Author
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Smith, Lowrey |
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Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/27/2003 Publication Date: 3/1/2004 Citation: Smith, L.A. The effect of load and air temperature on aerial application ground speed. Applied Engineering in Agriculture. 20(2):153-156. Interpretive Summary: A common cause of yellow streaks across fields of small grain crops is non-uniform application of fertilizers with high nitrogen content. Such streaks, associated with aerial application, could be the result of an increase in aircraft ground speed as the fertilizer load is depleted. If the fertilizer volume delivery rate from the plane remains constant, the application rate decreases as ground speed increases. A study was conducted to determine the effect of load, air temperature, and flight slope (ascent or descent during application) on aircraft ground speed. Water was used to simulate fertilizer load and the following data were logged at one second intervals during each spray pass: time-of-day, spray time, altitude, ground speed, and boom flowrate. Twenty-seven applications were made using flight protocols designed to minimize the effect of other parameters on ground speed. Data analysis revealed that ground speed of an Air Tractor 402B increased 6.4 km/h (4.0 mile/h) as load was reduced from 8.9 kN (2000 lb) to 1.8 kN (400 lb) for conditions of level flight and constant air temperature. For a specific load and level flight, an increase of 2.8 degrees C (5.0 degrees F) in air-temperature caused ground speed to decrease by approximately 1.3 km/h (0.8 mile/h). At a specific air temperature, load changes had less effect on ground speed when the plane was fully loaded than when nearly empty. A positive flight slope (ascent) of 0.05 m/s (0.15 ft/s) reduced aircraft ground speed by 0.8 km/h (0.5 mile/h) compared to ground speed with level flight. Nominal speed for application is approximately 217 km/h (135 mile/h); therefore, a speed change of 6.4 km/h (4 mile/h) represents a 3 % change in speed. Assuming a constant rate of fertilizer delivery from the aircraft, a 3 % increase in ground speed reduces the application rate by 3 %. A three percent change in nitrogen application rate would be very difficult to detect and would certainly not cause dramatic differences in leaf color in adjacent application passes. Therefore, it is unlikely that speed change due to load change causes sufficient change in application rate to produce yellow streaks across a field. Technical Abstract: Most aerial applicators will agree that a spray plane flies more slowly when fully loaded than when empty with the same engine power and RPM settings. However, the magnitude of this difference has not been well documented and is affected by various environmental factors. A study was performed to determine if the ground speed changes due to load changes were sufficient to have a significant effect on the application rate of granular materials. An Air Tractor 402-B (turbine-powered), equipped with a SATLOC swath guidance system and an AutoCal Automatic Flow-Controller was used to collect the required data. Data logs from the SATLOC system provided height, ground speed, and spray-time data, and AutoCal data files provided flowrate data from each spray run. Test protocols were developed to minimize effects of parameters other than load on ground speed. The plane was loaded with 275 gal of water for each test to simulate the approximate weight of a fertilizer load. Results indicated that ground speed increased approximately 4 mile/h as a load changed from 2000 lb to 400 lb. For a specific load, an increase of 5 degrees F in air temperature reduced ground speed by approximately 0.8 mile/h. The effect of a specified load change on ground speed increased as load was decreased. For a nominal application ground speed of 135 mile/h, these results show that speed change due to load change is approximately three percent. A three percent change in applied nitrogen would be difficult to detect and would not be sufficient to cause color streaks. |
