Efficacy of unmanned helicopter in rainwater removal from cherry canopies

Rain-induced fruit cracking causes significant economic loss for fresh market sweet cherry growers annually. To prevent cherry cracking, timely removal of rainwater from fruit is the key. This study evaluated the efficacy of an unmanned middle-size helicopter to remove rainwater from Y-trellised cherry canopies. Helicopter downwash in hover at four altitudes, with and without a payload, was quantified with six anemometers deployed in tree canopies. Results showed that payload and altitude significantly affected hover downwash, which was greater at higher altitude of 7.6 m above ground level (AGL) than lower altitude of 4.9 m AGL with payload. In the absence of payload, hover downwash peaked at the altitude of 6.1 m AGL. In the efficacy study, 5.0-mm rainwater was applied to cherry canopies by a rainfall simulation system, followed by the helicopter flying over canopies at three altitudes (4.9, 5.5 and 6.1 m AGL), two travel speeds (1.3 and 2.7 m s−1) and with or without payload. Rainwater removal at bottom (1.1 m), middle (1.9 m) and top (2.7 m) of the canopies was calculated based on the change of leaf wetness of target canopies in 10 min after rain. Overall, helicopter with payload flying 2.7 m s−1 at 6.1 m AGL removed significantly more rainwater (96.3%) from top section of canopies than groups without treatment (71.2%) and compared to other payload and travel speed conditions. Results also confirmed that the unmanned helicopter could provide sufficient downwash to remove rainwater effectively from bottom and middle canopy sections.