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De Havilland decoder part one

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  • Beermat
    1 Registered Rank Loser
    • Oct 2009
    • 3620

    #81
    So, Goshawk = evaporatively-cooled Kestrel, Peregrine = downdraft - oops, downdraught Kestrel?

    I'll do some diagrams at some point - I want to check the maths first - or even better get Trak-tor to do it!
    www.whirlwindfighterproject.org
    It's all good. Probably.

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    • Beermat
      1 Registered Rank Loser
      • Oct 2009
      • 3620

      #82
      Just to say, though, that I have the 55100 sub-series at 0.7 radius angled for flat distribution at 25 degrees and with efficiency optimised for 170 mph with a Wright Cyclone on 16/11 ratio (the cruise of the DC-1 for which it was designed). It also worked for a Pegasus-engined Empire 'boat at 150 mph.

      By extrapolation it looks like 60 mph increments, such that a 55200 sub-series blade would be 'flat' at 31 degrees at 0.7, optimum efficiency meant for 230 mph, intended max speed of a Roc. 55300 is an unknown, but probably 38 degrees intended for a 290 mph optimum (with a Merlin on standard reduction, for example).

      All of this is wrong in that this happened without understanding the '15 degrees-off' rule from 1938.

      Do that, and a Lancaster - say optimised for 230 mph cruise - would be a 200. Old system would put it at 31 degrees. New system would have it at 31-15= 16 degrees, at 0.7r. HS130B table has the 6353 as.. 16.8 degrees at 0.7r.

      Not bad. Not bad at all.
      Last edited by Beermat; 19th October 2017, 14:22.
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      It's all good. Probably.

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      • Beermat
        1 Registered Rank Loser
        • Oct 2009
        • 3620

        #83
        Douglas Adams would have loved this.

        The answer is.... 42

        Will explain shortly.
        www.whirlwindfighterproject.org
        It's all good. Probably.

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        • Beermat
          1 Registered Rank Loser
          • Oct 2009
          • 3620

          #84
          I couldn't get the Spitfire geometry as shown in the RM to make sense. But then I discovered that if you use the US convention of centering everything on the 42 inch station along the blade regardless of blade diameter or 0.7 R/r or whatever..

          Everything snaps into place. Here is a diagram showing how a constant pitch variation with length - that gave 'butter-cutting' twist at 25 degrees at 42 inches - was completely messed up by de Havilland in their keen-ness to give the Spit blade butter-cutting ability at 15 degrees.

          This the new blade had - around the 0.7r mark, which everyone agreed was all-important. However, the blade now had two pitch distributions, an inboard terminating at the beginning of the telescope, around 33 inches out, and an outboard one that met the new thinking about the correct angle of 'constant pitch' being a lot less than actual constant speed blade angle - 15 degrees less.

          EDIT - THIS IS WHERE I WANTED TO PUT THE KILLER DIAGRAM, BUT THE FORUM UPLOAD PROBLEM HAS STRUCK
          Last edited by Beermat; 20th October 2017, 13:43.
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          It's all good. Probably.

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          • Beermat
            1 Registered Rank Loser
            • Oct 2009
            • 3620

            #85
            Here it is:

            Click image for larger version

Name:	twist2.jpg
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Size:	479.8 KB
ID:	3677185
            Last edited by Beermat; 20th October 2017, 15:03.
            www.whirlwindfighterproject.org
            It's all good. Probably.

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            • Beermat
              1 Registered Rank Loser
              • Oct 2009
              • 3620

              #86
              Does anyone know what the 'A' and 'B' suffixes meant? Was A post- 1938 twist revision? and B, like the Spitfire, meant twisted by telescoping?
              Last edited by Beermat; 20th October 2017, 16:02.
              www.whirlwindfighterproject.org
              It's all good. Probably.

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              • aircraftclocks
                Rank 5 Registered User
                • Sep 2006
                • 312

                #87
                Beermat
                I could not locate any information on what the A or B suffix mean.
                I did however locate blade shape data from the 1950's with a diagram descriping how the measurements were made. Given you have got right in to doing the maths, I will let you crunch the data.

                Propellers covered include:
                Blade Assembly No. P.454906A-20, Propeller type D14/445/1 and 2
                Blade Assembly No. P.455960, Propeller type 55/14
                Blade Assembly No. P.4551172T/A-17, Propeller type 55/8
                Blade Assembly No. P.4551775A-17, Propeller type 55/21, 55/24
                Blade Assembly No. P.4551778A-17, Propeller type 55/12
                Blade Assembly No. P.2541971A-78-1, Propeller type D29/446/1, D97/446/1
                Blade Assembly No. P.2541974A-78-1, Propeller type D18/446/1, D42/446/1
                Blade Assembly No. P.4542712A-42, Propeller type D16/446/1
                Blade Assembly No. P.4542962A-36, Propeller type D17/446/1
                Blade Assembly No. P.454300A-42, Propeller type D20/445/2, D20/445/2, D20/445/4, D20/445/5
                Blade Assembly No. P.4542172A-42, Propeller type D1/445/2
                Blade Assembly No. P.2012550A-57-1, Propeller type 81/313/1
                Blade Assembly No. P.2011368TA-57-1, Propeller type D113/312/1, D25/312/1
                Blade Assembly No. PR.1941774A-78-1, Propeller type D100/446/1, D124/446/1
                Blade Assembly No. P.4543000A-42, Propeller type D87/445/1, 2, 3 and 4
                Blade Assembly No. PR.1512753A-111-1, Propeller type D112/313/1
                Blade Assembly No. P.4542718A-42, Propeller type D68/4451/1
                Blade Assembly No. PR.2531003A-77, Propeller type D45/435/1
                Blade Assembly No. PR.2531009A-77, Propeller type D47/435/1

                Let me know if there are any in particular you would like to have.

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                • Beermat
                  1 Registered Rank Loser
                  • Oct 2009
                  • 3620

                  #88
                  Hi

                  That data would be gold-dust for me - thanks.

                  Specifically, the earlier blades from the '55' series are of great interest -

                  Blade Assembly No. P.455960, Propeller type 55/14
                  Blade Assembly No. P.4551172T/A-17, Propeller type 55/8
                  Blade Assembly No. P.4551775A-17, Propeller type 55/21, 55/24
                  Blade Assembly No. P.4551778A-17, Propeller type 55/12

                  Also this apparent early 54 series one:

                  Blade Assembly No. P.454300A-42, Propeller type D20/445/2, D20/445/2, D20/445/4, D20/445/5

                  I am ready to have the theories blown away by some actual measurement - does the data include pitch/twist?
                  www.whirlwindfighterproject.org
                  It's all good. Probably.

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                  • Schneiderman
                    Rank 5 Registered User
                    • Jan 2008
                    • 797

                    #89
                    On a related note, Matt et al, have any of you got climb-to-height data for a Spitfire I or II fitted with a CS DH prop. The only data that appears to be easily available online are for the 2-pitch fitting or for a CS unit on the Spitfire V, which is another kettle-of-fish altogether.
                    Last edited by Schneiderman; 21st October 2017, 12:05.

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                    • aircraftclocks
                      Rank 5 Registered User
                      • Sep 2006
                      • 312

                      #90
                      Beermat
                      The data includes angles at different stations.

                      Will need to get it into a form that is easy to read as some of the photos are a bit blurry. It will be a couple of days before I can get on to it.

                      Comment

                      • Beermat
                        1 Registered Rank Loser
                        • Oct 2009
                        • 3620

                        #91
                        No worries, A.C. Thanks for doing that.

                        Ralph, I'm sorry - I don't have any more performance data on the Spitfire than the easily-available web stuff.
                        Last edited by Beermat; 21st October 2017, 21:44.
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                        It's all good. Probably.

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                        • Beermat
                          1 Registered Rank Loser
                          • Oct 2009
                          • 3620

                          #92
                          I have finished the decoder. Turns out that the Lancaster and Spitfire prop blades were very close equivalents, tracing them back through various US references to their Hamilton Standard versions. Oddly, while the Mk.I Spitfire had essentially the same design as on the Short C-class Empire boats, the Lancaster needle-type Hydromatics, the Fairey Battle and marks of Mosquito, for the few Spitfire Mk.V's with Hydromatics a completely different design was used. Go figure. The blade angle is not an operating angle of any kind, it is just a handy mathematical reference to describe the twist. At this hypothetical pitch at 42" along the blade, the pitch distribution is flat. (Only it's not where blades have been telescoped).

                          There are gaps, where the information runs out. Largely around the 'home grown' blades.

                          Thanks Craig.

                          Nice film about DH blades here: https://www.youtube.com/watch?v=PY8oQ3XNreY - Ralph, these all appear Clark-Y to me, circa 1940.
                          Attached Files
                          Last edited by Beermat; 1st November 2017, 10:54.
                          www.whirlwindfighterproject.org
                          It's all good. Probably.

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                          • Dev One
                            Rank 5 Registered User
                            • Feb 2010
                            • 200

                            #93
                            Just a little bit of info on Mew Gull prop. diameter should be 6'9" - I know this because back in the '50's Peter Clifford dinged the Mews 7'0" prop during the Kings Cup heats whilst we were eliminated. So my father offered him use of our Proctor prop & the stop settings were changed appropriately. (32 from 28 rings in the back of my mind). The race speed for the Mew with this prop was the fastest post war. It turned out that our supposedly standard 7'0" prop had been cropped due to tip damage & it was 6'9" Dia.
                            Keith

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                            • Beermat
                              1 Registered Rank Loser
                              • Oct 2009
                              • 3620

                              #94
                              That's interesting, thanks. So there could be a row going down from the 7'6" in 3" increments at least as far as the 51109, which is what your prop essentially was - assuming it was a DH bracket, or course.
                              www.whirlwindfighterproject.org
                              It's all good. Probably.

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                              • Beermat
                                1 Registered Rank Loser
                                • Oct 2009
                                • 3620

                                #95
                                One thing - the reference angles for all the telescoped blades are guestimates. They can be calculated precisely by tricky maths involving several factors and a couple of integrals, but I do have a life.. if ever anyone wants to make a new one, l can demonstrate.. :-)

                                Now I guess it's Rotols.. unless you fancy doing the book, Anneorac?
                                Last edited by Beermat; 1st November 2017, 10:58.
                                www.whirlwindfighterproject.org
                                It's all good. Probably.

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