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A controversial Whirlwind Theory..

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  • Ex Brat
    Rank 5 Registered User
    • Mar 2013
    • 27

    #21
    The graph in your post last evening means nothing without labels. As I now understand it, your research is trying to establish;

    Why was the maximum speed of the WW at altitude less than that of the Spitfire I - is that correct?

    And that you put this lack of comparative performance down to your idea that this was because of the propellers fitted to the WW reduced the available thrust by their having higher drag than the one installed on the Spitfire, and the reason for the greater drag (you say) was due to the blades becoming Mcrit? Am I correct?

    And you have not considered;
    • Engine hp available against weight of the aircraft
    • Drag of the aircraft, both profile and induced
    • Wing planform
    Did you consider the comments made by Harold Penrose regarding modifications made to the WW after it had undergone testing at Farnborough?
    In June the first prototype was ready for testing with a new nacelle-ducted exhaust system, but decreased top speed was inevitable because of the greater drag and loss of injector effect.


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    • Beermat
      1 Registered Rank Loser
      • Oct 2009
      • 3639

      #22
      The vertical axis is altitude and the horizontal one True Air Speed. I am sure you knew that really. It is a poor reproduction but as I am working from a camper van in Dorset while on a family holiday I cannot provide what you are rather obstinately demanding. The numbers, as I have already explained, while available do not matter as much as the shape of the curves on the graphs. If it still means nothing to you then there is no more I can do. For what it's worth the vertical runs from 10,000 to 22,000ft and the horizontal I have marked up.

      No, I am not trying to establish why the WW was slower at altitude than the Spitfire. I am trying to establish why the Whirlwind was much slower and apparently less powerful at height than a) the prototype was, b) the specification dictated and c) it should have been given it's performance lower down. I use the Spitfire for a comparison between drop off in performance with height without altitude-related problems (other than progressively less dense air into the supercharger) and drop off in performance with height with some additional factor exacerbating, as per WW.

      This has been understandably attributed to the superchargers alone and Rolls blamed since 1940 but it has never made sense to me as it was all proven and predictable engineering, developed from the supercharged Kestrel, all other Rolls products behaved similarly to each other and not like this and what's more it only manifested itself on the production aircraft with DH props. That was my first clue.

      Yes, it was down to Mcrit. This of course reduces with altitude. What actually happens in the real world is more and more of the blade, moving inboard, passes through Mcrit as one climbs - and fatter blades do this sooner than thinner ones. Also RAF section blades do this sooner than Clark Y ones.

      Constant speed units do not care what the source of the drag is. They can't filter out wave drag. They will react by reducing the AoA of the blades. This reduces forward speed. The more wave drag on the blades, the slower the aircraft. Changing perspective for a moment, this actually applies to several aircraft I am studying in this context, and was major driver for jet development.

      I have calculated the areas beyond Mcrit for WW blades based on the US Hamilton equivalent on which DH based their blades, and also the drag rise on those areas. It's a bit 'back of fag packet' but the principle is demonstrated.

      This problem with US 9.6% thick blades was the reason DH (working with Vickers Supermarine and the RAE) thinned the Hamilton 6503 to make the 7.6% DP55409B of the Spitfire I. They didn't seem to feel the need for the WW, but it would have helped if they had.

      Just briefly, but unfortunately exactly when the WW flew, we were applying 1920's blade design to aircraft encountering very different speeds and altitudes.

      Apologies for not doing all of the maths again here and now for you. The data I used is out there and you are welcome to check it all adds up if you remain incredulous - though I can assure you it does.

      I have of course considered the hp and drag of the aircraft - it's a starting point in all this. There are some very nice calculations done by the Farnborough wind tunnel team who investigated a full sized one - and even found something odd about propeller efficiencies against flight tests. These are also available from the National Archives.

      Wing planform hasn't been a focus for me - can you expand on that, in terms of how it affects performance with altitude? Thanks.







      Last edited by Beermat; 14th August 2019, 11:31.
      www.whirlwindfighterproject.org
      It's all good. Probably.

      Comment

      • Ex Brat
        Rank 5 Registered User
        • Mar 2013
        • 27

        #23
        You called the theory controversial and wrote that you prepared for the arguments. Think of this as nothing more than testing those statements, not because I have any personal point to make, it is because I cannot understand what you are are wanting to prove or the relevance of the information you introduced to prove your claim.

        As I now understand it, you wish to establish what changes to the WW design caused such a drastic change in top speed at altitude between two flight test dates? Is this correct?

        If so, what were the dates of the tests?

        Comment

        • Beermat
          1 Registered Rank Loser
          • Oct 2009
          • 3639

          #24
          Yes, I wanted to establish what changes caused the Whirlwind to pass testing at Martlesham in March 1940 (I think, but I am in a van in Dorset with no references) and be given a service ceiling of 31,000 ft and then cause the first 263 WW Squadron Leader to call it useless above 26,000 in a communique to Dowding. There was no second set of flight tests, the aircraft passed the first and only and then entered service.

          The whole point is that it passed with a Clark Y Rotol prop of 8% t/c ratio at 70% and entered service with a RAF-6 DH prop of 9.6% and yet Martlesham said to the RAF that the aircraft were identical so that no-one seemed to pick up on the real difference - at the time or since.

          The aircraft in service was reported anecdotally as useless at height and this went to Dowding. Dowding, who was concerned for his pilots more than anything else then told Beaverbrook that he didn't care for the Whirlwind because of the danger from 109's at height and Beaverbrook halted production. thus anecdotes are very important to the story - more so than absolute figures. Ever since the engines had been blamed - and by association Rolls Royce - even though no one could be specific as to how and why. I have set out to prove this wrong and unfair on Rolls, by virtue of understanding what really changed between acceptance into service and what the service then said about the aeroplane.

          As there was no second trial, instead we have to look to tests with mods for any DH-equipped WW's performance curves. The one that shows performance with height was in - I think - Jan 1942, but this isn't too relevant. Of course it shows slower speeds than a Spitfire I (the aircraft was carrying two 250lb bombs externally), but that's not the point, it's what we can glean (when we know what other equivalent graphs look like and know what to look for) from the shape of the graph.There's no need to get too bogged down in this.

          Far from adding two and two and making five as would seem to be the accusation, I have made four. It's actually more of a stretch to say that an engine that was essentially a Kestrel, a tried and tested design with a tried and tested supercharger should suddenly develop 'non-specific' yet altitude-related ailments when applied to the Whirlwind (but not the tested prototype). That really is taking two and two and making five, though without an appreciation of propeller Mach issues it's an understandable leap. Once made, this guess at the causes quickly became 'fact' - my aim was to question this, and then tell what I found when I did.
          Last edited by Beermat; 14th August 2019, 21:51.
          www.whirlwindfighterproject.org
          It's all good. Probably.

          Comment

          • powerandpassion
            Never Be Afraid to Ask
            • Jul 2012
            • 1255

            #25
            I find these peregrinations fascinating, but two esteemed members of the forum butting heads like elk in the forest, distracting. Gentlemen, keep playing the ball, it is fascinating. Still, it would be fun to be a second to either of you in a duel, with historically accurate ball and powder, some wretched maiden rushing on a foaming horse in the distance to stop her lovers in their madness, gratefully succeeding and allowing us all to retire to a few pints in the pub.

            Comment

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