Convergence of fire
Fri May 27, 2011 10:53 am
OK...time to educate Mudge again.
This question is about the convergence of fire from a fighter. Is the convergence point preset at the factory when the gun bays are installed or are there adjustments that can be made to the guns to give the pilot the option of where he wants the convergence point to be?
Mudge the educable
Yes, I know. That's a pretty long sentence.
This question is about the convergence of fire from a fighter. Is the convergence point preset at the factory when the gun bays are installed or are there adjustments that can be made to the guns to give the pilot the option of where he wants the convergence point to be?
Mudge the educable
Yes, I know. That's a pretty long sentence.
Re: Convergence of fire
Fri May 27, 2011 11:17 am
The gun's could be adjusted in the field to each pilots whims. Some liked them to converge close in while others liked them a bit farther out.
Re: Convergence of fire
Fri May 27, 2011 12:51 pm
Thanks. Kinda' figured that. Just needed to be reinforced. 
Mudge the further educated :d
Mudge the further educated :d
Re: Convergence of fire
Fri May 27, 2011 2:50 pm
Like this.
The caption said to plug your ears.
I'm sure Jack can find a better one.
The caption said to plug your ears.
I'm sure Jack can find a better one.
Re: Convergence of fire
Fri May 27, 2011 3:02 pm
The night time ones are pretty demonstrative.
Re: Convergence of fire
Fri May 27, 2011 3:02 pm
Re: Convergence of fire
Fri May 27, 2011 5:37 pm
Two part answer - most (all?) 'fixed' aircraft guns have some sort of adjustment of line of fire built in.
Look up 'Dowding Spread'. - Most fighter pilots couldn't hit the proverbial barn door, so policy and rules in the 1940 era were for the multiple guns to give a shotgun effect. More skilful shooters - initially informally, later officially - set their gun harmonisation to a particular personally preferred point. However with wing guns, there would always be a closer area of convergence and a further area of divergence, as well as issues from aim due to wing flexing during high-g manoeuvring in combat (unanticipated in the 1930s, attacks being expected to be straight-line slashing attacks). That's one key reason for the preference of fuselage mounted guns that were firing down or near the axis of flight - P-38, P-39 etc, as well as being able to mount (bigger) guns and ammunition at all. The Spitfire's initial eight gun wing was, frankly, a bodge job, compared to the more normal single gun bay of many other fighters of the era, like the Hurricane. This was a weakness in an otherwise excellent fighter, and I'm not aware of any other fighter having a single gun set so far out on each wing.
Hope that helps!
Look up 'Dowding Spread'. - Most fighter pilots couldn't hit the proverbial barn door, so policy and rules in the 1940 era were for the multiple guns to give a shotgun effect. More skilful shooters - initially informally, later officially - set their gun harmonisation to a particular personally preferred point. However with wing guns, there would always be a closer area of convergence and a further area of divergence, as well as issues from aim due to wing flexing during high-g manoeuvring in combat (unanticipated in the 1930s, attacks being expected to be straight-line slashing attacks). That's one key reason for the preference of fuselage mounted guns that were firing down or near the axis of flight - P-38, P-39 etc, as well as being able to mount (bigger) guns and ammunition at all. The Spitfire's initial eight gun wing was, frankly, a bodge job, compared to the more normal single gun bay of many other fighters of the era, like the Hurricane. This was a weakness in an otherwise excellent fighter, and I'm not aware of any other fighter having a single gun set so far out on each wing.
Hope that helps!
Re: Convergence of fire
Fri May 27, 2011 9:48 pm
The 12-gun Hurricanes also had two pairs of guns far outboard of the main battery.
August
August
Re: Convergence of fire
Fri May 27, 2011 10:17 pm
Re: Convergence of fire
Sat May 28, 2011 12:13 am
I'm not aware of any other fighter having a single gun set so far out on each wing.
The F4F-4 had a seperate gun outboard of the main wing guns, although not nearly as far out on the wing as the Spit or 12-gun Hurris.
SN
Last edited by Steve Nelson on Sat May 28, 2011 3:16 am, edited 1 time in total.
Re: Convergence of fire
Sat May 28, 2011 1:17 am
Thanks August, Steve. Perhaps I should've said "I'm not aware of any other fighter having a single gun set so far out on each wing, although I'm sure other WIX members will provide endless examples shortly." 
Beyond my blushes, and avoiding quibbles, the point was that a designer was aiming to provide an 'adequate' weight of fire in the late 1930s to overcome early armour and the level of robustness that stressed skin construction offered. The Mk.XII Hurricane was a classic example of 'adding a bit' to the existing best compromise (the RAF's 'eight gun fighter'*) of multiplying rifle calibre guns rather than going for fewer heavier calibre cannon or machine guns. The twelve gun wing was supplanted by the four cannon setup and never saw the use anticipated. (As a side note, the prototype Hurricane was actually fitted in early stages with two fuselage guns either side of the cockpit - I believe as part, not whole armament. Additionally anything firing through the arc of the propeller** requires an interrupter gear, which added weight, complexity and a reduction in firing rate.) The Hurricane's two four gun bays just outboard of the propeller offered two 'blocks' of fire, which didn't hosepipe under manoeuvring as the wing was thick and rigid. The Spitfire's wing was a remarkable design, but the guns certainly seemed like an afterthought (IIRC, the eight gun specification was arrived at during both type's gestations - comment welcome) and wing flex (I understand) as well as the gun's own spread made the fire less concentrated. Not to mention Mk.I/II Spitfires were more complex and time consuming to rearm and maintain the armament than Hurricanes; the Hurri having two hatches with several covers on the wing upper surface, the Spitfire having eight on the upper and four more - for ammunition on the underside.
The Continental approach favoured through prop-arc guns on the pilot's line of sight,sometimes through the prop hub (how much adjustment the through engine guns would have I don't know) while some countries - notably Germany, went for a mix of calibre including heavier cannon. Note that the Zero, while an advanced design in many other ways had a throwback element in having the breeches of two guns in front of the pilot - required in the Great War and 1920s when guns jammed regularly, hardly ever so in W.W.II.
James the footnotable,
* Designed to use up an awful lot of .303 calibre ammunition available, rather than upgrading - as happened later - to more effective .5 in or 20mm cannon.
** Not 'through the propeller', please.
Beyond my blushes, and avoiding quibbles, the point was that a designer was aiming to provide an 'adequate' weight of fire in the late 1930s to overcome early armour and the level of robustness that stressed skin construction offered. The Mk.XII Hurricane was a classic example of 'adding a bit' to the existing best compromise (the RAF's 'eight gun fighter'*) of multiplying rifle calibre guns rather than going for fewer heavier calibre cannon or machine guns. The twelve gun wing was supplanted by the four cannon setup and never saw the use anticipated. (As a side note, the prototype Hurricane was actually fitted in early stages with two fuselage guns either side of the cockpit - I believe as part, not whole armament. Additionally anything firing through the arc of the propeller** requires an interrupter gear, which added weight, complexity and a reduction in firing rate.) The Hurricane's two four gun bays just outboard of the propeller offered two 'blocks' of fire, which didn't hosepipe under manoeuvring as the wing was thick and rigid. The Spitfire's wing was a remarkable design, but the guns certainly seemed like an afterthought (IIRC, the eight gun specification was arrived at during both type's gestations - comment welcome) and wing flex (I understand) as well as the gun's own spread made the fire less concentrated. Not to mention Mk.I/II Spitfires were more complex and time consuming to rearm and maintain the armament than Hurricanes; the Hurri having two hatches with several covers on the wing upper surface, the Spitfire having eight on the upper and four more - for ammunition on the underside.
The Continental approach favoured through prop-arc guns on the pilot's line of sight,sometimes through the prop hub (how much adjustment the through engine guns would have I don't know) while some countries - notably Germany, went for a mix of calibre including heavier cannon. Note that the Zero, while an advanced design in many other ways had a throwback element in having the breeches of two guns in front of the pilot - required in the Great War and 1920s when guns jammed regularly, hardly ever so in W.W.II.
James the footnotable,
* Designed to use up an awful lot of .303 calibre ammunition available, rather than upgrading - as happened later - to more effective .5 in or 20mm cannon.
** Not 'through the propeller', please.
Re: Convergence of fire
Sat May 28, 2011 3:16 am
Interesting topic!
Speaking of the Wildcat, both the "solid wing" F4F-3 and later folding wing FM-2 only had two guns per wing. I'm not sure if the outer gun was deleted due to the difficulties you specify, or wheher it was decided that it just didn't add enough firepower to make it worthwhile.
I've always wondered why the later model Bf-109s didn't have internal wing guns. The E model had wing mounted cannons, but from the F on, the only built-in armament was a pair of cowl mounted machine guns and a cannon firing through the propeller hub. I guess it was reasoned that the wieght savings and structural simplicity gained by deleted wing armament was a good trade-off for the decreased fireower.
I think most, if not all, variants of the Zero had wing armament supplementing the cowl guns. The A6M2 had a 20mm cannon in each wing, and the A6M5 had a pair of wing mounted machine guns and cannon.
As you mention, it's surprising how long the "guns in the cockpit" approach hung on. Both the early P-40s and all p-39s had the gun breeches accessible to the pilot. I've also always wondered why the U.S. stayed with machine-gun only armament long after most other countries had switched over to (or added) cannon.
SN
Speaking of the Wildcat, both the "solid wing" F4F-3 and later folding wing FM-2 only had two guns per wing. I'm not sure if the outer gun was deleted due to the difficulties you specify, or wheher it was decided that it just didn't add enough firepower to make it worthwhile.
I've always wondered why the later model Bf-109s didn't have internal wing guns. The E model had wing mounted cannons, but from the F on, the only built-in armament was a pair of cowl mounted machine guns and a cannon firing through the propeller hub. I guess it was reasoned that the wieght savings and structural simplicity gained by deleted wing armament was a good trade-off for the decreased fireower.
I think most, if not all, variants of the Zero had wing armament supplementing the cowl guns. The A6M2 had a 20mm cannon in each wing, and the A6M5 had a pair of wing mounted machine guns and cannon.
As you mention, it's surprising how long the "guns in the cockpit" approach hung on. Both the early P-40s and all p-39s had the gun breeches accessible to the pilot. I've also always wondered why the U.S. stayed with machine-gun only armament long after most other countries had switched over to (or added) cannon.
SN
Re: Convergence of fire
Sat May 28, 2011 1:14 pm
Kinda interesting to note that the F8F was reverted to 4 .50 caliber machine guns, just like the earlier F4F's had in the war, due to the fact (and as I read somewhere recently) that the Japanese planes, without protective armor, were much easier to shoot down and therefore did'nt need as much lead on target to bring them down.
Mark
Mark
Re: Convergence of fire
Sat May 28, 2011 10:26 pm
My observation about the Hurricane was not an attempt to gotcha you James, I was just adding another example of a contemporary fighter with widely spaced guns.
As to the Bearcat, it isn't clear that 4 x .50 would have been adequate armament even against Japanese aircraft. Late-war Japanese fighters were not as fragile as their predecessors. The initial Bearcat armament was recognized as a shortcoming, thus the replacement by 4 x 20mm.
August
As to the Bearcat, it isn't clear that 4 x .50 would have been adequate armament even against Japanese aircraft. Late-war Japanese fighters were not as fragile as their predecessors. The initial Bearcat armament was recognized as a shortcoming, thus the replacement by 4 x 20mm.
August