Otto Celera 500L

The Otto Celera 500L is a business and utility light aircraft developed by American startup, Otto Aviation.

By November 2021, 55 successful test flights had been completed, as introduction is targeted for 2024–2025.

It has a single RED A03 diesel piston engine in a pusher configuration and can seat six passengers. It is named after the latin word for 'fast,' celer.

History
Otto Aviation Group, LLC was established in 2008 by Bill Otto to develop the Celera 500L. William Otto has been a research scientist at Los Alamos Scientific Labs, systems engineer then chief scientist at North American Aviation. Otto Aviation is privately funded since 2008 and is seeking a Series B fundraising round: 200 million dollars are needed for FAR Part 23 certification in three years. Construction of the airplane commenced in 2015.

The aerodynamic prototype made its maiden flight in January 2018, and began performance testing in September 2019. Otto publicly announced the aircraft and its development program in August 2020, and noted that 31 test flights had been flown to date. By then, a weight-optimized conforming prototype with cabin windows and longer landing gear was expected to fly within 18 months. FAA certification and deliveries are targeted for 2023–2025. By March 2021, the prototype had achieved over 35 hours of flight tests, interrupted by the pandemic until Q3 2021, before two additional flying prototypes join the program.

By October 2021, the company had raised more than $50 million. The prototype should reach a fuel economy of 30 mpgus in cruise, to be improved with integrated heat exchangers replacing radiators nacelles. A second turbo-compressor should allow reaching a 38,000 ft altitude, and a third for 50,000 ft.

In 2022, Otto announced a partnership with ZeroAvia to build a hydrogen-powered version of its aircraft.

Design
The 500L is a mid wing monoplane with a single five blade propeller in a pusher configuration. This results in no aerodynamic interference from the propeller, which is as far back as it can be. Laminar flow is used for its wings, fuselage, and empennage.

Otto wants to compete with light business aircraft like the Cessna Citation CJ3+ jet or the Beechcraft King Air 350. The better fuel economy should lead to a low operating cost of $328 hourly. The cabin accommodates six club seats, is about 72 in tall, and will be equipped with a lavatory. It is expected to sell for $4.5-5 million, comparable with the HondaJet but with one third its operating cost.

Twin-stage turbocharging should enable a 40,000-50,000 ft cruise altitude, where full laminar flow can be achieved for an estimated 59% lower drag than competitors. It should reach a cruise speed over 400 kn and as contamination can disrupt laminar flow, performance should be certified with turbulent flow, with a less than 4,500 nmi guaranteed range. The single RED A03 turbocharged V12 four-stroke aircraft diesel engine of 500 hp can operate as two six-cylinder engines to provide redundancy. Otto targets a 3,500-4,000 ft balanced field length and a fuel economy of 16–22 nmi/USgal of Jet fuel. The flight controls are mechanically linked and it will be equipped with instrument flight rules avionics for single-pilot operations.

External analysis
With a 35 feet long fuselage and a 55 feet wingspan, the claimed 22-to-1 glide ratio should yield a 3.5 sqft equivalent flat-plate area drag. With 500 hp, this would allow a top speed of 300 kn at 30000 ft, and 430 kn true airspeed at 65000 ft, but the RED A03 critical altitude is 25000 ft. The propeller tips would have transonic wave drag and would operate in a disturbed wake, limiting propeller efficiency, and laminar flow would be difficult to maintain for a large part of the fuselage with windows and panel seams.

The configuration is similar to the 1948 Planet Satellite, or the 2011 EADS Voltaire electric aircraft concept. The claimed 59% drag reduction "would be quite a hard task to achieve", according to the Royal Aeronautical Society, while lift-induced drag would not be reduced by laminar flow. A 1:22 glide ratio like current airliners can be reached with its high wing aspect ratio, without a sensational drag reduction: better than other general aviation designs, but lower than most gliders. The 460 mph max speed is achievable, but the cruise speed has to be lower to reach the 4,500 nmi range. The fuel efficiency is difficult to compare with no specified payload, cruise speed and altitude. Pushing the laminar flow to the limit could hinder handling qualities or structural efficiency, and laminar flow tends to be unreliable in service, as it is highly susceptible to degradation from surface irregularities.

Specifications
The following data is estimated by the manufacturer in a pre production stage.