Remaining systems tasks on the DarkAero 1 prototype were the main focus in June. Several new fuel system components were assembled and tested. Aspects of the aircraft electrical system were revised to improve redundancy and handle edge cases that were identified. Additionally, components on the engine that were adequate for taxi testing were swapped out for versions that were better suited for flight testing.

Fuel System Work
Significant progress was made on the DarkAero 1 fuel system, which is nearing completion. This work began in May following sump tank tilt testing that initiated the design and fabrication of a revised sump tank. In June, the new sump tank was fitted with supply line fittings, drain valves, a pressure sensor, and vent fittings. 

The sump revision also provided the opportunity to incorporate several design improvements. The new sump features simplified mounting hardware that reduces the initial four mount points down to two while also integrating receptacles for the sump drain valves. The original sump design used a single drain valve that was positioned separately from the sump and required additional mounting hardware and a separate fuel line.

Revising the sump also allowed the drain location to be improved. The original drain valve protruded below the wing skin and would have increased drag. It also would have caused potential problems during a gear-up landing unless an external fairing was installed to protect the valve. The new drain valve is neatly tucked into the fuselage which minimizes drag and eliminates the need for a fairing around the valve.

A notable addition to the system was the installation of new vent check valves which were fabricated in-house. “Off-the-shelf” is almost always the most cost effective and convenient choice for small hardware items, but certain design requirements can force the need to manufacture hardware in-house. This was the case with the sump tank vent valves. The vent valves allow any air and fuel vapor in the sump to escape while preventing fuel from transferring between the wing tanks through the sump vent lines. There are two of these valves located on the sump lid, and they connect to vent lines that port back into the wing tanks.

As the fuel system is rebuilt with the new sump tank, a new fuel shutoff valve from Andair will be installed as well. The new valve is more refined and will replace the temporary valve that was used during initial ground testing. The valve is located in the center console and is easily accessible to the pilot.

The fuel system diagram was revised to reflect the updates and improvements made to the fuel system. More details on the fuel system work will be covered in an upcoming YouTube video.

Wire Harness Updates
Several changes were made to the wiring harness based on lessons learned during ground operations. The Master On switch was consolidated into the keyed Off-On-Starter switch. The switch originally intended for controlling a proposed electric version of the flaps was replaced with an On-Off switch for the backup ADAHRS unit. All resettable breakers in the panel have been replaced with fuses, which simplified the panel layout. Temperature monitoring was added to both the EarthX battery and the alternator capacitor to monitor these systems through the EFIS during flight testing. Lastly, connectors were installed on the main gear motors, allowing them to be more easily removed from the aircraft for service or modification.

Antenna Installation
The COM and ELT antennas were attached into their proposed locations for flight testing underneath the canopy fairing. Tests were conducted on the ground and in flight on a separate aircraft last month to investigate if this design would work, and initial performance was favorable. All of the antennas for the prototype are now internally mounted in the aircraft. This was a goal from the beginning of the project both to keep the airframe aerodynamically clean and to achieve better aesthetics. These antennas and their locations are still experimental, and additional ground tests are planned leading up to flight testing to confirm they all function properly. 

Engine Installation Updates
Although the engine was operated multiple times during static runs and taxi testing, some of the installation was only suitable for ground operations. These areas were recently updated to bring the engine to an airworthy standard. 

The UL520iS engine used in the DarkAero 1 has six cylinders arranged in a horizontally opposed configuration with two rows of three cylinders. The exhaust from each row of cylinders converges into a 3 into 1 collector. A short segment of exhaust pipe extending from each collector directs the exhaust out the underside of the airplane. The exhaust pipes used during taxi testing interfered with the exhaust tunnels, and they were only temporarily held onto the collectors. The proper airworthy setup was achieved by swapping out the last exhaust pipe segment to a different bend angle and welding a steel loop to the collector and the pipe so they could be held together with springs. 

The preliminary design for the cabin heat used a heat exchanger attached to the exhaust pipe of cylinder number 1. The exhaust heat exchanger was recently eliminated and the cabin heat duct was rerouted to the exit of the oil cooler. This removed about 2 pounds of weight and decluttered the space around the exhaust. The new cabin heat setup maintains the original downstream ducting and control valve so it will be possible to change back to the exhaust heat exchanger if the oil cooler does not yield acceptable results. 

Several of the fluid lines in the engine compartment were refined as well. This included changing the routing to reduce the potential for abrasion, installing additional fire sleeve, and installing segments of flexible lines in select areas to handle relative motion between the firewall and the engine.

YouTube
The DarkAero YouTube channel has grown steadily over the past few years and just recently passed 100,000 subscribers! Reaching this number was not something that was envisioned in the initial plan to document the development of the DarkAero 1. It has been so fun to share this journey, and as the first flight of the DarkAero 1 approaches, more exciting videos will be released!

A new YouTube video about the challenges of packaging the engine and accessories in the engine compartment was recently released. The video can be viewed here: 

Aerospace Mold Making Course
Session 5 of the DarkAero Aerospace Mold Making Course was held in early June. Additional demonstrations of vacuum bagging strategies and mold construction have been incorporated to enhance understanding of the course material. Bonus material was also added to the online version of the Aerospace Mold Making Course.

This includes the full bill of materials and step-by-step instructions for manufacturing an aluminum mold support structure. Students who have taken the in-person or signed up for the online version of the course now have access to these plans at no additional cost. This was one of the most requested pieces of equipment for students coming through the in-person course, and we are excited to finally have this included in the course materials! Use the link below to sign up for the next in-person session:

Sign up for the DarkAero Aerospace Mold Making Course

Aerospace Composites Course
The July session of the DarkAero Aerospace Composites Course is sold out! The next session will be in September, but it’s already filling quickly. Be sure to sign up early to claim your seat!

Sign up for the DarkAero Aerospace Composites Course!

Questions from students have often come up about how to implement composite panels in their designs. The latest article on the DarkAero Knowledge Base article highlights some lesser known benefits of structural composite panels and how they are leveraged in the DarkAero 1:

Looking Ahead
In July, the team will be focused on refining the landing gear retract motion and testing edge case scenarios. The sump tank testing will continue along with some remaining structural tests. A gradually shrinking list of miscellaneous systems tasks are being worked through in parallel to get the prototype ready for first flight.