Velocity

2013

NovAtel's Annual Journal of GNSS Technology Solutions and Innovation

Issue link: http://velocitymagazine.epubxp.com/i/164724

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Little Bird ed upwards, and a minimum of 10 feet lateral clearance between the main rotor blades and the closest ship structure. A careful survey of the helipad yielded a zone of approximately five feet fore and aft in which the safety pilot could allow the H-6U to land and insure safe structural clearance. Simple but highly effective markers were installed to create a visual cue environment that could enhance the flight crew's judgment regarding a safe landing zone. The proximity of the helicopter rotors to the yacht structure, while fairly tight compared to dimensions generally found on DoD vessels, is common in the super yacht world. Landing 10' over the pad On the pad Longitudinal (ft) Lateral (ft) Longitudinal (ft) Lateral (ft) 1 0.5 Aft 0.1 Right 1.5 Fwd 0.1 Right 2 1.2 Aft 0.7 Right 0.5 Aft 0.8 Right 3 1.0 Aft 0.2 Right 0.3 Fwd 0.6 Left 4 0.7 Fwd 0.1 Left 2.6 Fwd 0.1 Left 5 0.2 Fwd 0.5 Left 0.5 Fwd 0.3 Right 6 1.0 Fwd 0.4 Right 1.5 Fwd 0.7 Left GNSS/INS receivers on board the Allure Shadow logged raw inertial and GNSS data in order to be able to post-process the ship and helicopter conventional RTK trajectories. In post-processing data collected at the National Geodetic Survey's continuously operating reference station (CORS) "LAUD" located near Fort Lauderdale about 25 kilometres from the test area. Post-processing of the CORS data with the shipboard and helicopter GNSS/INS data used the Inertial Explorer® post-processing software from NovAtel's Waypoint® Products Group. The accuracy of each post-processed trajectory was about three centimetres. For performance analysis, the real-time ship-to-helicopter relative position vector was compared to the post-processed ship-to-helicopter relative position vector. The true test of the system's performance, however, came in the real-time testing as demonstrated in several successful autonomous landings. Tests were undertaken on July 4 and 5, 2012, at sea off the coast from Fort Lauderdale, Florida. Table 1: Ship landing guidance and control errors 18 velocity 2013 Test Setup and DescriptioN The ULB team used survey instruments to measure the lever arms (offset vector from the IMU to the GNSS antenna) and point-of-interest offset vectors while the ship was docked. During the survey, it was exceptional windy, leading to ship motion and lower accuracy lever-arm determinations than desired. The H-6U was equipped with the primary antenna on the "T" tail and a secondary antenna on the nose. A laser micrometer mounted on the belly center would measure absolute displacement of the belly above the heli-deck on initial touchdown and the final height after the landing gear had settled. Data links transmitted differential correction data between the ship and the helicopter and also transmitted the real-time relative ship-to-helicopter solution, output in the log RELINSPVA, back to the "command center" via radio link. The Test Results from July 4 For most of the morning, the aircraft performed maneuvers behind the boat, following its movement. Although a sea state of 3 or 4 (wave height between 0.5 and 2.5 metres) would have been preferred during the trials, the water surface was essentially flat, sea state 0. The H-6U was also allowed to approach the landing pad and hover over the landing point to provide a sufficient confidence level that the system was functioning as expected. The aircraft then performed a single automated landing before returning to the airport for fuel. Figure 1 shows the trajectories of the boat (green) and the aircraft (red) during these operations. The aircraft autonomously landed on the helipad at GPS time 316350–316772 seconds. The GNSS/ INS system on the helicopter reported a real-time relative position to the helipad center of 0.024m North, -0.028m East, and 1.09m Up. The helicopter belly height measured was approximately 64 centimetres; so, the real-time results seem to have about 40 centimetres of vertical error, which matches the For more Solutions visit http:/ /www.novatel.com

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