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Thread: I need a favour...

  1. #1
    Registered User rtfm's Avatar
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    I need a favour...

    Gentlemen,
    Hi. I am beginning to think about building the female molds for my wings. I don't want to shape the plugs by hand. My experience with shaping the plug for the fuse has illustrated quite clearly that my level of accuracy is less than adequate for such a critical component as the wings. I am going to have four plugs cut by a local CNC shop (as yet unidentified - but there are a number of them here).

    My problem is that I lack the necessary CAD skills to produce the files required. I believe that DXF files would be adequate.

    My wings are tapered, but with no washout. Riblett GA37A315 airfoil. Nothing fancy.

    So I'm looking for someone with the necessary skills, and a bit of time to devote to this.

    Any takers?

    Regards,
    Duncan
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  2. #2
    Registered User Jay Kempf's Avatar
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    Re: I need a favour...

    2 or 3d? Are you just looking to get DXF files for templates? Or 3D to have the mold CNC cut?
    Jay K.

    VT USA

  3. #3
    Formerly Unknown Target Inverted Vantage's Avatar
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    Re: I need a favour...

    If it's 3D, I can help, depending on your time frame.

  4. #4
    Registered User delta's Avatar
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    Re: I need a favour...

    How much harder would it be to add a little wash out?

  5. #5
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    Re: I need a favour...

    Duncan, The shaping of wing molds is far easier than the fuselage with all it's compound curves - hot wiring the airfoil shape is easy to do between root and tip templates and twist is also easy to incorporate . One method to get a wing mold is to hot wire the "female' shape (the 'offcut' left if you cut the rib shapes from a larger rectangle) into a set of rib blanks in stryrofoam attached to a base board (preferably a rigid boxed substructure ) and then lay up a sheet of thin fibreglass on a sheet of plate glass --even sheetmetal would do,- and then bond this to your 'inverse rib' set up to create a female mold . You may need a few spanwise webs between the 'rib offcut' pieces and right at the leading edge you will need to have a separate pre molded radius where the curvature is too high to match . Ideally you would hot wire just the first few inches of the airfoil and glass then finish it, make a splitter along the chordline and make a top and bottom section for the LE profile and offset the lower side one to create a jog for joining the wing shells.

    The labourious finishing operation can be 95% avoided by using pre molded glass and you only need a milimetre or two thickness unlike a mold laid up off a plug because when vacuuming wing skins there is no load on the mold itself --if built FIRST as a female you avoid all the plug making and go straight to a finished working mold . This method was used in Germany for sailplane prototypes and is used in general glass molding shops where possible to avoid time spent finishing .

  6. #6
    Registered User rtfm's Avatar
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    Re: I need a favour...

    Quote Originally Posted by Jay Kempf View Post
    2 or 3d? Are you just looking to get DXF files for templates? Or 3D to have the mold CNC cut?
    Hi Jay,
    3D - I'm looking to have the plug cut by the shop. All I have to do then is to lay in my glass/core/glass sandwich and vacuum infuse.

    Cheers,
    Duncan
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    Builder's Blog:
    http://rtfmaero.wordpress.com/

  7. #7
    Registered User rtfm's Avatar
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    Re: I need a favour...

    Quote Originally Posted by Inverted Vantage View Post
    If it's 3D, I can help, depending on your time frame.
    Hi,
    Thanks for the offer, mate. At this rate, I'll be finalising the fuselage plug over the next few week (plus fitting the windshield and incorporating the wing fillets). Then I have to make the molds themselves. So I'm not in a hurry. Just don't want to leave things to the last minute.

    Cheers,
    Duncan
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    Builder's Blog:
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  8. #8
    Registered User rtfm's Avatar
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    Re: I need a favour...

    Quote Originally Posted by delta View Post
    How much harder would it be to add a little wash out?
    Hi,
    Not hard at all - except, why would one want to? Washout unavoidably is less efficient than no washout, and with the Riblett airfoil, I'm not expecting any nasty stall behaviour.

    Regards,
    Duncan
    ====================
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    Builder's Blog:
    http://rtfmaero.wordpress.com/

  9. #9
    Registered User rtfm's Avatar
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    Re: I need a favour...

    Quote Originally Posted by Aircar View Post
    --if built FIRST as a female you avoid all the plug making and go straight to a finished working mold . This method was used in Germany for sailplane prototypes and is used in general glass molding shops where possible to avoid time spent finishing .
    Exactly what I plan to do, Aircar. I want the CNC shop to produce 4x femal molds, which I can use to directly infuse my skin materials onto. I'm hoping to have two wing halves (top/bottom) which I can then bond onto ribs/spar.

    Regards,
    Duncan
    ====================
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    Builder's Blog:
    http://rtfmaero.wordpress.com/

  10. #10
    Formerly Unknown Target Inverted Vantage's Avatar
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    Re: I need a favour...

    Quote Originally Posted by rtfm View Post
    Hi,
    Thanks for the offer, mate. At this rate, I'll be finalising the fuselage plug over the next few week (plus fitting the windshield and incorporating the wing fillets). Then I have to make the molds themselves. So I'm not in a hurry. Just don't want to leave things to the last minute.

    Cheers,
    Duncan

    I'll be more available mid-April if that's within your timeframe.

  11. #11
    Registered User craig saxon's Avatar
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    Re: I need a favour...

    Duncan,
    if you have not seen these two books, I suggest you seek them out. As Aircar suggests, don't make Plugs, go straight to female molds. You will only need a few female profiles of your sections. Muuuch easier than your fuselage plug.


    Advanced Composite Techniques
    Understanding Aircraft Composite Construction, Second Edition
    My avatar is a Thurston TA16 Seafire, not sure who built it, but if my project ends up as nice as this , I'll be wrapped.

  12. #12
    Registered User lawotschkin's Avatar
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    Re: I need a favour...

    Hi Duncan,

    as I wrote somewhere else here .. get a copy of Profili2 and define the wing .. it creates pos. as well as neg. molds as STL exports for you .. you can directly hand that over to a CNC shop .. its a 5 mins job .. no drawing, just typing in profiles & dimensions ..

    To cut wings .. a CNC routing machine will run almost > 8 hours .. I got quotes ranging from 6000 to 10000 Euros .. maybe its a bit cheaper over there ..

    If you want to directly create neg. molds consider in what material you want them done .. if its plastic (PU) or Alu the mold material (the blocks you cut your mold in) alone will be tousands of €€€ and the weight will be beyond anything you can handle in a homebuilding context ..

    If you want to create a neg. mold from a material that is affordable (EPS..) you will not achieve the desired surface quality or need special pastes to be applied on the foam ..

    I promise you .. at the end of the days you will make plugs and take the mold from them by yourself .. I was wrecking my brain around 18month on this .. happy to go the hotwired plug route now ..


    : )aniel

  13. #13
    Registered User rtfm's Avatar
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    Re: I need a favour...

    Daniel,
    Thank you for your post. Bloody hell - that's a lot of beer money! If that is what I'm looking at, I will HAVE to investigate hotwiring the wings myself. But that leads on to the next issue - how does one (practically speaking) do this?

    I'm guessing I'll be needing a helping hand. And I'm also guessing I need to hot wire the wing in sections.

    I'll spend some time reading the posts dealing with this here on HBA.

    Thanks for the tip about Profili

    Regards,
    Duncan
    Sigh... Nothing is easy!
    ====================
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  14. #14
    Registered User lawotschkin's Avatar
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    Re: I need a favour...

    ..I bought the Professional Version of Profili2 .. design your wing & send over .. I can then send the STLs back to you .. make sure the resolution is sufficient (enough points in the profile) else you won't receive a smooth shape .. take at least 400 points .. better 500 .. take as much as you can ..

    I can hardly imagine to build a wing in a negative process alone .. e.g. on producing the 3.1 x 1.1 meter mold for our horizontal stab we came to the limits of what is possible with 2 people .. consider the enforcement that the molds require to not flex around in a vacuum bagging process .. either you have 100Kg per mold of laminating ceramics or 50-60Kg of steel - or a combination of both .. honeycomb sandwich molds ends up 3 times the price and were unaffordable for us .. we are not professionals yet and there are surely lots of smarter ways to do than we do .. but the parts simply get too large to be able to handle them alone in the workshop ..

    Maybe if you build up the wing in a positive process (like Billski is doing on his KR2) there should be more parts of the process you can accomplish without a partner .. but not sure ..

    Building plugs & molds also needs a lot of material, stuff & time at the end .. I would recommend to make you first experiments in a smaller affordable scale e.g. here I made a naive sample piece of elevator .. of course we screwed it up completely .. the foam plug was crap, the laminate on it was crap, the other materials used were crap, the painting was crap and last but not least of course the molds & results we produced were crap .. mold making for a sample piece of elevator | Facebook .. the vert. stab. went far better then ..

    : )
    Last edited by lawotschkin; April 2nd, 2012 at 06:22 AM.

  15. #15
    Registered User lawotschkin's Avatar
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    Re: I need a favour...

    .. and always put some rovings into the edges to avoid broken edges like above .. : )

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