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

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    #31
    The tale is likely to jump about a little, at least for a while, as I've not got the conditions all united for doing things in a more ordained fashion. I've used up much more of my 4 x 4 stock than anticipated. Oh, I've got lengths, plenty of lengths, but not long enough for doing a whole spar span in one piece. The 1m stock was used for 60cm spars; the 40cm left are not long enough even for the tailplane..! I'm loth to mess about bodging spars, so I've taken the easy route, and ordered some more (quite a bit more; the postage is the same, so I'm refilling the reserves of other sizes, too...). Whilst awaiting arrival, then, I'll advance other tasks. Now then, where were we..? Oh yes; scalloping...
    Here's my scalloping rig; my cordless mini-drill with a sanding drum clamped to the bench...



    A bit delicate, having to avoid sneezing or the like, under threat of destroying the hard-earned fruit of my labours so far. Not helped by an interlude; the passage of our neighbour with his tractor, called in for ripping out a couple of unwanted tree stumps. It's all go, here..! Settled down again to finish the job...



    ... followed by final trimming, sanding, general cleaning-up and (temporary...) separation of the fin and rudder...



    Once again, the photos are somewhat flattering; there are defects that I see clearly that don't appear in them..! Still, I'm pleased enough with the result so far. I'll be able to have a go at covering, but I've still a couple of trials first with my test rudder, using dope and tissue, and I'll need a little bit more warmth to be comfortable with applying the stuff. The next few days may see an improvement, but I'm being prudent.
    Meanwhile, the wing is slowly getting built. Here's the last, 'dog-leg', part of the LE being glued up...



    ... with my trusty lump hammer doing its sterling job of keeping the joints tight shut.
    I have a secondary building board, which I'm pressing into service for starting on the tailplane (when the new balsa arrives...). The original plan has only the left tailplane shown, so I've cut that part from a copy, and its 'twin' from another, mirrored, copy, and joined them to form one complete plan...



    I'll be able to build the whole structure in one piece, then separate the elevators at a later stage. Hopefully this will help keep the unit nice and flat, and enable truer alignment of the spars and ribs. Again, it can be noted the extra ribs and spars drawn onto the plan before copying, to cater for the scaling up. I'll get busy making the ribs for this, but will need more wood to complete the piece.
    Patience, then, but things are nevertheless hotting up. I'll be covering the fin and rudder, then see about hinging (probably Doculam hinges..!), and start seriously thinking about how to command the surfaces. I'm leaning towards 'there and back' lines for now, but will probably do a mock-up with the micro-servos to try evaluating their integration. Lots more fun in perspective, then, but it'll be a bit disjointed as a log. Still, it's progressing; that's the main thing.

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      #32
      Busy elsewhere today, so not much got done, but I found time to glue up the first of the laminated wingtips ...



      A bit tricky, but it's really just a question of taking the plunge and doing it. In the end it didn't go too badly, I thought (I was afraid of cutting too short, and so ruining the whole laminated piece. Measure twice, cut once, eh..?).
      I've a bit of 4 mm square stock; enough to make a start at least on the elevators...

      ]

      Again, it's down to making choices and running with them, come what may. I can ponder this stuff for weeks; it won't make it any better when it finally comes down to it, and it's playing out quite nicely, for now. I've enough stock to finish this elevator and the other, but will have to hold off until the fresh stock arrives. A bit more tomorrow, then...

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        #33
        Here's as far as I can get with the elevators...



        ... with a very approximate trial fitting of the laminated surround. Too early to pronounce, but no major snags yet. I've a message from the delivery folks that the wood ordered should be delivered tomorrow; here's hoping.
        Meanwhile, it's time to get one of those painful moments out of the way: the cutting of the wing for its dihedral. Always a tense time, which I put off often enough, but has to be done. Some preparation, in an attempt to keep the wing from moving around once unpinned from the board...



        The original has dihedral of 1" at the tip; as I'm scaling 200%, I need 2". I've pinned two reasonably straight blocks each side, higher than 2", to act as guides, and will use my mitre block as a support of the right height (well, very slightly under, but close enough...). Now for the cut...



        Hmm... Not too bad, as it turns out. The root rib of this dihedral section is ply, thinking it'll add some strength when I re-join the wing sections. The lump hammer is back, of course, keeping the LE firmly in its place on the root rib, which has been glued in vertically, so as to marry with the inner, flat panel.. Here's the two sections, waiting to be mated again...



        Those with extra-keen eyes may be able to make out the white glue blob on the third rib from the left, where I inadvertently cut through the spar at the wrong spot. When I say I dread these delicate operations..? Still, no great harm done, I hope, but a warning to check, then double-check, each and every time.
        That'll have to set overnight; tomorrow, with any luck, I'll have wood to continue the tailplane. I've yet to look closely at servo mounting and control horns; maybe this evening (although we've guests, so...).
        Back soon, in any case.

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          #34
          Yes, the wood arrived as planned, so I could get on with the tailplane. Here we have the first elevator ribs being glued in ...



          ... and, some time later, the rest of 'em...



          The laminated frame has been glued up at the same time. One slight complication: the LE of the tailplane has been lifted slightly from flat, so as to get at least some profile to the tailplane. It won't be fully symmetrical as per the plan, but I simplified slightly by building it flat underneath. I'm not sure how, if at all, that'll affect its flying performance. It won't be a full-blown aerofoil, in any case. The aluminium profile is my straight-edge, being used here to weigh the ribs down flat to the board.
          Once that's set, I'll shape up the profile, then separate the elevators, after incorporating a joint between them. They'll then be ready for covering, as are the fin and rudder.
          Speaking of which... I've had a good look at 'pull-pull' systems, and did a small mock-up of the principle. Hmm... A bit complicated, I'm thinking, and delicate to set up correctly, especially in such a small space. I've another method to try out which may prove to be just as effective. If I delve into the mists of memory, I recall the very first rudder control used with the old escapement system. A narrow wire loop hangs from the rudder, and the escapement (or, in my case, the servo...) gives a right/left impulsion. If I adapt this to my project, I think I can have the rudder loop built in backwards, into the fuselage, and activate it completely hidden from the interior by the adjacent servo (it really is tiny...). Again, a mock-up will help me decide. The only real downside that I'm thinking of is the question of 'slop' with the wire loop being too wide. Maybe a version of the 'shrink tube' coupling could work..? More experimentation is in order...

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            #35
            Beautiful construction on the horizontal stabiliser and elevator.

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              #36
              Well, I did my dummy rudder control trial, and have concluded, for the moment, that it's possible to have a direct link between the rudder and the servo, inside the rear of the fuselage. I inserted a pin into the rudder, pointing forward, with a bend downwards at the fore end. This fitted nicely into the tiny hole in the micro-servo arm. Swinging the servo to each extreme turns the rudder in the opposite direction. There's not a lot of swing to be had, limited by the width of the fuselage rear, but I think there's enough to have a workable range of rudder throw. Anyone have any sample measurements I could make, to compare..? 1m20 span, slow-flying biplane, no aerobatics... Any older-timer models that can give me a clue as to throw needed (either in inches or cms measured at rudder tip, or angle of dangle..?). I'll be able to 'cheat' very slightly, in widening the rear, if I have to, but it looks to be enough to my inexperienced eye. Maybe a few dimensions from my end would help..? I'll see if I can get a decent photo or two, but my tests were a real 'lash-up' with masking tape and clothes pegs. I'll see what I can do...
              Meanwhile, I've started on the lower right-hand wing...



              It's a bit less fraught than the other, as it's straight (although swept back a bit...); the only difficulties should be the laminated tip and the dihedral. I've not glued in the root rib yet, as it'll be angled in the same way as the upper wing. So far so good, then...

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                #37
                Originally posted by derfred View Post
                Beautiful construction on the horizontal stabiliser and elevator.

                Thanks, Fred; as usual, the photos are somewhat flattering. (Just as well, maybe..,) The proof of this pudding will be in the flying, of course, and there's still a fair way to go yet...

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                  #38
                  You´re doing a beautiful job with the laminates, its a delight to see the final result and it will fly for sure. The only thing I´m a bit concerned is the wing strength, two hardwood spars wouldn´t have been a bad idea, specially for a plane that big but the covering will make everything stiffer so lets see.

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                    #39
                    Originally posted by aeradmifor View Post
                    You´re doing a beautiful job with the laminates, its a delight to see the final result and it will fly for sure. The only thing I´m a bit concerned is the wing strength, two hardwood spars wouldn´t have been a bad idea, specially for a plane that big but the covering will make everything stiffer so lets see.
                    S'not too late to add webbing between the spars, at least on a few inboard panels. Once covered, of course, it'd be a major task; I'll keep the option open for now, and see what it feels like when I get to joining the upper wings. Good call; I'm pretty happy for now that they'll stand up to a circuit, but won't be attempting any authentic Udet stunts anyway (as if I were capable..!). Rough landings might be a bigger threat; those, I'm capable of, I'm sure..!

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                      #40
                      Not too much done today, as it's turned bitterly cold again. I found courage enough for a couple of important steps, though. I'd gone through the list of ways of hinging the control surfaces, and decided on using flat, 'wallet'-type hinges. I was leaning towards Robart-type, but the ones that I have are far too fat for the delicate structure. Tape hinges and sewn hinges would have been inappropriate, I thought, for the way I've done the skeleton, but I had already envisaged the possibility of flat hinges, and had constructed with that as an option, which I've now taken.
                      Despite my grumbling about the DuBro hinge slot kit in previous builds, they worked perfectly for this build, thanks in great part to the way I'd laminated the spars as double thickness. The centre was easy to find, and, being quite soft balsa for the tailplane, no problem for the forked tool. Better yet for the fin hinge post, as I'd doubled that, too, from hardwood, but with a sliver of balsa sandwiched between. The tool was able, then, to make a clean slot of the correct width easily enough. Of course, once the hinges have been dry-fitted, it's tempting to see how the empennage will look on the fuselage, isn't it..? Did I resist such temptation..? No sirree...



                      The hinges can be made out with close inspection; although I can't myself see the metal hinge part, it's there, right enough I'm now trying to imagine a way of gluing the hinges in place before covering completely. That would allow a much more secure attachment, but may be delicate to execute. Again, reflection may help.
                      I'd asked, in a previous post, for any information concerning the rudder swing; not much need now, really, as it's automatically very limited by the form of the elevators, especially in the neutral position. I can juggle very slightly, by fixing the fin/rudder a bit further to the rear, but there's a limit as to how much that can be done without compromising the whole 'plane. I'll assume, for now, that the rudder has enough surface to work correctly; otherwise, how did Udet manage to fly it, eh..?
                      The other big step was the unpinning of the lower wing bare bones in order to fix the dihedral. Again, the original plans are quite skimpy in detail, giving just an indication of 1" at the tip. Doubled up this becomes 2" in my case. As the lower wing is slightly shorter than the upper, the angle will therefore be slightly higher. Not by much; I'll just hope that it's not too critical. I used the same jigging technique as before for the upper wing, as it seemed to work well enough...



                      My apologies if the photos are not crystal clear and razor sharp; my eyes see everything blurry, so I can't really judge their quality. Old age..! Wonderful, ain't it..?

                      Edit: Oops..! I've just realised that I'd completely forgotten the gussets for the tailplane..! That settles my plans for tomorrow, then..!
                      Last edited by Dad3353; 03-20-2018, 02:14 AM.

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                        #41
                        There's just enough room on the building board to display all the elements currently 'done' (but are they ever really finished..?)...



                        ... consisting of the two right wings, fuselage and empennage...



                        One can clearly see the tailplane and elevators, fully gusseted; I spent a fair while this afternoon scalloping...



                        ... which gives them a far more elegant appearance, almost 'steam punk', or even 'pop-art'..! Curious, I weighed the pieces before and after working on them, and witnessed a weight loss of 25% (22 gr reduced to 16 gr for the three pieces...). I also weighed all the wood on the table, and doubled the wing weight to account for the left side, and came up with a total wood weight of 135 gr so far. Not far off target, I hope.
                        Speaking of which, here's the preparations for the left upper wing, laying out the spars and counting the ribs. Note the 'mirror image' plan...



                        This was done last night, and the 'dog's-leg' in the wing prepared and glued up. This evening was spent gluing the ribs in place, after notching the TE...



                        I use the piece of scrap and a sheet or two of tissue as a swab to wipe away any excess glue blobs, and, of course, try to keep a check on square as each rib is placed. The notches help quite considerably with that, and are a Good Thing. The root ribs (ply...) have not been glued up yet. The most inboard one will wait until the rest are set; the other will wait more still for the wing tip to be adjusted. The wing will then be cut in two and lifted for dihedral; the rib can then be glued 'plumb'. Maybe tomorrow..? Meanwhile I'm looking into how to do the nose and motor mount. "So little time; so much to do"...

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                          #42
                          The left upper wing is now ready for dihedral, so out come the parallel bars, and away we go ...





                          The same mitre block as a height guide, of course, so if it's wrong, it's wrong for all the wings equally..!
                          Whilst that's setting, I've started a motor mount, using the suggested 'sandwich' technique of ply-balsa-ply. Here it is, in the clamps...



                          It's a bit small because the motor is a bit small..! I'm also getting ready to make a motor box, to protrude forward from a half-bulkhead fixed to the fore of the current fuselage. Work in progress...
                          Having lifted the upper wing from the board (to be sanded later...), there's room now for the last wing (left lower...). I'm becoming familiar with the routine of preparing for this; here's the dry fitting, just to be sure that all is lined up and ready...



                          ... and the ribs all glued up...



                          All except for the root rib, naturally, as the dihedral jig has to be used again when the wing is a bit more advanced. There's the upper spar to go in, then the laminated tip, followed by the LE first. Maybe later on this evening...

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                            #43
                            So, we need a motor mount. In my meagre parts drawer, I found an adjustable mount that could do the job; it even has the perfect holes ready for the tiny motor I'll be using. I fitted it up, and it could do the job, but... It's a bit on the heavy side (75 gr, including the motor...), and doesn't appeal to my 'DIY' instinct. Not that it's cheating, of course, but it's not in keeping with the rest of the build so far. Still, it's proved the principle, and enabled a pretty accurate (I hope...) estimation of where the thrust line should be, and the length needed. Out with the pencils, and see if I can come up with a home-made alternative. Here's the result, as of last night...



                            The metal mount is on the right, my sketch on the paper above, and the measured-up cutting plan drawn onto the ply. Our Eldest was, again, obliging enough to assist with his bandsaw (please understand 'assist' to mean 'doing all the work whilst I watch', hence the term 'lazy cutting'..! ). Here, then, is the result, being glued up...



                            The keen-eyed will be able to make out the pencilled numbering on the inside, where I matched up the tongues for best fit. The 'lightening' holes were swiftly cut away with a Forstner bit. We remembered only for the last one to not cut right through, but to invert the piece for the last cut, to reduce tearing. Not too bad, as it turned out, but could have been a bit neater. Still, mission accomplished, I think, with a weight reduction to boot: 45 gr for the mount and motor (yes, including screws, and even the elastic bands...). Once set, I'll start the upper decking of the Flamingo and prepare for the cabane, wing mounts and some access for the electronic gubbins, probably by having a removable cockpit area. Hmm... More stuff to be thinking about as I finish off the last wing (tip to glue up, and dihedral to establish with root rib...).
                            Back later...

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                              #44
                              The fourth wing is now complete and 'dihedraled', but needs still some trimming around the edges, LE and TE profiling and general clean-up...



                              It's now out of the jaws of the dihedral jig, resting.
                              Back to the fuselage, then. It's been patiently waiting, from its basic box shape, to have some curves added, in the shape of stringers, forming a 'turtle deck'. Again, some evolution is called for, as the fuselage is destined to contain more than the simple rubber motor of the original model. I'll be needing access to the battery, Rx, connections et al. To this end, I'm going to incorporate an access hatch, at the place of the pilot. For commodity, I've decided to have the access exactly between two fuselage formers, which will therefore include some of the turtle decking. I've shaped the stringer formers (thanks once again to our Eldest for the cutting out of the seven formers, all together...). They've been notched for stringers, and fitted to the fuselage. There's not much glue holding 'em on, but that'll be reinforced when the stringers go in. Meanwhile, a platform is being prepared, equally with formers, for the removable hatch (to be seen under press in the foreground...)...



                              I'll take better photos when it's a bit more advanced; it's not that easy to see under all those rulers and squares..!
                              I've also widened slightly the rear of the fuselage, to facilitate the rudder action I wish to use. Once these stringers are done, I'll see about fitting the servos at the rear.
                              I've still to decide what to do (if anything..?) about dihedral braces. I'm thinking along the lines of a couple of ply 'V'-plates, which will necessitate cutting the root ribs for their passage. I can't think of any other way of reinforcing the wing joints, so I'll just have to be brave, I think, and break out the saw. I really don't like cutting up assembled pieces; it feels so wrong, somehow. Still, if needs must...

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                                #45
                                As promised, here's the access trap provisionally in place ...



                                ... and removed ...



                                Nothing to access yet, of course, and I hope I've chosen an appropriate spot. I'll find out soon enough..!
                                In order to establish servo positioning, I have to prepare for posing the tailfin. To this end, I've added a sort of platform to the tailplane, to have some surface for the fin...



                                It needs checking for straight and level, naturally; the fin balances nicely in it's allocated spot (without the rudder, though; it would topple backwards under the extra weight...)...



                                . A sign of things to come..? I hope so. Meanwhile, stringers, to give the fuselage its 'turtle deck' shape behind the cockpit. The tailplane position fixes the position for the rearmost former for the turtle deck. Here, the first stringer is weighted down with a steel rule; it looks to be aligned as per the plan...



                                The rear stringers are all in, now; the 'plane is slowly taking on its future form ...



                                ... and the fore stringers, ready for accepting a nose cone...



                                'What's that fuzzy green blob at the rear..?' I hear you ask. Read on, dear reader, and all will be revealed...
                                Now that I've a base-line for the tailplane, fin and rudder, it's time to take the plunge, bite the bullet and see about fitting the rudder servo. It's being positioned, here, at the very rear of the fuselage (upside down in the photo...). Yes, I know; it's a very small servo...



                                One may note the extreme sophistication involved in gluing the servo support blocks in place 'the right way up', suspended from the upper longerons...



                                I'll be installing a rod (probably carbon...) into the rudder post, protruding forward, which will pass through the 'domino' on the servo disk and a bit beyond. As the disk rotates, it'll pivot the rudder in the opposite direction. There's not much 'throw' available, but with the size of the rudder, I'm hoping there'll not be much needed. It's limited anyhow by the width between the elevators.
                                Speaking of which, they need to be coupled, so as to work in unison. The hinges are all prepared, so I slotted them into place into the tailplane and glued a sliver of ply between the elevators. It seems OK, but, just in case, I've glued (with epoxy...) a carbon rod as well...



                                It's my first ever use of carbon, so I hope it'll do the job. I roughened up the rod with a sanding block and scraped it slightly with a knife to try to give some 'keying' to the epoxy. In theory there should be little real strain involved in normal operation. In theory...
                                Once I have the geometry working for the rudder, I'll set about installing the elevator servo. That'll be a bit more conventional, with a control horn (yet to be designed...) on the elevator pair, activated by a push-rod from a servo just fore of the rudder servo, through the rear of the 'plane. That's the plan, hoping there's enough room for all that.
                                With any luck, I'll not need to access any of this stuff after covering. I'll find out before it's too late, and have a 'Plan B', in which an access trap is let into the underside of the fuselage rear. I'd like to avoid that if possible, though.
                                Last edited by Dad3353; 03-31-2018, 02:13 PM.

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