All Moving tail question

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by berridos, Jan 20, 2011.

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  1. Jan 24, 2011 #41

    berridos

    berridos

    berridos

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    The way I understand you wouldnt it be pitch up for a U? The unbalanced drag is above the hinge axis pulling the tail nose up?

    Would it be very complex to account for that pitching moment and select an airfoil for the horizontal tail that has a very high compensating pitching moment? A GAW1 or something similar.
     
    Last edited: Jan 24, 2011
  2. Jan 24, 2011 #42

    Jay Kempf

    Jay Kempf

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    For the first point the idea is that the tips of the U tail are being dragged back along the thrust axis meaning that the AOA of the whole tail is increasing in the positive for the tail meaning that the stick force would be forward meaning pitch down for the wing.

    The second point is, I think, asking whether a lifting airfoil could compensate. This is not possible due to the first point. No airfoil could compensate for a large offset like that. Airfoil pitching moments due to speed are small compared to large tail moments we are talking about here. If an airfoil moment were large enough we wouldn't be able to design a tail long enough with enough camber to counteract say large flap deflections.

    I suppose a W tail could be designed with enough area and symmetrical to the axis and neutral to the hinge. Maybe that is the direction to go. The morale here is that you need to separate the elevator and rudder functions and design for them individually. The rudder is inherently stable but the elevator isn't. A gimbel with a W shaped tail might actually work. Not sure it is either a drag or structural optimum but it would work.
     
  3. Jan 24, 2011 #43

    berridos

    berridos

    berridos

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    A w tail would be equivalent to a ring tail somehow.
     
  4. Jan 24, 2011 #44

    Jay Kempf

    Jay Kempf

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    A W tail would have an equal amount of area above an below the hinge axis for the elevator function. Left to right it would provide area for the rudder function on a gimbel axis at the 25% chord axis. And it would miss the prop wash. Something I have not thought of until now. It would actually work. Never seen this config in any existing design.
     
  5. Jan 25, 2011 #45

    autoreply

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    Why not a simple + shaped tail? Think of the DO-335, bit without all the other stuff. It could pivot @ 0.2C, and all forces are symmetrical. It might introduce a problem, other people mentioned of the Cirrus; because your moving mass (whole tail) is so heavy, you might develop dampening problems. Hanging by means of a:
    Universal_joint.gif

    and because it's symmetrical; torsional loads are low (propwash-effects).
     
  6. Jan 25, 2011 #46

    berridos

    berridos

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    Yesterday before going to bed I disliked the idea of a W tail.
    But this morning I feel like I will give it a try and draw it in Catia. However I will try an inverted W, an M.
    Mainly because I reduce the interference at the center with the boom.
    I am conditioned by the bending radius of graphlite rods. However that can be solved by increasing the aspect radius of the M tail.

    One issue I liked about the U is that for landing I need about 5-6% negative incidence to carry the flaps, and as everything was curved upside I thought there would be some venturi effect and the negative incidence would be magnified.
    If I use an M, the effect is the opposite and when deflected with negative incidence the air can escape sideways and reduced the incidence effectiveness.

    I got a feeling that a + tail has loads of interference. And one of the design goals was to keep interference low
     
    Last edited: Jan 25, 2011
  7. Jan 25, 2011 #47

    berridos

    berridos

    berridos

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    I see another problem....
    The wetted area of central inverted v section of the w hasnt the same drag as the outer v section.
    Because the center section has endplates and the outer section nice tip vortices.
    So we would need to adjust the hinge axis so that the drag is equally split.
    In case of a w the axis should be adjusted a hair higher having more surface below the hinge axis.

    The way to proceed would be to make the outer section a little longer, test the plane and keep on cutting off tiny sections until it feels balanced. However I wont be the test pilot.

    The question is interesting but I dont want to be a victim of non profit marketing to myself.
    Still not sure if the design will have a net benefit against beeing a total bluff..

    Any reference on the drag behaviour of curved wings?
    Any reference on the drag behaviour of curved wings with contained vortices?
     
    Last edited: Jan 26, 2011
  8. Jan 26, 2011 #48

    berridos

    berridos

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    Shouldnt the area split in small sections and weighted by the momentum (vertical lever arm) to the hinge axis.
    Sort of a numerical integration.
    That would make it more feasable.
     

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