Matt Thurber, editor-in-chief at AIN Media Group, has been flying since 1975 and writing about aviation since 1978 and now has the best job in the world, running editorial operations for Aviation International News, Business Jet Traveler, and FutureFlight.aero. In addition to working as an A&amp;P mechanic on everything from Piper Cubs to turboprops, Matt taught flying at his father’s flight school in Plymouth, Mass., in the early 1980s, flew for an aircraft owner/pilot, and for two summer seasons hunted swordfish near the George’s Banks off the East Coast from a Piper Super Cub. An ATP certificated fixed-wing pilot and CFII and commercial helicopter pilot, Matt is type-rated in the Citation 500 and Gulfstream V/550. Based in the Pacific Northwest, Matt and his team cover the entire aviation scene including business aircraft, helicopters, avionics, safety, manufacturing, charter, fractionals, technology, air transport, advanced air mobility, defense, and other subjects of interest to AIN, BJT, and FutureFlight readers.

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Matt Thurber

After exploring the benefits and application of laminar-flow aerodynamics with the <a href="https://www.ainonline.com/aviation-news/business-aviation/2022-06-15/otto-reveals-plan-hydrogen-powered-19-seat-celera">Celera 500 experimental aircraft</a>, Otto Aviation is embarking on one of the most challenging endeavors in the aviation industry: design, certification, and production of a clean-sheet business jet. The U.S. company insists its Phantom 3500 isn’t yet another light jet, promising to match the performance and comfort of existing midsize jets at light jet prices and operating costs.
Examples of clean-sheet jets coming to market are relatively rare, and the process is costly and time-consuming. The HondaJet took 12 years from first flight of the prototype to certification and reportedly cost billions to develop. The single-engine SF50 Cirrus Jet first flew in 2008 and achieved FAA certification in 2016, and this was a program run by an experienced original equipment manufacturer (OEM), although this was also its first turbine-powered airplane.&nbsp;
Otto Aviation has been working on the Phantom 3500 for three years, and the <a href="https://www.ainonline.com/aviation-news/business-aviation/2020-08-28/otto-aviation-reveals-celera-500l-business-airplane">Celera 500,</a> which was powered by a Red A03 diesel engine, did generate useful data on laminar-flow aerodynamics, according to CEO Paul Touw. After raising sufficient funds, the Otto team flew the diesel-engine-powered Celera 500 in 2019 and 2020. “It had unbelievable results,” he said. “And that’s what led to the ability to move forward, to build the actual first product.”
Having completed the systems requirement review and conceptual design, Otto in January validated some of its suppliers. In October, Touw expects to finish the preliminary design review, “which means the design will be completely finished. Then we are ordering parts for the first aircraft, flight test vehicle one.”
Items with long lead times have already been ordered, including the landing gear from Mecaer and FJ44 engines from Williams International, for arrival by the end of next year. The next step will be assembly of the first Phantom 3500, systems-level testing, and first flight in 2027. Certification is targetted for 2030.
<h2>Hydrogen Power Plan Shelved</h2>
The U.S. start-up has switched its energy to the Phantom program after previously working on a <a href="https://www.ainonline.com/aviation-news/business-aviation/2022-06-15/otto-reveals-plan-hydrogen-powered-19-seat-celera">hydrogen-powered 19-seater called the Celera 750</a>. This design, which was announced in June 2022, would have used a hydrogen-fuel-cell powertrain developed by ZeroAvia to deliver range of up to 1,000 nm. However, the company has no plans for further development of any of the Celera variants.
The Phantom 3500 design is supported by $25 million worth of wind tunnel testing, according to Touw. This included wing cross-section tests at NASA’s Ames Research Center in Mountain View, California; slow-speed handling characteristics tests in Wichita; and high-speed tests at the European Transonic Windtunnel (ETW) in Cologne, Germany. “All three of those tests were successful,” Touw said. “Our prediction on that [drag polar] curve, and what we tested in the ETW, were almost within a couple of percent of each other, so we had an extremely accurate confirmation of our design.”
With such a great dependence on natural laminar flow, Otto needed to evaluate the effect of wing contamination, such as bugs impacting the leading edge. “We did a lot of testing of FOD and bugs on the leading edge of the wing to see how that would affect laminar flow,” he said. “It turns out, if you go high enough into the really low Reynolds number portions of our atmosphere, those issues disappear.”
When comparing the Phantom 3500 to other aircraft, Otto is competing with midsize and super-midsize jets. With NBAA IFR range (four passengers, 100-nm alternate) of 3,200 nm, the Phantom’s Williams engines burn 60% less fuel than the Bombardier Challenger 3500 or Embraer Praetor 500 and 600, according to Touw. On a 1,000-nm trip, the Phantom would burn 115 gallons of fuel, while the larger airplanes would burn 300 gallons, “and we do it in the same amount of time.”
The Phantom’s flat-floor cabin is 6.4 feet tall and 7.5 feet wide with a volume of 800 cu ft, compared to the Challenger 3500’s 930 cu ft cabin, which is 6 feet tall and 7.2 feet wide. At 40,600 pounds mtow, the Challenger is a much heavier airplane, about twice as heavy as the 19,000-pound Phantom. The two-pilot, Part 25-certified Challenger can carry four passengers 3,400 nm (NBAA IFR range, 200 nm alternate) versus the Phantom’s 3,200 nm, which it achieves by flying higher at its maximum altitude of FL510, 6,000 feet higher than the Challenger’s FL450.&nbsp;
A more apt comparison might be with Honda Aircraft’s in-development Echelon, which also aims to deliver midsize jet performance in a light jet package. The Echelon’s range is lower at 2,625 nm, and it will carry up to 10 passengers and cruise at 450 knots, about 20 knots slower than the Phantom and Challenger 3500. The Echelon’s maximum altitude is FL470. Like the Phantom, the Echelon will be certified under Part 23 regulations and will also be a single-pilot jet.
<h2>Laminar Flow, Less Drag</h2>
“Natural laminar flow allows us to make the wing bigger without the consequence of more drag,” Touw said. Because of that big wing, we can take off and land out of shorter runways than a Challenger 3500 or Praetor 500/600 or Cessna Latitude or Longitude. The aircraft is also lighter…so the airplane’s wing tanks get smaller, the landing gear gets smaller, the engines are smaller, the structure is smaller. So per pound, it’s also less expensive to manufacture.” Touw also claims that the smaller Williams engines will cost 50% less to maintain than the midsize jets’ Honeywell HTF engines, thus helping keep Phantom operating costs lower.
The Phantom 3500’s wing is swept 23 degrees and will have leading-edge slots, Touw said, “that helps create a bit of a vacuum pressure that pulls laminar flow back on to the wing, all the way back to almost 85% on the top of the wing and almost 100% on the bottom of the wing. So the wing is almost 90-plus percent in laminar flow, even at Mach .80 and even with a 23-degree sweep. It’s the combination of the right sweep, the right shape of the wing, and that slot that creates these conditions to almost re-laminarize the back of the wing. It’s a pretty magical trick, because if you can get that wing in almost all laminar flow, it almost disappears from a drag perspective.”
While some business jets are certified to fly at FL510, that altitude isn’t always the most efficient for long-range cruise. “Our airplane flies most efficiently at Mach at 51,000 feet,” Touw said. “In fact, it would like to end its trip at 53,000 feet. But our engines are not certified to 53,000 feet, so we’re going to certify it for 51,000 feet.”
The design feature that enables the Phantom 3500 to be most efficient at its maximum altitude is the laminar flow reduction of skin friction drag, he explained. “You can afford to make the wing bigger, and that’s what allows us to fly at a higher altitude. We have a much lower wing loading than most business jets, [which is in the] 80s or 90s [pounds per sq ft]. Ours is in the 50s. That’s what allows us not only to climb much faster; we take off fully loaded…and get to 51,000 feet in about 28 minutes, and then that’s where it likes to fly. We don’t have to step climb to get to 51,000 feet.”
Otto will build four Phantom 3500s for the flight testing and certification program, all of which Touw said will conform to the final design, thus eliminating the step of producing a non-conforming prototype. The airframe is all-composite, and Leonardo will build the fuselage at a facility in Grottaglie, Italy. Touw didn’t identify the wing manufacturer, nor which avionics will be selected, although he said it will be either Garmin’s G3000 Prime or Honeywell’s Anthem.
<h2>Monitors Replace Windows</h2>
A unique feature of the Phantom 3500 is that it will have no cabin windows, which contributes to natural laminar flow on the fuselage. One window is required for the emergency exit that will be in the lavatory in the rear fuselage. Instead of windows, passengers’ view of the outside world will be on 42-inch 4K monitors on the cabin walls, four on each side. Touw sees this option as more comfortable for passengers, especially at the FL510 maximum altitude.
“What we can do with camera technology and video and all of our video processing is we can change the views so that you’re not getting all that glare, and that makes for a much better experience, so you never have the desire to want to close the windows,” he said. “At night, we augment the view with synthetic vision of the world. You’re not looking at a blank screen, you’re looking at a synthetic view, which is gorgeous, a little bit like being in Google Earth at night. We’ve got satellite, 100-megabit capability, so we also have access to about 10,000 movies that are streaming through Netflix and all of the different services. If you want to watch movies, you can put those up. Finally, if you want to do a conference call on Zoom or Teams, all the people can go up on the screens. It’s a supernatural vision infotainment system. It goes way beyond just a window.”
As a new OEM, Otto Aviation faces significant challenges in not only designing a clean-sheet jet but also standing up an efficient production process. Currently located at Meacham Field in Fort Worth, Texas, Otto is planning to build a factory in Florida, likely at Cecil Field in Jacksonville. The manufacturing process will rely on resin transfer molding, where resin is injected into molds containing carbon fiber composite material. This process is not new to aerospace; Airbus uses it to manufacture major structural components for the A220.
Touw admits that the tooling needed to manufacture the Phantom 3500 will be expensive, but eliminating labor involved with metal manufacturing (cutting, drilling, and riveting) will be more efficient. Robotic manufacturing will also help keep costs down, he predicted.
Otto Aviation has raised nearly $200 million for the Phantom 3500 and is about to launch a series B funding round, although it is likely that the program will require well more than $1 billion to make it through to certification and production. The company employs about 100 people and supports another 200 full-time-equivalent contractors. “We have to purchase all of our expensive equipment and tooling,” he said, “so we have a lot of other expenses. [But] we’re well funded.”

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