Blenheim as a torpedo bomber?

Discussion in 'Aviation' started by tomo pauk, Jan 20, 2016.

  1. tomo pauk

    tomo pauk Creator of Interesting Threads

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    How good or bad idea is to modify the Blemheim into a torpedo bomber? What engines - low level Mercury, or Perseus? crew, gun armament?
     
  2. RCAFson

    RCAFson Well-Known Member

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    IIRC, the Bleinheim bomb load was 1000lb so using it with a 1600lb torpedo might be problematic.
     
  3. GrauGeist

    GrauGeist Well-Known Member

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    The Swordfish could carry a Mark XII torpedo, so why not?

    The Mark XII weighed 1,545 pounds and the max. load of the Blenheim was 1,200 pounds.

    As it turns out, the Beaufort Torpedo bomber was based on the Blenheim, so it was certainly considered.
     
  4. nuuumannn

    nuuumannn Well-Known Member

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    You might have a problem with undercarriage clearance, which would necessitate lengthening it, increasing the size of nacelles, then comes weight increases etc... It was almost done, actually; a torpedo carrier variant based on the basic Bristol 142 was drawn up.

    The Beaufort (and Botha) was built to Spec 10/36, which was actually a combination of two specs reworked, the first being for a land based torpedo bomber M.15/35 and a general purpose land based recon machine, G.24/35. To the former, Bristol submitted the 150, which was in effect a torpedo carrying Bristol 142, which became the Blenheim, but with mods for the different spec. These included a longer cabin and bomb bay to enable the torpedo to be carried internally, as well as local strengthening etc. It was to be powered by the 890 hp Perseus. To the latter the firm submitted the 149, basically a 142 that could carry larger and heavier loads.

    The Blenheim and proposed variants were designed by Frank Barnwell, and between the Blenheim and Beaufort there was little commonality, particularly after Leslie Frise at Bristol realised that both specs could be met by one design, and so forth the Beaufort was born. Initially however, it was intended that there was commonality - as was the case between the Beaufort and Beaufighter, but the Beaufort was altogether larger and could carry heavier loads than the Blenheim, so by necessity was a completely new aeroplane.
     
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  5. Juha

    Juha Well-Known Member

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    Not necessarily, the Finnish AF Blenheims could carry max 850 kg (1,874 lb) to 972 kg (2,143 lb) depending on the version.
     
  6. tomo pauk

    tomo pauk Creator of Interesting Threads

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    #6 tomo pauk, Jan 21, 2016
    Last edited: Jan 21, 2016
    Blenheinm I carried 1000 lbs of bombs, along with 2000 lbs (278 imp gals) of fuel. The Mk.IV upped the fuel to 3355 lbs ( 466 gals), while still retaining the high-altitude Mercury VIII engine (840 HP at 14000 ft).
    Mk.V ('Bisley') received the low-altitude Mercury XV (955 HP at 8500 ft), carrying same bomb load and fuel as the Mk.IV; some sources give also that engine, but with 905 HP (on 87 oct fuel?) for the Mk.IV .

    Max take off weight went from 12500 lbs for the Mk.I, to 15800 for Mk.IV, and finally 17040 for Mk.V. Tare weight (ie. no fuel, bombs, ammo) went from 8077 lbs -> 9790 -> 10775 for the Mk.V.

    So my idea is to trade the increase of fuel (and respective fuel tanks) and nose turret for torpedo load, obviously installing the low-level rated engine for better take of performance.

    edit: Hmmm, the Mercury XV was geared same as the VIII, the result of using greater boost via 100 oct fuel was increase of power down low.
     
  7. Shortround6

    Shortround6 Well-Known Member

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    The idea seems good to me, considering that the RAF had a total of 30 torpedo bombers in all of the British Isles in Sept 1939 (others were in the Colonies) and those were Vickers Vildebeests

    [​IMG]

    Most anything would be an improvement.

    Considering that some Blenehims were fitted with two external bomb racks for four 40lb bombs each behind the regular bomb bay
    [​IMG]
    Ground clearance may not be much of an issue, or fit longer tail wheel strut. Since the tail wheel doesn't retract this shouldn't be an insurmountable problem.
    There were medium supercharged Mercury engines, giving 830hp for take off and 890 hp at 6000ft on 87 octane fuel. Running the fully supercharged engines on 100 octane boosted take-off/low altitude performance without sacrificing higher altitude performance (in this case higher altitude being around 9000ft and up.

    The Converted Blenheim would NOT be as good as as the Beaufort being slower and shorter ranged. Defensive armament may not be as good either but it could be available in 1939-40 when the Beaufort was not. It might have also been shipped out to the colonies, ie Singapore to replace the Vildebeests there in Dec of 1941.

    Doctrine or RAF rules/regulations that might have prevented it include the pre-war prohibition of more than 38lb tyre pressure to prevent rutting of the grass fields while taxiing. This prevented designers from simply fitting the same size tire with more plys and using higher pressure to handle the load and instead forced the fitting of larger diameter/wider tires and wheels.
    Although fitting a slightly larger tire doesn't seem to have been a huge problem.

    [​IMG]

    The Blenheim gear being of the semi-retracting variety.

    [​IMG]

    Landing the plane while loaded might a problem however. The tube under each wing outboard of the engines are for the rapid dumping of fuel in the outer tanks. The Blenheim could take-off at higher weights than it was rated to land at and might require the dropping of the torpedo in an engine out emergency landing scenario, something the Blenheim was not very good at anyway.

    Blenheim was a bit of victim of it's own early success (fastest bomber in world in 1937?) and the same obsession with numbers that lead to 2000 Battles. It was good enough to serve/stay in production as is while better planes are designed and built (some of which failed) and the obsession with numbers and shortage of design staff (working on those better planes) meant whatever improvements the Blenheim saw were small and late. The MK V finally getting clamshell landing gear doors that not only fully enclosed the wheels but didn't add sq ft of extra drag when the landing gear was down like the "apron" style doors did, see engine out scenario.
     
  8. stona

    stona Well-Known Member

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    Which Service are you proposing this for? I always tend to lack at the practical issues :)
    Cheers
    Steve
     
  9. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Same costumer as for the Beaufor and ill-fated Botha - RAF.

    Thanks for pointing out that tidbit.

    Indeed, the 'medium superhcraged' being the Mk.XX for example. Looking at the power chart of it, the take off power on 100 oct fuel would amount to maybe 950 HP. The Mercury XII should do even better at 100 oct fuel, 1000+ HP for take off. Granted, availability of 100 oct fuel prior 1940 is not guaranteed, so better stick to 'conservative' boost.
    There was also the range of Perseus engines with good low-leve performance needed for torpedo bombers, Marks XIc, XIIc, XIVc, offering up to 890 HP for take off.
     
  10. Juha

    Juha Well-Known Member

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    Hello Tomo, Blenheim Mk IV had Mercury XV engines.
    Finnish Blenheims used same engines as the RAF planes, only 87 oct fuel, our airfields were small and had rather soft sirfaces. So the load carrying ability would not have been a problem, only the ground clearance. I think that the bombload differences between the FiAF and the RAF Blenheims was a result of different bomb dimensions
     
  11. tomo pauk

    tomo pauk Creator of Interesting Threads

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    I'm interested in what kind of bomb load your Blenheims carried.

    Indeed you're right that Mercury XV was installed on the Blenheim IV.
     
  12. Juha

    Juha Well-Known Member

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    Hello Tomo
    I don't have just now time to look individual loads but one randomly picked up example. In the early morning of 15 July 1944 the Bomber Sqn 42 sent 16 Blenheims on a mission, their cumulated load was 8280 kg consisting of 48 x 100 kg, 60 x 50 kg and 240 x 2 kg bombs. The Bomber Sqn 48 sent 6 Blenheims, their cumulated load was 5060 kg consisting of 46 100 kg bombs, 2 50 kg bombs and 24 15 kg bombs.
     
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  13. parsifal

    parsifal Well-Known Member

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    wonder what the range would be if the Blenheim were asked to haul a torpedo around

    Ive got this nagging suspicion that somewhere a torpedo carrying Blenheim was tested......
     
  14. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Blenheim I with 1000 lbs (all in bomb bay) and 278 gals - 975 miles (afer allowances are deduced in worth of 64 gals)
    Mk.IV with 1000 lbs and 466 gals - 1460 miles (allowance of 60 gals)
    For comparison - Beaufort I with 1000 lbs and 570 gals makes 1510 miles; 1390 miles with torpedo.

    My guess is that, if we trade 720 lbs worth of fuel (100 imp gals) on the Mk.IV so torpedo can be carried, with fuel now of 366 gals, the range of 1000-1100 miles, depending on how good/bad the torpedo is faired in?

    But then there is the Hampden - a torpedo and 2 x 500 lbs of external bombs, for 1540 miles.
     
  15. Juha

    Juha Well-Known Member

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    And there was Wimpy, which could carry 2 torpedoes. But Wimpy and Hampden were bigger planes, so easier targets to AA gunners. Anyway Hampden was used as a long-range torpedo-bomber up to 1943 off Norway.
     
  16. Juha

    Juha Well-Known Member

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    BTW
    there are two stories of the successes of British air gunners in my site, one rather famous Blemheim case and one not well known success of a Hampden TB I when attacked by two Bf 109Gs off Norway on 7 July 1943. The results of air combats were sometimes surprising.

    See Air gunners
     
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  17. ChrisMcD

    ChrisMcD New Member

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    #17 ChrisMcD, Jan 25, 2016
    Last edited: Jan 25, 2016
    Effectively the Beaufort was a Blenheim beefed up to carry a torpedo and a dedicated radio operator. The raised deck between the pilot and the rear gunner was to give the radio operator a decent place to work and the fuselage was lengthened to allow the torpedo to be carried as "semi-recessed". One of the main problems with the Blenheim was that it was very cramped.

    Wilfred Freeman insisted that the Beaufort needed more power, so it was fitted with Bristol Taurus engines - which were not sufficiently developed. But at least were better than the Perseus's fitted to the truly awful Blackburn Botha

    Most Beauforts would have had Twin Wasps - but the ship carrying the first load was torpedoed - so a lot had to soldier on with the Taurus

    Still the properly engined Mk II's did very well with the RAF in Malta and the RAAF in OZ
     
  18. stona

    stona Well-Known Member

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    I’m going to make a post just to put the state of the RAF’s maritime capability in the pre-war years and at the outbreak of WW2 into perspective.
    Here is not the time to go into the details of the development of naval aviation after WW1. I would suggest that the loss of expertise to the RAF which occurred in 1937 when the FAA was handed over to the Admiralty had a serious impact. The two land based torpedo squadrons left to the RAF had never exercised with the fleet and did not serve as repositories for everything that had been learnt in the preceding years. When the FAA was transferred to the Admiralty Coastal Area/Coastal Command almost lost its ‘raison d’etre’.
    At the outbreak of war, almost twenty years after the Navy’s first torpedo trials, the aircrews of Coastal Command would have to start re-learning all the lessons already learnt by others at great cost to themselves.

    The RAF’s maritime capability was largely ignored in the 1930s. In 1934 there was only one land based torpedo squadron, the only increase was in flying boat squadrons, but here it should be remembered that one of these ‘squadrons’ comprised just 4 aircraft.
    By September 1939 the number of Maritime squadrons had risen from 5 to 18, but 16 of these were in the General Reconnaissance and Trade Defence categories. 12 of these 16 squadrons were employing aircraft that could double as bombers. Just 2 were strike squadrons. An Air Staff memorandum of June 1936 was explicit.

    “Such shore based air forces should be available equally for the air war proper and for employment in support of naval operations in accordance with the requirements of the situation at any given time.”


    It’s why General Reconnaissance aircraft like the Anson and later Hudson were equipped to carry bombs.


    Then there was the constant agitating by the Deputy Director of the Plans Division in the Air Ministry to reduce the number of aircraft devoted solely to maritime work. This man, a certain Group Captain Arthur Harris, started his campaign as early as 1936 and famously carried it on later as C-in-C Bomber Command.
    At the outbreak of the war the RAF’s maritime strike capability was nominally 2 squadrons of torpedo bombers. In fact a total of just 12 Vildebeest biplanes were operational. Even this was a light bomber converted to drop torpedoes and in 1939 was already obsolete.
    Next post, when I have time, will cover what happened next and will pertain more directly to the thread title :)

    Cheers

    Steve
     
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  19. stona

    stona Well-Known Member

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    #19 stona, Jan 29, 2016
    Last edited: Jan 29, 2016
    There was a need for a better torpedo bomber but efforts to create one were hampered by the results of the Air Staff’s decision to go for the Blackburn Botha, over which a discrete veil should be drawn. Trials in 1939 only confirmed what a terrible aircraft it was. It was never used as a torpedo bomber.

    Just as important were the financial and doctrinal constraints imposed by Air Ministry thinking. Take a look at the RAF’s bombing force in 1939 and though it is usually criticised with hindsight for being largely obsolete in fact none of its aircraft had been designed earlier than 1932 and more than half later than 1935. The late expansion plans were aimed at creating a bombing force of modern aircraft by 1941, with a large proportion of four engine types, like the Stirling. To do this the Air Ministry considered it essential to do away with specialisation in its force. This did not bode well for a specialist aircraft like a torpedo bomber. An Air Staff memorandum of February 1936 explains.

    “It is essential that the major proportion of our air forces should be ‘ubiquitous’ if we are to achieve and adequate measure of defence against air attack as well as to meet our many other commitments in Imperial Defence. Ubiquity requires not only the avoidance of specialisation in training and equipment, but also unification of organisation and control.”

    Offensive maritime operations had no place the Air Staff’s concept of a future conflict, even if it had the torpedo bomber would now be an aircraft contrary to the idea of ubiquity. Air Vice Marshall Ludlow-Hewitt, another future bomber leader, made this clear whilst still Director of Operations and Intelligence when he wrote.

    “It appears that the torpedo bomber will in future be so highly specialised a type we will not be able to combine it with any other.”

    Funding for the RAF was tight in the 1930s and torpedoes were expensive (about £2,000 at 1930’s prices) and required regular maintenance in storage, unlike bombs. The RAF also reckoned that training to drop torpedoes would add 16 weeks to a pilots training. The Air Ministry essentially handed the whole matter of torpedo aircraft over to the FAA, whilst refusing to relinquish control of the 4 land based torpedo units (2 in UK and 2 in Far East) to the Navy.

    The body at the Air Ministry that oversaw air launched weapons was the Bombing Committee and it had a subsidiary Torpedo Sub-Committee which, in the words of the Director of Staff Duties responsible for these bodies “never functioned.”
    This gives an idea of the low priority accorded torpedo attack. If more proof was needed an Air Staff letter makes it clear.

    “…on occasions, shore-based torpedo-carrying aircraft may be required to attack warships reported to be in range. The Air Staff have, however, always regarded this method of attacking warships as unsuitable employment of aircraft.”


    Just as the junior service resisted any form of close air support, believing the job of destroying enemy forces in the field was that of the Army, it also believed that sinking the enemy’s warships was the job of the Navy.
    It is important to understand the historical context in which decisions were made. They were not made in a vacuum, and they were not made with hindsight. Sometimes they were made by people lacking in foresight too.

    We will get to the aircraft…..honest.

    Cheers

    Steve
     
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  20. Shortround6

    Shortround6 Well-Known Member

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    Thank you for the historical perspective. I might add that it didn't really need "hindsight" in many cases. Unfortunately in too many cases large blinders were used to ignore the lessons of WW I or willful disregard of those lessons was employed to justify the decisions made in the planning/procurement of aircraft and their deployment.
    Inadequate testing/development of weapons (and all to often depending on hope/wishful thinking rather than tests and training) hampered the RAF even in it's "dream mission" (strategic bombing) let alone planes/units devoted to periphery tasks like maritime reconnaissance/coastal patrol.

    There had been a fair number of coastal patrol/anti-sub aircraft operating around Britain and the North Sea in WW I. They were actually fairly successful in keeping U-Boats out of the coastal areas or at least reducing their effectiveness. Unfortunately too often a quick analysis resorted to a "scoreboard" mentality. AS in how many U-Boats were sunk vs how many convoys came though the patrolled areas without being attacked. ( the true goal of anti-sub operations).
    The Anson was a lousy anti-sub plane however good a trainer it may have been. It carried a lower bomb-load than many WW I flying boats that less powerful engines. It had short range-endurance for a reconnaissance plane over water.
    All too often the RAF high command had a rather distorted notion of what constituted "twin engine" safety when flying over water. Twin engines seemingly was considered "enough" with no thought given to both engines having generators or hydraulic pumps. Cross over fuel systems so dead engine's fuel tank/s can feed the live engine. Feathering propellers were a luxury the RAF couldn't afford (many Ansons (especially the early ones) had fixed pitch props) so many planes struggled to make landfall flying on one engine. "Cheap" purchase price was often paid for by lost aircraft and aircrew on operations that better equipped planes would have brought home to be repaired and to fly again.
    Wishful thinking and/or blinders also comes in on the whole Botha Debacle.
    With the Blenheim as a baseline (the only all metal, retracting landing gear monoplane bomber the British even had flying at the time) the idea that you could go from a 3 man crew to 4 man and bigger fuselage and add even more "stuff" ( empty weight of a Botha MK I was 3,700lbs more than a MK I Blenheim (46%)) and keep the same size engines and still wind up with even a useful airplane relied more on divine intervention (the sleeve valve gods??) than good planing.
     
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