Design Report

Task: The challenge was to design, build, and flight test a tube-launched, electric powered, remotely piloted fixed-winged aircraft that can satisfy the mission requirements. Details of the requirements can be found in the project's Request for Proposal (RFP).

The final aircraft design (left) and the aircraft that flew (right)

Important Contributions
Aerodynamic Design
Since the challenge was to tube-launch a fixed-wing aircraft, and the tube size was specified, this directly put constraints on the size of the wings. The wings had to be within span and chord limits that would allow it to fit in the launch tube. Thus, selecting a good airfoil became paramount to the success of our UAV since a good airfoil would give more room for changes in other aspects of the wing design (like span). In order to select the airfoil, I came up with a selection process, depicted in the flowchart, along with certain criteria that can be seen below. Based on this selection process, the Selig S1210 airfoil was selected. Details can be found in the design report.

Criteria for selecting an airfoil and flowchart depicting the airfoil selection process.

Other aspects of the wing design were dictated by tube-size and manufacturing constraints. Details of the 3D wing can be seen here.

XFLR5 & CFD Analysis
During the design and analysis phase it was important to analyze the aerodynamic characteristics of the UAV so other sub-systems, especially controls, could work on their design and use the correct aerodynamic properties of the aircraft. XFLR5 was the primary analysis tool used to determine airfoil/wing performance in conditions that we expected the UAV to fly in. Multiple designs were tested before the final design was selected. Despite the quick, and somewhat reliable lift estimates provided by XFLR5, it did not provide reliable estimates of drag. Therefore, I ran a CFD analysis of the final design simulating flow over different angles of attack in order to determine the necessary aerodynamic coefficients. Once again, I employed macros to increase my productivity. A snapshot of one of the simulations can be seen below.

CFD simulation of final aircraft design with streamlines and pressure distribution over the UAV surface.

Tail Design (Individual Trade Study)
As part of the deliverables for the class was an Individual Trade Study where each student would study the merits and demerits of a possible modification that could improve the final design. Since our tail design was rather clumsy and bulky, I took up the study of trade-off between different tail designs.
The original tail (pictured below) was made of wood and foam and needed a complex folding mechanism for the stabilizers to fit in the launch tube. Instead of this I proposed attaching a boom to mount the stabilizers giving us more room inside the tube to fit the vertical and horizontal stabilizers. A boom also gave us more flexibility with changing the moment arm for the stabilizers without adding too much weight. I plotted the weight vs length of moment arm (that affects the volume coefficient, V_V, in the graphs below) in order to evaluate the designs. From the plots, it's clear that there is a reduction in weight with the new design and therefore the new design was implemented on the final aircraft. Details of the analysis and its impact can be found in this report.

Original tail design (left and top right) and the alternative design evaluated (bottom right)

Vertical stabilizer sizing vs Weight for Original (left) and alternative (right) design for different volume coefficients.

Equations of Motion for launch and constraint diagram
Since the launch section of the flight profile is not common, we could not find the EOMs that would govern the vehicle dynamics in that phase of flight. In order to be confident about our design, we decided to derive the EOMs and calculate the flight profile using MATLAB. I worked with a teammate, Daniel Ellinwood, to derive the EOMs and plot the flight profile that can be seen below. This analysis enabled us to tweak our launch system to give us better ground clearance in the launch phase.
Earlier in the design process I had performed a similar analysis to determine the power loading and wing loading constraints imposed by the launch system.

Estimated flight profile upon launch from tube calculated based on EOMs we derived.

While these were my design contributions to the project, every member of the team was involved in the build phase. Having worked with composite materials before (at Formula SAE), I lead the team's layups of fibre glass on the foam wings. In the build phase I learnt a lot about dealing with other materials, and some of the practical aspects of UAV building that I previously was not aware of. When the UAV took flight, that was the most satisfying moment of my life and reinforced my will to continue working as an engineer and to transform the world.

The first flight test of the UAV where is successfully took flight. Out of the 4 teams in the class, only our team had a successful flight. This was the happiest moment of my life, and is a testament of my desire to be an engineer.

For more details about the UAV and the project please refer to the Design Report.