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De Havilland decoder part one

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    #21
    Yes I did read that, however it still comfortably outperfromed the Whirlwind

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      #22
      Not arguing that, just noting the effect. Fatter blades actually were generally better until you hit critical Mach, which you do early with fat blades. This test aircraft comfortably outperformed DH-equiped Spitfires, up to a certain height. What do you reckon these were - 9% Clark-Y?
      Last edited by Beermat; 9th October 2017, 22:26.
      www.whirlwindfighterproject.org
      It's all good. Probably.

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        #23
        Beermat
        You are correct the blade number is 50, an OCR error. In some fonts 5 and 6 are hard for it to pick up and I missed it!!!

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          #24
          No sure about the aerofoil but Joukowski/Clark Y type seems plausible. It was the 3001700 prop, so t/c was 11.9%.
          What do you make of the DH 2-pitch prop being described as 55713?

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            #25
            I strongly suspect someone read a different part number as the blade drawing number. If I recall correctly it does re-appear as a serial number in the description. I believe this happened a few times - possibly the same staff member? It certainly doesn't work as a bracket prop blade number, ending in 13.
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            It's all good. Probably.

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              #26
              I have solved the thickness/chord problem - or rather spotted my own error in making an assumption.

              So, the Hamilton Standard tables for the 6353 do describe the de Havilland 5,000-series bracket AND 55,000 series Hydromatic blades. They are telescoped in the edition I have, but they can be re-plotted to de-telescope them.

              Click image for larger version

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              Useful? I don't know. But satisfying. Now for the other series..
              Last edited by Beermat; 10th October 2017, 09:25.
              www.whirlwindfighterproject.org
              It's all good. Probably.

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                #27
                How about Type P-3-5-5-1 / Serial No. DH 545959 for the 11' 3" prop trialed on the Hurricane 1? What's that telling us?

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                  #28
                  Hmm.. nothing useful, yet. The problem here is that this makes it a left-hander (5), if this were the blade number.

                  Again it looks like the person doing the transcribing has found another stamp and used that. It is either a hub component - Anneorac has lists of these - or an actual serial number.

                  The 3-5-5-1 type, I believe, relates to the hub: 3 = number of blades, 5 = shank size (ie 5,000 series), 5 = shaft spline, (SBAC-5), 1 is - well, I am not sure - might just be 'type 1'. In many ways this relates to the US practice - in American this would read '3E50-1' (well, in fact 3EX, owing to the different spline).

                  This is backed up by K9793 having a type 3-5-5-7 for its trial of a two-pitch screw.

                  At 11' 3" unless the design was 'experimental' it would likely have been a 54403 tried on the Hurricane 1.
                  Last edited by Beermat; 10th October 2017, 11:22.
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                  It's all good. Probably.

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                    #29
                    Going back a few posts. I've just realised that I had my wires crossed.
                    Your comment in #22 refers to the trials with CS Rotol props, which were (as far as we know) metal. A 1939 article regarding Rotol props only mentions metal alloy, looks like Hyduignum came later. The t/c fell in the range 8.9 - 9.1%, depending on which actual prop it was. The transcription of Rotol ids is no better than for the DH. On the scant evidence we have its hard to say how they compared to the DH in CS mode. Against the DH 2-pitch installation it climbed considerably faster (as would be expected) and reached maximum speed a little higher. Mind you the data is all rather ambiguous and occasionally contradictary.
                    Last edited by Schneiderman; 10th October 2017, 11:28.

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                      #30
                      Yes, and of course that performance differential of the two metal prop types properly documented on another type does provide the circumstantial evidence for my Whirlwind theory, coming full-circle on this.

                      With the Spitfire we do have evidence of higher efficiency 'low down' with the thicker (9%) Rotols than the 7.6% de-H's. But we also have that thing about limiting revs to improve speed, showing earlier hitting of 'the wall'.

                      With the WW we have the reverse, in that the de-H's were thicker even than the (probably around 9%) Rotols. I expect the DH WW was better low down, took off better etc (than the Rotol one, not necessarily the DH Spitfire) - but as you say it's very hard to tell, it was never really performance tested.
                      Last edited by Beermat; 10th October 2017, 11:40.
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                      It's all good. Probably.

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                        #31
                        For what its worth the CS Rotols gave the fastest climb of all props tested on the Spitfire I and II. The WW on CS Rotols tracks them, +/-, to 18000ft and then starts to drop behind, and is seriously adrift above 2500ft where it even falls behind the really thick fixed pitch prop.

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                          #32
                          What I fail to understand is why the DH props on the Spitfire (earlier) and WW (later) are so different. I can see no logic for adopting a thicker section when the performance of the thinner had one had been proven acceptable for service use. The one-size-fits-all telescoping etc. does not answer that.

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                            #33
                            The first offers a useful comparison I hadn't thought to do - of course one has only 840hp to begin with driving each of the WW's Rotols, so revs will start to drop and your CP will start to fine down to zero-lift to minimise drag sooner than those in front of 1,030hp. Also, don't forget that the WW had compressibility-averse RAF sections.

                            The second - when did the Spitfire first fly with DH props? The WW's first flight with them, on L6844 was October 1938, and this was delayed by several months - are you sure the WW's DH props didn't pre-date the Spitfire's?

                            Being 4,000 series these props aren't part of the 5,000 / 55,000 series 'one size fits all' thing - the name of which I am going to steal, by the way. The 4,400 sub-series would appear to have been modelled not on an HS production blade at all, but on a Navy Bureau of Aeronautics design, number 5868. It's all a bit strange, as the 4,300 sub-series as per Blenheim look somewhat different, and much more Hamilton Standard. I am working on the 4,000 series now!
                            Last edited by Beermat; 10th October 2017, 12:20.
                            www.whirlwindfighterproject.org
                            It's all good. Probably.

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                              #34
                              Really? I thought that the first WW prototype flew in Oct 1938 and always had Rotol props while the second flew at the end of March 1939 with Rotol props and changed to DH some time later. The first documented test of DH props on a Spitfire was 15th May 1939.
                              How do we know that the aerofoil section on 55409B was not the same RAF6-based as on 54409? It may be thinner over all but would still have been a poor choice, especially on a larger diameter prop turning at the same revs.

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                                #35
                                No, it was the other way around, the DH propped WW flew first, first prototype, L6844, October 1938, always had DH props, Second prototype, L6845 1939, always had Rotols. This was my point all along, the Rotols only went on one aircraft and that was the one that was tested with everyone saying it was a production standard machine when it most definitely was not, for that very reason!

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                                So the thicker DH prop pre-dated the thinner one.

                                Re the 55409 section - I guess we don't know for definite in the tested cases, but I have inspected a 55409 and it definitely wasn't RAF section - and the 5,000 series drawing that P&P has shows a Clark-Y, albeit for a Fairey Battle.

                                But I was getting muddled before when I said about the WW Rotol having RAF sections - apologies - we don't know that about the Rotols, and in fact they probably, on balance, weren't.
                                Last edited by Beermat; 10th October 2017, 14:20.
                                www.whirlwindfighterproject.org
                                It's all good. Probably.

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                                  #36
                                  So is the Martlesham test data on L6845 Rotol or DH? It looks like all the early, uncamouflaged, pictures are Rotol
                                  Last edited by Schneiderman; 10th October 2017, 14:18.

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                                    #37
                                    With this only partially documented material it is like comparing apples with onions. Apples and pears would be a doddle in comparison.

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                                      #38
                                      So the Martlesham test data was all on Rotol.. L6845, second prototype. In fact the picture on the right was taken at Martlesham.

                                      L6844 (DH) was never formally tested - except to see whether it's handed rotation was any different from the un-handed L6845. It was never measured for performance, just handling.

                                      All we know is the production WW's had problems at height that L6845 didn't. And it would appear the only difference was the props.
                                      Last edited by Beermat; 10th October 2017, 14:46.
                                      www.whirlwindfighterproject.org
                                      It's all good. Probably.

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                                        #39
                                        Its a little strange that so little attention was paid to the WW at the exact same time as the Spitfire and Hurricane were being trialled with all manner of propellers. I know that priority may have been on handling issues and that some of the S and H results may have been considered appropriate for the WW too (dubious) but it smacks of official indifference to the aircraft.

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                                          #40
                                          The whole thing was a very curious episode.

                                          For example, designing an aeroplane with intakes in the wing roots squarely behind the inner half of the propeller arc on each side - and then making the propeller un-handed so on one side the duct is completely the wrong shape.

                                          There were cooling trials that showed this in the overheat on one side. And yet no-one seemed to notice the cause (Thanks to Dodge Bailey for pointing this one out).

                                          Sending an aeroplane for test with one set of propellers and then putting it into service with another. And when questions were asked about performance differences, claiming it was an identical aeroplane.

                                          Running all kinds of trials on other aircraft that showed large variations in performance with prop changes - and still not trying it on the Whirlwind.

                                          Sending one aircraft to Rolls Royce to have the supercharger intakes moved and adding 30 mph at a stroke - and then forgetting about it (after converting the aircraft back!)

                                          ..and then finally letting Rolls Royce continue to shoulder the blame. Yes, there was a war on - but one would have thought people would pay more attention, not less, to troubleshooting a new aeroplane.
                                          Last edited by Beermat; 10th October 2017, 20:04.
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                                          It's all good. Probably.

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