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A Sky-Mite for the littl'un ...

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    A Sky-Mite for the littl'un ...

    Our four-year old grandson is fascinated, like most small boys, by my 'planes. I made him a kit 'plane, a rubber-powered West Wings Topaz, which we fly together when it's fine, but he said, wistfully, the last time he was visiting 'You've got big 'planes. I've got a small 'plane, but you've got big 'planes'. I've decided, then, to rectify this, and make him a big plane.
    Everything is relative; to us, 'big' is anything with a span of more than 1 metre. I looked for a simple build, then, for an electric trainer-style, easy enough to build, using parts I already have on hand, or can obtain easily and quickly. The choice came down to the Fly-Mite. I ordered the plan, which was delivered promptly, and have now pinned it to its very own building board; a bit smaller than my main board, but enough for the whole fuselage and the half-wings...



    I've still my Prima to finish, and another to start after that, so I've created a space for the small board to be put to one side, on a folding trestle table...



    I should be able to bring it out to work on, then put it away when the others need the main space. We'll see how it works out.
    The plans have all the details for the woods used, but all are in imperial units, whereby here in Europe, everything is metric. Before starting, then, I get pencil and paper to list the sheets and sticks needed, converting the units as I go, so as to draw up a list of stuff needed, and prepare an order for anything not in my modest stock...



    Not being very experienced in 'scratch' building, this was an 'interesting' moment, with some head-scratching, but I've now my list. I've another 'plane to prepare, so I'll combine the two lists and consolidate all into one order, to save on postage costs.
    The next step will be deciding how to mark out and cut the outline of the fuselage sides (they're sheet...). It's a bit of a chore taking the plan to be photocopied (and it'd only just be long enough...), so I might try tracing paper. We'll see...

    #2
    I was slightly optimistic about the photocopy; the fuselage doesn't fit onto an A3 sheet, even diagonally, so I made two copies, and tiled them together. I was careful to firstly trace a straight line along the length of the original plan so as to align the fuselage correctly from the two copies. The resulting montage was then stuck down onto thin card, and presented to the balsa sheet...



    I can fit the two flanks onto one sheet by placing them head to toe, like sardines. Here one can faintly see the first outline and the template in place for assuring that there's room for the second...



    A roughly diagonal cut separates the two pieces, which are then placed one on t'other to be cut together...



    ... and here they are..!



    They're put aside for now; I'm going to prepare the ribs. I made a photocopy of the plan for those, too, which was also glued to card, used as a template for cutting a pair of ply templates on the bandsaw. A stack of future ribs has also been taped together...



    The ply templates are drilled, along with a supporting block...



    ... followed by the stack of future ribs...



    ... for the passage of bolts to hold the ply and future ribs as a 'sandwich'...



    The whole caboodle (a technical term...) can now be cut on the band-saw, very slightly over-sized (I can relax and take photos; it's our eldest doing the cutting...)...





    The support block is carefully removed...



    ... and the stack of ribs sanded to meet the ply template. Too fast for the camera, but you get the idea...



    ... and here is the result..! A family photo, showing the cut-out photocopy, the card backing, what's left of the balsa stacks and the pack of ribs, bolted still to the ply templates...



    They'll stay like that until I'm ready to start the wing. For now, the wood ordered has arrived, so I can go back to a more conventional order of building, starting with the tailplane.
    Coming soon...
    Last edited by Dad3353; 01-25-2018, 12:15 AM.

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      #3
      The wood ordered doesn't have the 5x5 sticks asked for on the plan (well, 3/32, but who's counting..?), so I strip some from a 5mm sheet. Same for the 5x3 sticks needed for the diagonals; handy thing, this Dupro stripper..! It shouldn't take long to assemble all these pieces, but I'm taking my time. I'll have to wait for the PVA to dry, anyway. Here's the tailplane all glued up; it'll need a bit of trimming, of course, and sanding down, but it's a start...



      The article describing the steps has an unusual (in my limited experience...) piece of advice, to tack the elevator to the trailing edge (TE...), so that it be shaped together with the tailplane, then detached. I've done that, with just the merest spot of PVA at each end, where it'll be trimmed anyway. Here's the same shot, but under press, to keep the diagonals nicely flat...



      That's all for this evening; tomorrow, probably the tail fin and rudder...

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        #4
        Some progress today,with the creation of the fuselage formers from square stock...



        ... and the cutting of the tail-fin and rudder (on the right...



        Several other pieces, too, such as a motor mount (left, between the fuselage flanks...), different to that on the plan, as I'm using a brushless outrunner, not a Speed 400 can and gearbox. The nose hatch will be modified, too, along with the formers that shape the nose cowl (top left...). The fore cabin former has been cut from ply, and needed preparing for reception of the landing gear. To this end, it made sense to make the latter (bottom left...), in order to get the appropriate alignment. Here it's placed over the plan...



        ... it looks to be a decent match. The gear will be bound to the ply former, not with brass wire as specified, but with strong thread, and coated with epoxy. I'm pretty sure that'll be just as strong; any more and it will be the wood that breaks, anyway.
        Next step will be the forming of the fuselage, taking pains to maintain the elements square and true. Tomorrow, in all likelihood.
        Last edited by Dad3353; 01-30-2018, 05:52 PM.

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          #5
          The first formers glued to the fuselage flank, using the mitre box as both guide for square and support while the glue dries ...



          It's all extremely delicate whilst in this state, so I'll give it plenty of time for the PVA to go off before moving it. The article by the designer of the 'plane calls for epoxy for this step, but I used PVA just the same. I see no advantage in epoxy for a joint like this.
          Once ready, it'll be time to turn it over and glue to the other flank. Tomorrow..?

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            #6
            Now for the other flank. A careful balancing act, to put enough pressure on the glued joints without risking distortion of the framework...



            Time passes...

            Not too bad, and starting to show some potential as a 'plane, at least...



            On goes the underside sheeting. The plan calls for 2mm5, the same as the fuselarge sides, but I find that to be rather execessive, so decide to use 1m5 instead. It's cross-grain, so I can't use a single piece. Here's the 'mummy', all strapped up...



            While that's drying, it's a good moment to consider how to fit the servos and pushrods, whilst the rear is still accessible. Side by side they are a bit cramped, so I go for a 'tandem' configuration...



            Wing-bearer reinforcement is called for on the plan; I try out the emplacement of the servo tray whilst they're clamped up...



            ... followed by a dry run with the pushrods-to-be...



            Once the rear is sheeted, it'll be quite a job to play about with the linkages, so I'll try to get them as close as I can to their final state before then. I have to choose a method of exiting the pushrods through the flanks. Tubing, cut off flush..? Slot 'windows' let into the flanks..? Fairings (as I used on the Prima...)..? I'll sleep on it. Goodnight, all.

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              #7
              In a tight fuselage like this, I have kept servos side-by-side by mounting one inverted and leaving space if a control arm of one needs to go over/under the other servo.

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                #8
                I've been playing around with a few ideas for hinging. I did an experiment with Blenderm on some gash wood, which worked well, giving a very free-moving pivot. I then read about using covering film in the same way, so repeated the experiment using the Oracover I'll be using for the Sky-Mate. Quite conclusive, for the use the 'plane will get, and with some not negligible advantages over more traditional methods. Here, then, is the 'over-under' Oracover method applied to the rudder and fin...



                ... and here's the opened joint, showing where the two pieces of film are joined, glue-face to glue-face...



                Three 'spare' hinges can be seen to the right; it looks like black and white, but it's transparent orange on a blue background giving that effect. They were very easy to make, using simply two small pieces of film, which, once joined, are then cut into hinge-sized slices. They may not last ten years, of course, but seem to be pretty robust just the same..!
                I deliberately hinged first, before covering, so that the final film would cover over the hinges, providing further consolidation...



                The white hinges are all but invisible; the orange ones can be seen by transparency, but are not unsightly, to me at least.
                I would have liked to adopt this same technique for the elevator, and would have constructed differently had I had the idea earlier, but there is not enough surface on the tailplane for ironing film, so I revert to using pin-hinges. These are slid into slots cut into the joining edges of the tailplane/elevator. I have already done this type of hinging before, and each time it's a nightmare. I have the Dupro set of 'forks', but am really not impressed by either their efficiency or their longevity. In the softest of balsa they can do their work without too much destruction, but anything even slightly hard and they twist and bend, deviate from their course and generally do almost as bad a job as my simple X-acto blade. Still, they managed to get these meagre four hinge slots done, but I'll be looking for alternative tools or hinging systems for the next 'build'.
                As can be seen, I 'filmed' the hinge area of the tailplane so as to be able to glue the hinges in place, applying glue on the inside of the structure, and will 'pin' the hinges by drilling small vertical holes for passage of a cocktail stick through both the TE and the hinge. This will be covered over by the final Oracover film. That should hold it all in place. I'll do the same for the elevator once the tailplane is set. I must not forget to trim the elevator LE to a 'V' profile (not necessary with the 'tape' hinges, of course...)
                Altogether going reasonably well, I'd say. Once the 'feathers' are ready, it'll be time to finalise the linkage to the control rods. Soon; very soon...

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                  #9
                  The empennage is ready to be attached to the fuselage, but I'll wait until the wings are on, to line everything up together. The undercarriage has been sewn and glued to the bulkhead, the servo tray glued in and the underbelly sheeting almost finished...



                  Time to get the wings under way, so space is cleared and the pieces laid out The article explaining the build wants the spars joined with the dihedral brace first, then each half-wing built flat, one after the other. I'll not be doing that; I'll build both halves flat, with a one-piece trailing edge (TE...) and leading edge (LE...), and separate them to install the dihedral plate. This should ensure a nice straight, warp-free wing (I hope...). I've equally decided that I'll use rib caps, so the ribs will be shimmed 1mm, not flat to the board ...



                  The plan calls for a hard balsa main spar, but I don't have that in the dimension required. I've replaced it with a samba spar, a couple of millimetres less wide, but I think it'll do the job just as well; maybe better.
                  I now need to prepare the TE; to this end I rig up a sanding station, to create the profile of the TE...



                  I haven't macro-photo facilities, so good eyesight is needed to see that I've taped a 1mm rod along the edge of the workbench (OK, it's a table; I use it as a workbench, OK..? ). The TE is placed the length of the rod, and a 5mm brass square tube placed behind, sandwiching the TE. Profiling can begin, safe in the knowledge that the rod and brass tube will prevent sanding away too much. It's a bit brutal t first, using the Black & Decker to speed things up a bit, then finishing by hand with various grades of sandpaper. All ready, then for 'nicking' the TE where the ribs will slot in. Probably this afternoon, and the gluing-up can begin.

                  Comment


                    #10
                    I’ve also been working on this plane. With the cold weather, I’ve had nothing else to do and hope to be done in a couple of days — a total of two weeks. I’ve installed a Grayson Hobbies 100W motor and wanted to put the battery (Floureon 3C 1500mAh, 75mm long, 116g) foreword of the firewall. So I had to cut an access in the firewall and move the landing gear to the aft side to go around this gaping hole. The fore electronic bay has the motor, ESC and battery. The top of the compartment is removable, held by a screw on either side which goes through the fuselage and an extended flap on the inside of the cover. With this configuration, it is now at 434g and just slightly tail heavy, with the wings and tail plane still needing cover and paint.

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                      #11
                      The ribs have been glued in place; they fitted perfectly, with no retouching required at all. A firm sliding fit over the main spar, and an easy push-fit into the slotted TE, so I'm well pleased with that. Time, then, to fit the dihedral brace. As the wing has been constructed flat, one side can be glued in straight away...



                      ...followed by the central and root ribs. I've 'recycled' the ply templates used for shaping the ribs, as root ribs, thinking that they'll be more robust than the balsa ribs of the plan.
                      The wing is now cut in half (not so difficult, it's only a matter of slicing the LE and TE spars...), and the right wing lifted to the dihedral angle. The brace can now be glued to the left wing, still pinned flat on the board. The plan specifies 4" at the wing tip whilst the other wing is flat; this is checked and found to correspond. A lucky coincidence..? I think not..!
                      With the gluing of the dihedral brace comes the re-joining of the wing halves, gluing and clamping the ply root ribs, as well as the LE and TE...





                      Some very slight 'persuasion' is employed, in the shape of a hammer-head, to ensure that the free-floating wing stays firmly flat to the board at the root.

                      Time passes...

                      ... and more time yet (the PVA sets slowly in these nearly freezing conditions; it's very cold in my unheated workroom, and we've some slight snowfall...), but the whole assembly can, at last, be unpinned. It's tempting to see how it'll look on the fuselage...



                      There remains still much to do, but it's satisfying to see the potential slowly becoming realised.
                      Next step..? Central sheeting, wing tips, and I've decided to add rib caps, to help with the film covering.
                      To be continued...

                      Comment


                        #12
                        Originally posted by Cheetahpop View Post
                        I’ve also been working on this plane...
                        Excellent..! You're working very quickly, too. That's one good thing about these Build logs, and forums in general: they bring to the table different ideas and solutions otherwise unthought of. Battery placing, for instance. It hadn't occurred to me that the undercarriage would interfere..! I may have to rethink this, so thanks for showing your solution. I'd not thought about a tail wheel either, but it's not too late to dream something up for that.
                        What will you be using to cover the wings, tissue, iron-on..? I'll be filming mine with Oracover, in the same way as my Prima; that way the littl'un will have a 'plane just like his granddad's..!

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                          #13
                          Thanks for the kind words! I have enjoyed reading about your work. Thanks for posting it! As for covering, I’m an old fashioned tissue guy. Instead of dope, I shrink it with water and paint it with thinned acrylic paint (other guys in my area use latex). Unfortunately, the hose of my air brush is clogged, so I’ve been brushing it on and lost track of the number of coats. I’m already contemplating another wing with ailerons and flaps, lol. I will add some green diagonal stripes so it doesn’t look like Big Bird.

                          Experience is a good teacher... the battery is about 1/4 the total weight, and it can never be too far forward. I’d hang them in front of the motor if I could figure out how. My last weight check was 451g, a whisker shy of a pound. I have the receiver and covering the tailplane to go.

                          One of my quirks is providing a non-tool hatch for battery installation. There’s a section of belly planking, ~5-1/2”, I left out. With overlaps, a finger grip Dremeled out of one end and a couple of 1/16 reinforcement strips on the inside, I can flex it in and out of place. You want to keep the overlap very thin on the finger grip end. 3mm is plenty, so you don’t have to flex it too much.

                          Comment


                            #14
                            The ribs for this Sky-mite are 1.5 mm (1/16", if you prefer...). The wing is not sheeted, and has only one spar, flat to the bottom of the wing. It will be covered with Oracover. My thoughts...
                            1 - Is it a Good Idea to add caps to the top and bottom of the ribs, or will Oracover behave itself over such a structure..? When I built my Electra, all those decades ago, I didn't even know about rib caps, and it covered very well, but I think the ribs were slightly 'beefier'. It's a 'plane for the littl'un, and will get flown only very occasionally, and certainly not in any acrobatic mode (well, not on purpose, anyway..!) Caps or no caps; that is the question.
                            2 - I wish to simulate the same decor as my Electra and Prima (orange and white Oracover...). To do this, I'll need to have the front of the wing, top and bottom, in white, but the rear (rear of the spar...) in transparent orange. This means a seam along the span. For the underside, there is a spar, but for the upper surface, there is not. Should I add a span-wise strip along the top of the ribs where the seam will be..? I'm rather afraid that the film will not take well to joining across an open structure. To strip or not to strip; that is the question.
                            I've answered my own questions by just doing it. Starting with the span-wise strip, then 1mm rib caps, I hope I've made the covering a bit easier, albeit with a weight penalty. As I'm not looking for optimum performance (I'm privileging robust and reliable build methods...), I think I can live with that. Here, the top sheeting, wing strip and upper caps have been done...



                            ... and a closer look ...



                            Still more to do, of course: the underside caps, LE forming, tips to glue up, LE location peg, TE reinforcing for hold-down bolts, fibreglass ribbon. A long enough list, but one by one, they're done. As it's still pretty darned chilly here, I've perched the wing above our wood stove, to help the resin to go off a bit quicker. No, it's not hot at all where it is, but a great deal warmer than in my 'den'..!



                            I'll turn my attention back to the fuselage, to finish off the motor mount, and start think of how to make the nose hatch (what I'd call a 'bonnet' for a car; some may think of it as a 'hood'...).
                            Back later...

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                              #15
                              On all the 'planes I've worked on so far, I've had the motor mount slide into place between runners. This enable easy modifications such as down and side-thrust. Here's the rear runners being glued into place...



                              While working on the motor side of things, it's time to solder the bullet connectors etc. needed for the drive train...



                              Back to the covering, then. Here's the transparent orange being applied...



                              ... and the result, with the white ...



                              Still more left to do, but another dummy assembly is in order...



                              In this configuration, the C of G can be approximately checked; it looks to be well within scope, with a fair margin of manoeuvre in the Lipo position. I now need to receive control rod 'windows' in order to finish sheeting the rear of the fuselage, before fixing the empennage in place and connecting up. The fuselage is yet to be covered, too. Then it'll be simply a question of attaching the radio 'gubbins' and seeing what works and what doesn't..! Soon, I hope.

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