In September we focused on final assembly of the wing systems and control surfaces as well as upgrades to our CNC mill and canopy mold. We also completed some of the final closeouts in the fuselage that will allow us to begin systems installation next month. In between work on the wing and fuselage we were invited back by our alma mater at the University of Wisconsin-Madison to talk about our journey so far with DarkAero. 

Wing Assembly
At the beginning of September we completed the installation of the flaps and then in the last half of the month we assembled and installed the ailerons. We took our time with the ailerons due to the design of the counterbalance that sits on the outboard edge of these parts. The counterbalance was a critical part to get right with its importance in preventing flutter on the ailerons. We are about two weeks away from having the wing on the DarkAero 1 prototype fully assembled. This includes the installation of flap and aileron control systems, fuel sump and seat bottom attachment, and wing tip fabrication and installation.

Wing Tips
For the wing tips, we debated using a 3D printing process but ultimately we were able to develop a process that allows us to go from final design, to tooling, to final part in less than 48 hours. We did a trial run of this process on our horizontal stabilizer tips, which yielded good results. We have since successfully repeated this part making process on the vertical stabilizer tip, and we will be doing it once again on the wing tips next month.

Fuel Sump
We finished molding the fuel sump, purchased the remaining sump hardware, and partially installed these components in September. One of the more interesting parts we are testing in our fuel sump is called Holley HydraMat. HydraMat will serve as a filter on the fuel pump inlet as well as allow the pump to continue to pull fuel in unusual attitudes while eliminating a traditional flop tube. The large area of the HydraMat will make it virtually immune to blockage in the event of particle contamination in the fuel system. Going into October we will be constructing the outer brackets to allow the sump to sit level in the wing as well as performing final closeout and sealing of the sump. 

Tormach Upgrades
In October we will be doing some pretty involved machining to construct our engine mount and landing gear hardware, which means our Tormach CNC machine will be generating a lot of metal chip debris in the process. The Tormach PCNC 1100 we own did not have a full shroud to contain the chips that can be generated from removing material on larger jobs. Improvising, we constructed a three sided enclosure from acrylic and aluminum angle to contain the mess. Additionally, our previous coolant system was not going to be adequate enough to handle the task of machining our next parts. We replaced it with an improved flood coolant system which provides higher coolant flow for better chip removal. 

Fuselage Work
We have been working through a number of outstanding tasks to reinforce the fuselage prior to doing final systems installation. These include installation of carbon fiber reinforcing tapes on the firewall bulkhead as well as at our wing attach brackets. Just like with the reinforcing angle installed on our wing and tail structures, these tapes prevent peel failure at the interface between our carbon fiber skins and bulkheads. 

We also installed the piano hinge that will attach the lower cowling to the fuselage. Fitting the cowling to the fuselage was quite satisfying to see, not just because of the accuracy of our fit up, but also because of how much more rigid the cowling became after being attached. 

Wind Tunnel Model
As stated in previous updates, the Wisconsin Technology Council awarded us 3D prototyping services from Midwest Prototyping, which we will be using to construct a 3D printed wind tunnel model of the DarkAero 1. In the last week of September we finalized many of the dimensional details of the model after discussions with Midwest, and came up with a design for deflectable control surfaces on the model. We will be getting this model printed in the coming weeks and look forward to testing it in the coming months. Our goal is to further validate and build upon the virtual wind tunnel simulation (CFD) work we have already completed.
 

Canopy Mold
Forming a good canopy that meets our quality standards has been an ongoing challenge this year. We originally went down the path of using acrylic, which was easier to form but yielded high optical distortion. Additionally we did not feel comfortable with acrylic’s tendency to shatter in the event of an impact like a bird strike. Since then we have been working to form the canopy from high strength polycarbonate. One of the major challenges of working with polycarbonate has been the higher forming temps involved with it. We were able to successfully get to the required forming temps with our vacuum former, but ran into a number of defects stemming from our mold. Since this test we have been doing a number of small scale tests to isolate and eliminate these defects by experimenting with different mold material choices. In September we were able to narrow in on a solution for a new male mold material that will get us to a successful polycarbonate canopy form. We will have more details on this redesigned mold in the coming weeks.

Presentation at the Wisconsin School of Business
We were invited by our alma mater at the University of Wisconsin-Madison to speak to students at the School of Business about our journey up to this point starting DarkAero. It was humbling to share our story with the next generation of leaders in engineering and business. We still have a lot to learn in the business realm but the experience we have gained up to this point has given us a good foundation. We thank the UW-Madison School of Business for giving us the opportunity to speak, and hope to come back again in the future.  

YouTube Videos
We published four new YouTube videos in September documenting aspects of our prototype progress and other behind the scenes design and manufacturing information. If you have not seen them yet, we recommend checking them out. A link to our latest video about manufacturing repeatability is listed below:
https://www.youtube.com/watch?v=ziEnDjEHJuk

Looking Forward
Going into October our goal is to complete the installation of all wing systems and control linkages as well as begin construction on our engine mount, landing gear components, and install the fuselage systems. We will be constructing the upgraded male canopy mold, and are shooting to get a good form off this as well. The EAA chapter in Viroqua, Wisconsin has invited us to speak at their chapter meeting on October 10th. This should be a fun event since the audience will be familiar with kit aircraft. We hope to film the talk and put it on YouTube.