Martian Propeller Performance at Low Reynolds Number

ISEF Category: Engineering Technology: Statics and Dynamics

Subcategory: Aerospace and Aeronautical Engineering  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

A propeller that works on Earth can fail on Mars for a simple reason, the air is too thin. That changes how much lift the blades make and how much power they need. If you can predict that behavior at low Reynolds number, you are doing real aerospace engineering. This project lets you compare hand-built data with models used in industry.

What Is It?

This project studies how a small coaxial propeller performs in a Mars-like flow. A coaxial rotor means two propellers sit on the same axis and spin in opposite directions. That setup can cancel swirl and change thrust, which makes it useful for drones and Mars aircraft.

The core idea is scaling. You are not building a full Mars helicopter. You are building a smaller test system that matches key flow behavior, especially Reynolds number, which compares inertial forces to viscous forces. If two setups share similar Reynolds number, their airflow patterns can act in similar ways, even if the fluids are not identical.

You then compare your measured thrust and torque with two prediction methods. Blade element momentum theory, or BEMT, breaks a propeller into small blade sections and estimates force from geometry and airflow. OpenFOAM is a computational fluid dynamics tool, or CFD, that simulates fluid motion on a computer. Together, these let you test how well theory matches reality.

Why This Is a Good Topic

This is a strong science fair topic because you can change one clear variable, measure real forces, and compare experiment data with models. The project connects to Mars flight, drone design, and low-Reynolds-number aerodynamics. You can learn how scaling works, how to control variables, and how to judge whether a model predicts real data well. That gives you both an engineering build and a serious analysis story.

Research Questions

• How does helium-air mixture ratio affect the thrust produced by a coaxial rotor at matched Reynolds number?
• What is the effect of rotor speed on thrust-to-torque ratio in a Mars-like chamber?
• Does coaxial rotor spacing change the efficiency of the upper and lower rotors differently?
• To what extent do BEMT predictions match measured thrust across low Reynolds numbers?
• Which blade pitch setting gives the highest thrust per unit torque under Mars-equivalent flow conditions?
• How does chamber pressure change the agreement between experiment data and OpenFOAM results?

Basic Materials

• 3D printer and CAD software for rotor parts.
• Coaxial motor mount and propeller shaft hardware.
• Sealed acrylic chamber with ports for air handling.
• Vacuum or pressure-rated fittings, gaskets, and clamps.
• Helium and air supply with safe regulators or flow controls.
• Digital kitchen scale with at least 1 g resolution.
• Small torque sensor or force sensor if available.
• Tachometer or optical RPM sensor.
• Data logging device or Arduino-compatible microcontroller.
• Safety goggles and gloves.

Advanced Materials

• High-quality 3D printer with fine layer control for blade surfaces.
• Load cell and instrumentation amplifier for thrust measurement.
• Inline torque transducer or calibrated reaction-arm setup.
• Pressure gauge and flow meters for chamber control.
• Transparent sealed test chamber rated for low-pressure work.
• Laser tachometer or encoder for rotor speed.
• Boundary layer or flow visualization tools, if available.
• Access to computational resources for OpenFOAM.
• MATLAB, Python, or similar tools for postprocessing.
• Calibration weights and geometry measurement tools.

Software & Tools

• OpenFOAM: Simulates airflow around the rotor and helps compare CFD predictions with measured thrust.
• Python: Processes thrust, torque, and RPM data, then fits model curves.
• ImageJ: Measures blade geometry and checks printed parts for shape consistency.
• Fusion 360: Helps you design the rotor, hub, and chamber fixtures.
• Tracker: Can track motion or vibration if you record the rotor during testing.

Experiment Steps

1. Define the exact performance metric you will test, such as thrust, torque, or thrust-to-power ratio.
2. Choose the one geometry variable you will change first, such as blade pitch, rotor spacing, or blade count.
3. Build a scaling plan that matches Reynolds number as closely as your chamber and sensors allow.
4. Design controls that separate fluid-property effects from geometry effects, including a baseline rotor and repeated trials.
5. Plan a prediction workflow that compares your measurements with BEMT and then with CFD results.
6. Set up a data table that links chamber condition, RPM, thrust, torque, and uncertainty in one place.

Common Pitfalls

• Using a scale that cannot resolve small thrust changes, which hides the real rotor trend.
• Letting chamber leaks change pressure during a run, which breaks the Reynolds number match.
• Comparing raw thrust values without normalizing for rotor speed or air properties, which makes the data misleading.
• Printing blades with slight shape differences between trials, which adds geometry noise to the results.
• Treating BEMT or OpenFOAM output as ground truth instead of checking both against measured data.

What Makes This Competitive

A strong version of this project does more than report thrust. It shows careful scaling, clean uncertainty analysis, and a fair comparison between experiment, BEMT, and CFD. You can raise the level by testing more than one blade design, by checking how well prediction errors change with Reynolds number, or by separating coaxial interaction effects from single-rotor behavior. That turns the project into a real validation study, not just a build.

Project Variations

• Test a single rotor first, then compare it with a coaxial pair to isolate interference effects.
• Swap the chamber gas mix for different effective viscosities and compare how the thrust curve shifts.
• Compare several blade geometries, such as two-blade versus three-blade rotors, under the same Mars-equivalent flow target.

Learn More

• NASA Mars Helicopter Ingenuity background: Search the NASA Mars helicopter pages and mission updates for design context and performance constraints.
• NASA Glenn Research Center educational materials: Search NASA Glenn for low-Reynolds-number aerodynamics and rotorcraft resources.
• MIT OpenCourseWare Flight Vehicle Aerodynamics: Search MIT OpenCourseWare for lecture notes on lift, drag, and propeller theory.
• Journal of the American Helicopter Society: Search for review articles on rotor performance, coaxial rotors, and low-Reynolds-number flight.
• PubMed: Search for articles on low-pressure gas dynamics and rotorflow studies only if you want a broader methods background.
• OpenFOAM documentation and tutorials: Search the official OpenFOAM documentation for mesh setup, boundary conditions, and rotor simulation examples.