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Laser Cutting

Although we now almost exclusively use hot-wire-cut foam to make our wings, we have built wings using assemblies of laser-cut plywood components glued together with epoxy resins. These are then covered with thin aero-modeler-grade films, see Figure 18.11. Such wings can be extremely light and stiff, but they are rather time consuming to assemble and require some skill to achieve the best results. The film coverings can also be susceptible to ground-handling

Foam wings after cladding

Figure 18.10 Foam wings after cladding: glass fiber, Mylar, and filled glass fiber.

Table 18.4 Typical properties of glass-fiber-reinforced plastics.

Material

Specific

gravity

Tensile

strength (MPa)

Compressive strength (MPa)

Polyester resin (Not reinforced)

1.28

55

140

Polyester and chopped strand mat laminate 30% E-glass

1.4

100

150

Polyester and woven rovings laminate 45% E-glass

1.6

250

150

Polyester and satin weave cloth laminate 55% E-glass

1.7

300

250

Polyester and continuous rovings laminate 70% E-glass

1.9

800

350

E-Glass epoxy composite

1.99

1770

S-Glass epoxy composite

1.95

2358

The composites have Young’s modulus of 72-85GPa and Poisson’s ratio 0.25.

damage. Laser cutting does, however, guarantee very accurate component sets to start with. Laser cutting can also be easily applied to sheets of acrylic to form lightweight reinforcement patches. Currently we try to restrict the use of such laser-cut parts to avionics base boards, wing ribs at the ends of hot-wire-cut foam parts, servo mountings, and horn reinforcement patches, see Figures 18.12 and 18.13.

Aircraft with wings fabricated from laser-cut plywood covered with aero-modeler film

Figure 18.11 Aircraft with wings fabricated from laser-cut plywood covered with aero-modeler film.

Avionics base board and servo horn reinforcement made from laser cut plywood

Figure 18.12 Avionics base board and servo horn reinforcement made from laser cut plywood.

Foam reinforcement ribs made from laser-cut plywood

Figure 18.13 Foam reinforcement ribs made from laser-cut plywood.

 
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