In March we continued progress on the DarkAero 1 prototype with a focus on the firewall forward hardware including installation of the CHT and EGT wiring and an update to the nose gear retract mechanism. Additionally, we implemented improvements and upgrades to the wiring harness to prepare it for final installation in the aircraft.  

EGT and CHT Sensors
In March we received the exhaust gas temperature (EGT) sensors and the cylinder head temperature (CHT) sensors. The CHT sensors were installed on each cylinder head, and the EGT sensors were installed on each exhaust pipe. The exhaust pipes only needed to have a hole drilled in each to allow for the EGT sensor placement. Once these sensors were installed, their wiring was neatly bundled and constrained leading back to the firewall to meet up with the electronics in the central tunnel avionics box. Understanding the cylinder head and exhaust gas temperatures of each cylinder will be useful data in helping us dial in cooling as well as for monitoring engine health during flight testing.

Firewall Material Testing
Given the potential severity of a firewall forward thermal event, we wanted to verify that the combination of firewall materials we selected for the DarkAero 1 would meet certified FAA requirements for firewall thermal capability. Verification of our firewall was accomplished with a test rig consisting of an extruded aluminum frame with a flame source that could be directed at sample segments of the firewall. The test process specified by the FAA was followed for several different combinations of test materials.

We were able to verify that our combination of titanium and insulation met the FAA requirements for fireproofing. We will also be conducting a series of tests to verify the fireproofing of the wire pass throughs, the nose gear wheel well, and the exhaust tunnels. 

Some of the testing process can be seen on our YouTube channel linked here: 

What is the best FIREWALL material?

Wiring Harness Upgrades
The central tunnel avionics box is a core module in the electrical system that all of the wiring in the DarkAero 1 feeds into. We made a number of changes to the box that came out of our first pass on fully wiring up the box. The changes included creating an access hole to ease installation, adding wire constraints to secure the primary bundle, increasing the size of the instrument panel connector, and adding shrink tube sleeving to the instrument panel wire bundle. These changes will improve the serviceability and reliability of the box and its wiring. To complete the box for final installation, we will be adding connectors to the incomplete bundles at the other end of the box and shrink tube protecting the remaining wire bundles as well. We will be extending some of these improvements to the instrument panel to get both the panel and the box ready for final installation.

Engine Mount and Nose Gear
The design of the nose gear retract mechanism has gone through several iterations over time. A number of requirements need to be met by the nose landing gear design, and we are faced with many design constraints as well. The overlap of these requirements and challenges all feed into the design, analyze, build, test, and learning process. Prior to going forward with manufacturing our latest design, we mocked up a test stand with several of the key components to prove out the nose gear retract mechanism. From this testing we learned that the design would fully function, but it would require modifications due to the flex observed in the system. Before diving head first into those modifications, we paused to thoroughly assess whether there were other ways to improve the overall design.

Through several brainstorming sessions, we came up with a new design for the retract mechanism that is superior to the old design. It is more robust, requires fewer custom parts, is easier to manufacture and assemble, improves serviceability, is lighter, and cuts the retract time in half. The new design moves away from an electrical linear actuator to an electrical gear drive. It will retain a similar independent backup provision for extending the gear if there is a failure of the primary actuation motor. The new design is coming together rapidly, and we already have several of the key components in-house and are starting to test them. Additionally, stock and other hardware will be arriving soon. We are coordinating with a few machine shops to outsource half of the machined components to minimize impacts to the schedule.

In parallel to the redesign work, River was able to write prototype code for the logic boards that control the landing gear’s up/down actuation, cockpit position lighting, and locking mechanism. Keegan also finalized the installation of the retract mount points for the nose gear doors along with verifying the open/close positioning of the doors. 

We filmed a progress update video highlighting this work, which is linked here: 

Nose Gear Refresh: Trying Something New (+Progress Update)

Fuel System & Wing Lines Routing
Nate continued his work on the wing lines routing that includes the tubing for the pitot tube, angle of attack, and sump vents, as well as the wires for the magnetometer and wing tip lights. One of Nate’s projects this past month involved interfacing the sump vent lines with the fuel tanks at the wing tips. The sump vents route into the main tanks at the wing tips rather than overboard to free atmosphere. This approach keeps any fuel that burps out through the vent lines contained in the fuel system. Nate designed and manufactured the manifolds that interface the vent lines into the wing tanks and these will be installed in the next week.

Cabin Work
Our remote intern Michael has been designing and rapid prototyping several 3D printed components for the cabin of the aircraft. These included armrest access covers and covers for the nose gear door hinge mounts. With everything modeled in Onshape, we were able to easily share the necessary design elements with Michael. Michael was able to create CAD models of the printed components and test them for fit and function. Once he was satisfied with the final iterations, they were shipped to our shop. We are pleased with these first samples and look forward to testing them in the prototype. In addition to the 3D printed components for the cabin, we also had Michael print 1-to-1 scale parts for several of the main gear machined components. With these parts in hand, we can now perform test fit ups for the full main gear struts and perform motion studies for the air shock and retract path. This will allow us to identify any potential modifications to these components before they are manufactured. 

Looking Ahead
We are excited to see all the individual subsystems of the airplane coming together! Every day we move closer to completion of the prototype. Looking ahead to April, our focus will be on manufacturing components for the engine mount and nose gear refresh as well as finalizing the wiring harness.