Alternative fowler flap mounting

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by autoreply, May 4, 2012.

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  1. May 4, 2012 #1

    autoreply

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    It just occurred to me that it might be possible to mount Fowler-like flaps in a much simpler way as the common guided rails or an offset hinge, which have both a lot of drag and are structurally and mechanically rather complex.

    Let's say we connect the flaps to a simple tube that's hinged on the upper rear wing spar and on the upper flap LE. And we use a triangular plate that's hinged vertical at the wing spar and has a single joint on the lower part of the flap LE. Both the triangle and the tube are (with the flap up) parallel to the span. If we now extend the flap it will move rearwards (and sideways) and dependent on the position of the upper tube will also extend downwards. Canting the axis to which the "triangle" hinges to the wing aft will result in the flap extending both downwards and aft (and, dependent on the upper tube) also deflect downwards.

    I know some airliners use a similar, but vertical mechanism. The above strikes me as easier in almost any way. You can bolt/screw/glue the joints for "tube and triangle" directly to the spar and since you're not limited by the airfoils thickness and length, you can have much deeper flaps.

    I can see 2 clear disadvantages.

    *Flap rotation is intrinsically coupled to how much you extend them rearwards, like in the slotted flaps with a hinge point below the wing. You can notably reduce this by moving the "tube's" hinge point not only spanwise, but also chordwise. It isn't as discrete as a total Fowler flap, but you can get close to full rearwards deflection with only a minor flap deflection (circular instead of a straight trajectory if you plot rearwards deflection against change in flap pitch)
    *The spanwise movement, though this might actually be an advantage, in a low-winged aircraft you could also employ flaps under the fuselage.

    Anything else? It occurred to me as a neat solution, but since it's nowhere (I'm aware of) used in actual designs, I wonder what's wrong with this setup?
     
  2. May 4, 2012 #2

    orion

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    A picture is worth a thousand words... (hint?)
     
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  3. May 4, 2012 #3

    Jay Kempf

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    Really hard to visualize... sketch?
     
  4. May 4, 2012 #4

    bmcj

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    Can't picture it... (photo?)
     
  5. May 4, 2012 #5

    berridos

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    My brain is smoking but i just dont manage to fit the triangle...
     
  6. May 4, 2012 #6

    Himat

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    As i picture it, you have hinged the flaps as the airbrakes?
    But with unequal length "wishbones" to use a phrase from car suspension to get a certain amount of rotation. Wich the set up reminds me of. (If I did understand the idea.)

    Drawbacks?
    Maybe the forces in the hinge "members"?
    Make the sideways deployment work. (The geometry can be a challenge.)
    Drag due to large gaps when extended. (Sideways movement again.)
     
    Last edited: May 4, 2012
  7. May 4, 2012 #7

    autoreply

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    Apologies, these things are very hard to explain, even more so if you have to do it by electrons. I have recently re-installed my PC, but haven't come to installing Catia yet. The analogy to an airbrake is a good one, though what I had in mind is different.

    I'll give it another try. Let's look at a typical sailplane airbrake:
    [​IMG]

    I have shamelessly nicked that picture from the HP24 project site. Here are some more pics, so you'll perfectly understand how it works:
    http://www.hpaircraft.com/hp-24/update_24_february_07.htm


    Now forget that you're looking at an airbrake at the above picture. The MDF plate on the lower left is the lower wing skin, the MDF plate in the middle is the upper wing skin and just visible is the rear of our leading edge. That flat plate on top is our Fowler flap. If we would retract it, it would move to the right (when standing behind the wing) and move forward of course. Thus we have a simple mechanism that moves the flap aft and thus increases wing area, but it doesn't pitch down, so our lift increase is modest.

    Now take that upper bolt and replace it with a ball joint to which we join the leading edge of our flap. The flap is now free to change it's pitch.

    To constrain the pitch of the flap, we add another joint, on top of the flap. This one is connected by a truss (member) to where the hollow steel shaft runs through the upper and lower skin. If we make it so long that the flap will have considerable extra pitch when the flap is extended rearwards, once you retract the flap, it will also decrease pitch until it's neutral, if properly sized.

    By varying the position of the "upper member" on the wing, you can vary the pitch behavior of the flap.

    Now change the vertical tube in the picture for a triangle (simply to be much stronger in bending) and that's pretty much what I had in mind.


    Hopefully someone can understand it now. Otherwise I'll give it a shot with Catia next week.
     
  8. May 4, 2012 #8

    Hot Wings

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    Kind of like an anti servo linkage, but rotated 90 deg to the main hinge line?
     
  9. May 4, 2012 #9

    Rom

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    It sounds like there would need to be a telescopic mechanism coming out of the drag spar that the hinge would be attached to. That could be advantages to increase the cord by extending it strait for the climb and and deflecting it for landing.
     
  10. May 4, 2012 #10

    Himat

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    Maybe I didn't get it, but to me it look exactly as a double wishbone car suspension set up. Twisted and distorted, but basicaly the same. (You newer intentional fold the suspension on a car flat.)

    In this case only the lower member is a full wishbone, the upper member is just a simple link. I do think it would work. By playing around with the hinge points and wishbone length you get quite large rom to tailor the movement as you like.

    Aerodynamic drag from the sideways moved flap ends could be an issue.
    Still, I wonder why no one have used this idea before.
     
  11. May 4, 2012 #11

    DaveK

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    Sounds like the flaps on the 747SP, which have a rotary actuator with an arm attached to the leading edge of the flap and another arm that attached mid-chord of the flap. As the rotary actuator rotated the arm moved the leading edge back and down and the rear arm guided the the flap back and tilted it down. Acted a bit like a fowler but without a true fowler motion. Was lighter than the normal 747 flap system, but didn't generate as much lift, but the SP was lighter and didn't need it.

    Boeing 747SP - The 747SP.com Forum - 747SP flap system Schematics
    This shows a couple photos of it.
     
  12. May 4, 2012 #12

    autoreply

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    Indeed. You can tailor it such that you get most of the rearwards deflection in the take-off position without a track that's complex and has a lot of concentrated loads on awkward places.
    Yep, but if you change the "triangle" to just 3 welded tubes that shouldn't be too much of an issue. With the flap fully deflected you have a massive rearward pull, but because of the geometry you have the largest lever at exactly that position such that retraction forces are still fairly low.
    Hence the topic. My experience is that almost everything has been tried in aviation before, so if it's not used, there must be something wrong with it I'd think.
     
  13. May 4, 2012 #13

    Himat

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    In this case it could be two different reasons:
    An all or nothing aproach. The designer is satisfied with a plain, split or offset hinge flap, if not he goes with the full fowler flap, track and jackscreew option.

    The sideways mowement of the flap is that "strange" that it's not serious considered. Remember, there are a lot of conservative designers out there. They tend to copy what they know.
     
  14. May 4, 2012 #14

    autoreply

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    If I understand that correctly, that's the same mechanism as used on the B36 and the DC6:
    RC Model DC-6A FlapTest - YouTube
    B-36D Flap Test 3-10-2010.avi - YouTube

    That's vastly different from what I'm proposing though. When the above mechanism is enclosed within the wing you're limited to a relatively low backwards "throw", otherwise you get very weird effects when changing flaps. You're also limited to about half the depth of what I propose because you're otherwise putting the mechanism through the spar. As I see it, my mechanism (that folds spanwise) has almost unlimited flap depth without any mechanism hanging under the wing and much lower loads as the 747SP system or a conventional rail.
     
  15. May 4, 2012 #15

    DaveK

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    Okay, I get it now. I can see the sideways (along the wing) displacement being a concern.
     
  16. May 4, 2012 #16

    autoreply

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    Yes me too. I can also see an advantage: When they move inboard, you can extend the flaps underneath the fuselage. Have sailplane-style spoilers on the trailing edge that gets "uncovered" by the flaps (they move up with the ailerons, but stay flush when you move the aileron downwards). That increases your total flap area.

    Another interesting feature is that by adding a single extra truss you can have a double-slotted flap. The penalty in completely, compared to "traditional" double-slotted-flaps is much smaller.

    http://www.freepatentsonline.com/4614320.html?query=PN/4614320+OR+4614320&stemming=on
     
    Last edited: Sep 24, 2012
  17. May 5, 2012 #17

    Head in the clouds

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    I'm just going to wait for next week :speechles
     
  18. May 5, 2012 #18

    Workhorse

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    I think this is something similar to the Lisa flap deployment?.
     
  19. May 5, 2012 #19

    berridos

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    i could sware I saw something like you describe on an airliner or similar recently.
    For a Homebuilder I believe it would be more affordable to build than machining tracks. Additionally it is a very custumizable system allowing for trial and error by varying the length of the different members.
    The attachment of the members also seem to be easy to calculate and build.
    The pitty is I cant use it because i am building a highwinger and the flap would stop against the aileron or fuse or leave a gap between aileron and flap
     
  20. May 5, 2012 #20

    Workhorse

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    Nope, when deployed towards the aileron the flap would be far away and below, so it might grant the free full range of aileron movement, perhaps with some overlap if I'm true guessing AR's proposal.
     

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