Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

22 Autumn 2015 | Unmanned Systems Technology Delair DT18 specification Delair DT18 Fixed-wing unmanned aerial system Wingspan: 1774 mm Length: 110 cm Motor: brushless dc electric with electronic speed controller Propeller: twin blade Airframe: composite structure Landing gear: none Maximum gross take-off weight: 2 kg/2.3 kg where unregulated Standard payload: still imaging camera with fixed focal-length lens Comms links: 2.4 GHz, 868/900 MHz and 3G/4G The DT18 has a 1774 mm wingspan and is 110 cm long with a maximum fuselage height of 10 cm. Normally taking off at an all-up weight of less than 2 kg, its airframe consists of a fuselage with a front-mounted motor and propeller, and a payload bay just behind plus wing assembly and vee- tail. There are four flight control flaps on the wing plus two on the tail. The fuselage contains only one bulkhead, a wooden one right at the front, ahead of the motor. The fuselage is in two parts, having eight screws attaching the lower payload bay. The main fuselage section is made in two halves that are permanently bonded together. It is internally accessed by removing the payload bay and, if necessary, by removing the motor/propeller, which fill a tubular aperture in the front of it. The composite fuselage halves are each formed in an aluminium female mould. The mould is waxed to assist subsequent removal of the item, then paint is applied to form the final outer surface. Within that, layers of composite material are laid up. Fabrics of glass rather than carbon fibres are mostly used, and these are impregnated with resin, again by hand (pre-preg skins are not used). In some places either carbon or Kevlar fibres are used for reinforcement. In places, foam is also used to form a layer in the resin matrix, particularly in the wing. When the fabric and foam have been soaked with resin, the mould and its contents are placed in a vacuum bag. Pumping air from that sealed bag removes unnecessary resin and consolidates the composite. Curing takes place at room temperature. The partly hollow wing is created as two equal halves, left and right, allowing the thin lithium-polymer battery to be slotted inside it, spanning the two sides. When seen in cross-section, the battery is sandwiched between a pair of longitudinal dowels, the leading one of larger diameter than the trailing one. Like the battery, those dowels link the two sides. The wing-battery assembly is then attached to the fuselage as one piece, with two screws running from each half of the wing down into it. The wing has a pair of servo- operated control flaps on each side of the craft. Where the wing is mounted to the top of the fuselage there are three electrical connectors. One of those is for the battery, and it connects directly via an aperture in the underside of the wing, while the others are for the flap servos and a pitot tube. The servos are high- quality 5 V PWM-control items, which are water-resistant. Each side of the wing is made in upper and lower halves, which are permanently bonded once three longitudinal wooden spars have been put in place. One of these is at the inner abutment to the other half and consequently has apertures to allow the dowels and its half of the battery to insert in through it. The other, outer spars flank the battery compartment. The lay-up of the composite wing, which in places is reinforced with carbon fibre, allows the control surfaces to be cut and scored, such that the skin forms the necessary hinge. The mostly enclosed servo mechanism and the associated wiring are inserted before the upper and lower halves are permanently bonded, as is the pitot tube extending from the right-hand side. Anatomy of the Delair-Tech DT18 Components of the DT18