Hargrave box kite
replica by Andrea Casalboni
To begin with we must build the main kite structure which is
composed of 2 longitudinal longherons and the 4 cross-spars. We start with
the 2 rods of dimensions 28x28x2440 mm which are the 2 main longitudinal
longherons. The central part of these 2 spars must be rounded off, while
at about 30 cm from each of their respective ends, they must be thinned in
height. At a distance of 42 cm from the ends we must create 2 lock slot of
roughly 35mm and with a slope of approx. 60 degrees. The ends of the cross
spars will be required to fit into these lock slot.
Next we proceed to the construction of the structure through which the binding ropes pass. For this we use the 30x28x120 mm beech rods. These rods must be shaped so as to create a cavity which will support at least twice the amount of binding rope. In addition it becomes necessary to use the 10x10x120 mm beech rods which will function as a support for the cross spars. All these parts are to be rounded toward their ends so as not to have any sharp corners which might otherwise cut the binding ropes. The binding is actually performed after the various parts are glued together. For the binding we use hemp of approx 1mm diameter. We suggest that the hemp be immersed in water prior to being used so as to prevent a lengthening once the final structure is constructed. When this binding becomes dry we can place a layer of vinyl glue on top to bind the whole structure.
Construction of the wing ribs. These
wing ribs must be assume a curved shape. To realize this wing ribs is
necessary to create a forming die (stamp) for ensuring that an equal
curvature results in all the sticks. This structure may be simply
constructed using a board (plank) 20-30 cm long and roughly 90 cm in
length. At the centre of this board, and perpendicular to it, we fix a rod
of 28mm thickness and 10mm width. This rod will determine the exact height
of arc described by the rods. In order to maintain the wing profile sticks
curved, it is necessary to overlay 3 layer of rods of dimensions
4x12x840mm glued together by means of vinyl glue. The packet of rods is
placed on the structure, the crossing previously fixed being placed
exactly in the middle of the sticks after which the ends of the sticks are
fixed to the table by means of clamps. In this way we curve the sticks and
once the glue has dried we shall have achieved an arc which is precise and
stable with respect to time.
Forming die for the curvature of the wing ribs
Construction of the cross spars. These sticks are composed of 3 parts
for each cross member: the main stick of 1500mm length, and the other 2 of
748 mm length. The main stick additionally supports the 2 support blocks
of the secondary sticks.
All the sticks are to be tapered from 55mm from the centre up to 35 mm
from one ends. Additionally, they must be shaped so as to create a
load-bearing profile with flat underside and curved upper side. To the
main stick are attached the two 30x55x135mm fir rods which must first be
cut to 60 degrees on the side on which the secondary sticks touch upon the
primary. Even these blocks must be profiled and fixed , by means of
binding, to the median part of the primary stick in order that the all of
the resulting sticks form 4 equilateral triangles. One end of the main
stick is inserted in the groove which was cut into the main longitudinal
longheron, like a secondary stick. Meanwhile, at the other two ends,
toward the perimeter of the box, are to be attached the two 10x20x60mm
beech rods. These latter rods form a fork which is to be inserted in the
stick that forms the corner/edge of the box. The rods will protrude by 15
mm from the edges of the respective stick and even these will be fixed by
means of bindings.
Construction of the box corners.
Construction of the sail/rig.
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