The areas of focus for DarkAero in October were the main landing gear and build instructions. The design details of our main gear were released, and the first revision of our horizontal stabilizer build instructions was posted to the DarkAero Knowledge Base. Several new tools and resources were also published to the Knowledge Base that should be useful for the broader experimental aviation community. 

Main Landing Gear Progress
The design details of the main landing gear on the DarkAero 1 were not published until recently. We had a preliminary design for the main gear, but we knew we were going to revise and improve it based on lessons we learned while building the nose landing gear. To avoid confusion, we held off on sharing information on the main gear until we finished the updates. Now that the revisions to the gear struts and suspension are complete, we are excited to reveal more information on the final design! 

The main landing gear utilizes a trailing link with an air shock for suspension on a composite gear strut. This configuration is particularly well suited to provide both energy absorption during hard landings and a smooth ride over bumps on the runway. The wheels and brakes are made by Beringer and were selected for their light weight and braking capacity. The gear was designed to withstand landing loads specified under FAR Part 23 for certified aircraft. We filmed a YouTube video covering the landing gear design which can be viewed here:

Landing Gear Design for the DarkAero 1! | Carbon Fiber, Tricycle Retractable, Trailing Link

We were able purchase the air shocks as well as the aluminum stock and bushings that will be used to make the trailing link components. The trailing link will be CNC machined in-house on our mill and the composite strut will be fabricated from molds we will be manufacturing in the coming weeks. 

Landing Gear Electrical Work 
In parallel with our work on the gear hardware, we have narrowed in on a solution for the gear retract logic. The gear are retracted using electric linear actuators on each strut. Each strut has a travel limit in the up and down position and needs to be locked into position at each of these points and unlocked prior to any movement. In order to control the logic for each actuator, we will be testing the use of the STG-850 mini PLC by Barth Elecktronik. The Barth unit will provide a reliable logic solution that will simplify the wiring of each strut with localized logic. In the future, we would like to use this device to pull in data that can automatically deploy the gear during landing conditions in order to prevent an inadvertent gear-up landing. The gear will also include a manual release that will be actuated by the pilot from the cockpit in the unlikely event of a power failure or other gear malfunction. This override allows the gear to deploy under gravity in combination with a passive gas strut assist that will lock them into their final extended position. 

Wiring Updates
Work was done to reconfigure the center tunnel avionics box. Two additional MIL-SPEC connectors will be added to the wiring at the rear of the box in order to improve its serviceability. This will allow the box to better accommodate the engine sensor loom and our landing gear wiring. After these changes have been completed, we will move on to the updates needed to install the remaining wiring in the cockpit and do our first test of the harness. 

Build Instructions
The first revision of the horizontal stabilizer build instructions is now available on the DarkAero Knowledge Base. We released a draft of our cowling build instructions to kit reservation holders last year and used the feedback we received to make improvements. The instructions will be an online, digital-first experience, but we also formatted them so they can be printed and physically utilized in your workspace. They can also be viewed on a computer or tablet offline without an internet connection. 

We had several key requirements for the instructions and their format. We wanted them to exist as a maintainable, living document to tighten the loop between builder feedback and future revisions. We also wanted them to easily tie to video content hosted on our YouTube channel where we have been sharing videos that show how to perform certain steps and procedures like applying epoxy or cutting carbon fiber tubes. Lastly, the instructions are integrated with the aircraft 3D CAD itself. Since the DarkAero 1 was designed using Onshape Cloud CAD, the builder can view the 3D models and exploded views just by having a website link. 

We encourage you to explore the latest revision of the instructions and let us know what you think. It is important to us to create an enjoyable build experience, which is why we are seeking early feedback. 

Check out the build instructions on the Knowledge Base here: 

DarkAero 1 Build Instructions Chapters 1-2

Wind Tunnel Testing
Our validation work in the wind tunnel at the University of Wisconsin - Madison College of Engineering was paused since March as normal operations at the University were impacted by the pandemic. This past month we were able resume work in the wind tunnel lab and continue building upon the CFD aerodynamic modeling we had already conducted. Based on the tests we ran in the spring, we made some changes to improve the scale model mounting pylon to allow testing at higher speeds in the wind tunnel. We were able to test and validate these changes, and now we are able to utilize the full speed regime the tunnel is capable of. We have several more test sessions to go and lots of data to analyze, so we will report more on this work once the testing wraps up.
 

Intern Projects
Nathan continued his work from September, plumbing the fuel sump and integrating it with the rest of the fuel system. This included building mounting structures for the fuel sump between the wing tanks, installing hardware in the sump for the supply and return fuel lines, and finalizing solutions for the sump drains and fuel quantity measurement. Nathan’s efforts on the fuel sump have been extremely valuable as he has pushed progress on the fuel system forward while maintaining a keen eye for system safety, reliability, and functionality under all possible operating conditions. 

This past month Michael published an engine comparison guide to our Knowledge Base. This guide covers four-stroke engines with at least 80 horsepower that are in production. One of the major objectives of the guide is to allow kit aircraft builders to easily evaluate engine choices based on weight, power, and price. We occasionally receive inquiries about other engine options beyond the UL Power UL520iS engine that we designed the DarkAero 1 airframe around. The engine comparison guide reveals how difficult this engine is to beat in terms of power to weight ratio and value. Michael’s engine comparison tool can be accessed on the DarkAero Knowledge Base here:

View the Engine Comparison Tool

Ryan was able to publish a version of the wing proof load test tool similar to what we used to plan and document our wing load tests in August and September. The purpose of this tool is to provide a template for economical 'sandbag' wing load tests. Basic wing geometry parameters are input in the tool which then utilizes Schrenk's approximation method to create a target spanwise load distribution to follow during wing proof load tests. Ryan’s wing load test tool can be accessed on the DarkAero Knowledge Base here:

View the Wing Load Test Tool

In the Press
We were featured in the Canadian EAA Publication Bits and Pieces in an article written by DarkAero reservation holder Richard Visscher. Richard was the second person to place a deposit to reserve a DarkAero 1 kit and has been a longtime supporter. His article can be found here:

In Search of the Ultimate Kit Aircraft: DarkAero 1, Chapter 1

Looking Ahead
In November we will be continuing with fabrication of the main landing gear components and installing them in the fuselage. We are also expecting to receive the propeller shortly which will lead into the fun tasks of mating the propeller to the engine and installing the spinner. We have more tools and resources we are developing for the DarkAero Knowledge Base that should be ready for release in the next few weeks as well.