Alec Blade - Design Build Fly

The 2025 Flying Mocs Design/Build/Fly (DBF) project set out to design, fabricate, and test a remote-controlled aircraft capable of completing AIAA's DBF competition missions, including external payload transport and autonomous glider deployment. Organized into three subsystems, Aerodynamics and Structures, Propulsion and Systems, and Payload, the team leveraged CAD modeling, computational simulations, and iterative prototyping to meet technical objectives. While the aircraft achieved structural soundness and subsystem integration, final flight readiness was not attained, preventing competition entry.

Despite missing the competition, the team validated a significant number of design and operational objectives at the subsystem level. The team was also able to stay within the predicted budget. Major accomplishments included demonstrating robust structural design, functional electrical systems, and modular payload attachment methods. Notably, the team produced four complete prototypes, more than any previous UTC Flying Mocs DBF team, and achieved the most stable and controllable flight performance in the program's history. The work completed lays a strong foundation for future Flying Mocs teams to build upon and improve.

My Contribution

I coordinated the design, fabrication, and testing of the aircraft. I oversaw subsystem integration across aerodynamics, propulsion, and payload, ensuring structural, electrical, and weight-balance compatibility. I personally set up and executed all Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations, analyzing aerodynamic performance, structural stresses, and load-bearing capacity to guide design decisions. In addition to managing build progress and test schedules, I conducted ground, taxi, and flight trials as the primary pilot, advising and implementing configuration changes between prototypes to address performance issues.

Team Management

The team was divided into three main subsystems to create three sub-teams with a single team lead working in conjunction with the sub-team leads. Aerodynamics and Structures, Propulsion and Systems, and Payload account for the three main sub-teams. Each sub-team had an assigned lead, and they worked together to ensure integration and compliance.

Design Approach

The design process for the aircraft followed a structured systems design approach grounded in function-based design and objective evaluation. As illustrated to the right in Figure 1, the team began by constructing a function tree to map out all primary and supporting functions required to fulfill the competition missions. This hierarchical breakdown ensured that each subsystem could align their designs with overarching mission requirements.

From this function tree, each sub-team established clear and measurable objectives relevant to their assigned functions. For example, the Aerodynamics and Structures team defined goals such as generating sufficient lift, minimizing drag, and ensuring aircraft stability during flight, as shown in Table 1 below. These objectives not only guided the design phase but also later served as benchmarks for subsystem performance validation.

To compare competing design alternatives, the team established decision-making criteria derived directly from the objectives. These criteria were then weighted using pairwise comparison, shown in the Table 2, to reduced subjectiveness and increase quantitative decision making. Ultimately, decision matrices were created to evaluate which design met our goals the best. An example of a decision matrix is shown in Table 3.

By aligning functional decomposition with a quantifiable selection framework, the team ensured that each design decision was traceable to mission goals.

Table 1: Aerodynamics and Structures Table

Table 2: Wing Design Pair Wise Comparison

Table 3: Wing Design Decision Matrix

Figure 1: Function Tree

Final Design

Aerodynamics and Structures

The final aircraft structure featured a carbon fiber truss fuselage, designed for internal component access and lightweight strength. The wings, constructed from PETG with a NACA CLARK Y airfoil, were built using a modular, interlocking rib and spar design with an emphasis on manufacturability and load-bearing. The wing had a span of 71.75" and was supported by a main 72" carbon fiber spar and two 36" rear spars connected by a carbon fiber sleeve. To ensure secure attachment to the fuselage, the wings were fastened at both the front and back using heat-set insert nuts embedded in the wing ribs, which aligned with pass-through holes in the fuselage to allow bolting the components together. This fastening system maintained structural integrity while enabling straightforward disassembly for transport and maintenance.

The tail section used a dual boom configuration with PETG-printed horizontal and vertical stabilizers and a single elevator. Modifications to tail placement and spar integration significantly improved pitch control and stability after early test flights exposed CG and wing deflection issues.

A simple drawing of the complete wing, fuselage, and tail wing assembly is shown below as Figure 2 where the units are in inches.

Figure 2: Aerodynamics and Structures Assembly Drawing (inches)

Propulsion and Systems

The propulsion system utilized an E-flite Power 90 brushless motor driving an 18-inch 2-blade propeller, mounted to the carbon fiber nose cone. This setup was powered by a 22.2V 6S LiPo battery (3200mAh) through a 130A electronic speed controller (ESC), with both a blade style fuse and an arming plug implemented for safety. The fuse served to protect the ESC and motor from electrical damage in the event of a current surge. If the battery output exceeded safe limits, the fuse would absorb the damage and fail before the ESC or motor could be compromised. The arming plug provided an additional layer of safety by physically disconnecting power to the motor during handling and maintenance, preventing accidental throttle input and sudden propeller activation, which could pose a serious hazard to operators.

A separate 6.6V receiver battery powered the servos and receiver. This redundant power source acted as a critical safety measure: in the event of propulsion battery failure, the receiver and control surfaces would remain powered, giving the pilot the ability to maintain limited control and attempt an emergency landing.

The electronics were housed in the fuselage with careful attention to CG balance. Two MG90S servos, one per aileron, provided roll control, while a higher-torque servo actuated the elevator. The tricycle landing gear configuration offered sufficient clearance for the fuel tanks and glider and was designed to provide a 5° angle of attack during takeoff.

A wiring diagram is provided below, Figure 3, for a comprehensive overview of the electronics' setup.

Figure 3: Electronics' Wiring Diagram

Payload

The payload system consisted of externally mounted fuel tanks and a glider deployment mechanism, both custom-built. The fuel tanks were simulated using 32 oz SmartWater bottles mounted via PETG 3D-printed pylons and pipe clamps into T-slots on the wing ribs. A flush-fit insert was designed to fill the slot when pylons were removed, minimizing aerodynamic disruption.

The glider was made from foaming PLA to keep weight under 0.5 lbs, featuring an MH32 airfoil and functional control surfaces powered by onboard servos. An electronic release mechanism with a servo-triggered string release system was used to detach the glider mid-flight. The electronics included a SpeedyBee flight controller with ArduPilot firmware, and LEDs.

Drawings of the glider and fuel tanks are shown below as Figure 4 and 5 respectively, where the units are in inches.

Figure 4: Glider Drawing (inches)

Figure 5: Fuel Tank Drawing

Simulations

Structural

Structural integrity was assessed using finite element analysis (FEA) in SolidWorks. Simulations modeled the wing under distributed lift forces and the tail under aerodynamic disturbance loads, assuming linear elastic and isotropic material behavior. The simulation applied 15 pounds of lift force across the wing ribs and 2 pounds to the tail wing.

Results showed primary displacement at the wing tips (1.68 inches) and at the top of the tailplane (1.85 inches). Stress analysis identified high-stress zones at the dual-boom tail structure and around spar sleeves at the wing-fuselage interface. The carbon fiber spar sleeves effectively distributed loads and minimized mid-span spar stress, validating the robustness of the structural layout for the expected aerodynamic forces.

Figure 6, shown below, illustrates the FEA displacement results.

Figure 6: FEA Displacement Results

Aerodynamic

Aerodynamic performance was simulated through computational fluid dynamics (CFD) using SolidWorks Flow Simulation, with a focus on lift and drag behavior at various flight conditions. Simulations examined angles of attack from 0° to 15° and speeds ranging from 10 to 70 mph. The results indicated that minimum flight speed without payload was approximately 15 mph at a 5° angle of attack. To achieve sufficient lift for full payload (over 20 lbf), speeds of around 50 mph or more were required. Drag remained low at lower speeds but increased steadily with velocity.

The center of pressure (CP) was calculated to be 12.95 inches from the propeller face, critically located behind the aircraft’s CG (which varied between 11.89–12.72 inches depending on the configuration), ensuring longitudinal stability. A maximum drag coefficient of 0.05 was achieved at cruising speeds, meeting the design goal for aerodynamic efficiency.

Figure 7, shown below, reveals the relative pressure distribution of the plane during a cruising speed 20 mph.

Figure 7: Relative Pressure Distribution

Prototype Testing

Prototype 1

The first prototype was primarily a proof-of-concept for component integration and basic flight readiness. PETG filament sleeves connected the wing spars, and a swiveling front landing gear was used. Ground tests included a drop test, wing tip test, and an initial flight attempt. While the drop test passed, the PETG sleeves failed during the wing tip test, leading to a temporary aluminum sleeve solution. During the flight attempt, poor CG placement—behind the center of pressure—caused an immediate stall and crash on takeoff. The fuselage and wings sustained only minor damage, but the tail wing was destroyed, prompting redesigns to address both CG positioning and structural sleeve strength.

Prototype 2

This iteration focused on correcting the shortcomings of Prototype 1 by replacing PETG sleeves with carbon fiber filament sleeves, fixing the swiveling front landing gear, and adding 1.875 lbs of nose weight to shift the CG forward. The changes improved takeoff performance, with the plane lifting off at 35 feet, but the added nose weight caused the carbon fiber sleeve to fracture, forcing a return to the aluminum sleeve. In flight, poor sleeve fit allowed significant wing deflection during banking, leading to a crash in a 180-degree turn. The crash destroyed most of the structure, including wings, tail, spars, and propulsion components, though the central fuselage and some electronics were salvageable.

Prototype 3

Prototype 3 introduced a major spar system redesign, replacing the front sleeve connection with a single continuous 6-foot spar and moving the tail wing 3 inches closer to the fuselage. The tail cone was shortened and reprinted in PETG to reduce weight, and a heavier, more rigid front landing gear was installed for a 3-degree resting angle of attack. A smaller 17-inch propeller was added to prevent runway strikes. These changes improved structural rigidity—passing the updated wing tip test—but the aircraft failed to achieve takeoff during taxi trials. Reduced thrust from the smaller propeller and a lower pitching moment from the shortened tail wing were identified as the likely causes of the performance shortfall.

Prototype 4

The final prototype blended the structural improvements from Prototype 3 with the successful configuration elements from Prototype 2. The tail wing was returned to its original position, the 18-inch propeller was reinstated for greater thrust, and the landing gear was adjusted for a 5-degree angle of attack. This prototype achieved a smooth and stable takeoff and was reported as the easiest to control. However, during flight, the aircraft lost altitude despite full throttle and elevator input, likely due to a tailwind reducing relative airspeed and top fuselage coverings detaching mid-flight, causing additional drag. The resulting crash on uneven terrain ended testing, but Prototype 4 still demonstrated the most complete and stable performance of all iterations.

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