Attention Tailless Nerds!

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Aerowerx, May 5, 2019.

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  1. May 11, 2019 #41

    Aesquire

    Aesquire

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    Source = Northrop Flying Wings by Pape & Campbell.
    N9M #1 crashed during aft CG & control tests. Investigation concluded that there was a control reversal and the pilot was pinned into his seat by the control column. ( Low pressure pulling elevons up? ) #2 initial test flights showed severe reversal of elevator control forces at high lift coefficients. ( solved by designing a full power hydraulic control system )

    MX-334 #1 hit propwash from tow plane after release, pitched up, stalled, flipped nose up, over onto back, went into spiral. Pilot was unable to reach the controls of the prone cockpit, so released the bottom escape hatch, ( now on top ) unstrapped, crawled out, and sat on wing for a moment before deciding he wasn't doing anything useful there, stepped off, and deployed chute, made good landing. ( can't blame CG for this one, sometimes prop wash /turbulance is just too much to overcome )

    YB-49, stall testing, normal CG, flipped nose up over tumble, recovered @ 1000 ft. Pilot Cardenas said centrifugal force pulled arms up, but luckily the throttles were over head, and got one engine up to 100%, to recover. Must have been a wild ride.

    YB-49 #2 crashed, possibly from excess speed in dive after tumble/spin recovery.

    YB-49 stall testing with gear down to slow plane, stalled, snap rolled, recovered.

    I may be wrong about something here?

    I know that with hang gliders, and a variable CG, that holding near stall ( rear ) CG position can induce a tumble. Full speed ( fwd ) position invites over speed. And a high speed cruise position ( fwd of best L/D ) is best for turbulence. hmm.
     
  2. May 11, 2019 #42

    simflyer

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    After Arup designs, Flying Pancake etc., some getting homebuiltable.

    Thread UFO - useless flying objects gives links to ausie Dave Rowe's UFO:



    Verhee's Delta D2:



    Dyke Delta:
     
    Last edited: May 11, 2019
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  3. May 13, 2019 #43

    mm4440

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    You forgot the Wainfan Facetmobile. There are more in the works. Low AR aircraft can be great flying machines if they are kept light.
     
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  4. May 13, 2019 #44

    delta

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    And have tails.:D
     
  5. May 13, 2019 #45

    Aerowerx

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    My copy of the book arrived today.

    It is new, but I suspect a "print on demand". It could have been packaged better, as there is a ding on the back cover, which I am not going to complain about.

    Nice picture of the Falter 1 on the back cover, with Nickel himself at the controls. For those that don't know what the Falter 1 is, it is a cloth-wing ultralight/microlight using the principles outlined in the book.
     
  6. May 21, 2019 #46

    RCBinChicken

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    That last sentence gives me hope for everything I planned to achieve! :D

    I'd also like to heartily concur on the ventral strakes, from an RC model perspective. My current "bash around" plane is, frankly, a messy/lousy build that I revised several times, a sort of prop-in-slot delta affair with a (small) single vertical. But I gave it "slabs" of foam on its underside, to very crudely mimic (in side view only) the big combined engine nacelles of something like an XB-70. I didn't expect them to have many non-cosmetic effects, but to my surprise, with careful throttle handling, she's happy at anywhere between 0 and 90deg AoA! Flies best high alpha at "walking pace" around 60deg, can "walk" her through a (netless) soccer goalpost with the rudder, turn around and walk her back through! All my other deltas start to wing-rock like an Easter Island statue anywhere above 25deg. If my haphazard strakes can make that much difference, would love to see what some properly designed ones can do. :)
     
  7. May 21, 2019 #47

    Victor Bravo

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    Although this represents additional thread drift, can any of our more educated folks offer an opinion as to whether an unswept (Fauvel style) wing is or is not prone to the same kind of tumbling problems that the trike in the video had? The Fauvel gliders do not have that reputation that I am aware of, but they have the mass pretty much in the center... and a forward GC... and if there is a likely pitch tumble issue with the Fauvel configuration I would like to know about it. Yes, this does have something to do with an idea I have for an aluminum Pelican :)
     
  8. May 21, 2019 #48

    Aerowerx

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    Not sure I am qualified to completely answer your question, VB, but the problem with earlier trikes/hang gliders with cloth wings is that if the dynamic pressure gets higher on top than on the bottom surface... Well, lets just say you better make sure your life insurance is paid up.

    Any tailless aircraft design needs special attention to all the little details, whether it is a plank, swept, or delta wing.
     
  9. May 22, 2019 #49

    Hot Wings

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    I'd say they are not prone to tumble - based on this:
    note 2:50 to 2:60
     
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  10. May 22, 2019 #50

    Victor Bravo

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    Very good... thanks for posting that :)
     
  11. May 22, 2019 #51

    bmcj

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    No, you got that wrong. Aerobatics is flown by the “wired”. :eek:
     
  12. May 23, 2019 #52

    pictsidhe

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    I watched a fauvel do some impossibly tight loops and other manouevres at Shuttleworth. I bet it could tumble if you get the cg in the wrong spot. But, I've not heard of it having problems, so copy all the critical dimensions well and you should be OK.

    The official cause of the Facet Opal loss was pitch instability, though there is a chicken and egg argument about the spar failure. The SB13 had a bit too much short period pitch instability for good flying.
    The longitudinal damping of an aircraft is going to depend on the effective MAC of the entire plane. With a conventional plane, having the tail out on an arm greatly increases the effective MAC and therefore damping. A high aspect plank is going to have the least damping, a low AR delta the most. A swept wing is going to depend on the sweep and AR. Perhaps adding a dynamic stabiliser would help, such as the bobweight in the Spitfire elevator linkage.
    An Alumican? I'm eagerly awaiting the showdown with Propastie's Dragon. He's won the naming contest, though. ;)
     
  13. May 23, 2019 #53

    Heliano

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    I happen to have a few hours' experience flying the Fauvel, built in the forties in my country, a loooong time ago. Let me point out to a crucial difference: control surfaces vs. weight shift. Weight shift has a problem: it is weight that commands the aircraft when in a static situation. In a dynamic situation, when accelerations occur, it is inertia. Depending on what kind of acceleration (rotational, traslational, intensity, etc.) anything can happen. Such cases do not happen if the aircraft pitch axis is commanded by control surfaces. That is why some consider weight shift control as intrinsically marginal. I see the tumbling as a control problem, not a stability problem.
     
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  14. May 23, 2019 #54

    fidalgoman

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    I got to meet Mr Kasper before his death and to examine his glider at his home in Bellevue, WA. One very important point he made was to keep the Center of Mass as close to the aerodynamic center as possible. Many designers push the mass forward thinking it will help in tumbling recovery but in reality it creates such a large pendulum moment that the elevons cannot overcome it. Here's an old super 8 video of some of his tumbling aerobatics. Notice he is doing forward and backward flips, so the proof is in the pudding as they say. By the way Mr Kasper was an aerodynamicist for the Boeing Co.

    It is important to note that one size does not fit all. Geometry of the wing makes a huge difference. A plank, pancake, forward sweep, aft sweep, delta, aspect ratio, etc make huge differences in how aerodynamic forces respond to control shape and input. Mr. Kasper's wing used sweep and trapped vortex at the tips of his wings to prevent stalling. A plank would not. So it's very important that we don't lump all flying wings into the same basket. Each is unique unto itself.
     
    Last edited: May 23, 2019
  15. May 23, 2019 #55

    Aerowerx

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    Exactly!!!

    You go "outside the envelope" in terms of control effectiveness and, as I said before, you better have your insurance up to date.
     
  16. May 23, 2019 #56

    Aerowerx

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    Which is true for ALL aircraft designs, tailless or tailed.
     
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  17. May 24, 2019 #57

    pictsidhe

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    I'd rather try my luck at altitude and spend the insurance money on a plan B 'chute.
     
  18. May 24, 2019 #58

    Dennis K

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    First let me make it clear I have no time in the Fauvel but did attend the 1987 Nurflugal semanar at Elmirea where a former owner (Jack Lambie ?) discribed flying his. He claimed it was very stable and easily trimmeable for hands-off flight. He discribed leaning slightly foreward or backwards to decend or climb while eating his lunch. His only complaint was a tendency to shed its lower fins in the fastest, most uncontrollable ground loops if either one cought anything, such as a dandylian, upon touchdown. Incedentally, I own Vampyr (Pelican) plan #39.
     
  19. May 24, 2019 #59

    Arfang

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    J.C. Debreyer described his Pélican as ''stable, easy, well dampened and robust''

    Jean-Claude Néglais, who logged over a thousand hours in AV-36/22/222 wrote an article about his experience with the Fauvel wings, he didn't mention any tumbling issues. I have attached the full article below, it's only in french unfortunately. Let me know if you need help translating it.

    J.C. Néglais also mentions this method to trim a Fauvel by leaning forward or backward or moving the seat/food container/water bottle .

    Beware the Vampyr, as you probably know no prototype ever flew and it has some issues with weight and balance. One of our members built one a few years ago:

    https://www.homebuiltairplanes.com/forums/threads/vampyr-flying-wing.8086/page-3#post-100598

    From what I know, it ended up being overweight.
     

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    Last edited: May 24, 2019
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  20. May 24, 2019 #60

    Hot Wings

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    Google translate did a readable job - here it it in Word.
    Thanks for the article!

    I should have my plans in about a week and would like to start building this fall. I'm interested in collecting any and all information related to the AV-36 and AV-45.

    I'd also like to build a data base of all known examples of this type with some history, condition and who built and is flying them, even if they no longer exist.

    Edit: Should have read the doc completly befor posting. Didn't factor in the size limit. Replaced file with more complete Google Translate version.
     

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    Last edited: May 24, 2019

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