Dwarf Dip III (oz6709)

About this Plan

Dwarf Dip III. Rubber competiition model. Coupe D'Hiver class.

Quote: "Winner in Coupe d'Hiver events for uncomplicated small rubber-powered models is also a fine sport flyer. Dwarf Dip III, by Charlie Sotich.

THE Coupe d'Hiver event can be a lot of fun while still being a challenge. These models do not have to be extremely complicated to be competitive. The Coupe d'Hiver event is somewhere in between the sport models and the Wakefield class. The sport flyers can use this event as an introduction to competitive flying while the FAI flyers can use it as a fun event to relax with. A two-minute maximum is a lot easier to chase than one of three minutes on a windy day.

The rules for this event are in a sense rather unusual. They limit the performance of the model, but they do not really restrict the design very much. The Coupe models only have to comply with the following rules:

A) Maximum weight of lubricated rubber motor is 10 grams (.35 oz).
B) Minimum airframe weight (including propeller but minus motor) is 70 grams (2.47 oz).
C) Minimum fuselage cross-section area 20 sq centimeters (3.1 sq in).

You will notice there are no restrictions on the wing and stabilizer areas. If you want, you can make a 300 sq in wing or just a 50 sq in wing; you are not restricted. Remember that you only have 10 grams of rubber for power and a minimum total weight of 2.8 ozs. The 10 grams of rubber will not get a 300 sq in model up very high, and a 50 sq-in model weighing 2.8 ozs will not glide too well. In between these extremes, there is a wide latitude of area for experimentation, if you desire. There are no length restrictions, so you can make it as long or short as you want with no extra penalty.

The Dwarf Dip series of Coupe d'Hiver models began in 1962. The basic objective was to get a model that would perform well under most contest conditions. The basic design has proved to be successful and only slight changes have been made to arrive at the present configuration. The size of the model was based on the following reasoning: The weight of the finished model should be no more than what the rules require, since any excess weight will reduce the rate of climb and also hurt the glide.

The wing area should be made as large as the weight will allow, to get the best glide, but still strong enough to fly in the wind and take some abuse. Based on experience with Wakefield models, a wing of 200 sq in would be too heavy if made strong enough. The weights of some small (160 sq in) unlimited rubber models designed to fly with old 50-gram Wakefield motors seemed to be reasonable, so this was picked as the starting point. The wing loading for this size model is very light, just 13/4 oz per 100 sq in. To get the best results from a wing with such a light loading, a very thin cambered airfoil works best. A long tail moment arm and large stabilizer were used to provide stability with a rearward center of gravity location. This allows the plane to fly with less angular difference between the wing and stab and helps improve the performance.

A few notes seem appropriate concerning some of the features of the Dwarf Dip. The diagonal rib construction used in the wing is a bit more trouble to make than the nor-mal parallel rib construction; however, it is well worth any extra time it may require. With the thin airfoil, the diagonal rib structure seems stronger uncovered than a conventional wing frame covered and doped. A good Coupe d'Hiver model is likely to last a few years because of its slow-flying speed, so a structure which resists warping is very desirable. The stab construction with diagonal sliced ribs, provides a very light structure which resists twisting, although it does bow up at the tips.

The fuse for the dethermalizing sys-tem is mounted on the side of the body to make it more easily accessible. When the model is wound and ready to be launched (ROG), the fuse is easier to adjust if it is just behind the wing rather than at the usual tail-end position..."

Hi Steve - Here is Charlie Sotich's Dwarf Dip III from American Aircraft Modeler 1969 Annual.

Direct submission to Outerzone.

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