We have recently started working on designing a way to attach the battery for our plane to the fuselage. You can read our blog post comparing an electric and gas powertrains to learn more about why we chose the battery design. The majority of the work has been on research, with some team meetings for brainstorming and design sketching. We will be using lithium-ion batteries in our plane.
Lithium-ion batteries are rechargeable batteries that are commonly used in devices such as phones and computers, in electric cars and planes, and even the Mars Curiosity Rover. They have the most power for the lowest mass of most available battery options.
Concerns
Weight Distribution
The primary concern for the placement of the battery is weight distribution throughout the fuselage, as we need to make sure the fuselage will be able to support the weight of the battery cells and busbars we will use while keeping the center of gravity in an optimal place. Busbars are a metal strip or bar that conducts electricity between high- or low- voltage electrical equipment. They’re usually made of copper, brass, or aluminum. There are different types based on the need- some are hollow rods, others are flat strips, solid rods, or solid bars. We have been thinking of distributing the components of the battery along the bottom front of the fuselage, in order to reduce strain on the fuselage and to avoid excess weight on only one place. The flattest rectangular or stacked arrangement of battery cells is best, as it will need the least complex busbar system. Our recent simulations show that the weight of the battery and electrical components shouldn’t be a problem, as the fuselage will be able to support it. However, the current primary issue is making sure the center of gravity is in a good place which means farther forward with the addition of the weight of the batteries, and we have discussed in the past moving the wings back a bit if needed to balance the weight. In the image, the busbars are the copper colored strips of metal in the image above, and the batteries are inside the grey metal casing. Our battery will be fairly different from this image shape-wise, and will be flatter, while this battery system is more of a box. (image)
Other Considerations
We need to make sure the battery does not block air from the motor, or that the engine does not warm the battery cells too much, which would decrease their performance. Lithium batteries can produce flammable and toxic gasses when overheated, which is definitely something we would like to avoid. Overcharging and high temperatures can cause a chain reaction of self-heating from battery to battery, which can eventually lead to anything from the release of smoke and toxic gasses to an explosion.
We need to make sure all wires and plane structure around the batteries are well protected and safe. Again, the current main priority is design, working on distributing the weight well across the fuselage, but keeping in mind the other considerations. Although this is more of a problem for later, we need to keep in mind that the battery is easy to access for charging, maintenance, and battery inspection while on the ground. Typical things that need inspection are corrosion, ventilation systems, wires and terminals, and looking for evidence of any damage.
Research
Sources
The brunt of our research has been reading many sources about different battery concerns, specifications, types, and inspection routines. The EAA, Skybrary, and AVStop websites have all been extremely useful resources for our specific concerns.
This Skybrary page was an excellent starting point for our research. It provided an overarching introduction to basic battery information, including vocabulary and types of batteries in a clear and easy to understand format.
The EAA site was most useful for battery information as it pertains to homebuilt airplanes, which is exactly what we are working on. This page spoke about ways to avoid problems with batteries in homebuilt aircraft. It will be useful for our design considerations, showing us potential issues we can avoid through our design choices.
Finally, this AVStop page provided a comprehensive list of battery considerations and requirements, with excellent illustrations linked as well. We plan to keep the information learned from all of these pages in mind as we work on the batteries, and will definitely continue to reference them in the future.
What Other Planes Do
So far, we have read about a number of new electric planes in testing and use. It has been fairly hard to access any kind of plans or model for these planes, so most of the information about their batteries has come from images of the nose and video tours of the airplane. While not strictly necessary, plane plans are very useful for seeing exactly how a component was positioned or attached, and may help us solve a specific problem we have encountered.
Here is one image of the design of the Rolls Royce ultrafast electric plane. It has been interesting to read about the safety considerations they had, and to see where they decided to position their batteries. This plane uses the same type of batteries we will be using, lithium-ion. They used lightweight materials to contain the batteries in order to cut down on weight. The battery cells seem to line the bottom of the fuselage in the front, which is very similar to our planned battery placement. Finally, they made sure the case containing the batteries was extra-strong, which may be an element we end up incorporating into our design. (image)
Most ultralight planes use gas, so it can be challenging to find examples of battery-powered ultralight planes online. It’s harder to design when there are fewer resources and less information available, but we still have quite a bit to go off of. Reading about the battery systems in the EMG-6 (here), has only reinforced ideas we previously thought were important. In their design of the EMG-6, they made sure the battery was easy to access, and had sufficient ventilation to cool it, similar as stated above. However, the EMG-6 differs from our plane in battery placement. The battery cells appear to be stacked behind the seat of the plane, much further back than our plans. However, the fuselage shape and center of gravity is obviously quite different on the EMG-6 than our plane, so it surely makes sense for their design. (image)
Future Plans
We need to research more into the design of other electric planes, and more specifically their battery placement, to see if we can learn from them. Next steps will include 3D modeling our design plans, then refining and testing them with the help of other design team members and the physics team.