Of course, the primary reason for operating a UAV, or indeed any vehicle, is to carry a payload, whether it be cargo, sensors, cameras, and so on. The approach adopted at Southampton has been to try and separate as much as possible the payload from the rest of the airframe design. Moreover, if the payload can be sited near the airframe’s center of mass, it is then possible to swap payloads of varying weight without significant impact on the UAV. In our work, payloads have typically been cameras, often attached to dedicated radio downlink systems, but we have also carried flight-launchable maritime autonomous underwater vehicles (AUVs) for example, see Figure 2.11. From the airframe perspective, what is supplied is a structural mounting point together with (typically) 12 V electrical power supplies. Payload masses are usually around 10-25% of the take-off weight. Electrical powers of up to 150 W are readily available if generators supported by internal combustion engine are fitted, typically attached to the main engines. Greater power levels can be provided either by dedicated generators or by loading the main engine more heavily, but this can compromise take-off performance.