Discussion Thread: The design of a tailless flying wing

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Aerowerx, Oct 8, 2015.

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  1. Oct 8, 2015 #1

    Aerowerx

    Aerowerx

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    Recently there has been quite a bit of interest in flying wings here on HBA, spread over several different threads. So to make it more organized, I thought I would start a thread just on this topic.

    I would prefer to keep it specific to "Horten style", with no vertical surfaces, but other ideas (winglets, close coupled rudders, Weltensegler tips, etc) are welcome. Questions are certainly welcome, but please try to back up proposals with some type of valid evidence, if you are proposing an idea.

    What I have in mind, for myself, is an LSA size craft with a range of 300-500 miles, cruise 120 mph, stall 50 mph. At this time my primary design tools are Excel and XFLR5, and of course my trusty HP42s calculator (yes, I still have one---can't beat the quality!).
     
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  2. Oct 8, 2015 #2

    cheapracer

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    Marske has been at it for 50 years, I guess that's why his wing is what it is - centralised elevators as far from the centre of lift as practical (long lever arm) and the ailerons as close to the CoG as practical for less pitch disturbance.

    Food for thought.

    I myself wonder if 2 small fins set some distance from the centreline and splayed out towards the rear, would help yaw stability by offering more frontal area on the advancing side and vice versa.
     
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  3. Oct 8, 2015 #3

    Topaz

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    If you're really serious about this, then you'll want to start gathering more information about the design mission, payload, etc. For an example, take a look at the motorglider design thread I've got running. The first section where I develop my requirements. You don't have to take it to that level of detail if you don't like - but you'll get more realistic results if you do - but start fleshing out the requirements and specifications for your aircraft.

    A flying wing is designed exactly like any other aircraft. You'll have additional work to do in the stability and control arena, which you'll adapt from Nickel, to keep the lift distribution to be one that provides good stall behavior while keeping induced drag at least moderately low (hopefully inside the "region with slight losses" in Figure 6.2.2 from Tailless Aircraft.Otherwise, you'll proceed much like any other design.

    I think an LSA on the higher-power end of that performance range would be a nice fit for a flying wing. Since you want your design to be "Horten-like", I presume that means a swept flying wing, as opposed to a flying plank or similar. In that case, I would include tip verticals that both reduce induced drag as winglets, and double as yaw stabilizing and control surfaces, because it's a combination that both improves the performance of the aircraft and provides positive yaw-axis control at all times. But that's just me.

    Nothing wrong with using Excel, XFLR5, and a calculator. I've been using my Excel and HP50g on my own project. :gig:
     
    Last edited: Oct 8, 2015
  4. Oct 8, 2015 #4

    Victor Bravo

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    Not to stifle creativity by any means, but what is wrong with the existing PUL-10 for that mission?

    It is a clear Horten derivative, nearly the size you are targeting, and any minor changes in size/payload/power to center it in any given LAS / UL / Microlight range are pretty straightforward. Other than the upright seating, it is about as Horten as you can get. It would lend itself reasonably well to electric, hybrid, or whatever Smart Car or Honda Fit engine conversion that was desired. You could easily stretch it to fit the motorglider rules if you really wanted retract gear and higher efficiency. You could steal some of Airbus and Siemens' "E-Fan" powerplants, or a bio-diesel-plankton-seaweed-Jatropha-oil engine, and create a futuristic whiz-bang next-gen politically-correct green deal.
     
  5. Oct 8, 2015 #5

    bmcj

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    If we can fly something with a tail but no wings, we should be able to fly something with a wing but no tail!

    saturnV3.jpg
     
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  6. Oct 8, 2015 #6

    Norman

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    And the power loading should be much more reasonable.
     
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  7. Oct 8, 2015 #7

    RPM314

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    Don't lock yourself into a purist 'no verticals' frame, there's plenty of beneficial things that exist out of plane. Even if you just want it like that for aesthetic reasons, verticals can still look good. Exhibit A:
    20150530_180241 (1).jpg

    I'd definitely recommend following Topaz's lead for designing to a set of requirements, but maybe you were intending this thread for discussing general design features. If so, then let me kick things off:
    -What kind of cockpit arrangements are you envisioning? Real hortenesque prone layout, or closer to the fuselage end of the spectrum? From your post it seems like you're thinking single place too.
    -What kind of aspect ratio are you thinking? The higher you go, the more problems happen with freedom flutter ('murica!) and pitch damping.
    -Have you considered a c-wing? Structural and control run issues aside, it offers the pitch control and trim efficiency of a tail while preserving the awesome tailless look.
    -I've been interested by Weltensegler tips for a while now, but there's precious little research about them. It basically stopped when Northrop ran out of funding for its test aircraft. I'm currently trying to get the hang of XFLR5 stability analyses, and once I do I'm planning to run a big batch of tests on their lateral and directional stability characteristics. Variables would be sweep, taper ratio, dihedrals of the two wing sections, crank point (in terms of span), etc. I'll definitely make the results public here.
    -In addition to the traditional calculation tools (kudos on that), check out desmos.com. It's a graphing calculator that I've found pretty useful in the past. You can just type in functions, points, data tables, etc. and it's pretty flexible. Like from Raymer's homebuilder's book, I put the equations for L/D, climb speed and propeller thrust into the calculator and it's all displayed visually, which is a lot easier and faster to process than big blocks of numbers.

    Good luck to you!
     
  8. Oct 8, 2015 #8

    autoreply

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    Winglets (or tip fins, whatever you call them) are a no-brainer today, unless you're after stealth. See the SB15 for a very thorough design analysis.
     
  9. Oct 8, 2015 #9

    Sockmonkey

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    Yeah, the yaw authority plus handling tip vortexes really gives you more pluses than minuses.

    Question: structural issues aside, say you have a FW where the most of the span is unswept with a constant chord and the tips are highly swept back and tapered extending well past the rear edge of the center span. Like if you stuck Horton wings on the tips of a plank wing. Would it suck? And if so, how?
     
  10. Oct 8, 2015 #10

    Topaz

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    I can foresee some structural issues - mostly weight - but the bigger question for me is, "what do you gain by doing this?"
     
  11. Oct 8, 2015 #11

    Sockmonkey

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    Mostly better lift distribution I'd hope. Just curious as to how it would perform in general.
     
  12. Oct 9, 2015 #12

    Norman

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    That's basically what Igo Etrich's Zanonia seed gliders evolved into. Then he tried to put an engine on the front of it and the thing was a disaster so he put a tail on it and called it "Sperling" which later evolved into the "Taube". The Weltensegler also had swept outboard panels but was so flimsy that it only flew a few times. There was also a hang glider called "Exulans" with slightly foreword swept inboard panels and variable sweep outboard panels. As I recall it was too ungainly to foot launch so they dropped it from a balloon and the sweep mechanism failed (talk about your life hanging by a thread). The SZD-6 Nietoperz was a nice looking sailplane with foreword inboard and aft sweep outboard. Models of these planes are flying but in many cases it seems that the models are better engineered than the originals. As Topaz said the cranks in the spar make it heavier but since carbon fiber is cheaper and a lot stronger than aircraft grade spruce there's no reason that you couldn't do a better job than they did with wood back then. Personally I find the idea of decreasing sweep toward the tip more interesting, like #3 in this drawing:
     

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    Last edited: Oct 9, 2015
  13. Oct 9, 2015 #13

    Tiger Tim

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    I would think there's data available, this is exactly the planform used by the Canadian NRC Tailless:
    [​IMG]
    https://en.m.wikipedia.org/wiki/NRC_tailless_glider
     
  14. Oct 9, 2015 #14

    bmcj

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    Naturally, but since most swept flying wings have negative lift at the tips, the winglet design has to be adjusted for that.
     
  15. Oct 9, 2015 #15

    bmcj

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    Wow, shadows for landing gear... that has got to be light weight and low drag! :gig:
     
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  16. Oct 9, 2015 #16

    RPM314

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    A misconception as far as I'm aware. Sweeping the wing and having more lift at the root than the tip provides a nose-up moment, and yes the extreme case of this is negative lift at the tips, but it's not required by any means.
     
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  17. Oct 9, 2015 #17

    Sockmonkey

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    Hmm... Maybe have those tips be all-flying elevons mounted just outside the rudders.
     
  18. Oct 9, 2015 #18

    Aerowerx

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    Lots of comments. Too many to reply to individually, so I will lump them all together.

    There has been some interesting discussions of flying wings in recent months, but they are spread over several different threads. My intent in starting this thread is to have a single place to discuss the unique design problems of flying wings, along with the various options (like winglets).

    At this time I do not have a specific design project, as in Topaz's motor glider, as I am still trying to understand the theory, in addition to still learning XFLR5. All I have are some general ideas as to what I want to see, at least for my (future) design.

    What I was thinking was upright or semi-reclined (20-30 degree angle on the seat back) position. I am still vacillating on being 1 or 2 seats, and I have been having trouble getting the CG right (using XFLR5) for a tandem arrangement. For tandem seating the pod/cockpit would have to be 12 or so feet long. Yes, I have seen the PUL-10, and it is a Horten design, by Reimar Horten, but one comment I have read about it is that the cockpit is too wide and causes some kind of problem with the air flow to the pusher prop.

    From my own virtual experiments, and from what I have been reading in "Tailless Aircraft", the only real problem with a pure flying wing (no vertical surfaces) is the lack of yaw damping.
     
  19. Oct 9, 2015 #19

    cheapracer

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    I am aware the first flight of the Facet Opal that there were no fins - short flight and the very first thing they did next was put the fins/rudders on, I'll try to find out why.

    There is literally nothing that can't be learnt starting from this page and all of the links and all of the PDF downloads ....

    On the 'Wing...
     
  20. Oct 9, 2015 #20

    Norman

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    While I was searching for pictures of Pterodactyls I found this mislabeled picture of the NRC plane

    Pterodactyl.jpg
     

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