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RE: [AWECS] Rigid v. Soft Wing Debate Again:search of new materials

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  • North, David D. (LARC-E402)
    We (NASA LaRC) are experimenting this summer with wire cut EPP foam arc kites with various different coatings. EPP is relatively cheap, can be recycled, and
    Message 1 of 28 , Jul 21, 2011

      We (NASA LaRC) are experimenting this summer with wire cut EPP foam arc kites with various different coatings. EPP is relatively cheap, can be recycled, and very tolerant of “unscheduled landings” and we believe can perform fully-autonomous re-launch from a water surface. The EPP holds a very nice profile tolerance compared to the not very good profile tolerance of a ram air kite. We are able to produce foils with good thickness-to-chord ratios (8%) and aspect ratios of up to 20. Our goal is to improve L/D from 3-8 for current ram air kites to maybe 10-12 which would improve specific power output (power/kite area) by up to a factor of ~8.

       

      The EPP foam is a solution that is mid-way between a soft wing and rigid wing that has benefits of both.

       

      We are building a servo motor controlled kite flying system that can measure kite speed, trajectory, line forces, and line speed and should be producing data within a few weeks.

       

      We are also doing some experiments with a simplified optical tracking system that uses only one or two (cheap) cameras for flight control. No control system instrumentation onboard the two-line kite (no GPS, no IMUs, no gyros, no telemetry).

       

      Stay tuned. Will keep you all informed of progress.

       

      Dave North

      NASA Langley Research Center

       

      From: AirborneWindEnergy@yahoogroups.com [mailto:AirborneWindEnergy@yahoogroups.com] On Behalf Of dave santos
      Sent: Thursday, July 21, 2011 9:09 AM
      To: AirborneWindEnergy@yahoogroups.com
      Subject: Re: [AWECS] Rigid v. Soft Wing Debate Again:search of new materials

       

       

      Pierre,

      The good news is that there are many great new and old fabrics, and they continue to get better. Peter Lynn has reported the leap in flying hours performance from around 500hrs to 5000hrs in just a few decades. We know that alumized coatings enable over a decade of outdoor UV life for fabric covered aircraft that fly several hundred kph. A sub-micron alu vapor coat would really weatherize at low weight/cost. We have essentially inert teflon based alternatives and graphene next. We can even return to natural fibers with just a moderate hit in performance. If one allows fading, stains, and patching, kites can live far longer than rated.

      All in all its a new golden age.

      dave

    • dave santos
      DaveN, Yes, EPP foam is wonderfully crashworthy and its easy to insert a carbon tube for extra stiffness (stock tube sleeve-sets for tapered COTS spars).
      Message 2 of 28 , Jul 21, 2011
        DaveN,

        Yes, EPP foam is wonderfully crashworthy and its easy to insert a carbon tube for extra stiffness (stock tube sleeve-sets for tapered COTS spars). Bonding a fabric skin to EPP is harder, but it can simply be stretched on. A foam/spar/skin composite is super for a versatile triple load-path structural system, with the spars easily replaced and skin patched. Even EPS foam becomes robust in this sort of composite. This is KiteLab's basic construction method for high L/D powerwings deployed under soft pilot-lifters,

        daveS
      • dest6a
        When you talk about low-density foam, paper or cloth wings, I say you will not harvest serious amounts of energy from kites. To do so, requires large air
        Message 3 of 28 , Jul 21, 2011
          When you talk about low-density foam, paper or cloth wings, I say you will not harvest serious amounts of energy from kites. To do so, requires large air loads, such as those from 10g to 40g maneuvers. There is no way to avoid the high air loads when one extracts large amounts of energy from kites (such as the energy from one unit of kite wing area equal to that from 400 units of HAWT rotor area.) Where have you seen aerobatic sailplanes capable of 8 to 10g maneuvers that use cloth wings? But even manned sailplanes limited to 10g because of the pilot, are not good enough. Carbon sailplanes (using RC) for dynamic soaring (DSing) are capable of 40g maneuvers or more. That's what is needed.

          Dennis

          --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@...> wrote:
          >
          > DaveN,
          >
          > Yes, EPP foam is wonderfully crashworthy and its easy to insert a carbon tube for extra stiffness (stock tube sleeve-sets for tapered COTS spars). Bonding a fabric skin to EPP is harder, but it can simply be stretched on. A foam/spar/skin composite is super for a versatile triple load-path structural system, with the spars easily replaced and skin patched. Even EPS foam becomes robust in this sort of composite. This is KiteLab's basic construction method for high L/D powerwings deployed under soft pilot-lifters,
          >
          > daveS
          >
        • North, David D. (LARC-E402)
          Dennis, We are using unidirectional fiberglass strands bonded to the surface of the foil to transfer aero loads (normal to surface) into the skin of the top
          Message 4 of 28 , Jul 21, 2011

            Dennis,

             

            We are using unidirectional fiberglass strands bonded to the surface of the foil to transfer aero loads (normal to surface) into the skin of the top surface of the foil in the ¼ chord region. These loads are transferred out to the wing tips and then into the flying lines. This type of structure in an arc kite is extremely efficient in terms of weight because it is a catenary structure (no bending moment). All loads are dumped in unidirectional fibers which have an extremely good strength-to-weight ratio.

             

            Dave North

             

            From: AirborneWindEnergy@yahoogroups.com [mailto:AirborneWindEnergy@yahoogroups.com] On Behalf Of dest6a
            Sent: Thursday, July 21, 2011 3:22 PM
            To: AirborneWindEnergy@yahoogroups.com
            Subject: Re: [AWECS] Rigid v. Soft Wing Debate Again:search of new materials

             

             

            When you talk about low-density foam, paper or cloth wings, I say you will not harvest serious amounts of energy from kites. To do so, requires large air loads, such as those from 10g to 40g maneuvers. There is no way to avoid the high air loads when one extracts large amounts of energy from kites (such as the energy from one unit of kite wing area equal to that from 400 units of HAWT rotor area.) Where have you seen aerobatic sailplanes capable of 8 to 10g maneuvers that use cloth wings? But even manned sailplanes limited to 10g because of the pilot, are not good enough. Carbon sailplanes (using RC) for dynamic soaring (DSing) are capable of 40g maneuvers or more. That's what is needed.

            Dennis

            --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@...> wrote:
            >
            > DaveN,
            >
            > Yes, EPP foam is wonderfully crashworthy and its easy to insert a carbon tube for extra stiffness (stock tube sleeve-sets for tapered COTS spars). Bonding a fabric skin to EPP is harder, but it can simply be stretched on. A foam/spar/skin composite is super for a versatile triple load-path structural system, with the spars easily replaced and skin patched. Even EPS foam becomes robust in this sort of composite. This is KiteLab's basic construction method for high L/D powerwings deployed under soft pilot-lifters,
            >
            > daveS
            >

          • dave santos
            Dennis, Most of us agree that rigid carbon wings moving at high speed are wonderful, but it will take a decade or more for ultra-reliable flight automation to
            Message 5 of 28 , Jul 22, 2011
              Dennis,

              Most of us agree that rigid carbon wings moving at high speed are wonderful, but it will take a decade or more for ultra-reliable flight automation to evolve to allow these wings to survive long enough to pay back the high capital-cost. 

              Meanwhile we will make lots of power just as "NASA" (DaveN, etc.) informs us, with softer wings using tensile load-path networks. Soft wings are already pulling ships, so the concern about soft-wing power is fortunately not being confirmed, rather its hard wings hard-pressed to show such results. Meanwhile the hybrid option of semi-rigid fast moving wings, in stable orbits, hung under soft slow moving wings, with inherent stabilities, is fully workable.

              daveS
            • dest6a
              How fast will the soft wings go? How much power will they generate relative to HAWTs operating at the Betz limit? I think the driving force toward
              Message 6 of 28 , Jul 22, 2011
                How fast will the soft wings go? How much power will they generate relative to HAWTs operating at the Betz limit? I think the driving force toward high-speed, high-performance wings is enormous.
                Dennis

                --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@...> wrote:
                >
                > Dennis,
                > Most of us agree that rigid carbon wings moving at high speed are wonderful, but it will take a decade or more for ultra-reliable flight automation to evolve to allow these wings to survive long enough to pay back the high capital-cost. 
                > Meanwhile we will make lots of power just as "NASA" (DaveN, etc.) informs us, with softer wings using tensile load-path networks. Soft wings are already pulling ships, so the concern about soft-wing power is fortunately not being confirmed, rather its hard wings hard-pressed to show such results. Meanwhile the hybrid option of semi-rigid fast moving wings, in stable orbits, hung under soft slow moving wings, with inherent stabilities, is fully workable.
                > daveS
                >
              • Joe Faust
                Message 7 of 28 , Jul 22, 2011
                • dave santos
                  Dennis, This is an old topic on this forum, but review is good. Joe may have link page on this question. The parafoil speed record is around 120mph (Flexifoil)
                  Message 8 of 28 , Jul 22, 2011
                    Dennis,

                    This is an old topic on this forum, but review is good. Joe may have link page on this question.

                    The parafoil speed record is around 120mph (Flexifoil) and fabric covered wings have gone several hundred mph (Early WWII warbirds). Much higher performance is possible if we merely continue to improve materials and methods.

                    You are right to suggest a focus on performance, in which case the reasonably good soft wing may have superior early safety, power-to-weight, and ROI (return-on-investment).

                    We will certainly adopt rigid airframes as they prove suitable,

                    daveS

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