Characterization of a new ultra-low volume fuselage spray configuration on air force C-130h airplane used for adult mosquito control.
Air forces (Usage)
de Szalay, Ferenc
|Publication:||Name: U.S. Army Medical Department Journal Publisher: U.S. Army Medical Department Center & School Audience: Professional Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2009 U.S. Army Medical Department Center & School ISSN: 1524-0436|
|Issue:||Date: July-Sept, 2009|
|Product:||Product Code: 3721100 Military Aircraft NAICS Code: 336411 Aircraft Manufacturing SIC Code: 3721 Aircraft|
Ultra-low volume (ULV) mosquito spraying has become increasingly technologically advanced since it was first introduced in the 1960s as a replacement to thermal fogging. (1) Examples of technological advancements are new nozzles designs to produce optimal sized droplets and computer modeling of droplet fate under a variety of metrological conditions. These technologies help reduce spray volume and are important tools to minimize the use of pesticide.
Aerial ULV sprays are the primary method used to interrupt insect-borne epidemics. (2-4) For example, the US Air Force (USAF) used airplanes to control mosquito outbreaks after major hurricanes, and other public agencies have used aerial ULV sprays to decrease disease transmission and control nuisance mosquitoes. (5-7) ULV applications have been used outside the United States to interrupt malaria transmission. (8)
A crucial element of ULV technology is the creation of an effective aerosol cloud that will optimize target pest mortality while reducing pesticide use and nontarget species mortality. (9,10) Maximum efficacy is achieved by dispersing uniform droplets of the correct size. For mosquitoes, the optimum droplet size is 1 to 25 [micro]m in diameter as demonstrated by laboratory and small scale ground ULV studies. Aerial sprays probably need to produce larger droplets in order to reach the target. (11-13) However, many aircraft spray systems create a spectrum of droplet sizes between 1 [micro]m and 150 [micro]m. (14) Extremely small droplets may not be lethal and large droplets (>50 [micro]m) can settle out too quickly and are less likely to contact flying mosquitoes. Larger droplets are also wasteful because they contain more toxin than needed to kill the pest. (15) Because of their potentially high deposit peaks close to the aircraft flight line, large droplets also represent a potential hazard to nontarget organisms and thus create unfavorable environmental effects. (16)
The USAF typically uses a modular aerial spray system (MASS) on the C-130H airplane with ULV flat fan nozzles installed under the airplane wing. (17) The wing boom configuration requires pressurized tubing installed along the length of the wing, which results in residual pesticide waste when the equipment is cleaned after spray operations. Furthermore, the tubing is located in the interior of the wing, which makes installation and repairs more difficult. The USAF has recently modified the MASS on the C-130H airplane to use fuselage-mounted spray booms, as shown in Figure 1. The fuselage booms do not require auxiliary equipment for installation and reduce pesticide waste because the pressurized tubing is shorter.
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The fate of droplets released from airplanes is strongly affected by airplane generated turbulence. (18) However, it is not known how airplane vortices affect droplet size and drift when a fuselage boom configuration is used with the C-130H. Effective aerial mosquito control operations also need to predict the drift of the aerosol swath. Although keeping pesticide droplets aloft for a longer time is advantageous to increase the chance that droplets contact the target pest, it also makes it more difficult to predict swath drift patterns. The US Forest Service has developed computer models to predict pesticide drift for agricultural applications (ie, crop dusting). (19) An earlier version, the Forest Service Cramer Barry Grimm model, has been integrated into the Agricultural Dispersal (AGDISP) model which can model the lower volumes and smaller droplets used in ULV mosquito adulticide sprays. (20) Standard parameters for over 173 spray aircraft are available in the AGDISP model's library, including the C-130H airplane with wing booms and flat-fan nozzles. However, parameters for the new fuselage spray boom configuration are not available. Computer model predictions validated by field testing are helpful to estimate the effects of changing parameters (eg, altitude, nozzle type, etc) on droplet dispersal. While the model has been well-validated for large droplet/ low altitude agricultural applications, (21) few field trials have been conducted to confirm its predictive ability for the small droplet/high altitude applications used in ULV mosquito sprays.
This study reports on the characterization of droplet size and drift generated by USAF C-130H aircraft with the newly developed ULV fuselage boom configuration. Droplet size and downwind dispersion were measured using into-the-wind and crosswind field trials, respectively. The resulting droplet size and application parameter data was then input into the AGDISP computer model to compare the model's predictions with the empirical field results.
Study Site Description
The fuselage boom tests were performed from December 2004 to February 2005 on the Avon Park Air Force Range (APAFR), an approximately 42,000 ha facility in Highland and Polk counties, Florida. The field site was chosen to minimize disruption of drifting droplets by vegetation. (22) As shown in Figure 2, site vegetation was dominated by shrubs or open woodlands. Primary roads on the APAFR are aligned along cardinal directions, which facilitated realignment of sampling stations when wind direction changed between test dates.
Field Characterization of Droplet Size
Applications were made by USAF C-130H airplane with fuselage mounted booms containing nozzles that were directed towards the ground. The airplane was equipped with a Satloc GPS [global positioning system] Agricultural Navigation System (Hemisphere GPS, Calgary, Canada) to record airplane position and time when the spray system was turned on. Fuselage boom configurations were tested with flat-fan TeeJet(R) nozzles (Spraying Systems Co, Wheaton, IL) sizes 8001 and 8005, which were rated by the manufacturer to deliver 0.4 liters/min and 1.9 liters/min per nozzle at 216 kPa, respectively.
The airplane flew at 310.4 km/hr and the spray system activated 30 seconds prior to reaching the sampling transect (Figure 2) and was left on until 30 seconds after passing the transect (60 seconds total). Wind speed, direction, air temperature, and humidity were recorded 2.5 m above ground surface using a Swath Kit Weather Station (Droplet Technologies, College Station, PA) and at spray altitude using the airplane's self-contained navigation system.
[FIGURE 2 OMITTED]
The MASS delivered an application rate of 45.3 ml/ha that was based on standard operational practices of public health agencies using a common mosquito control pesticide, Anvil(R) 10+10 (Clarke Mosquito Control Products, Inc, Roselle, IL; hereafter Anvil). We conducted multiple trials in the same location, which would have caused excessive pesticide accumulation. Therefore, our sprays used only the pesticide carrier, BVA spray oil 13 (BVA Inc., Wixom, MI), without the pesticide.
On December 4, 6, and 8, 2004, and February 15, 2005, the airplane flew directly into the prevailing wind (into-the-wind trials) at 46 m above ground. To quantify the droplet spectra, 9 sampling stations were positioned every 61 m along a 488 m transect perpendicular to the prevailing wind (Figure 2). The airplane flew directly over the center station. Slide rotator devices (John Hock Company, Gainesville, FL) held spinning Teflon(R) coated glass microscope slides (25 mm by 15 mm, approximately 420 rpm, effective slide speed of 3.6 m/second) that collected the droplet cloud as it passed over the station. Microscope slides were collected 30 minutes after the airplane passed to allow enough time for airborne droplets to drift through the transect. Droplet data from all stations were pooled to determine the characteristics of the droplet spectra.
In addition to characterizing the droplet size spectra with "into-the-wind" tests, crosswind trials were used to compare actual drift in field trials with predictions by the AGDISP model. On February 16, 2005, we conducted a crosswind trial at a release height of 46 m above ground, which is standard for the USAF mosquito control operations. Although we ran 2 trials, a wind shift during the second trial disrupted the application and the data was lost. Also, we only used the 8005 nozzles for the crosswind trials because 8001 nozzles clogged repeatedly during the into-the-wind trials. On February 11, 2005, 2 trials measured spray drift released at 91 m, which is an altitude proposed for potential nighttime mosquito control operations with the C-130H airplane. In all crosswind trials, droplets were collected with rotating microscope slides at 8 stations arranged along the prevailing wind direction. On February 16, 2005, stations were set 154 m apart (154-1,219 m) on a transect downwind from the release point (Figure 2). On February 11, 2005, we spread the stations 451 m apart (451-3,658 m) along the transect in anticipation of greater drift from the higher release altitude.
All slides were processed within 6 hours after the trial was conducted. Droplets on slides were measured under a compound microscope equipped with a reticule. A total of 100 droplets were measured or the entire slide was scanned, whichever came first. Measured drop diameter was converted to airborne drop diameter with a 0.59 correction factor (Anvil 10+10 Resource guide) that accounted for the spread of droplets when they impacted the glass slide. (23) These data were used to determine volume median diameter (D[V.sub.50]) and droplet density at each sampling station. (24) The D[V.sub.50] represents the droplet size which divides the droplet spectrum in half by volume, or in other words, where 50% of the spray volume is contained in droplets smaller than the D[V.sub.50]. Also of interest are the DV10 and D[V.sub.90] values which are the points in the droplet distribution where 10% and 90% respectively of the spray volume is in drops smaller than this size. (10)
AGDISP Computer Model
Droplet size data obtained from the into-the-wind field trials with 8005 nozzles were input into the AGDISP computer model (version 8.08, USDA Forest Service) to predict crosswind droplet trajectories and deposition. Operational parameters and meteorological conditions recorded during the trials at Avon Park were used as input values for the AGDISP model (Table 1). To allow placement of the spray boom relative to the trailing edge of the wing, the AGDISP model has a library of aircraft (including C-130H with wing booms) and droplet spectra produced by different nozzle types under varying application scenarios. However, the specific parameters of the C-130H fuselage spray system are not included as a standard. Consequently, where possible we used values measured in our field trials (eg, boom placement, nozzle position, application parameters, meteorology, and DV10, DV50, and DV90 droplet sizes) to test the model's accuracy. Predictions for downwind deposition of BVA oil released from spray altitudes of 46 m and 91 m were modeled. Output values regarding droplet deposition and trajectories for droplets sized 22.3, 54.3, and 104.1 [micro]m were plotted. Predictions of droplet trajectories made by AGDISP were then compared to empirical data derived from crosswind field trials.
Flight parameters and meteorological conditions during the trials are given in Table 2. Meteorological conditions were acceptable during the into-the wind and crosswind trials. Humidity and temperature were typical for ULV mosquito control operations. Boom pressure was relatively constant during the into-the-wind trials (621--641 kPa) in December, but was slightly lower during the February trials (472-486 kPa). Wind speeds measured at the ground were within acceptable ranges (1.6 to 6.4 km/hr) during the into-the-wind trials.
Over 7,000 droplets were measured in samples collected during the into-the-wind and crosswind field trials. The 2 nozzle types produced different cumulative volume curves during into-the-wind trials (Figure 3). Average volume median diameter (D[V.sub.50]) was 11.4 [micro]m (SE [+ or -] 1.0) for 8001 flat-fan nozzles and 54.3 [micro]m (SE [+| or -] 2.2) for 8005 nozzles. Droplets from 8001 nozzles produced a narrow range of relatively small droplets: D[V.sub.10] was 1.7 (SE [+ or -] 0.6) [micro]m and D[V.sub.90] was 30.8 [micro]m (SE [+ or -] 1.6). The larger orifices of the 8005 nozzles delivered a wider range of droplet sizes: D[V.sub.10] was 22.3 [micro]m (SE [+ or -] 2.1), and D[V.sub.90] was 104.7 [micro]m (SE [+ or -] 0.6). Thus, the cumulative volume curve of 8005 nozzles generated a lower slope than the 8001 nozzles.
The distribution of drop sizes in spray clouds produced during the into-the-wind trials was also different between the 8001 and 8005 nozzles. The 8001 nozzles produced smaller droplets, with 40% of drops in the smallest class size and 75% were <7 [micro]m (Figure 4). In contrast, 8005 nozzles generated a wide range of size classes with 1.2% of drops <7 [micro]m and 22% of droplets in the 7 to 25 [micro]m size range (Figure 4).
On February 16, 2005, the crosswind trials with a spray release height of 46 m had droplet sizes ranging from 42.5 [micro]m to 10.1 [micro]m (Table 3). The swath drifted much further when the spray was released at 91 m above ground on February 17 (Figure 5). In both crosswind trials the largest droplets were deposited at the first collection station and the mean droplet size decreased downwind.
[FIGURE 3 OMITTED]
AGDISP Computer Model Predictions and Field-Trial Results
Droplet spectra data for 8005 nozzles and meteorological data from into-the-wind field trials were input into the AGDISP model to predict droplet fate (Table 1). The model predicted heavy deposition near the airplane when spraying at 46 m above ground with the fuselage booms (Figure 6). Deposition was predicted to reach a maximum of 13.8 ml/ha at 92 m from the release point and then rapidly dropped to 4.7 ml/ha by 300 m downwind. From this point, deposition gradually decreased to <0.5 ml/ha at the maximum predicted range (1,582 m). Average deposition over 1,582 m was predicted to be 3.5 ml/ha. Between the release point and the standard operational swath width of the C-130H (610 m) the model predicted an average deposition of 6.0 ml/ha.
When release height was increased to 91 m, the predicted deposition was more spread out (Figure 6). Deposition was first predicted at approximately 200 m downwind of the release point, when deposition gradually increased to peak at 3.5 ml/ ha at 770 m. Deposition was predicted to remain within half of the maximum over the remaining model's predictive range.
When we modeled droplets sprayed from the four 8005 nozzles on C-130H fuselage booms, the AGDISP model predicted different trajectories for small (set at 22.3 [micro]m, which is our D[V.sub.10]) medium (54.3 [micro]m, our D[V.sub.50]) and large (104.7 [micro]m, our D[V.sub.90]) droplets and for sprays released at 46 m or 91 m above ground. Overall, AGDISP predictions followed standard ballistics such that smaller droplets released at greater altitudes drifted further than larger droplets released at lower heights. However, the model also predicted droplet trajectories would be affected by airplane vortices. For example, all droplets released on the windward side at 46 m were affected by airplane induced vortices, which first lifted them and then allowed them to drift downwards (Figure 7). In contrast, droplets released on the leeward side of the airplane were entrained in down-ward vortices that pushed them toward the ground until the vortices broke apart or droplets deposited. The model predicted that small droplets (eg, 22.3 [micro]m) remain airborne approximately 450 m downwind of the release point, and most medium droplets (eg, 54.3 [micro]m) reached the ground by 250 m. The large droplets (eg, 104.7 [micro]m) also fit the previous pattern but reached the ground faster (approximately 130 m downwind) than the other size classes (Figure 7).
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When the droplet trajectories were modeled from a release height of 91 m, trajectories were different than when released at 46 m (Figure 8). Overall, an increase in spiraling caused by vortices was predicted in all drop sizes; this was more pronounced in droplets from the windward side of the airplane. Most notable was that small and medium droplets from the leeward side of the airplane were not pushed to the ground, but were brought back in contact with droplets from the windward side and crossed paths with these droplets' trajectories (Figure 8).
These trials characterized droplet spectra and dispersal to evaluate if the USAF C-130H fuselage boom configuration is effective for adult mosquito control operations. Under optimal conditions, aerial spray operations produce droplets that adhere to mosquitoes but do not drift beyond the intended spray area. (25) We found that both flat-fan nozzles (8001, 8005) produced droplets within the optimal range for mosquito control (7 to 25 ^m), but they had very different droplet size distributions.
In general, droplet distributions from flat-fan nozzles show that the largest numbers of drops are found in the smallest size classes while the greatest volume is found in the relatively scarce but larger size classes. (26) In this study, the 8001 nozzles produced a narrow spectrum of smaller droplets, and consequently, the majority of the volume sprayed was comprised of small droplets (ie, D[V.sub.90] = 30.8 [micro]m). Although most droplets were within the most effective size range (7 to 25 ^m), droplets < 7 [micro]m comprised 35% of spray volume. In contrast, 8005 nozzles produced larger drops but a more even size class distribution (Figure 4).
We tested the fuselage boom configuration for its potential usefulness for ULV adult mosquito control with the C-130H airplane. The narrow droplet spectra and ideal D[V.sub.50] of the 8001 nozzles would appear to make these a better choice for mosquito adulticiding. However, these nozzles produce many droplets considered too small for effective mosquito control. In addition, the small orifice size required 5 times more nozzles than 8005s to produce the desired flow-rate, and they often became clogged during field trials. The 8005 nozzles produced relatively large drops which equates to additional chemical waste if they deposit without contacting the target pest. Characterization tests with intermediate nozzle sizes (eg, 8002, 8003) would be useful to further examine the efficacy of fuselage booms for mosquito control.
We used rotating microscope slides to measure droplet sizes for 2 flat-fan nozzles, which is a widely used method to characterize droplet size. (9,27-29) A more precise method to determine droplet size is a wind tunnel equipped with laser-diffraction equipment. Recent wind tunnel studies with 8001 nozzles at wind speeds of 225 km/hr produced a D[V.sub.50] of 55.2 [micro]m, which is nearly 5 times larger than in our study. (30) Volume median diameter for 8005 nozzles at wind speeds of 225 km/hr were 87.7 [micro]m, which were also larger than in our results. However, the Hornby et al (30) data suggests that increased wind shear at faster speeds can create smaller droplets. Since the C-130H airplane flew at 370 km/hr, this might have caused the smaller droplet size we measured with the 8005 nozzles. However, wind shear alone probably cannot account for the very small DV50 that we measured with the 8001 nozzles. A possible explanation is that minute oil droplets from other sources (eg, engine exhaust) were trapped on the microscope slides and were counted as sprayed material. This would be more likely to affect the data from the 8001 nozzles because they made smaller droplets than the 8005 nozzles. Adding florescent dye to the spray material (eg, Barber et al (22)) might help to distinguish between sprayed material and environmental contaminants in future studies. Also, we may have undercounted the largest possible droplets because these would be rare and might have dropped out of the air column before they impacted our sampling stations.
[FIGURE 6 OMITTED]
Making accurate predictions of pesticide droplet dispersal is desirable (19) and, therefore, we compared AGDISP model predictions to our downwind field data. The overall AGDISP predictions and empirical data followed a similar and expected pattern of larger drops falling first and smaller drops drifting further. For example, in crosswind field trials from a 46 m release height, the average droplet size measured at the second collection station (305 m) was ~25 [micro]m (Table 3). In comparison, at 305 m downwind, AGDISP predicted that 22.3 [micro]m droplets would still be airborne but that 54.3 [micro]m droplets would have already reached the ground around 225 m downwind. Taking into consideration the influence that wind speed and direction can have on these small to medium-sized drops, the disparity between the model and the empirical data may be considered reasonably similar at this level of resolution. AGDISP predictions regarding trajectories of large droplets were also fairly closely confirmed by field trials. AGDISP predicted 104.7 [micro]m droplets to reach ground level 130 m downwind (Figure 7), and many droplets of this size were collected at the 150 m collection station, although 104.7 [micro]m droplets from the leeward side are not predicted to reach the ground until 430 m.
However, we found that some AGDISP predictions were different than observed in our field data. For instance, a greater disparity existed between AGDISP predicted trajectories and field data for droplets released from 90 m. The AGDISP model could not predict droplet fate past 400 m, but many droplets were still airborne at this distance. The AGDISP model also predicted further drift than we observed in the crosswind trials. For example, the trajectory path of all modeled droplet sizes from 91 m predicts droplets will still be aloft at approximately 500 m downwind from release. In contrast, we collected many droplets sizes at the 500 m sampling station during the field trials (Figure 5).
[FIGURE 7 OMITTED]
Our comparisons between predicted and empirical data indicate that the AGDISP model is more accurate at assessing the environmental fate of larger droplets and their movement closer to their release points. In general, AGDISP made the most accurate predictions of droplet fate at 46 m release height, but was less accurate for sprays released at 91 m above ground.
Fuselage sprays from 8005 nozzles produced wide pesticide swaths that suggest they would be appropriate for military aerial ULV operations where a minimum 600 m swath width is required. (31) Additional operational evaluations will be necessary to determine effective swath width for C-130H fuselage booms using sentinel mosquito mortality and various pesticides.
A potential reason for inaccuracies in AGDISP models is that the model is unable to use continuous weather data. Obviously, even modest changes in meteorological conditions (eg, wind direction) could have significant effects on droplet fate. Modeling ULV sprays at high altitudes is also difficult because the model does not calculate downwind drift past 3,600 seconds. This is an artifact from the model's origins in depositional spraying (19) and, subsequently, the development of better algorithms that accurately incorporate field conditions would improve the AGDISP model.
In conclusion, the fuselage boom configuration we tested would be desirable for use in military operations because setup and maintenance is simple and it produces less pesticide waste than the wing boom configuration. Our trials suggest that 8001 and 8005 flat-fan nozzles produce a droplet spectra and swath dispersal that would be effective for ULV mosquito control operations. However, we also found that small changes in wind speed and direction substantially affect droplet dispersion and deposition behavior. Therefore, continual monitoring of current meteorological conditions should be an ongoing consideration during ULV mosquito control operations. Increased wind speed and directional variability also make it difficult to predict insecticide dispersal characteristics with the currently available AGDISP modeling software.
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We thank the staff at the Avon Park Range, especially Paul Ebersbach and John Bridges, for their help in the coordination of these activities. Additionally, we extend our thanks to the men and women of the Air Force Spray Flight from the 910 Airlift Wing who participated in this project.
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Maj Mark Breidenbaugh, BSC, USAFR
Maj Karl Haagsma, BSC, USAFR
Ferenc de Szalay, PhD
Maj Breidenbaugh is the Chief Entomologist, Air Force Aerial Spray Unit, 757 Airlift Squadron, 910th Airlift Wing, USAFR, at the Youngstown Air Reserve Station, Vienna, Ohio.
Maj Haagsma is a Research Entomologist, Air Force Aerial Spray Unit, 757 Airlift Squadron, 910th Airlift Wing, USAFR, at the Youngstown Air Reserve Station, Vienna, Ohio.
Mr Latham is the Director, Manatee County Mosquito Control District, Palmetto, Florida.
Dr de Szalay is an Associate Professor, Department of Biological Studies, Kent State University, Kent, Ohio.
Table 1. Parameters entered into the AGDISP model to predict droplet fate from fuselage boom spray applications. Drop size distribution used field collected data. Aircraft Lockheed C-130H airplane, weight 63,047 kg; speed = 371 km/h Release height 46 m, 91 m; flight lines = 1 Nozzles 8, 8005 flat-fan, positioned at 3.61, 3.71, 3.81, 3.91 m from aircraft centerline, both sides Drop size [DV.sub.10] = 22.3 [micro]m; [DV.sub.50] = distribution 54.3 [micro]m; [DV.sub.90] = 104.7 [micro]m Material BVA oil (specific gravity = 0.85; nonvolatile fractions = 1; active = 1; rate = 45.3 ml/ha Swath width 152 m (maximum allowed), Swath displacement = -76 Wind speed 6.4, 7.5 km/hr at 46 m or 91 m above ground level Temperature and 18.3[degrees]C and 70% for 46 m and 17.1 relative humidity [degrees]C and 92% for 91 m Stability day-weak (sunset to 1 hour after sunrise, weak) Canopy none Surface roughness 0.0075 m Table 2. Parameters of the BVA-13 spray-oil field characterization trials of the C-130H airplane ULV fuselage boom configurations. Application Flow Boom Rate Rate Pressure Date of Trial (ml/ha) (L/min) (kPa) 4 Dec 04 * 45.3 8.5 634 6 Dec 04 * 45.3 8.5 641 8 Dec 04 * 45.3 8.5 621 15 Feb 05 * 45.3 8.5 483 16 Feb 05 ([dagger]) 45.3 8.5 486 17 Feb 05 ([dagger]) 45.3 8.5 472 4 Dec 04 * 45.3 8.5 634 Average Wind Nozzle Speed (km/hr), Configuration Date of Trial ground/altitude Size (number) 4 Dec 04 * 3.2/13.7 8005 (8) 6 Dec 04 * 3.2/17.7 8005 (8) 8 Dec 04 * 6.4/12.9 8001 (40) 15 Feb 05 * 1.6/6.4 8001 (40) 16 Feb 05 ([dagger]) 6.4/13.0 8005 (8) 17 Feb 05 ([dagger]) 7.5/12.1 8005 (8) 4 Dec 04 * 3.2/13.7 8005 (8) Temperature Relative Date of Trial Humidity 4 Dec 04 * 16.1[degrees]C 51% 6 Dec 04 * 25.6[degrees]C 59% 8 Dec 04 * 24.4[degrees]C 79% 15 Feb 05 * 20.6[degrees]C 70% 16 Feb 05 ([dagger]) 18.3[degrees]C 70% 17 Feb 05 ([dagger]) 17.1[degrees]C 92% 4 Dec 04 * 16.1[degrees]C 51% * Into-the-wind flight trials ([dagger]) Crosswind flight trials Table 3. Average BVA oil droplet size (pm) collected at stations down-wind of release point, February 16, 2005. C-130H fuselage boom configuration; 8005 nozzles; crosswind--6.4 km/hr; release height--46 m. Distance Downwind 154 m 305 m Mean [+ or -] SE 42.5 [+ or -] 2.5 24.9 [+ or -] 2.6 Distance Downwind 457 m 610 m Mean [+ or -] SE 13.9 [+ or -] 2.8 7.8 [+ or -] 0.5 Distance Downwind 762 m 914 m Mean [+ or -] SE 8.4 [+ or -] 1.2 5.7 [+ or -] 0.8 Distance Downwind 1,066 m 1,219 m Mean [+ or -] SE 6.0 [+ or -] 0.3 6.2 [+ or -] 0.4
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