Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: fdiron on March 25, 2002, 08:14:51 AM
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Why didnt B17s have 20mm guns in the turrets instead of 50s? The B29 had a 20mm tail gun. Seems like they could have retrofitted the b17s to use single or double 20mm guns.
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Most likely "Weight". The 17 didn't have the horses the 29 did so they had to take into account the weight of the gun and ammo for a 20mm vs. twin .50cal.'s.
Also I imagine they looked at the superior range of the .50cal vs. that of the 20mm.
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I thought 20mm rounds went farther and faster than 50 cal ?
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The British were working on mounting Hispanos in turrets for the Lancaster for amny years. They finally got one that passed all required tests just as the war ended.
The Hispano, which the British and Americans both used as their aerial 20mm cannon, was simply too heavy to be readily mounted in a turret.
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The .50cal while not having the hitting power of the 20mm it does have a longer and flatter trajectory and a higher rate of fire so making it better for A2A gunnery.
Karnak, you sure about the Hispanos? I thought US 20mm'ers were versions of the Swedish Orlekion 20mm.
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At last! An explaination for the AH B-17's killing power....the top secret 20mm field mod.
Sorry, HTC....someone had to do it. :)
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Oerlikon ain't no Swedish but Swiss and afair MG/FF was born as a Oerlikon...
Hispano-Suiza HS-404 20mm cannon was Spanish/Swiss designation thought it was made in France before adopted by Brits.
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There were 20mm cannons fitted to the B17. Some BGs had a single 20mm cannon fitted in place of the rear 2 x .50cal during 'field modifications'. The advantage of this was that it could take out incoming aircraft at a longer range and it's large bulky appearance also scared the enemy in not taking that approach. The disadvantage of the rear 20mm is that it didn't have such a wide firing arc like the .50cals. I would post an image but my scanner isn't working! :(
One B17 also used a 20mm forward cannon in place of the chin guns - the 20mm was fitted through the front of the bomb aimer glass. This proved unreliable and caused excessive stress to the forward fuselage compartment and therefore was withdrawn from service rather than endanger the aircraft.
I did suggest to HiTech quite sometime ago about incorporating the rear 20mm cannon to the B17 as a perk option. Who knows!
Regards
NEXX
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Least place you want to add weight to in B-17, is it's tail.
Adding bigger 20mm guns in the tail would mean excessive changes in the structure and due to bigger size would have much more limited traverse/pitch
B-17 is tail heavy plane.
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Reliabilty was an issue early in production too.
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didn't some guy in the pacific have a 75mm(or was it a 37mm?) cannon fitted to the front of a b17?
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My step dad crewed a B25 in N Africk but he said that in the 10 or so sorties in the 75mm armed plane that they shot at many tanks but only had one kill . He stated that aiming it was very tough to do accurately and the one tank they disabled was from a very near miss. "The plane seemed to stop in mid air from the recoil", was his words and I've heard the same from other published accounts.
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Hi everyone,
by coincidence, I just today received a copy of "Rohrwaffen in Flugzeugen der Luftwaffe bis 1945 - Waffenstände" ('Barrel Armament in Aircraft of the Luftwaffe until 1934 - defensive gun positions').
It seems that the Luftwaffe had two reasons to adopt larger calibres: One was the extended range 20 mm guns gave them, the other was the greater effectiveness against heavy fighters.
Since bullets fired rearwards from a moving platform have a slower "airspeed" than those fired forward, a bomber's defensive guns tended to out-range the attacking fighters' weaponry. As protection against frontal attacks however, the Luftwaffe relied on 20 mm cannon with relatively little ammunition: They'd have little time to fire, but the attacker had to be engaged at long range to deter him. The 20 mm nose guns preferably should have a wide downward field of fire, too, to enable them to double as ground attack weapons.
With regard to the weapons: As early as 1938 work had begun on providing 20 mm defensive guns with the explicit goal of increasing the firing range. However, against the fighters of the Battle of Britain era, the Luftwaffe considered 7.92 mm and 13 mm machine guns effective, though apparently they weren't happy about the limited field of fire of their positions. (I'd say that was partly due to the lack of tail turrets, and partly due to the limitations of hand-operated weapon mountings.)
Against heavy fighters (Beaufighter, Mosquito etc.), even a 4 x 13 mm battery was considered inadequate, and 2 x 20 mm were demanded for heavy bombers. The Heinkel He 177 nevertheless had to make do with a single hand-operated gun due to the lack of space in the aircraft's tail.
Coming back to the B-17, I think the reason that they weren't converted to 20 mm armament simply was the lack of time for that. The USAAF had been firmly convinced that the "Flying Fortress" would be able to defend itself against any fighter attack, and had the B-17F flown as Luftwaffe bomber in the Battle of Britain, the result would undoubtly have proved them right. The problem was that by 1943, the fighters had improved firepower and protection, too, and the destroyers made it even worse for the USAAF.
As it was, the first Schweinfurth raid of August 1943 shook the USAAF's confidence for the first time, and the second probably shattered it in October of the same year. Only now the USAAF had reason to think about substantially increased armament, but the time needed to get a new weapon into mass production (or erect a new plant for an existing weapon) and for broad-scale introduction of this new weapon probably would have been at least 12 months. The USAAF didn't have this time, and the obvious solution was to provide long range fighter escort, for which in October 1943 there were two promising candidates: the P-38 and the P-51.
What would the USAAF have done without the long-range fighter option? I think they'd most probably have found it easier to mount more 0.50" gun positions instead of going to a larger calibre. The YB-40 had an additional dorsal durret and twin guns in each waist position, and perhaps this would have been copied for the B-17 bomber squadrons, which of course would have suffered from an impact on payload and range.
Regards,
Henning (HoHun)
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Originally posted by Andijg
The .50cal while not having the hitting power of the 20mm it does have a longer and flatter trajectory and a higher rate of fire so making it better for A2A gunnery.
Uhm, the 20mms come in many flavors and the Hispano (and whatever it's designation was in the US... M2 or smthing) has quite similar trajectory and is arguably better for A2A gunnery.
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I belive Dornier Do-24T, Dutch version of that flying boat, was one of the first planes having a Hispano cannon in dorsal turret after the wing. German versions were having usually MG151/20 or Mk-103 cannon instead.
Huh Mk-103 30mm??
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Here's nice pic from Do-24T which is having, I believe, Hispano cannon in dorsal turret.
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damn!! thats a big gun, and a wierd looking kid!! i don't trust him with that gun;)
interesting fact:
mk1 hispanos had a problems with the shells exploding on impact (instead of inside the plane), and some exploded just as they left the gun barrel!
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MK 103 was a varation version of the MK 108, both of which were 30mm. The MK 103 had a lower ROF, but a significantly higher muzzle velocity. The barrel was also lengthened in some versions.
MK 108: Length (mm) Weight (kg) Rounds per min Speed m/sec
1054 62 660 540
MK 103: Length (mm) Weight (kg) Rounds per min Speed m/sec
2285 146 420 720
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Originally posted by fdiron
Why didnt B17s have 20mm guns in the turrets instead of 50s? The B29 had a 20mm tail gun. Seems like they could have retrofitted the b17s to use single or double 20mm guns.
It was much more difficult to upgun a turret than it was to hang bigger guns on a fighter.
The 20mm Hispano weighed around 60 kg with belt feed against 30 kg for a .50". It also had much heavier recoil, and was a lot longer. A 20mm turret needed to be bigger overall, and that meant a major redesign to the plane to take it.
There were also problems with the reliability of the Hispano in US production, which were not solved until after the war.
Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/
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Originally posted by fdiron
I thought 20mm rounds went farther and faster than 50 cal ?
The muzzle velocity of the Hispano and the .50" was about the same, but the .50" had a much more streamlined projectile which gave it a longer maximum range.
I doubt that this made much difference at normal combat ranges.
Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/
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Originally posted by MrLars
My step dad crewed a B25 in N Africk but he said that in the 10 or so sorties in the 75mm armed plane that they shot at many tanks but only had one kill . He stated that aiming it was very tough to do accurately and the one tank they disabled was from a very near miss. "The plane seemed to stop in mid air from the recoil", was his words and I've heard the same from other published accounts.
I don't doubt that was the impression from inside because firing the gun would have given quite a jolt to the plane. However, when you compare the weight x velocity of the shell with the weight x speed of the plane, you'll realise that the plane had about 300 times the momentum of the shell. So firing the gun would have had a negligible effect on the plane's speed.
Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/
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Originally posted by HoHun
Hi everyone,
by coincidence, I just today received a copy of "Rohrwaffen in Flugzeugen der Luftwaffe bis 1945 - Waffenstände" ('Barrel Armament in Aircraft of the Luftwaffe until 1934 - defensive gun positions').
Hi Henning,
I have always been puzzled by how slow the Luftwaffe was to fit powered turrets to their bombers. The defensive armament of their bombers in the Battle of Britain was way behind that of contemporary RAF bombers. Even the 13mm MG 131 single turret which came later was only half-powered - a simple, single-speed motor moved the turret to about the right position, after which the gunner aimed by hand. I think only the 20mm turrets were properly powered, and they saw little use.
It was well known that hand-aimed, flexibly mounted guns were far less accurate and effective than those in a fully-powered turret. Is there any explanation for the lack of such German turrets in the book?
Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/
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Originally posted by Nath[BDP]
MK 103 was a varation version of the MK 108, both of which were 30mm. The MK 103 had a lower ROF, but a significantly higher muzzle velocity. The barrel was also lengthened in some versions.
There was a bit more to it than that...the designs for the MK 108 and the MK 103 were quite different. The similarities were only in the calibre, and in the M-Geschoss HE shells both used for air-to-air fighting.
Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/
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I remember reading that B17 crews were filing reports about the 50 caliber AP bullets bouncing off the cowl and windshields of FW190s. It seems to me that the USAF should had at least test fitted a B17 with a 20mm gun. However, I imagine the same Generals who ordered bombers to continue flying without escort would have rejected retro-fitting of B17s with cannons due to the time element.
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Hi Tony,
>Is there any explanation for the lack of such German turrets in the book?
It's actually more like a magazine - it's a "Waffen Revue" volume, if you're familiar with them. (The author of the "Waffenstände" volume is Manfred Griehl.)
It does not mention any reason for the lack of powered and manned turrets in German bombers, except for the volume poblems.
However, reading between the lines, I think the Luftwaffe generally thought the value of defensive armament to be limited, and that they had achieved a good compromise with regard to weight and survivability in their bombers. Remember that while the British were highly enthusiastic about the value of powered turrets before the war, the "Battle of Heligoland Bay" showed that their bombers were easy prey for day fighters nevertheless. The RAF withdrew their bombers to night attacks, and of course, the Luftwaffe had learned that bombers were highly vulnerable, too.
>Even the 13mm MG 131 single turret which came later was only half-powered - a simple, single-speed motor moved the turret to about the right position, after which the gunner aimed by hand. I think only the 20mm turrets were properly powered, and they saw little use.
Thanks for the clarification - Griehl had listed that point, but not explained it well enough for me to understand :-)
Anyway, it seems that the Germans mostly skipped the powered and manned turret in favour of the powered remotely-controlled turret similar to the B-29's armament. Messerschmitt, Arado and and the Luftfahrtgerätebau Berlin each developed such a system, and AEG actually built a variety of different systems for the task. However, all of these systems seem to have had problems with accuracy, and they weren't ready for production before the German bomber programs were cancelled.
The reason for skipping the manned power turret probably was the 1939's "Bomber B" specification which called for a medium bomber with a pressure cabin. As with the B-29, remotely controlled turrets were the only way to achieve reliable pressurization, so they were in the specification, too. The Bomber B programme lead to the Ju 288 (found to be superior to the competing Do 317 and Fw 191), but all three Bomber B aircraft were to utilize the Jumo 222 which was a failure, and so the entire programme was cancelled in early 1944.
The He 177, the moderately successful Bomber A, was canceled in July 1944, too, pretty much eliminating the need for bomber armament that way. All future plans for bombers were based on jet engines and using high speed as their primary defense so that comparatively light armament would have sufficed. The Ju 287 for example was to be armed with a remotely controlled twin turret only.
Regards,
Henning (HoHun)
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Both the YB-40(Fortress) and XB-41(Liberator) were duds, for once the other bombers dropped their bombs they could not keep up with the empty bombers.
*fixed error
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HL-131 tail-turret prototype for He-177:
(http://www.kolumbus.fi/staga/hl131.jpg)
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YB40 was the gunship version of the B17.
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Originally posted by Tony Williams
I don't doubt that was the impression from inside because firing the gun would have given quite a jolt to the plane. However, when you compare the weight x velocity of the shell with the weight x speed of the plane, you'll realise that the plane had about 300 times the momentum of the shell. So firing the gun would have had a negligible effect on the plane's speed.
My Father ferried a brand new B-25H from Savannah, Georgia to Nadzab, New Guinea. The other pilot was a man name Charlie Knight, my father's best friend through all of pilot training. My father went into the 345th BG/501st Sq, which was equipped with C/D models. Charlie went to the 500th which was equipped with G/H models (75mm).
My father's memory is that Charlie told him shooting the big gun dropped the airspeed about 10-15 mph on a "gun run" against shipping. He said this would be with several shots fired.
Charlie did not survive the war. He launched as a "weather ship" into stormy skies with low cielings prior to a mission. He did not return. His aircraft was found crashed in the New Guinea jungle after the war.
Charlie Knight.
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Originally posted by Toad
My father's memory is that Charlie told him shooting the big gun dropped the airspeed about 10-15 mph on a "gun run" against shipping. He said this would be with several shots fired.
Charlie Knight.
I've no argument with that - the cumulative effect of several shots in quick succession would certainly be noticed. I was merely responding to the old myth that the plane stopped in midair whenever it fired :)
Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/