R.A.F. main fighters gun convergence

Discussion in 'Weapons Systems Tech.' started by greybeard, Sep 16, 2012.

  1. greybeard

    greybeard Member

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    Please, I would know values of convergence (or harmonization) for machine guns and cannons of main British WWII fighters (Hurricane, Spitfire).

    Thank you very much,
    GB
     
  2. stona

    stona Well-Known Member

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    #2 stona, Sep 16, 2012
    Last edited: Sep 16, 2012
    Originally it was 400 yards,though I've not seen an original reference for this. This had been reduced to 250 yards by the BoB

    Here's what Dowding had to say,

    "A great deal of discussion took place before and in the early stages of the war as to the best method of harmonisation of the guns of an 8-gun fighter: that is to say the direction, in relation to the longitudinal axis of the aircraft, in which each gun should be pointed in order to get the best results.

    There were three schools of thought. One maintained that the lines of fire should be dispersed so that the largest possible “beaten zone” might be formed and one gun (but not more than one) would always be on the target. The second held that the guns should be left parallel and so would always cover an elongated zone corresponding with the vulnerable parts of a bomber (engines, tanks and fuselage). The third demanded concentration of the fire of all guns at a point.

    Arguments were produced in favour of all three methods of harmonisation, but in practice it was found that concentration of fire gave the best results. Guns were harmonised so that their lines of fire converged on a point 250 yards distant: fire was therefore effective up to about 500 yards, where the lines of fire had opened out again to their original intervals after crossing at the point of concentration."

    Steve
     
  3. davebender

    davebender Well-Known Member

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    That's fine for shooting enemy infantry. It doesn't work when shooting WWII era aircraft with a .30cal MG. You need dozens of hits to kill a fighter aircraft and a hundred or more to kill a bomber.

    You can afford a larger "beaten zone" when firing 20mm cannon as even a single shell will cause significant damage.
     
  4. Airframes

    Airframes Benevolens Magister

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    Which is why this system was not used, the harmonisation at 250 yds being preferred instead.
     
  5. Shortround6

    Shortround6 Well-Known Member

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    THe British may have compromised. There are some diagrams in Anthony G. Williams and Emmanuel Gustin's book "Flying Guns World War II" that show several impact patterns, both for the 8 gun Spitfire and the two 20mm and four .303 They are superimposed on a silhouette of an He 111 to give a bit of perspective. What individual pilots or squadrons did was sometimes another matter.
     
  6. stona

    stona Well-Known Member

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    I'll go with Dowding and the men that flew eight gun fighters in combat for real.

    ".....in practice it was found that concentration of fire gave the best results."

    My italics. Not in theory,in practice. Hence harmonisation at 250 yards. I have read accounts in which some individuals claim to have harmonised their guns at much closer range.

    Cheers

    Steve
     
  7. Shortround6

    Shortround6 Well-Known Member

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    The compromise may have been that while the guns all crossed the sight line at a given range ( or close to it) they may not have done so at the same height. Also while 250yds may have been the preferred distance during/end the BoB that still leaves almost 5 years of war for somebody to have the bright of idea of changing back, if not 400yds then some other distance with the guns at different heights. I beleve the diagrams in the book were copied from official publications.
     
  8. stona

    stona Well-Known Member

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    Yes,Dowding was specifically referring to an eight machine gun armament. What was done later with mixed or cannon armament might have been different.

    Steve
     
  9. greybeard

    greybeard Member

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    Thank you very much for prompt replies.

    Indeed, it seems the question of harmonization of the eight .303 caliber early during BoB, from 400 to 250 yards, is the sole datum left about RAF fighter gun boresighting. On the contrary of USAAF and US Navy, not to mention German Luftwaffe, whose manuals (specific as well as part of pilot's one) detail gun convergence, it looks British didn't have any official guidance.
     
  10. Greyman

    Greyman Active Member

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    Point form:

    Sep 1938 - harmonised to a point 350 yards ahead --- 'concentrated pattern'
    c.Sep 1939 - harmonised to a large box pattern 400 yards ahead --- 'horizontal harmonization' (British Forces in France continued to harmonise to a point 350 to 150 yards ahead, depending on Squadron)
    c.Dec 1939 - two squadrons switch to a large circular pattern 200 and 400 yards ahead --- 'circular harmonization'
    Jan 1940 - ten squadrons switch to concentrated pattern
    Feb 1940 - full RAF switch to concentrated pattern
     
  11. greybeard

    greybeard Member

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    Thanks Greyman! Oddly, this seems to confirm how data were dispersed and fragmented. Again, it looks there weren't official manuals and entire matter relied on individual squadron's philosophy. Documents like US AAF Manual 200-1 or US Navy Technical Note F-43, not to mention related section of single flight manuals like P-47, P-38, P-51 ones, look missing for RAF. At this point would miss just some sort of "official" confirmation that the matter was really "unofficially" dealt. If so, though, would be a pity for historians, left without solid elements to study tactics and their effectiveness.

    S!
    GB
     
  12. Shortround6

    Shortround6 Well-Known Member

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    There are hints that such documents exist. Again I refer you to "Flying Guns World War II" and the diagrams I mentioned. they seem to be copies of official publications. One set of diagrams has "H.Q.F.C. , A.S.I. Part I,Section B, Leaflet 6 A." running down the side and is a diagram of gun groups from a Spitfire Vb against a Heinkel 111 at 5 different ranges.
     
  13. greybeard

    greybeard Member

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    Thank you Shortround!

    Unfortunately, I've not the book you mentioned. I note, though, it gives hint of an official document. Also, I think I missed last statement by Greyman, about "full RAF switch to concentrated pattern", which should mean they all harmonized to 350 yards from February 1940 onward (although I'm skeptic this could be true for all fighters, with all kind of weapons). Would be useful to know his source.

    I think it's curious that there's lack of these publications in any form on the internet; I can find plenty of flight manuals about British fighters, but none that I know reports a "gun convergence" section. Maybe there was an unique official guidance, but so far none made it public, seemingly. Could it be still classified? Or maybe I'm too inquisitive?
     
  14. Greyman

    Greyman Active Member

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    There are definitely official RAF publications with regards to gun harmonisation out there. Just not a lot of information on the internet. It's something I am certainly working on. :)

    When I said 'full RAF switch to concentrated pattern' I meant the eight-gun fighters (and 250 yards was the directed range, though many had them converge closer).
    Naturally this wasn't so for every fighter. For example, Blenheim fighters still harmonised their guns to 250 yards but convergence wasn't necessary and the weapons in the gun pack simply pointed parallel. The wing gun couldn't be altered and still had to converge all by its lonesome in front of the aircraft at 400 yards. Early cannon Spitfires could only converge at a minimum of 300 yards, and the outer guns of early (and perhaps all) cannon Hurricanes to 400.

    The FAA had their own separate path with regards to gun harmonisation and found that while their Fulmars had just as good or better success with a concentrated pattern, their losses to defensive fire were much higher.

    Sometime in 1942 the RAF appears to have switched to 'spread pattern', which introduced a very slight spread pattern to all of their fighters. This seems to have persisted until the end of the war.
     
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