Externally Sourced Components

To hold costs down and to make the best use of economies of scale, we buy in as much of our UAVs in part form as possible. The cost savings achieved by using commercial off-the-shelf (COTS) parts can be prodigious. A good-quality aeromodeler-grade petrol engine will cost a few hundred dollars. A specialist engine from a dedicated UAV manufacturer will cost thousands, while a military-grade engine developed specifically for a particular UAV project may well cost hundreds of thousands by the time development costs have been allowed for. It is thus much more cost effective to limit one’s design choices to make use of what is available off the shelf and can be simply bought in, than to try and customize everything for the aircraft in hand. And by using 3D printing we turn a whole series of custom-designed and aircraft-specific airframe parts into being externally sourced as well: we simply send our part designs as CAD files to external manufacturers with the prerequisite 3D printing facilities and they then ship back the parts we need in the quantities required, see Figure 18.1. This approach to manufacture means that on a typical UAV it is only parts made of hot-wire-cut foam and the prototype wiring looms that we make in-house; all the rest of our airframe manufacture then simply

Small Unmanned Fixed-wing Aircraft Design: A Practical Approach, First Edition. Andrew J. Keane, Andras Sobester and James P. Scanlan.

©2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.

Table 18.1 Typical properties of carbon-fiber-reinforced plastic (CFRP) tubes.

Property

Units

CF fabric

CF unidirectional

Density

g/cm3

1.60

1.60

Young’s modulus 0°

GPa

70

135

Young’s modulus 90°

GPa

70

10

Ultimate tensile strength 0°

MPa

600

1500

Ultimate compression strength 0°

MPa

570

1200

Ultimate tensile Sstrength 90°

MPa

600

50

Ultimate compression strength 90°

MPa

570

250

Poisson’s ratio

0.3

0.3

D SLS nylon parts as supplied from the manufacturer

Figure 18.1 3D SLS nylon parts as supplied from the manufacturer.

becomes an assembly operation with standard hand tools. Even the foam is produced directly from our CAD files using fully digital approaches.

 
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