Bristol Hercules prior BoB: how much was in use, and what variants?

Discussion in 'Aviation' started by tomo pauk, Nov 4, 2013.

  1. tomo pauk

    tomo pauk Creator of Interesting Threads

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    As title says - I'm interested in the service use of different variants of Bristol Hercules engine in the early ww2. A good info is appreciated :)
     
  2. Shortround6

    Shortround6 Well-Known Member

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    Very little operational use. A number of prototypes flew with them but first Short Stirlings in an operational squadron don't show up until Aug 1940 and then the factory was bombed stopping production. First 'service' use of Beaufighters is after the BoB. First use of Wellingtons with Hercules engines is in 1941. 4 Saro Lerwick flying boats were in use in 1939.

    Hercules II had a single speed supercharger, gave 1300hp for take-off and 1375hp at 4,000ft. Depending on source it went from around 1700 to 1800lbs. Rated on 87 octane fuel-max boost 3.25lbs.
    Hercules III had a two speed supercharger, gave 1375-1400hp for take-off and 1375-1410hp at 2,750ft and 1250hp at 16,750ft (?)

    Many sources to not quite agree. The Hercules III could be run on 100 octane fuel but the power ratings changed very little. The Big change came with the Hercules VI engine.

    Problems with Hercules production led to both The Beaufighter and Wellington being produced with Merlin engines until production got sorted out.
     
  3. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Thanks for the feedback :)
     
  4. merlin

    merlin Member

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    The Saro Lerwick first flew in the autumn of 1938.

    I used to think that the altitude problems with the Hercules could have been sorted, if they had just put in the supercharger that was used on the Bristol 138 (high altitude) test aircraft. Then I read that they did (can't find the quote), but had problems - surging I think. The problem though was Fedden's obsession with 'snail volute' rather than 'turbine entry' - once that that was incorporated i.e. '100' fine.

    So, there is scope for that to be sorted earlier, yet perhaps an alternative should have been required - just in case e.g. double-row Pegasus or double-row Tiger. Is there anything else - that could have been utilised with a delayed Hercules apart from what happened OTL??

    Comments please
     
  5. Shortround6

    Shortround6 Well-Known Member

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    The supercharger on the Bristol 138 was a two stage and the second stage was remote from the engine and was not even engaged until the plane was flying at over 30,000ft. Most of these companies did NOT have multiple design staffs. Only a few projects could be worked on at a time without ALL the projects slowing down.
    Bristol could build Hercules engines in very small numbers for prototype aircraft. They could NOT make satisfactory sleeves (engines that would last more than a few dozen hours without oil consumption (and oil fouled plugs) ) going through the roof in large numbers, like even several dozen engines per month.

    A two row Pegasus is a different class of engine, more equivalent to a Wright R-3350 or Bristol's own Centaurus (originally type tested in 1938?) while the Tiger (already a double row engine) needed a total redesign to become a viable engine even in 1939/40.
     
  6. merlin

    merlin Member

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    Yes, oops with the Tiger, ironically the only alternative to the Hercules at the time OTL was the Vulture - though it may be more akin in power to a theoretical Double-row Pegasus. While the Vulture was killed off, complete success with the Hercules took more years!!
    The only other alternative, I can think of is the Deerhound, but that might prove worse with cooling problems!!
    Whilst, Alvis were able to build some French engines, those probably wouldn't be suitable, is there any suitable US engines that could be built in the UK (and by who - Armstrong) - that would give an earlier in service date!
     
  7. wuzak

    wuzak Well-Known Member

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    Vulture was in a different power class to the Hercules, and somewhat heavier.

    The Deerhound was redesigned twice before it was cancelled. The redesigns did, I believe, largely solve the cooling problems, but otherissues remained. Plus they had only built a handful of engines before the axe fell - it was never going to be ready in the timeframe.
     
  8. Shortround6

    Shortround6 Well-Known Member

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    The only real possibility is the Wright R-2600 which was compatible in size and weight and was used/proposed as an alternative for a number of Hercules powered aircraft. However there are two versions which interest us here, the 1600 hp version (first used in 1938 at 1500hp in the Boeing 314 Flying boat) and the 1700 hp version which doesn't become available in numbers until the summer of 1941. The first used an aluminium crankcase and the second one a steel crankcase so it is more than just dumping British 100 octane in the tanks, winding it up another 100rpm and opening the throttle to allow more boost.

    The Wright R-2600s weren't know for their altitude performance either though.
     
  9. merlin

    merlin Member

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    Wuzak:

    Deerhound work was stopped when their factory was bombed in 1941.

    Shorthound6:

    Interesting about the Wright R-2600, (curious that it and the Hercules both powered flying boats), that'll be the one that was used for the A-20 - a mainly tactical bomber.

    So, both the early Hercules R-2600 are good for low medium altitude - so flying boats and tactical medium bombers are ok, but not too good for fighters or heavy-bombers e.g. OTL Stirling!?
     
  10. wuzak

    wuzak Well-Known Member

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    At which time it was nowhere near production ready. If the MAP didn't axe the program it would surely have recommenced after the bombing?

    And it may be that Armstrong-Siddeley were moved onto gas turbine work at that time. I'm not certain of that.
     
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