Otto Aviation Hopes To Torpedo The Business Jet Market With Its Curious New Design. Will It Sink Or Swim?

Hellen Wadman

Otto Aviation’s striking Celera 500L business aircraft prototype over the Mojave Desert. Otto Aviation Otto Aviation is looking for investors to advance its unconventional “Celera” business aircraft from a prototype to a production airplane built in the thousands. The media attention the company has garnered since formally unveiling the Celera […]

Otto Aviation is looking for investors to advance its unconventional “Celera” business aircraft from a prototype to a production airplane built in the thousands. The media attention the company has garnered since formally unveiling the Celera 500L last week is no doubt pleasing.

But with the spotlight comes scrutiny and the questions that all startup aviation manufacturers face. The answers often determine whether a new effort even reaches the market. In Otto’s case the mere appearance of the Celera with its bulbous fuselage, pusher propeller and short, thin wing, leads to questions.

The man responsible for the project, and the Celera’s distinctive shape, is William Otto Sr., a former researcher at Los Alamos National Laboratory, chief scientist at North American Aviation (subsumed by Boeing in the 1990s after a series of mergers) and founder of aviation accident investigation firm, Otto Laboratories.

His son, Bill Otto, told me that his father was moved to revisit some old studies he had done after a fruitless search for an affordable business aircraft in the late 1970s. That research was on the Mk.46 torpedo, a lightweight ship or aircraft-launched anti-submarine torpedo that remains a NATO and U.S. Navy-standard weapon. Otto’s design refinement of the outlines of the Mk.46 led to his idea for a similarly-shaped composite fuselage for the Celera.

That shape emphasizes laminar-flow (smooth, uniform airflow across a surface) aerodynamics which yield low drag and high efficiency. Most passenger airplane designs optimize the wings and tail for laminar flow, less so the fuselage. Otto Aviation looks to maintain laminar airflow across the fuselage by putting the propeller behind it all (like a torpedo) at the back the aircraft rather than the front as with a typical turboprop design.

The other key part of the Celera’s efficiency equation is the unconventional choice to forgo a jet and instead use a 500 hp V-12 turbodiesel engine supplied by German firm, Raikhlin Aircraft Engine Developments GmbH (RED).

According to Otto, the combination produces fuel efficiency and cost that is well beyond that of current turboprop or pure jet business aircraft. While the Celera 500L’s claimed cruise speed of 450 mph isn’t quite as fast as most business jets, it handily beats the 350 mph cruise speeds of turboprop business aircraft like the Beech King Air.

Otto’s assertion that the Celera – a name derived from the Latin word “celer” for swift or quick – has a range of over 4500 miles and fuel economy of 18 to 25 miles per gallon is remarkable given that similar sized aircraft (Celera features a 6’2” high stand-up configurable cabin for six passengers) struggle to achieve 2 to 3 mpg. The company projects its operating expenses at just $328 per hour, again remarkable compared to the $2000-plus per hour cost of most business jet aircraft.

It’s the kind of cost-performance balance that could produce a new segment of mass air travel and torpedo Otto’s business aircraft competition – if it works.

How Do They Do It?

While the Celera looks odd, its pusher configuration, laminar flow shaping and internal combustion powerplant are all design principles/technologies well known to the FAA, suggesting that its path to certification, planned to begin in 2023 and finish in 2025 could be as smooth as its shape.

“The shape looks odd but it is very conventional, particularly once you come into the airplane,” Bill Otto says.

Surprisingly, convention includes a traditional mechanical flight control system with push-rods and bell-cranks rather than the expected (and lighter) contemporary fly-by-wire electronic controls. The Celera prototype has an even older type of cable/pulley flight control system according to Otto. Construction of the prototype stretches back to 2008 when the younger Otto got involved in writing the business plan and gathering initial investors.

By 2017 the aircraft had begun taxi and flight testing. Otto Aviation says Celera has actually made 31 test flights as of August. Those flights were likely made before Otto’s chief technology officer and aerodynamicist, David Bogue, joined the company. Mr. Bogue previously worked as an engineer with Boeing and until some time in 2020, as an aerodynamicist with supersonic transport startup, Boom Supersonic.

Bogue is highly confident in the Celera’s design and its path to certification. “It’s just good engineering,” he says. That extends to its aerodynamics. Bogue says Celera has a superior lift to drag ratio that stems from its laminar flow design and routine operating altitudes “above 40,000 feet” where laminar flow is enhanced.

To be efficient, the airplane must maintain an essentially flat pitch attitude or angle-of-attack (AoA) in flight, including during the approach-to-landing phase. That’s difficult Bogue admits, saying that the design of Celera’s flaps is critical to maintaining an AoA close to zero.

“There’s landing attitude which has to be dealt with and you have to have enough [pilot] training to make sure that this is safe operationally,” Bogue says. Citing his career background as a designer he adds, “I’ve got 9500 aircraft flying right now. I don’t intend to crash one.”

The blisters you see atop the rear of fuselage are dedicated to cooling the turbodiesel engine’s exhaust which is the “single hardest task” with the airplane Bogue acknowledges. The thin air available for cooling at altitude and the considerable turbo boost pressure necessary to get power from the diesel are the source of the problem.

But a large amount of fuselage interior volume available for cooling is expected to offset the cooling challenge. This, along with a redesign of the tail of the Celera including deleting the big, drag inducing blisters, should solve the problem says Bogue. He adds that he has CFD (computational fluid dynamics) analysis showing that it will work.


Of course, Otto will have to demonstrate that all of its eyebrow-raising claims on speed, fuel efficiency, cost and range have been achieved. And this is where it gets confusing.

We asked Otto’s CTO if its claimed performance numbers have, after 31 flights, been validated?

“We don’t have the production engine yet so for that reason we haven’t achieved the altitude that is required to achieve the top speeds,” Bogue replied. The Celera prototype has flown with a single-turbo version of the RED A03 V-12 turbodiesel he reveals. Otto will be getting a twin-turbo version of the engine from RED soon he says which will be integrated before certification.

As an aside, we asked Bogue about the scalability of RED’s engine for mass production. Oddly, he said that he wouldn’t comment on its production potential though he acknowledged that Otto has looked at other engine suppliers.

“But right now we’re single-sourced for this engine. It’s not like we can drop another one in its place,” he says. He added that Otto is happy with the turbodiesel’s performance/reliability, affirming that it is “near what we need for a certified aircraft”.

Returning later in the conversation to the idea of performance validation Bogue says that Otto has “neither confirmed nor denied” meeting the numbers projected in its press release and on its website. He did confirm that independently validated flight performance data will be available to customers prior to selling the aircraft but he refused to say when. Pressed further, he said the company would offer verifiable data by the end of 2021.

Surprisingly, he then said that Otto’s Celera performance has already been independently validated.

For a company seeking investment, this is perplexing messaging.

Show Me

Run the Celera’s claimed performance and design past some informed onlookers and you get interesting observations. We had retired Lockheed Skunk Works engineer, Jon Sharp, take a cursory look at the Celera 500L. In addition to his Skunk Works background, Sharp is a championship-winning Formula 1 air race pilot and designer whose “Nemesis” air racer sits in the Smithsonian.

His first reaction was that the Celera’s propeller is in the wrong place.

A pusher propeller which sits behind the fuselage and wings experiences disturbed airflow, hurting its efficiency. Even with laminar-flow and other designs which seek to smooth airflow, the propeller has difficulty achieving optimal thrust. It’s an approach he saw first hand in air racing where pusher Formula 1 race planes could not go as fast as or beat traditionally configured race planes with front-mounted propellers despite small, super-light airframes and decades of optimization.

“I think this airplane would suffer from the same problem, especially with the [exhaust] cooling ducts back there.” He says that a redesign may help but the prototype might be losing as much as 20% propeller efficiency. That would likely impact its performance.

Sharp also opined that the Celera’s NACA-style duct intakes for the engine don’t look large enough to swallow air in sufficient quantity for the engine to make high power at 40,000 feet operating altitude. The wing also looks small for a relatively large airplane with the Celera’s 12,500 pound maximum takeoff weight (the same as the Beech King Air B200 and 250 twin turboprop business aircraft).

“At 40,000 feet you need a lot of wing and a lot power to go that fast. I wish them the best of luck but I think they’re overstating their performance.”

Tim Slater says that the Celera’s RED A03 V-12 turbodiesel engine might be able to provide surprising performance but its claims are “lofty” and information is scarce. Slater is both an aviation airframe and powerplant mechanic with 15 years experience and the president of Chicago-based Centurion Fleet Services, an automotive diesel repair, modification, and engine-building specialist. He’s been following RED for years.

The German company has offered scant information on its design which it says has been chosen by Russian aircraft manufacturer, Yakolev to power the Yak-152 primary trainer, 150 of which the Russian Air Force reportedly planned to acquire by 2020. That acquisition does not seem to have gone forward yet and its not clear that the A03 will be the engine of choice.

As for the A03’s ability to offer enough power to get Celera to its 450-mph cruise speed at altitude Slater says, “Making 500 horsepower at 40,000 feet would take an insane amount of turbocharging, turbo pressure. It’s not something I’ve seen before outside of tractor-pulling engines which can have up to 200 pounds of boost at sea level.”

But the A03 won’t make a full 500 horsepower at altitude. Even with multiple turbos Slater notes that RED only claims the ability to make 500 hp at 25,000 feet, not at 40,000 feet. He points out that the limitation is not unique. A turboprop engine like the ubiquitous Pratt & Whitney PT-6, which has a 750 to 850 maximum shaft horsepower rating at sea level produces less than 300 hp at 28,000 feet.

Lower altitude will challenge the A03’s capability he says. “I don’t know if this is an engine that will be rated to maintain any kind of continuous power setting like 500 hp at 25,000 feet.”

Slater notes that Otto’s speed claims are ambiguous as are its fuel efficiency claims which don’t specify altitudes or power settings. He thinks the Celera’s top speed and cruise speed numbers will vary considerably. He agrees that exhaust cooling is a major problem, one impacting reliability and thus cost.

The A03 is certified by the European Union Aviation Safety Agency (EASA) and Slater looked at its certificate. The V12 has smaller displacement than he thought (only 378 cubic inches) suggesting it needs even more turbo boost and thus has even hotter exhaust than he suspected. It’s also quite heavy (800 pounds) for an aero engine, possibly compounding weight issues despite the 500L’s extensive use of composites.

Slater questions the Celera’s claimed need for only 3,300 feet of runway in all conditions and lastly wonders why, after 31 test flights, the aviation community has not heard more about it?

Markets, Sirens & Klaxons

Bill Otto says the company anticipates going to market and “getting to revenues” with the Celera 500L in 2025. As for the purchase price he says, “We’re targeting the Pilatus PC-12 price range.” That would put the new business airplane’s sticker at about $5 million.

In the meantime, the company is searching for investors and discussing manufacturing with some potential partners though it appears Otto may choose to do that itself. With the Celera’s mid-size business jet-like premium cabin, Bill Otto says the aircraft is a candidate for potential buyers on the passenger and on the cargo side.

An envisioned cargo version of the airplane could fit three standard cargo containers within, on par with short-haul cargo aircraft like the Cessna Caravan. A future Celera 1000 could double the current cabin size.

But passengers and the air taxi market are the first prime target for the Celera.

“Our costs are significantly less on a per-passenger basis,” says Bill Otto noting past air taxi market pricing. “That would enable a more profitable model with pricing similar to what Eclipse [a light jet] has done. In addition, we’re talking about a first-class cabin. In an Eclipse 500, you sit shoulder to shoulder, squeezing into its small cabin. We do think our cabin comfort will play a big role.”

With an advertised $328 per-hour operating cost, Otto Aviation says that a seat on the Celera would sell for about what a business class or first-class ticket on an airliner would cost, making the private aircraft very attractive. Assuming a $1000-$1,200 per seat price, six passengers would yield $6000-$7,200 for a flight (one way or round -trip isn’t clear), enough to turn a comfortable profit Bill Otto says.

The math might be more challenging these days with airlines under pressure. A quick look at business and first class tickets for a flight from Chicago to Washington DC (ideal for Celera’s claimed performance) turned up nonstop, round trip fares of $515.

For those who remember the very light jet (VLJ) era of the 2000s the logic sounds familiar. A New York Times article reporting on a 2007 flight from Boca Raton to Tallahasse, FL on a DayJet Eclipse 500 air taxi flight describes a scenario that Otto would likely use in its own business case. DayJet was the largest VLJ air taxi operator of the day but the air taxi market never took off and after a short time it went bankrupt.

Teal Group analyst, Richard Aboulafia, says that air taxis are great conceptually but a host of practical considerations from competitive ground travel modes to consumer habits and pricing make their adoption challenging.

“The air taxi market has never been an aircraft technology question, it’s been a utilization question and a price point question. The numbers that Otto has given are so impressive that they could have an impact.”

But Aboulafia admits he can’t reconcile Otto’s performance and cost numbers.

“The performance promise aspect of their offering is so remarkable, that if it can actually do that, I’d say anything is possible. But a single 500 hp engine taking six people 4500 miles at near jet speeds – I just can’t make that work in my head.”

Otto’s ambiguity regarding the validation of its claims is another problem according to Aboulafia.

“It’s on their website. They’re looking for people to fund them. The idea that they would be secretive about technical data should set off sirens and klaxons. You don’t invest in something you can’t verify.”

New companies with private or business aviation airplanes historically start out with the general aviation owner/operator market, Aboulafia points out. Pitching the Celera as a commercial aviation product suggests that Otto Aviation is explaining their relevance to a broad user market as a way to attract investment.

“I like to give newcomers the benefit of the doubt but they have some explaining to do,” Aboulafia opines. “Unless they do it quickly, my assumption is that this is offered to generate investor money first and sell product later.”

Bill Otto says he recognizes that what the company is attempting to bring to market comes with some risks. Chief among those may be promising more than it can deliver.

If the Celera can do what is claimed, Otto Aviation should truly be hailed. If not, the firm may have already torpedoed itself.

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