Effect of the debugged in tim for the BoB?

Discussion in 'Aviation' started by wuzak, Nov 7, 2014.

  1. wuzak

    wuzak Well-Known Member

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    #1 wuzak, Nov 7, 2014
    Last edited: Nov 7, 2014
    What would the effect of having a reliable Hispano 20mm cannon with belt fed ammo in Spitfires and Hurricanes in time for the BoB?

    The Spitfire's performance my be degraded against the Bf 109, but would that be outweighed by the damage the 20mm could do on the bombers?
     
  2. stona

    stona Well-Known Member

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    It's a fine balancing act.

    Initially one might suspect that the damage inflicted upon the bombers would be greatly increased.

    In November 1939 Dowding wrote that he estimated as many as 300 .303 strikes would be required to bring down an He 111. About a year later he received an anonymous letter (dated October 3rd 1940) via the RAF Staff College at Andover. It quoted the opinion of an anonymous "test pilot who was attached to a squadron and bagged four huns." The opinion would have reinforced what Dowding already knew, that the existing armament was good for destroying fighters but "is rapidly becoming obsolete for use against enemy [bomber] formations."

    The maths doesn't make happy reading. A two second burst from eight .303 machine guns will deliver about 300-320 rounds down range (assuming about 1100-1200 r/min for each gun). If Dowding's estimate of 300 to down a bomber is even close then a fantastically high standard of marksmanship would be required to shoot down a bomber in one firing pass, and one pass is all the attacking pilot might get.

    There is no doubt that a 20mm cannon would have inflicted more damage on the Luftwaffe's bombers. The fundamental problem that the change in armament cannot address was the inability of most pilots to hit anything, whatever weapons they were equipped with.

    RAF scoring can be misleading. The system of giving fractional scores means that a substantial percentage of pilots (nearly 40%) have at least some sort of credit, two halves appear to be one whole in the statistics, but only about 15% claimed a whole aircraft in one go so to speak.
    221 of the Luftwaffe aircraft shot down in aerial combat during the battle were shot down by just seventeen pilots.

    The competent pilots would surely have scored more highly if armed with cannon, but the rest would probably have done no better. The damage inflicted on Goering's precious bombers would have been increased, but maybe not as dramatically as it might first appear.

    Cheers

    Steve
     
  3. Shortround6

    Shortround6 Well-Known Member

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    It is not a question of " may be degraded" but how much. And the question isn't really speed but climb rates. Climb rate being the easiest thing to measure and climb rate being an indication of surplus power. Surplus in the sence ot it is the power you have to either maintain speed in a turn at lower than max speed or to maintain height in a turn at a given speed.

    It also depends on how many of the .303s you are willing to give up.

    two 20mm with 240 rounds of ammo weighs 444lbs. The 240 rounds weigh 150lbs so cutting ammo to 90 rpg only saves about 38lbs.

    The eight .303s with 350rpg ( Spit MK II) weigh 439.5lbs. Taking out four will save about 220lbs

    So what effect will about 220-225lbs have on climb? Not much at sea level but at 25,000ft?

    It may be minor.
     
  4. gjs238

    gjs238 Well-Known Member

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    Effect of the .50 BMG on the BoB?
     
  5. stona

    stona Well-Known Member

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    .50 calibre machine guns were considered before the war. Tizard wrote that 'everyone' was for developing it without specifying who everyone was. It did not include Dowding, who wrote that tests (with a Vickers not a Colt) had shown that it could not penetrate armour plate. No mention is made of the ammunition used in the tests. This was the last chance for adoption of a .50 calibre machine gun before the war.

    In August 1940 tests at Farnborough confirmed that a 20mm cannon was a far more destructive weapon than the .50 calibre machine gun, and from then on the RAF was always going to adopt cannon.

    Cheers

    Steve
     
  6. wuzak

    wuzak Well-Known Member

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    Sorry, I mean th Hispano, but I can't change the title now.
     
  7. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The .50 BMG prior 1940 (or prior 1941?) have had he RoF of some 600 rpm, vs. 800 later in the war. The AP ammo introduced in 1943, a copy of the Soviet projectile, was far better than the earlier ammo. In aggregate, the BMG used in 1944 was a far more formidable weapon than in 1939/40.
     
  8. Shortround6

    Shortround6 Well-Known Member

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    The US also changed the .50 cal ammo at some point in the late 30s. Not just as to the type of bullet referred to by Tomo (which came later) but they increased the velocity by almost 400 FPS.

    M1 ball had a MV of 2500fps while M2 Ball and velocity of 2850-2900fps depending on source barrel length. WHEN the British did their tests and with what ammo make make a lot of difference to their choices.
     
  9. stona

    stona Well-Known Member

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    The test with the Vickers which Dowding referred to was shortly after it was introduced, so 1933/34.

    Ralph Sorley, who was largely responsible for the adoption of the eight gun fighter, essentially decided that the greater range and hitting power of a .50 calibre machine gun (Vickers or Colt) was outweighed by the lighter weight and greater cyclic rate of the .303 Browning.

    Sorley wrote of the Colt .50 that "although it possessed a better hitting power, the rate of fire was slow and it was a heavy item of installed weight and ammunition."

    He conceded that .50 calibre gun was attractive from the point of view of relative hitting power but a major deficiency was that it "did not lend itself to the rapid build up of lethal density within the limits of weight which could be allowed for such a fighter [meaning the new monoplanes to become the Spitfire and Hurricane] at such a time"

    It's the old weight of fire versus rate of fire conundrum. The Air Ministry was somewhat obsessed with the very limited time it expected a fighter to have to deliver a lethal blow. Two seconds became something of a benchmark and Sorley knew that you couldn't mount enough .50 calibre guns in the wings of the first generation monoplane fighters to resolve that conundrum. In the absence of a suitable cannon the eight .303 calibre machine guns was really the only option

    Sorley wrote later, with disarming honesty, that the question of an appropriate gun for the RAF's interceptor fighters was "something of a nightmare during 1933-34"

    Cheers

    Steve
     
  10. gjs238

    gjs238 Well-Known Member

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    I understood the topic of the thread, but was suggesting that perhaps the .50 BMG could have been adopted earlier than the 20mm Hispano - in time for BoB.
     
  11. Shortround6

    Shortround6 Well-Known Member

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    At that time (1933-34) he was certainly correct. The Big Browning only even hitting 600rpm with short belts of ammo. Long Belts slowed it down. While it's bullet was heavier than the .5in Vickers it didn't have the big velocity difference it would later have. And the Ammo, if anything, was slightly heavier than the later ammo. Bullet was about 43 grains heavier (2.8 grams) while the powder charge was only about .67 grams lighter. Not much but about 200 grams per 100 rounds.
    And that is for Ball or AP. Tracer and Incendiary bullets were even lighter.
     
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