Testing continued on the DarkAero 1 prototype in July, with landing gear drop tests and remaining structural tests being the main focus on the airplane over the past month. The DarkAero team also attended the annual EAA AirVenture airshow in Oshkosh, WI.

Landing Gear Drop Testing
The initial phase of drop testing was focused on a level landing with all three tires contacting the ground simultaneously as specified in FAR Part 23 Appendix C for Basic Landing Conditions. Accelerometer data obtained from initial drop tests showed that impact g-loads on the airframe were higher than predicted at target drop heights. These loads could be reduced through tuning of the landing gear suspension and further testing, but the decision was made to first add structural reinforcements in select areas of the airframe prior to advancing to different drop configurations to increase the structural margin of the airframe. The reinforcement work was completed in early July, allowing the drop testing campaign to resume.

Starting fresh, drops were conducted at incrementally increasing heights, with a number of additional calibration drop tests conducted at a fixed height while varying the pressure in the air shocks. After sharing test data with the shock manufacturer, the decision was made to switch to smaller diameter main gear shocks with increased operating pressure. Given that “off-the-shelf” air shocks were used for the trailing link main landing gear, it was easy to change the shocks to a different model. After the update, further drop testing was conducted with the new suspension hardware. A combination of smaller shocks, different tires, and correct tire pressure improved the response of the suspension system and was effective in reducing the g-load levels on the airframe.

Twenty four drops were conducted in a level landing configuration, with roughly half of the drops representing edge case or aggressive landing conditions. Given the clean sheet landing gear and airframe design, a thorough inspection was conducted in between each drop to look for areas of delamination or damage in the composite airframe structures and yielding in the metal landing gear components. No damage was found after the highest drop height, which allowed the initial phase of the drop test campaign to be deemed complete.

One of the major outcomes of the level landing drop tests was validation of the interface between the nose landing gear assembly and the composite airframe. While the nose landing gear was tested previously on an independent drop test rig, the interfacing structures on the airframe were not part of that test. The highest drop heights proved out the connection between the nose landing gear and firewall where it attaches. This was at the furthest forward CG condition, which generates the highest loads on the nose gear.

The next phase of drop testing will test level landings with the nose wheel just clear of the ground. This will put minimal load on the nose gear, but much more load on the main landing gear.

Airframe Modifications 
A small but useful modification that was recently made to the airframe was the addition of two service holes in the fuselage sides aft of the seatback to improve access to control system hardware. This was a proposed change that had been under consideration for some time, but it had not been committed to the prototype aircraft because it was considered more of an optional feature. The control system hardware aft of the seatback was accessible without the service holes but with some inconvenient contorting. The final decision to add the holes was made in anticipation of remaining control system refinement work that may come about in flight testing. The holes were specifically positioned to sit in close proximity to critical control system hardware and sized to minimize any impact to the structure. After the access holes were cut, it became apparent just how valuable the improved accessible will become when servicing the control system on both the prototype aircraft and future customer kits. 

Another modification made to the airframe was the installation of a central hardpoint in the wing to support the base of the flap lever. This was identified as an area requiring additional reinforcement to reduce compliance in the flap controls. The hardpoint was created by bonding a carbon fiber billet plate to the aft shear web in the center wing section.

AirVenture
The EAA AirVenture airshow was held in late July in Oshkosh, WI. The DarkAero team attended the show on July 24th to meet with customers, suppliers, 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!

DarkAero Growth
DarkAero has been growing to expand engineering and manufacturing services. The capability of the team at DarkAero has been increasing as new engineers and technicians have joined in on the DarkAero 1 and other aircraft programs supported by DarkAero. Additional capacity was added to the manufacturing team in July as more composite technicians were brought onboard. If you’d like to join DarkAero, check out the DarkAero Careers page and apply today! Interested candidates can inquire at careers@darkaero.com.

Looking Ahead
In August the team will continue the remaining ground tests to validate the airframe and controls prior to first flight.