Consensus on Lightest FAR 103 Wing Design

Discussion in 'The light stuff area' started by WhiskeyHammer, Apr 22, 2019.

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  1. Apr 22, 2019 #1

    WhiskeyHammer

    WhiskeyHammer

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    This might be as silly question but is there any consensus on what the lightest wing design is for a homebuilt ultralight?

    Planes like the Invader Mk 3, the SkyDock, and the Backyard Flyer Swing Wing appear to be the only planes without some kind of strut or wire bracing. So I'm guessing that the the strut based designs are probably some combination of stronger and lighter.

    Which fixed wing ultralight would you recommend I study for a good lightweight wing design?

    Bonus Question: It doesn't look like there are many (if any) kit or production fiberglass composite FAR103 ultralights. Is this just a market thing (i.e. the production techniques are too expensive for the level of demand) or is there a technical reason why composites are commonly seen on ultralights?
     
  2. Apr 22, 2019 #2

    RPM314

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    Strut and/or wire bracing markedly reduces the maximum bending load that the wing must endure, and typically the weight of adding these truss structures is more than offset by the reduction in the strength required of the wing's beam structure (spar). Generally, any structure meant to resist a bending load will be made more efficient by increasing the structure's depth.
    An aircraft wing is designed to some required strength, so it's not that a braced wing is stronger than a purely cantilevered one, but that a braced wing will achieve the same constant strength with a lower weight due to its higher efficiency.

    The more knowledgeable members here can go into more detail on the composites question, but fiberglass builds really are the heavier option for ultralights compared to tube-and-rag. Since the thickness of composite skins required to actually take the loads on an UL would be hopelessly too thin to avoid buckling and hangar rash, a composite skinned aircraft will be heavier than ideally required. A moldless aircraft may support the skin better but suffers from the fact that the volume filled by foam in a low aspect wing represents a large chunk of dead weight. Add to that the fact that woven composites are much more difficult to analyze than more conventional materials and as such composite homebuilts are typically designed with large safety factors.
     
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  3. Apr 22, 2019 #3

    fly2kads

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    The Ivanov ZJ-Viera was a composite, cantilever-winged ultralight. They went with a fabric covered D-tube wing, rather than a fully-skinned surface.

    The SkyPup and Goldwing are additional examples of cantilever ultralights.
     
  4. Apr 22, 2019 #4

    Dana

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    The simplest and lightest is probably a wire braced ladder frame wing like Quicksilver uses. Later strut braced Quicks were heavier and less rigid, the only advantage is they can fit better under a lower hangar door.

    The Lazair was pretty light too, an aluminum D-tube with foam ribs and aluminum capstrips, with Tedlar plastic film covering.
     
  5. Apr 22, 2019 #5

    DaveK

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    All things in engineering are compromises, the trick is making good compromises. For the same weight cantilever wings tend to be heavier than wire braced or strutted. Wires are light, but cause a lot of drag (a single wire has as much form drag as a whole wing airfoil section). So you trade lightweight of the wing for needing more power to stay aloft or needing a longer wing to keep the power required down. But bigger engines and longer wings weigh more! Bigger engines burn more fuel (aka more weight or lower flight time). You also have ease of construction to consider, many ultralights were purposely made to be easy to build from easily assembled materials. A wire braced ladder wing (two tubular spars separated by compression struts and looks like a ladder from below) is really simple to assemble. The D-tube spar of the Lazair is harder to construct, but is cleaner and is more rigid only needing one strut.

    So take a few examples.
    Quicksilver with wire bracing -- simple to construct, lightweight, but very draggy and needs a big engine. High sink rate engine out, but climbs reasonably well because of the bigger engine.
    Lazair -- Strut braced with Dtube leading edge and long wings, needed only two little engines to fly because it is pretty clean drag wise. Low sink rate engine out, but not the greatest climb rate (small engines). Harder to construct than Quicksilver or a ladder frame, but cleaner wing.
    Challenger -- Strut braced ladder frame. Simple to construct, reasonably lightweight, but less drag than the Quicksilver so can run a smaller engine.

    Many ways to do reach the same 254 lbs constraint, but have different pros and cons. The trick is do the pros and cons match what you are trying to do? What is your mission within the UL designation? If you want to do some soaring the Quicksilver isn't your bird. If you want the lowest possible running costs (sips fuel) then maybe something like the Lazair. There is a reason all airplanes are not built exactly the same, there is no single best way to do it, it all depends on the mission.

    Regarding fiberglass. Glass itself is rather flexible so you need deep structures to give enough stiffness. It is also more complex to analyze. Due to the low weight you are dealing with on a UL you end up with really thin structures to make the weight. Thin structures are damage prone. It also generally needs molds and a lot more work to build parts. Aluminum tube ladder frame can be built with a few simple tools, not so with fiberglass. That is why you don't see if often. It worked well with the Falcon UL fuselage tub, but even then the wing and canard were aluminum with tedlar covering.
     
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  6. Apr 23, 2019 #6

    BJC

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    One of the lighter is the Gossamer Albatross.


    BJC
     
  7. Apr 23, 2019 #7

    rtfm

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    While not a Part 103 plane, the SD-1 has wings which weigh about 12kg - they use a foam/glass spar, foam ribs and 1mm ply skins.
     
  8. Apr 23, 2019 #8

    pictsidhe

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    Look at the various human powered aircraft for good examples of huge area and span with minimal weight. Wire braced.
    The Ison *max designs have a large following and its wing has been used on several other designs. If you aren't sure what you are doing, it would be a great one to use.
    Having spent far too much time messing around with airfoils mathematically and in XFLR5, I'd say that many ultralight airfoils are thinner than optimum. You'll get the best aerodynamic performance at 103 speeds with an airfoil around 15% thick. That gives a healthy spar weight saving over a Clark Y. Going thicker won't hurt things too much. Especially if you have flaps, which just love thicker foils. I have pencilled in a 21% root and 12% tip on my tapered cantilever wing.
     
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  9. Apr 23, 2019 #9

    BJC

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    Nice airplane, and claims to be under the Part 103 weight cap, but does not meet the Part 103 performance requirements.


    BJC
     
  10. Apr 23, 2019 #10

    henryk

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  11. Apr 23, 2019 #11

    saini flyer

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    A tandem wing design with 4 SD-1 wings fixes that Part 103 performance (Stall) requirement.
     
  12. Apr 23, 2019 #12

    BJC

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    How does one get both wings in a tandem wing configuration at a high Cl for slow stall speed?


    BJC
     
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  13. Apr 23, 2019 #13

    Victor Bravo

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    I believe you would have to completely abandon the tandem wing "stall-proof canard" thing, and set both main wings at the same incidence, and move the CG back a ways. THEN you will likely have some serious pitch stability issues, which means you would want to put a horizontal tail on it, which requires a longer fuselage, which will make it heavier, which may well knock you out of ultralight weight.
     
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  14. Apr 23, 2019 #14

    Victor Bravo

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    One other light weight wing that may be relevant to this discussion is the Fauvel derivative ultralight from Jean-Claude Debreyer, the Pelican. He used a thick wing section (17%), made out of wood, and achieved reliable flight on 12 horsepower. It was originally flown successfully with 9HP, but he soon went up to 12. The Pelican used very traditional wooden structure, a built-up box spar and built-up "stick" ribs. The thick airfoil (yielding a very tall and lightweight spar) was able to be built as a cantilever wing without any external bracing.
     
  15. Apr 23, 2019 #15

    pictsidhe

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    I am surprised at the lack of 103 biplanes. two wings braced together effectively makes an extremely deep spar.
     
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  16. Apr 23, 2019 #16

    BJC

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    Still see the old Easy Riser occasionally.


    BJC
     
  17. Apr 23, 2019 #17

    Victor Bravo

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    Yes, but a bucket full of brass and steel turnbuckles, and steel tangs, and steel bolts, and steel cable, and another whole set of ribs and another set of spars and compression struts, and then a set of interplane struts, and then a set of cabane struts... all that adds up too.

    That being said, I think the original Graham Lee Nieuport may have been capable of being a legal ultralight????
     
  18. Apr 23, 2019 #18

    Dillpickle

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    The old Sunseeker ultralight made weight and had a fabric covered Composite D cell wing. Tapered, light, pretty.... Steel cage, aluminum boom, stabilator. But for a modern cheap light wing, Robert Baslee builds and supports the Dream Classic and Dream strut braced. Probably one of the faster cheaper lighter ways to build a wing. There is a youtube vid I believe titled "ribs" showing the construction.
     
  19. Apr 24, 2019 #19

    addicted2climbing

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  20. Apr 24, 2019 #20

    Dillpickle

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    I admire this airplane too. would be slightly cheaper to Fabricate the bent .020 vs the tubing. The trade is the time Vs. weight. Correct me if I'm Wrong, but wasn't there a plastic fitting of some kind Ed used to attach the rib to the spar? how much are those, what do they weigh, and are they available? And if you want to drive EVERYONE crazy with cute overkill, fab a Rangerlike fuse for the Biplane....
     

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