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Thread: Cedar strip airplane

  1. #1
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    Default Cedar strip airplane

    I've decided to build a light airplane using the cedar strip method. I have watched a huge number of Youtube videos of people building strip canoes, and it all looks reasonably straightforward. However, all the online builders are working from plans, and don't have to make any design decisions.


    My first design decision is "is it OK to lay a keel first, along both the bottom and the top?" The front of the plane has to accommodate a 225mm diameter ring (to allow air into the engine compartment, and to provide for the prop shaft). I don't actually know how to incorporate this into the keel, or if this keel needs only to be a single strip of 19mm x 6mm wood - i.e. for decoration sake only. If for decoration, then how do I bond the "ring" to this?

    This is what I've come up with so far...

    I'll build the fuselage in three sections. The green section is a fairly straightforward "canoe". The yellow section is a single piece cowl/engine covering. And the orange section (as you can see) comprises the roof and the turtledeck

    Do I run a keel along the entire length of the green section? And the yellow? Or do I do this for all three sections? It would certainly look great with a strip of dark wood.

    Are there any canoe builders on this forum who might be able to help with this?
    Side view of the three sections.jpg

  2. #2
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    Default Re: Cedar strip airplane

    Welcome to the Forum.
    I've built a few cedar strip boats but I can't comment on this since it's not a boat but an airplane that will be subjected to very different forces then a boat. Knowing nothing of these forces renders me mute.
    I was born on a wooden boat that I built myself.

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    Default Re: Cedar strip airplane

    Hi,
    I'm not concerned with the strength of the fuselage (it'll be plenty strong enough), but more interested in building technique - specifically as it pertains to the keel. For example, is it a good idea to run the keel the length of the "canoe" and build the strips up to this? And I'm assuming I'd need double (or triple) layers of the strips at the nose and the tail for the strips to bond to?

    Duncan
    Last edited by rtfm; 08-12-2021 at 08:43 PM.

  4. #4
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    Default Re: Cedar strip airplane

    Another question:
    What is the preferred glue? I've seen guys use polyurethane, epoxy and ordinary Titebond. Epoxy is the strongest, but I think that might be overkill. The strips will be covered inside and out with glassfibre. Polyurethane is moisture curing, so no mixing required. That's a plus when working alone.

    Duncan

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    Default Re: Cedar strip airplane

    And one final question (for now):
    Staples or nails or clamps?

    Duncan

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    Default Re: Cedar strip airplane

    You need complete access to the engine, top and bottom. Thus, easily removable cowls.
    And you need hard-points on the firewall for the engine mounts. There is a LOT of torque during turns and turbulence. Also hard-points for the gear, and attachments for the wings and tail feathers.
    Apart from that, sure, lots of wooden airplanes are flying. Veneer-layered aircraft go back to WWI. I fly a Fox Moth, which has a fuselage that is just a plywood box. Emeraudes and Diamants come to mind.
    In general aluminium is lighter and less work, but doesn't do compound curves very well; so it's your project, fill your boots.
    Early Canadian flying boats had strip-planked hulls.
    I'd strongly suggest you join whatever experimental aircraft society exists where you live. There will be a huge compendium of knowledge which, if you are polite, will be very willingly shared.

  7. #7
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    Default Re: Cedar strip airplane

    Hi,
    Thank you for your observations - all valid, of course.
    However, I should have provided some Bio - I am very familiar with aircraft design and construction, and am a long-standing member of groups like HBA. My current project is a CNC-cut plywood single seater.

    My questions however relate specifically to the construction techniques of cedar strip planking, which I have not done before. If you notice my questions above, they have to do with the practicalities of actually how to construct strip planking.

    Thanks,
    Duncan

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    Default Re: Cedar strip airplane

    Bearing in mind the above posts, I don't think you need a 'keel', what purpose would it serve? Any hard points, for u/carriage etc would pick up on bulkheads. Likely you will need more moulds to keep the strips faired, other than the bulkheads that will be part of the finished structure.
    Fastenings: Better to arrange a clamping method and avoid pins etc. They are really only to hold the strips in place until the adhesive goes off. If you only apply a couple of strips at a time then lots of little clamps would do.
    Bit curious as to the design? Are the 'tail feathers' on a seperate boom, or?

    Like DH above, I have only been around ply on longeron builds, Jodels, Emeraude and DH Rapides. Did build a Volksplane many years ago and helped with a Taylor Monoplane.

    Edit:
    Bear in mind that PU adhesives need a bit of clamping pressure, whilst epoxy does not.
    And, thinking again.... Maybe your keel idea could just a central slightly wider strip, fitted first, that the others are faired into as they taper at the ends.
    Last edited by Andrew2; 08-13-2021 at 01:42 AM.

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    Default Re: Cedar strip airplane

    Hi,
    I was thinking more of the aesthetics than anything else. A nice dark strip running right down the spine would look grand.

    Yes, all hard points would be anchored to permanent bulkheads. And thanks for the advice re: clamps.

    The design... This is a Flying Flea, so it has two wings. The fin/rudders (two of them) are mounted on the rear wing.

    Duncan

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    Default Re: Cedar strip airplane


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    Default Re: Cedar strip airplane

    I'm very familiar with the rest, it is only the fuselage using WRC planking which is causing me some hesitancy. I have a supplier of WRC ready milled here in Brisbane, they suggest Polyurethane atmosphere-curing resin. I have software which has worked out the exact dimensions of the formers (14 in all) and a CNC router to cut all the pieces. I'm ready to go as soon as I get my courage up...
    Attached Images Attached Images

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    Default Re: Cedar strip airplane

    Ah, that explains things.
    Actually, I ran ito Mignet's grandson, who lives quite close. Didn't realise that he had built derivatives of the 'Flea' until about 20yrs ago. Even sold a few to the Military. He showed me around the old wine place that he had used as a factory.
    What engine are you planning to use?
    A2

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    Default Re: Cedar strip airplane

    I don't want to usurp this boat-oriented forum with airplane things, but quickly:

    A Generac big block (990cc) prepared by Valley Engineering in the States. They also supplied the wooden prop. All up (engine, starter, exhaust, oil in crank - in other words, a running engine) 53kg, and they *claim* it produces 50hp - time will tell.

    So - my plan of attack for the fuselage is as follows:
    (1) 19mm x 6mm WRC, already milled and ready to go. I have no REAL idea of how much I'll need, so I'm planning to buy planks in $100 lots, and see how far I get.
    (2) Source some really dark wood for the backbone (aesthetic) strip.
    (3) Polyurethane resin - supplied by Boatcraft Pacific here in Brisbane (who also supply the WRC planks). They make the stuff and call it "Purbond" https://boatcraft.com.au/Shop/index....bd793ab9246d73
    (4) Add lots of cutouts in the formers to allow space for clamps.
    (5) Double-up on the front and rear sections of the "keel" strip to provide sufficient "meat" for the strips to bond to, and to bond the nose "ring"
    (5) Glass outside and inside. How many layers?
    (6) Build the "canoe" section first
    (7) Then tackle the cowl section (removable)
    (8) Finally, tackle the turtledeck section (hardest of the lot). This will be bonded permanently to the "canoe" for rigidity reasons

    Issues still to be resolved:
    (1) Identifying the cutouts for the main gear and wing struts

    Have I missed anything?

    Duncan

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    Default Re: Cedar strip airplane

    Before you start stripping with PU, I recommend you make a test. PU glues foam, and unless you use beveled strips and clamp really hard from the top, I predict you won't like the outcome. Altough epoxy is more tedious to use, it's far safer when it comes to such thin strips.

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    Default Re: Cedar strip airplane

    Hi.
    That's good advice from someone who's been there. Thank you. I'm well acquainted with epoxy, so that's not a big deal.

    Duncan

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    Default Re: Cedar strip airplane

    Purebond sounds like Gorilla glue that is common in the USA. They say its is extremely inexpensive but $72/Liter does not look cheap to me. Anyway, I don't allow polyurethane glue in my wood shop. Much hyped and oversold stuff that only sounds good. Plain Titebond is perfectly adequate for gluing strips and easier to use that most anything else. For a strip layup with glass on both sides, you could use flour paste like we made in the kitchen as a kid or anything that gets hard and the structure will be plenty strong. Since cedar is not very strong, why use a glue that is way stronger on a face joint? Mainly you don't want the interior to get wet.

    OK, I am getting crotchety as an old man but it gets tiresome dealing with stuff designed by a marketing department.

    Good luck with your wooden airplane concept. Wood is an extremely effective material to build an airplane with as proven by the large number of old string and cloth planes still able to perform great alongside the modern graphite wonders. Not knocking the new designs but sometimes it gets to overkill, especially in costs. As a past (part) builder of a low tech plane made with common stuff found in the farmer's barn as well as graphite, they can both do what they are supposed to do.

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    Default Re: Cedar strip airplane

    I am curious, why wood strip? In aircraft weight is critical, wouldn't foam strips serve the same purpose (the core between your glass faces) and be much lighter?

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    Default Re: Cedar strip airplane

    Quote Originally Posted by rtfm View Post
    I don't want to usurp this boat-oriented forum with airplane things, but quickly:

    A Generac big block (990cc) prepared by Valley Engineering in the States. They also supplied the wooden prop. All up (engine, starter, exhaust, oil in crank - in other words, a running engine) 53kg, and they *claim* it produces 50hp - time will tell.

    So - my plan of attack for the fuselage is as follows:
    (1) 19mm x 6mm WRC, already milled and ready to go. I have no REAL idea of how much I'll need, so I'm planning to buy planks in $100 lots, and see how far I get.
    (2) Source some really dark wood for the backbone (aesthetic) strip.
    (3) Polyurethane resin - supplied by Boatcraft Pacific here in Brisbane (who also supply the WRC planks). They make the stuff and call it "Purbond" https://boatcraft.com.au/Shop/index....bd793ab9246d73
    (4) Add lots of cutouts in the formers to allow space for clamps.
    (5) Double-up on the front and rear sections of the "keel" strip to provide sufficient "meat" for the strips to bond to, and to bond the nose "ring"
    (5) Glass outside and inside. How many layers?
    (6) Build the "canoe" section first
    (7) Then tackle the cowl section (removable)
    (8) Finally, tackle the turtledeck section (hardest of the lot). This will be bonded permanently to the "canoe" for rigidity reasons

    Issues still to be resolved:
    (1) Identifying the cutouts for the main gear and wing struts

    Have I missed anything?

    Duncan
    Duncan, slight issues with some of your questions.. In your first post, you talk about not having plans to work from. Not exactly how one usually goes about building a/craft.. ? The supplimentary question 'identifying the cut outs' might be just your phraseology, but does sound like you are working it out as you go along. Again, not, ermm, mainstream? The struts and gear need very precise mountings onto hard points, usually with metal brackets. (you know this..)
    I could be taking this completley the wrong way, but Q 5 is a bit suck it and see, rather than considered design. Or, are we talking about the computor process?
    Last one: The rear wing seems to rely on the struts, or does it have a centre mount to the fuselage? Huge torsion loads, if as in the drawing.

    To add, on glue joints: Each time we did a mix for a certified aircraft repair, it involved some bits of the same wood and was distructively tested to check. Basicly a joint was left to cure, then one part was held in the vice and the other whacked with a hammer to make sure the wood failed, not the glue.
    Back then we used Aerolite, then Aerodux. Epoxy is streets ahead on almost all fronts.
    On the keel again.. I would stain the WRC strips rather than introduce another wood, just for aethestics. WRC is not a terrible strong wood, but is good for a core, so consider that when covering with the cloth and epoxy. The skin is important.
    Last edited by Andrew2; 08-13-2021 at 12:49 PM.

  19. #19
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    Default Re: Cedar strip airplane

    When planking boats with such thin (1/4) strips, the resultant panel of strips is generally sheathed on both sides with a structural skin of fiberglass or carbon.
    If designing an airplane for such construction, Id think that the scantlings of a strip composite part would be derived from the loads of the airplane and a knowledge of the mechanical properties of such composites.
    Dave Gerrys boat strength book is a good start for designing a boat, but Id think you need to do some serious engineering, like with numbers, first.

  20. #20
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    Default Re: Cedar strip airplane

    Speaking as a structural designer for military aerospace, I'd be scared to death of watching this thing take it's first flight.
    You haven't talked about how to get the loads from the front wing to the pod, and then the reaction loads from the rear "wing" via attachments to the pod.
    As far as you have shown, there is no attachment. These attachments are critical to your continued life.

    Can you show the wing connection?

    Somehow that strip planked shell has to transmit loads to the wings.

    So many people have died in "aircraft" made to some unusual construction, that there is a huge number of requirements.

    Maybe you have that all figured out and just haven't brought it up, since we all "only" work on boats.

    The very first thing you need to do is make samples of strip planked skins with the different materials you think you could use and break them to see which is strongest.
    Second it to compare your tests to strength requirements at different places in the pod.
    Third is to build something strip planked. So you have some idea of the actual techniques required to get the curvature on that thing.
    Fourth is to estimate the weight of the pod with all reinforcement so you can tell if you increased the weight of the aircraft beyond reasonable limits.

    If you want a clear finish strip planked pod, than you can change the wood anywhere you want to get the color design you want. It doesn't matter since the strength is in the glass. Unless you have a high load introduction point, or fasteners passing thru.
    Also using another species of wood to get a dark color will usually increase weight.
    You can get dark or light cedar by carefully purchasing each individual cedar board.

    I strongly suggest you paint this thing. You won't believe how much easier and quicker it is to build for paint.

    If you won't do any of that, please, please do a final sandbag load test when the plane is finished.

    Now you can tell me I'm silly, you understand all that, and you are going to do what you want anyway.

    I don't really think the basic idea is bad. I talked extensively with a coworker about the same idea. He died in a crash before it really went anywhere.

    To answer your questions.
    Staples or nails to position strips for gluing. The weight of a clamp can twist a strip out of position, unless you have very unusual clamps - lots of them.
    No way to tell if you need multiple layers of strips until you show us the joint you are making. Joining a skin to a interior bulkhead is usually done with a fillet of reinforced epoxy, with a outside lamination of glass if it needs really high strength.
    You don't need a "keel" unless there is a specific high load you need to accomidate. You can answer your own question if you know what is needed. Lamination of multiple layers of wood will do just fine for gaining additional strength. However it may be difficult to do in a typical internal tool design. How are you going to hold the shape formers (bulkheads) so that they are aligned? The ones that will be removed. Typically they should be about 1' apart to get a smooth exterior, without a lot of fairing compound.
    The "ring" should be built first, installed in the tool which shapes the pod. The ring would have to be faired to the shape of the skin, before stripping starts. The ring should have a separator sheet placed on it before it is used to provide the required shape for the strips. Once the strips are complete and the glue dried, the interior tool and the ring would be removed.
    Then the interior glass would be applied. So you need to know the glass cured thickness, so you can place the required separator, leaving room for bonding in the ring.

    Sorry if I'm being patronizing, but I am concerned.
    Last edited by upchurchmr; 08-13-2021 at 05:17 PM.

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    Default Re: Cedar strip airplane

    Hi Andrew,
    Taken at face value with no back story, some of my statements/questions may seem a bit Heath Robinson. So, the back story:

    Correct - no plans - at the start. I have had to draw my own. Most of the design was fairly straightforward, being based on my earlier designs and on well established aircraft design principles and examples. I mentioned not having plans to begin with as an example of the obstacles I've had to overcome. But I now have a full set of plans which cover the formers for the fuselage, the necessary bulkheads, the landing gear, wings and wing attachments.

    As for "cut-outs" I was referring to this:

    Formers.png

    As for the struts, I am re-using the struts from my earlier design (the Fleabike) which itself is basically copied from the HM293 - hundreds of which are flying. The main gear also is a direct copy from Grunberg's modification of the HM293 design. No issues there.

    Q5: I plan to bond three strips of WRC from former 3: I was asking if this was a good idea. This has nothing to do with the aircraft design, but of the strip plank construction technique, of which I am not an expert.
    Side view with formers.jpg
    The second Q5 (sorry for the typo) is still an open question. I came across a guy who built a kayak out of balsa, and covered it with tissue-paper thin glass fiber and had many years of good service from it. I thought this a bit extreme. My plan was to cover my fuselage inside and out with one layer of 225g fibreglass and one layer of 85g. My question was to elicit members experience.

    Wing struts: All Flying Fleas have a pivoting front wing which is attached to the fuselage via two 25mm steel tubes fastened to hard points on the fuselage at about the 23% chord point on the wing, and an additional brace (normall a cable) further outboard also on the 23% chord. This triangulates the wing attachment. This is my intention for the rear wing. The front wing pivots on a bushing at the fuselage, and has two struts outboard. Pretty standard Flea configuration.

    Staining a decorative strip of WRC is a great idea. Thank you.

    I hope this clears up some of my omissions.

    Duncan
    Last edited by rtfm; 08-13-2021 at 05:28 PM.

  22. #22
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    Default Re: Cedar strip airplane

    Wow, there are about 1000 versions of the Flying Flea.

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    Default Re: Cedar strip airplane

    Quote Originally Posted by narfiwillem View Post
    I am curious, why wood strip? In aircraft weight is critical, wouldn't foam strips serve the same purpose (the core between your glass faces) and be much lighter?
    Hi,
    Wood because it is beautiful. Foam is very plain, and the plane would have to be painted. There are a zillion painted planes.

    Duncan

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    Default Re: Cedar strip airplane

    Quote Originally Posted by rtfm View Post
    Hi,
    Wood because it is beautiful. Foam is very plain, and the plane would have to be painted. There are a zillion painted planes.

    Duncan
    Fair enough
    Beauty is reason enough, harder to cover your sins though :P
    You will also want to make sure you have a plan for UV protection.

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    Default Re: Cedar strip airplane

    Quote Originally Posted by upchurchmr View Post
    Wow, there are about 1000 versions of the Flying Flea.
    Hi,
    Not really that many. Most builders opt for a variation of the original HM14, or go with the more modern HM293 or HM380. There are some others which do not copy the original "Mignet formula" like the Pulga in South America, but not many.

    My "Skyflow" is a radical re-design of a very tried and true configuration. In fact, having said that, the only REAL change is the shape of the fuselage. Remove the fuselage, and paste in the fuselage of the HM293 (for example) and we're back where we started - with some minor changes.

    I believe that if we want to enthuse a new generation of pilots to get into a Flea and experience its unique flying qualities, the plane they get into my look the part. Hence the Skyflow.

    Duncan

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    Default Re: Cedar strip airplane

    Quote Originally Posted by Rumars View Post
    Before you start stripping with PU, I recommend you make a test. PU glues foam, and unless you use beveled strips and clamp really hard from the top, I predict you won't like the outcome. Altough epoxy is more tedious to use, it's far safer when it comes to such thin strips.
    OK, PU is out. Thanks.

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    Default Re: Cedar strip airplane

    You can try PU, maybe you can get along with it, I would not use it for a clear finished hull, but that's just my opinion.

    The sandwich engineering is the same for foam and wood core, wood is just a heavier spacer for the load bearing skins. If you want you can use paulownia (kiri) and stain it, it's lighter then cedar. You can even stain balsa if you want, and that's as low on weight as wood goes.
    If you don't know how to calculate the required sandwich for the fuselage and don't want to hire it out, use a Al spaceframe and treat it as a fairing, then you can get away with 3mm balsa and 85gr/sqm fiberglass.

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    Default Re: Cedar strip airplane

    When planking boats with such thin (1/4) strips, the resultant panel of strips is generally sheathed on both sides with a structural skin of fiberglass or carbon.
    If designing an airplane for such construction, Id think that the scantlings of a strip composite part would be derived from the loads of the airplane and a knowledge of the mechanical properties of such composites.
    Dave Gerrs boat strength book is a good start for designing a boat, but Id think you need to do some serious engineering, like with numbers, first.

  29. #29
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    Default Re: Cedar strip airplane

    Cold molded, no glass, keep it light and stiff
    Always impressed with these, seems advanced for 1912 ish...

    5CF08EEB-A00F-4770-B776-E89AFA692AE2.jpg

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    Default Re: Cedar strip airplane

    Lots of questions answered now. Another: A glance at the net shows all PdeCs with a high front wing and a low, smaller rear wing. You have put the front wing lower and the rear high. Apart from the visibility forward being a bit compromised, how are the aerodynamics altered? The original Flea had problems between the wings, resulting in nose overs in certain attitudes. The Royal Aeronautical Soc did a re-run of the plans and sorted it.
    Lots of canards about, Rutan et al, But their front wings are much smaller than the rear.

    About being concerned with putting a/craft stuff in this section, you could ask for the thread to be moved to the Bilge and keep us updated as you progress.

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    Default Re: Cedar strip airplane

    Hi rtfm

    Am I correct in assuming the wood is non structural and just acts as a fairing with a frame that takes the stresses?

    There is a guy in NSW by the name of Allan Newhouse who builds very nice strip plank kayaks, he posts on woodworkforums as anewhouse https://www.woodworkforums.com/searc...rchid=36748364

    He was very approachable when I met him at the Hobart wooden boat festival and I think he would be an excellent person to contact for Australian advice.

  32. #32
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    Default Re: Cedar strip airplane

    If the cedar strips are only a "core" material, you could save a lot of weight by going to balsa. End grain balsa is the traditional wood core material. (Think of the DeHavilland Mosquito bomber. Wood inner and outer skins with an end-grain balsa core.) If you are relying on the strips for structure beyond core properties, I would think you would need some strips off the longitudinal axis. I built and fly an (aluminum) plan and am building a cold molded sailboat (cedar strips with +/- 45 degree cedar veneers). I've always wanted to build a wood plane, but have not found a design just right for me. Good luck.

    Dean

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    Default Re: Cedar strip airplane

    Quote Originally Posted by DeanP View Post
    I've always wanted to build a wood plane, but have not found a design just right for me.
    Two good places to start looking at plans/kits for wooden aircraft.

    https://fisherflying.com/
    https://www.teammini-max.com/

    I especially like the Fisher Dakota Hawk, but ultimately ended up starting an aluminum build with my son.

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    Default Re: Cedar strip airplane

    Quote Originally Posted by Andrew2 View Post
    Lots of questions answered now. Another: A glance at the net shows all PdeCs with a high front wing and a low, smaller rear wing. You have put the front wing lower and the rear high. Apart from the visibility forward being a bit compromised, how are the aerodynamics altered? The original Flea had problems between the wings, resulting in nose overs in certain attitudes. The Royal Aeronautical Soc did a re-run of the plans and sorted it.
    Lots of canards about, Rutan et al, But their front wings are much smaller than the rear.

    About being concerned with putting a/craft stuff in this section, you could ask for the thread to be moved to the Bilge and keep us updated as you progress.
    The Bilge section? If that's a place for anything not specifically wooden boat oriented, then yes, I'll ask. And very happy to keep you updated.

    You're correct: the basic "Mignet formula" is a larger front wing, higher than the rear. This is actually the worst possible configuration aerodynamically - but very easy to build. The front pivoting wing is held in place with simple struts, and the rear wing is fixed to the aft fuselage. Couldn't be simpler. However, the front wing dumps all its downflow directly onto the rear wing. Mignet was mistaken in thinking that this would form a "slot" which energised the rear wing. He was wrong. If one reverses the vertical orientation of the wings, the rear wing flies in completely clean air. A far superior configuration.

    There's not a HUGE deal of difference between tandem wing aircraft, Fleas and Canards. Each has its own design peculiarities, but all three variants have to contend with the same downwash of the front wing. My configuration (unless I am vastly mistaken) is superior. We'll see...

    Regards,
    Duncan

  35. #35
    Join Date
    Aug 2021
    Location
    Brisbane, Australia
    Posts
    43

    Default Re: Cedar strip airplane

    Quote Originally Posted by Andrew2 View Post
    Lots of questions answered now.
    That's a beautiful cold molded plane, BTW.
    Last edited by rtfm; 08-15-2021 at 06:58 AM.

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