MAAA Wingspan

38 39 WING SPAN NOVEMBER NOVEMBER WING SPAN MAAALogo. a project ARTICLE BY TIM NOLAN With COVID-19, there has been the unprecedented opportunity for many of us to start a project in the workshop, to learn a new skill, try something different, or repair and refurbish a model. Wingspan is our publication and if you would like to see more examples of projects, or how people go about tricky modelling tasks, this is the perfect forum so please drop me a line and we can find modellers who will be more than happy to share with you how they build the various elements of a model. I am writing this to the encourage you to try a scratch build, and not an ARF. The result is something that you can be proud of and you’ll have something a little different at the field which may spark another conversation or encourage someone else to have a go. With a friend, Stephen Rice, stranded in Sydney with the work and the COVID-19 lockdown, we took the opportunity to build a model that we first saw a very long time ago. It was rather odd-looking but one that appeals because it is different. A few close friends had also expressed an interest in building one of these as well, so the decision was made to kit up three of them - the Sorrel Brothers Hiperbipe. Never heard of it? Then Google is your friend. A homebuilt aerobatic aircraft with a reverse stagger on the wing. Image 2 (the old plans) The plans were sourced and then the discussions began around size, materials, construction techniques, engines, colour schemes etc. All a great opportunity to chat with friends and enjoy the company of other like minds. We settled on making our model at just under 1.8m – about 1⁄4 scale. In looking at the design, dating back to the 1976, it was time to update some of the materials and structures used for the larger version. Sheeted foam wings with carbon joiner tubes, 3mm plywood for the fuselage sides, individual servos for each control surface and do away with the complicated mechanical mixer built into the fuselage. We made a pattern for the cowl and then a fibreglass mould. For the landing gear we found some carbon legs from F3A Aerobatic aircraft, the tailwheel was an old one from Scale Aviation that had been in my recycled parts box (don’t laugh - we all have one in some form or another). This model has been built using simple techniques and materials, using mainly 3mm plywood from Bunnings and Balsa wood. As modellers, we sometimes forget the range of skills that we have acquired over our modelling time - carpenter, cabinet maker, fibreglass experience, cutting and sheeting foam wings, how to wire servos and current loads, battery management, computer radio programming, covering models (either iron-on or with dope and fabric), aerodynamic balancing of the model, control throws, painting... the list goes on. All that before we even get to the field to fly. Image 3 and 3A (fuselage sides, with Stephen Rice for scale) The sides were hand cut, and just built over the plans. Being a flat sided and square fuselage made it a little easier in some ways, so now it is starting to look like something. Image 4 (fuselage boxed up) The foam wings were cut by my good friend, Zak Kiternas, using handmade Laminex templates (see image 5B below). These are sanded smooth and secured to the end of the blank foam blocks (image 5C) . The bow has a nichrome wire under tension and a small current is passed through the wire so, as it get hot, it cuts the foam (image 5D small cutting bow) . The secret is to get the heat correct so there is a nice clean cut. When this is done correctly there is what looks like fine hair left on the cut surface. This is ultimately lightly sanded before bonding the balsa skins on. We used a carbon tube as the joiner (25mm OD) and, rather than using another carbon outer, I made a fibreglass outer/socket by wrapping a few layers of Glad Go-Between Freezer Film around the tube and then a light layup of two layers of glass and epoxy (image 5E) . This was removed when cured and the cutting template (Image 5D.1 tube cutter) was placed on the jackets and used to cut a neat hole for the outer tube to be glued into. It is critical at this point to ensure the alignment and provisions for any sweep and or dihedral and included. (image 5F) . The sockets were then glued into location. I left them a little long to secure the plywood root rib before sheeting, and this provides an anchor point for the carbon tube in the root of the wing. A similar structure was installed to support the other end of the tube in the wing. Image 1 The finished Sorrell Brothers Hiperbipe Image 5D