Since the previous update, it has been confirmed that the project objective will be a proof of concept scale model (1:10 factor) of the mechanical spray system for an AT-502B crop duster. The major constraints of this project will mostly be dependent on the device's compatibility to the AT-502B, which was chosen due to its popularity in the industry. Table 1 provides a list of these constraints. The first constraint is the maximum boom width, which is limited to 75% of the aircraft’s wingspan per EPA regulations. Additionally, the device will be constrained by the aircraft’s ground clearance height, in which the device’s retracted height should be half of this value so that it does not interfere with landing and takeoff. Figure 1 provides an illustration of the constraints on the aircraft. The aircraft’s wings have 6 points of attachment for the current boom hanger system, which will need to be utilized by the new device. The device must also comply with the given goals of the project, which include lowering the system 6”, moving the system forward 3.6” and having 15° of rotating freedom along the rolling axis (scaled values). The device will need to be operable at the plane’s speed of 160 mph as well.
These physical constraints present several challenges. The limited retracted height of the device is four times smaller than the desired lowering height, implying that the system will need to move a significant distance. The current spray system consists of rigid pipes (see Figure 2), which may not be a possible option at certain points in the new system due to the amount of motion needed. The wings of the aircraft have 6 attachment points for boom hangers (3 on each wing), which may provide challenges for designing the adjustable roll angle as this movement will result in uneven distances between the boom and the wings at different points of attachment. The operating speed also presents drag forces on the system which will need to be considered since with moving parts the possible points of failure increases.
Table 1. Major Project Constraints
Figure 1. Constraints labeled on AT-502B [2]
Figure 2. Current spray system of AT-502B [3]
The values for the goal of moving the mechanical spray system were derived from previous studies and improved. However, fluid dynamics analysis will need to be completed to determine the range of turbulent flow around the aircraft’s body and wings, allowing for confirmation of the validity of the mechanical system’s repositioning location. As a reminder the intention of the mechanical spray system is to move the boom away from the turbulent flow to reduce potential drift. Should this analysis determine that the location contradicts the goal or is excessive, a better location can be chosen prior to design.
Another technical analysis that would need to be completed is control system analysis for the self-adjusting roll angle of the spray system. This system will consist of two altitude sensors, one on each end of the boom, and a controller to adjust the angle and until values are equalized. This analysis would be used to ensure stable transitioning as the controller and motors adjust the angle of the boom to prevent disturbances in the spray pattern.
To address the drag from the flight of the aircraft, a finite element analysis will be done on the mechanical spray system. The load for this analysis will be the drag force on the system, applied perpendicular to the system’s front face to replicate the aircraft traveling parallel to the ground and the spray system while it is working. The load value will be calculated using the drag equation [1], and the expected outcomes of the analysis are deformation/failure at critical points such as where the device attaches to the wings and moving components of the device. This will allow for review of the components under the most stress and revisions to the design as necessary.
All original analyses will be done at a full scale level (AT-502B dimensions). Dimensional analysis will be completed in order to determine the values of velocity and loads at the 1:10 scale size. The analyses will be redone in order to verify that the two systems are equivalent and that dimensional analysis was done correctly.
A soft issue to consider is the fabrication of the spray system at a scaled size. The current spray booms have 2” pipe connections with ¼” NPT nozzle connections and reduction to 1:10 ratio will result in an inoperable spray system. To address this issue, the nozzle may have to be designed into the boom for the scaled device. The rigidity of the original spray system will also be another issue to consider, as certain parts will require movement. Rotatable joints or hose lines may have to be considered at the location of motion, but components that do not require motion may be left rigid. For these issues, success will be measured by the functionality of the systems, as it is required for the spray system to spray liquid and the device to reposition without leakage. Replicating the aircraft and fitting all functioning components (motors, microcontroller, batteries, other electronics, hopper tank) will also be another soft challenge. Although this does not fall within the scope of the design of the mechanical spray system, it is required for the validation. All of the components must be functional and fit inside the aircraft to avoid altering airflow around the plane and prevent inaccurate results during validation.
Citations:
Glenn Research Center, The Drag Equation, NASA. Available at: https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/drageq.html#:~:text=The%20drag%20equation%20states%20that,times%20the%20reference%20area%20A.&text=For%20given%20air%20conditions%2C%20shape,for%20Cd%20to%20determine%20drag. (Accessed: 15 September 2023).
AT-502B – Agriculture Aircraft (2021) Air Tractor. Available at: https://airtractor.com/aircraft/at-502b/ (Accessed: 29 September 2023).
AT 502 Spray System, Zanoni Equipamentos. Available: https://www.zanoniequipamentos.com.br/en/product/at-502-spray-system. [Accessed: 29-Sep-2023].
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