The Razorback construction thread

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by rtfm, Jul 11, 2008.

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  1. Mar 22, 2014 #781

    rtfm

    rtfm

    rtfm

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    Hi,
    So far it's unanimous. That's unexpected... So no-one likes the forward swept tail. Interesting.

    Wiz - the X-Plane image is with the rudder deflected, making it look like the rudder is short of the end of the tail.

    Cheers,
    Duncan
     
  2. Mar 25, 2014 #782

    timberwolf8199

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    With the low wing config the unswept LE looked good. With the tandem, I too would have to say that I prefer the swept version. That said, the picture provided doesn't let the forward sweep of the wing impact the eye. A different angle may cause the brain to seek balance and prefer the opposite.
     
  3. Mar 25, 2014 #783

    bmcj

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    Where are Al and Art Mooney when you need them?
     
    Last edited: Mar 25, 2014
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  4. Mar 26, 2014 #784

    rtfm

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    Hi,
    It's raining steadily here in Brisbane at the moment, and since my workshop (although under cover) doesn't have closed in sides. It's generally very unpleasant there when it rains. So today I'm sitting at the PC and double-checking placement of my front wing before I start cutting the plug.

    I've been in contact with a copule of companies who do CNC hotwire cutting. I was hoping to get them to produce full wing plugs from which I could make molds. The problem is, getting suitable computer files to them. I've been using Profili Pro to draw my wings. But it only handles multi-panel wing ribs, and single panel foam panels. Not both. I need a multi-panel foam plug. I wrote to the developer, and yes, he has such an application in the works, but it won't be ready for another six months.

    Bugger.

    So I may have to try cutting the panels myself. I could, of course, visit one of the shops I've been speaking to, present them with the CNC cut ribs, and ask them to hotwire the foam based on this. And then I can jig it all together and make a mold. I've never used anything more than a four-inch hobby shop hotwire tool. But HITC tells me he has one. He also says they're not that easy to use, and I could end up with a lot of wasted foam before I have mastered the technique.

    So till I get some additional income which I can channel towards the wings, it is slowly but surely completing the plug, cutting the wing recesses (using my hand-sanded wing inner sections as a guide), finishing the surface.

    Cheers,
    Duncan
     
  5. Mar 26, 2014 #785

    autoreply

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    I don't get the problem? Do you have taper/twist, sweep, an airfoil you designed yourself?

    Lining up 2 airfoils (or a few more with different sections) is pretty straightforward in any CAD environment right?
     
  6. Mar 26, 2014 #786

    Jay Kempf

    Jay Kempf

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    I don't think Duncan is a CAD guy.
     
  7. Mar 26, 2014 #787

    rtfm

    rtfm

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    CAD = BAD = SAD :)
     
  8. Mar 26, 2014 #788

    autoreply

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    Still don't understand the trouble? How are your airfoils defined; point clouds? In that case, you can simply give coordinates for the respective trailing edges etc right? Any company that does CNC-wire cutting can translate that do actual parts?
     
  9. Mar 26, 2014 #789

    Hot Wings

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    Not all companies that do hot-wire foam cutting are set up to do airfoils with taper. Some can't even cut a taper, just architectural pieces. Add sweep to some taper and the problem gets even more complex, especially if you want to cut more than one core from a large block of foam - like EZ's or Q's. Each machine is going to need custom made files to cut a tapered piece due to the differing widths between the towers moving the wire. Good software takes care of this once the table and software are matched, but not every shop has such software. The job can still be done if the shop's CNC software can't do the translation, but that would require some extra CAD work to make a virtual core with the same length as the distance between the towers, and an operator that knows how to set it all up.
     
  10. Mar 26, 2014 #790

    berridos

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    G code is pretty easy. Lazycam from Mach3 outputs the g code for every shape you propose- You even can do G code in excel
     
  11. Mar 27, 2014 #791

    rtfm

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    ...and you see, this is where you guys lose me. Hot Wings' post was interesting, largely because he is speaking a language I don't know.

    I'm going to give the hot wiring a go myself, and limit myself to a fixed dollar value as a cut-off point. Profili will generate the required airfoil templates, as well as the progress marks to guide the hotwire speed. My mate HITC has a hotwire I can use. If I can't end up with a wing with which I am completely happy by that dollar point, I'll give up and find a local company which will do it for me.

    Duncan
     
  12. Mar 27, 2014 #792

    Hot Wings

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    Until you have actually done it from sketch to final product even some people with CNC experience don't fully understand how different a 4 axis hot-wire cutter can be.

    If it were me in your shoes I'd have the templates CNC cut and then hand hot-wire the cores with a partner that has done that before. Hundred of cores have been cut by hand and turned out just fine. IMHO CNC for foam cores is using more technology than needed. Unless you have access to the CNC cutter for zero or very little cost or are producing cores for multiple planes It's really not justifiable.

    If you want to get real picky with the templates consider offsetting the template from the ideal airfoil to account for the thickness of the surface laminates, especially where the top and bottom skins overlap. While you are making files for the CNC shop you might also make a few female templates for the nose at several stations to use as a guide during final finishing. The cost shouldn't be much, if any, greater than cutting just the male templates.
     
  13. Mar 27, 2014 #793

    Aircar

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    Duncan - I thought you had agreed to delete the gull from the rear wing (Didn't Autoreply recommend and you accept that ?) --it would double the work in shaping and profiling the rear wing and adds nothing --not to mention the crank in the spar and how graphlite would not like that.

    "Manually" cutting styropor cores of that length is not difficult --just so long as the wire tension is high enough (when hot)and the rate of cutting is not too high (wire 'sag' minimized) -you must also leave a bit extra on the trailing edge on one side and glass the other side before cutting the last bit of the opposite one (otherwise it will warp by being too thin and you cannot lay up on it properly --if you are intending to vac bag or something then you can only do one side before even cutting the opposite side foam (the vac pressure ).

    Once again - study the Venture fuselage and maybe even photoshop a straight wrap canopy onto it to see the difference in appearance.--a simple blown canopy adds 'character' and matches the rest of the compound curves to harmonize it . that is 2c worth.

    Jarno -on the off chance you see this --I got your last two PM's and had to delete some old outgoings to be able to reply but then the library closed --now that I tried again YOUR inbox is full!! (can't win. :depressed)....
     
  14. Mar 27, 2014 #794

    Jay Kempf

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    Duncan,

    You can get counter top material scraps from your local cabinet shop. You can then stick good laser prints on to that and cut out your own templates with a band or jig saw. You can then measure and stick and pin those to your foam blanks and hot wire manually. Been doing that for years. It is good to have two blokes to do the hotwire cutting. HITC I am sure can be bought with beers and not that Fosters crap but some good beer. (sorry in advance for that last bit)
     
  15. Mar 27, 2014 #795

    rtfm

    rtfm

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    Gentlemen,
    Aircar:
    I had a long look at the non-gull wing rear wing, and it looks Meh... So I checked out the stress graphlite rods would be under to fit the 8 degree change from inner to outer panels, and the bend radius is well within limits. In fact, the bend makes a small enough difference not to have to worry about it. I'll keep away from sudden bends, of course.

    I'll take another look at the Venture, and see if I can photoshop a blown canopy onto the Razorback.

    Jay:
    No-one here drinks Fosters. Not that I'm aware of, anyway. I'm going to see Alan tomorrow (hopefully) to talk through the process, and to get his hot wire. Then I'll try my hand at some smaller bits and see how I get on.

    I'm using Profili Pro to generate the rib templates. Profili does all the smart bits of adding tabs to support the ends, creating a cutting guide for the templates and so on.

    Regards,
    Duncan
     
  16. Mar 27, 2014 #796

    autoreply

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    Cleaned it out, 500 new messages to go again. I trashed your last post by the way (double) :)
    If you're doing that, the spar will tear itself apart long before you reach limit load. Try it with hoop stress; the spar caps will tear themselves from the shear web. Bends that go "along" with the natural bending of the wing are far better, gull wings are a nightmare to get right. (You basically want to remove all peal potential anywhere near that area. That's hard)

    If you can do the foam core cutting by hand; do it that way. CAD/CAM is rarely as practical/cheap/fast as some manual labor.
     
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  17. Mar 27, 2014 #797

    rtfm

    rtfm

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    Sigh...
    Far be it from me to insist on a design feature which guys like you think ill advised. But it's really disappointing to have to chuck out a cherished feature in favour of some vanilla flavoured substitute.

    I've changed the rear wing to a simple 6 degree dihedral, and will try to get used to the look.

    Mumble, grumble, mutter...

    Duncan
     
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  18. Mar 27, 2014 #798

    autoreply

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    Yeah, life is a b*tch. It CAN be done, but it's engineering nightmare.

    Half-pylon wing with fairings might give a very similar look to gull-wings? (Think Akaflieg Munchen Mü31?)
     
  19. Mar 27, 2014 #799

    rtfm

    rtfm

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    Hi,
    I'm trying to get used to the non-gull wing look.

    What I was thinking of doing was to encapsulate the bend in a metal sleeve extending some six inches or so on either side of the bend. I decided to do this on the front wing when I was considering the Corsair-type low wing, and I was going to attach the landing gear to this sleeve. I thought I would re-use that method on the rear gull wing to keep the spar caps rigidly constricted. If the collected wisdom agrees that this will be insufficient to keep the spar caps from tearing apart from the shear web, then i guess I don't have a choice.

    Regards,
    Duncan
     
  20. Mar 27, 2014 #800

    bmcj

    bmcj

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    It seems to me that if your core has a constant taper and a uniform airfoil throughout without any twist, you could start with a longer blank, anchor the hotwire at one end (presumably where the taper goes to zero), and follow a root template at the other end? (This might be a one person operation.)
     

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