Motivation and Planning

GIPHY
The main goal of the project is to design a testing stand for rotary wings, where one can measure the efficiency of the blade-motor combination (aero-propulsion system for rotary wings) and correlate the motion to the outputted lift generation. We aim to create a generic stand and focus on the design of different blades and a mechanism that can change pitch angle mid-rotation, exploring different flight configurations and replicating a vertical flight condition (given the right proportions).
The context of this project is the increasing interest and technology development of urban and advanced air mobility vehicles, which are directly related to vertical flight solutions. However, the understanding of the aerodynamics in these vehicles is still ongoing research, particularly in the context of tilting, propeller–wing interaction and corresponding aerodynamics and using experimental methods.

Design
The project consists of two main components being the Mechanical System and the Electrical System.
Design Criteria:
Objectives
- Design and create a motorised pitching mechanism
- Manufacture wings with varying density and shape
- Build an electrical instrumentation system to collect relevant measurements
- Analyze results
Constraints
- Dimensions ———- Limited to the size of the motor
- Budget ————— $500
- Time —————— 14 weeks
Outputs
- Pitching System
- Motor Control System
- Lift Measurement System
- Deflection Measurement System
Objectives
- Manufacture a pitching system with enough degrees of freedom that allows it to rotate along with the motor
- 3D print high aspect ratio wings with varying density and airfoil shape that can safely rotate at high speeds and withstand the centrifugal force of the motor
- Create a robust base to house and stabilize the system on a level surface
Constraints
- Dimensions ———- Limited to the size of the motor
- Materials ————- 3D printing, 8020, nuts and bolts
Outputs
- Pitch angle
- Wing specifications
Objectives
- Build a Motor Control System that incorporates
- Brushless DC Motor – Generate rotation
- Motor Controller – Feed information to the motor
- Potensiometer – Control motor speed
- IR Sensor – Measure rotation speed
- LCD Screen – Display relevant information
- Arduino nano – Connect, manage, supply, and store information of the system
- Build a Lift Measurement System that incorporates
- Load Cell – Measure change in mass generated by the lift in the system
- Load Cell Amplifier – Translate load cell information to a microcontroller
- Arduino nano – Connect, manage, supply, and store information of the system
- Build a Deflection Measurement System that incorporates
- Laser Distance Meter – Measure distance in the z direction from a fixed point to the wing
- Arduino nano – Connect, manage, supply, and store information of the system
Constraints
- Motor controller current
- Load cell precision
- Laser range
Outputs
- Rotation Speed (RPM)
- Lift Force (grams)
- Deflection Length (mm)
Mechanical System
A key challenge of the project is the simulation of a rotary wing system on a small scale. This means reducing the size of the blades and mechanism to work in tandem with the control of aerodynamic parameters such as the pitch angle and blade rotation. The mechanical system includes two main areas of development:
- Blade Design and Selection
- Pitch Mechanism

Blade Design and Selection
The blade selection process consisted of 3 major components: simulation, selection, and manufacturing. The airfoils were simulated with an XFOIL user interface, XFLR5, under our anticipated conditions and the best performing blade was selection, the Sikorsky GS-1.

XFLR5
The GS-1 blade was then 3D printed along with the NACA0012 with an embedded nut for attachment to the rest of the system. Many trial blades were manufactured during the extent of this project, however, the final design favoured a 160mm blade span and a 25mm chord length with filleting around the nut encasing to mitigate stress around the connection. The final NACA0012 and the Sikorsky GS-1 blades can be seen pictures below in purple and pink, respectively.

Pitch Mechanism
The pitch mechanism is the mechanical component that mimics a swashplate in a vertical flight system. The goal is to translate the input from the helicopter flight controls (or the motor, in this case), into the motion of the main rotor blades. The design and kinematics of a swashplate can be convoluted, which can prevent the execution of the project. Therefore, in this project, the goal was to design a new version of the swashplate that could be still applicable for vertical flight context, but on a lower level of complexity.

The new design is composed of three main elements:
- Lower disc: which is stationary and attached to the base of the motor. The pitch angle to the entire system is given to this component.
- Upper disc: it rotates together with the blades/motor, and because it is in direct contact with the lower disc, it transmits the pitch angle to the blades as they are rotating.
- Ball joints: they connect the upper disc to the blades, and transmit the motor rotation. They were designed as ball joints to add extra flexibility in terms of adjustments, in case there were any issues with the assembly. Once everything is in place, their degree of freedom can be removed as the system is locked.
This mechanism and the three different components are all printed as one part, to avoid issues as misalignment during the assembly. the figure below shows how the ball joints are connected to the blades, and how the extra degree of freedom is locked with the nuts pressed against the blade.

Electrical System
The Electrical System component of the project is entirely dedicated to the measurement requirements. Three different parameters are explored:
- Aerodynamic force: using a one-direction load cell, the design system measures how much lift is generated by the rotary wing system, as a function of the pitch angle enforced by the mechanism and the motor RPM.
- Tip deflection of the blades: depending on the density and the span of the blades, the tip can deform during the performance of the prototype, leading to different lift measurements.
- Motor RPM: although the motor RPM is a parameter that can be controlled by the user, it is of interest to know if the overall system affects the motor performance, and how this parameter is related to the lift generation.
Measuring Force
The force distribution over the rotary wing system is composed of mainly three forces and three moments:

Side Force: responsible for lateral movement of the vehicle
Roll Momentum: responsible for the maneuverability and control of the vehicle
Lift Force: responsible to overcome the weight of the vehicle during flight

Drag Force: the consequence of the presence of the Lift and it represents the air resistance to the motion of the aircraft
Pitch Moment: torque produced by the lift on the airfoil. In this case, changing the angle of attach of the blades during the rotation modifies the lift force and, consequently, the pitch moment

Yaw Moment: in the rotary wing case, it is the torque around the motor axis, which is not relevant in this project
The load cell is an integral part of the project’s functionality, and much attention was given to optimising its performance. The load cell was connected to a load cell amplifier which was then connected to an arduino nano to allow for data extraction and measurement control. The load cell was placed below the pitching apparatus to measure the change in force exerted. This change in force will represent our lift generation for the system.

Measuring Blade Deflection
For very flexible wings, the deflection at the tips due to the aerodynamic load during flight may lead to a non-uniform pressure distribution through the wing span. The same can occur in the rotary blades. This deflection can result in a loss of aerodynamic efficiency, and consequently performance of the motor-blade system.
To explore that, an analog distance sensor (Sharp/Socle GP2Y0A51SK0F Analog Distance Sensor 2-15cm) is used to measure the tip deflection of the blades during the measurements. Also, the blades were manufactured considering different infill densities to ensure tip deflection. The goal is to measure cases with and without tip deflection and assess how much this can impact the system’s efficiency.

Controlling Motor RPM
The motor controlling system consisted of 5 main components to create a functional electronic network.
The IR sensor connected to the arduino to measure RPM of the rotary system. Reflective tape was attached to the bottom of one blade and each time the tape would pass over the sensor, an RPM was counted. This method proved useful until very high RPM was achieved by the system and the sensor could no longer sample at an appropriate rate.
The motor is connected to a motor controller which then connected to the power source and the arduino. The controller allowed for the power supplies to the motor to be controlled by the user. A key aspect of this controller is the ability to switch connections easily to generate either clockwise or counterclockwise rotation.
The LCD screen is connected to the arduino to display RPM gathered from the IR sensor, and relative power of the system given the controlling code.
The potensiometer is connected to the arduino and allows the user to control the overall speed of the motor as well as startup and cool down.
The arduino allowed for the interconnection of all of these components and a single code was used to gather and share information between these electronic systems.

Results
Testing the design
Fixation of the entire system
The current configuration was used to perform the first set of measurements and validate the hardware choices, particularly regarding the sensor hardware. All tests were performed inside an acrylic box for safety. The picture below shows how the metal structure was fixated to the acrylic box to ensure a clamped condition.
Because the enclosed space was not initially considered in the dimensions of the project, the blades had to be shortened to avoid collision with the acrylic enclosure walls.


The following figure shows the initial testing set up:

The big challenge with the initial configuration was the amount of vibration near the motor support and at the “cross tip”, underneath the motor. To solve these issues, the configuration was modified by adding a support beam near the motor fixation and clamping the “cross tip” to the table.
In terms of the data acquisition, there were two issues: the first was the sampling frequency for the distance sensor. Because the motor only starts at 20% of its power, which generates an RPM that is well above the sampling frequency of the sensor, no tip displacement could be measured. Additionally, it was seen that the RPM sensor was not always consistent with the reading, meaning that in some cases it would record the correct data, but in others, it would stop recording data above 20% of the motor power.
The figure below shows the new configuration with the new modifications.

Pitch Mechanism
Once the excess of vibration in the structure was solved, another issue was seen with the prototype, but now involving the 3D printed pitch mechanism. It was seen that after 2-3 runs with the blades and pushing the motor up to 40% of the power, an imbalance between the blades was seen. Further investigation showed that the issue was a plastic deformation at the interface between the upper and lower discs of the pitch mechanism. The yellow arrow in the picture bellow shows the misalignment between the two parts

The figures below also show the gap between the disc (figure on the left), and the plastic deformation at the upper disc (figure on the right). Because these two parts were printed together, the fact that they could easily be separated after the third measurement run indicated how much the plastic components are limited to high velocity and high friction applications such as this project.
Because the severity of this issue is expected to increase if the system were given a higher fixed pitch angle (local force applied on one side of the rings), further investigation on the manufacturing methods is necessary. Both in terms of manufacturing steps as well as available material to produce these discs.


With the exception of a few issues with the configuration and operation, overall, the design met the basic requirement of the project which was to measure aerodynamic data efficiently.
Measured data:
The collected load cell data was cleaned and analysed for meaningful results. The raw data was plotted along with a 2 second and a 5 second moving average for both the NACA0012 and the Sikorsky GS-1 blades. The clear step changes in motor RPM can be seen in each plot as the power increased from 0, 20, 30, 40, and back down to 0%. The Sikorsky GS-1 blade outperformed the NACA0012 in terms of lift generation. This outcome was anticipated due to the intricate geometric camber of the GS-1 as opposed to the symmetrical foil shape of the NACA0012.


The lift results for each RPM step were plotted for the NACA0012, the GS-1 and a base blade. The base blade is a manufactured propeller blade that was delivered with the drone motor package. The base blade was tested without the pitching apparatus and therefore due to the professional manufacturing and significant decrease in friction within the system, the base blade did out perform our 3D printed blades. There is still a clear correlation between an increase in RPM and an increase in generated lift, with the Sikorsky GS-1 outperforming the NACA0012 at each interval.

Education
Beginner
This project has a strong assembly component, allowing young students to explore the design aspect of it without losing some of the fundamental aspects of rotary wings.
Mechanical System: the complexity of the prototype can be adapted to consider lower levels of complexity for the wings, ignoring the pitching mechanism.
Students can make use of the free program OnShape to model the fixation support and the blades, initially assuming them as flat panels.
- A simulation can be done using the free program SimScale, where students can have a simpler visualization of the problem to be solved, as well as improve their design choices before assembling the prototype.
Manufacturing: once a CAD model is done, all parts of the system can be obtained using 3D printing technics.
Electrical System: students can implement the measuring techniques starting with the measurement of the motor rotation using a dynamometer. Depending on how the student chooses to control the motor, a direct study can be done correlating motor RPM and the system’s efficiency for each blade considered.
Learning Outcomes: Students with low coding skills and adventuring into aerospace research can benefit from a prototype that can generate aerodynamic forces, without too much theoretical background in the field. The main learning outcome is the correlation between aerodynamic shapes and output efficiency, hopefully encouraging students to move up to the next level of complexity.
Intemediate
At the intermediate level, the steps to assemble the prototype demand more complex knowledge usually obtained in engineering classes.
- Mechanical System:
- Similarly to the Beginner Level, students also need to use a CAD program to model the supporting structure and the blades, but at this level, it is recommended a higher level software such as SolidWorks or Fusion. Additionally, the students should be able to have a simple version of the pitching mechanism and start exploring the implications of it to the aerodynamic system.
- Additionally, students can add to the project a study on different blade profiles and the aerodynamic implications for each case. It is recommended students to use an open-source program, such as XFLR5. Students with an aerodynamic background can also make use of basic aerodynamic theories to complement this study.
- Electrical System: the measurement aspect of the project can be expanded to include the force measurement, with a simple load cell, or a combination of them. Depending on the capabilities of the student, they might want to consider measuring more than one direction to enhance the final analysis.
- Students can also explore their knowledge of error propagation and the implications of the final set of results. Particularly depending on the quality of their data acquisition system.
Learning Outcomes: Students on this level are encouraged to expand the correlation between the experimental setting and a numerical/analytical method. That will provide them a better understanding of the physical aspects of the problem and assist with any optimization to the system they might want to explore.
Advanced
After mastering the fundamentals and correlating with basic theories, a more advanced version of the project would consider more advanced tools and a more complex prototype design.
- Mechanical System: Additionally to expanidn the prototypes to include a more complex version of the mechanical components, students are also encouraged to use a more complete aerodynamic model to correlate their results and to expand on the blade selection study. Particularly using CFD tools, both 2 and 3D.
- Students are also encouraged to make use of a Wind Tunnel, if available, to explore the effects of incoming flow to the rotary wing system.
- Once a more complete aerodynamic solution is used for the blade study, students can start exploring different blade configurations, varying not only the airfoil profile but also different profiles and chord dimensions over the span.
- Electrical System: Students can also expand their project by including the tip deflection at the blades and developing a more complete and compact electronic system for their data acquisition solution. censoring.
Learning Outcomes: Students on this level should master basic concepts enough to propose different solutions and even different ideas for the prototype design. Including the pitching mechanism. Additionally, students should be able to troubleshoot based on their knowledge of the aerodynamics involved with the system (rotary wings) and modify their approach also based on their knowledge of the phenomenon.
References
- Shreyas Srivathsan and Juergen Rauleder. “Wind Tunnel Measurements On The Effect of Propeller Tilt On Propeller–Wing Interactional Aerodynamics,” AIAA 2024-4146. AIAA AVIATION FORUM AND ASCEND 2024 . July 2024.
- Shreyas Srivathsan and Juergen Rauleder. “Experimental Wind Tunnel Investigation on Propeller-Wing Interactional Aerodynamics,” AIAA 2023-1752. AIAA SCITECH 2023 Forum. January 2023.
- Shreyas Srivathsan, Pranav Sridhar, Marilyn J. Smith, Juergen Rauleder. ” Experimental and Computational Investigations of Propeller-Wing Interactions,” https://doi.org/10.4050/F-0080-2024-1337
- Huai-Te Yu, Luis P. Bernal, Kenneth O. Granlund and Michael V. Ol. “Aerodynamics of Pitching Wings: Theory and Experiments,” AIAA 2014-2881. 32nd AIAA Applied Aerodynamics Conference. June 2014.