About this Plan
Slingback. Radio control sport sailplane model. Wingspan 59 in.
Quote: "Pat McCauley guides us through the construction of this pretty Slingsby style chuck-about, for days when the wind just isn't quite up to it.
I enjoy flying slope soarers in all (dry) weather conditions and have a selection of models to cover the seasons - or so I thought. Late one autumn afternoon when all the thermals had popped off and the wind had dropped to a whisper, my large, heavy soarer was only capable of scraping back and fourth along the ridge at head height. Getting side-tracked my concentration wandered, so did the model and I had to walk down the hill to retrieve it.
During the walk I realised how pleasant the weather was and noticed that a functional lightweight model was buzzing the ridge top and indulging in the occasional loop. I reflected that it would be very relaxing to fly a light 'chuck-about' for an hour or so at the end of the day in pleasant conditions or on days when the wind was simply very light.
Being an addicted builder I reckoned I could justify another addition to my glider fleet. A lightweight design which could be put in the car on trips to the slope with other models, just in case the wind dropped.
Browsing through my plan collection I had nearly settled on Yellow Bird (oz10568) a Radio Modeller free plan, when I came across Keith Humber's series of Slingsby Cadet designs. Like many of my generation I learned to fly full size gliders to A and B certificate level with the ATC in the era of Slingsby T21's and Cadet Mk 3's. Nostalgia took a hand. I liked the look of Keith's Kirby Cadet Mk3 (oz11577) but decided that the hassle of rigging the ailerons and struts in 'iffy' wind conditions might compromise the hassle-free concept. A slightly more streamlined, 2 channel, Slingsby lookalike without struts or pylon mounted wing started to form in my mind, and so Slingback was conceived.
Slingback is not as quick and easy to build as some functional lightweights but is not difficult and is a lot easier than a scale model.
Wings: It is best to start here as the wings take up most of the building time and will be needed to complete the fuselage. As the flying characteristics have turned out to be well suited to the novice flyer and the wing construction is a little unusual, employing a single full depth spar, I will describe its construction method in some detail.
Pin or tape the wing plan to your building board cover with a clear plastic sheet (Solarfilm backing is perfect). Cut out all the parts necessary for the 1/16 sheet underside outline (both wings) including cap strips. Pin down and glue the parts for the right wing as you cut them and put the identical parts for the left wing aside. When dry, unpin it then remove and reverse the plan. Cover the left outline with another plastic sheet and pin down and glue the left wing parts over it. When the left outline is dry unpin and leave it to one side until later.
You should now have two identical 1/16 wing outlines each comprising of LE, TE and root sheet with 14 No. 1/4 in cap strips. During the glue drying process, cut out the 1/8 'very hard' balsa main spars to 5/8 depth by 29.5 inches in length and the false LE to 3/8 by 29.5. The main spar will, at a later stage, be planed and sanded in situ to exact depth with its top surface tapered between R4 and the tip. Now cut the dihedral angle at each main spar and false LE root end, using the dihedral template. Trim the main spars and LE at the tip to the exact length. Cut out all the wing ribs using your preferred method, I used the single template method. It is quick, easy and results in an airfoil adequate for the purpose in a model of this size and type (Fig 1). Templates for the sandwich method of rib production are on the plan for those preferring it.
Pin and glue the false LE in place on the right wing outline. Stack one set of R4 - R16 together lining up their LE at 90P and cut vertically through the stack at the front of the main spar position. Pin and glue the front parts of these ribs and the main spar in place lining them up square as you proceed..."
Slingback from Silent Flight, February 1997.
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