Lifting body discussion

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Jeremy, Jan 31, 2007.

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  1. May 18, 2010 #81

    gtex09

    gtex09

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    Dear All,
    At this stage I just believe what I try and the results I get. Today I'm still modifying the wings like I said, i.e. making sure that the root airfoil profile is smooth after the separation point, and that this point is located around 35% of the chord.
    This is close to the standard 23012 profile, more or less. If this point is correct, and just enlarging a bit the elevons, then that will be OK. But I believe that the turbulent limit thickness will maintain a threshold in the elevon behaviour.
    Now, when you just look at the Facetmobile design, it seems that the separation point has been located far away from leading edge, like, if you want, on the laminar airfoils.... On laminar airfoils, the recompression of the air, at the separation point, is around 55% to 65% of the chord. This is somewhere pushing far back the separation point, and then making sure that the turbulent flow is small in the elevon area.
    So, first I'll try the already described modification. Then, if the behaviour at "high speed" keeps the same, I'll go to the concept of laminar airfoils, knowing that we do not need a high CL of the airfoil for low speed, thanks to the plan shape of the craft and the Polhamus effect at those low speed and high AoA.
    I'll be pleased again to read your comments.
    Cheers.
    GTex09
     
  2. May 18, 2010 #82

    gtex09

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    G'Day dear Tom,
    Thank you for the Arup movies and drawing.
    I guess that the upper speed was limited due to the skin drag. Because with 70hp engine, they should have obtained an higher speed that 100mph. This is the reason why I still believe that the right way is to reduce the overall skin drag, especially the drag due to turbulent airflow. So again, we have to push far behind, as much as possible, the separation point, then go to laminar airfoils. In the case of the real scale 1:1 wing, the reynolds number on the wing, at 4m, and at 70m/s, is already 2.10E7, then the thickness of turbulent airflow is around 50mm (2inches)...This is occulting the elevon movement at low amplitude.
    Then again, I thinck that I have to try it.
    I'll keep you informed.
    Cheers
    GTex09
     
  3. Jun 8, 2010 #83

    gtex09

    gtex09

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    Hello dear all,
    So now we start having something very interesting...
    The flight handling characteristics of the design are OK.
    Very stable, flying low speed as well as high speed, within a ratio of 4:1, no risk of spin, very light and controllable stall, difficult to get-in.
    So as explained in the FMx-05 PAV report from BW, and explored and continued in this development, this aircraft allow an easy building technics that I'll now explore, with the scale 1:1.
    Here's the link to the last flights of the scale 2/5th model :


    I'll keep you informed of the next steps.
    Cheers. ;)
    Gtex09
     
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  4. Nov 10, 2010 #84

    danF

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    gtex09

    Great work! I attended Barnabys seminar at AirVenture 2010 of the MKX designs. One thing he did was to check airflow disruption on scale models by coating a section with material that flows but remains adhered to the plane to make visualization easier - artists powered tempura paint and 30wt oil.

    Another potentially great tool is software from Europe (Austria?) It is supposed to be a replacement for Microsoft flight software and uses powerful design tools for you to design your own plane and then fly it. Will search for the proper name and post.

    DanF
     
  5. Nov 12, 2010 #85

    danF

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    gtx09

    My error, I meant Barnabys FMX designs.

    In looking at my seminar notes we discussed overall efficiency improvement ideas. Barnaby mentioned wing tips can produce about 5% improvements due to reduced tip vortices's. Span extension is superior to winglets, the idea is to sweep back/reduce tip chord. Paul Lipps is doing this on his prop designs. Another seminar on prop design showed the same good reduction in tip vortices's with small tip chords.

    Looked up the e-mail of design work and the person is using X Plane Advanta. He feels the newest version is a very powerful tool for design based on the software interaction with airflow. Any users comments welcome! :grin:

    DanF
     
  6. Nov 12, 2010 #86

    gtex09

    gtex09

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    Hi DanF
    Thanks a lot for your encouraging comments.
    I'm on the way building scale 1:1 ultralight, and in parallel I'm also building the same with scale 0.4 (2/5th)...
    I want to check again with the small improvements done on version GTx9-07, basically on MAC profile as well as on the elevons chord, trying to cancel the upper elevon.
    I also introduced a retractable landing gear, to check the difference I'll get with this previous version regarding drag.
    Regarding the software you just mentionned, unfortunatly I don't manage Xplane.
    All my engineering was done with Acad, followed by simulation with Nurfluegel, some structure validation with Catia.
    But for all steps, I checked finally with representative models, large size, applying sometime the old methods -like wires attached to the surface- to check airflow attachment in several conditions (Just connect on my youtube channel and you'll have a good overview)
    Anyway, I would be interested to see how the design is behaving within the Xplane software you mentionned. If you know somebody you could introduce the data inside, then I could send the key coordinates to him and try to make it "flying" in the simulator. One interesting should be simulate the behavior at high AOA, to check the vortices and the Polhamus effect, included the stability in all axis at low speed.
    Any comments of course welcome !
    Cheers,
    Gtex09
     
  7. Dec 8, 2010 #87

    Bart

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  8. Dec 12, 2010 #88

    gtex09

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    Hi Bart,
    What I'm doing is prepare a new version with all the previous improvements done on this concept from the beginning.
    This new model will fly soon, I hope to validate all my design.
    Actually on top I prototyped a retractable gear which I would like to be activated by cables, in the real scale 1:1 version.
    This gear should be simple and reliable.
    Keep in touch. Cheers.
    Gtex09
     
  9. Dec 12, 2010 #89

    Bart

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    Thanks, Gtex09,

    Can you please tell us more about your airfoil, especially the sharp leading edge? Would a more rounded and/or larger leading edge make a difference?

    How about vortex generators or flow fences?

    Thanks again.
    Bart
     
  10. Dec 12, 2010 #90

    gtex09

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    Dear Bart,
    Well, what I can tell you, is that every thing comes from NASA and NACA notes available on internet.
    A lot of stuff to read !
    Basically, I worked on the concept of a low aspect ratio shape.
    When you combine this to the flying wing studies from Horten, you understand that you get a good behaviour with a combination of :
    - a profile with a maximum thickness around 25 to 30% of the chord, in the center of the allwing (which could be named the fuselage, but which is part of the wing actually)
    - a laminar profile with a maximum thickness around 50% of the chord, when you go from the center to the tip of the wing.
    The concept of working with panels gives you the opportunity to obtain, in a simple way, a natural twist of the wing, which gives you a circulation with the right shape (see horten works)
    The MAC profile of my wing is a laminar flow profile, close to the Roncz Low Drag profile, and modified to integrate a sharp edge.
    This airfoil does have a positive Cm, close to zero, and a mean line in "S".
    Drawback is that the Clmax is not so high. This is the reason why the plan shape of the craft is important, because rapidly you can, with a sharp leading edge, obtain a vortex at the leading edge and get a Polhamus effect...Basically, you increase the Clmax when you have some good angle of attack of your wing. You can use it at low speed when taking off and when landing.
    If you put rounded leading edges, or even larger ones, then you will get more Cl max, but also increase Cd. You will not get the Polhamus effect so easily...So it will not show the same behaviour that the one we get today on the previous versions.
    Well, I don't know if I'm really clear in my explanation, but the combination of all those things gives really a very stable, strong and simple to build ultralight machine.
    To answer your last question, there is no vortex generator, only the shape of the wing and the sharp edge.
    Cheers,
    Gtex09
     
  11. Dec 12, 2010 #91

    gtex09

    gtex09

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    Dear Bart,
    Perhaps also to give you some more details, please find attached the wing sections at various span positions.
    Cheers.
    Gtex09
     

    Attached Files:

  12. Dec 13, 2010 #92

    Bart

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    Thanks very much, Gtex09, I have much reading to do.

    It will not surprise me when you put that BMW engine in your plane, if it climbs faster than Scotty Winton's Facet Opel. You will have probably lower wing loading and much more thrust.
     
  13. Aug 17, 2011 #93

    olgol

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    Gtex09, have you made any more progress with your project? Are you building the real 1:1 machine already or not?
     
  14. Aug 17, 2011 #94

    topspeed100

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    Is there a clear definion what is a lifting body an da flying wing ?
     
  15. Aug 17, 2011 #95

    Norman

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    Well... There was but people, either through self interest or ignorance, have muddled the two over the years.

    Very broadly a flying wing is any heavier than air aircraft that lacks a horizontal stabilizer i. e. the lift and pitch trim are provided by the same wing. Ideally there would be no fuselage either but the pink parts and the hot part have certain minimum space requirements that don't fit within a realistic airfoil shape with a chord of less than 3 meters.

    Canards are one example where people started muddying the water pretty early. However a canard is simply two lifting surfaces roughly in the same plane set so that the forward wing stalls before the aft one, just like the conventional layout, and the pitch control is usually on the aft wing

    There was a guy named Vincent Burnelli who designed some airplanes in the '30s with wide, airfoil shaped, fuselages. Before the Northrop 'wings became well known he called his planes "lifting fuselage" then in the late '40s he started calling them "flying wings" then after the NASA lifting bodies came out in the '60s he started calling them "lifting bodies". This is a case of the self interest I mentioned. Other than the wide fuselage Burnelli's planes were entirely ordinary with a big wing up front, that provided most of the lift, and a little wing in back to provide pitch trim. He did draw some flying wings in the '60s but since he hadn't actually built anything in 20 years I don't think the people calling him a "flying wing designer" are being very sincere

    When I hear "lifting body" my first thought is of the NASA lifting bodies of the '60s because that's the first time I heard that term. Those were basically designed to be dynamically controllable reentry vehicles. The first one, the M1-F1, was basically a half cone with some fins. A later model, the X-24A, looked like a potato with fins. These aircraft clearly had a fuselage but no wings. They were characterized by extremely low aspect ratios and, not surprisingly, low lift to drag.

    Some people have been calling delta winged aircraft lifting bodies. Deltas are low AR but not as low as the NASA lifting bodies. Generally a delta will have a distinct fuselage and wing but that's not necessarily the case. Deltas are usually designed for supersonic flight and that requires very thin wings but if you're going slower you can use thicker airfoils. When you use a 15% section at the root of a delta the wing can be thick enough to mostly contain the fuselage inside the airfoil contour. Is it right to reclassify a shape just because the airfoil is adapted for the speed. I don't think so. So IMHO delta wings are not lifting bodies but, if they don't have a little wing at the back for pitch trim, they are flying wings.

    Basically it's arbitrary but I use aspect ratio to differentiate. If the AR is significantly less than one and there's not a horizontal extension from the sides that's obviously big enough to be called a wing, not just a stabilizer, it's a lifting body. If the AR is 1 or greater and it doesn't have a stabilizer it's a flying wing.

    Clear as mud, eh
     

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  16. Aug 17, 2011 #96

    Rom

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    Looking at Wikipedia, where the lift is produced produced by the body of the craft vs the airfoil is a lifting body. There is no strict definition, so if you are the designer you may use the designation you feel approprate.
     
  17. Aug 18, 2011 #97

    bmcj

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    I think "lifting fuselage" was a very apt name for Burnelli's creations, whereas the name "flying wing" was innapropriate. I might have have also favored the use of "lifting body", but now that name has become synonymous with the NASA blunt wingless craft, so no longer fits the Burnelli concept.

    As far as the modern "lifting body" definition goes, I would go out on a limb with a generalization that they create lift with the bottom surface, whereas a wing creates lift with the top surface. (Before you shoot me, I did say it was a generalization :gig:)

    Bruce :)
     
  18. Nov 6, 2011 #98

    rogpoyn

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    Hello I'm Roger. I have been lurking on this thread for a while and was just wondering if there are any updates. You guys have impressed me with your rc planes. Not being an rc guy myself I have a crap load of questions to ask. Roger in OK
     
  19. Nov 6, 2011 #99

    topspeed100

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    I have been watching byrds ( ducks ) when they land and take of..that is masterity of lifting bodies at work...really...I have learned a lot for my latest design ( 4 seater 80-100 hp ) fast mover from byrds ( Albatross wings are amazing ). One thing though that I keep eye on is that it does look like a byrd at any angle.
     
  20. May 26, 2013 #100

    gtex09

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    Hello... Just one picture to update the status of my project, on going building phase.
    Regards.
    GTex09
    GTx9-11-C...en construction Mai13.jpg
     

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