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Thread: 'Paddle Blade' Propellers on the Lancaster: when were they introduced?

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    Default 'Paddle Blade' Propellers on the Lancaster: when were they introduced?

    Can any experts out there tell me when the 'Paddle Blade' type propeller (Im sure there is a technical name for this Blade type but I dont know it) was introduced on the Lancaster as opposed to the 'Pointed Tip' type? I am particularly interested in 1 Group Lancasters (if they were introduced on a Group by Group basis). Thanks ,B

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    Paddle bladed props came into service with Packard-built Merlin engines and gave rise to the designation of Lancaster MkIII.

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    Hello,

    Non-Standard Mk. Is : JB127 ex-Mk. III had paddle-blade propellers fitted in November 1944 and NF910 was experimentally fitted with four-blade propellers.

    See:
    Lancaster - The Story of a Famous Bomber.
    Robertson,Bruce (comp. & ed.)
    Hemel Hempstead:Harleyford Publications,1974(4th imp.)
    p126

    Col.
    Last edited by COL BRUGGY; 13th August 2012 at 16:08.

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    Hi Bill,does that mean that all MKIIIs had paddle Blades? Also were paddle blades fitted to MKIs at all ?
    And finally when did the MKIII Lancaster enter Service?
    You have saved me a lot of reading!
    Thanks Bill and Col as well.I have the Harleford book so will look it up. B
    Last edited by barnsley; 13th August 2012 at 15:52.

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    As a mere Met Man, can I ask what was the reason for the change? Was it that the tips of the earlier props when on faster engines were actually producing less thrust because they were approaching the speed of sound?
    Just interested?
    Peter Davies
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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    Barnsley,
    Packard Merlins were introduced in 1942 with American magnetos and, initially, Bendix carburettors. However, by mid 1943 almost all Lancs reaching the squadrons were Mk III's. If a Mk I Lancaster had its Rolls-Royce engines replaced by Packard engines, it became a Mk III. It was possible for a Lanc to have both types of Merlin installed, but they had to be symetrically installed owing to the slightly higher power rating of the American engines. (There were not many instances of this however). This matter of the power rating I believe, gives the clue to why paddle bladed propellers were used.
    The Lancaster was fitted with the Rolls-Royce Merlin 20 or 22 (Mk I), and the Packard Merlin was virtually the same engine but was designated as the Merlin 28.
    The Packard engines were very popular with the ground crews, primarily because every new engine came with its own set of tools. A bonanza for engine fitters!

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    Apologies for the slight thread-hijack, but Col mentions 'NF910 was experimentally fitted with four-blade propellers.'

    Is there any reason why some Merlin-engined Halifaxes flew in operational service with 4 blade props and the Lancaster stayed with 3 bladed ones? If it's not a daft question, what was the benefit of the 4 over the 3?

    Simon

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    Not an expert on Lancs, but I can offer some general comments on propeller design and theory.

    The paddle blade made more efficient use of horsepower - more of it was turned into thrust. The downside would be a very slightly heavier propeller.

    The four bladed prop offers a similar advantage over a three bladed - more efficiency. A secondary benefit can be a smaller diameter prop for a given thrust produced. This can allow the engine to operate at a higher speed (for better horsepower per pound of engine) before the prop tips get into the transconic range. Near supersonic blade tips are very efficient at turning horsepower into noise, but not very good at turning it into thrust. The down side is a 33% (roughly) increase in weight over a similar three bladed prop.

    The designer has to decide what is more important - a bit more thrust or a bit less weight. Different airplanes in different situations will have different "right" answers.

    All this careful engineering can be completely thrown off by supply issues. One manufacturer could be told "all you get today is three bladers" because that was all that available at that time.

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    I think that the linking of Packard Merlins with paddle blade props is a red herring. As is well known, De Havillands manufactured Hamilton Standard propellers in the UK from 1935 onwards, initially of the counterweight type, then the Hydromatic full feathering type from about 1941/42 (initially just 3-bladers), most prominently on Stirlings, Mosquitos, Beaufighters, Lancasters, Hercules-powered Halifaxes, also Albemarles and others, including Flamingos and the like. However DH also developed a large four-blader Hydromatic (non-feathering type) for use on fighters, such as Typhoon and Tempest, with a smaller and lighter hub made possible by increasing the prop operating oil pressure.

    I now quote from an article published in "Flight" of 2 March 1956: "Enterprise in Airscrews" (no author stated, presume by staff members - subject was the history of the DH Propeller company ). ".... in 1942, difficulty in obtaining specialized American machine tools had hindered the expansion of Hydromatic production. The Merlin-engined Lancaster was one of the types for which the rack-and-pinion airscrew was intended, but production was postponed when large quantities of American-built Hydromatics suitable for Lancaster became avaiable under lease-lend. Production later resumed for the Mosquito, but the rack-and-pinion eventully gave way to the Hydromatic." The book, "DH - A history of de Havilland" by Martin C Sharp also notes in Chapter 29, page 215, that, "The peak of propeller production was was reached around D-Day when 5,059 new and repaired propellers left DH factories in a month, including a proportion made from American componenets." So it was not just complete aircraft provided for the British armed forces under lend-lease, but various engines (Packard Merlins for Lancasters and Spitfires, also supplied to Canada and Australia for their Mosquitos), plus some R-2800s Double Wasps for Warwicks, R-2600 Cyclone 14s for Miles Monitors, R-1830 Twin Wasps for Sunderlands, (surplus and obsolete) R-1535 Twin Wasp Juniors for Miles Master IIIs, and Lycoming O-290s for Austers, as well as various propellers either complete or as componenets. Rotol, as well as props of their own design, also built Curtis Electric propellers under license (fitted to Beauforts, etc).
    I know that 75 (NZ) Squadron was receiving Lancasters with paddle blades (EVERYBODY called them paddle blades, as opposed to "tooth-picks"!) by March 1944, but the earlier "toothpick" blades were certainly in service by 1942 on Stirlings, Mosquitos, Lancasters and Beaufighters.
    Something else to be borne in mind is that American-built engines had "SAE" splines on their propeller shafts whereas British engines had quite different numbered splines (such as 1000, 2000), so presume that you had to choose your particular prop to suit your spline; don't think that adaptors were possible in this instance. However I believe that many Hydromatic props built up in UK were a mixture of American and British components so you could use American blades, piston and dome, and barrel halves, spider, etc, but the spline could be made to suit American or British engine splines.
    David D
    David D

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    I'm afraid my year was the only one at Bristol to not be given a course of propellor theory, so I'm not able to give a proper answer. I'm told that the most efficient propeller has only a single blade: adding blades is not for increased efficiency but other reasons. Generally it is to be able to absorb more power at the same diameter - or much the same power from a smaller diameter. Wider blades is another approach, as seen on German aircraft and indeed in the paddleblade vs toothpick approach in the US and UK.

    It is true that the 4-blade propellers on the Merlin Halifax were more efficient than the preceding 3-blade, but presumably the other route of modified shape could have been followed. They were more needed on the Halifax than the Lancaster because of the former's higher drag, in turn caused by the earlier (higher) engine position, Gallay radiator design, and bulkier turrets. Just a couple of years' aerodynamic advances, plus the central allocation of BP vs FN turrets.

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