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Thread: Delta wing airfoil

  1. #31
    Registered User Monty's Avatar
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    Re: Delta wing airfoil

    Quote Originally Posted by jedi View Post
    Reference post #2. " Would it fly, yes. How well? [There is] only one way to tell."

    If you want numbers you need to do the work or have someone else do the work for you. I appears you are looking for the second solution. So am I (and many others).
    I don't expect anyone to do the numbers for me. What I would like is constructive reference to appropriate documents or publications, or commentary from those that might have actual real world experience with this type of planform. Honestly the model aircraft people are more helpful than this place. Unfortunately the reynolds #s are not comparable.

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    Registered User BoKu's Avatar
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    Re: Delta wing airfoil

    This is one of those cases where xfoil would probably tell you everything you need to know. My guess is that you'll see a big separation bubble at the forward edge of the flat section starting at fairly low angle of attack. That nobody around here has tried it is probably not a good sign.
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  4. #33
    Registered User jedi's Avatar
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    Re: Delta wing airfoil

    Quote Originally Posted by BoKu View Post
    This is one of those cases where xfoil would probably tell you everything you need to know. My guess is that you'll see a big separation bubble at the forward edge of the flat section starting at fairly low angle of attack. That nobody around here has tried it is probably not a good sign.
    I do not have experience with xfoil but it is my impression that the xfoil equations do not support the LE "vortex lift" flow of delta wings at high angle of attack. Can anyone with xfoil comment on that?
    The most elegant theory can never change reality but even a mediocre theory can predict reality most of the time.

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  6. #34
    Registered User Monty's Avatar
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    Re: Delta wing airfoil

    Quote Originally Posted by BoKu View Post
    This is one of those cases where xfoil would probably tell you everything you need to know. My guess is that you'll see a big separation bubble at the forward edge of the flat section starting at fairly low angle of attack. That nobody around here has tried it is probably not a good sign.
    I don't really place much stock in 2D vortex panel methods. Especially in a case where span-wise flow and 3D effects predominate. I was hoping for some publications to help validate CFD analysis, which I can do....

    Click image for larger version. 

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    Unfortunately I think most of this work is in the dark world or internal documents..oh for the days of NACA.

    Monty

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    Re: Delta wing airfoil

    Would any of these reports be of any help?

    19930090363-min.pdf

    Low-speed static stability and rolling characteristics of low-aspect-ratio wings of triangular a.pdf

    naca-rm-a6g24.pdf

    The first report describes a configuration close to what you are suggesting:

    Click image for larger version. 

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  9. #36
    Registered User Monty's Avatar
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    Re: Delta wing airfoil

    Quote Originally Posted by Arfang View Post
    Would any of these reports be of any help?

    19930090363-min.pdf

    Low-speed static stability and rolling characteristics of low-aspect-ratio wings of triangular a.pdf

    naca-rm-a6g24.pdf

    The first report describes a configuration close to what you are suggesting:

    Click image for larger version. 

Name:	img148.jpg 
Views:	28 
Size:	35.0 KB 
ID:	78953
    That last report has some good info. Virtually no penalty in cruise. About .2 CL hit for the double wedge at low mach numbers. I would expect my wing to be between the two somewhere. That study was for a plank wing. I would expect since there is a great deal of spanwise flow with a delta it will present more like an actual airfoil to the flow, and should not be much worse than a 0.1 CL hit. At least this brackets the problem. Thanks!

    Monty

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    Moderator Topaz's Avatar
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    Re: Delta wing airfoil

    Quote Originally Posted by Monty View Post
    Keep squinting....Have you used an English wheel??
    Nope. I'd do a non-structural fillet in composites, like, well... most people. But my real point is this: Your flat-box delta has flat-wrap conic leading edges (in the form of a strake) and, one presumes, a flat-wrap conic trailing edge aft of the main box. So, in the end, not really any different than a conventional-airfoil wing fore and aft of the box, in terms of the wing-fuselage intersection. You're still going to have to merge the conic projections with the fuselage shape somehow.

    Quote Originally Posted by Monty View Post
    Please see original post. How much difference does it make?? No one has given a number. I want a number, not a feeling.
    Well, if this is really your question...

    Quote Originally Posted by Monty View Post
    ... How much performance will be lost from a lack of airfoil?? ...
    That's not a question someone is going to be able to give a numeric answer for without 1) A better definition of "performance" as you intend to mean it here, as in which parameters are you wanting to measure. Cruise drag? Low-speed lift and drag? Pitching moment? Yaw moments at low speed and some given yaw angle? 2) A heck of a lot of CFD, and pretty high-end CFD at that. Vortex lift isn't something you can just toss up on XFLR5 and get a reasonable answer, and the answer, like structural FEA, is going to depend a lot on how you mesh and set up the model and problem. 3) An actual model to run the CFD upon.

    Separated flow is still devilishly hard to model accurately even with "prosumer" CFD software, although that situation is improving as the high-end codes the "big boys" use are filtering down to us layfolk. Boeing could give you a very clear numeric answer to your question (once the parameters are defined and the model provided) but I would imagine that few here on HBA have access to that level of code. Orion used to have some semi-empirical ways of estimating values and coefficients for vortex lift, but in the end he'd send out his model to a paid consultant with appropriate software to get actual numeric answers. His Raspberry design being the most prominent one described here on HBA.
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  12. #38
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    Re: Delta wing airfoil

    Quote Originally Posted by Monty View Post
    I don't really place much stock in 2D vortex panel methods. Especially in a case where span-wise flow and 3D effects predominate...
    After a bit of reading on vortex lift, and on Ed Heinemann and the A4 development, I think you're on the right track. As long as you stay in the neighborhood of the A4's thrust/mass ratio, a RIFPIB plank delta will work fine.
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    Re: Delta wing airfoil

    Quote Originally Posted by Himat View Post
    I canít remember what book, but one aerodynamic book had a story from the development of the A4 Skyhawk. One of the aerodynamic engineers had done a lot of testing of different airfoils and could not decide. One of the seniors told him to cut a plywood sheet to the same outline and thickness as the wing tested. All in all, the plywood sheet did not perform that much worse.
    Actually, Bill Husa (Orion) published a paper on "Airfoil selection" that included that information. Copies are available on the web; here's one link.
    https://rtfmaero.files.wordpress.com...-bill-husa.pdf

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    Registered User Toobuilder's Avatar
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    Re: Delta wing airfoil

    Considering what passed for an "airfoil" on the F104 and the F117 (and the Hiperbipe, for that matter), I'll bet you won't suffer that much with this concept.

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