Tandem Wing Pusher

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Starman, Oct 30, 2010.

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  1. Nov 6, 2010 #121

    Starman

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    Richard thanks for doing that, if that could be done again when the wings are more locked in then that would be fantastic. but they are close now, 2000 lb gross, 60 mph stall and a front rear distribution somewhere around 70% - 30% front rear.

    I'll get to more of your comments but for now, concerning what you have above.

    I like things that have a lot of reserve capacity and strength, so I like the idea of being able to cruise along at 200 mph with the engine loafing along, the throttle barely cracked open, then when you get to the end of the box canyon you point the nose up sixty degrees, floor it, and it will accelerate upwards.

    So I want to make the wings beefy enough to take around 300 hp. But, assuming that I might not be able to get a slicked up V8 model done in a few months, I think I'll put an 0-200 on the back first and leave the tube frame exposed, with a glider type cockpit or simple aluminum frame a la ultralight

    That way, if I go to the local EAA chapter for assistance they won't think I'm a nut. I am a nut, but anyway ...

    Also I have a plan that goes something like this. I'll make the first version look as plain Jane and boring as possible by leaving the fuselage skins off, and the 0-200 in back exposed, so I can test fly it and people won't pay it much attention. When I go to the big fair people will say something like: "well that's kind of cute idea in a way ... but it's kind of gross too". So it won't get no steenking attention, but maybe some people will want it like that. OK that's fine.

    Then when no one is looking I'll put the V8 engine in and the skins on the fuselage and blow some minds.

    It's kind of like in the 'Cindarella' type of kiddy movies, you know, where the starlet is sort of plain Jane, but later she takes her glasses off and lets her hair down and you wouldn't kick her out of bed for anything. And remember Voyergeur, about getting me dates with hot women.

    I'll get to your other great comments later but for now.

    I'm studying my dragonfly and VariEze plans, looking at how to adapt them but someone is suggesting I make molds from the start. With CF do you need to make molds for all the parts?

    Next on the agenda, if anyone is willing to offer suggestions, is attachment methods of the parts. For example, the cockpit bolts to the frame with four bolts in a square or rectangular pattern on a vertical plane with a certain spacing, but how is it best to orient the bolts.

    There will be an open top 'trough' going across the plane where the wings go so a wing can be dropped on. What to consider is what is the ideal (easy and fast!) way to attach it. I envision something as simple as a single vertical bolt (+ locating pins) going through the center of the wing and into the frame, with a wired locknut which can be easily checked. It could be two bolts front to back or side to side or four bolts. in all case the wing will have an incidence block under it and some kind of removable? frame on top to distribute the pressure from the bolt(s).

    Today I started experiencing some mind blowing synchronicity around this, meeting people. I mean, it could be mind blowing for some people, but my mind's already been blown earlier.

    Edited to change the "i" to "ee" in the word 'stinking'
     
    Last edited: Nov 6, 2010
  2. Nov 6, 2010 #122

    Starman

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  3. Nov 6, 2010 #123

    Starman

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    As I was looking at equations for calculating maximum wing lift due to flaps. The more chord the flaps have the more lift you get, so I figured I would maximize it. If this kind of flap is at the front of the wing it's a slotted LE flap, if it's in back a slotted TE flap, you can make a plastic deformation modeling of a slotted airfoil go smoothly from one end of the spectrum to the other, and if you stop in the middle you have a slotted wing. This is the worlds first slotted wing, AKA maximum flaps.

    Of course if less flap chord is better that's good too. Goal for the front wing is that it must generate maximum possible lift from it's wing area.
     
    Last edited: Nov 6, 2010
  4. Nov 6, 2010 #124

    Starman

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    I was wondering about those longer span wings on the rear and what could happen to the ends when the front wing stalls, since they aren't in the down wash. With a weight/lift distribution of 70% f/30% r the front wing becomes bigger than the rear and so it won't have that problem. Like the Dragonfly, with equal span wings.

    I was thinking that if the front wing tips are lower (or higher) than the rear ones that the tip vortexes starting off of the front wing might help cancel the rear ones, but as I see in your diagrams, the vortex looks like it's too big to be affected by that.

    It is my impression that as you make the front wing carry more of the load that total wing area becomes less - up to a point.

    Here's a nice thought exercise for you budding design students, find the optimum front/rear lift ratio to get the smallest overall wing size.

    For safety reasons when front wing stalls the rear wing must be at 70% of it's Clmax or less.

    For example, assuming:

    20 psf front wing loading
    9 psf rear loading
    2000 lb weight
    front wing Clmax 2.0
    rear wing Clmax 1.0

    A plane with a 50/50 lift distribution will have a 50ft front and 110ft rear for a total of 160 ft wing area.

    A plane with a 80/20 lift distribution will have 80 front and 44 rear for 124 total

    A conventional plane with a 110/-10 lift will have 110ft front 30-40ft rear for a total of 145 ft.

    So, the front wing biased tandems like Dragonflies have the least total wing area for a given stall speed. (except for really long tail planes)
    _____________________________

    So here's your Mission Impossible challenge, if you wish to accept it. Which lift distribution has the least wing area?

    I already got it pretty close using the above method but if you have one of those aerodynamics programs that is just dyin' to run around a little you can see what comes up. Keeping in mind that with a single passenger the CG shifts to the rear so it needs a little more margin.
     
    Last edited: Nov 7, 2010
  5. Nov 6, 2010 #125

    Starman

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    Q: "For bolting on the cockpit ... four bolts in a rectangular pattern on a vertical plane, but how is it best to orient the bolts"

    A: Sideways, that way you could lift up the back of the cockpit and put the two bottom bolts in while the nose rests on the ground, then lift the nose up and put the two top bolts in.
    __________________

    Another thing that's interesting to think about, for me, is: what spatial arrangement of the four wingtips might help cancel out the wingtip vortexes, if any? An X wing layout front view seems like it might do the trick, or if the back wing is shorter than the front by the right amount and following directly behind the front it might cancel.
     

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  6. Nov 7, 2010 #126

    Sky High

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    As for Drag, if the Diana 2 has a 50:1 L/D, for its 500 kg weight, thats 4903 N / 50 = 98N of drag more or less......quite a lot less than the 278N I have calculated for the tandem wing.

    As for power, yes some larger 850kg gliders (1 & 2 seat) have 56 hp engines (41Kw), but they are self launching, the number I quoted was for level flight and no other consideration, so its actually more like the sustainer setup in modern gliders. If you look at them the Discus 2 CT has approx 15.3 Kw (20.517hp) and the ASG-29E has 13.5 Kw (18hp)...granted they are not doing 185 knots which is in fact close to their Vd, on the other hand the AR5 is half the weight of a ballasted 18m sailplane.

    In the graphs, the first & second (larger view of Cl v. Cd) are T2 section polars that are set up for the respective sections with design speed, weight, AR for (Magenta) one of my 18m designs, (Red) the tandem wing, (Green) the Diana 2, (Yellow) the ASG-29 and the Naca section with 2 setups, (Blue) for the tandem wing setup and (Tan) for the AR5. Note how much the Naca Section performance changes due to the setup. For the tandem wing, the goal was very low drag in the cruise configuration (about 32 drag counts) and higher CL's at higher Alpha's, the mid CL section wasn't optimised as that would compromise either end.

    The last 2 graphs show why the stall speed is so high. The downwash from the body and the fwd wing lower the performance of the aft wing, such that span efficiency is around 52% and no where near elliptic (see the local lift distributions) and even the combined distributions are non-elliptic, and while the the fwd wing sees a 10x increase in CL at the stall, the rear wing sees barely 1.2x which doesn't help the stall speed too much and hence my comment about the need for changes to the configuration before to make it a better platform. The other thing to remember is that XFLR5 isn't particularly good at high CL's, so this is more of an indication than an absolute.

    Cheers
    Richard
     

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  7. Nov 7, 2010 #127

    Starman

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    Wow, that seems bad. The solution to the poor performance of the rear wing is to make it carry less and be smaller.

    This is the same plane with a 90% front - 10% rear weight distribution. It looks like a conventional plane but it's still a canard/tandem wing with the pitch control on the front and ailerons in the back, giving it the typical canard stall/spin resistance.

    Adding leading edge slats increases Clmax to around 3.0 so the front wing can be around 60 ft area and still have a stall speed of 54kts.

    I think that's close to a minimum overall wing area layout.

    I do realize I have to pay close attention to flutter, and I know how to do that with weights in the outboard leading edges of the wing in addition to on the controls.
     

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  8. Nov 7, 2010 #128

    autoreply

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    Sorry, but those comparisons are irrelevant, we could even say they're bullocks.
    You can't compare the drag force at one speed to the drag force at another speed. You can't look at the HP a "sustainer" has, because they actually climb. They only need 2-4 hp for horizontal flight.

    The only way to objectively compare different aircraft is drag coefficient and aspect ratio (where you then also need to know wing area), or - if you're only looking at frontal drag, the flat plate equivalent area.

    As for the interference; yepz, there's a reason we don't see that many tandems/canards anymore.

    How did you get the profiles (of the DII and the ASG-29?) Care to share?
     
  9. Nov 7, 2010 #129

    Jay Kempf

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    I have been staring at this and built a weight and balance spreadsheet (just first order of magnitude). I can make any configuration zero out on a cg scaled between the wings. The question is if you heavily bias the weight of the airframe on the front wing and you heavily bias the aerodynamic center, don't you have an arrow being shot feathers first from a stability standpoint? If the front wing stalls and all the weight is on the front wing and the rear wing is still lifting then what you got is a tuck as opposed to a stall. Am I looking at this wrong?

    Force diagrams in static space lie! :)
     
  10. Nov 7, 2010 #130

    Sky High

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    with a few corrections for the more obvious things that xflr5 does wrong....the flat plate drag should be around 0.932, so not as good as the AR5
    The wing sections/fuselage shapes I get by digitally removing them from the airframes, generally accurate enough that they don't require too much smoothing, if any. Try to do them every 250mm so I can identify where the section changes occur if they are there. Just got the JS-1 done and I have the majority of the sailplanes from the last 15 years or so done.
     
  11. Nov 7, 2010 #131

    Starman

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    :) for later
     
    Last edited: Nov 7, 2010
  12. Nov 7, 2010 #132

    autoreply

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    Do I understand correctly that you measured them from the wings, by means of a laser scanner or so?
     
  13. Nov 7, 2010 #133

    Topaz

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    I'm curious about that, too. Where are you getting accurate lofts of these gliders? Oftentimes I've considered buying an existing canopy for my own design, but would need to match the forward fuselage loft of the parent aircraft. If you've got a source, I'd love to hear about it.
     
  14. Nov 10, 2010 #134

    Starman

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    I guess I'm going to build molds and make this out of carbon fiber, the fuselage, not sure about the wings.
     
  15. Nov 10, 2010 #135

    Starman

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    Like this, fuselage is locked now.
     

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    Last edited: Nov 10, 2010
  16. Nov 13, 2010 #136

    Voyeurger

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    Really cool graphic Starman. You've got a good eye no doubt.
     
  17. Nov 13, 2010 #137

    Voyeurger

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    Seb,
    Sorry for the late reply. I have been in Maine (the state farthest removed from where I live, by far) the last nine days arranging the cross country trip of my beautiful little amphib kit. 80% completed, and "the Good Lord help me" left to go. When I take a break from my head scratching, I'm going to post the thing in "Projects" or "Builds", I forget the exact name now.

    Yes, I let my enthusiasm get the better of me, but I DID post that you should tell me to mind my own business if you felt I was over reaching. And so you have. You DID mention two things that stuck in my mind (I think one in Form Over Function). I paraphrase 1) "Are we just going to keep on talking or actually DO something?" and 2) later you mentioned you'd do some drawings, preferably with ANSYS (Fluent) which was out of your reach financially (holy crap! BILL GATES would need a co-signer for an ANSYS suite). I had been pretty much a fly on the wall up to that point, and it felt to me like I was watching the future members of the Beatles meeting each other for the first time at a party that I was serving cocktails at. I heard John Lennon saying he'd like to try out with the others but he couldn't afford to move up to an electric guitar. Well, I would have called Fender guitars then, as I called ANSYS here. Heck, I never expected to hear back from them at all, nevermind almost immediately. When I DID get the call, after I hung up, I was like the big dumb defensive lineman in a football game that has a deflected ball just drop into his hands. Oh SH#T, what do I do NOW? I hope I'm not in trouble (maybe I should NOT have caught this ball).
    I just wanted to bring the band together, at least through to a design that everybody really liked. Of course, it goes without saying, but just to buck Jay up a mite, any design that had the love and faith of those participating would be bullet proof aerodynamically because Orion would sign off on it (in a perfect world) even if I had to cough up his hourly rate, and assuming he could accomplish the task timewise during a single visit to the crapper (just leave the Golf magazine behind one day). The only reason I mentioned analysis and Seb in the same paragraph was that the Fluent system graphics showed the stress hot-spots in the color ranges everyone's familiar with.
    I was wrong to throw Seb into the fray like that, I HAD written him, but he hadn't gotten my e-mail or back to me. Then Fender Guitars was all over me wanting to know if the Stratocaster should be painted any special color before it was delivered to John. (ANSYS was very intrigued, immediately, seriously, unbelievably)

    I would STILL love to see it done. Everybody throws in what they want, everything. THEN, one by one eliminate for any reason that detracts from comfortable, fast, KISS.

    I'm really warming up to you geeks.
    Your friend,
    Gary
     
  18. Nov 13, 2010 #138

    Voyeurger

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    Tandem Wing Relations

    I'll bet you were not aware of the fact that Albert Einstein almost married his first cousin for the simple reason that she was extremely buxom.
    Thus we have "the theory of relative titty"

    ATTN: Moderator, give me just this one.
     
  19. Nov 13, 2010 #139

    Voyeurger

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    How come I like this so much if I haven't even looked up decollete yet ;)? I'm with Topaz. Marry her before she finds out how much better she could do.
     
  20. Nov 13, 2010 #140

    Voyeurger

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    One MUST have a young leggy girl to pose for the press at the unveiling of a prototype, mustn't one?:ponder:.
     

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