30 in drops from progressively greater heights, first from a 50 m crane and then from a SwissDrone helicopter UAV in cooperation with the German Aerospace Centre, DLR. Afterwards, the box and release mechanism needed to ensure they would work together at speed. The Dutch Ministry of Defence helped here, by providing access to testing facilities with airfields and trucks, and with the development of the cargo bay and release mechanism. In one set of tests, a truck carried a container modified with a rig from which boxes could be dropped from a height of 4 m and at truck speeds of up to 90 kph. The rig supported a prototype of the box carrier and its release mechanism. The main focus of these tests was to discover whether the boxes would fall free of the release mechanism cleanly and that the air brakes would always deploy reliably when suddenly exposed to the airflow. To achieve this, the box was fitted with a fifth flap on the lid, which creates a rotation that counteracts the forces when the box is released from the cargo bay. By rotating the box, it allows all the air brakes to deploy and for the box to reliably open and fly to its drop point. Once all the tests had been carried out on the ground and proved that the system works and is safe to fit to an aircraft, airborne testing could begin. The principal vehicle used for this was the optionally piloted Pipistrel Sinus, fitted with cargo pods developed by Wings For Aid and VanBerlo under the wings. The tests revealed that 100 m is a comfortable height for airborne drops, while CFD analysis of the box and trajectory equations proved that 50 m is necessary for the box to reach terminal velocity. That means the box can be dropped from any altitude, although the greater the drop height, the more local wind conditions will affect accuracy. Although the altitude window is quite wide, the team found that the box reaches its terminal velocity of 40-60 kph early in its fall, as predicted by the theory. The box’s predictable behaviour allowed the team to create an algorithm defining the exact moment to release it for an accurate landing. “We can go up to 1 km, or 3000 ft, and the behaviour of the box will still be similar and the contents will be intact,” Koperberg says. Gravity assist During initial testing, the boxes simply fell out of the carrier under gravity when the hatches were opened; for that the box had to weigh at least 10 kg. One issue that arose during ground testing was that the wind pressure on the box would force it to cant forwards before it cleared the carrier, and could hang fast. Each carrier module therefore now incorporates guide rails to keep the box December/January 2021 | Unmanned Systems Technology While a 20 TEU container is the long-distance transport option, the MiniFreighter’s local mobility is provided by this combination of van, ground control system and trailer (Courtesy of Wings For Aid) Amazilia provides the dedicated ground control station, integrating the computers, radio transceivers and antenna interfaces into a rugged transport case (Courtesy of Wings For Aid)