Why so few planes that fired thorugh the propeller hub?

Discussion in 'Aviation' started by Rufus123, Sep 17, 2013.

  1. Rufus123

    Rufus123 Member

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    I am going to guess that many plane designs do not work will with this set up?

    Was it the inverted V that got it to work on the 109?

    Would this have worked on a Spitfire or would it require too many design changes? Would it work on a Mustang?
     
  2. GregP

    GregP Well-Known Member

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    #2 GregP, Sep 17, 2013
    Last edited: Sep 17, 2013
    Most V-12 engines were very simply not designed with the ability to shoot through the V even considered by a designer.

    Wouldn't work for a Merlin or Griffon and would only work for the Allison if it were an "E" series engine with a driveshaft.

    Definitely not a possibility for radials ...

    In fact, it was abnormal for a WWII fighter.
     
  3. Shortround6

    Shortround6 Well-Known Member

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    You have to design the engine from the start to have clearance for the gun or gun tube ( the receiver is ALWAYS behind the engine). Otherwise there is just too much stuff in the way. The prop shaft has to be the right distance from the crankshaft which affects the size of the reduction gears and the reduction gear case ( part of which is usually part of the crankcase casting). Intake manifold may or may not allow room, this may be the easy part. Accessories and supercharger have to be placed to allow room for the gun. Picture of Hispano V-12:

    hs12y2.jpg

    Germans mounted superchargers on the side of the engine to free up space at rear of engine.

    trying to add it at a later date requires changing some fundamental parts of the engine.
     
  4. Aozora

    Aozora Well-Known Member

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    Just off the top of my head the only engines able to accommodate centre-line weapons were:
    DB 600 series
    Jumo 211 213 series
    Hispano-Suiza 12Y series
    Klimov M-105 series (derivatives of 12Ys)
    Some Allison V-1710s

    Can't think of any other important, production engines.
     
  5. Shortround6

    Shortround6 Well-Known Member

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    the Allison didn't really accommodate the gun in the engine but used an extension shaft to allow the gun to be placed between the propeller/reduction gear and the engine.

    At least one Italian engine and one model of the Ranger Inverted V-12 were arranged to have the gun on the outside of the V with the reduction gear made large enough to allow the Prop shaft to line up with outside of the crankcase. Can't find the proper picture right now but:

    Unknown-6.jpg

    Imagine gun mounted to top of engine with prop-shaft raised to take the barrel. Of course the increase in frontal area tends to put a damper on the idea.
     
  6. wuzak

    wuzak Well-Known Member

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    This shows why the Merlin couldn't have a hub cannon.

    http://www.digitalcombatsimulator.com/images/mustang/mustang-7.jpg


    With regards the Ranger, for the hub cannon (in the XP-77, for example) to be mounted the reduction gear and prop shaft were above the crankcase (teh Ranger being inverted), so about as far away from the centre of are of the engine as possible.

    This shows layout for an "improved" XP-77 with a 37mm cannon in place of the 20mm...

    http://d1kqib0uq4v1gs.cloudfront.ne...mproved-bell-xp-77/improved-bell-xp-77-04.jpg
     
  7. davebender

    davebender Well-Known Member

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    Fighter aircraft built in France, Germany and Soviet Union which were powered by V12 engines had hub cannon. That's three major aircraft producers.

    USA didn't believe in cannon, hub or otherwise. Not much point in having a hub mounted M2 .50cal MG.

    Except for Ki-61 all Japanese fighter aircraft were powered by radial engines.

    Italy was in similar position until they began license production of DB601.

    Britain is the real puzzle. They could have required RR Merlin and RR Griffon engines to be designed for a hub cannon. Then Spitfires could have centerline mounted weapons similar to Me-109. An arrangement many RAF fighter pilots considered superior to wing mounted weapons. After RR Merlin engine development began it's too late to change specifications. You fight with what you developed during peacetime.
     
  8. Aozora

    Aozora Well-Known Member

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    #8 Aozora, Sep 18, 2013
    Last edited: Sep 18, 2013
    Why should Britain be a puzzle simply because it didn't necessarily follow a small contingent of countries that made provision for centreline cannon? The USA didn't demand that Allison design the V-1710 for hub cannon. The only pre-war German fighters to use hub mounted weapons were a few 109 prototypes with the 109s only regularly adopting centreline cannon with the advent of the F series in late 1940. When Japan did get the DB 601 none of the fighters designed around the licence-built variations used hub cannon. In fact the only country adopting such weapons as a matter of policy during the 1930s was France - Russia followed once it adopted and adapted the French 12Y into the Klimov series.

    To require Rolls-Royce to design the Merlin and Griffon for hub cannon would have meant throwing away everything that had been learned about the rear mounted supercharger in order to design a completely new side mounted system (possibly with the help of the French). This would then have led to protracted and probably even more problematic development of the Merlin, higher costs, and a possibly inferior supercharger - all to facilitate a centreline cannon which wasn't a part of RAF policy of the time, apart from some experimentation with spec F.10/27.
     
  9. wuzak

    wuzak Well-Known Member

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    Why the French?

    As far as I can tell, the Hispano didn't have a side mounted supercharger - just a small one.
     
  10. davebender

    davebender Well-Known Member

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    A rational decision. However IMO it wasn't a good decision as a centerline mounted 20mm cannon has such an advantage over wing mounted weapons.
     
  11. wuzak

    wuzak Well-Known Member

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    When Rolls-Royce designed the Merlin did the RAF have a cannon worthy of the name?
     
  12. davebender

    davebender Well-Known Member

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    Germany had no 20mm aircraft cannon worthy of the name when Daimler-Benz began designing DB601 engine. That didn't prevent them from planning for a future when aircraft cannon might become important.
     
  13. Jabberwocky

    Jabberwocky Active Member

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    False.

    The US military establishment officially recognised the necessity of using cannon on aircraft as early as 1936. It sent research groups to Europe to see what was being done there and began work on its own cannon. The USAAF actually ordered 40,000 20 mm cannon before Pearl Harbour.

    The US used 37 mm and 20 mm cannon in its fighter aircraft during the war, they just bollocked up the designs, meaning they were forced to rely on the M2 as their primary armament. The US also tested aircraft with the 23 mm Madsen and various 20 mm Oerlinkon designs. Then there were the four different .60 (15.25 mm) and four different .90 (23mm) cannon tested and eventually discarded during the war.
     
  14. Marcel

    Marcel Well-Known Member

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    In Finland they had machineguns mounted inside a Brisol Mercury engine, firing through the propellor. And these were radials. This was on Fokker D.XXI's
     
  15. Aozora

    Aozora Well-Known Member

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    I doubt whether the advantages of having a centreline cannon would have outweighed the problems inherent in having to design a new supercharger system, when there was already such a deep fund of knowledge that had been built up over years of experience in designing and running high powered aero engines. Why create new risks and further impede the development of the Merlin based on the hope that some time in the future a cannon suitable for the installation would emerge? Experience with the 12Y and derivative engines shows that the small, side mounted supercharger wasn't nearly as efficient or capable of future development as Rolls-Royce's, and it was the supercharger that was central to the Merlin's success.

    Both Daimler-Benz and Junkers were designing their engines and superchargers from scratch at huge expense, and it still took years of headaches and development before the installation of a centrally mounted cannon was perfected. It is significant that Japan and Italy used variants of the DB 601/605 series yet did not adopt central cannon, indicating that making such an installation work, even with an engine designed to have central cannon and with a fund of experience from the Germans, was not as easy as you would like to believe.

    Rifle calibre machine guns yes, but there was no possibility of mounting anything bigger to fire between the cylinder banks without creating some serious engineering problems.
     
  16. stona

    stona Well-Known Member

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    Not proven, not provable so that's just what it is........your opinion.
    The RAF's cannon armed fighters did just fine without a centreline weapon. That's weapon, singular, by definition.
    Cheers
    Steve
     
  17. Shortround6

    Shortround6 Well-Known Member

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    If you use a 9 cylinder radial it is quite possible to run barrels or blast tubes or bullet channels between the cylinders. this was done of the Gloster Gladiator for one:

    50-gloster-gladiator.jpg

    and Fokker 21

    http://www.dutch-aviation.nl/pictures/Fokker/Military/Fokker D21 with Bristol Mercury engine.jpg

    BUT the guns still need to be synchronized. And it is quite a bit different than firing though the propeller hub.

    With a 14 or 18 cylinder radial this possibility goes away.

    DaveBender
    The French started the through the propeller cannon idea in WW I with a 37mm cannon (single shot) through the prop hub of a Few Hispano V-8 powered fighters. The French were the major proponents of this during the 20s and early 30s. However NOBODY had a good aircraft cannon during this time. The first German aircraft cannon during the 30s was a large, heavy, powerful weapon with a low rate of fire. Perhaps it was not worthy of the name when Daimler-Benz began designing DB600 engine or Junkers began designing the Jumo 210 but the idea was certainly there and NO, they were not allowing or planning for the future 6-7 years down the road. They were trying to run simultaneous programs but the relative failure of the first gun sent them to fall back positions.
    The First French fighters in the 1930s to use 20mm guns in the prop hub (the Dewoitine D.501 with fixed landing gear) used Hispano licensed Oerlikon FF S guns called Hispano H.S. 7. These had a lower rate of fire than later 20mm guns and the first HS 404 guns had a rate of fire of just 400 rounds per minute. Designing an engine around one of these guns as the primary armament of the fighter took a lot of faith. 1000hp engines of the time provided ONLY enough power for ONE cannon and 2-4 Machine guns. The cannon didn't really mature until 1938-39 and even then???
    The Germans don't get the through the hub gun to really work until 1941. Even MG 17s having trouble with over heating forcing the installation of wing mounted guns to get acceptable fire power.
     
  18. davebender

    davebender Well-Known Member

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    That's to be expected when an airforce starts from scratch during 1935.

    If Germany had army and navy air services operating throughout 1920s (i.e. similar to most other nations) I suspect hub cannon technical problems would have been solved long before 1941.
     
  19. Aozora

    Aozora Well-Known Member

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    Theoretical and unprovable - it's also possible that had the Germans had air services operating through the '20s the development of their aero engines and other technologies would have gone in a completely different direction. In fact, more than likely, they would have been as war weary and bankrupt as the other major powers, so that their air services would have been just as poorly funded and forced to use left-over WW1 technology for years afterwards.
     
  20. Shortround6

    Shortround6 Well-Known Member

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    #20 Shortround6, Sep 19, 2013
    Last edited: Sep 19, 2013
    You expect wrong and you don't listen or read. The German air force did NOT start from scratch in 1935.

    That is a misconception you have being either believing or trying to foist off for quite a period of time.

    The Luftwaffe had hundreds of aircraft IN SERVICE in 1934. They started design and construction of aircraft in 1932-33 if not before. The Dornier F first flew May 7th 1932, it was renamed the Dornier 11 in 1933 and the first production examples were completed in late 1933. In Oct 1933 they established an auxiliary bomber group. By March 1st 1934 the auxiliary bomber group had only 3 Do 11s due to late delivery of engines to Dornier but had 24 Ju 52/3e bombers.
    The Arado 65a prototype fighter first flew in 1931, the Arado 65d first flew in 1932 and production models (65e) were being delivered in 1933.
    Heinkel had a number of designs in production before 1934. I have listed them before but you chose to keep repeating the claim that the Germans didn't even start to re-arm until 1935. A very easily refuted form of revisionism.

    The Luftwaffe issued a requirement for a fighter armed with either one cannon or two machine guns in 1932. Once again work did NOT start in 1935.
     
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