Ongoing ground testing and refinement of the DarkAero 1 prototype remained a focus of the team in February. These tasks primarily centered around the fuel system and control system. Efforts to expand the team continued as well.

Fuel System Testing 
On the outside, the wing of the DarkAero 1 looks like it could be found on other composite kitplanes, but on the inside it has a number of “experimental” design elements. The objective of flying both fast and far meant the wing had to be relatively small to minimize drag, while the internal volume of the wing had to be maximized to accommodate a large fuel volume for long range missions. The overlap of aerodynamic, structural, and fuel system requirements led to the nonstandard Hollow Grid wing construction that was employed on the DarkAero 1. 

There is no guarantee that a new design will work automatically, so physical testing has been used extensively to prove out the wing. A series of leak tests were recently performed on both of the wet wing tanks to confirm complete sealing before they are filled with fuel. This was accomplished by pulling a slight vacuum on the tanks and monitoring their internal pressure over time. Each tank maintained its pressure state over 48 hours. 

In addition to vacuum testing the tanks, positive pressure tests were performed to simulate the range of hydrostatic pressures generated in the tanks by the fuel column height during maneuvers such as an aggressive forward slip. Both tanks passed these tests, indicating readiness for the installation of the fuel sump and filling the tanks with fuel. Furthermore, the function of the dual redundant wing tank vents was confirmed as excess pressure was bled through the vents.

Another recent series of tests related to the fuel system included pressure tests on the sump tank and its check valves to confirm that pressure differentials between the wing tanks do not produce undesirable flow through the system. Areas for improvement were identified in the system and design iteration ideas will be tested in the coming weeks. The latest round of fuel system tests has provided more confidence in both the structural integrity of the wet wing and the behavior of the fuel system. 

Control System Testing
Refinement and testing of the control system has been an iterative process over the last few months, and this continued through February in parallel to the fuel system testing. Based on initial load test findings, changes were made to the flaps and aileron controls to increase their stiffness, and the effectiveness of these changes was explored through another series of load tests. The flap hinges were stiffened with additional composite work, and the flap hinge free play was decreased through implementation of hinge pins made to tighter tolerances. A stiffer detent bracket for the flap handle was installed, and the structure that supports the flap actuation hardware was reinforced as well. All these improvements contributed to the flap system deflecting significantly less during simulated aerodynamic load testing. A final round of load testing remains to deem the flaps airworthy prior to flight testing. Acceptance criteria for the DarkAero 1 control system is being established through referencing standard acceptance criteria for control system behavior on existing military and civilian aircraft. 

Calculations and testing revealed it was necessary to increase the force of the springs that provided positive centering to the split rudders on the DarkAero 1. The tight cavity around the rudder hinges limits how large of a spring can be implemented, and this had presented a roadblock in the initial design process. However, a concept for a new spring mechanism with increased force was recently developed, and the design is currently being refined prior to implementation. 

DarkAero Growth
DarkAero has been growing to accelerate flight testing the DarkAero 1, manufacture DarkAero 1 kits, and expand engineering and manufacturing services. Interviews for new engineers and technicians have been ongoing, and the team is growing. If you’d like to join DarkAero, check out the DarkAero Careers page and apply today! Interested candidates can inquire at careers@darkaero.com.

DarkAero Courses
Session 8 of the Aerospace Mold Making Course was held in February. Students who attended included both hobbyists and professionals, and their applications included kitplanes, cars, sailboats, and helicopters. The course covered mold construction methods that ranged from prototyping methods for one-off designs to CNC machined molds for mass production of composite parts. 

The next session of the Aerospace Mold Making Course has not been scheduled yet, but the online version of the course is available for immediate access: 

Sign up for the Online Aerospace Mold Making Course!

The DarkAero Aerospace Composites Course has also remained popular, with only one open seat still available in the next session on March 22-23: 

Sign up for the DarkAero Aerospace Composites Course!

Looking Ahead
In March, the team will continue working through the remaining ground tests for the control system and structures of the airframe. The main landing gear drop test and load test of the wing to fuselage interface are also on the horizon. Expanding the team and getting new team members up to speed will remain a focus.