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Free-flight 1935 Udet Flamingo, electrified for RC, built 200%...

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    #46
    Now that I have the rudder servo in place, I can do some tests to see how it will work. Just as well, as the tests are not at all conclusive; quite the opposite...



    I was afraid of too much rudder movement; in reality it's not going to be enough. After sorting out the minor niggles, such as getting the domino to pivot without binding, getting a fresh set of NiMh for testing, and fixing the empennage in position with masking tape (which sticks very well to itself, I find... ), I finally got the servo to react to my little servo tester. Carefully engaging the carbon rod to connect the rudder and... A couple of millimetres of 'throw', but much more than that in fin wobble..! The base was held down firmly enough, but the leverage from the carbon rod overcomes the fin's rigidity and the tip moves more than the rudder..! A full piano hinge would do the job, maybe, but I didn't want to start building a piano into this 'plane..! Wire guy rigging would do, too, but seems a bit extreme. I've moved the servo right to the very rear, to see if I can get more throw, but even there it's minimal, even if I hold the fin steady (one really needs four arms to hold it all together..!).
    A re-think is in order, then. I was looking for a simple method, but the geometry seems not to be suitable. I'll get the sketch pad out and draw up a 'pull-pull' rig, to see how I could fit that in. My intention was to avoid, if at all possible (or rather: reasonable...) having control runs through the flanks. Quite apart from the aesthetics, it's always a complication, trying to get cables or rods as straight as is needed, and lined up with openings. Thinking cap on, then...

    (Of course, I could always claim the last word, and declare the 'plane to be 'Free-Flight', after all..! It's my stubborn streak holding me back from such extremes... )

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      #47
      Slow progress, but progress just the same. Once again, small, but critical, steps, which I dread until they're done and on to the next one. This time, it's deciding where to attach the lower wings to the fuselage. I managed to report the plan position onto the frame, and have glued 'spare ribs' in that position, but on the inside...



      These will serve as departure for the wing fixing system (yet to be established, but it's getting closer...). I'll probably be putting a pair of cross beams in there, as if extensions to the spars, with ply doublers as dihedral braces. I've made the braces, but needed to have the positioning sorted first, and that's now done.
      Speaking of which, it's also time for the dihedral braces for the upper half-wings, before joining them. I chose to not cut completely through the ribs for passing the braces, but to only cut halfway. I've slotted the braces with the matching cut, so that they assemble in ''egg-crate' fashion (I think that's the term..?). Here's the elements for the left half-wing all prepared...



      The three bays on the right are the flat central part, all to the left is the slightly swept-back (remember the 'dog's leg'..?) dihedral part of the wing. The brace to the fore is lying flat, the other is half-engaged in its ribs. Here's the dry fitting before gluing (never too prudent, and even then there are often surprises..!)...



      Then come the crucial moment, when all the preparation has to be complete (or not..!), and all the surfaces are glued up , fitted together and clamped. Yes, it's a porcupine; one can never have too many clamps...



      The angle had been set previously when gluing up the root ribs of the dihedral part, and the clamping-up was done using the same height reference at the tip, and corresponded very well to that of the braces. In making the slots, I hope I've learned enough to make the second half-wing a little bit neater. I tried all sorts of combinations of cutter, saws, Dremel cutting wheel and various blades. It would, in hindsight, have been much simpler had I laid all of this out before assembling the wing, when the ribs were still flat, but that, too, is part of the apprenticeship. I'm pleased so far with the result, assuming that, when I remove the clamps, it doesn't all just spring apart..!
      Meanwhile, further thoughts on the servo front... I've had a close look, and done quite a few diagrams and full-scale drawings, and will abandon the idea of 'pull-pull' for the rudder. It's just too risky, as I have no real idea of the throw needed, the length of horn or servo arm, the cable lengths nor how they can pass through the skin of the 'plane. I'll apply some 'Occam's Razor' thinking and go for the simplest, most evident way as being (possibly...) the best. The servos are really tiny; I think I can lodge one inside the tailfin itself, with the arm through the side, activating a pushrod to the adjacent rudder. As usual, I'll do a bit more dummy mock-ups to confirm, but what I've tried so far seems to be about the best system (or least worst..?). Pictures will better illustrate; I'll see about that when I've glued the other wing. I'll probably do a bit of doping tomorrow, too, as the forecast is somewhat optimistically positive. Back soon...

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        #48
        Great idea for the rudder movement. Simple and elegant.

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          #49
          Quite a good day today; some tangible progress, with promise for more to come. The dihedrals for the upper wing are looking good, now that they're released from their clamps, so I turn my attention to the lower wings. After much cogitation, and some discussion with Our Eldest, a plan of action unfolds as to how to attach them. I'd glued a pair of 'spare ribs' inside the fuselage where the wings should go, according to the plans. These ribs, as all the others, were made in batches, bolted together in a stack. There were three stacks; the bolts were put through randomly, but by chance and coincidence, the foremost holes line up. The idea is to make these holes big enough to allow a 5mm dowel to pass through from side to side. This aligns nicely, again, by good fortune, with the innermost ribs of the lower wings. A dowel long enough to go through these inner ribs will serve both as fixation for the wings, and also as a dihedral brace. The rear holes in the ribs does not line up so well, so a third series of holes has been created, again aligned so as to respect the dihedral. The 'spare ribs' are inboard, and so cannot be used for gluing the wing root ribs; a 4mm insert is fitted to the frame adjacent to the ribs to provide a surface for gluing.
          Here's a picture of the result so far (only a dry fit, of course; the wings will not be fitted until covered...)...



          The lower wings are 'skewered' to the fuselage; the upper wings are to the rear, awaiting patiently the installation of the cabane. The tailplane and fin are merely to give some idea of the total volume of the 'plane.
          Here's a close-up of the dowels, hoping that the explanation above is thus made a bit more clear...



          I shall most likely reinforce the inner ribs with light ply, as the balsa alone will probably not wear well over time. Still I'm very pleased with the result, although it was quite a combat easing the dowels through the tight holes (I call it 'swizzling'; the rods have to be turned to reduce binding, whilst at the same time coaxing them further and further. It's the same combat to remove 'em, too..!).
          That's enough for today, I think. I've been lucky enough to have not broken anything, despite my clumsy movements, so I'll make another cuppa and think about what to do tomorrow.
          To be continued...

          Comment


            #50
            The original, free-flight 'plane has inter-wing struts, which are simply glued between the wings. Probably fine for the type of use it gets, but I won't be trusting my double-size model with that method. I've cut out the balsa struts, but included a tongue at top and bottom, which will fit into slots let into the upper and lower surfaces of the wings. These, of course, are not allowed for in the plans; I've added a doubling rib and spacers for the thickness of the tongues at the appropriate spots. I shan't be able to cut slots in the covering film, so I'll inlay 1mm sheeting between the ribs at that point, trying to keep the total wing surface as smooth as I can. Here's the doubling rib for a lower wing being glued up, with a yet-to-be-shaped strut just behind...



            The next photo shows the upper wing slots clamped up to dry, and the struts poised just for show in the lower slots...



            Once dry, the slotted part of the wing will be sheeted, and the slots cut into the sheeting. Will it all line up..? I certainly hope so..!
            I've cut out the pieces for the undercarriage (I've even painted the wheels..!), and also for the cabane struts. Again, the FF 'plane has these simply glued onto the frame, but I'll have to find a more robust way of attaching the wheels and wings. For the moment I'm thinking of using cocktail sticks as pins, but this may well evolve. Hmm... There's always summit more to think about..!

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              #51
              More news..? Yes, indeed. The inter-wing struts can now be dry-fitted (Dry-fat..? Dry-fut..? ) into their slots, which leads on to another challenge. I need to establish the geometry of the cabane; the plan has sparse details both of angles and means of fixing, so a jury-rigged mock-up is called for. Here, then, is the Flamingo, still in dry dock, but beginning to spread her wings...



              The centre of the upper wings is simply taped for the moment, and will be straight and horizontal when the wings are joined. I'll very likely reinforce that middle section with dowels, in similar fashion to the lower wings. Here is my first positioning of the cabane struts, simply leaning on the upper wing ribs and the sides of the cabin, just for the photo...



              There is no provision on the plan for attaching either end of these struts, so I'll have to improvise something. The fixing of the fore struts to the cabin should be easy enough, if I cut a slot into the sheeting there and sink them through. The rear struts should normally do the same, but as I've chosen to have that part removable for access, that won't work. I'll cheat, I think, and advance the feet of those struts forward a little, and provide sockets cut into the flanks a little.
              The fixing to the wings at the top end poses problems, as there is nothing solid enough there. I'll probably have to add thick rib doublers, wide enough to be socketed to accept the struts. I'd like to avoid sheeting here if I can, but may be obliged to, to allow for the film to be pierced by the passage of the struts. I'll find out a bit later; firstly I'll have to consolidate the current rig in order to establish dimensions. It's probably time to join the upper wings now, although that will make future manipulation even more delicate than it already is..!
              Onward and upward, though...

              Comment


                #52
                I've joined the upper wing halves, using dowels as reinforcement. here they're clamped up ...



                ... with a (rather over-exposed...) close-up showing the dowels skewered through...



                I've sheeted the upper wing slots since; they're now drying under press (Well, I say 'press', it's a pile of modelling magazines. That counts as 'press', doesn't it..? ).
                Cabanes. Hmm. I've cut slots for the 'feet' of the cabane struts, which rest on sheeting inside the fuselage. I've decided to have a thin ply 'canopy' at the other end, on which the upper wing can rest. Here's how I'm planning to get the struts and this 'canopy' set up, by inverting the fuselage over the 'canopy', with chocks for keeping the struts in place. This is just a dry run, obviously; I'll have some adjustments to make before gluing it all up...





                It looks less like a Flamingo, and more like some alien dragonfly, especially with the motor mount in place..! Does this look like a suitable way of setting up a cabane..? Any useful suggestions or warnings..? I may reinforce the 'tween struts along the ply canopy edge with thin carbon rods. First, though, I'll have to make sure of the alignment in all dimensions. I'll be patient with this step, I think..!

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                  #53
                  A picture of the sheeting over the inter-wing strut slots, the lower wings flat on the board, the upper wing upright just behind ...



                  The cabane jig all set up; it'll be dismantled, but at least I've some Idea as to how to go about it...



                  The undercarriage legs, assembled together for symmetry. There's a small piece of plastic film between the legs to prevent them being glued, one to the other...



                  Aha..! Serious stuff, now..! There are several steps that can only be taken after covering, but before that can be started, the mandatory 'naked wood' pictures need to be taken. All well and good, but the 'plane is far from able to support its own weight..! No matter; lashing of masking tape are used to enable some photos of the whole 'plane. Don't look too closely, though; she's very fragile in this state...









                  It's not easy trying to get a decent shot of the whole 'plane in a rather cramped room, and without being able to move the subject for fear of a total collapse..! It's the first time, too, that the fuselage and wings have been joined completely (albeit 'dry', of course...), and a broken spar is revealed in the process...



                  How and when did that occur..? Dunno; I'd not noticed anything amiss until taking the pictures. Clumsiness on my part, surely, and maybe not the last wound she'l receive..! Not yet off the board and already needing repair..! Doesn't bode well,eh..?
                  More reflection, and a few more details to sort out (the nose job, servos still, how to attach the undercarriage and more...), but I can now maybe get started on covering some of the elements at least. Progress..!

                  Comment


                    #54
                    Despite the copious tea, slightly dispirited today. The ideal mood, however, for doing unwanted chores, so I got stuck into repairing the broken spar. The break is at just about the worst place possible for replacing the spar, as it's exactly where the dihedral ply is glued in. I've decided to use a carbon splint instead. I carefully mill a groove down the spar each side of the break, the length of a piece of carbon rod I have handy, using my cordless minidrill...



                    The rod is scratched up with abrasive paper, the groove filled with epoxy and the rod laid in and covered with a plastic film, then a metal rule, a stout block of wood and the trusty lump hammer...



                    It's left to set; nominally two hours, but the epoxy is still tacky eight hours later. Never mind, it'll not be touched for a couple of days, so has been put to one side to cure fully...



                    The table has been cleared; it's time to start with some covering. Out comes the iron, the generous sample of Doculam I received (thanks again, George..! ) and a lower wing. A bit less than an hour later, the wing is covered...



                    Not too bad, I feel, except for an unfortunate clumsiness with the heel of the iron which severely dented one side of the laminated tip. Not willing to strip off the whole wing, I decided to treat it as a puncture and apply a large patch over the whole last panel and tip, so doubling, in effect, the film at that point. It's not as neat as it could have been, but a great deal better than leaving the dent or trying to replace the complete panel. Hopefully it'll not be noticed once the tissue goes on.
                    Enough for today; hoping that the weather brightens up somewhat, as this dismal rain is not helping morale. It's my own fault, of course; I shouldn't have pegged out the washing.

                    Comment


                      #55
                      The splint has been bound, with extra-strong cobbler's thread, and webbing added to the next two bays, on both left and right sides of the wing ...



                      If it's to break, I suspect that it'll be elsewhere..!
                      The second lower wing has been filmed; here's the family group, tucked away in a corner of the 'workshop', resting...



                      The width of the Doculam is more than the width of the wing; the offcut is, by sheer coincidence and good fortune, just the right width for covering the fuselage, although there's not much 'wiggle room' there...



                      My 'free sample' is going to be enough to cover the whole 'plane, but only just; I'll have to be sure of wasting none. For future builds (Yes, I've a couple 'on hold', including another biplane..!), I'll need more stock. The film I'm using is excellent from all points of view (strong, easy to apply, easy to store, lightweight...). I'd not be adverse to ordering a decent quantity, or sharing a roll with anyone (preferably in Europe, to limit shipping costs, which are exorbitant from the US ...). No panic for now, as I won't even be starting my next build until the Flamingo has left the nest, but some things can take a while to organise; best to get feelers out early.

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                        #56
                        Not much done today, despite the slightly more clement weather. Warm enough, indeed, to get some covering done with dope. I went for an easy kill as a first real task; after shaping the inter-wing struts to a semblance of aerodynamics, I applied a layer of tan-coloured tissue, using the thinned (50-50...) dope mix. I didn't trim to shape for the first one...



                        ... but did better for the other side and the second strut...



                        In doing this, I've come to the conclusion that, despite its allure, nitro-doping is not for me. For those already practised in this arcane skill, the results are, without doubt, superb, but the results I'm likely to obtain will never be proportionate to the not inconsiderable inconveniences of the stuff. Yes, I dabbled in the technique as a nipper, but, frankly, as I read somewhere recently, nostalgia is not what it used to be. It's expensive, difficult to obtain, difficult to store and, although only doing a few square centimetres this afternoon, fills the whole building with heavy fumes that linger, even with all the doors and windows open wide. Goodness knows what it does to the lungs an' all; it doesn't inspire much for those like myself with already delicate health at best. I really can't imagine inflicting this on the whole household over the next month or so; it's not at all given that I'd be in any state to finish the job..!
                        No, I'm happy with the Doculam, as with the tissue covering, but this stuff is too much for me. I managed to get a result using Eze Dope on the little Topaz I built, and covered my dummy rudder with tissue using it, too. It may not be as 'old school' as the model chosen would suggest, but at least it'll get done, without compromising our staid domestic routines. Hats off to those able to use the stuff; I'll duck my head down modestly and use lesser materials, I think. Another trial is in order, as I made some mistakes when last I tested it. Tomorrow, though, as I still can't work in the workshop while those fumes are so present.

                        Comment


                          #57
                          The doped tissue has been stripped from the struts, sanded again and doped again, this time with Eze Dope...



                          I can't say that the finish is ten times better (it's not, but it's not worse either...), but it took little time, and no impact on the local atmosphere. Once dried, they're good to go; I'll probably give them another coat, just to protect a little more...



                          While letting the struts dry in their own time, I've started on the nose cone, which I will make removable, so as to be able to work on the motor and connections if necessary (although I hope not to need to..! ). I start with a frame, magnetised to hold it to the front bulkhead of the fuselage...



                          Those magnets (the four black dots...) are incredibly tiny. I was pleased, too, to, at last, have some success with superglue (a 'first' for me..! ), which I used to stick them into the minute recesses I milled out for them. Being very careful to check for polarity, other magnets went into the fuselage. I'd assured alignment by firstly drilling a tiny guide hole in both frame and fuselage; they line up nicely, and the frame clings on with a quite hefty 'snap'. The dots in the fuselage are visible here...



                          After some measurements, trials and a couple of false starts, the rest of the nose is beginning to be built up,..



                          The rubber band and masking tape are just to hold stuff in place whilst the sticks get stuck; they're drying now, and I'll continue tomorrow. Meanwhile I have to order battery connectors, as the Lipo's I will be using have a smaller plug than the XT60s I have used previously. I could change 'em for the larger ones, but I'll not want extra weight for no good reason. I'll get the order done now...
                          More tomorrow, probably; maybe the covering of the empennage..?

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                            #58
                            Before covering, I have to work out exactly how the rudder is to be controlled. To this end, I've been playing about with the position of the tailfin-rudder assembly, as there has to be some clearance for the inter-elevator link to turn, and have enough 'throw' on the rudder, without touching the elevators. I used the dimensions from the plan; in hindsight I'd have been better served to open up the inter-elevator gap somewhat to allow for rudder swing. Never mind, it's too late to change that, so I have to cheat a little, and move the fin rearwards a little. I finally settle on a reasonable compromise, hoping that the rudder will have enough freedom to fly the 'plane..!...



                            Once the position has been decided, I can set the micro-servo into the root of the fin, through the tailplane platform on which it rests...



                            I'll add a false rib above the servo and sheet each side, as the servo arm will protrude out to the left, through the covering. A rod will then feed back to a control horn (yet to be made...) on the rudder. It'll have to work; there's no turning back once it's covered. I'll do a dummy run before that, though, just for my own peace of mind.

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