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Thread: Bi-directional spruce for fuselage skins

  1. #16
    Registered User Hot Wings's Avatar
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    Re: Bi-directional spruce for fuselage skins

    That's why it is worth it to suffer through the learning curve with this stuff.

    I'll second that!

    It's so fast and easy to simply drag parts or sub-assemblies around in 3D and then double check the CG that this one feature is almost worth the time investment. Once you get a database of common parts built up even first round "what if" go pretty quick.
    Conventional wisdom and practices yield conventional results. If that is good enough for you:
    Problem solved.

  2. #17
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    Re: Bi-directional spruce for fuselage skins

    Just some thoughts...epoxy is the obvious choice because you only need to bring the plies in contact with each other without a lot of clamping pressure. But, I can't help but think how difficult the whole process will be. Boat builders refer to this method as "cold molding". Seems they have two or three people working together and vacuum bag the laminations in small sections. Working alone and bagging doesn't seem possible. [I can't even imagine how you would bag it anyhow] I guess you could use temporary staples but seems you would have to staple into the underlying stringers for them to grip. Gosh, think about how many batches of epoxy you'll have to mix because (if you're working alone) you'll only be able to do small sections given the set time of the epoxy. Seems AS&S can provide Sitka spuce spar stock as thin as 1/8" thickness if you don't want to bother with resawing and planing. Have you considered using a different wood? You'll have a fortune invested in all that spruce.

    I'm a bit of a woodworker myself and have built a wood strip canoe, so I share your passion but I'm overwelmed by the thought of this project. Have you considered just one layer of stripping with fiberglass skins?

  3. #18
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by Jay Kempf View Post
    Yup,

    Anything that has a volume can have a weight. Anything that has a weight can have a CG. Anything that can have a CG can be reconciled against a datum to lead to an overall weight and balance. By putting things in like different amounts of fuel, different sized occupants, engine oil lumps, etc... you can do all of the limits of the CG by just reconfiguring the model for each case. In Solidworks we have a suppressed state for any feature or component so that you can just turn things on and off and remeasure. It also gives you moments of inertia for sections, whole assemblies, radius of gyration, yadda so you can inspect and feed those numbers directly into spreadsheets to calculate anything you want. That's why it is worth it to suffer through the learning curve with this stuff. Most times I find a number I don't like it is because I input something wrong not because the computer is in error. Sometimes I have to fake it out for things like sandwich composites such that I don't have to detail the plys. I have made custom material specifications in the software for say 1/4" foam core with .010 of carbon BID both sides. I put in a composite density for that and shell the feature to that thickness and get a very accurate weight and CG. Go back and change the shell dimension and reapply the material for another thickness core and reanalyze the model and you can run through all kinds of cases in a hurry for optimizing structures. I also do first run strengths looking for structural hot spots using these fake models.

    The moral being you don't have to put all the planks on to look at this. Just put a skin on. If you want a whole bunch of skin segment models just slice up the overall skin into pieces after you put the overall skin on.

    You made a mistake talking about all that...Now, it's likely I may bug you with questions about certain things...LOL...solid works being one of them (ive been interested with it)....but ya know, I've resisted getting involved with other cad programs and that sort of thing because it takes up so much of my limited brain resources...nevertheless...you be speaking my language!...Don't be surprised if i ask ya foe help on something in the near future...hope ya don't mind...

  4. #19
    Registered User Jay Kempf's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by Wagy59 View Post
    You made a mistake talking about all that...Now, it's likely I may bug you with questions about certain things...LOL...solid works being one of them (ive been interested with it)....but ya know, I've resisted getting involved with other cad programs and that sort of thing because it takes up so much of my limited brain resources...nevertheless...you be speaking my language!...Don't be surprised if i ask ya foe help on something in the near future...hope ya don't mind...
    Any time. Putting aircraft into non aircraft specific modelers takes some creativity. Most modelers have similar command sets so normally you can take a technique and port it over to another platform. I know what works for me which is some evolved tricks and techniques that produce stable models. Catia and PROe think they have a lock on this stuff. But any modeler will work if you play to it's strengths. Solidworks lets you do a loft and then slice it up any way you want. And the edges of the slices are real geometry when done. That is not the approach for making manufacturing models and drawings but it is a good approach for doing what you are currently doing which is doing proof of concept models before detailing.
    Jay K.

    VT USA

  5. #20
    Registered User fly2kads's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by Wagy59 View Post
    yes I was thinking that too...but it seemed I was going to end up with an entirely different way of constructing the thing and I'm just not there yet...But I'm with you! I know what your're saying...That's why when I started moving towards the spruce fuselage skins and then started doing some basic calcs (mostly in my head) I realized that, well heck, i no longer need as heavy a frame so I went from 3/4 and i inch frame to 1/2"...which still makes it really really really strong..actually stronger
    What you are touching on here is something that I find very interesting. At one end of the spectrum, you have a load bearing frame with an aerodynamic fairing, a smoother version of the old fashioned fabric covered structure. At the other end of the spectrum is a monocoque shell with local support for cutouts, and perhaps a few formers to resist buckling. In between, there is a large middle ground of semi-monocoque structures where the load is shared between frame and skin. There is a lot of opportunity to optimize the structure for weight/strength, materials, and build process (e.g. Skin laid up over a temporary mold vs. doing it in-situ over frame/stringers). There are a lot of factors that go into making a decision on where to land along this continuum. I think it starts with your goals for the project, a fully developed set of load cases, the materials you want/have to work with, and an assessment of your fabrication capabilities. This construction technique allows for a lot of flexibility.
    Detego likes this.

  6. #21
    Registered User Hot Wings's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by Wagy59 View Post
    You made a mistake talking about all that...Now, it's likely I may bug you with questions about certain things...LOL...solid works being one of them (ive been interested with it)....but ya know, I've resisted getting involved with other cad programs and that sort of thing because it takes up so much of my limited brain resources...nevertheless...you be speaking my language!...Don't be surprised if i ask ya foe help on something in the near future...hope ya don't mind...
    Get on YouTube and search for SolidWorks tutorials. Considering your familiarity with AutoCad you should be able to pick up Solid in much less time than it took to learn AutoCad. Solid is a bit different but once you get the hang of how it puts things together the usefulness increases pretty quickly. I'm pretty much self taught over the last year, but just finished a formal class to find out what I didn't know (quite a bit with the newer versions) and am now finding that I open Solidworks first for a lot more things than I do my 2D CAD.

    Take a class at the local college and you can get a student version (same as the full retail version, but with watermarks on the files) of Solidworks for not much money. compared to the retail cost it's worth taking a class every year to renew the license.
    Conventional wisdom and practices yield conventional results. If that is good enough for you:
    Problem solved.

  7. #22
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by davidb View Post
    Just some thoughts...epoxy is the obvious choice because you only need to bring the plies in contact with each other without a lot of clamping pressure. But, I can't help but think how difficult the whole process will be. Boat builders refer to this method as "cold molding". Seems they have two or three people working together and vacuum bag the laminations in small sections. Working alone and bagging doesn't seem possible. [I can't even imagine how you would bag it anyhow] I guess you could use temporary staples but seems you would have to staple into the underlying stringers for them to grip. Gosh, think about how many batches of epoxy you'll have to mix because (if you're working alone) you'll only be able to do small sections given the set time of the epoxy. Seems AS&S can provide Sitka spuce spar stock as thin as 1/8" thickness if you don't want to bother with resawing and planing. Have you considered using a different wood? You'll have a fortune invested in all that spruce.

    I'm a bit of a woodworker myself and have built a wood strip canoe, so I share your passion but I'm overwelmed by the thought of this project. Have you considered just one layer of stripping with fiberglass skins?
    Now I'm laughing because your right!...but I can do it...I'm not worried about it....lots of work, yes....Not doable..no....it's doable..just work that's all..I'm like youand I am very comfortable with with wood and have been fooling around with wood for decades..I can even build out of aluminum..just dont want to!

  8. #23
    Registered User Jay Kempf's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by fly2kads View Post
    What you are touching on here is something that I find very interesting. At one end of the spectrum, you have a load bearing frame with an aerodynamic fairing, a smoother version of the old fashioned fabric covered structure. At the other end of the spectrum is a monocoque shell with local support for cutouts, and perhaps a few formers to resist buckling. In between, there is a large middle ground of semi-monocoque structures where the load is shared between frame and skin. There is a lot of opportunity to optimize the structure for weight/strength, materials, and build process (e.g. Skin laid up over a temporary mold vs. doing it in-situ over frame/stringers). There are a lot of factors that go into making a decision on where to land along this continuum. I think it starts with your goals for the project, a fully developed set of load cases, the materials you want/have to work with, and an assessment of your fabrication capabilities. This construction technique allows for a lot of flexibility.
    There's the rub now isn't it? Do you build a structure strong enough to wrap or do you figure out a way to build a shell and then put some structure fitted inside. What I like about the one off method is that the later decision doesn't really come with the need to build molds. So it all boils down to HOW you are going to build it which is the approach I always take when I start a new project. Pick the method and then the details fall in behind. All are valid. Wood is a great composite material with a long history and a few limitations. What's nice about wood is that we all know the tools and techniques already. I prefer composites, but that is because I have become comfortable with them over the decades.
    Detego likes this.
    Jay K.

    VT USA

  9. #24
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    yeh I know aircraft spruce can do that but I'm wondering if i can get it cheaper by re-sawing myself..I'd have talk to them and see...And getting the pieces up close and personal to each other doesn't worry me..and actually I watched a show on tv a year or so back about a guy that has become quite successful building those 40's vintage speed boats for rich people..and some are pretty large, actually, ...and there was a segment where they filmed one of the guys fitting and gluing those mahogany pieces on to the boat frame all by him self and it was amazing how fast he was doing that...He'd slap the next one up, look at it, take it off..plane a a bit off the edge somewhere or another, put it back on, look at it, then glue that baby on ,put some clamps on it and move on...was amazing how fast he could do that..and when they were finished, the seams between the planks were virtually invisible

  10. #25
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by Jay Kempf View Post
    There's the rub now isn't it? Do you build a structure strong enough to wrap or do you figure out a way to build a shell and then put some structure fitted inside. What I like about the one off method is that the later decision doesn't really come with the need to build molds. So it all boils down to HOW you are going to build it which is the approach I always take when I start a new project. Pick the method and then the details fall in behind. All are valid. Wood is a great composite material with a long history and a few limitations. What's nice about wood is that we all know the tools and techniques already. I prefer composites, but that is because I have become comfortable with them over the decades.

    I wish I could become more comfortable with composites..dont get me wrong..i love the stuff and have made a few things with fiberglass and composites...I've thought of building a stool (like in little stool picture) out of composites....but man, A properly built airplane out of wood, for me is the ultimate thing!....I still remember the first time I walked up to a sailplane and an airplane that was mostly or all wood, and it just does something to me ......I dont get that feeling at all out any other airplane or boat or whatever made out of metal or composites..not that I don' like em, mind you...just don't get that magical feeling from them

  11. #26
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    I think I must of been a forrest critter in a former life

  12. #27
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    I think I must of been a forrest critter in a former life Hmm.. I didnt do it..although I do repeat myself on occasion

  13. #28
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    One other thing..beware of people that don't like cats.

  14. #29
    Registered User Hot Wings's Avatar
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    Re: Bi-directional spruce for fuselage skins

    Quote Originally Posted by Wagy59 View Post
    One other thing..beware of people that don't like cats.
    More importantly beware of people that cat's don't like!
    SVSUSteve and Detego like this.
    Conventional wisdom and practices yield conventional results. If that is good enough for you:
    Problem solved.

  15. #30
    Registered User Wagy59's Avatar
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    Re: Bi-directional spruce for fuselage skins

    You just made me spit my coffee out from laughing..or it could of been beer,,I'll never tell

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