# 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 $50 million. The prototype should reach a fuel economy of 30 mpg$_{‑US}$ (7.8 L/100 km) in cruise, to be improved with integrated heat exchangers replacing radiators nacelles. A second turbo-compressor should allow reaching a 38,000 ft (12,000 m) altitude, and a third for 50,000 ft (15,000 m).
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 (180 cm) 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 (12,000–15,000 m) 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 (740 km/h) and as contamination can disrupt laminar flow, performance should be certified with turbulent flow, with a less than 4,500 nmi (8,300 km) guaranteed range. The single RED A03 turbocharged V12 four-stroke aircraft diesel engine of 500 hp (370 kW) can operate as two six-cylinder engines to provide redundancy. Otto targets a 3,500–4,000 ft (1,100–1,200 m) 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 ft (11 m) long fuselage and a 55 ft (17 m) wingspan, the claimed 22-to-1 glide ratio should yield a 3.5 sq ft (0.33 m$^2$) equivalent flat-plate area drag. With 500 hp (370 kW), this would allow a top speed of 300 kn (560 km/h) at 30,000 ft (9,100 m), and 430 kn (800 km/h) true airspeed at 65,000 ft (20,000 m), but the RED A03 critical altitude is 25,000 ft (7,600 m). 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 (400 kn; 740 km/h) max speed is achievable, but the cruise speed has to be lower to reach the 4,500 nmi (8,300 km) 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.
Data from manufacturer's site
General characteristics
* Capacity: 6 passengers
* Cabin height: 6 ft 2 in (1.88 m)
* Cabin volume: 448 cu ft (12.7 m$^3$)
* Powerplant: 1 × RED A03 diesel piston engine, 550 hp (410 kW) approximate at takeoff
Performance
* Cruise speed: 400 kn (460 mph, 740 km/h) estimated minimum
* Range: 4,500 nmi (5,200 mi, 8,300 km)
* Service ceiling: 30,000 ft (9,100 m)
* Maximum glide ratio: 22:1
* Fuel economy: 18–25 mpg$_{‑US}$ (13.1–9.4 L/100 km)