- 01 Mar 2022 06:49 AM
Pushing the Envelope: Joby Aviation in 2022
By Mike Hirschberg
Vertiflite Mar/Apr 2022
Joby Aviation has made significant strides in its efforts to demonstrate the capabilities of its electric vertical takeoff and landing (eVTOL) aircraft with the US Air Force and advance its civil certification with the US Federal Aviation Administration (FAA). The company has been pushing the boundaries in terms of aircraft performance, experiencing the highs of record-setting highs and the lows of losing its first pre-production aircraft in an accident.
DoD Flight Testing
In early February, Joby published a blog post that gave additional insights into its development work with the Defense Innovation Unit (DIU), the US Department of Defense (DoD) organization focused on discovering and scaling critical commercial technologies (see “US Air Force Primes the eVTOL Industry,” Vertiflite, March/April 2021). Joby’s relationship with DIU began in 2016, the year prior to test flights of the company’s first full-scale technology demonstrator, the uncrewed S4 generation 1.0.
The blog post, by Josh Vanderlip, Joby’s government operations lead, noted that “DIU has a strong track record for identifying disruptive technology companies and conducting deep due diligence on experimental products that have potential government application.” DIU contracted with Joby to allow observation of flight testing activities and report on the capabilities of electric propulsion.
It was through the DIU that Joby first gained access to a secure flight test site in 2017 at US Army Garrison Fort Hunter Liggett in southern Monterey County, California, about halfway between San Francisco and Ventura, California.
More importantly, Vanderlip noted, “With uninterrupted access to testing facilities, we were able to conduct over a thousand test flights across multiple sub- and full-scale prototypes, enabling rapid iteration and validation of our design. Access to DoD expertise, feedback, and facilities has and will continue to be an invaluable resource towards developing and certifying the Joby aircraft for broad DoD and commercial use.”
The progress that Joby made in flight testing its three full-scale prototypes over the past five years also positioned Joby for the Air Force’s Agility Prime program, which is reported to have committed $40M to support flight testing and evaluation (see “Turning Point,” Vertiflite, July/Aug 2021).
In February, Joby delivered two simulators to the Air Force’s Air Education and Training Command’s Detachment 62 in San Antonio, Texas. Det 62 will be conducting research into training requirements for eVTOL aircraft.
Progress to Certification
On Jan. 6, Joby announced that the second of its pre-production S4 aircraft had received an FAA Special Airworthiness Certification and a US Air Force Airworthiness Approval. Joby has also begun conformity testing with the FAA, the company announced on Feb. 10. The tests — which sought to confirm the material strength of a carbon composite that will be used in the body of the aircraft — were conducted at a facility belonging to Toray Advanced Composites in Morgan Hill, California, and overseen by an on-site FAA Designated Engineering Representative (DER).
In early 2020, Joby became the first (and so far only) eVTOL company to receive a signed G-1 (stage 4) certification basis with the FAA, having received an initial (stage 2) signed G-1 from the FAA in 2019.
As Joby seeks to develop its network of operators (see sidebar), its eVTOL aircraft has been demonstrating its performance — far beyond what many observers thought was possible with a current-technology eVTOL aircraft — and setting records.
The Santa Cruz-based company announced in a tweet on Jan. 21 that its first pre-production S4 aircraft had reached a true airspeed of 205 mph (330 km/h). The flight demonstrated the ability of the Joby air taxi to fly up to and beyond 200 mph (322 km/h), the stated top speed for the aircraft, and achieved what it said was the fastest flight of any eVTOL aircraft, and far beyond what other all-electric VTOL aircraft developers are planning.
Collectively, the original uncrewed 1.0 technology demonstrator (N541JA) and the first 2.0 pre-production aircraft (N542AJ) have now made more than 1,000 test flights — all remotely piloted to date. Other than initial tethered and untethered hover tests at Joby’s facilities in Santa Cruz, N542AJ has been flying at US Army Garrison Fort Hunter Liggett in southern Monterey County, California. The second 2.0 aircraft (N542BJ) began flying earlier this year from Joby’s new manufacturing plant at Marina Municipal Airport (KORD) in California. Flight tracking software first caught the second aircraft on the ground on Feb. 5. The aircraft was built in Santa Cruz, ferried by helicopter to Marina, and then made what is believed to be its first circuits of the airport on Feb. 10 and 11. [Note that Joby announced on March 24 that the second aircraft made its first flight sometime in January.]
Shortly after announcing the 205-mph speed record, Joby revealed on Feb. 2 that its eVTOL aircraft had reached an altitude of 11,000 ft (3,350 m), comfortably past its target altitude of 10,000 ft (3,050 m). The flight was one of several the company has conducted above 7,000 ft (2,133 m) in recent months. Though Joby expects most of its commercial flights to occur at 5,000 ft (1,500 m) or below, the company sought to use the high-altitude flights to prove out the S4 flight envelope, a crucial element of the FAA certification process and in demonstrating the potential military utility. Joby’s new speed and altitude achievements add to the company’s previous flight accomplishments. In July 2021, a Joby aircraft completed a 154.6-mile (248.8-km) flight on a single battery charge, spending more than an hour in the air (see “Joby Flies 155 Miles in 77 minutes,” Vertiflite, Sept/Oct 2021), in what is likely the longest flight of an eVTOL aircraft to date.
As the company continues its path toward FAA certification, future flight tests could be more in the public eye. According to documents submitted to the Federal Communications Commission in December, Joby has requested to conduct demonstration flights over the San Francisco Bay.
Loss of Aircraft 1
However, the timing of these plans will need to be re-evaluated following an accident with N542AJ. On Feb. 16, the company announced that “one of its remotely piloted, experimental prototype aircraft was involved in an accident during flight testing at our remote flight test base in California.”
According to the data from the aircraft’s Automatic Dependent Surveillance–Broadcast (ADS-B) transmitter and Joby social media followers, the aircraft has been operating from a dirt strip on the southern end of Hunter Liggett. The aircraft was flying circuits of approximately 4.5 miles (7.5 km) the near El Piojo Reservoir Dam. The ground level is about 1,000 ft (330 m) above mean sea level. The FAA accident report states that the location was Jolon, California, as that is the nearest town — 6.25 miles (10 km) away — and the postal address for the fort.
The accident, which resulted in no injuries, is currently under investigation by the company and the National Transportation Safety Board (NTSB) — as an uncrewed aircraft in a remote area on US government property.
Experimental aircraft like Joby’s are typically highly instrumented, so the amount of data available for the whole flight — and particularly during the failure — will be highly instructive for future improvements for the fly-by-wire aircraft. This was the case during the accidents in 2015 of the Leonardo AW609 and in 2016 of the Bell 525 Relentless. Joby had previously announced that the first pre-production prototype generated 65 terabytes of test data in 2021, flying more than 5,300 miles (8,530 km).
“Safety is a core value for Joby, which is why we have been expanding our flight envelope with a remote pilot and in an uninhabited area, especially as we operate outside expected operating conditions,” the company said in a statement filed with the US Securities and Exchange Commission (SEC). “Experimental flight test programs are intentionally designed to determine the limits of aircraft performance, and accidents are unfortunately a possibility.”
The ADS-B data report ground speeds as high as 276 mph (240 kt or 445 km/h) — it’s not clear what the winds aloft were, but even if there were a 40 mph wind, that is still quite a bit higher than the 200 mph planned top speed. Interestingly, the data also indicate that throughout the flight, the vertical rate of flight was being constantly varied between about ±1,280 ft/min (±6.5 m/s). The last data recorded in the ADS-B track was at 7:56 am local (15:56:19 UTC).
Looking at ADS-B data over the past few months indicates a methodical approach to expanding the flight envelope under the Air Force’s Agility Prime initiative, with incremental increases on each flight. Photos of the aircraft now show that the original retractable, wheeled landing gear has been replaced with streamlined skids to reduce drag at high speeds.
With separate demonstrations of speeds well above 200 mph, ranges beyond 150 miles (240 km) and altitudes up to 11,000 ft (3,350 m), it is clear that the five-seat Joby S4 has capabilities significantly beyond the “limited performance” that had been expected from eVTOL aircraft for so many years. Although all of Joby’s flights were made uncrewed (i.e. no payload, other than extensive test instrumentation), they did prove the aircraft power and aerodynamic limits allow for performance that is significantly higher than has been publicly stated for the S4.
For comparison, a five-seat Bell 505 Jet Ranger X has a maximum speed of 144 mph (232 km/h) and a range of 383 miles (617 km). The five-seat Robinson R66 has a cruise speed of 130 mph (200 km/h) and a range of 400 miles (650 km). The US military operates the five-seat Boeing AH-6 Little Bird with a maximum speed of 145 mph (233 km/h) and a maximum range of 205 miles (331 km). A faster helicopter in the US inventory is the AH-64E Apache Guardian, with a maximum speed of nearly 190 mph (304 km/h) and a combat range of 300 miles (480 km) — with a gross weight about four times that of the Joby S4 Generation 2.0.
Even compared to conventional general aviation airplanes, the S4 compares surprisingly well. The maximum cruise speed of the ubiquitous four-seat Cessna Skyhawk is only 143 mph (230 km/h), while the popular four-or-five-seat Cirrus SR22 can cruise up to 211 mph (339 km/h).
The record for the fastest all-electric aircraft was set in November by the Rolls-Royce “Spirit of Innovation” with a highly optimized, single-seat demonstrator designed solely to set speed records. It hit 330 mph (532.1 km/h) over a 9-mile (15-km) circuit and clocked a maximum speed of 387.4 mph (623 km/h). In contrast, the Joby S4 was designed to carry a pilot plus four passengers for economically compelling AAM market applications, making its high-speed demonstrations all the more impressive.
The goal of Joby’s envelope expansion for Agility Prime was to steadily increase performance beyond normal operations to understand if, when and how failures might occur, so that this risk can be mitigated in flight tests, rather than in service. Conceptually, this is similar to component-level bench testing, which involves endurance and/or performance tests that exceed what is expected to be seen in normal use. By design, these tests involve steadily higher risk of failure.
With the first S4 2.0 having flown hundreds of flights — many on the order of an hour long, and taking a beating exploring the aerodynamic boundaries — its last contribution will be providing insights into one potential failure mechanism, with gigabytes of data to analyze for future improvements.
The eVTOL sector’s ability to conduct these higher-risk tests without people onboard is unique. Joby intends to continue conducting all of its envelope expansion testing on a remotely piloted basis first; this has allowed Joby to move quickly through its test program without taking unnecessary risks too early in the program. Doing envelope expansion and higher-risk testing at a remote location also ensured that there were no injuries or property damage on the ground, and allowed for undisturbed examination of the accident site.
With the second Joby 2.0 pre-production prototype now on flight status, and several more aircraft in assembly for completion later this year, 2022 looks to continue the company’s upward trajectory. Because the first aircraft was flying much faster than expected operations and it had already expended much of its useful life, the second aircraft will help to minimize delays in the company’s flight testing and certification plans: receiving its Part 135 air carrier certificate in 2022, its airworthiness type certification in 2023 and launching commercial operations in 2024. [Joby announced on March 24 that the second aircraft resumed flight testing and had by that time "made 38 flights, reaching speeds of more than 90 miles per hour."]
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