DarkAero Keeps It Light

The Karl brothers bring a new carbon fiber speedster to market.

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The Karl brothers (left to right): River, Ryley and Keegan with the DarkAero 1 kit. Major composite airframe structures like the wings, fuselage and tail will ship premolded and preassembled.

My usual rule for writing about new planes (or products) is to wait until they’ve actually flown. When I was a kid, Popular Science always seemed to have some artist’s rendition of a futuristic aircraft on the cover, but half the time you got midway through the article and then realized it had never flown, if it existed at all. Good for selling magazines but disappointing if you yearned for the nuts-and-bolts story of a fantastic new flying machine.

A rendered image of
the DarkAero 1 in flight.

As of writing this article, DarkAero has yet to fly their prototype aircraft, but I’m going to break my rule because I think the way they are approaching kitting an aircraft is, if not revolutionary, at least significantly different than how things are usually done and as such deserves a look. It strikes me that DarkAero embodies a variety of the characteristics attributed to millennials: collaborative, predicated on the latest technology, and strong use of social media to communicate about their product to builders and potential customers. This is not surprising, given the average age of the three cofounding brothers is a solidly millennial 33.

This is the first of a two-part series exploring DarkAero. First, we’ll introduce you to the brothers, explain how they decided to kit their own aircraft, and show you their approach to manufacturing and kitting the DarkAero 1.

In Part 2, we’ll take a deeper dive into the airplane itself. DarkAero is hoping to conduct the first test flights of the prototype by the end of this year, and once the plane finishes its Phase I test flying, KITPLANES® will do a flight review of the DarkAero 1.

Computational fluid dynamics (CFD) simulation of the DarkAero 1 (left). SimScale simulation software was used to virtually fly the plane and analyze aerodynamic forces. A 1/12-scale model was tested in the University of Wisconsin wind tunnel (right). The green light is a laser “sheet” that illuminates smoke streams in the wind tunnel used to visualize fluid flow.

Family Affair

Ryley (the oldest Karl), Keegan and River (the youngest) grew up in rural Frederic, Wisconsin. They all had an interest in building things in their youth, and that was the primary source of their entertainment. This included building model airplanes, playing with Legos and taking things apart to see how they worked—pretty typical “future engineer” stuff.

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All three brothers attended college at the University of Wisconsin—Madison and all studied engineering, albeit different fields: Ryley pursued a degree in aerospace, Keegan went for mechanical and River did electrical. After college all worked in industry for several years. Their academic and professional experiences provided them with a broad foundation that served them well when starting DarkAero. Each had something significant they could contribute to the endeavor.

The DarkAero 1 was designed specifically around the UL520iS, because of its high power-to-weight ratio and modern architecture that reduces pilot workload.

Ryley says the mission of the DarkAero 1 is “high-speed, long-range flight, which demands optimization of aircraft design in terms of aerodynamics, efficiency and structures.” So how did they arrive at that mission? Ryley credits a number of factors leading to the founding of DarkAero.

First, Ryley started building a Cozy Mk IV in 2010 and says Keegan and River inevitably got pulled in to help. This gave them a good understanding of the challenge of building a composite kit aircraft. In parallel, they also attended AirVenture every year to check out other kit aircraft, so they had a pretty good understanding of what was the state of the art.

In addition, the brothers had been following the progression of manufacturing technologies like 3D printers and affordable CNCs that were becoming available to hobbyists. All of these things came together, and the brothers saw a way to combine their various skill sets with the latest technology to try and improve upon what was available in the kit aircraft industry. Although the DarkAero 1 was originally conceived as an airplane for themselves, the brothers believed that other aviators would also be interested in the design if they could bring a kit to market. They had been talking about starting a business together since they were in college and realized that if they made a business out of building the DarkAero 1, it would allow them to invest in the manufacturing and technology at a level that couldn’t be justified if they were only creating a one-off for themselves.

Keegan inspects the aft fuselage floor mold (left) and the plug to form the single-piece lower wing skin mold (right). This plug was machined in six sections, then fitted together to form an assembly nearly 24 feet long.

Building the Prototype and the Production Process

DarkAero has developed the prototype aircraft and the production process for kits in parallel—a gutsy decision that assumes the prototype performs as predicted and won’t need major structural revisions. However, this is not uncommon in Experimental composite aircraft where startups often have limited resources yet need to outlay significant capital for molds. Thus, the DarkAero prototype was built using what will become the production molds.

The team put a lot of effort into creating high-quality, precision molds for all airframe structures of the DarkAero 1 from the very beginning. The performance they are targeting relies heavily on optimization of the aircraft structures for weight reduction, as well as achieving the ultra-smooth skin surfaces required to achieve significant amounts of laminar flow for drag reduction.

The internal structure of the left wing. There’s no central spar but rather a distributed internal skeleton that supports the external stressed skin. One benefit is that the entire wing is a large wet-wing fuel tank.

“There wasn’t a way around this approach of significant investment in tooling from the start,” says Ryley. “If we built a prototype aircraft using prototype-style manufacturing methods, the prototype aircraft wouldn’t be fully representative of the production aircraft. We started proving our manufacturing methods on smaller structures first and then worked our way up to bigger structures. Doing tests on small parts first sped up development and also minimized the financial impact of the development process.”

“What’s important to note about the manufacturing is that we spend a significant portion of our time developing the prototype in parallel to the production plane,” adds Keegan, who spends much of his time machining the DarkAero 1 molds and parts. “Before any plane parts were even made, we did time studies, research and testing to understand what manufacturing methods made sense—not just on our end, but also the builder’s end. This is what drove us down the path of infusion, hollow grid, machined parts, etc. Designing a new kit aircraft is more about solving a manufacturing problem than it is solving a ‘What new design does the market need?’ problem.”

The wing proof load test simulates both positive and negative G’s. The DarkAero 1 is rated for normal category (+3.8/-1.5) G loads.

Collecting customer feedback has been an ongoing process for DarkAero, since it’s important to pull in a variety of data points to get a thorough understanding of the market, says Ryley. “It would have been nice going into the project to have a broad survey of the market and data on customer wants and needs, but logistically there isn’t a good way to obtain this. We understood the airplane we were building was going to satisfy a niche segment of the market of pilots looking for a high-performance two-seater, and there is some historical data on this. But ultimately, we had to take a calculated risk based on our read of the market and just go for it.”

Ryley posing with a trial canopy formed in-house on a custom-built thermoformer. Although successive iterations were approaching acceptable optics, DarkAero decided to partner with a canopy manufacturer to speed things up.

Going Public

The brothers made their public debut of the project at AirVenture 2018. At that point they had just the wing, horizontal stabilizer and vertical stabilizer of the aircraft built. They signed up for the 2018 AirVenture booth in the fall of 2017 and treated the event as a “line in the sand.” They agreed that whatever progress they had made up to that point, they were going to display it and see what people thought.

“It was a different experience attending AirVenture to showcase our own work rather than attending to view airplanes as spectators,” says Ryley. “The feedback we got was invaluable since we were able to speak face to face with potential customers and allow them to view the progress on the prototype in person.”

Ryley laying carbon fiber cloth into the fuselage side molds for infusion (left). Multiple layers are stacked in a specific sequence and orientation to yield the proper strength and stiffness. After demolding and trimming, he inspects the fuselage sides (right).

Something the team didn’t anticipate was the strong interest in their carbon fiber work. “I think we had become accustomed to it and just saw it as another material to build airplanes with,” says Ryley. “But everyone asked about clear-coating the structures and preserving the appearance of the carbon fiber weave. I’m glad we didn’t paint anything prior to the airshow since our carbon fiber work is part of what differentiates us.” DarkAero is currently doing testing on various finishes and can’t yet comment on whether the DarkAero 1 can be something other than (to quote Ford à la Rutan) “Any color as long as it’s white.”

The assembled DarkAero 1 prototype, upright …

Since its public debut, DarkAero has maintained an active presence on social media to keep customers in the loop on prototype progress and to obtain ongoing feedback on the design (see end of article for social media addresses). Ryley says one thing that has been fun with social media is attracting new people into Experimental aviation who were previously unfamiliar with it. “There are a lot of people in the world who have a desire to build things, and Experimental aircraft are a great avenue for that. We have been able to tell some of our story through social media and inspire new people to take an interest in Experimental aviation and kit aircraft.”

…and inverted.

Flight Testing—and Beyond

So where does Ryley see DarkAero heading? “The scope of this whole project has grown over the years and our vision for the company has become bigger, which somewhat warps our own perception of goals and progress,” he says. “The big focus for a long time has been just building the DarkAero 1 prototype and getting it through flight testing. This has been a long road of solving design and manufacturing challenges. When I stop and take a step back to think about how far we have come, I remember that just building an airplane of any kind is an accomplishment. Getting through the prototyping process is something we are looking forward to celebrating.”

Ryley points out that once they get through flight testing, the team will be facing a pretty dramatic shift in focus to ramping up kit production and sorting out challenges associated with scaling up manufacturing, logistics and team building. DarkAero has a growing list of customers who have reserved production slots for DarkAero 1 kits. One of DarkAero’s goals since the start of the project has been to create an improved build experience for a composite kit aircraft. They anticipate having to dedicate serious resources to helping the first kit builders prove out the build experience, and satisfying these early customers will be another important focus for them.

Snapshot of a resin infusion midway through the infusion process (left). The darker color is resin flowing into the laminate stack and wetting out the carbon fiber, which sits below a layer of green flow media. Resin infusion has a good fiber-to-resin ratio and results in a void-free surface finish (right) that eliminates the large amount of filling and sanding typically required with composite kit aircraft.

That said, even though kits are not yet available, DarkAero has already started to roll out builder resources on the DarkAero website. Some of these resources take the form of Excel spreadsheets that allow builders to simulate various systems. For example, the avionics sheet allows builders to determine the associated cost, weight and even wiring bundles for different panels. Another spreadsheet provides a detailed guide to hardware used in the plane.

Ryley and Keegan in front of the Tormach CNC mill used to machine landing gear and engine mount components. Coincidently, Tormach headquarters is located only 20 minutes down the road from DarkAero, which made shipping pretty easy!

“We weren’t aware of a tool that gave good planning insight when it came to wiring the aircraft,” says River, DarkAero’s electrical and avionics engineer. “We wanted something that would allow us to virtually rearrange components in the plane to see how this would affect cost, weight, balance and wiring logistics. The spreadsheet tool we came up with helped us sort out these concerns on our end. We also realized that providing the tool to builders now will help them answer some of the questions they have about different panel arrangements they may want to put in the plane. The sheet could even be modified to help builders of other kits solve these same questions on their aircraft.”

DarkAero will have 3D computer models of the whole airplane, as well as assemblies, available online for builders to manipulate and see animations of how parts are assembled. As far as I know, DarkAero is the first E/A-B company to offer this level of sophisticated digital guidance to the builder. They’ve put a tremendous amount of effort into the “instructions” aspect of the build (which, let’s admit, is sometimes lacking in kits), and it looks more like something you’d expect from Silicon Valley than Madison, Wisconsin.

Keegan holding the nose gear strut. He machines the majority of the landing gear components in house.

DarkAero 2?

If you call your airplane the DarkAero 1 it begs the question, Is there a DarkAero 2 in the works? “Long term it would be exciting to take everything we have learned building the DarkAero 1 and improve upon it to make a DarkAero 2,” says Ryley. “Everything we did on the DarkAero 1 was basically built with off-the-shelf parts and technology. There is a lot more that can be done in terms of supplier collaboration to create more customized materials and hardware to improve upon what we have done with the DarkAero 1. One airplane at a time though!”

Hopefully, you’ve enjoyed this introduction to DarkAero and the Karl brothers. Next month we’ll take a close look at the airplane itself. Until then you can learn more about DarkAero through a variety of social media including their website, Facebook, Instagram, the DarkAero YouTube channel or LinkedIn.

The Karl brothers in front of the computer-controlled oven built to cure carbon fiber components. The oven has three sections that are each 8 feet long and can be configured into either a two- or three-segment oven depending on the size of the part to be cured.

2 COMMENTS

  1. GM got millions for research. They already found the best carbon fiber coating treatment. You can’t compete with federal funding so use theirs. I read that it cost around $500 a gallon but goes a long way..

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