Inspiration
Aviation and global shipping accounts for roughly 1.14 billion tons of CO2 emissions with over 4.56 billion global passengers in 2018 alone [1]. With many experts believing that the number could triple by 2050, there is a clear need for a more climate-friendly mode of aviation. While much work is being done on electric aviation, much of that is restricted to short-distance domestic service as opposed to the long-distance flights that make up the backbone of our modern aviation and transportation industry.
Another possible alternative is using existing aviation technology while flying in the ground effect. The ground effect is a set of flight characteristics encountered while flying near the ground which allow for more efficient flight with less drag. This creates aircraft which require less thrust to reach similar velocities, allowing for fuel savings and more efficient flight.
After learning about the potential of ground effect, our team endeavored to build a concept vehicle which would demonstrate these benefits on a small scale. GREG (Ground Effect Glider) was the resulting vehicle we built over the course of TreeHacks 2024, and we were successfully able to demonstrate its flight capabilities while laying out a future path for improvements and demonstrating the effectiveness of the ground effect.
Capabilities
The GREG plane does everything an RC plane does. It’s not just a bunch of foam and wood. It can fly, and it has flown!
- Along with a DC motor and propeller to provide thrust, we also have control surfaces actuated by servos. These servos and DC motor are hooked up to a radio receiver, so all parts of the plane can be controller by a radio transmitter in the hands of the pilot. The best part, the special design of the wings helps it utilize the ground effect when it’s close to the ground. The additional winglets at the end of the wing provide yaw stability.
- We also have electronics in the payload bay that can measure the distance from the ground, an IMU to measure rotation, and store the data in an SD card.
How we built it
Before the hackathon, we planned out what our build process would look like. We made a checklist of all the things we thought we needed to do to finish the plane in 36 hours. We knew this was critical to getting this complicated design built in time.
We also looked into GEV and the common designs for planes of this style. We consulted with Stanford Aeronautics and Astronautics Professor Ilan Kroo, who is an expert in the field of sustainable aviation. We educated ourselves on aircraft electronics, and how we could control the plane with a pilot transmitter so that we had the appropriate parts by the start of TreeHacks.
The wing and tail of the aircraft were constructed primarily using foam board. The wing shape was designed in a way to maximize the ground effect on GREG, and thus required anhedral connections accomplished using hot glue. Carbon fiber rods were added as structural members for the wing. Additionally, a curved sheet of balsa wood was added on top of the foam board to create an airfoil shape garnering improved aerodynamic effects. Foam rudders and an elevator were added to give control over the flight. The avionics bay was constructed as a rectangular fuselage made of plywood (for motor mounting) and insulation foam. It was covered with a balsa wood cover and connections were secured with tape and hot glue.
We used an RC plane control rod kit that provides control horns to attach to wing elements so that they can be controlled with micro-servos. The control horns were assembled such that the servo motion would move the rudder and elevator. These were then wired to a receiver that received radio signals from the transmitter. The motor was controlled by an electronic speed controller that was also attached to the receiver.
A sensor suite was prepared for data acquisition onboard the vehicle. This included an IMU and time of flight sensor operated by a Teensy microcontroller. When integrated into the aircraft, autopilot capabilities can be achieved.
Challenges we ran into
As you would expect, we faced every challenge that a hardware project would face. Here’s a best-of-the-best list of all the best issues we faced:
- The wing was too long to stay rigid when we mounted the fuselage to it. It sagged so much that our propeller was starting to hit the ground. We had to add spars, carbon fiber rods and more to make it more aerodynamic and rigid.
- The weather! All the rain on Saturday made it really hard to do flight tests. Indoor flights (like flying in an empty car garage) led to some pretty tough crashes that resulted in a broken propeller.
- Getting mass balance correct is pretty essential to steady flights. With hot glue everywhere and imperfect cuts, it was hard to estimate the centers of gravity and pressure very accurately. We had to be smart and move the battery accordingly.
- One of the biggest challenges, none of us had built or manually flown an aircraft before! It’s not easy to configure all the electronics, or pilot a plane that’s been built from scratch and has a lot of imperfections.
- The propeller broke on landing every time, and then we ran out of propellers!
Accomplishments that we're proud of
During this project, we could have modified an existing RC plane to be better suited for ground effect. However, we decided to build the plane from scratch, because what’s a better way to learn how to make something than to build it from scratch?
Without a doubt, the accomplishment we are most proud of is our first successful flight of the aircraft. Going into the weekend, we were not sure if it was even possible to build an RC plane of this size in 36 hours. However, when the plane took off for the first time those worries were gone. In fact, we had the plane ready for glide testing in 24 hours! The videos show off our excitement.
What we learned
The biggest lesson we learned was without a doubt the value of iterating through designs and rapid prototyping. In a 36 hour period, there is not a lot of time to meditate on decisions. Running a unit test on hardware requires a lot of moving parts to come together, and a crash in the real world isn’t as easy to fix as a missing semicolon. To combat this, we learned to trust our own decisions and to rely on each other to make decisions on the fly that would be critical to the success of the final product. Despite our best efforts, things do break. We learned how to take every failure and turn it into a chance to make our design better.
Many technical lessons were also learned over the course of this weekend. We learned to manufacture low mass and high rigidity structures, and how to couple our theoretical knowledge of mechanics and aerodynamics with our physical ability to cut, shape, bend, and glue. Additionally, we learned to interface with a radio controller in order to remotely send command inputs to the glider in flight.
What's next for Ground Effect
There’s a lot more that can be done with this idea, and what you’re seeing here is only the most basic of prototypes.
To utilize the ground effect, the plane needs to be close to the ground and maintain its altitude at that level. This is extremely difficult with a manually piloted plane with no intelligent control systems. Our goal is to utilize the time of flight sensor and the IMU that have already been incorporated on-board, and develop an active control system that maintains altitude and the desired pitch angle. The team has prior experience in building these systems, and is confident in its ability to make this a reality. Then, we can incorporate cameras and GPS to help the plane fly to specific waypoints, further improving the autonomy stack.
We also want to get further data analysis working, by measuring pressure at the wing-tips or the current draw at various flight altitudes. With some of that aerospace-grade aerodynamic analysis to quantify the ground effect, the team could optimize the wing geometry and improve performance.
Going beyond the plane we have, the possibilities with commercializing the ground effect plane are endless. Aerial cargo transport and commercial travel that is more efficient than current air transport but much faster than sea transport.
References
Built With
- machining
- teensy
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