class
- 176
- Jun 25, 2013
The round cut outs in the sheet metal to the left of the gun lead to a "scanning window" in the fuselage(both sides). Most American a/c with "tunnel guns" had them.
MiTasol
2nd Lieutenant
Do not worry about it, that is the joy of this forum, most of us are here to both learn and to teach. All the older members know the truism about making mistakes - there are them that have, and them that are going to.
vikingBerserker
Lieutenant General
I thought it had crashed at Mine's Field (now the Los Angeles Municipal Airport)?
Here a picture of it from the French chapter of my book:
Here a picture of it from the French chapter of my book:
the French DB-7, MAC 34, 7,5mm Cal:
the two rear guns are slightly staggered to the port side despite this
upper gun could fire 30° on each side and 0 to 80° elevation.
lower gun 30° each side and 0 to -80° elevation
source : erection manual DB-7
the two rear guns are slightly staggered to the port side despite this
upper gun could fire 30° on each side and 0 to 80° elevation.
lower gun 30° each side and 0 to -80° elevation
source : erection manual DB-7
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- Thread starter
- #19
I believe this is the location: 1941 Ad Austin Co. North American Aviation Inglewood CA - ORIGINAL FT6
It's essentially across the street (Imperial Highway). It's described as being in Inglewood, but apparently that's because Nasa's mailing address was in Inglewood.
None of the buildings at Mines Field ever had that architecture, to my knowledge.
It's essentially across the street (Imperial Highway). It's described as being in Inglewood, but apparently that's because Nasa's mailing address was in Inglewood.
None of the buildings at Mines Field ever had that architecture, to my knowledge.
MiTasol
2nd Lieutenant
I just came across this for the A-20 installation. Clearly 2084677 limits the arc of the arm the gun is mounted on to 90 degrees which confirms my first post on the subject was wrong.
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