Two (oz9966)

About this Plan

Two. Open Rubber competition model.

Scan from DBHL, cleanup by theshadow.

ref DBHL-7650.

Direct submission to Outerzone.

Update 13/6/2023: Added article, thanks to RFJ.

Quote: "Two. George Sharp's medium-sized Open Rubber design

George Sharp has being flying Contest Free Flight for more years than he cares to remember. Since the early '60s he has flown most classes of Rubber and has even been known to indulge in Glider. Currently he flys Coupe, Vintage and Open Rubber with the emphasis on the latter. The design shown here is his preference for the 'basic' contest flights and even very windy flyoffs. The design is well developed and even incorporates some modern materials. It is simple to build and fly and would make an ideal first serious contest model - and its name? - one step up!

The origin of this model dates back to the mid 1960s following my release from the RAF. I needed a straightforward model of adequate strength to withstand the rough and tumble of flights during a typical British day and also to have sufficient performance to stand a reason-able chance in any flyoff. The first model had a wing of 200 square inches but it was not long before it was usually beaten in flyoffs by larger models with inherent performance advantages as well as being more visually discernible at longer distances.

The next development was to increase the wing size to 250 square inches using a slightly fatter fuselage with a larger propeller and more rubber - up from 60 grams to 100 grams. Robustness was adequately maintained, the performance enhanced and flyoff successes were increased. However, the early 1980s saw modellers increasingly using 300 square inches plus wing models and my models became uncompetitive. At this juncture I decided on a new strategy of flying small robust models during the 'elimination' flights and using lightly built 300-320 square inch wing model for flyoffs - successes became more frequent.

During the late 1980s I started to use Tomy timers on my smaller models so enabling stricter control over distances travelled on elimination flights, thereby (hopefully!) cutting down retrieval times -remember that electronic tracking devices were then not generally used. At about this time Dave Hipperson started to use VIT and auto-rudder on his small rubber models and I followed suit. This move led to greater consistency and performance from the model enabling it to be flown in very windy conditions but the traditional wing construction was a little on the weak side and prone to damage in such conditions, particularly when the model was blown over on to its

back on landing. However, new materials, such as carbon and Kevlar, later became universally available and I introduced a carbon fibre spar to the model in the early 1990s which reduced the potential for damage. The model has remained basically unaltered since apart from a tapered high aspect ratio wing version with the Benedek 7406F section which has enhanced performance.

The square wing version published here has proven to be consistent and durable and should make an ideal first competition model for any reasonably competent modeller who has built a few of the more basic designs. The model can be trimmed without the VIT and auto-rudder but performance and consistency will be lost.

Fuselage: Commence the construction of the fuselage by laying out the plan of the basic fuselage side over a building board. I use a deal board but chipboard will do fine. Rub a dry bar of soap or candle over the plan where glue joints are to be made. Select straight grained wood for the longerons which will probably need to be spliced to increase their length over the usual standard length available. Pin the longerons for the first side to the board. I prefer to push dress pins through the wood keeping straight lines straight when carrying out this operation by offering the longerons up against a metal or similar straight edge. Cut and glue all straight spacers (diagonals are added later) in place together with the wider inserts at the nose and rubber anchorage positions. For all joints I prefer to use PVA glue of the water resistant type.

When you are satisfied that the glue has set on the first side, remove all pins and again using a metal straight edge for alignment, secure the second two longerons over the top of the first by pushing pins right through into the building board. When dry remove all pins and carefully separate sides from board and each other using a knife as necessary and thoroughly sand smooth both sides of each, using a sanding block and fine glass paper.

The next stage is to join both sides together. Pin the sides upright (90° to the building board) over the basic plan and ensure that the sides remain upright at all times. Only pin the sides over that portion of the fuselage where the sides are parallel and add spacers top and bottom. When thoroughly dry pull the sides together at the nose and add spacers ensuring that the taper is even on both sides and conforms to the plan outline. Next pull the sides together at the rear end of fuselage again ensuring that the sides follow the plan outline. You might find it easier, in order to accurately preserve the outline, to add one or two pairs of spacers at the motor anchorage point and at the tailplane leading edge position before sticking the extreme rear end together..."

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