Progress continued on the DarkAero 1 prototype in July, with testing and small remaining systems tasks being the main focus over the past month. The team attended EAA AirVenture, and DarkAero’s composites manufacturing was featured in CompositesWorld.

Fuel System Work
The revised fuel sump tank was recently tested, and it met its design targets for function and performance. Following a successful leak check, a range of tilt tests were conducted to simulate various flight conditions. Since the left and right wing tanks are both connected to the sump tank, the purpose of the tilt testing was to understand how much fuel could potentially transfer between the wing tanks through the sump tank during uncoordinated flight maneuvers. The sump tank is designed to limit fuel transfer between the wing tanks with the installation of check valves in the supply lines and vent lines. 

One end of the sump was connected to a separate test tank positioned higher than the sump to simulate the fuel in the wing tank. Fuel was drained from the low end of the sump into a catch tank, which represented the other wing tank. By weighing the catch tank before and after each test iteration, the rate of fuel transfer between the wing tanks could be determined for specific flight attitudes.

The check valves performed well, reducing the fuel transfer to a negligible amount. The shallowest tilt angle tested was 5 degrees. At 5 degrees of tilt, the worst case fuel transfer rate was achieved at just 0.6 gallons per hour. Steeper tilt tests resulted in even less fuel transfer because the check valves sealed better at steeper angles. 

Additional testing was conducted to verify the HydraMat used on the fuel pump pickup functioned as intended in the aircraft fuel system. This involved pumping fuel out of the sump using the electric fuel pump and observing the flow rate and level of aeration coming from the fuel pump discharge. The HydraMat was able to pick up the majority of the fuel in the sump, with less than 0.4 gallons of fuel left in the sump when the first trace of air was detected in the fuel pump discharge. 

Firewall Forward
The heat exchanger for the oil system on the DarkAero 1 requires a supply of cool air to carry heat away from the engine and the oil system. Air reaches the cooler through a duct that runs from an opening at the front of the cowling back to the cooler. The size, shape, and location of the inlet are all important variables that must be established correctly to achieve adequate performance out of the oil cooler. Placing the inlet opening in a high pressure area helps create the necessary pressure gradient to force air through the cooler, and aligning it with the oncoming airflow helps it operate efficiently while minimizing drag.

Although the DarkAero 1 has not flown yet, it is still possible to study the airflow and air pressure around the airframe using simulation tools like CFD and then use this information to guide the design. This image above shows an overlay of the pressure distribution on the cowling in cruise conditions. Blue represents low pressure areas, while all other colors represent varying degrees of high pressure. The proposed test configuration for the oil cooler inlet and duct on the prototype are also shown in their intended positions. A few streamlines of air in the region of the inlet are faintly shown as well. 

The inlet connects to a diffuser on the front of the heat exchanger with a section of flexible tube. Both the inlet and the diffuser are additively manufactured from high temperature nylon using an industrial MJF (Multi Jet Fusion) 3D printer, so the inlet and duct are outsourced components. The inlet was recently manufactured, and this design will be further refined as the system performance is measured in flight testing. Any necessary changes to the design can be updated in the CAD realm and then rapidly 3D printed so that different configurations can be quickly iterated through.

Instrument Panel Wrapped
The instrument panel of the DarkAero 1 was skinned with a vinyl decal to label all of the switches and controls. Getting it placed correctly and adhered took a couple of attempts, but once the right technique was determined, the application was straightforward. Labeling and placarding the instrument panel has made the pilot interface feel more official, and it also shows how simple the interface is, which has been a design goal from the beginning of the project. 

AirVenture 2023
The EAA AirVenture airshow was held during the last week of July in Oshkosh, WI. The DarkAero team attended the show on July 28th to meet with customers, students, and the broader aviation community. The UL Power Aero Engines booth served as a central location for DarkAero enthusiasts to meet up. It was fun to connect with others who share a passion for aviation, and attending AirVenture always injects a boost of energy in the DarkAero project. Thank you to UL Power, and to everyone who stopped by to chat!

YouTube
A new YouTube video about the fuel system and the sump tank testing was recently filmed. An early release of this video is available to YouTube community members, and the public release will be available later this week! 

Community members can watch the video now at the link below:

[EARLY RELEASE] The Revised Fuel Sump Tank

Courses
In the July session of the DarkAero Aerospace Composites Course, John Register of RCON-NDT returned to demonstrate ultrasonic inspection techniques on composite materials. His discussion allowed students to delve into the practical use of ultrasonic inspection tools to identify composite defects such as delamination, disbond, unbond, porosity, and FOD (Foreign Object Debris or Damage).

Ultrasonic inspection works by projecting sound energy into a structure and analyzing the response of the returning signal. The return signal will mainly be the backwall echo if no defects are present, but voids, cracks, or delamination will create their own echo which can be detected by the inspection equipment. Having this ability to “see” beneath the surface is game changing for verifying the quality and integrity of composite structures. Students were excited to see these tools in action on test samples manufactured in class as well as on real aircraft parts. 

The full ultrasonic inspection demonstration was recorded and will soon be available through the online version of the course! The online course resources are accessible to all DarkAero Aerospace Composites Course alumni who have attended in-person or enrolled online. If you’d like to enrich your knowledge of composites and accelerate you composites project, check out our courses using the link below: 

DarkAero Courses

For those looking to enhance their expertise in composite part manufacturing, and those embarking on creating their first composite part, it is important to have knowledge and skills in mold making. There are a limited number of spots remaining for the August 17th - 18th Aerospace Mold Making Course. Enhance your knowledge and skills by registering for the course at the link below:

Sign up for the DarkAero Aerospace Mold Making Course!

In The Press
DarkAero’s composites manufacturing was recently featured in CompositesWorld. The article can be accessed through the link below:

Composites Manufacturing for General Aviation Aircraft - CompositesWorld

Looking Ahead
A gradually shrinking list of miscellaneous systems tasks are being worked through in parallel to get the prototype ready for first flight. The task list includes work on the flaps, cabin interior, landing gear, and control system. A few tests remain on the landing gear, fuel system, and airframe structures. In August, the team will continue to tackle these items.