About this Plan
Iago. Free flight model for electric, CO2 or Cox PeeWee power.
Quote: "Iago. A 36 inch version of the 54 in Santiago design from from 1943. Reduced and devveloped by Eric Marsden.
Iago is a reduced and simplified version of Jaques Bluzot's 54 in sparker of 1943, for 3.5 cc engines. His model has wings tongued and boxed onto elegantly curved wing roots - Iago has a straight-through wing with fairings added to clean up the fuselage line. I had originally intended to call it 'Sunny Jim', because the lines bring to mind, in the curious way these associations have, a bounding, yellow and red clothed figure which was the logo of a brand of cereal in the 1920's, named Sunny Jim. However, a birthday present of rolls of red and white Airspan led to the model straying from the necessary red and yellow colour scheme, and most folk look quite blank when one speaks of the 1920's, so I thought it would save a lot of bother to simply reduce the name just as I had done the model - and Iago is 'James' still. We have merely removed any odour of sanctity - but EerIgo was a grave temptation.
The model's size is the result of following a long term plan to cover as wide a range as possible of model sizes and types for the KP 01, and to find out just how large a good flying model could be built for this power unit. My previous largest was the JU.K53, of 36 in span, 140 sq in and 140 grams, which flies very much in character, making little height, and descends quite positively at the end of the power run. Iago is a much cleaner design, 180 sq in at this span, and the prototype comes in at 130 grams, to make an interesting comparison.
STRUCTURAL VARIATIONS The wing was built more heavily than needed to provide some leeway for the final design - with 3/16 x 5/16 laminated leading edge, 1/8 x 7/16 laminated trailing edge and four 1/8 sq spars. The ribs of 1/20 quarter grain 8/10 lb stock, were set at 1-1/4 in spacing, and the centre section area sheeted also with 1/20 balsa. This has permitted the use of a lighter wing of adequate strength which should allow some tolerance in the weight of balsa used.
The original Santiago seems to have had an undercambered section, but my simple Dr Eiborl sections are much easier to build and cover, and I tend to work with the beginner in mind, after so many years of working with school model clubs. I'm sure that the wing could be built with a 1/8 sq leading edge spar in the fashion of the small rubber model, with front spars of 1/8 sq, rear spars of 3/32 sq and trailing edge 1/8 x 3/8i, to produce a model with positive 'flyaway' abilities, when a D/T would probably be advisable.
A 1/16 or 1/32 ply template is useful for cutting wing ribs, and is particularly useful for taperwings or elliptical tips, since the use of the 'tilted rib' method of obtaining smaller chord sections makes rib cutting quite easy.
Building the fuselage is helped with the use of two or three removable card formers which establish the taper in the fuselage vertical sections. The underfin, of 1/16 sheet, suitably edged, fits between the lower rear longerons, and is held firmly with slivers of balsa glued between fuselage and fm.
The first fuselage belly bay between F1 and F2 was filled with a balsa block, and carved and sanded to shape, then removed and hollowed to about 1/16in. thickness. After the undercarriage was wiped out during early test flights of a version built with far too great a wing incidence, the fuselage was rebuilt with 1/16 sheet flooring back to F5, the bottom planked on the frames back to F5 also, and 3/32 webs added across the bottom of frames F3 and F4.
The stringers run from F5 to F9, and the frames can be relieved between the stringers by sanding with a piece of dowel wrapped with glasspaper. I find very useful a selection of six inch lengths of dowel round which is glued medium and fine glasspaper at either end. Two or three different diameter tapered pieces, which can be rasped and sanded to shape in a power drill are also very handy. Whilst suitably grained sheet will wrap around the decking formers fairly easily, soaking in warm water, with a touch of household ammonia softens sheet so that it will wrap without cracking or splitting, and may be held in place to dry with drafting tape. It pays to cut these pieces slightly too wide, and trim to a dead fit when dry.
POWER SOURCES: The KP 01 weighs 32 grams, I think, whilst the Cox Pee Wee is 28 grams with prop. The TD 020 with tank is the same, and with the tank removed to permit use of an eye-dropper is likely to be similar.
A Cox TD 010 would have ample power for this model, but would need around ten to twelve grams of nose weight added to the model to bring it into balance. Since the .010 will fly a model of this area weighing up to eleven ounces - Schoolboy (oz1030) with S/C radio - this poses no problem. When the firewall is moved aft to keep the nose length as drawn, the CG of the engine is forward of the centre of mass of the KP unit, so that the few grams difference in weight may well be balanced out, or need only slight ballast in the noseblock for good glide. For these engines, and perhaps CO2, the F1C bulkhead of 1/16 ply is suggested, with pieces of 1/16 ply glued on the back to provide extra depth for the fixing screws..."
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Update 18/03/2019: Added article, thanks to theshadow.
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