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Thread: Beverley Shenstone (or is it Ludwig Prandtl?) and the Spitfire's wing!

  1. #1
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    Beverley Shenstone (or is it Ludwig Prandtl?) and the Spitfire's wing!

    As someone who is slightly enthusiastic about the Spitfire, I was more than a little sceptical about this:

    https://www.thedailybeast.com/the-sp...-saved-britain

    and decided to waste a bit of time digging into the truth of the matter. Much to my surprise, there's a book about the question and this, rather neat bit of work

    https://www.aerosociety.com/media/48...suggestion.pdf

    I knew about the He70 fast mail plane:



    but was assured, as a teenager in the ATC, that it was just a superficial coincidence. Suddenly I discover that it's certainly not a coincidence, even if it was correlation rather than causation, because both designers were heavily influenced by Ludwig Prandtl's work on wing theory during WWI which demonstrated that an elliptical wing was the most efficient way to generate lift. This was first demonstrated by the Baeumer Sausewind in the early twenties:



    Sadly, while apparently very efficient and economical, the Sausewind also demonstrated another feature of the perfect elliptical wing: the whole wing stalls at once, making landing and high G manoeuvres more exciting than most pilots would desire, a problem never really solved without some compromise, even in the Spitfire.

    I remember reading that some PR Spitfires had a lethal stall and, suddenly putting two and two together, I suppose that means that the deliberate wash out added to the standard Spitfire wing at a cost of some drag, was removed to improve high speed and high level performance at the expense of nasty stall characteristics. I love making connections like that, but I do wonder if the people who are rebuilding this:

    https://www.independent.co.uk/news/w...-a8646841.html

    are aware of this 'feature'? I assume there was a pilot's notes for this model, but with such a limited run, I wonder...

    *edit* And on checking, these:

    http://zenoswarbirdvideos.com/Images...PIT9MANUAL.pdf

    are the notes used for the PR model in question and while they note that the ground attack version gives less warning of a stall, they don't mention the PR version...

    Anyway, it's given me an evening of pleasant discovery, so I just thought it would be nice to share
    Last edited by M4tt; 21st January 2019 at 13:59.

  2. #2
    Quote Originally Posted by M4tt View Post
    As someone who is slightly enthusiastic about the Spitfire, I was more than a little sceptical about this:

    https://www.thedailybeast.com/the-sp...-saved-britain

    and decided to waste a bit of time digging into the truth of the matter. Much to my surprise, there's a book about the question and this, rather neat bit of work

    https://www.aerosociety.com/media/48...suggestion.pdf

    I knew about the He70 fast mail plane:



    but was assured, as a teenager in the ATC, that it was just a superficial coincidence. Suddenly I discover that it's certainly not a coincidence, even if it was correlation rather than causation, because both designers were heavily influenced by Ludwig Prandtl's work on wing theory during WWI which demonstrated that an elliptical wing was the most efficient way to generate lift. This was first demonstrated by the Baeumer Sausewind in the early twenties:



    Sadly, while apparently very efficient and economical, the Sausewind also demonstrated another feature of the perfect elliptical wing: the whole wing stalls at once, making landing and high G manoeuvres more exciting than most pilots would desire, a problem never really solved without some compromise, even in the Spitfire.

    I remember reading that some PR Spitfires had a lethal stall and, suddenly putting two and two together, I suppose that means that the deliberate wash out added to the standard Spitfire wing at a cost of some drag, was removed to improve high speed and high level performance at the expense of nasty stall characteristics. I love making connections like that, but I do wonder if the people who are rebuilding this:

    https://www.independent.co.uk/news/w...-a8646841.html

    are aware of this 'feature'? I assume there was a pilot's notes for this model, but with such a limited run, I wonder...

    *edit* And on checking, these:

    http://zenoswarbirdvideos.com/Images...PIT9MANUAL.pdf

    are the notes used for the PR model in question and while they note that the ground attack version gives less warning of a stall, they don't mention the PR version...

    Anyway, it's given me an evening of pleasant discovery, so I just thought it would be nice to share
    That's an interesting line of enquiry and thanks for posting those links. I've never read anywhere that the wash-out was removed for the PR Spitfires. I'm not saying it wasn't, just that I've never read anything to that effect. The only mods to wings I recall reading of were along the lines of removing the guns and adding tanks to the leading edges. I thought the stall characteristics were due to the weight of fuel carried and the consequent disturbance of the centre of gravity.

    As I understand the design, the angle of attack was greatest near the wing root and flattened towards the tip, wouldn't this mean that a straightened wing would have a steeper angle of attack along its entire length? I'm assuming a corrective redesign of the join at the fuselage would have been too much effort.

  3. #3
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    Quote Originally Posted by jools View Post
    That's an interesting line of enquiry and thanks for posting those links. I've never read anywhere that the wash-out was removed for the PR Spitfires. I'm not saying it wasn't, just that I've never read anything to that effect. The only mods to wings I recall reading of were along the lines of removing the guns and adding tanks to the leading edges. I thought the stall characteristics were due to the weight of fuel carried and the consequent disturbance of the centre of gravity.

    As I understand the design, the angle of attack was greatest near the wing root and flattened towards the tip, wouldn't this mean that a straightened wing would have a steeper angle of attack along its entire length? I'm assuming a corrective redesign of the join at the fuselage would have been too much effort.
    That could well be true, but in an aircraft in which you are trying very hard to maximise the range, height and speed at the expense of everything else, it would make absolute sense to remove an artificial cause of induced drag. The spitfire was unique at the time in having an increased angle of attack +2 near the roots and a decreased -.5 at the tips. This was explicitly and deliberately added to ensure that the roots began stalling early, buffeting the tail to make the stall very noticeable, but keeping the effects away from the wing control surfaces and losing lift gracefully. The effects on both stall and spin recovery were important. However, like the Whitley, although no where near as pronounced, the twist in the wing was a significant cause of drag which was a partial explanation of why the Spitfire, with the magically thin and low drag elliptical wing, wasn't much faster than the Hurricane. I'm assuming that the two angles would be substantially reduced, even eliminated entirely so that a balanced and trimmed aircraft would present the smallest frontal area across the whole frontal area, so its overall drag would be reduced as well as its induced drag.

    As such removing, or very much reducing, the twist would take the wing closer to the mathematical ideal at the expense of a sudden and brutal stall and poor spin recovery. With experienced and well trained pilots who knew to allow an excessive safety margin the danger at low speed would be more than offset by superior performance, especially at height and higher mach numbers. It's only a hypothesis, but it's a tempting one. I'm sure there's a resource somewhere that has all the different types of Spitfire wing. I'll go looking.


    Well, that was quick:

    http://spitfiresite.com/2010/04/conc...g-types.html/2

    The D type wing.

    I also found this:

    https://www.aerosociety.com/media/49...e-spitfire.pdf

    which is pretty cool.

    Ok, I've spent half an hour staring at MKIX and MK XI and I really can't tell.
    Last edited by M4tt; 22nd January 2019 at 08:10.

  4. #4
    Some more interesting links there, thanks. I see one mentions the Meredith radiator - so clever. The maths was probably done with brains plus a slide-rule!

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