AP 13 (oz16626)

About this Plan

AP-13. Free flight towline glider model. Wingspan 2.6m.

First published in L'Aquilone #40, 1938.

Quote (google-translated): "The A. P. 13 glider model airplane, including the construction table with details of each individual piece, is on sale at Editoriale Aeronautica for 12 lire. It is a model specifically designed for competitions and because it is capable of high flight characteristics. In the study of its aerodynamic shapes, all the measures aimed at ensuring, above all, a low sink velocity and high stability with respect to all the assemblies were taken into account. In the construction, however, an attempt was made to simplify the individual pieces and their connections as much as possible, in order to make this superior model accessible even to builders of medium capacity. We also sought to achieve maximum overall robustness, because only a model that can safely withstand the inevitable abnormal stresses of initial launches can provide the builder with the necessary information for proper setup, which will lead to the achievement of the best flight characteristics.

The wing, with a considerable span (2.60 meters) has, despite its excellent aspect ratio, a large surface area. This not only reduces the wing load for a given total weight, with a notable advantage in sink rate, but above all, allows the chord to remain unchanged. Where the length of the ribs, below a limit, the behavior of the airfoils is more similar to that of a flat sheet, aerodynamically inefficient, than that of the best gliding airfoils. The profile itself, adopted in the A.P. 13, is highly efficient, being highly curved but very well-formed and with a thickness well-proportioned to the length. It is the C.1 profile, developed by the designer according to equations given by the German scholar Cupper, and proven very advantageous through long practice.

The rectangular planform of much of the wing allows many ribs to be kept equal, simply reducing the work. Toward the ends, after the elbow, the wing tapers and carries a kind of adjustable aileron on the rear section. This has the dual purpose of ensuring, during tests, the absolute aerodynamic symmetry of the two wings and therefore, at will, straight or curved flight, and at the same time giving this part of the wing a profile with a raised trailing edge, which allows for a better distribution of lift according to the span and therefore greater aerodynamic efficiency.

The wing has a central spar made of 3 mm solid plywood, of quick construction, on which the ribs are inserted. and a small front spar that facilitates the connection to the fuselage and contributes to the robustness of the wing. With this type of spar-rib connection, the rib protrudes from the edge of the spar itself, on which the covering paper is not glued. The covering operation is therefore a bit delicate on the bridge, but in this way the paper is stretched only between the spar and the rib and the spar does not mark the outside, which it rigorously preserves with a non-negligible aerodynamic advantage in a racing model. The wings are attached to the fuselage with bayonet couplings.

The rather long fuselage (about 1.30 meters) not only maintains good penetration throughout, but is also designed to fully connect to the wings and empennage. It is also quite long at the front, to allow for proper centering at the front third of the wing chord with a small addition of weight, and therefore without exceeding the minimum load limits. However, drift stability is ensured by the special empennage, which is of an original and very efficient design.

The empennage consists of two V-shaped rudders, which simultaneously act as stabilizers and fins. Being large in surface area, they have sufficient vertical and horizontal projection to ensure their dual function. Symmetrical in profile, they also have an adjustable section on the trailing edge to allow for any maneuver. The rudders are thus fully connected to the fuselage and well connected to the connections.

The entire wing-fuselage-rudder connection was also designed to maximize the aerodynamic flow. This flow, drawn rearward by the V of the wing, flows over the back of the fuselage and escapes the rudders, providing a significant stabilizing effect. The V-rudder is also effective during tow climbs, which generally occur at high angles of attack, because no active parts are thus masked.

The fuselage, with plywood or poplar veneer frames, features 12 sturdy basswood strips lengthwise and is also covered in thin waxed paper. We recall in this regard how, during the competitions in Bern, our model airplane enthusiasts had to note that the foreign competitors, the modern ones, were covered with thin fabric. They had a great advantage, especially in rainy weather. The A.P. glider model airplane 13, due to its simple and sturdy construction, is particularly suitable for covering experiments with sturdy, highly tensile materials, such as thin fabric (especially silk) suitable for the purpose and varnished with elastomer or another suitable stretcher. For example, a canvas or silk covering can be used for subsequent coverings of the model after the initial tests (taking into account the overall weight). It may be more convenient to do this with ordinary paper.

And now, let's get to work, while the summer holidays and good weather last! Eng. FIDIA PIATTELLI"

Direct submission to Outerzone.

Update 11/3/2026: Added further article from 2015, thanks to Pit.

Supplementary file notes

Article.
Article (2015).

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