Progress on the DarkAero 1 prototype continued in May, with systems tasks occupying the team’s focus. Landing gear retract testing was conducted with all three gear struts cycling as a system, hardware in the fuel system was revised, and seat belts hardpoints were installed in the prototype. Redesigned versions of the COM and ELT antennas were validated on the ground and in flight as well.

Landing Gear Retract and Extend Testing
The retract motion of the landing gear was recently tested with all three gear struts operating as a system. This was simulated in the CAD world many times before, but it was rewarding seeing the full retract motion in the real world. One pleasing result was how uniform and deliberate the retract and extend motion was across all three gear struts.

In this round of testing, the landing gear used their respective motor encoders to know when to speed up and slow down and used their limit switches to stop at the limits of travel. The system was connected to a laptop to allow the control logic to be edited between tests and tune the retract motion. Previously, the landing gear were slowly driven individually using a small battery and no control logic.

The gear were cycled up and down repeatedly throughout the retract testing. Overall, the system performed as expected “out-of-the-box”, but there are still a few tweaks that are being implemented to refine the retract and extend motion of the landing gear.  

More information about the control system that drives the landing gear was shared in a recently released YouTube video that can be viewed here:

Designing Smarter Landing Gear

The emergency extend operation of the landing gear was also tested. This function utilizes a gas spring on each gear strut to drive the strut into the down locked position. The basic functionality of the gas springs was proven out, but the force and damping of the springs will be further refined to match what is needed in service.

Seat Belts
Work on the seat belts began last year, but the seat belt installation was paused as painting the airplane began. This project resumed last month. 

Crow Safety Gear supplied the harnesses for the DarkAero 1 prototype. They were eager to support the project and sent multiple harnesses to determine which one would work best for the aircraft.

The original design (left) utilized two individual straps mounted to the top of the seat bulkhead. This configuration required reinforcing structure to be added to the seat bulkhead to handle the loads from the shoulder straps. After reviewing the design further, the mounting configuration of the shoulder segments was changed to a V-harness (right) with both shoulder straps converging to a single mount point that bolts into the top of the wheel well bulkhead in the aft baggage compartment. The new design is lighter than the two individual straps and simpler to install compared to the original design since less reinforcement structure is required. 

The tradeoff is the V-harness will run through the baggage compartment, which means the straps need to be pushed to the side as bags are loaded. This was deemed as an acceptable compromise since the V-harness is already a common setup for many other two seat aircraft with baggage space behind the seats. 

Fuel System
A new sump tank was fabricated based on lessons learned from the sump tank tilt testing conducted in April. A small leak that originated from the drain port on the fuel sump was detected during the fuel sump tilt testing. This was an area of concern before the testing began, and it brought into question the potential for a sump tank redesign. 

A quick fix of attempting to seal the area with additional PRO-SEAL may have worked, but given the critical nature of the fuel system and the significance of the drain, the more substantial redesign fix was agreed upon. The redesign was limited to the bottom half of the sump tank which was updated to reduce the potential for leaks and to improve the function of checking for and removing fuel contamination. 

The original design used a single drain valve that was installed off to the side of the sump with a connecting line that ran to the aft face of the sump. This location represented the lowest point in the fuel system, but only when the aircraft was parked on level ground. If the aircraft was tilted in any direction, the lowest point would land away from the drain port. 

The new design solved this potential problem by sloping the sump so the lowest points in the system land at the outboard sides of the sump. Left and right drain valves will interface directly with the sump in these low points. This shape ensures that even if the aircraft is parked on uneven ground, the lowest point will always be positioned over a drain valve. 

Additionally, the new design maintains the same internal volume while eliminating the need for a remote drain and its associated fittings, manifold, and fuel line. Lastly, the revised design consolidated the five mount brackets into just two. These brackets interface with features on the bottom of the sump that make it easier to position and install. 

The new tank mold was machined out and the revised sump bottom was infused. The new tank is currently being reassembled with hardware for testing. 
 

Antenna Testing and Installation
The COM and ELT antennas were recently redesigned and validated through both ground and in-flight testing. A number of different antenna designs were built and tested, but eventually a simple angled dipole design was settled on for both antennas. The performance of the latest design for the COM antenna worked well enough to receive signals from all of the communication frequencies available at the local airports tested. These antennas will next be fixtured under the canopy faring inside the aft baggage area where they will be further validated during flight testing of the prototype. 

Online Aerospace Mold Making Course

The Online Aerospace Mold Making Course is LIVE! 

Five sessions of the DarkAero Aerospace Mold Making Course have been held in-person, and now the course is available online as well! The Aerospace Mold Making Course was developed to share the knowledge and hands-on skills required to design and build high-quality molds which are required to make high-quality composite parts. The online course can be accessed here:

DarkAero Online Aerospace Mold Making Course

Looking Ahead
In June, 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.