In August, the DarkAero 1 prototype was disassembled for work on several components and systems including the control system, exhaust tunnels, wiring harness, and brake lines. The airplane was then reassembled for a second round of ground vibration testing. Paint and painting equipment were purchased and set up as well.

Rudder Pedals
The rudder pedals were updated to incorporate necessary changes that were identified during taxi testing. The original design employed a “black metal” approach where an equivalent welded tubular steel design was converted to carbon fiber. The original design was made of filament wound carbon fiber tubes joined together with “forged” carbon fiber tube connectors that were developed in-house. Filament wound tubes are strong and light, but they are difficult to join at right angles. The molded tube connectors solved this problem, but they were not a feasible solution for production. 

The new design is both flight capable and easily manufacturable. It still uses filament wound torque tubes to join the pilot and copilot pedals, but the rest of the pedal structure is made up of parts that are cut in 2D shapes from carbon fiber plate and then assembled into 3D structures. The foot pedals are made from infused Soric core sandwich panel stock that is cut in a flat pattern and then folded and bonded into the final foot pedal shape. The position of the pedals can still be independently adjusted to accommodate occupants of different heights. After the parts for the new rudder pedal system were bonded together, the assembly was installed in the fuselage and tested. The updated design offers improved ergonomics and increased stiffness over the original design. 

Exhaust Tunnels
The exhaust tunnels required changes that were identified leading up to the first engine start. The previous tunnels were molded with compound curves that were difficult to properly heat shield. Although several combinations of flexible shield material were tested, none of them held up to the FAA’s Part 23 standards for firewall heat shields, so the design was updated to allow for more rigid materials to be used as fire protection. Updated cutouts to match the new exhaust tunnels were cut into the firewall bulkhead and bottom skin of the fuselage. The new exhaust tunnels were created from a flat sheet of Soric core sandwich panel that was cut to shape and then folded into a 3D structure. The updated geometry allows the tunnels to be protected with Fiberfrax and titanium, which is already used as the firewall heat shield. Added benefits of the new design include improved manufacturability and easier implementation of adjustable cowl flaps.

Wiring Harness Updates
Several aspects of the wiring harness were updated to prepare for high speed taxi tests and ultimately flight testing. This work included installation of Mil-Spec connectors at the wing-to-fuselage wiring interface, routing the wiring for the headset jacks, and connecting the mechanical switches for controlling the lights on the aircraft. Previous engine testing uncovered a faulty CHT sensor that was also replaced. 

In addition to these updates, a basic dipole antenna was attached to the belly of the airplane and connected to the COMM radio. Initial performance tests with the antenna have yielded surprisingly good results. This design will be explored more going into the next round of taxi testing. If the belly mounted dipole antenna does not provide acceptable performance, a more traditional antenna will be used in its place. 

Brake Lines
The DarkAero 1 uses hydraulically actuated brakes that are located on the main landing gear wheels. The hydraulic brake lines start at the brake calipers on the main wheels and run up the gear struts to the fuselage. The brake lines ultimately connect to the brake master cylinders, which are attached to the pilot rudder pedals. In a fixed landing gear aircraft, this brake line routing is straightforward. However, the main gear on the DarkAero 1 are retractable and swing through more than 135 degrees of rotation to fold up into the fuselage. Constraining the lines and maintaining proper bend radii is challenging for this type of configuration. During taxi testing, the lines were run from the calipers, up the struts, and into the fuselage, but the routing had not yet been finalized where the gear struts pivot. A solution was identified and implemented to manage the brake lines at the gear pivots. 

Ground Vibration Testing
The airplane was reassembled following the systems work for a second round of ground vibration testing (GVT). Once again, Sam Jaeger organized and led the testing. The objective of the second GVT was to characterize higher frequency modes identified in the first test. 36 measurement points were collected, and the data is now being used to refine the vibration model of the aircraft. 

Production Shop
In August, the lower wing skin mold and the three section oven were moved to the pilot production shop. These were the last remaining pieces of equipment for composite part production that needed to be relocated. This equipment was left behind during the original move due to its size and weight. The ovens and lower wing skin mold both required more thought to avoid damage while moving them. Eventually, a plan was established to rent a U-Haul and muscle the equipment to its new home with enough manpower. It was all moved safely, which was a relief. With this tooling out of the hangar, enough space was cleared to set up a paint booth for painting the DarkAero 1 prototype. 

Preparation for Paint
An inflatable spray booth was purchased for use while painting the prototype. The booth measures 26ft x 15ft x 10ft and is large enough to fit all sections of the aircraft. A 4 gallon kit of PPG HS CA8620G primer was purchased as well. Many inquiries have come in about what the final paint scheme will look like. While the exact details have not been finalized, it will likely look similar to the rendered images of the DarkAero 1 that have been shared previously, with the primary structures painted light colors, and a few areas of clear coat on non-structural areas to show off the carbon fiber work. 

Courses
The tenth session of the Aerospace Composites Course was held in August. The course has continuously been improved, as the material and hands-on demos have been refined and expanded through student feedback after each session. 

A short trailer highlighting the course can be viewed here:

The next session is almost full, but a few open seats are still available in the September 16-17 and October 6-7 sessions. Seats can be reserved by using the following link:

DarkAero Aerospace Composites Course

If you are unable to attend the Aerospace Composites Course, but would like to begin learning the material, an online version of the course is now available. A number of people have already enrolled in the online course over the past month, and we are looking forward to teaching more students through the course. Sign-up for the online course using the following link if you are interested:

DarkAero Aerospace Composites Online

The second session of the Mold Making Course will be held on September 22-23. The two-day course provides a foundation of knowledge and hands-on training so that building molds does not become a barrier in the process of creating composite parts. Two spots remain in the September session and several spots remain in the November session. Seats can be reserved by clicking the following link:

DarkAero Mold Making Course

YouTube
A new YouTube video was released highlighting the first taxi test. The video can be viewed at the following link:

First Taxi Test! - DarkAero 1

Looking Ahead
In September, we will continue on remaining projects including the flap controls, main landing gear actuation, and painting of parts. Additional taxi testing is planned as well. We’re also looking forward to holding the next sessions of the Aerospace Composites Course and Mold Making Course.