composite wing construction

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by slociviccoupe, Apr 1, 2011.

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  1. Apr 1, 2011 #1

    slociviccoupe

    slociviccoupe

    slociviccoupe

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    Hello, Looking at building my own first airplane. Have built planes for others while employed at steen aero lab but this one will be for me. Really wanting to build something that qualifies in the ultralight category. something like the sd-1 minisport. Or would really like to find a canard pusher that will qualify in ultralight.

    but my questions is can a plane that has a solid foam core wing with a composite material bonded to it be built differently to conserve weight and be just as strong.

    my idea was to take say a cozy, vari eze, or a long ez foam wing core that has been cnc cut. slice it and make ribs out of the core instead of a solid foam core. then would bond carbon to the sides of the foam ribs. the foam ribs would have lightening holes cut in them to reduce weight. Ribs would be slid and bonded to a carbon fiber tube spar. then a carbon skin that was made from the negative of the foam from the wing core would be bonded to the upper and lower sides of the wing. seems most ultralight aircraft wings are made this way with the exception of the composites. mainly made with wood and foam. I live in fl and have seen what humidity does to wood planes, even wood coated in epoxy grows mold down here inside of wings.

    essentially im wanting to make a side by side 2 place ultralight canard. but willing to build a sd-1 minisport but with more composite techniques if i can't find a way to build an ultralight legal canard. I have the help of trinity composites who makes carbon jet ski hulls and some aircraft parts for the laying up of the composite parts.

    reading this it seems i am uncertain on what i want to build. i really like the look of the canards. just visually apealing. but also like the way the sd-1 minisport is. with its low hp needed to fly. my problem is with both planes i want a second seat. flying isn't much fun without someone else. Im wanting to aim for ultralight certification because i do not have a private pilots license as of yet. hope to accomplish this while building the plane. shooting to build an ultralight but if it comes in a lil heavy and is a light sport aircraft i won't mind either as ill be getting pilots license anyways.


    any help is appreciated. just looking for info on different composite construction techniques.
     
  2. Apr 1, 2011 #2
  3. Apr 1, 2011 #3

    TFF

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    2 seat ultralites are not legal any more. Light Sport took its place. You can build a canard but to be an ultralite it must weigh no more than 254lbs. Light sport has a weight limit too 1320lbs.
     
  4. Apr 1, 2011 #4

    wsimpso1

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    This has been talked about a bunch before. Try using the advanced search tool.

    Solid foam is pretty darned good for weight as you only need to skin the outside with a reasonable layer of glass (3 UNI in Rutan aircraft - 21 oz/yard for cloth plus resin).

    Hollow requires more to build it. More time, more cost, more tools, more fuss, more design effort. Let's cover a bit of it. Standard way is foam cored skins and ribs. Outside still 21 oz/yard or so. Then there is the inside at another 14oz/yard. Why the inside? You are making a strong, stiff skin and using very few ribs. A lot of this stuff is heavier than the foam at 2 lb/ft^3. The the ribs need to be taped to one skin, flanges need to be transferred for the other skin, which is more cloth and resin. Then adhesive. This stuff will easily run to more weight than the foam that you skip...

    The other way to build hollow is to use an uncored skin, which has orders of magnitude less bending stiffness than cored skins and will need a lot of ribs and probably more layers of skin cloth too. This is heavy and it feels flimsy compared to the cored skins too. I saw a carbon fiber wing skin recently for an LSA where the composite fabricator omitted the cores, and it was a wet noodle. Believe it.

    What is the reason for making the skin strong and stiff? Think about the aero loads. The pressure inside the wing is ambient, the pressure outside is much lower as you have air moving at some amount faster than your airspeed. The wing skins are trying to be pulled away from the wing. In a really slow airplane, that is not too big, somewhere on the order of the max wing loading. On a faster airplane, it can be several times the max wing loading. In wings skinned in fabric and in metal, they use a lot of ribs for a reason, and you can see the skins bulge between ribs.

    Anyway, just start adding up the weights of all of this stuff. Blue foam is 2lb/ft^3. Composite cloths are sold by weight/square yard. Unless you are vacuum bagging, they generally require about as much resin as the cloth weighs. Do the math. Unless you have a very large chord, solid foam is a pretty darned good way to build a composite wing. I am building a hollow wing as I need to put my fuel someplace and there is internal hardware too. So I have a wet wing with landing gear and bellcranks and fuel system details all inside. And I vacuum bag. But my control surfaces and tail are hotwired foam with glass on the outside...

    https://www.homebuiltairplanes.com/forums/composites/920-wing-constuction-method-advice.html
    https://www.homebuiltairplanes.com/forums/composites/850-questions-questions-2.html
    https://www.homebuiltairplanes.com/forums/composites/4128-strip-method-other-8.html

    Now if you just gotta bend a carbon fiber and resin sheet over foam ribs, you will need a lot of ribs. Do your math on this too. I would bet that you could skip skinning the ribs. There will be a lot of them, and the loads per will be pretty low. Again, you have to do your analysis.

    Billski
     
  5. Apr 3, 2011 #5

    wsimpso1

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  6. Apr 3, 2011 #6

    Vigilant1

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    Are there any foams useful for building a wing that can be cut with a hot wire but which are also resistant to fuels? When I last looked at this (years ago) there weren't. A foam like this would take some of the worry out of storing fuel in the vicinity of a wire-cut foam core (ala Cozy, Varieze, etc).
     
  7. Apr 3, 2011 #7

    wsimpso1

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    Only styrene can be hotwired without emitting really nasty toxic gaseous products.

    Urethanes are very poisonous when burned. It is the same result as with solvent based polyurethane paints - No filter mask can make you safe.

    The fuel safe foams (I am partial to PVC foams) won't cut readily with a hotwire, and are kind of pricey to be throwing away many cubic feet of it.

    Reality bites. But when we do it correctly, it can be loads of fun too.

    Billski
     
  8. Apr 3, 2011 #8

    BBerson

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    The current issue of Sport Aviation shows a composite wing under construction. http://www.sportaviationonline.org/sportaviation/201104#pg82

    I can't see the thickness of the foam used for the skin from the photo or if it uses an inner skin to make a true sandwich. Does anyone know?
    I assume the foam skin panels were cut to size and inserted between the ribs and spar(not on top).
     
  9. Apr 4, 2011 #9

    rtfm

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    Mr Bill Simpson - you have, sir, done it again. And I think it is high time you desisted from offering good, sober advice, because I have once again decided to follow it. I have been scheming, drawing, planning and costing a hollow wing with ribs for months now, trying to defend the extra effort and complexity. But I now think that for simplicity's sake, and because it will offer a far more rigid wing, I shall be going with a solid foam core, even though it is a bit heavier.

    I have done the numbers, and they add up.

    One more of these outbursts of common sense from you, and it will have to be pistols at dawn...

    Regards,
    Duncan
     
  10. Apr 4, 2011 #10

    slociviccoupe

    slociviccoupe

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    was thinking more along the lines of the same way the wings of this plane are constructed. foam ribs sheeted in glass or carbon, a carbon spar, and then a full carbon wing skin instead of fabric.

    Parker P1 High Altitude Airplane

    would be changing the spar to meet my certain wing specs, my ribs would be made in a molded sandwich type mold that would enclose the lightening holes in the foam ribs completely, also would create the flange used for bonding the rib to the wing skin. one layer of carbon tape would have to be applied to the flange of the rib to seal and bond the 2 sides together. with the right molds, right layups, and vacuum bagging should be easy to make parts and assemble, then replicate. And with the correct prep of the molds should get near perfect finishes on the wing skins and ribs.
    my wing skins would just be 1-2mm thick carbon made in a mold then bonded to the top and bottom of the wing. would not have any foam in the wing skins but only in the ribs and main spar.

    will be looking into this method on either the sd-1, or the full composite version of the kr2 super 2 here.

    KR Super2
     
  11. Apr 14, 2011 #11

    Zightz

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    Hi, just an idea....a few years ago there was an ultralight out of Canada.....Company defunct now but a friend of mine had one and it used two kinds of structure...and was super **** strong and very clean. The wings used a blue foam core rib one per foot.... with an aluminum skin...your choice of spar.....although I belive the main wing spar was a hollow tube aluminum spar. The horizontal and vertical surfaces were solid bluecore foam with aluminum skins once again....very light and very strong. There were also full span ailerons ...solid foam core with aluminum skins. Some creative thought and some creative math should give you a canard ultralight....it did me ...I also love the canards for many reasons. Empty weight of pic shown is only 230 lbs....My friends looked sort of ugly but flew very well and was super strong. Mine is way better looking and way more of an airplane. but in the end we all just want a safe way to get into the air and bomb around. this works and is also very clean in design....to keep it in the Par-103 I had to slow it down I am doing this with a smaller HP engine and some design tricks. Eureka ultralight aircraft, Eureka experimental aircraft, Eureka experimental light sport aircraft (ELSA), Lightsport Aircraft Pilot News newsmagazine. No sense in making life any tuffer than it already is....so I thought I would put my 2 cents in. I wish you all the best in your search and finding your safe wings....ENJOY Sincerely, Dave Wright

    eurekaultralightaircraft.jpg eurekaultralight.gif eureka2.jpg
     
    Last edited: Apr 14, 2011
  12. Apr 14, 2011 #12

    BBerson

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    Hi Dave,
    Do you remember how the aluminum skin was bonded to the foam?
     
  13. Apr 14, 2011 #13

    wsimpso1

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    In the article on the Brazilian project, they said that they filled the wing with foam. The photos show a wooden main spar and leading/trailing edge spars, all of wood, and foam ribs, which I am sure set the shape. The second photo shows it all after filling and shaping the foam filling, and it being skinned with what looks like a couple plies of BID or similar cloth.

    To me, it appears that they built a solid foam wing with spars and glass on the outside only. Just like I advocate...

    Billski
     
  14. Apr 15, 2011 #14

    BBerson

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    I think the Brazilian design used the same method Ken Rand used for the KR-1. The KR-1 uses 1" foam sheet glued between foam ribs set at 20" center spacing. And a thick block is at the leading edge. The plans called for Dynel skin, but most used fiberglass(outer surface only).

    I just looked at my old KR-1 plans to confirm how he did the skin.
     
  15. Apr 15, 2011 #15

    Will Aldridge

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    This idea came up in my design thread, what effect on strength would lightening holes in the solid foam core have? Lets jsut say that the holes were sized and spaced like they would be in an aluminum rib, running the spanwise length of the core? Earlier in the design of my plane I was thinking of using about 6 pcf foam for impact resistance and doing a little number crunching in my cad program I found I could get the weight of the core down about equal with 2pcf foam by cutting lightening holes in it. I know the saving won't be so dramatic with a lighter density foam but a few pounds could be saved if it wouldn't destroy the structural integrity of the wing.

    So please critique the idea. What are the problems associated with it?
     
  16. Apr 18, 2011 #16

    slociviccoupe

    slociviccoupe

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    they do it in model airplanes, so with the right engineering and load testing im sure it could be done in full scale.
    Weight saving holes in foam core wings
    just wondering if this method of lightened sloid foam core would be less weight and or stronger than a foam rib built up style wing like most kr's are built.
    Im also very interested because id like to implement the newest style and current composites to build a light weight extremely strong kr2 wing.
     
  17. Apr 18, 2011 #17

    wsimpso1

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    Do you math. Blue foam weighs 2lb/ft^3, fiberglass is described by its weight per unit area (ounces/square yard), it will take about as many pounds of epoxy as fiberglass, and here is a convenient one, lamination of glass/epoxy is about as thick in thousandths as it has ounces per square yard...

    The AR5 did have foam removed from the cores on the leading edge, and then Tom glassed the recess he created - he must have concluded that the glass/foam layer was too flimsy without making it a sandwich. You will have to do your own math on whether that saves any weight for your bird. Fiberglass/epoxy is 36 times denser than blue foam, and then you have to slurry the foam too, which is about 25 times denser than the foam. To save any weight, the foam removed has to weigh more than the slurry, glass, and epoxy, any ribs, etc. And core foams tend to be 4 to 8 lb/ft^3 too.

    You really will have to do your own math...

    Billski
     
  18. Apr 20, 2011 #18

    Topaz

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    Having gone through most of these thought-exercises myself, having heard Bill's advice and then actually run my own numbers, I'll tell you this: Listen to Bill. In most cases, any weight savings from hollow-core is marginal, and within the error band of the estimating process. And the labor saved with going solid-core is the clincher.

    I know it seems counter-intuitive. But he's right.
     
  19. Mar 17, 2013 #19

    Zightz

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    Sorry to be so delaied in responding...Dead computer. The skin was glued on to the ribs which had a very thin bond strip glued to each rib. There was also areas of the skin on the aircraft that were rivited. check out the website in my answer and see if you can get further info from any owners of a Euraka aircraft?
     
  20. Mar 17, 2013 #20

    Hugh Lorimer

    Hugh Lorimer

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    Have a look at the wing construction on my three projects on www.hughlorimer.co.uk I considered solid foam with lightness holes but came to the conclusion built up was best.

    Hughie.
     

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