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Thread: Airplane Wing Pods Question

  1. #1 Airplane Wing Pods Question 
    Forum Radioactive Isotope zinjanthropos's Avatar
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    I've been on several planes in my life and have always wondered what those pods on a wing actually do. Recently I was on a Boeing 737 (I think) and there were 3 pods under each wing. I've also seen pods on top of a wing and wings without pods. Anyway on my last flight I noticed one of the pods under the wing shaking for the whole 4 hour trip. When we landed I asked a steward what those pods were for and he said they were anti shock stabilizers. I wasn't satisfied with that answer and in talking with others I have also heard them called air flap fairings and someone else said they were extra fuel tanks. What are they really and where on the wing can one expect to see them, top or bottom of wing? I'm leaning towards them being fairings, an aerodynamic pod housing a mechanism for the flaps but I'm not sure.

    By the way, the steward said the pod that was shaking does it all the time because it's behind an engine. Didn't exactly fill me with confidence. Are these things designed to take a certain amount of shaking? Is it a good idea to put them behind the engine?


    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Moderator Moderator Markus Hanke's Avatar
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    They house the mechanism involved in deploying the wing flaps; they are in that particular pod-like shape for aerodynamic reasons. Here's a good explanation :

    Aerospaceweb.org | Ask Us - Whitcomb Area Rule & Kchemann Carrots


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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Still confused... the pods beneath the wings are flap track fairings housing a mechanism. The pods on top of the wings are Whitcomb anti-shock pods? The Kuchemann Carrots are pods at the trailing edge of the wing that lower drag, top or bottom of wing I'm not sure?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    What ever additional features engineers can cram into these "pod" shaped forms is not their main purpose. Their main purpose is to make the cross area of the plan fit as smooth a curve as possible when sampling it from nose to tail. I think Whitcomb called them "antishock bodies" because they also appear to mitigate the shock wave developed on a wing when moving at or near the speed of sound. I image the change from straight to swept wing also conforms to Whitcomb's area rule. This despite weather they knew about the area rule at the time. A 737 (the ones I've seen) have 3 pods per wing. I have never seen one shake beyond moving along with the wing flexing.

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    Hi Everybody,

    I'm new to the forum. This thread caught my eye because I was the design manager for the CFM56 when it was certified back around 1980. Yep, I'm a old cuss.

    My thanks to Markus Hanke for the nice article. The Convair 990 was an early GE not-to-successful entry into commercial aircraft with a version of its very successful J79 engine (F4 and other fighter aircraft). It contained an idea not seen since, combining a turbine and fan in a single structure driven by the exhaust of the J79.

    cinirob

    PS: I spend some time debating with anti-relativists so you may see on some other threads.
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    Quote Originally Posted by zinjanthropos View Post
    the steward said the pod that was shaking does it all the time because it's behind an engine. Didn't exactly fill me with confidence. Are these things designed to take a certain amount of shaking?
    Yeah. An airplane especially a large one is designed to flex.

    A 737 has so much experience built into, you can be confident it's well maintained.
    A pong by any other name is still a pong. -williampinn
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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Quote Originally Posted by Pong View Post
    Quote Originally Posted by zinjanthropos View Post
    the steward said the pod that was shaking does it all the time because it's behind an engine. Didn't exactly fill me with confidence. Are these things designed to take a certain amount of shaking?
    Yeah. An airplane especially a large one is designed to flex.

    A 737 has so much experience built into, you can be confident it's well maintained.
    I have sat in the same area before with a good view of the pods and never have I seen one shake like the one I mentioned in the OP. In fact I have never seen one shake, period. Honestly it frightened me a little, I mean how scared can you be once the plane is airborne. I think when I asked the chief steward about it when I deplaned, that he gave me the cutesy answer just because other people were standing around. ANyway I was glad to get back on the ground after that flight.

    I know this is probably the wrong sub-forum to ask this question but if this equipment and the area rule are such an efficient system then why haven't birds evolved pods, or have they?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Genius Duck Dywyddyr's Avatar
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    Quote Originally Posted by zinjanthropos View Post
    I know this is probably the wrong sub-forum to ask this question but if this equipment and the area rule are such an efficient system then why haven't birds evolved pods, or have they?
    That one's easy: pods aren't necessary IF the shape already conforms to the area rule.
    They were added after Whitcomb discovered the rule to bring the design something close to ideal.
    Aircraft designed later don't have pods but still conform to this rule.
    I.e. the pods are a "quick fix", used to ensure conformity on a design that didn't/ couldn't do it any other way.
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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by zinjanthropos View Post
    I know this is probably the wrong sub-forum to ask this question but if this equipment and the area rule are such an efficient system then why haven't birds evolved pods, or have they?
    That one's easy: pods aren't necessary IF the shape already conforms to the area rule.
    They were added after Whitcomb discovered the rule to bring the design something close to ideal.
    Aircraft designed later don't have pods but still conform to this rule.
    I.e. the pods are a "quick fix", used to ensure conformity on a design that didn't/ couldn't do it any other way.
    I should have thought of that one. I wonder how much more aircraft designers & engineers can learn from studying birds. Do you think we've tapped out on that resource?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Genius Duck Dywyddyr's Avatar
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    We learn (quite) a bit from looking at birds 1, but one factor why they're not quite so much "use" is that aircraft are rigid structures, birds are dynamic (to put it grossly 2).
    Birds (sort of) reconfigure themselves, wing angle, rate of flap, span etc to "optimise" their flight. Until we develop metals (or other materials) that can do anything like this reliably then we're stuck with machines that are designed for one portion of the flight regime almost exclusively, even to the detriment of other portions.
    Eg an airliner will be designed primarily for efficient cruise (due to fuel costs, travel time etc.) and THEN attention will be turned to safe landing and take-off. That still leaves things like climb performance (time taken to achieve cruising altitude) as somwhere down the list as "nice to have but don't go overboard getting it right".
    Birds have had millennia, we've been doing it for ~100 years 3.

    1 Plus, apparently, we're not yet smart enough to learn: Unfortunately, these nature inspired designs are too complex for current computer simulations of fluid dynamics so Lazos in unable to say for certain why this particular shape is so efficient.
    2 Only just finished my first coffee of the day.
    3 And I've yet to see a bird that can compete with an SR-71 on a photo-recce mission!
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  12. #11  
    Genius Duck Dywyddyr's Avatar
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    Quote Originally Posted by zinjanthropos View Post
    I know this is probably the wrong sub-forum to ask this question but if this equipment and the area rule are such an efficient system then why haven't birds evolved pods, or have they?
    Er, of course the OTHER answer to this is that the area rule is a only requirement where there's transonic/ supersonic airflow. (Which, in the case of birds 1 isn't much of a problem and is probably more relevant than my previous answer).

    1 Including African AND European swallows.
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  13. #12  
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    Quote Originally Posted by Dywyddyr View Post
    Birds (sort of) reconfigure themselves, wing angle, rate of flap, span etc to "optimise" their flight. Until we develop metals (or other materials) that can do anything like this reliably...
    The Wright brothers pioneered deformable wings with canvas gliders and eventually powered craft; the controlled whole-wing warp allowed their planes to roll (or not!) and soon inspired the ailerons all planes employ today.

    Organic suppleness as in early planes or the animals that inspired them, isn't smart under jet power.
    A pong by any other name is still a pong. -williampinn
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    The aircraft industry would like to return to deformable wings etc because they could "cleaner" and reduce drag. I have heard about piezo-electric materials being considered to do that in aircraft. I don't know if it is still being researched.
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    Quote Originally Posted by cincirob View Post
    The aircraft industry would like to return to deformable wings etc because they could "cleaner" and reduce drag. I have heard about piezo-electric materials being considered to do that in aircraft. I don't know if it is still being researched.
    It is my (tenuous) understanding that the ISS uses Kynar or similar piezo materials for active damping of the structure. I say "tenuous" because I know that such things were studied in detail in the late 1980s, but I do not know for certain whether the ISS actually ended up using them. And I'm too lazy to google for the answer.
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    I don't know about the ISS. Aircraft and engine designers would like to reduce the use of hydraulics and I think that explains their interest.

    Boeing's Dreamliner (B787) opted for more electrical systems and increased the amount of electrical generation by the engines instead of using bleed air. Overall efficiency improved as a result.
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