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

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    I've enquired for a set of registration letters from Callie Graphics, and bitten that bullet; they'll be on their way very shortly, I'm sure. Meanwhile, more setting up of the control surfaces prior to fitting the tailplane and fin. The linkages looked good, but it soon became apparent that the nano-servo I'd fitted for the elevator was having trouble with raising the levered weight of the elevator. Checking it with my finger, I could recognise that, with such a short horn, it was too much for the little mite. Hmm... It's been glued into the tail of the fuselage. What to do..? A simple answer, really: charcuterie. The block into which the servo had been glued was carved out with X-Acto blades and a biggish cutter. I happen to have a few alternative servos, of various physical sizes, so chose the next size up (quite a bit more expensive, too...), and 'adjusted' the remaining wood in the cramped quarters to settle it in. More checks for clearance of the servo arm, control rod length, swapping over the 'dominos' and using a clevis instead of an 'L' bend... It's now been adopted, and the Gorilla Glue is now going off overnight, so I'll consider that as 'done'. Much more 'oomph' (but it's quite a lot bigger, so...). The same nano-servo is built into the tailfin for the rudder, but doesn't have to combat gravity in the same way, and should be satisfactory (he said, with a false air of authority and confidence...). Quite a kerfuffle, and only really do-able with the aid, once again, of Our Eldest. At least he is able to actually see the tiny grub-screws involved, and can thread the rods through the holes in the 'dominoes' that I can hardly see at all. Still, better to find all of this whilst still on the bench, rather than when at fifty metres altitude ...


      I'm now in the position of being able to do some real weighing, and have to establish the C of G. All well and good, but the frightening truth is going to create some not insignificant problems. In fact, I've two weights to play with: the 'light' version, with a pair of lightweight wheels I've made up, a tiny 375mA Lipo and absence of copilot/passenger. In this configuration the scales tip at a tad over 700 gr. Well over my initial estimation of 250-300..! There's more to come, however, if I choose the 'scale' wheels, a more powerful Lipo and add the second figurine, we're around the 900-950 mark (roughly 2 lbs in old money...). Now for the complications. In 'light'mode, the 'plane is totally tail-heavy, even if I pile everything I can up front. The only remedy would be to add weight to the nose; this could be partly achieved by fitting a bigger, more powerful motor. In the 'all-in' set-up, however, and including a more powerful motor, the balance for C of G comes to exactly where it should be. 'No problem, then' I hear you mutter. Quite, but for the thorny issue of modifying the front end to accept a motor with a larger diameter. It's easy enough if I remove the nose cone, with its dummy radial engine (although in doing that I lose some more weight from the nose, too..!).
      The present motor, chosen with a light 'plane in mind, is a mere 60w, and weighs little. Using the 700gr option, I'd need to add lest to the nose, the weight goes up, probably to the 900gr figure, and the tiny motor won't be able to do more than putter about on the taxiway. I've another motor on hand, which balances nicely in the 'all-in' configuration, but may prove to be too powerful at 250w, and another couple being delivered at a more reasonable 100w and 140w. These are all, however, wider diameter, and slightly longer. I'll have to think about how best to modify the existing nose cone, or maybe make a completely new one.
      The Good News, then, is that the C of G can be brought to a credible position (just about the thickest depth of the upper wing, it would seem...). The Bad News is that There'll be some midnight oil burned to get mods done in time for end of the month. No pressure, then, eh..?


        Well, the mods are all done; it went off better than expected for the most part. Some head scratching, and not a little balsa dust, but all is now firmly ensconced with the upgraded equipment. The motor finally chosen is rated at 160w, with a 3s Lipo, so there's some hope that she may yet fly. Final build tomorrow, then; the 'plane is currently upside-down on the building board whilst the fin sets.
        I've not been posting pictures of late, but here are some photos of various details that needed attending to, in no particular order...
        Wheels... I've prepared a pair of lightweight wheels as an option. The ones bought are, indeed, light, but have a somewhat anachronistic aspect to 'em, so I've used them as a base for a more 'scale' appearance. Thin balsa circles have been cut out and shaped to the wheel diameter...

        Once painted and varnished, the disks are 'Gorilla' glued to the plastic wheels, and clamped...

        I may not use these wheels; it all depends on the C of G being obtainable with them. I'll find out tomorrow with the final assembly.
        Here's the parts needing to be upgraded, with the original motor, ESC and Lipo in the foreground, the new parts behind 'em...

        Here, the new motor is being checked, with the beefed-up Lipo in provisional position...

        This is how it'll look before sliding on the nose cone, all bound up, with the ESC strapped beneath the Lipo. I'm not expecting heat issues, as the ESC is capable of far more than this motor will draw, and there should be ample air moving about in that general region...

        A tailwheel seemed like a Good Idea, rather than the more 'scale' skid, and, just about visible, one can see a pair of hooks right at the rear...

        They are there for the rigging of the empennage; I've installed tiny tubes at appropriate spots on the tailplane and fin for the passage of the fishing line (I've forgotten the term... 'trace' or similar..?). The rigging will pass from one of the hooks, up through the tailplane, further up to the top of the fin, down the other side, through the tailplane again and back down to the other hook. With any luck, judicious fine adjustment of the tensions will maintain the empennage positioning. If nothing else, it'll serve as a further 'scale' feature..!

        That's all for this evening. With any luck I'll be putting some finishing touches to the whole thing tomorrow, with maybe a photo-shoot outdoors, or even a video of the Flamingo rolling..! Nearly there...



          A short video of her very first outing. More detail stuff is needed before any 'maiden', but all complete and working (although not yet reliable, as is seen in the video..! ). Here's a few more photos...

          Phew..! Under the bar by not much, but under the bar just the same, before the 'end of June' deadline. Flight will come later, when I've sorted out a couple of niggles and glitches; the registration lettering is to be received too, in a couple of weeks or so. More pics then, then...


            Very nice It will take off in 3 meters



              Thanks, Fred.(Now maybe I can get back to editing a few plans..! )



                For completion, whilst waiting for the inevitable 'maiden' to polish off the affair, there are a few details that need tidying up. The lower wing is held firmly to the fuselage by the rubber bands which strap on the undercarriage. The upper wing is similarly banded to the cabane. As the wings are removable, however, I had not built in anything to keep the wings attached to the inter-plane struts, and so the tips could part. How to keep the wings together..? I decided to use a system tried and tested in the real world, using guys, or flying wires ('haubanage'., in French...). Not dummy wires, using thread or elastic, but steel wires, to take some light tension. I had built in to the wings small hooks, which will be familiar to those accustomed to ladies lingerie. I have steel fishing wire, which loops onto these hooks. My problem was tensioning them. When properly tight, I could no longer pass them over the hook, either to mount them, or, if already mounted, remove them. I needed a way of tensioning after their installation. My solution is to use clevises, with their associated M2-threaded barrels. The 'hook' end was easy, as a wire could be looped onto the closed clevis, permanently. For the barrel, however, a tiny hole has to be drilled, for passing the wire loop. Here's the result...

                The wire is passed through a crimp, through the clevis or hole in the barrel, then looped back to pass back through the crimp. Once crimped (ordinary stout pliers, with serrated jaws, did a fine job...), the loop is pretty well fixed, with no chance of slippage. I fixed the clevis part first, definitively, then prepared the barrel part, by threading it into the clevis just a couple of turns...

                I could then pull tight the loop, by pulling on the free end...

                ... unscrew the barrel and squeeze the crimp. The barrel is then screwed back into the clevis until the required tension is reached...

                The wire doesn't like being twisted, so a certain number of reverse turns are needed before attaching the two parts; screwing the two together removes the twists. This spin-off benefit makes it very unlikely that the threads will unscrew themselves in flight.
                I've a similar system to install for the empennage, where there is also a wire hooked from the lower fuselage, around the tailplane and fin, then back down. I'll be able to adjust the tension there, hopefully to render these elements quite rigid, and maybe even correct, if necessary, any slight misalignment. That's a job for tomorrow.
                I've received the Callie graphics; our Eldest is helping with the application (he spent several years with sign-writing, including 'wrapping' cars and trucks, so I'm in very safe hands there...). More photos when that's done, very shortly...


                  With assistance from our Eldest (well, I held the 'plane steady; he did the work..! ), the 'registration' has been applied to the Flamingo. Not totally 'scale', of course, but at least she's identifiable now..! Whilst in the 'finishing off' mode I completed the haubanage , which went off quite well. I can now disassemble the 'plane and re-rig without too much fuss. Here, then, are some photos of the Flamingo, all done excepting any retouching needed after flight trials. Maybe this week-end (although it's a bank holiday Saturday, and stormy weather is forecast...). Enjoy...

                  Last edited by Dad3353; 07-11-2018, 06:54 PM.


                    Looks really great! I´m curious to know how it flies


                      14th July is a national Bank Holiday here in France; I didn't know if there would be anyone at the club site, but popped along just in case. Two members there, both pleased to look over the Flamingo, and offered, not to 'maiden' her, but at least to give her a rolling test. Here it is...


                      Not the most glorious, I'm afraid. Too much 'play' in the rudder control horn, and an out-of-alignment tail-wheel were blamed, plus a sudden gust of wind (dead calm up till then...). Not too much of an issue, but the prop adaptor snapped, so I'll have to change that. I'm not keen on these 'collet'-type adaptors, but there seems to be little choice. Next week-end is forecast storms and showers, so I'm not sure of her next outing. Nearly there, though..!


                        Here we are, then, the very first flight ...


                        Nothing broken, and at least she flew..!
                        Lessons to be learned : µ-servo embedded in the tailfin is too weak; I'll have to rethink control of the rudder. Probably pull-pull, with a more beefy servo under the pilot. More later, once I've cogitated a bit ...


                          It seems to have a tendency to turn right. is the vertical stabiliser well aligned? How is the motor aligned? Are the wings twisted? You can also use a lower diameter prop to reduce the torque effect but you´re right about the rudder control, if it´s weak you have to fix it.


                            Originally posted by derfred View Post
                            It seems to have a tendency to turn right. is the vertical stabiliser well aligned? How is the motor aligned? Are the wings twisted? You can also use a lower diameter prop to reduce the torque effect but you´re right about the rudder control, if it´s weak you have to fix it.
                            Yes, quite a few things to check, but I've started on a different (pull-pull...) rudder command, anyway. The prop is, in fact slightly too big, and I have others, technically more suited, which will be tested with the watt-meter. I like the wooden one, though, for the photos..! The buddies at the Club have keen eyes, too, and soon spot if there's anything amiss; they're not used to stick'n'paper biplanes, though. It's all a learning curve..! ;-)


                              You can try, after fixing the rudder, to do a hand launch facing the wind, maybe at 3/4 throttle. Have you balanced the plane laterally ? Sometimes a heavy half wing can do that.


                                No, I've not thought of that. Good thinking, I'll check that. Cheers.