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Thread: Cedar strip airplane

  1. #71
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    Default Re: Cedar strip airplane

    Quote Originally Posted by Sandlapper View Post
    You are undoubtedly talking about small staples and relying on coating the wood strips with enough epoxy to stop water entry. A layer of glass and epoxy did not prevent the trimaran from taking on water. The larger staples that penetrated both layers of the wood mold could not be filled with normal epoxy coating. It is a different case with different materials but still....
    That sounds like poor application, rather than a fault with the technique.
    To not have enough epoxy on to fill staple holes would mean not having enough epoxy on to fill the weave of the cloth. Epoxy and glass is keeping the water out of countless boats all over the world every day for decades now - it is a system that is well tested and well proven.

    Me thinks there's some missing information here, or else we're talking about different things.

    I built both these using strips and encapsulating in epoxy/glass inside and out. I never had any trouble with water ingress and no trouble filling staple holes.

    2014-03-08 15.04.14.jpg

    IMG_2140.jpg

    Edit; You don't fill the holes with thickened epoxy, you saturate the surface with thin epoxy and the glass traps it in. Sounds to me like you didn't use glass on the outside, and you mention layers of wood, did you cold mold it - different technique to what is being discussed here (still should have the staple holes filled however).
    Last edited by gypsie; 08-18-2021 at 10:47 PM.
    It's all fun and games until Darth Vader comes.

  2. #72
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    Default Re: Cedar strip airplane

    Quote Originally Posted by rtfm View Post
    The Gougeon Bros book was a fascinating read - especially the section on how to ensure a completely clear glass covering. Thank you.

    Duncan
    Gougeon brothers are the gospel, undoubtedly.

    The Strip Built Kayak by Nick Shade is the reference is used for the kayak i built, very straight forward.
    https://www.guillemot-kayaks.com/cat...uilt-sea-kayak
    It's all fun and games until Darth Vader comes.

  3. #73
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    Default Re: Cedar strip airplane

    Duncan
    Those struts at 40x40 sound a bit hefty and would need fairings. Then they are cantilevered out of the fuselarge. Might it not be better to use triangulated struts of rectangular section (or round). The loads would be much lower and spread along the fuselarge.
    Last edited by Andrew2; 08-19-2021 at 10:19 AM.

  4. #74
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    Default Re: Cedar strip airplane

    You're right. 40x40 is a bit on the tubby side. 25x25 is available. Actually, I will fair the struts like this:
    Foam fairings for struts.jpg
    I can cut a zillion of these from a single 800mm x 600mm x 50mm block from the local hardware store. Slide them over the square tubing, epoxy and glass with 2oz cloth and voila!

    "Normal" Fleas have triangulated struts of 25mm round tubing, and a cable to provide triangulation. I'll be doing away with two of these three pieces (and reducing windage in the process), by firmly anchoring these struts to the bulkhead so that no triangulation is necessary. The loads would be borne by the bulkhead, which is why I need the bulkhead very firmly keyed into three longerons in addition to being bonded to the inner skin of the cedar strip layup.

    Duncan

  5. #75
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    Default Re: Cedar strip airplane

    We used to use wood wrapped in tape and dope Still think the cantilevered struts would be better as triangles, much lighter and spread the loads better. Tubes in tension/compression rather than bending loads. Is oval tube not available? or 16/20mm round of the right quality should do the job.

  6. #76
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    Default Re: Cedar strip airplane

    Quote Originally Posted by gypsie View Post
    That sounds like poor application, rather than a fault with the technique.
    To not have enough epoxy on to fill staple holes would mean not having enough epoxy on to fill the weave of the cloth. Epoxy and glass is keeping the water out of countless boats all over the world every day for decades now - it is a system that is well tested and well proven.

    Me thinks there's some missing information here, or else we're talking about different things.

    I built both these using strips and encapsulating in epoxy/glass inside and out. I never had any trouble with water ingress and no trouble filling staple holes.

    2014-03-08 15.04.14.jpg

    IMG_2140.jpg

    Edit; You don't fill the holes with thickened epoxy, you saturate the surface with thin epoxy and the glass traps it in. Sounds to me like you didn't use glass on the outside, and you mention layers of wood, did you cold mold it - different technique to what is being discussed here (still should have the staple holes filled however).
    You are missing the whole issue of liquids drawing away from sharp edges which has been discussed here many times. That drawing away from sharp edges means that the liquid, epoxy in this instance, prevents epoxy, paint or whatever from getting into and filling the hole or the edge. Having watches people try again and again to fill pin holes or cracks with paint or epoxy without success shows the validity of the argument.

    Sorry it is so difficult to make this simple point. Of course the sharpness and and extent as well as the surface energy of the two interfaces has great effect on the outcome.

    As for me and my experience, I have been dealing with epoxy and the many problems that were solved in cooperation with epoxy manufacturers/distributors for 50 years. Many problems that were common in the early days were reduced or eliminated so that current users don't run into them any more.

  7. #77
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    Default Re: Cedar strip airplane

    Quote Originally Posted by rtfm View Post
    You're right. 40x40 is a bit on the tubby side. 25x25 is available. Actually, I will fair the struts like this:
    Foam fairings for struts.jpg
    I can cut a zillion of these from a single 800mm x 600mm x 50mm block from the local hardware store. Slide them over the square tubing, epoxy and glass with 2oz cloth and voila!

    "Normal" Fleas have triangulated struts of 25mm round tubing, and a cable to provide triangulation. I'll be doing away with two of these three pieces (and reducing windage in the process), by firmly anchoring these struts to the bulkhead so that no triangulation is necessary. The loads would be borne by the bulkhead, which is why I need the bulkhead very firmly keyed into three longerons in addition to being bonded to the inner skin of the cedar strip layup.

    Duncan
    fwi, bunnings steel is cheap chinese stuff charged at a premium. Better to find a steel shop who stock Aussie steel

  8. #78
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    Default Re: Cedar strip airplane

    Thanks for the tip.

  9. #79
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    Default Re: Cedar strip airplane

    If you want the most secure longeron to skin and bulkhead to skin/longeron form a fillet with thickened epoxy, then laminate glass over the fillet overlapping the skin and longeron or bulkhead.
    On most boats this is overkill.

    Wherever you need to attach a strut to the bulkhead will be a different issue and you ought to show us your idea.

  10. #80
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    Default Re: Cedar strip airplane

    Excellent - thank you. And yes, I'll share my proposed strut attachment idea as soon as I work that out myself...

    Cheers,
    Duncan

  11. #81
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    Default Re: Cedar strip airplane

    Duncan. An old friend of mine has been restoring and building airplanes for decades using wood and fabric and more modern materials . I spoke to him this morning and he is happy to share his knowledge re glues etc with you.
    His name is Rick Morris (he is alsao a maker of very fine wines) I will send you his email in a PM

  12. #82
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    Default Re: Cedar strip airplane

    Excellent on all counts. Thank you.

  13. #83
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    Default Re: Cedar strip airplane

    rtfm - have you heard of a timber called Paulownia? http://paulowniatimber.com.au/index.php
    Grown in Australia, it has similar properties to Cedar. I'm not saying its right for this application - but cedar is more expensive than gold in Oz, could be worth looking into.

    I'm considering using it to make an SUP.
    It's all fun and games until Darth Vader comes.

  14. #84
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    Default Re: Cedar strip airplane

    Quote Originally Posted by gypsie View Post
    rtfm - have you heard of a timber called Paulownia? http://paulowniatimber.com.au/index.php
    Grown in Australia, it has similar properties to Cedar. I'm not saying its right for this application - but cedar is more expensive than gold in Oz, could be worth looking into.

    I'm considering using it to make an SUP.
    Hi. I took a look at paulownia - but it's not that attractive for a clear-coated fuselage. If I were painting the fuselage, I'd certainly want to save some money. But if that were the case, 10mm foam would be better.

    Duncan

  15. #85
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    Default Re: Cedar strip airplane

    Hi guys - me again,
    I'm still in the concept design stage, so no chance of a tangible plane for a while. The single seat design has evolved into a two-seat design with the occupants in a staggered seating position, so that they both have plenty of shoulder space, but the physical width of the fuselage is reduced to a minimum. But I'm thinking through the various stages, complexities and construction stages, and I'm a bit stuck.

    How would you build the aft section (coloured as wood)? I'm just not sure how to get the cedar strips to conform to the concave contours (with the break in the middle).

    Any ideas?
    AFB Stagger Tail Dragger.jpg

  16. #86
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    Default Re: Cedar strip airplane

    I've found that when heated, you can get a pretty good bend in 1/4" white cedar, but not of course, a sharp angle. I just wonder why you would want that crease in the fuselage for aerodynamic reasons. At any rate, if you force yourself into making that section in two parts you'll have to reinforce it, adding weight and complication to the build.

    I'd suggest taking some strips of the wood you intend to use, mill it to the width and thickness for the plane, and then heat it with an electric heat gun and find out just how much bend and twist it will take. You may well find that it will almost conform to that drawing, close enough that a small change will allow one-piece construction.
    -Dave

  17. #87
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    Default Re: Cedar strip airplane

    Quote Originally Posted by Woxbox View Post
    I've found that when heated, you can get a pretty good bend in 1/4" white cedar, but not of course, a sharp angle. I just wonder why you would want that crease in the fuselage for aerodynamic reasons. At any rate, if you force yourself into making that section in two parts you'll have to reinforce it, adding weight and complication to the build.

    I'd suggest taking some strips of the wood you intend to use, mill it to the width and thickness for the plane, and then heat it with an electric heat gun and find out just how much bend and twist it will take. You may well find that it will almost conform to that drawing, close enough that a small change will allow one-piece construction.

    Its true that heating wood will be effective in allowing it to be bent. The mechanism is the same as bending wet wood but to a different degree. Both depend on extracting water from the cell walls which allows the wood to accept a new permanent shape. It only works when the moisture content of the wood is below the saturation point. The result of trying to bend really dry wood will be a failure as it has no water remaining in the already collapsed cell walls.

    One great thing about bending "dry" wood is that it will take the new shape very quickly with very little rebound or lost time waiting for the new shape to set. Instrument makers have taken full advantage of this for centuries. Many third world boatbuilders fit huge timber planks to hull ribs by holding them in fire long enough to boil out water so they can be bent to the hull with human effort. Sometime looks like a blackened disaster but it will clean up.

  18. #88
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    Default Re: Cedar strip airplane

    Actually bending wood with heat has nothing to do with water.
    The heat softens the lignin - the natural stuff that holds wood fiber together.
    When it cools it returns to the same strength, but if it is bent while it cools, you get a permanent bend.

    If you bend too much, just re heat and bend it back. Repeat until you get a shape that fits the forms without pressure.

    I use an electric heat gun, on the 1500 degree F setting.
    That way it does not take too long, but you need to watch to see you don't scorch the wood. Won't actually matter if your sanding will take off the burnt look.
    If you are bending, heat both sides of the strip. Also if you are twisting the strip, which is what is generally the most useful situation.
    Its hard to fasten down a strip without edges sticking up if you don't twist the strips before fastening.

    After you do about 3 strips you will have the technique down. I actually enjoy bending/ twisting and fitting the strips this way.

    Per your #85. You can do the aft panel if you give the break a radius. Bigger the better. Wouldn't that be better for Aero also?
    Or you could put a physical break or kick there, if you have a former there. If you double the former along the edge, you can put one angle on one side, then one on the other, and just edge butt the strips. At this point you might want to use epoxy for that joint instead of wood glue, to get more strength. Of course, the actual strength comes from the outside and inside glass/ epoxy. You might want to do a test piece and destroy it to see if the joint gives up much earlier than a straight piece. If so, double up the glass over the joint for about 1" each side. Might affect your wood grain look. Actually it will, but maybe not too much.
    Actually the outside and inside glass will not lay down on a sharp joint anyway (without a vacumn bag). So you need some kind of radius. The inside radius can be made with a fillet of filled epoxy.

    Have fun.

    All the strips I have heat bend/ twisted are as dry as they possibly can be - no damage.
    Last edited by upchurchmr; 09-05-2021 at 01:28 PM.

  19. #89
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    Default Re: Cedar strip airplane

    Hi guys,
    Thank you for your suggestions. The sharp break in the roof section was a stylistic choice on my part, but the aero guys agree regarding the aerodynamics, and now with the complexity of actually building the @#$%^ thing this way, I've finally given in, and the aft section will now look something like this: Not as eye-catching as the original, but still pretty. And I can build it in one piece. Thank you.
    AFB Stagger Tail Dragger.jpg

  20. #90
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    Default Re: Cedar strip airplane

    Quote Originally Posted by rtfm View Post
    Hi guys,
    Thank you for your suggestions. The sharp break in the roof section was a stylistic choice on my part, but the aero guys agree regarding the aerodynamics, and now with the complexity of actually building the @#$%^ thing this way, I've finally given in, and the aft section will now look something like this: Not as eye-catching as the original, but still pretty. And I can build it in one piece. Thank you.
    AFB Stagger Tail Dragger.jpg
    BTW, I notice that the leading wing is now high. Is that a design change or just an artifact from an older sketch?
    -Dave

  21. #91
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    Default Re: Cedar strip airplane

    Hi,
    I did my sums, and found that the rear wing had great difficulty escaping the front wing turbulence. Almost all turbulence is above the wing, not below it. I didn't really have a choice, even though the front-low, rear-high configuration is (to my eyes) far prettier. Ah, well...

  22. #92
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    Default Re: Cedar strip airplane

    So, Mignet was right
    Your fin is now on the fuselage?
    A2

  23. #93
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    Default Re: Cedar strip airplane

    Seems like it. Of course, there have been a number of biplanes with wings the other way round, and they seem to fly just fine. But it's simpler aerodynamically this way. And yes, the fin is on the fuselage.

  24. #94
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    Default Re: Cedar strip airplane

    If it's all about the appearance - then why not build in whatever is structurally sound and relative simple (6mm foam core?) And overlay with whatever vinyl wrap suits your taste?
    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

  25. #95
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    Default Re: Cedar strip airplane

    It's not ALL about appearance - but aesthetics sells. And what could be more aesthetically hard-core than a cedar strip plane? But to be honest, the challenge is to use the cedar strip method to build a safe plane. As in all design projects, everything is a matter of compromise.

  26. #96
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    Default Re: Cedar strip airplane

    Quote Originally Posted by rtfm View Post
    It's not ALL about appearance - but aesthetics sells. And what could be more aesthetically hard-core than a cedar strip plane? ......
    How about cold moulded mahogany?

    tryane.jpg

    https://www.blipfoto.com/entry/3525433
    Last edited by P.I. Stazzer-Newt; 09-06-2021 at 08:28 AM.
    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

  27. #97
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    Default Re: Cedar strip airplane

    Like the above, I am beginning to think, that rather than experiment with new and exciting (possibly too 'exciting') methods of construction, why not just build it in the known composite methods and epoxy a 1mm strip veneer layer on the top? One gets the effect, but not the possible grief of trying a new construction method?

    A2

  28. #98
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    Default Re: Cedar strip airplane

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    How about cold moulded mahogany?

    tryane.jpg

    https://www.blipfoto.com/entry/3525433
    Marcos Cars, of marine plywood chassis fame, built a single seat commuter trike a bit like the above. 250cc twin bike engine and it could be stacked on it's flat back end to save space. Not sure if it got beyond the prototype stage, but remember a photo of it.
    Last edited by Andrew2; 09-06-2021 at 12:07 PM.

  29. #99
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    Default Re: Cedar strip airplane

    That's beautiful. I know nothing about cold molded construction. Sounds difficult, compared to cedar strips. But I'll check it out.

  30. #100
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    Default Re: Cedar strip airplane

    Hi,
    "Known composite methods"? That is equally foreign to me. Besides, I like working with wood. From watching numerous videos online, cedar strip planking seems pretty straightforward...

  31. #101
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    Default Re: Cedar strip airplane

    My usual suggestion is for you to make a simple boat or kayak in order to understand strip planking. Or Canoe.
    Or one of those boat like bassinet's if there is someone expecting a baby.
    Too bad you are so far away or I'd provide a tool to make 4' of the nose of a kayak.
    Such a thing only takes 5 frames for the tool, and 2 each 2"x4" boards plus glue (wood glue).
    A little fiberglass and some epoxy if you want to do the entire process.

    You can treat it like a mounted deer head and hang it on the wall in your garage for a conversation starter.

    Cold moulded construction requires a more solid and substantial tool to make the skin on.

  32. #102
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    Default Re: Cedar strip airplane

    The other aspect, which you don't want me to say, is that at the end of the process what you have is a Flying Flea.

    I really don't want to be unkind, but building any airplane is a lot of work. I've flown this airplane, which is made of wood. A Piel Diamante. Very efficient practical airplane. Fast. Good load-hauler. No problem in a gusty crosswind. Excellent in grass strips. And the canopy shell is strip-built and varnished.

    piel diamante.jpg

    Dave

  33. #103
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    Default Re: Cedar strip airplane

    Quote Originally Posted by Dave Hadfield View Post
    The other aspect, which you don't want me to say, is that at the end of the process what you have is a Flying Flea.
    You say this as though it were a bad thing... ? There are many reasons why Fleas are (in my opinion) superior to "regular" planes.

    However, today's pilots have ALL qualified on 3-axis planes, so to insist that we have to stick to 2-axis only is absurd. In fact, it is a barrier to getting today's pilots flying a Flea. The Skyflow doesn't have ailerons - but instead, the entire rear wing pivots differentially ever so slightly providing full aileron functionality.

    I was at an airshow some time back, and dozens of planes were lined up with spectators walking by admiring them. In the middle of the line was a very well turned out HM293, and the comments ranged from "cute", "weird" to outright laughter. If we (rather, "I") want to compete with the sleek glass designs on the market currently at exorbitant prices upwards of $100k, we need something equally as sleek at at fraction of the cost. My Skyflow kit will market for somewhere between $12k and $15k complete (minus engine and instruments, of course). Now that, to my mind, is an attractive proposition.

    I really don't want to be unkind, but building any airplane is a lot of work.

    Dave
    It doesn't have to be. With CNC cutting of parts for example, my current airplane took three days to complete the fuselage from scratch. The wing halves can be built in a single day. Another day to apply the shear webs, and a third day to bond the skins. Let's call it a week, with some down-time. And that's working on my own.

    The days of taking years to build a plane are gone.

  34. #104
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    Default Re: Cedar strip airplane

    I've built some wood strip kayaks and a couple of small boats with the same technique. I use spruce strips since that's the best local wood for the purpose in Scandinavia. The advice from the kayak designer (Björn Thomasson) is to seal the wood after sanding with a quickly applied layer of epoxy before glassing. The purpose is to minimise the amount of epoxy that's soaked into the wood since it only increases weight. Sand the epoxied wood lightly after it has cured before applying glass and the epoxy.
    Wood is regarded as an "active core" since it contributes to the strength. In the direction of the wood fibres the wood provides most of the strength. In the direction across the fibres the glass provides the strength. Epoxy provides very little strength and should be minimised. Wood strips are ideal for a long and narrow object like a kayak, where the dominating forces are length ways.
    I've considered using Paulownia but cannot make it grow in our climate. The idea was to make a kayak where I started by planting the seed...
    /Erik

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