In May, we continued making progress on the DarkAero 1 prototype. The nose gear remained in focus for the past month as we worked to move the system towards completion and testing. The wiring for the instrument panel was completed and progress was made towards preparing the airframe for installation of the wiring harness.

Nose Gear and Engine Mount
A large portion of the nose gear is built from CNC machined components, most of which are made in-house on our CNC mill. We were able to complete the in-house parts including the upper drag link, drag link mount, lock latch, torque links, trunnion pivot shaft, and idler gear lock. These components were all machined from aluminum. 

We were able to assemble and perform preliminary tests on the mechanism that locks the nose gear in both the up and down positions. The function of this mechanism is similar in principle to a rotary latch. When the nose gear extends to its limits of travel, either up or down, a latch catches on the drag links and locks them into position so the strut is constrained and cannot move. The locking mechanism was something we designed in CAD, but we knew it would have to be proven out with physical parts. There was no good way to thoroughly test the lock with a mock-up, so we just went straight into machining the final parts. We adjusted the geometry of the latch through a few iterations and got it to work the way we wanted. Seeing the mechanism lock and function as intended was a rewarding moment.

The CNC machined arms that support the strut and allow it to pivot were outsourced so they could be manufactured in parallel to the parts we were already working on. We are expecting these parts in early June. Once the arms arrive they will be riveted onto the engine mount which is already complete and assembled.    

In addition to the machined components, there are many miscellaneous bushings, fasteners, and other hardware required to complete the new nose gear. These were all purchased and are ready to be incorporated into the final assembly. One purchased component we are excited about is the sleeve bearing that allows the nose gear strut to slide in the trunnion to compress and absorb landing loads. In our previous design, this sleeve bearing was made from oil impregnated bronze, but we changed it to a self lubricating polymer called ATGF. This change dropped the weight of the component from 1.0 lbs to 0.2 lbs, resulting in a weight savings of 0.8 lbs. Keeping the empty weight down translates into more utility and performance, so we are always thrilled to find simple design changes to trim weight.

In parallel to the work on the new engine mount and nose gear, our intern Sean has been working through building the test rig and writing the test plan that will be used to perform the nose gear drop tests in accordance with FAA Part 23. These tests cover the full envelope of worst-case landing scenarios, allowing us to verify the new design will hold up in service. The test rig is a simple, reinforced wood structure that represents the firewall and wheel well structures with mount points to attach the engine mount and nose gear. The drop testing will be performed in a rigorous fashion similar to our wing load testing where we collected data and video throughout the entire process. We look forward to sharing more information as we get into testing. 

We are excited to wrap up construction and testing of the new nose gear assembly. We have mentioned this in previous communications, but it is worth revisiting; designing, building, and testing a clean sheet set of retractable landing gear is a challenging process. Just creating a basic design requires considerable engineering effort, but our objectives for the design go beyond achieving basic functionality. We have many overlapping requirements we are trying to meet including being lightweight, simple, reliable, serviceable, durable, manufacturable, easy to assemble, and cost effective. Taking a hasty approach would mean missing the mark on several of these targets.

Main Gear
As the nose gear nears completion, we are returning our attention to the main gear, which has been on pause while we've been updating the nose gear. The remaining tasks for main gear are to complete the retract mechanism, assemble the system, test the functionality and landing load capability, and install it in the aircraft.

Electrical System and Instrument Panel
In the last update, we showed the changes that were made to create the initial VFR layout of the instrument panel. The internal wiring to accommodate these changes is now finished. This marks the completion of the last of the three main modules that make up the avionics network. 

Our focus now turns to making the needed changes to the airframe bulkheads to secure the wiring in the airplane. These changes include enlarging bulkhead holes such as the firewall pass-through and the hole in the forward baggage floor to accommodate wiring to the cockpit and aft portion of the airframe. Once these changes are complete, we can get each avionics module fit up inside the airframe and connected with the wiring harness.

YouTube
We released several new YouTube videos capturing progress and answering questions about the DarkAero 1 project. Click the links below to view the videos:

New Engine Mount and Nose Gear Machining

What's Left to Finish the DarkAero 1?

CARBON FIBER vs METAL | Which is better?

News
We are honored to announce that we were recently part of a publication by our alma mater at the University of Wisconsin-Madison in the journal Composites (one of the most recognized scientific journals related to composites). The publication was made possible by the work of Alec Redmann and the UW-Madison College of Engineering Polymer Engineering Center.

A new, high force dynamic mechanical analysis (DMA) test machine was used on our prototype honeycomb panels to study their thermomechanical properties over a range of loading frequencies. The testing equipment, developed by NETZSCH Group, is so new that these specific tests on honeycomb panels are some of the first ever conducted. This testing provides more insight into the performance of our airframe structures that goes beyond common static or impact test procedures.

The link to the publication can be found here: https://www.sciencedirect.com/science/article/pii/S2666682021000311

Disclaimer: the published results do not necessarily represent final production materials or processes. They are only meant to demonstrate high force DMA as an evaluation technique.

Looking Ahead
In June we plan to finish putting together the new nose gear assembly, test the new retract and emergency extend mechanisms, and drop test it. Pending a successful series of tests we plan to install the new nose gear assembly into the aircraft. We will also be continuing construction on the main landing gear. The main avionics modules will be fit up inside the airframe and connected through the harness, which we'll be working on doing the final installation for.