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  1. #1

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    thickness of the aeroplane body

    My mold of yak52 is ready. The scale is 3.8. I would like to know your opinion what kind of glassfibres would you use for front / back parts. The weight might be 10 kg ( 22 pounds ). Suitable engine in cowling might be Fuji B2 80.

    Thanks a lot for answers

    Hannu Kunttu

  2. #2
    Mike James's Avatar
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    RE: thickness of the aeroplane body

    The answer partially depends on how your internal structures are made, but...

    With the Yak 52, most of your load-bearing structures can be "unitized", so that just a few key formers share the loads. (the wing joint/landing gear support/firewall area) If so, then the fiberglass parts can be built rather lightly.

    I recently built an 18 pound fiberglass plane, and did several experiments with cloth weight. The best combination for that particular plane was one layer of 4.5 oz. cloth, followed by a layer of 2.5 oz cloth. I think that if you plan for a total cloth weight of "8 to 10" for 2 layers. (6+4, 4+4+2, 3+3+3, etc.) you will be fine. It might be worthwhile to use a little extra cloth, or perhaps some carbon tow "bands" back in the tail section, to prevent twisting, if you plan on aggressive flying.

    Cool project. Let us see some photos when you're ready. I've added a YAK 52 image, so others here can see what we're talking about.
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    Mike James
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  3. #3

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    RE: thickness of the aeroplane body

    Mike:


    Kind of vague here, but you have any estimates as to thickness of cloth based upon diameter of fuselage or length of empanage?

    I would assume that a fiberglass fuselage of about 6 inch diamater would require an overall thicker cloth than one of about 2 inches like used in gliders.

    Then too, if the portion from wing to stabilizer is 18 inches in distance, it could require a thinner cloth than one of about 36 or greater.

    I have seen some awfully thin fuselages on 1/2A or small electric A/C and likewise know they would fold up if built four times larger.

    I am thinking here now of unsupported, or non-plywood reinforced finished product.

    What thickness of cloth should be aimed for for the different diameters or lengths?

    Wm.
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    RE: thickness of the aeroplane body

    Two words: Sandwich Panel.

  5. #5
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    RE: thickness of the aeroplane body

    I must agree with DAVIDFEE. I built a molded 33% scale sukhoi 26. Fuselage about 12.5" dia at firewall. 1 layer of 4 oz. "S" glass, 3/32" balsa core, and 1.8 oz. Kevlar were primary lamination schedule. Add to this uni longerons top and bottom, left and right and that was it. I of course added buildups around fire wall, wing spar pass thru, and stab. I also added about .5" x .020: carbon uni to each side of rudderpost to give vertical good strength/stiffness. ALL of the bidirectional cloth was at a "Plus'n'Minus" 45 degree orientation. Carbon uni took the bending load, bidirectional took the torsion load and shear load. This fuselage is over 6 feet long, qualified to take all out aerobatic loads, and weighs about 4 pounds. I had only a fire wall, and partial bulkheads where the "Cross your Heart" spars were pinned. Get a vacuum pump and vacuum bag a sandwich structure!!! And spray primer in the mold!!! this will reduce/eliminate pinholes!!
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    RE: thickness of the aeroplane body

    Thanks everyone for help.

    Here are several main dimensions. Diameter of the cowling is about 11 inches. Wingspan is about 100 inches and length of fuselage is 82 inches.

    As Mike James told how to handle loads ( the wing joint / landing gear support / firewall area ), I am thinking that I will use that way. I use the pipe which connects wings and landing gears. Only the firewall is made differently, there is a box which goes inside the cowling.

    Hannu Kunttu

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    RE: thickness of the aeroplane body

    One question more Mike what unit you use this "I think that if you plan for a total cloth weight of "8 to 10" for 2 layers." Our gountry we use square meter and kilograms. Is it square inch and pound?

    Hannu Kunttu

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    RE: thickness of the aeroplane body

    Hannu,

    Here in the US we use those crazy English/imperial units... so we use ounces/square foot.

    Approximate conversions:

    oz/ft^2, g/m^2
    2, 65
    3, 100
    4, 135
    5, 170
    6, 200
    8, 270
    10, 340

  9. #9
    Mike James's Avatar
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    RE: thickness of the aeroplane body

    Hi everybody,

    This is an interesting conversation.

    (Yes, my number examples, like "6+4" were in ounces.... i.e. 6 oz cloth + 4 oz cloth)

    William:
    I never really thought about this in terms of "weight vs. length", but that's one way to look at it, and you're right of course that each plane deserves it's own plan. I don't keep figures on this, because most of the fuselages I've built have been so similar in size (say, 60 to 90 inches length) that I can almost always use the same formula.

    I tend to overbuild the first fuselage, as a safery concern, then determine through flight testng if I can build it lighter. Using a pretty standard flight testing plan, going from "gentle" to "aggressive", I want to know that the plane can take whatever I'm going to do with it without a failure. If the first one can, then I consider building the next one lighter, until a failure occurs. Then I'll use the previous, stronger one as the "production" version. Last year on the Berkut project, I used the "6 to 8" method. on that fuselage, which was about 12 inches in diameter and about 70 inches long, and it was fine. The plane we rung out the most in test flights ( a "3.5 + 3.5" layup ) was the lightest one, and it was plenty strong.

    I think the biggest determining factor is where the loads go. Whenever possible, I try and think of a fiberglass fuselage as simply a fairing around the structure. Some loads will be transmitted to the skin of course, but since every plane is different, and the shape affects how loads get transmitted, it would be hard for me to put a precise "formula" on it. Aside from crash damage, I've never had a fiberglass fuselage fail from flight-induced stress. This includes Pattern and other aerobatic types. If you're doing a pylon racer, turbine-powered jet, or a plane designed for heavy cargo lifting, my ideas may be inappropriate. You would need more reinforcement, whether it's in the internal structure, or the composite shell itself.

    One other thing...
    All composite structures don't necessarily have to be super rigid. A small amount of flex at certain points in the structure can be tolerated, as long as it doesn't cause flutter or some other divergent flight problem. Some very high quality aerobatic planes I've looked at felt flimsy in my hands, but were plenty strong enough for flight loads.

    Lots of trial and error in composites...
    How the thing is shaped, how it's built, how the internal structure takes flight and ground loads, and how it's maintained... All have an effect, best learned through a combination of studying what everybody else does, and then creating your own experiences to prove or disprove the idea.
    Mike James
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  10. #10

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    RE: thickness of the aeroplane body

    Why not make the fuselage shell the structure, rather than just being a fairing around the structure? Add a few minimal formers where absolutely needed. Think uni-body construction vs body-on-frame.

    my 2 pennies...

    -David

  11. #11
    Mike James's Avatar
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    RE: thickness of the aeroplane body

    Your method will work as well as mine, David. It just depends on the airframe. I wouldn't agree that either method is the ideal one for every project.

    For example, the pusher (Berkut) that I did last year is built so that most of the load-bearing parts converge at one point... in this case, at the rear of the airplane, where the firewall, landing gear supports, and wing spar all meet. No reason to build a super-strong frontal fuselage in that case.

    Another one I'm working on, a 1/6th scale Piaggio "Avanti" is very similar. The main wing spar and main landing gear, as well as support for the engines and fuel system , all converge at one point. The front of this plane will be built as lightly as possible.

    But...
    If you feel that your entire structure must be a load-bearing part, then by all means, add more formers and reinforcements. The way modern turbine jet kits are constructed is a lot like that, since there are both weight-carrying and thermal issues throughout much of the fuselage. I think that in that case, (and others, I'm sure) that your method would be better. That's what I'd do too.
    Mike James
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  12. #12

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    RE: thickness of the aeroplane body

    A single layer of 5.7 oz carbon @ +- 45° orientation with core at stress points. (simple) Or 2 layers of .005 Uni with the same orientation and core. (best)
    \"Make everything like your going to make the front page of NASA Tech Briefs\"
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    RE: thickness of the aeroplane body

    Mike,
    I don't think our ideas are as different as it maybe sounds at first. My suggestion of the sandwich panel is so that lighter glass can be used and still yield a part with much increased stiffness. Because the part is stiffer, fewer bulkheads (not more) are required to support things like the vertical and horizontal stabilizers. The tail will not twist. The core material does not need to be applied everywhere either. It can be localized in high stress areas.

    The way I view a fuselage is that it is there to a) hold the motor, wing and tail in alignment and b) direct air smoothly over the contents.

    Some structure will be required to hold the compotents in place, so an analysis of the loads is important, as you have suggested. The bigger the fuselage, the thicker the skin needs to be to maintain stiffness... hence the sandwich suggestion. mmm ... this is making me hungry.

  14. #14
    Mike James's Avatar
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    RE: thickness of the aeroplane body

    David, you've got my interest, and I think it would also be serving this thread, if you could post some info and photos showing some examples of your sandwich technique. I understand the concept, and have built sandwich structures before, (firewalls, formers, etc.) but have never built a complete fuselage that way. (Now, I'm hungry too.)

    I'm always looking for better ways to do things, so why not give us a little lesson here, if you have time. We can all learn something. Have you done this technique with "ordinary" fiberglass, rather than carbon or Nomex? (less expensive) And... I assume you vacuum bag these?
    Mike James
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    RE: thickness of the aeroplane body

    I don't have any pictures of exactly what I'm talking about, but it if I steal a picture from Michael Luvara and his thread here, then it could look something like this: (edited... see bottom photo below) The core material can be balsa or foam as well. Yes, the sandwich will typically be vacuum bagged to maximize bond strength and minimize epoxy weight. My first experiments were without vacuum, however, and that worked great too.

    If the skin of the fuselage is stiff, then many of the loads (wing spar, landing gear, engine mount, etc.) can be carried to the skin by minimal internal formers. By doing this, the loads are spread over a larger area, so the structure can actually be built lighter.

    You're right, though, that every application is different and the loads specific to the airframe will need to be addressed in each case... and will likely result in a different structural solution.

    I think the sandwich panel method will be most useful when the fuselage has large, rather flat surfaces. If it is a long tube, perhaps foam stringers could be sandwched into the layup. If it's small with a more sherical shape, then the sandwich might not be needed (or even useful). In the SDSU DBF plane last year, we used sandwich panels for all the bulkheads. They weighed next to nothing, but added immense stiffness to the structure. But, since this fuselage pod was "egg-shaped," and we made it using the lost foam method, I couldn't do a sandwich panel for the skin. It didn't need it anyway, since it was so spherical.

    BTW, your Avanti is a beautiful project.
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  16. #16
    Mike James's Avatar
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    RE: thickness of the aeroplane body

    Cool. Thanks, David.
    Mike James
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    RE: thickness of the aeroplane body

    Some people have asked things about my YAK55. I have a home-made 55 scale 1/5, engine Laser 200V. I like introduce one picture of it. Later I'll post a picture of my 52 project.



    H. Kunttu

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    RE: thickness of the aeroplane body

    Hello

    It takes time but there are the picture of my YAK52.
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  19. #19
    SCALECRAFT's Avatar
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    RE: thickness of the aeroplane body

    All good advise from what appears to be guys who really make and fly these composite models.

    I have not read all the posts, so if i repeat, pleas forgive me.

    A few thing to consider.

    I/we have around done around 15-20airframes, all composite models since 1990. All warbirds. On average 48" span to 80" (80" midwest texan fuse only)

    This has lead me to consider the layers (size and amount),//// A) where I will grab the model when starting, and handling, B) in tail heavy models (zeros, texans, corsairs, tyhpoons) laying up the cowl or forward section "heavy" with thicker glass or more layers, C) using the geometry of the fuse and shaping the glass reinforcements to yield stiffness beyond carbons and kevlars (8oz glass seam tape in a triangle type shape as a horizontal fuse support) and stuff like that.

    Also laying a fuse half in to sections horizontally by overlapping the flattest section by around 1" which results in a doubling of that small area.

    All supported and working with ply formers in certain locations

    Just what works for me.

    steve

  20. #20

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    RE: thickness of the aeroplane body

    I would use nomex honycomb. It is readily avaiable in .125 thickness, I think that would be an easy to build material because it is so flexable, very light. So light, in fact the rest of the plane can be built lighter (slightly) because it won't have to support as much weight in the fuselage.  I have used nomex for many things. It is very strong and survivable. Bicycle frames, catamaran parts, and much more I have experienced with nomex.  If a rock hits a sandwich panel (landing) with foam and dents it the foam will have a depression and will hold the fibers in the depresion, making for a not so strong in  compression over all.  Nomex will crush, but if the dent was not to bad, the firbers are allowed to return to their original shape, therfore maintaining their compression  strength. There will be a small pockets of crushed sandwich, but the strength of the entire fuselage will be almost the same as new. I have experiment with down tubes on on a bicycle frame.  Rocks would hit the carbon nomex tube wall and bounce off, and no marks or dents whatsoever, even after years of abuse.  For the down tubes I wraped single layer 5.7oz carbon,
    over standard plastc pipe and while still wet wrab nomex over and masking tape tightly over entire length.  When cure take out  plastic mandrel, pull off the tape and add the final 2 layers od carbon, or glass.  It is complicated and  takes a long time but extremely  survivable. I didn't use vacuum but that would be even better

  21. #21

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    RE: thickness of the aeroplane body

    How do you prevent the Nomex from printing-thru to the surface with such thin skins.  The stuff works great with a few layers of 3K carbon, but lighter skins seem cause honeycombs to print-thru.  How have you worked around this?

    Adam


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    RE: thickness of the aeroplane body

    I never had a pronlem with print-through with one layer of 5.7 oz. carbon on the inside. If you are going thinner then I think I have a solution; wet-out the inner layer (of which ever fiber reinforced) and allow it to cure, then wet-out over that layer with a thin layer of resin and that becomes the bonding for the honeycomb. I have never done this but I think it might be better than my older system. Their might be very slightly more resin being used, but it might be the best way. There are a few things that might be considered; adding microspheres to that bonding layer might be a way to increase bonding strength while also reducing weight at the same time.

  23. #23

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    RE: thickness of the aeroplane body

    I have a project need to know if this help me with this yak 52, has 90 "wing, fuselage by 75, weighs about 22 pounds that I recommend engine
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  24. #24

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    RE: thickness of the aeroplane body

    Hei

    My project is going up a little. I start to made the mold of the wing. Why that the reasons is because the plane weight was very near that the rules limit is. Some picture for my jops.

    Hannu
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  25. #25

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    RE: thickness of the aeroplane body

    I ask help

    The mold of wings are ready. This is my first composit wing. So I don't know which kind of construction is good in this kind of situation.

    Background:

    Wing tubes (2) take a load from landing gare, they are so long.
    I am thinking to use sandwhich structure on the shell of wing
    I have 2mm balsa for shell

    Questions:

    Which kind of thickness of shell composite
    Which kind of spar and structure inside the wing

    Diameters of half wing:
    lenght is 1150 mm
    width of base is 545 mm
    width of beak is 290 mm
    thickness is 74 mm / 38 mm

    What about the waxing the mold. How you can make sure that the hole of rivet is release sufficiently.


    Hannu
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