Progress continued on the DarkAero 1 prototype in February with our efforts focused on electrical system updates, nose gear door fabrication and installation, firewall forward tasks, and fuel system plumbing. 

DarkAero 1 Interior Rendering
We are excited to share the latest work from Carlos Z: the DarkAero 1 cockpit rendering! We have had many inquiries about the cabin and instrument panel, and we hope this latest rendering helps to convey more of the pilot experience. A few key features of the cabin design and layout can be seen in the rendering. The DarkAero 1 uses side-by-side seating, which allows the airplane to be flown equally from either the left or right seat. This will allow the pilot and copilot to share the flying workload on long cross country flights. The dual controls utilize side sticks, which have ergonomic benefits compared to a center stick or center yoke. The bubble canopy provides a clear, unobstructed field of view for both the pilot and copilot and also helps you feel like you are one with the sky rather than in an airplane. The prototype DarkAero 1 will utilize a VFR setup, but as the rendering shows, there is adequate space to install a capable IFR instrument panel. This latest rendering definitely gets us excited to fly and we cannot thank Carlos enough for his creativity and effort in helping us bring the DarkAero 1 to life!

Electrical System Update
After fully wiring up the harness for bench testing and validation, we came up with a number of modifications to improve safety, installation, and reliability of the harness. The bundle going through our center tunnel box was completely removed to allow for modifications to be made to the box. These modifications included additional mounting hardware for wiring, a bigger ground plate, and hardware to mount our fuel pump relays. With the box fully wired up, we were able to investigate the ease of installation of the box with the rest of the airframe and wiring harness. We were not satisfied with the logistics of our initial solution. We will be modifying our wiring bundles in the center tunnel box to reduce slack by adding connectors at the firewall. 

The wiring in our instrument panel was also removed to allow for changes to the interface and components like our Airmaster propeller controller to be installed. For prototype testing, we will be configuring the panel to match a single display version of the render you see above with a tablet display serving as the backup EFIS. Eventually we will upgrade the interface to match the full IFR setup you see in the render. 

Nose Gear Doors Installation
In addition to the electrical wiring upgrades, we have been working on the nose gear doors. This involved finalizing the door configuration, CAD modeling the parts, machining a prototype mold, manufacturing the parts, completing the assembly and installation, and writing up notes for the build instructions. We had an initial two door configuration with “J” style hinges modeled, but after further review we opted for a three door configuration for several reasons. The doors extend past the firewall and into the engine bay. Past the engine bay, the bottom of the fuselage curves up making it hard to get the geometry correct with the hinges regardless of the hinge type. Additionally, it's challenging to fit a hinge in the engine bay area. A two door configuration with no hinges firewall forward leaves too much unsupported door area. A third door eliminates the two door issues while also keeping the doors from being simultaneously tied to both the bottom cowling and fuselage, making it easier to remove the lower cowling for engine service. The next steps will be to fabricate a few small parts along with procuring some off-the-shelf hardware to allow the gear doors to interface with the nose gear strut. 
 

Battery Box
There are many options for electrical system architecture on the DarkAero 1, and there is enough room on the firewall to fit two standard 12 volt aviation batteries. A two battery configuration provides some options for redundancy, but a robust electrical system can be built using a single battery as well. We will be using a single EarthX lithium battery in the DarkAero 1 prototype. This past month we finished work on an enclosure to house and cool the battery in the engine compartment. The enclosure was fabricated from aluminum sheet metal, which was fun to work with since the majority of parts we have built up to this point were molded composite or CNC machined. The enclosure includes the external mounting hardware to hold our master relay, ANL fuses, and battery capacitor. The enclosure also mounts to a SCAT duct to allow bleed air from the engine cooling plenum to be funneled over the battery for temperature control. This design represents a starting point for the box that we will likely iterate on and refine as we get into testing and collect measurements on the cooling box performance. 

Firewall Forward Work
We have been progressing through the remaining tasks to finish up the firewall forward package with a recent focus on wiring logistics. We have remained efficient with our use of space in the engine compartment and strategically positioned wires to not interfere with other hardware. The result has been a clean and organized arrangement for the firewall forward package. The last tasks with the engine will be the installation of the throttle cable plus CHT and EGT sensors, through-hole wiring connectors at the firewall, fabrication of intake ducts for the inlet manifold and oil cooler, and installation of our redesigned engine mount with our nose gear retract mechanism. 

Fuel Sump and Wing Lines Routing
This past month Nate sealed up the fuel sump, and we arrived at a solution for routing the wing tip wiring, fuel vent lines, and pitot tube lines on the aft portion of the wing. The fuel sump top and bottom halves were closed up using a fuel tank sealant and constrained with an arrangement of fasteners. The number of fasteners was originally established to provide compression for a sheet gasket but we kept the pattern despite the use of sealant instead of a gasket. There are a number of changes we will be making to the fuel sump for production. These include making the sump out of fiberglass to reduce the number of steps required for adequate corrosion protection, moving the fuel sampling ports to the corners of the sump to allow fuel sampling on a broader range of pavement slopes, and slightly modifying the tank geometry. 

Nate fabricated a number of brackets to hold the fuel sump vent lines, pitot tube lines, wiring for the wing tip lights, and wiring for the magnetometer. Phenolic plate, a non-conductive composite material, was used for the raw stock for these brackets since it is compatible with the aluminum vent lines. The brackets were bonded into the wing and next we will be using them to route the various lines and wires they hold. 

YouTube 
We released a short update to our YouTube channel to get everyone up to speed with where the project is at, and we highlighted some of our progress over the past month. You can find it on our channel here:

DarkAero 1 Progress Update (Feb 2021)

We also created a video detailing five key facts about carbon fiber. We had to learn a lot about carbon fiber before building the DarkAero 1, and we receive a lot of questions on the material so we decided to share some of our insights on it. If you want to engineer a part made from carbon fiber, we definitely recommend checking the video out here:

Carbon Fiber - 5 Things You (probably) Didn't Know

Looking Ahead
In March we will continue finalizing firewall forward component installation and configuration. We will also be pushing to have the instrument panel and center tunnel avionics and wiring wrapped up and ready to be installed in the airframe. Work on the fuel sump and wing lines routing will be wrapping up as well.