1. Introduction

This project involved the design, manufacture and flight testing of a 1.8 m wingspan fixed-wing Unmanned Aerial Vehicle (UAV), developed as a second-year MEng group design project. Starting with only an empty fuselage and tail assembly, the team was tasked with developing the aircraft’s wing, avionics system and flight control architecture from the ground up. The objective was to create a lightweight, reliable and aerodynamically efficient aircraft capable of stable flight while satisfying strict constraints on size, weight and manufacturability.

My primary responsibility was the mechanical design and CAD of the wing, translating the team’s aerodynamic and structural parameters into a manufacturable model. I also performed the aircraft’s static stability analysis and designed the slotted flap deployment mechanism. During the build and test phases, I coordinated manufacturing activities and supported the integration and validation of the complete aircraft.

2. Concept Development and Aerodynamic Design

2.1. Design Requirements

The project imposed several design constraints, including a maximum envelope of 0.9 × 0.25 × 0.3 m for each wing half, a strict mass budget of 1.5 kg, and the requirement to integrate telemetry and autopilot capabilities. These limitations forced the team to balance aerodynamic performance, structural integrity and manufacturing practicality throughout the development process.

The primary aerodynamic objective was to maximise the aircraft’s usable speed range across a Reynolds number range of approximately 120,000 to 350,000, with a catapult take-off speed of 12 m/s. This required a wing capable of generating efficient lift at low speeds while maintaining low drag during higher-speed flight. To achieve this, extensive trade-off studies were performed covering airfoil selection, wing geometry, aspect ratio, taper ratio and high-lift devices.

2.2. Airfoil and Wing Optimisation

A detailed aerodynamic study was carried out using XFLR5 and other airfoil analysis tools. Several low-Reynolds-number airfoils were investigated before finally selecting the NACA 4412 profile, which combined a thickness-to-chord ratio of 10–15% and a camber of 3–5% to balance profile drag, stall angle and available internal structural space. This airfoil offered an excellent compromise between aerodynamic performance and structural practicality. The runner-up candidate, the Selig-Donovan SD7032, was ultimately rejected as it would be too thin to meet the required structural stiffness.

The final wing geometry was carefully optimised to improve lift distribution and reduce induced drag. Wing taper ratio, aspect ratio and control surface sizing were iteratively refined through simulation, converging on a taper ratio of 0.65 and ailerons spanning 300 mm (around a third of the half-span) at a maximum deflection of ±25°, leading to a highly efficient wing configuration that combined good low-speed handling with strong cruise performance.

2.3. Static Stability Analysis

The aircraft was designed with stability as a key objective. I calculated the static margin using analytical formulas, combined with lift-curve slope and geometry data obtained from XFLR5’s Vortex Lattice and 3D Panel analysis. Targeting a static stability margin of at least 15% for robust handling across a range of conditions, I positioned the wing as far rearward as the design allowed, achieving a static margin of 22.5%, comfortably exceeding the target and resulting in strong inherent longitudinal stability.

Lateral stability was less of a concern for the team, since the high-wing configuration conferred passive stabilisation through the moments generated by skin friction drag during sideslip, complemented by the effective sweep introduced by the wing’s taper.

3. Structural Design

3.1. Wing Architecture

Once the conceptual design of the wing had been finalised, I modelled each individual component in CAD according to the defined aerodynamic and structural parameters, keeping manufacturability in mind throughout, then bringing them together into a single CAD assembly.

The final full wing design consisted of:

• Six CNC-cut Styrofoam wing sections
• Six laser-cut plywood reinforcement ribs
• Four carbon fibre spars
• Two ailerons
• Two slotted flaps
• Reinforced fabric skin covering

This configuration resulted in a lightweight yet highly rigid structure capable of withstanding both flight loads and ground handling conditions.

3.2. Carbon Fibre Spar System

A major part of the structural work focused on the spar arrangement. Carbon fibre tubes were chosen as the primary load-bearing elements due to their exceptional stiffness-to-weight ratio. The original front spar design ran along the wing’s tapered leading edge, meeting at a 3D-printed ABS joiner at the wing’s centre join, a joiner later found to concentrate stress dangerously at that point. To resolve this, the front spars were relocated rearward to a constant-chord section of the wing, reducing their length to 580 mm from an original 894 mm. The ABS joiner was also replaced with a machined aluminium tube (15 mm outer diameter, 10 mm bore) connecting both wing halves. Switching from pultruded to roll-wrapped rods for this front spar also reduced its weight from 37.8 g to 30 g per wing.

Each wing half also incorporated its own rear spar, running from the outer rib to the central rib and serving as the hinge axis for that half’s aileron. A late manufacturing correction that increased its diameter from 8 mm to 10 mm ended up reducing the peak bending stress from 17.8 MPa to 9.7 MPa, a welcome side effect of an otherwise unplanned change.

3.3. Slotted Flap Development

One of the most interesting aspects of the project was designing the slotted flap deployment mechanism.

Unlike simple plain flaps, slotted flaps allow high-energy airflow from beneath the wing to re-energise the upper surface boundary layer. This delays flow separation and improves lift generation at low speeds, resulting in a considerably reduced stall speed and improved low-speed handling.

I designed and modelled the hinge components in CAD, then integrated them into the full wing assembly. Two hinges, positioned at each end of the flap span, supported the bending loads experienced in flight, complemented by a servo rod attachment at the flap’s midspan. I tested multiple hinge concepts before arriving at a solution that delivered both sufficient strength and reliable deployment geometry.

The hinges themselves were built from acrylic and plywood parts bolted together, with the pivot formed by a plastic screw rather than a metal one. Acrylic was chosen for its stiffness and resistance to splintering under load compared to plywood, while nylon nuts and bolts were used throughout to save weight over steel fasteners.

To verify the bonded joint between the hinges and the wing structure, I tested epoxy resin against hot glue by incrementally loading a test joint until failure: hot-glued joints failed at just 2.8 kg (1.4 kg per hinge), while epoxy-bonded joints held up to 6.2 kg before the surrounding foam itself gave way, confirming epoxy as the stronger choice.

4. Manufacturing and Assembly

4.1. Wing Construction

Following completion of the design phase, manufacturing began from the engineering drawings I had produced for the foam sections, plywood components and flap hinge mechanism.

A university workshop technician produced the Styrofoam wing sections using CNC hot-wire cutting from these drawings, while I programmed the laser-cutting of the plywood structural components and hinge parts from the corresponding .dxf files.

Particular attention was given to maintaining dimensional accuracy during manufacturing, as even small geometric deviations could noticeably affect aerodynamic performance.

The wing sections were bonded together using epoxy resin and reinforced with a heat-shrunk fabric covering. In addition to improving durability, the covering contributed to the overall stiffness of the structure and created a cleaner aerodynamic surface.

4.2. Wing Structural Verification

Before final integration, the wing underwent structural verification to confirm it could withstand the loads expected in flight. FEA analysis of the wing structure confirmed that deflection would remain within acceptable limits under loads of up to 5g.

The wing was then subjected to a physical loading test: weight was incrementally added to the wingtip while measuring deflection, both to confirm the wing met the minimum load-bearing requirement and to obtain an experimental measurement of bending stiffness. The wing passed with margin to spare, verifying both the structural design and the FEA predictions that had informed it, clearing the aircraft for flight testing.

4.3. Final Aircraft Integration

Once the wing was complete, I worked closely with another team member to integrate it with the fuselage, propulsion system and avionics package. Several iterations were required to optimise component placement, improve weight distribution and minimise vibrations.

This stage transformed the project from a collection of subsystems into a complete, flight-ready aircraft.

5. Avionics and Flight Control System

5.1. Electronics Architecture

The aircraft featured a fully custom avionics system built around an Arduino Mega microcontroller. This replaced the initially planned Arduino Uno after development trials revealed its 2 KB of dynamic memory to be insufficient for the combined sensor, GPS, data-logging and PID autopilot code, while the Mega’s 8 KB gave the necessary headroom. The system was responsible for processing pilot commands, collecting sensor data and controlling the aircraft’s flight surfaces.

These components connected to a single custom soldered board acting as the wiring hub. It distributed power and the I2C sensor bus, and organised servo outputs and receiver inputs on opposite sides of the board for easy assembly and fault-finding, offering a flexible platform that could be expanded and modified throughout the project.

5.2. Sensor Suite and Data Logging

A wide range of sensors were incorporated into the aircraft, including:

• GPS receiver
• Barometric pressure sensor
• Three-axis accelerometer
• Three-axis gyroscope
• Three-axis magnetometer

All sensor data was recorded to an onboard SD card at a 1 Hz logging rate for post-flight analysis. This allowed flight performance, aircraft behaviour and sensor performance to be evaluated after each mission.

5.3. Autopilot Development

In addition to manual flight capability, the aircraft included a basic autopilot system based on PID control for roll and pitch stabilisation.

For safety, the throttle and rudder channels were wired directly from the receiver to the electronic speed controller and rudder servo, bypassing the Arduino entirely, so that a controlled descent remained possible even in the event of a full autopilot failure. The controller was designed to assist with aircraft attitude stabilisation and reduce pilot workload during flight.

6. Flight Testing

6.1. Test Objectives

The final stage of the project was a single flight test of the complete aircraft, with the following objectives:

• Verifying flight handling and stability characteristics
• Measuring maximum and minimum flight speed
• Assessing autopilot reliability
• Evaluating telemetry and data logging performance
• Testing structural integrity under real flight conditions

6.2. Flight Performance Assessment

The test flight lasted 2 minutes and 16 seconds, flown in challenging weather conditions with wind speeds of 5.7 m/s and gusts of up to 10.8 m/s. Despite these conditions, the aircraft demonstrated stable and predictable flight characteristics.

Take-off was smooth and the aircraft required only small control inputs to maintain stable flight. The stability margins incorporated during the design process proved effective, and the aircraft exhibited the balance of manoeuvrability and robustness that the team had originally targeted, with no structural issues observed at any point during the flight.

Unfortunately, no data on the aircraft’s usable speed range, the project’s primary aerodynamic objective, could be collected: the pitot tube used to measure airspeed had been damaged beyond repair on a different team’s aircraft during their test flight earlier that day, with no replacement available.

6.3. Telemetry Analysis

The onboard logging system successfully recorded sensor data throughout the flight.

Magnetometer data showed strong, synchronous patterns during the aircraft’s turns, with seven distinct rolling manoeuvres clearly identifiable in the log, confirming the telemetry system’s ability to capture real flight dynamics. Pressure sensor readings traced the aircraft’s altitude profile, showing periods of steady altitude interspersed with climbs, and a sharp rise consistent with the aircraft’s first landing approach partway through the flight. GPS data closely matched the flight path observed on video, correctly capturing the aircraft’s circular pattern over the test site.

Accelerometer data proved largely inconclusive, as the combination of gravitational, manoeuvring and gust-induced accelerations in dynamic flight was too complex to interpret cleanly, and derived roll/pitch estimates were undermined by the assumption of steady level flight, which did not hold given the gusty conditions.

6.4. Flight Demonstration

The successful flight represented the culmination of the entire design, manufacturing and testing process. It demonstrated that the aircraft could safely perform its intended mission while validating the aerodynamic, structural and electronic systems developed during the project.

Footage from the test flight, showing the catapult launch, stable cruise and landing approach, is included below:

7. Conclusions

This project provided a complete introduction to the multidisciplinary nature of aircraft development, covering the entire engineering lifecycle from initial concept generation through to flight testing.

My contribution centred on the CAD and mechanical design of the wing, the aircraft’s static stability analysis, and the design of the slotted flap deployment mechanism, complemented by the manufacturing drawings, coordination and final integration work of the aircraft. The resulting UAV successfully demonstrated stable flight performance and vindicated the engineering decisions taken throughout the project.

Beyond the technical achievements, the project offered valuable experience in teamwork, leadership, problem-solving and systems engineering, closely reflecting the challenges encountered during the development of real-world aerospace vehicles.