We are now making significant progress with our bush survey and ground truthing.  However, each step forward has the potential to raise new problems, some obvious, but others requiring a bit of detective work.

A few weeks ago, we went back to our piece of bush near to the North Shore Model Aero Club strip and flew several transects with our vegetation stress camera.  We launched in a 15-20kph wind (as a full-scale pilot I have real difficulty thinking in terms of kph and not knots!) and began the survey, but the aircraft reported wind of up to 30kph.  This caused our transects to be 'bent' - the autopilot attempts to arrive at the waypoint, but in a cross wind, the track becomes significantly curved.  No problem for the aircraft, but the images must overlap significantly for us to use Pix4UAV to synthesise the orthomosaic.

We decided to bring the aircraft back overhead the GCS and commenced a manual approach, using the GCS computer to bring the A/C down in 50ft increments and the hand controller to steer the Hawk.  (Our trainer suggested that manual steering and a lower parachute deployment is a better option than a full auto approach in stronger conditions). In Heading Manual mode, the autopilot maintains airspeed and stabilises the A/C.  It appears that shortly after entering Heading Manual mode, the pilot engaged Partial Control mode.  This allows the pilot to control both roll and pitch, and airspeed.  No problem here - the pilot is an accomplished model aircraft flyer.  At an appropriate height the pilot cut the throttle and deployed the recovery parachute.  The chute deployed properly and the A/C began its descent.  However, close to the ground there was significant turbulence and the A/C began to pitch and roll violently.  It landed safely, but the parachute began to drag, cartwheeling the A/C over the rough ground, breaking the main spar and one elevator, and damaging the vertical stabiliser.  All this can (and has been ) fixed.

When we analysed the images from the vegetation stress camera, we found that we had more images than were recorded in the photo log file.  This is a potential problem, as the images must be geo-referenced for entry into and processing by Pix4UAV.

A quick chat with Dr. Tim Brooks at Skycam revealed something more that we didn't know - when the aircraft is put into Partial Control mode, the camera can continue photographing, but the images are not recorded in the photo log.  Problem solved - just match the photographs to the point in the photo log where the last image was recorded and discard the rest.

Our student, Hins, processed the images and we find that we collected a good set, but that there is a strip down the middle of the bush with no images; the result of the curved transects.  One solution is to enter intermediate waypoints into the flight path to force the A/C to fly straighter transects.

Major lessons learned:  when the aircraft is landing under parachute, the ground team need to get to the touchdown point quickly to secure the aircraft, and when the wind is up around 15 - 20kph and forecast to rise, it's probably better to stay in the UAV Ops HQ and write papers, or if desperate for a flying fix, practice with the flight simulator!