A challenge to you all

Discussion in 'The light stuff area' started by stan40353, Sep 11, 2011.

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  1. Jul 1, 2012 #721

    Grimace

    Grimace

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    I was reading through this thread in its entirety. I got hung up on the engine discussion and skipped to the end. LOL

    I think designing for any one particular engine is a mistake. Currently, I'm working through Raymer's book on a VW powered single-seater, but what made sense to me, and what I've kept in mind throughout my design, and what I think makes sense for a project such as this, is to design an aircraft that can meet your design within the larger portion of a range of variables.

    For instance, design a plane that meets Pt103 criteria with 95lb 18hp motor and also a 38hp 30lb motor. Then when people ask what motor to use, you can say, "Anything between 30 and 95lbs, 18-38hp." (This isn't a suggested range on my part, I'm just throwing out some approximate imaginary numbers here to use use for argument's sake). The only thing that needs to change is the engine mount, max weights, and maybe the location of a few accessories, or maybe the wing location by a couple of inches. Just account for it. If your design can account for both extremes, then the average joe schmoe is going to have an easy time finding an engine that will work... today, 5 years from now, 20 years from now... and that will add to the appeal and longevity of your design. Engine optons will change and evolve over time. Just set up a reasonable range, design to both ends of that range (assume the worst case scenario within any calculation), and trust that whoever builds it will be able to EASILY find something that fits within that range. In my case, I am designing something for a VW engine, but leaving enough space under the cowling for a turbocharged O-200. A Rotax 912/914 will also fit, as will a corvair motor. How do you manage to design for engines weighing 40 pounds more? Well, structurally, you design to the heaviest engine. Aerodynamically, you design to the biggest, lowest power engine. And you make sure to leave yourself some wiggle room. I weigh 160, but am designing for a 220lb pilot. If I wind up having to lop 30 pounds off that requirement, well, no big deal. I can make the change with a couple strokes of a keyboard rather than a reiteration of the design. If I need to switch from a battery in the nose, to one in the tail, that's doable too. Is it "optimized"? I guess not. But planes like these shouldn't be optimized to some crazy degree, they need some margin built into them to suit different builders' preferences.

    Foir a single-seater, I think you will find that the weight difference between a light and heavy engine can easily be accomodated by relocating the battery and moving the wing a very small amount, maybe an inch or two. Or moving the fuel cell. And if all else fails, you can move the wing an inch or two without royally screwing up you previous calculations. So, as a designer, forget the decision about which engine to use. Just focus on a reasonable range of options that may exist and account for their variances.

    With that said, I like the strongback design concept. What an awesome way to make a super-simple fuselage over the course of a weekend for cheap!!!!
     
    Last edited: Jul 1, 2012
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  2. Jul 1, 2012 #722

    rtfm

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    Hi,
    I agree with you entirely. My approach has been to set a reasonable weight range (for the engine) and carry on designing from there. This is the most sensible approach I believe. A lot can change in the time it takes to go from keyboard to the runway.

    Strongbacks:
    While I am still working away at the Razorback plug - which is looking more and more like the final product, BTW - I have decided to build a Strongback or Profile airframe version of the plane. Here's what I've done so far:

    • Sent the profile file to the CNC shop. They have cut the profile (paper only) for me to view (this Wednesday). If all is well, they will cut the template in 4.5mm acrylic sheet, and I'll pick it up this Friday.
    • I have ordered the foam. I had to buy 10x sheets (2400x600x50), but I'll be using six of them, so that's not too bad. The reason I'll be using so many sheets is partly because they are so narrow, and partly because they are only 50mm thick (2-inches). I want a 4-inch Strongback, so I'll be joining them two deep. This also gives me a very convenient centre line, which is going to be useful.
    • I have ordered the 1.2m x 25mm (1-inch) CF rod which joins the open space between the roof and the rear of the front section. This means I'll have a rod directly in front of me, which isn't great, but also not that bad.

    The plan is to hotwire the foam this weekend, glue the two sheets together, and shape the edges. I think I can do this in one day. Then comes the vacuum bagging. I've not done this before, so it may take longer than I think. If I don't finish it this weekend, I'll do so next weekend.

    Lots of pictures to come.

    Regards,
    Duncan
     
  3. Jul 1, 2012 #723

    stan40353

    stan40353

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    looking forward to pics Duncan. and man i am itching to build something!! my mind is racing!! so many wonderful ideas here!!! what to do what to do!
     
  4. Jul 2, 2012 #724

    PorcoRosso

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    Should I start planning now, I would most likely take the biplane approach over any, shorter wing length so less worry of flex on the wings, and overall more lift in less space. Once I have a concept design (-glances over at what the power outage led me to do-)
    PICT5278.jpg
    I should be able to search up an efficient airfoil to use, and from there be able to paint a picture of what lift I can get. The glider flies nicely without any airfoil, just a flat plane; Adding an airfoil will let me reduce the wing length as to not look like a bomber out of WWI. From there it's into Autodesk/Google Sketchup and a calculator. I find joy in how you can determine whether a plane can fly (ideally) using mathematics alone, from there on, nothing to do but to refine and build it. :gig:
     
  5. Jul 2, 2012 #725

    Grimace

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    Hi Duncan. That's really exciting and it seems to me that that CNC'ing the guides for the panel will be the most precise way of going about it, but personally, I imagined something like a table saw, only with a hot wire, that one could hand-guide through the foam. Your way is probably more precise, but my way would be a bit cheaper. What does CNCing something like your templates cost anyway? I take it that it isn't terribly expensive.

    Another thought I had was to produce concave sanding blocks that could be used to profile the edge of the foam.
     
  6. Jul 2, 2012 #726

    rtfm

    rtfm

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    Hi,
    I've tried doing this once before, and it is hellish hard to draw the profile to scale. I made more measurements than you can imagine in order to get the shape right, and ended up with an approximation only. I was drawing directly onto 3mm MDF. Then the next problem was to cut the MDF sheet so that the curves were smooth. Bloody well impossible, mate. This exercise turned my template into a further remove from the CAD I started with. Finally, I used the template and a router to make a second template, and tried sandwiching the foam between them to sand down. More inaccuracies. What I ended up with was OK, but it took a lelluva lot of work. Many weekends' worth.

    By getting the template cut at the CNC shop ($100) I end up with a perfect shape. And this time, I'm hot-wiring the foam. No sanding for me...

    And yes, you're on to it with the shaped sanding blocks. A nice elliptical one for a pleasant and aerodynamic shape round the edges.

    My main issue at the moment is how to glass the beast. I think I'll vacuum bag a couple of layers of 4-inch glass tape along the edges first. Then vacuum bag the flat parts - first the one side, and then the other. A three-step approach will probably be best for a novice like me.

    Cheers,
    Duncan
     
  7. Jul 4, 2012 #727

    deskpilot

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    Something I read whist researching Bi-planes: The lower wing, even if of the same proportions as the top one, will only add about 20% more lift, not double as many suspect. Can't remember where I read it. Staggered wings result in a slightly wider range of CoG?/CoL? movement at differing speeds.(Brain fade)
     
  8. Jul 4, 2012 #728

    Dana

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    It's not nearly that bad. There is an interference factor so it's not double, but it's not that much unless the wings are unreasonably close together. More like 20% less than double. There are tables showing the interference factor as a function of wing spacing divided by chord.

    -Dana

    Computers run on smoke. If it leaks out, they don't work.
     
  9. Jul 4, 2012 #729

    litespeed

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    That explains a lot- now I know why hitting it with a axe stops it, all the smoke gets out.

    So I guess a shotgun will have the same effect.

    Have to try that.
     
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  10. Jul 6, 2012 #730

    stan40353

    stan40353

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    70 hour work weeks are no fun!!! ugh
     
  11. Sep 22, 2012 #731

    JonnyPJohnston

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  12. Oct 31, 2012 #732

    Literider

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    Head in the Clouds, you are a perfect contributor for this thread, and your Macro is indeed an awsome start, and maybe finish. Are plans available? Could it be scaled up to a 2 seater?
     
  13. Oct 31, 2012 #733

    Head in the clouds

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    Hi LR, welcome to the forum. Why not start a thread in the New Member Introductions area and tell us a little about yourself?

    Thank you for the kind words, and there's certainly a lot of really valuable information for the Light Stuff end of things in this thread.

    You may have seen that I branched off into a new thread called AirToy to put together my interpretation of all we'd learnt from the Challenge thread. Unfortunately I've not had a lot of time to work on it, since I'm also building a folding wing 2 seater at present, see AussieMozzie thread.

    The Macro series were good little planes and very easy to build but I was making them when there were no workable rules in place at all and although the weight was within our Australian ultralight limits the wing area was a long way short and it wasn't structurally practical to extend the span and/or chord sufficiently because it would have gone overweight in the process, and needed more power which of course meant still more weight...

    Yes, a two seat side by side version would be easy enough and would be very similar to a CH601 structure, tandem would be a quite different structure. But since any of these would have to be in the Experimental category there really wouldn't be anything special about it, given all the existing ones already.

    The only way I can conceive of having a very small plane and legal within Pt103, and with easy dismantling, would be where I am headed with the AirToy. Biplane to keep the span small and for a superior and light structure, ladder wing construction and a narrow 'sit astride' fuselage a bit like the Aeromax but still enclosed, with a cowling from the engine to the rear of the cabin.

    I'll try to get a bit more done on it soon.

    Enjoy the forum,

    Alan
     
  14. Mar 6, 2013 #734

    stan40353

    stan40353

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    im back. i been away. seriously bad auto accident. but i am fine now
     
  15. Mar 6, 2013 #735

    PTAirco

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    As a rough estimate, given equal size wings, a gap of at least one chord length and a moderate amount of forward stagger - you're looking at a ratio of about 1.2:1.0 for the upper/lower lift distribution. Start varying those givens and things head off in other directions. The further apart the wings, the less interference of course and negative stagger will have other effects. Biplanes are not as hideously inefficient as people think and for a part 103 UL, it is a very logical choice.
     
  16. Mar 6, 2013 #736

    cluttonfred

    cluttonfred

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    Welcome back, glad to hear you are OK.

     
  17. Mar 6, 2013 #737

    Head in the clouds

    Head in the clouds

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    Hi Stan, sorry to hear about your accident, and glad you're OK now. I wondered what had happened to you, last I remember you were soon to be going to Tours for a visit and then hope to get started on a kit or something with help from folks you met up with at the local airport. Did this accident happen before any of that? Cheers, Alan
     
  18. Mar 13, 2013 #738

    wizzardworks

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    Group, Although I have no experiance with ultralights other than looking at them and watching them fly at Sun-N-Fun fly ins I have read this ENTIRE thread. It seems like to be different than the very few triangulated aluminum tubes I have been seeing we might consider some alternatives that look more "aeroplane" like. The profile fuselage Duncan has proposed is an example. No one is going to take off in this proposed ultralight in a driving rainstorm so an enclosed cockpit doesn't seem necessary. I am concerned about the amount of foam in a constant thickness profile both from a weight and cost point of view. If there is to be e-glass facings on the foam the foam doesn't have to be cut from a large sheat in one or two pieces. With a full scale drawing from a large format printer rectagular bars could be laid out on the patern and held together with glass tapes at the joints. Think balsa flying models we built 50 years ago). The pieces could include the curved fillets at the join points. Also the top and bottom stringer could be stood on edge and be tapered from 8" wide to 2-1/2" wide at the tail and the intermediate pieces of truss about 2/3 the width of the stringer at the attach point for both the verticle and diagonal pieces. The seat back cabin top and floorboards would be a widening of the taper as appropriate. Form follows function logic.
    Concerning hot wireing foam from templates. Has anyone else built their hot wire bow with two wires separated by the thickness of the panel you are cutting. The templates are the for inside wire. The cut part has had equal heat on both surfaces to prevent it drawing out of shape as it cools. Leave it sit in the waste side cores until use more for damage/ cleanliness protection until use. Connect the hot wires in series at twice the voltage.
    I follow Danielle's member projects log thread and really like the look of her wings. It is a Dakota Hawk with the geodesic strapping bracing. It look really light and extremely torsionally stiff. Covered in the fabric used on traditional ultralights it might meet the design goal of this thread. Takes a lot of clamps but home made ones cut from rings of PVC pipe would seem appropriate. (skilsaw down the length and chopsaw the bands)
    The wing folding for trailer transport might be another thing to look at. There should be little problem getting the tail pklane span down to 7 feet with enough chord width for the tail volume needed. That leaves the main wing to find a way on to the trailer. I would propose a 4 piont fastening of the wing to the top of the fuselage. The left rear attach point would be slightly outboard of the fuselage and a ball and socket type joint (like a double ended heim joint) The flap handle and linkage would be permanently attached to the wing hanging down on the left side of the cockpit. Pull th pins out of the aleiron linkage and then tilt the wing off the other three mounting point and turn it around to hang from the ball jointed corner. That should be reasonable for a 40 pound wing with the weight being handled to a large extent by the ball joint connection.
    My engine choice would be the Axiro. It started out as a kart engine and is still sold that way. There are also available aero engines with reduction drives and retractible props used mainly on self launch sailplanes with over 600 sold at one point. They make 1 rotor and two rotor variants and have some GA units with two-two rotor units (110 HP?) belted to a single propshaft. I have also seen ultralights at Sun-n-Fun with this engine flying.
    There hasn't been much discussion about a light weight undercarrage. A tail skid and two main wheels seems the lightest by intuition at least. But what to use for wheels and brakes.
    The concensus seems to have only considered conventional layouts either biplane or high wing. Just to get out of the box, drum, or packaging of any type could a tail wheel tractor engined canard be a possibility. Getting the wing to take off AOA problems of tricycle engined pusher canards would seem possible. The pilot would be closer to the main wing MAC due to the 75 pounds of firewall forward weight in front of the canard. If necessary some tubin skis extending forward of the wheels a few inches off the ground to prevent empyy tip over?
    Final thought for today. No matter whether you build from sheat metal, wood, foam and glass, steel tube or whatever else there are parts required from many of the other diciplines. Everybody ends up with drill motors, angle grinders, a drill press, band saw, electrical tester, a bunch of assorted clamps, things to measure with electrical tester. The real time consumed seems to be in the veryifying of measurements and finding a way to the datum point to measure. Plans that aren't clear or kits with dubious instructions seem to be the real time consumers in this hobby.
    wizzardworks
     
  19. Mar 13, 2013 #739

    nerobro

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    Hmmpf. Seems like a really complex solution.

    If I were to do this, I'd start with the engine. We need ~30hp. Which is an amazingly hard area to find engines in. 20? sure, 60? sure. But 30? Where are the 30-40hp engines?

    A simple/cheap airframe is not a difficult thing. And geodetic is definitely not simple. :)

    Has anyone thrown up designs here yet? I have some ideas off the top of my head for VERY simple designs that would get people in the air cheaply.
     
  20. Mar 13, 2013 #740

    jedi

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