Dryad (oz1766)


Dryad - plan thumbnail image

About this Plan

Dryad. Rubber twin model. 40in span advanced design model flying boat with twin rubber motors. Aeromodeller February 1946.

Quote: "An advanced design for a model flying boat. Dryad, by HE White.

THIS model, portrayed on the front cover this month by C Rupert Moore, is a fairly advanced design both from the technical and practical point of view. It is not a simple structure, either to describe or to build, but a job that should provide a fairly skilled and experienced aeromodeller with something to get his teeth into during the close season for model flying.

It was decided above all to attempt to design a model flying boat of semi-scale appearance, with an airframe which was practical from every model-aerodynamic and structural point of view. The model must be capable of being trimmed and able to Withstand the rough treat-ment which flying models usually experience during trials, and yet it must look as much as possible like a real flying boat without being an actual copy of any existing full-sized machine, because this would seriously limit its flying capabilities.

After some experiments with various types, the 'Catalina' type was decided upon, involving a low hull with good lines, the main plane supported on a central streamlined pylon with bracing struts. The twin motors are carried outboard on the wings and the tail-plane is mounted high up on the fin. The nacelles carrying the motors are built into the wings and not suspended below them. Three-bladed propellers are used in order to reduce the height of the wings as far as possible, without sacrificing the advantage of using large airscrews with rubber motors.

The Hull. Begin as if you were making a simple slab-sided fuselage, building up the two sides, one on top of the other, on the drawing board. Now make up the two 'basic' formers and cement them in position with the two sides. Make sure the alignment is correct by resting the assembly upside-down on a flat board.

Next, insert the cross-pieces in the top of the hull and carefully join the sides at bow and stern. Nov turn the hull upside down again and insert the forward keel and the central stringer aft of the step. At the various former positions, build in the pairs of struts forming the triangular keel supports both fore and aft of the steps, finally completing each former by cementing in place the two halves of each bottom strut. This part of the assembly needs great care and continual watch must be kept to see that the lines and symmetry of the hull are kept perfect.

Now cut out the stringer-formers which support the side and deck stringers, and cement them in place. Follow up with the stringers, still keeping careful watch on the general alignment, and firmly cement the rails in place which support the bracing struts. If this somewhat tedious job is done carefully it is possible to make a very strong and rigid hull frame. Build up the struts, formers, etc., which make up the central pylon, and build in the details of the tail emplacement.

We are now ready for the 'sheet-work.' Most of the sheet used in this model has been salvaged from superannuated pre-war models, and is about .025 in thick. The larger pieces, however, were produced by carefully sanding 1/16 in soft sheet until the required thickness was attained. Cut paper patterns of the two pieces for the forward hull-bottom by offering up stiff paper to the hull, marking out with pencil, and cutting out, making a final careful test to see that the patterns fit exactly at the keel. Overlapping a little at the outer edge will not matter as this can be trimmed off.

Cover the portion of the hull aft of the step as shown, and then start on the pylon. The forward semi-circular section is easy to cover, and the after section, although it involves a compound curve, can be covered with two separate pieces only, one each side, if the grain is suitably chosen and warm fingers judiciously applied whilst the cement is setting.

Wings. Make tracings of the wings in the usual way, drawing in the position of the nacelles. Cut out the ribs and build up the basic wing-structures with the ribs and spars. Note that there is no leading-edge spar, and that the trailing edge may be built up, using 1/8 by 1/32 in strips. This is much better than using a bent V-section spar. Note also that rib No.1 is placed at an angle to suit the dihedral, and that rib No.4a is only inserted temporarily, for reasons which will appear later..."

Update 09/11/2018: Added article, thanks to RFJ.

Supplementary file notes



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