Attention Tailless Nerds!

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

Help Support HomeBuiltAirplanes Forum by donating:

  1. May 24, 2019 #61

    Norman

    Norman

    Norman

    Well-Known Member

    Joined:
    Nov 29, 2003
    Messages:
    2,877
    Likes Received:
    902
    Location:
    Grand Junction, Colorado
    I haven't heard that Fauvels had a tumble problem but there is something mentioned in "Tailless aircraft in theory and practice" that's interesting. Apparently once in a while the AV-37 would do a singe flip at the top of a loop.

    There are two tumble criteria that I know of.
    One is Irv Culver's crotch depth to MAC ratio. Using paper models of varying sweep and tapper Culver found that the models with crotch depth (the distance from the root TE to a line connecting tip TEs) to MAC ratio of less than 2:1 could tumble if the static margin was too short.

    The other is from some WWII spin research the NACA did with fighters with bombs or external fuel tanks mounted on the wings. They found that the spin axis depends on the mass moment of inertia. Basically after a stall the plane will try to spin around the axis with the highest inertia. Normally in a conventional plane the heaviest axis is the longitudinal axis but when you put a heavy bomb load on the wings the lateral axis gains a lot of inertia, usually not enough to overcome the horizontal stabilizer but sometimes enough to cause a flat spin (especially if the static margin is too short). In the absence of a horizontal stabilizer a wing-heavy airplane is free to spin around the lateral axis (tumble).

    So the solution from a design standpoint is to keep the wings as light as possible, especially outboard, and distribute the mass in the pod as far apart as practical.
     
    Aerowerx and pictsidhe like this.
  2. May 25, 2019 #62

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    4,580
    Likes Received:
    1,212
    Location:
    Marion, Ohio
    Been wondering when you would check in on this, Norm.

    Here we are on page 4 of this thread, and all I did was say that the 'Tailless' book was available at a reasonable price!
     
  3. May 25, 2019 #63

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,681
    Likes Received:
    374
    Location:
    Sahuarita Arizona, Renton Washington, USA
    The secret is in the title. There are a lot of Nerds out here that are not getting any (or adequate) tail.

    The solution may not be to go without any tail but to make the best use of any tail that you have.
     
    pictsidhe and RPM314 like this.
  4. May 25, 2019 #64

    BJC

    BJC

    BJC

    Well-Known Member

    Joined:
    Oct 7, 2013
    Messages:
    8,872
    Likes Received:
    5,728
    Location:
    97FL, Florida, USA
    It took longer to get to that comment than I thought that it would.


    BJC
     
  5. Jun 2, 2019 #65

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,562
    Likes Received:
    402
    Location:
    Flint, Mi, USA
    That makes me wonder about the construction of the wing itself. As in where along the wing chord most of the mass of the wing structure is. A heavy main spar VS a pair of smaller fore and aft spars.
    That's going to make more a difference in a Fauvel as opposed to a tailed design isn't it?
     
  6. Jun 2, 2019 #66

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    5,865
    Likes Received:
    1,486
    Location:
    North Carolina
    I was reading a paper on lateral control characteristics when stalled recently. Though it was about tailed aircraft. One major point was that higher yaw inertia would often help keep an aircraft from being autorotationally stable. The ones being analysed, it made little difference if that inertia was in the z axis rather than the x axis, ie weight at the wing tips. There was quite a bit of maths involved.
     
  7. Jun 4, 2019 #67

    Norman

    Norman

    Norman

    Well-Known Member

    Joined:
    Nov 29, 2003
    Messages:
    2,877
    Likes Received:
    902
    Location:
    Grand Junction, Colorado
    The lightest spar design is a tapered I-beam at the maximum thickness of the airfoil. Splitting the load between two beams won't save you any weight.
     
  8. Jun 5, 2019 #68

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,562
    Likes Received:
    402
    Location:
    Flint, Mi, USA
    No, I'm not talking about the amount of weight. I'm asking how much splitting the load like that would affect the pitch handling.
     
  9. Jun 5, 2019 #69

    RPM314

    RPM314

    RPM314

    Well-Known Member

    Joined:
    Mar 27, 2015
    Messages:
    722
    Likes Received:
    300
    Location:
    the wrong side of the clouds
    There's probably more mass and moment arm to play with in the central pod/fuselage, so I'd imagine the effect to be relatively weak.
     
  10. Jun 28, 2019 #70

    lvaero

    lvaero

    lvaero

    Member

    Joined:
    Sep 24, 2018
    Messages:
    22
    Likes Received:
    3
    Location:
    Spring, TX
    That's a great price. I cannot remember what I paid for my copy from the UK, but this book is probably the #1 book in our library, and worth multiple times its weight in gold!! Totally worth it!
     

Share This Page

arrow_white