Ultimate (oz15927)

About this Plan

Ultimate. Radio control sport scale model biplane. Wingspan 37 in.

Note this plan as printed shows a model with wingspan 37 in, but can also be enlarged to 133% to produce a model at wingspan 49 in. Both material sizes are shown thoughout.

Quote: "FREE PULL-OUT PLAN for 37ins wing span scale ULTIMATE 100-300 WINNER requiring '26' to '40' engines and four function radio. Enlargement options for 49ins span and 60-80 engines. Ultimate, by Dave Boddington.

I HAVE COMMENTED PREVIOUSLY on the size limitations of models imposed by the size of the pull-out plans in each issue of RCSA. To include all the information on one double sided sheet restricts the size of model considerably and to carry over the drawing to two issues is a compromise at best. Even when included on two sets of drawings the size of the model is still limited by the length of fuselage fitting on the length, or diagonal, of the sheet. So, the short nosed, radially engined WW1 biplanes lend themselves to this treatment, but a Luton Minor or Piper Cub would not be suitable candidates.

Almost every sizable town now boasts a 'Print Shop' capable of producing standard prints, reductions or enlargements for the retail customer. Maximum widths of prints are usually 33ins, but with no limit on length. Enlargements and reduction to a factor of two are possible, if you need to more than halve or double the drawing it must be done in two stages. Costs are reasonable and the quality and accuracy of the prints are very good. This facility is a great help to the modeller wishing to vary the size of a particular design, or simply for reproducing part of a drawing, to the same size, so that components can be glued to the material for cutting out. Much easier than tracing all the parts.

My first intentions were to design the scale model of my choice and then to present it in RCSA at a reduced scale. Any modeller interested in building the model only had to take the pull-out drawing into the 'Print Shop', have it enlarged by the appropriate figure and away he could go on the building. It occurred to me that this was perhaps wasteful, not everyone wished to build the larger models and would quite like to construct the model at the smaller size. I have designed and built many 'Mini' versions of 'standard' sized models over the years.

My thoughts then went to designing the practical pull-out scale plan to a size to fit on the standard sheet and also allow for a specific size enlargement where sizes of material would correspond to the enlarged drawing. For instance, if the pull-out plan model used a spar of a 1/4in.sq. the 50% enlarged version would utilise a 3/8in.sq. spar. Actually, enlargements have to be kept to a reasonable figure otherwise the strip and sheet components become out of proportion e.g. a 1/4in.sq. longeron would not need to be increased to 1/2in.sq. for a double sized model (four times the cross section area). It is not possible to give hard and fast rules in relation to enlarged structural sizes, experience is the best guide in this respect.

Having sat down and listed a few prototypes suited to this 'twin scale' treatment I started to draw-up a couple of models. The enlargement factor I decided upon was 133% i.e. one third larger and one of the first models to be worked upon was the pull-out plan for this issue, the ULTIMATE. Selection of wood sizes is critical if the enlarged version of the plan is to be comprehensible. For instance, 1/4in multiplied by 133% gives a thickness of 1/3in and I don't know any balsawood suppliers who market this thickness! On the other hand, 3/32 becomes 1/8 and 3/16 to 1/4 in. So, with a little care, it is possible to have sizes and strengths that make sense for both the smaller and larger versions.

Of course, there may be one or two slight discrepancies such as 1/16in sheet on the smaller version also being 1/16in on the larger model, or increasing to 3/32in. However the difference on the drawing is no more than the thickness of a line and is unlikely to present any real problem. You may have to make adjustments for engine bearer spacings, or engine mounts, fuel tank locations and the servos on the enlarged drawing may automatically look like giant types, but these are obvious differences and easily corrected.

Plywood is most commonly made, in Europe at least, in mm dimensions rather than imperial measurement. When you are sold a piece of 1/16in plywood it is most likely to be 1.5mm thick and 1/32in will be 0.8mm thick. For 1/8in plywood there is the choice of 3mm (undersize) or 4mm (overthick). This is an advantage for our purposes as the smaller model can have 3mm ply and the larger one 4mm, exactly a 133% enlargement.

Enlargements up to 150% can theoretically be made of the pull-out plans, while still keeping within the 33ins maximum width, but do remember that, at this stage, it is not automatically sound to halve again the component sizes. It may not result in a structurally sound model. The scale designs to be featured in RCSA have been designed to allow for structural integrity in both sizes. For the construction and flying instructions you also have 'two for the price of one'. My original notes are augmented by those of Jeff Barringer, who built the 36ins versions and liaised closely with Bert Smith, the builder of the enlarged (49 in) version.

THE MODELS Are you a masochist, or just an adrenaline seeker? Do you eat little boys for breakfast, or only have a third Shredded Wheat? Depending on your degree of machismo, so will depend on your selection of engine and aileron configuration. At the top of the macho league and you will be looking to fit a '40', or even a '45', but remember that your flight time will be restricted with a 4ozs tank and the tap wide open. Build the model light and you will be able to do some neat and enjoyable aerobatic sequences with an OS 26 four-stroke, it is a bit like deciding whether you preferred the Rothmans Aerobatic team best with Pitts Specials or Stampes.

Unless you want a roll rate faster than you can say 'Ultimate' you can confine the ailerons to the lower wing only. If you decide to go for the full-house aileron set I would suggest linking the top ailerons to the bottom ones with threaded pushrods, a 'Z' bend into one aileron horn and a clevis at the opposite end. OK, already hyped-up, let's get building.

Wings: Two sets, same planform and no dihedral makes this an easy task. Built directly over the plan, the only variations are at the centre section, the lower wing has the aileron servo mount and aileron actuation horns (plus wing fixing dowels) the upper wing has the screw mount fittings for the centre cabane.

Wing struts: Deciding upon a suitable method for fixing interplane struts is never easy and if you want to use your own favourite method you are welcome to go along that route. With the system proposed on the drawings you will have to form your own captive nuts by soldering a standard nut (8ba or 2mm) to a thin strip of brass. These, in turn, are pinned and epoxied to the inside of the lower and upper strut frames. When the frames are complete and sheeted the edges are rounded off. If you are unable to find 8ba bolts long enough (1-1/2in and 1-3/8in) you can use the end of a cycle spoke, with nipple soldered to the plain end, or threaded rod.

Tail surfaces: Yes, you must keep the rear end light if you want to avoid adding nasty lumps or lead in the cowling area. Use medium grade balsa for the tailsurfaces, but select a tough (stringy) wood rather than a 'carrotty' type that will sand easily. The tailsurfaces are straightforward, the elevators and rudder are not tapered, all edges are rounded. Note that the front and rear members of the fin extend into the top decking of the fuselage... "

From R/C Scale Aircraft, June 1994.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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