The remaining tasks on the wing of the DarkAero 1 prototype were the main focus in October with work wrapping up on the flap controls and fuel system. The first layer of primer paint was applied to the wing as well.

Paint
Since the beginning of the DarkAero project, one of the main goals with the DarkAero 1 design was to improve the experience of building a composite kit airplane. A major piece of that puzzle was to eliminate much of the filling and sanding operations that are normally required to prepare a composite airframe for paint. 

These design and manufacturing efforts were recently put to the test when painting the wing of the prototype aircraft with its first layer of primer. The only prep work performed prior to paint was scuffing the surface with a Scotch-Brite pad and then solvent wiping the wing.

A layer of primer was sprayed onto both the top and bottom wing skins. Paint has a tendency to highlight defects that are otherwise not obvious, so there was much anticipation of what the paint would reveal. This is hard to capture in photos, but there is little to show that will require filling and sanding. A few pinholes in the wingtip caps and some notecard size areas where the weave pattern is visible are all there is to correct.

Flap Controls
The major design elements of the flap controls were completed in September, allowing manufacturing of this system to proceed in October. This included the fabrication and installation of the flap torque tube, bearing blocks, flap handle, and flap position mechanism. 

The backbone of the flap system is a carbon fiber torque tube that runs underneath the seat bottom. The flap handle is directly connected to this torque tube, and the torque tube is supported by 3D printed bearing blocks. These bearing blocks were outsourced and manufactured through a process called Multi Jet Fusion (MJF). They were ordered at the end of September and arrived in early October. The bearing blocks are held in place by Click Bond studs bonded to the wing structure. The flap torque tube itself was used as a positioning fixture to establish alignment between the bearing blocks and Click Bond studs as they cured in position. This operation was accomplished with the wing supported with its trailing edge oriented upward. 

After the torque tube bearing blocks were installed, the flap handle and position mechanism were fabricated. The handle is made from aluminum tubing and is attached to the torque tube through a CNC machined aluminum adapter. The mechanism that controls the flap position was also CNC machined from aluminum. The position mechanism has detents for retracted, quarter, half, and fully extended flap positions. Several other small pieces of hardware were purchased to complete the handle and position mechanism. 

All of these components were assembled together to test the functionality of the handle. The flap handle is a mechanism that is impossible to “feel” in the CAD world alone, so it was satisfying to assemble everything and confirm the mechanism functioned as intended. 

Fuel System
In October, additional fuel sump updates were completed to accommodate the new fuel shut-off valve position. This involved opening up the sump to reroute the fuel pump port, closing the sump, installing additional mounting Click Bond studs for the sump, fabricating a center console mount, and building new fuel lines. 

Opening the sump provided an opportunity to confirm the peel strength of the Pro-Seal used to seal the top and bottom sump halves and also examine the Holley Hydramat. The previous Pro-Seal bond was solid, and required over an hour of wedging and peeling action to remove the two halves. This service test built confidence in the sump tank integrity going into the next phase of taxi testing and flight testing.

The Holley Hydramat has been discussed previously, but is worth mentioning again with the recent sump work. The Hydramat is installed inside the sump tank and serves double duty acting as a 15-micron pre-filter and also as a fuel pickup. It uses surface tension and fuel wicking to draw in fuel while excluding air. If any area of the Hydramat is uncovered, tiny pores in the media seal off through surface tension preventing air from being pulled into the fuel lines. When these pores seal off, it forces fuel to be drawn from other areas of the mat still in contact with fuel. It eliminates the need for the traditional and more complex fuel pickup systems.

Once the sump was opened, its internal fuel line routing was modified to adapt to the new fuel exit position on top of the sump.

In addition to the modifications to the fuel sump and fuel lines routing, a panel structure was manufactured that will become a new seat bottom. With the recent updates to the flap handle, center console, and fuel line routing, the previous Soric panel seat bottom required more modifications than were worth pursuing, leading to the construction of a completely new seat bottom.

DarkAero Courses
Session 12 of the Aerospace Composites Course was held in October. An exciting addition to the course is a new prepreg carbon fiber demo module. The prepreg material used in the course is different from traditional prepregs currently on the market. It has a nearly indefinite shelf life, does not require cold storage, and yields excellent surface finish without an autoclave. Recent testing of the material has produced excellent results. The module provides an easy way for students to get started with prepreg composites by demonstrating a path that eliminates many of the major hurdles that are traditionally encountered with prepreg composites.

The last session of the Aerospace Composites Course for 2022 will be held on November 4-5. The next session available won’t be held until January 2023! If you are interested in signing up, seats can be reserved at the link here: 

Aerospace Composites Course Sign Up! 

The Aerospace Composite Course is also available in an online format to reach those who cannot attend in person. It is offered at a reduced rate relative to the in-person course, making it an appealing option for college students or individuals who are just beginning to explore composite materials. A step-by-step infusion demonstration video was recently added to the course lessons.

The online course can be accessed here:

Online Aerospace Composites Course Sign Up! 

The next session of the Mold Making Course will be taught February 23-24, 2023. This course was born out of interest from students who attended the DarkAero Aerospace Composites Course and expressed interest in developing a deeper understanding of building tooling to create their own composite parts. The goal of the two-day course is to provide a foundation of knowledge and hands-on training so that building molds does not become a barrier in the process of creating composite parts.

Several sessions of the course have already been held, and the course material has continued to be refined. Learn more and sign up for the Mold Making Course here:

Mold Making Course Sign Up!

YouTube
Two new YouTube videos were released in October that cover the design of the DarkAero 1 wing. 

The first wing design video highlights the aerodynamic requirements the wing must meet to satisfy the mission goals of speed, range, and efficiency. The equations and math used to determine the wing size, shape, and airfoil selection are discussed. The video can be viewed at this link: 

Why we don't use winglets (DarkAero 1 Wing Design)

The second wing design video builds upon the first by providing an overview of the composite structures that allow the wing to withstand thousands of pounds of aerodynamic loads while still remaining exceptionally light. The video can be viewed at this link:

Exoskeleton wing design - how carbon fiber makes it possible

A third video will be released in November to continue the wing design discussion by covering its manufacturing. Stay tuned for this release in the coming weeks.

Composites Knowledge Base Expansion 
The DarkAero Composites Knowledge Base was expanded in October with the addition of several articles that complement the DarkAero Aerospace Composites Course. The articles are an excellent starting point for anyone interested in learning more about composite materials. Additional articles are already underway. The released articles can be read here:

DarkAero Knowledge Base - Composites

DarkAero Apparel
It’s officially fall in Wisconsin, and the temperatures are starting to drop. If you are entering fall weather as well and are looking for a way to stay warm, wearing a DarkAero hoodie and beanie is a great way to keep out the cold! Head over to the DarkAero shop page to get your own! 

DarkAero Apparel Store

In The Press
The effort to optimize the design of the DarkAero 1 to maximize its speed, range, and efficiency is never ending. This philosophy extends to every single part in the aircraft, including ones that may seem inconsequential, like bearings. Marsh Brother’s lightweight polymer bearings have replaced several conventional, heavier bronze bearings on the aircraft. Marsh Brother’s recent article covers more on how their bearings are used throughout the DarkAero 1:

Marsh Brothers Aviation Materials Expertise Adds To Low-weight Appeal Of DarkAero Composite Kit Aircraft

Looking Ahead
In November, attention will be placed on completing the manufacturing of the main landing gear actuation and main gear doors, and finalizing painting the aircraft in preparation for high speed taxi and flight testing.