Payloads - Camera Mountings
In our work, payloads have generally been sensors or dumb cargoes - we have not been involved with munitions and military UAVs so far. The most common payloads we have operated have been cameras, either still or video, both with and without steerable gimbals. Sometimes, these have simply been used to record images to on-board data cards, and sometimes these have been used to echo to radio downlinks. Housing static cameras is in most respects entirely similar to dealing with other avionics items, except for the need to provide a suitable window for lenses to see through - such windows can themselves become complex if they are to deal with poor weather or to be proof against dirt accumulated during flight. Static cameras typically require little more than a power supply and a relatively vibration-free location with a good field of view. We have two approaches to this. The simplest is to use a pusher configuration for the propulsion and to site the camera in the nose of the fuselage (in front of the forward undercarriage leg if fitted). Here it has an unobstructed field of view and is well away from likely sources of dirt that might otherwise foul the lens (as in the SULSA aircraft, see Figure 4.11). Alternatively, we fit an under-slung and removable payload pod placed between twin tractor engines (as in the SPOTTER aircraft, see Figure 4.12).
Figure 4.11 SULSA forward-looking video camera.
Figure 4.12 SPOTTER payload pods with fixed aperture for video camera (a) and downward and side ways cameras (b and c).
Figure 4.13 Simple two axis gimbal system and Hero2 video camera mounted in front of nose wheel.
If a steerable camera (or other sensor) is required, some form of gimbal may have to be included. We have designed and built these ourselves and also fitted those made by others, see Figures 4.13 and 4.14. High-quality systems are readily available commercially but they can be easily as expensive as the rest of the aircraft in total (it is, of course, not at all uncommon for the payload to be as expensive as the rest of the system in all classes of aircraft). Currently, stepper-motor-based systems linked to some means of assessing aircraft position and orientation are generally required if accurate pointing at targets is to be maintained. If the target itself is moving, then some form of image recognition capability will be required to maintain lock on the target and this will generally have to be on the aircraft to avoid the latency and bandwidth issues associated with video downlinks for ground-based image processing. An alternative to mechanically steering the camera is to use wide-angle high-resolution cameras and then use software to isolate the required part of the image as the aircraft and target maneuver. If the target is small or a long way off, then such systems are rarely competitive with high-quality well-stabilized gimbals supporting a powerful zoom-lens-based camera.