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Thread: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

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    Registered User danmoser's Avatar
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    Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    I've always wanted to explore the properties of this unique, bird-like wing configuration.

    The wing is usually sweptback with dihedral over most of the span, but the wing is bent (or cranked) downward near the tips with substantial anhedral.. this bent down portion is usually equipped with control surface, and can serve as both rudder and elevon.

    This is essentially splitting an inverted-V tail and putting each half of the inverted V at the wingtips.

    This arrangement is not commonly seen... but it's at least a century-old idea.. some examples through history:

    1. J.W. Dunne's D.6 tailless monoplane in 1911
    2. Fritz Wenk's "Weltensegler" tailless sailplane in 1921.
    3. A. Lippisch's Delta IVB and DFS40
    4. Blohm & Voss P212 & P215
    5. Jack Northrup's N1M

    This arrangement is sometimes touted as having many advantages in performance, stability and control.




    Some examples in recent ultralight soaring craft with this arrangement were inspired by Richard Miller, a diffuser tip proponent, leading to Bob Trampenau's Sunseed and an experimental prototype of the Fledgling hang glider sporting diffuser tips.
    Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-sunseed.jpg
    The more modern Exulans hang glider also has a similar arrangement..
    And the Stromburg Wing model aircraft group in Germany seems active, with many varieties of Weltensegler-cranked wings being flown.

    However, I am puzzled as to why this arrangement remains such a rarity.. What am I missing?
    The vulnerability to wing tip damage is sometimes mentioned as a criticism .. but is that it?
    Are there inherent disadvantages compared to other tailless aircraft arrangements?
    Attached Thumbnails Attached Thumbnails Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-diffuser.jpg   Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-sunseed.jpg   Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-stinton.jpg  

    Last edited by danmoser; September 27th, 2011 at 11:19 PM. Reason: pictures added

  2. #2
    Moderator Dana's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    If they're not being used, I suspect the theoretical advantages don't pan out in the real world.

    -Dana

    No trees were harmed in the transmission of this message. However, a rather large number of electrons were temporarily inconvenienced.
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    Registered User bmcj's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    I suspect the yawing moment (with the short moment arm) may be more than counteracted by the adverse yaw (with a large moment arm) and a sideslip effect, both to the opposite direction.

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    Registered User Norman's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    Quote Originally Posted by danmoser View Post
    This arrangement is not commonly seen... but it's at least a century-old idea.. some examples through history:

    1. J.W. Dunne's D.6 tailless monoplane in 1911
    2. Fritz Wenk's "Weltensegler" tailless sailplane in 1921.
    3. A. Lippisch's Delta IVB and DFS40
    4. Blohm & Voss P212 & P215
    5. Jack Northrup's N1M
    6. XP-56
    7. Stromer et al

    It's a very good feature for swept wings in the air but very inconvenient on the ground
    --------.~.
    --------/V\
    ------//----\\
    -----/(------)\--Norm
    ----(^^)-(^^) "For some years I have been afflicted with the belief that flight is possible to man" ~Wilbur Wright 5/13/1900

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    Registered User bmcj's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    Quote Originally Posted by Norman View Post
    6. XP-56
    7. Stromer et al

    It's a very good feature for swept wings in the air but very inconvenient on the ground
    Don't forget the flying wing from RAIDERS OF THE LOST ARK.

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    Registered User Norman's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    Quote Originally Posted by bmcj View Post
    Don't forget the flying wing from RAIDERS OF THE LOST ARK.
    That one certainly was a disaster on the ground
    --------.~.
    --------/V\
    ------//----\\
    -----/(------)\--Norm
    ----(^^)-(^^) "For some years I have been afflicted with the belief that flight is possible to man" ~Wilbur Wright 5/13/1900

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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    There are a couple of Styrofoam tailless chuck gliders with this layout that seem to behave quite well --the amount of 'delta three' (skewing of the fold axis in planform view ) is pretty influential and determines the apparent alpha of each tip and the effective airfoil across the kink region is a problem potentially --it seems that a gentle curve rather than a discrete kink might be better (approximating the curved tip feathers of a soaring bird in reverse ) but harder to fit control surfaces to if not all flying . There was a Polish tailess glider with the same type of tips in the early sixties or late fifties (Neopteryx or something like that ) but it wasn't configured for high performance or reported on in the literature . AV Weyhl wrote a long series of papers in The Aeroplane on tailless aircraft including this type of config --might look for them and see if he makes the analogy to the "V tail on the tips" or comments at all.

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    Registered User danmoser's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    It seems there are a few key parameters to get the wing stabilized correctly..
    These RC model guys with the "Dethgull" and "Robbe Vampir" seem to have workable designs.

    DethGull: a tailless gull wing - RC Groups

    And the Stromburg designs too..

    http://www.m-schoenherr.de/StromerE/default.htm

    I seems that the drooped down outer section needs to be toed-in a few degrees to lower the angle of attack... effectively inducing "jump twist."
    It does change in angle of attack in proportion with the rest of the wing.
    This could permit desirable lift distribution and low induced drag throughout the entire speed range.

    On the issue of ground clearance, having it as a high wing with a taller undercarriage/fuselage could alleviate the problem.
    Looking at the Sunseed HG, ground clearance compared to other flex & rigid wings today seems about the same.
    Last edited by danmoser; October 1st, 2011 at 04:17 PM.
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    Registered User danmoser's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    This "Gull-wing" configuration is closely related to the concept of "hyper-elliptic camber, " which has been recently determined to have some very interesting aerodynamic efficiencies:

    http://dnc.tamu.edu/projects/flowcon...rginiatech.pdf
    http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf

    Seabirds seem to have this cranked downwards "gull-wing" configuration, while many land birds like hawks, eagles and vultures seem to prefer the cranked upwards wing tip feathers.

    Both of these non-planar wing surface arrangements seem to have performance advantages over a strictly planar wing. Dr. Ilan Kroo has also studied this.. and derived the C-wing as a particularly efficient wing shape as well.

    http://ntrs.nasa.gov/archive/nasa/ca...1996039477.pdf

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    Registered User Norman's Avatar
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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    Quote Originally Posted by Aircar View Post
    There are a couple of Styrofoam tailless chuck gliders with this layout that seem to behave quite well --the amount of 'delta three' (skewing of the fold axis in planform view ) is pretty influential and determines the apparent alpha of each tip
    This is a big deal of free flight models but why should it be necessary if you have elevons?

    and the effective airfoil across the kink region is a problem potentially
    From the poind of view of a slug of air moving along a streamline it would look like a flap deflected 1 or 2 degrees, would it not?

    There was a Polish tailess glider with the same type of tips in the early sixties or late fifties (Neopteryx or something like that ) but it wasn't configured for high performance or reported on in the literature . AV Weyhl wrote a long series of papers in The Aeroplane on tailless aircraft including this type of config --might look for them and see if he makes the analogy to the "V tail on the tips" or comments at all.
    I don't recollect a Polish glider matching that description. The name you mentioned is similar to "Nietoperz" which can look a bit gull-winged from some angles but is in fact flat. Alexander Lippisch used drooping tips a few times like on the DFS39 and 40. The Boeing "Bird of Prey" has them. I have the flying wing articles by A. R. Weyl. I don't remember any mention of V-tails
    --------.~.
    --------/V\
    ------//----\\
    -----/(------)\--Norm
    ----(^^)-(^^) "For some years I have been afflicted with the belief that flight is possible to man" ~Wilbur Wright 5/13/1900

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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    It was the Nietperz --only mildly double cranked and reverse swept -- the reference to "vtail at the tips' was from the first poster on this thread I think --however in the thread on unjoined tails or twin hull configs I mentioned and posted a link to Luigi Pellarini's twin boom sesquiplane having two 'half V ' tails -- that is / on one boom and \ on the other side which has the same pro roll with yaw input as for downbent wing tips and approximates the analogy to the "V tail" on the wing tips (meaning I think the split V as just described ) 'Pellarini Air sedan' will probably pull up a picture of it hanging in a museum --the Pellarini designed transavia Airtruk (or Airtruck) PL 12 has two T tails on separate booms --in both cases the boom attaches mid span to the tail surface .

    The Blohm and Voss design with an actual -horizontal V tail ( < and > ) at each tip of a "tailess" swept wing --sometime called diffuser tips but don't know why -- is another case of control and stabilizing surfaces attached to but outside of a swept wing --small booms appeared on another version and it was recently revived and one SCALED design used the config (unswept though)

    I figured you might be up to speed on the Wehyl articles Norman --there is almost nothing of technical substance published in any of the mainstream aviation mags or Sport Aviation these days and only the archives (or books that collate the scattered remnants on obscure topics like flying wings or flying cars ) to refer to. Shame really.

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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    I think Klingon battleships also have the cranked down tips ( only guessing- don't read Klingon ) --I used to share a house in Ohio (in 1974) with a guy from Missouri who went on to work on the bird of prey . The mock up NAZI flying wing mentioned from Raiders of the lost ark is also a real design that I seem to recall got covered by Wehyl --I have some old Luftsport and Adler etc with many flying wing models of the gulled variety and the fact that they all seem to fly reasonably well with big variations in all the angles seems to indicate some tolerance . The skew airfoil section on the leading wing in a sideslip sees a really bad separation shape at the kink like ( as I write I have my styrofoam "hyperglider" chuck model in hand and have just tested it against my usually blase cat and can confirm both amazing stability and effectiveness against feline targets )--making cardboard mock ups and looking at them along a flight path gives a good idea of what the air sees and some idea of what might be going on to a first approximation I find --then balsa flying versions -- trying to sort out orthogonal axis and derivatives etc etc is also not as much fun and doesn't work on cats.

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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    More recently, the "Opensky project" by Kazuhiko Hachiya is using quite the same configuration.

    Projet OpenSky: les essais en vol continuent Ne Cede MalisFlying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-m02_3view.jpg

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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    Exulans (tailless foot-launched glider with adjustable wing sweep)
    www.infotech.co.za/exulans/exulans.htm
    This foot-launched design has a unique feature. Variable sweep! Check it out!

    -South Africa design=now I cant find them...

    http://www.delta-club-82.com/bible/708-hang-glider-exulans.htm

    Photo Hang glider : EXULANS (University Of Pretoria)

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    Re: Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"

    I'm curious if anyone has pilot reports on how aircraft with these Weltensegler-crank or diffuser tips perform in flight, and more importantly, how they handle.
    From what I've read about them:
    1. They are immune from Dutch roll problems.
    2. Tip controls produce favorable rolling & yawing moments when initiating a turn.
    3. Tip controls can be deployed (trailing edge deflected upward & outward) simultaneously to act as an airbrake while twist, pitch stability, and yaw stability are increased, just when they are needed most for landing.
    4. Very good yaw stability whether tracking in a straight line or turning.

    The Northrup N1M reportedly handled extremely well... early test flight problems were related to a weak powerplant and flow separation due to a thick airfoil causing a small elevator dead zone.. both problems were readily fixed.
    Attached Thumbnails Attached Thumbnails Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-n1m_ground_3.jpg   Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-n-1m_schematic_front.jpg   Flying Wing with "Diffuser Tips" AKA "Weltensegler Crank" AKA "Stromburg Wing"-stromburge.jpg  

    Last edited by danmoser; October 5th, 2011 at 10:43 PM.

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