Interest in a plansbuilt, LSA/microlight amphibian?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Jan 8, 2013.

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  1. Jan 8, 2013 #1

    cluttonfred

    cluttonfred

    cluttonfred

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    The choices out there for amphibious homebuilts are pretty limited if you don't have deep pockets for a sophisticated kit. I am primarily thinking of boat-hull amphibians, not regular landplanes on floats. Among the plansbuilt options out there, most are decades old and too heavy for U.S. LSA/Sport Pilot limit of 1,430 lbs (648 kg) gross for seaplanes. Even the Volmer VJ-22 Sportsman, while it could work if built light, is too heavy if already built and certificated at 1,500 lbs gross. Just about all of them are way too heavy for the European microlight limits of 495 kg (1091 lbs).

    If I were tackling an amphibian, I'd want to keep it light to stay within microlight limits and get adequate performance from an inexpensive engine like a 2.1 liter VW (Aerovee, Great Plains, etc.). A Rotax 912 would probably be a better choice for this application, but at two- to three-times the price. The VW engine also implies generous wing area and modest speeds, which has the side benefit of keeping the hulls stresses down (water is "harder" than it appears!). I think I'd want to go with a light plywood hull and either wood-and-fabric or aluminum-tube-and-fabric wings and tail surfaces.

    Let me stop there. Would anyone else be interested in a light amphibian along these lines? If so, what other characteristics would you like to see? Modern or retro? Monoplane or biplane? Open or closed cockpit? Tractor or pusher? Side-by-side, staggered or tandem seating?

    Cheers,

    Matthew
     
  2. Jan 8, 2013 #2

    Jay Kempf

    Jay Kempf

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    2 place or one place?

    A simple boat hull plane certainly could be built light for slower speeds some have been done. Expand on the Lazair amphib electric you would have something fun. That one fits into ultralight but you could double the weight of it and fit in LSA by scaling it up, enclosing the cockpit, etc... Build a smaller version of the SeaBee? There are lots of flying boat type designs to look at for a light weight version.
     
  3. Jan 8, 2013 #3

    cluttonfred

    cluttonfred

    cluttonfred

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    Hi, Jay. Definitely two-place...those are the numbers I was using above for LSA/microlight limits. You're right that there are lots of possible inspirations, here are just a few that come to my mind.

    Dornier Libelle
    doa-1.jpg

    Shavrov Sh-2
    sh-2-sh1p409c.jpg

    Loening OA-1
    800px-Loening_OA-1A_USAF.jpg

    Curtiss CW-3 Duckling
    cw-duckling.jpg

    Thurston Teal
    N897TB-13-740.jpg
     
  4. Jan 8, 2013 #4

    Jay Kempf

    Jay Kempf

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    The Teal is an interesting little plane. It grew up into a Lake, right?

    A small two seat composite amphib like a lake with less HP and even cleaner for better cruise would be nice. That is what the Swiss design is supposed to be but it is a complicated, controversial expensive design. I have always liked things like the Gruman Albatross. Always thought a small version of that could be done with a couple smallish engines. A small Sea Bee would be good too. The idea of a front cabin with front doors that open up so you can just stand up and walk onto a dock is a nice idea. A two seat simple version of that would be a good target. Say with a marine engine with a 2:1 belt drive reduction. I also like this model airplane that was called the Mallard which was a float with a fuselage built on it with a wing on top then twin tail booms and a horizontal tail between up out of the water. I also like retractable wingtip floats. So many good ideas to go after. I also liked the Aussie XTC. That could be scaled up and enclosed.
     
  5. Jan 10, 2013 #5

    cluttonfred

    cluttonfred

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    Yes, the Teal is a great-looking, very clean design by David Thurston, probably the most experienced living designer of water-based aircraft. If going for a more modern look, than a scaled down, lighter Teal would be a great jumping off point.
     
  6. Jan 11, 2013 #6

    Head in the clouds

    Head in the clouds

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    The thing about amphibs/floating hulls is that you can scale the plane down and get it quite small but the chop on the water doesn't get smaller with it. So any small floating hull needs to have a much bulkier looking hull than the look of a larger floating hull plane. Same with yachts/power boats etc.

    So if it's small it needs to look like the bulky Short flying boats or the Sea Bee rather than like the PBY Catalina, otherwise it won't have enough freeboard or operational capability in anything except smooth water, the Osprey 2 is a classic example of those problems.

    The one I most admire for LSA consideration is a twin Jabiru engined aly plane called a Pelican that someone in Canada put together. It'd have to have a single central engine for LSA of course but the configuration allows for that. Note how high sided it is and compare it with the video of the almost submerged Osprey.

    jabiru2200_pelican3.jpg jabiru2200_pelican2.jpg

    Seaplane taking off from Ravenglass - YouTube
     
  7. Jan 14, 2013 #7

    Himat

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    This is an important observation. The same is true for the wave period and length of the waves. To get a better ride the hull should straddle as many wave crests as possible. Scaling down a seaplane it get short witch reduce the ability to handle waves. I have had my dab at model seaplanes and this is then exaggerated. The wind is no problem when flying, but take off, landing and handling afloat get difficult. STOL performance does help, if there is waves there is usually a headwind too. The extreme case is when the take of run start at the bottom of two waves and end at the wave crest. But then, you need a decent speed range too.

    A light seaplane then probably not only need a slightly bulky hull, but a hull that is longer than “ordinary” light plane proportions. This again introduces larger bending moments in the hull. And we are maybe on the track of one reason that light seaplane design is more difficult than light airplane design.
     
    Last edited: Jan 14, 2013
  8. Jan 14, 2013 #8

    cluttonfred

    cluttonfred

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    Thanks Head in the clouds and Himat for your comments. That looong Shavrov hull, perhaps with proportionally more freeboard, is looking better and better as an inspiration. Here's a little clip to show what I mean.

     
    Last edited by a moderator: Mar 20, 2019
  9. Jan 14, 2013 #9

    Himat

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    Just one detail, when planing on the step the "hull lenght" of a conventional arranged seaplane is only from the bow to the step.
     
  10. Jan 14, 2013 #10

    oriol

    oriol

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    Although it will be posible to find a way to make a three axis airplane light and robust enough within the regulations, the most straighforward/cheap way to make it real is a two axis solution: like the Polaris or the ramphos.


    If you prefer to do it by yourself instead of buying one you can find cheap second hand engines and delta wings, you too can build the floaters or buy them. A trike is by far more easy to build and design than any conventional airplane.


    Of course you migh not like pendular aircrafts, if so maybe the last picture (a three axis microlight airplane) might serve as inspiration.
    However it is not clear how well it lands on water: there is just one big float/hull, no little ones below the wings).
    ByDanJohnson.com - Connie Amphib



    Oriol


    Fling boatIMG_7432.jpg NorthWingTrike_2.jpg polaris-flyingboat.jpg 347_1.jpg
     
  11. Jan 15, 2013 #11

    cluttonfred

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    Understood, Himat, Thanks, Oriol, but I am not personally very interested in the delta trike designs, just not my thing. I am leaning toward a tractor-engined, parasol wing design much like the Dornier Libelle I or Shavrov Sh-2 pictured above, but lighter. The result would be not unlike the Progressive Aerodyne Searey (below) but with a plywood hull and tractor-mounted VW power.

    searey.jpg
     
  12. Feb 3, 2013 #12

    cluttonfred

    cluttonfred

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    I found another, even better clip of the Shavrov Sh-2!

    [video=youtube_share;5wUZem2pbVo]http://youtu.be/5wUZem2pbVo[/video]
     
  13. Feb 3, 2013 #13

    WurlyBird

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    I am by no means capable of designing something like this but there are several subjects that I am very interested in that could be quite useful in a project like this. I am fascinated with mold-less composite construction and it has been used in boat building for quite some time as well as aircraft. A wood skeleton is fabricated and then covered with foam sheets and laminated. The hull is then pulled off the skeleton plug and the inside is laminated. I have heard of this process used for power boats as well as sailboats so the construction technique would hold up to a good amount of abuse. And layers of carbon or kevlar can be built in for ruggedness. Depending on the time you want to put into it quite complex hulls can be made which would be able to handle waves, wakes, and other water hazards better then a hull such as the Osprey 2. If you wanted to wire cut sections of the hull there is no limit to the shapes you could incorporate. If you combined construction techniques, a composite hull with tube and fabric wings could pretty easily be built to fit into LSA. I think it would be much more difficult to make an all composite aircraft that could do that, but that is more of a hunch then factual.

    Personally, I like side by side seating because it is a lot more comfortable for new passengers to sit next to you and to be able to look you in the face, I also think the wider body is going to give you more desirable water handling characteristics. If I were to design one I would lean towards water wings over sponsons because I believe they would make docking much simpler and would produce less parasite drag, they could even be incorporated into the lift production to some extent (Stubby biplane?). I have flown in Lakes, Seareys, and Buccaneers and the Buccaneer was my favorite. I am a big fan of wind in the face and believe that any project I am involved with will be largely open, or have it as an option. When I had a glider I was building it a second canopy to fly with just a motorcycle type wind screen and have the rest open. L/D would have been shot but it would have been fun for flying with the hang glider guys.
     
  14. Feb 3, 2013 #14

    cluttonfred

    cluttonfred

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    Thanks, WurlyBird, my thoughts are not far off from yours though I would prefer the simplicity of a plywood hull covered in glass or polyester cloth much like the small boats I have built over the years. The image below illustrates how simple it can be once the patterns have been worked out, in fact, the shape of the Diablo hull in that example is not far off from the shape of the Shavrov. I agree that a composite of tube-and-fabric wings and empennage over a plywood hull is appealing and should be quite light. As for the wind in your face option, I definitely hear you, but as someone who did most of his boating growing up in New England I can say that it's also important to be able to get out of the wind when needed. The best of all possible worlds might be a parasol design but with a sliding canopy that could be opened in flight. Cheers, Matthew
     

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  15. Feb 3, 2013 #15

    ultralajt

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    Seaplane hull must take a lot of punch!
     
  16. Feb 3, 2013 #16

    TFF

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    The Curtiss CW-3 would be easy to duplicate. Outgrowth of the CW-1 which naturally looks like a seaplane. I know the guy that owns SN 1 CW-1, and many have made homebuilt versions. Aircam but 50 years ago.
     
  17. Feb 3, 2013 #17

    WurlyBird

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    As I mentioned I am not capable of designing it and have searched quite a bit trying to find more sources to learn how, but it seems it is even harder to find peoples secrets on boat building. I have seen construction photos and descriptions of foam core boat hulls being built for large racing catamarans. I am sure it can be designed to handle the force of landing. From what I have read you can build up a hull equally as strong as one pulled from a mold, but without needing the mold. I mention the technique because it is one I am currently intrigued by.

    I also agree that having an escape from the wind is an important option. The Searey definitely has the best layout with the sliding canopy option. Though for the time I spent in the Buccaneer 2 the windshield was sufficient. The Buccaneer has the Searey hands down if you take bang for the buck into account. 2-4 times the price for comparable performance. I'm not saying I wouldn't buy a Searey if it was "affordable" to me though.
     
  18. Feb 3, 2013 #18

    Autodidact

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    Skene's Elements of Yacht Design, and several others are available from Amazon and can be had for a reasonable price (used). Skene's has tables and simple algebraic equations to determine the forces on planing hulls and the structure needed. It should be applicable to flying boat design when you consider that some boats are built very light.
     
  19. Feb 4, 2013 #19

    cluttonfred

    cluttonfred

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    Thanks, all, for the feedback.

    TFF, yes, the Curtiss-Wright CW-3 Duckling/Teal would be an interesting approach to take, very much like the Avid Amphibian. I posted some pics of the Duckling in my list of possible inspirations here: https://www.homebuiltairplanes.com/...uilt-lsa-microlight-amphibian.html#post160314

    WurlyBird, I agree that the Searey is a nice plane, but pricey, so I am looking to create a plans-built or partial kit design that would be significantly cheaper. Making it work on a large VW conversion is a key part of that -- about half the price of factory Rotax 912, but more work.

    Thanks, Autodidact, I actually have a copy of Skene's on order.

    I have been concentrating mostly on tractor-engined designs for ease of installation, engine cooling, etc. even though there is definitely an argument for the pusher to get the prop safely out of the way when docking. The tractor engine also makes it easier to get a fairly low thrustline to avoid a lot of trim drag from the nose-down pitching of high-mounted prop.

    Probably the cleanest design option I have found is a shoulder-wing, cabin monoplane with a cowled, tractor engine on short struts like these historic examples, the Shavrov Sh-7 and the Fleetwings Seabird. At this size and weight, though, cabin access and line handling for docking become problematic--side doors must not extend too far down or risk letting in water and the prop means you can't use a sliding or swing-forward windscreen as a door. A large aft door and a walkway might work, or maybe well-sealed doors and a raised-floor, self-draining hull in the cabin area so a little water is not a worry? I am still sketching....

    shavrov-7.jpg

    5040123973_44b98b5565_z.jpg
     
    Last edited: Feb 4, 2013
  20. Feb 4, 2013 #20

    SVSUSteve

    SVSUSteve

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    David Thurston is still alive?
     

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