- 20 Dec 2021 07:23 AM
Archer Hits Its Target
By Mike Hirschberg
Archer Aviation made the first flight of its Maker eVTOL demonstrator right on schedule.
At the unveiling ceremony for Archer Aviation’s Maker on June 10, 2021 (see “Archer Makes Its Mark,” Vertiflite, July/Aug 2021), company co-founders/co-CEOs Brett Adcock and Adam Goldstein boldly stated that it would fly before the end of the year. More recently, Archer contacted Vertiflite and other media outlets in mid-October to advise that the company planned to fly Maker on or around Dec. 17, the 118th anniversary of the Wright Flyer’s first flight. Even with heavy rainfalls hitting California in mid-December, the team successfully lifted off ahead of schedule on Dec. 16, and landed safety again at 10:30 am.
The two-seat electric vertical takeoff and landing (eVTOL) aircraft, which will only be flown uncrewed, made a modest first flight, but one of tremendous importance, not unlike the Wright Flyer in 1903. However, as anyone ever involved in flight test knows, hitting a first-flight target is exceeding difficult, and requires careful planning, top talent and more than a small amount of luck.
“The past six months have been an incredible journey, from unveiling Maker to watching it take its first flight,” said Adcock. “It’s been humbling to build a leading eVTOL company and educate the public on clean transportation alternatives. Today is a milestone for both Archer and the future of travel. I’m extremely proud of this exceptional team.”
The liftoff marks the completion of the company’s first full and complete systems test and validation of all hardware and software components operating as intended for flight. The flight test also resulted in the successful checkout of the company’s flight control system in flight and the end-to-end closed loop flight software. Now that flight has been achieved, Archer will move forward with an ongoing extensive flight test campaign into 2022 and beyond.
A relative newcomer in the world of electric vertical flight, Archer Aviation was started in 2018 with a vision for a quiet, sustainable urban air mobility (UAM) transportation platform. The well-funded startup soon began recruiting some of the top talent in the eVTOL industry to design and build Maker, its proof-of-concept demonstrator, and its five-seat production aircraft, and unveiled its plans in May 2020 (see “Archer Flies Out of Stealth,” Vertiflite, July/Aug 2020). The company went public through a special purpose acquisition company (SPAC) merger in September 2021 (see “SPACtacular Financing: Billions Coming for eVTOL,” Vertiflite, March/April 2021) that provided net proceeds of nearly $1B in additional funding.
Approved to Fly
Archer had been busy since the completed aircraft was unveiled in June 2021. Maker was built at the company headquarters in Palo Alto, California, but disassembled and trucked the six hours to Hawthorne, California, for its big Hollywood-type reveal in June — and then trucked back.
In November, Archer’s dedicated flight test team, consisting of experts in flight test, battery, propulsion, flight controls, software and avionics, moved from the company’s headquarters in Palo Alto to a new flight test facility (which the company prefers to keep private for the moment) to prepare for this important milestone.
As an uncrewed aircraft, Maker obtained its certificate of authorization (COA) and aircraft limitations from the regional Federal Aviation Administration (FAA) Manufacturing Inspection District Office (MIDO) in early November. The two documents are key components of the Special Airworthiness Certificate, which will be the FAA basis that permits the Maker aircraft to commence test flights. Archer noted that it has “worked hard to maintain a collaborative and transparent relationship” with the FAA through its Center for Emerging Concepts and Innovation (AIR-650, under the FAA Policy and Innovation Division, AIR-600) and the Los Angeles Aircraft Certification Office throughout the certification process.
The production aircraft will be certified under Federal Aviation Regulation (FAR) Part 23 Normal Category Airplane airworthiness standards for fixed-wing aircraft with 19 or fewer passengers, but Maker will only be flown without anyone aboard. The FAA’s Small Unmanned Aircraft Systems (UAS) Regulations (FAR Part 107) is only applicable up to 55 lb (24 kg). Aircraft above that weight need to use another means, and an experimental aircraft like Archer qualified for a “Special Airworthiness Certificate (Experimental Category).” The “aircraft limitations” are required to be issued for any aircraft operating under such a certificate and defines parameters that must be followed when using the test area approved by the COA.
On Dec. 2, Archer announced it had been granted the certificate. As part of its formal inspection, the FAA conducted a comprehensive review of Maker to confirm the aircraft adheres to the Administration’s safety standards. Following its inspection, the FAA issued Archer its Special Airworthiness Certificate, signaling Maker was safe to leave the ground and Archer was permitted to begin hover test flights with the aircraft.
Over the prior two months, the team was laser-focused on Maker’s integration and ground testing in order to prepare the aircraft for a successful first hover flight, as well as ensuring it met FAA requirements to fly.
After being fully integrated, Maker moved into its ground testing phase, which included verification of the control and propulsion systems, along with driving the motors at full power, and then putting those motors through stress testing to ensure all systems were operational and ready to withstand flight testing. After completing an untethered test, during which the Archer team verified that the entire propulsion and flight control system was functioning correctly, Archer’s flight test team approved the aircraft for its first flight.
Archer’s flight test team is led by Matt Deal, who previously managed eVTOL flight test operations at A³ by Airbus for its Vahana program. Deal oversees the day-to-day operations of the flight test team — including setting the test flight timeline and leading test flights — which was focused on integrated Maker’s mechanical and software elements for the first flight and beyond. While the lead up to Archer’s critical first flight is paramount, the integration and test process also allowed for essential two-way feedback to the engineering teams to refine functionality and software for both Maker and Archer’s production aircraft, which is currently in its preliminary design stage.
Now that aircraft has come together, Archer has revealed a bit more about the component testing.
In an early March 2021 interview with Archer Chief Engineer Dr. Geoff Bower, he told Vertiflite that at that time, “we’re building our demonstrator as we speak, putting it together…. a little later this year we’re going to do an unveiling of the demonstrator and then fly before the end of the year is our current schedule. And then in parallel with that, we’re doing the design of our product.”
Bower had studied under Prof. Ilan Kroo at Stanford University, and then was hired by him in 2011 when Kroo was the CEO of Zee.Aero, which built the demonstrators for what has evolved into today’s Wisk and its Cora lift-plus-cruise eVTOL. In 2016, Bower was hired initially as the lead aerodynamics and flight controls engineer at A³ by Airbus Group, but quickly was appointed as the chief engineer for the Vahana eVTOL demonstrator program. He, like most of the Vahana team, departed at the end of 2019 after the program ended and was snapped up by Archer.
Bower noted in March that Archer’s subscale models were designed to be dynamically scaled, following Froude scaling (defined as the ratio of the flow inertia to the external field). “The dynamics are basically the same as the full-scale [aircraft] or as close as you can get to it. So, if you have a quarter-scale model, when you fly it, if you were to slow the video down to half speed, it should look just like the full scale, and we use this primarily as a GNC testbed [for] guidance, navigation and control. So, it flies the exact same flight software control laws that will fly the full-scale vehicle, obviously with scaled gains. But it really lets us get beyond simulation to actual hardware tests with the physics that we expect for the full-scale vehicle.”
After the first flight, Bower confirmed that, “The first flight provided the first in-flight validation of the integrated flight control system stability and tracking performance.”
In December, Bower said their GNC team has been doing a lot of simulation testing and development in the software simulator, and testing it out on the “subscale vehicle that we’ve been flying for year and a half now, roughly.” The model, approximately 23% scale, has now made hundreds of flights.
When the aircraft was unveiled in June, it had the flight motors and propellers installed but not the batteries and some of the internals. To get from the unveiling to the maiden flight required six months of testing and integration activities.
At Archer’s propulsion test facility near its headquarters, “We have a propulsion test stand, so we’re spinning rotors, getting data that way,” Bower said in March. “We have a hardware-in-the-loop simulation. We have subscale models that we’re flying [and] software simulation.” A video released in December showing the Maker ground checkouts also included videos of the propeller test stands.
In a follow-up interview in December just prior to the first flight, Bower explained that one test stand is used for conducting acceptance test procedures (ATPs) on all the motors and propellers they receive. This includes basic performance characterization to make sure they meet minimum requirements, as well as balancing of the propellers. Archer’s propulsion test facility also has a test stand using a Maker propeller nacelle — the pylon that connects the tilting-propeller in front of the wing and the fixed lifting-propeller behind the wing. Archer can test both motors and propellers at a time on it.
Archer has a sizeable laboratory for its avionics testing with multiple hardware-in-the-loop (HIL) simulators to mature the controller designs. “There’s one that we call the Grand HIL that pretty much has all of the avionics hardware on the airplane.” And then we have some flight control computer HILs that have a subset of the hardware with more of the rest simulated, and this allows us to run closed-loop simulations of the vehicle in software, but on the actual flight control hardware.”
“We do a lot of testing of individual boxes and hardware on the avionics too before they’re integrated into those HILs,” Bower said. For instance, Archer’s state estimation platform allowed the team to test out the inertial navigation system. “We can put it in the car, drive it around, that sort of thing.”
Expanding the Team
In November, Archer announced a number of recent additions to its personnel, saying it had “constructed a best-in-class Flight Control and Software team as the company ramps up to its first flight.”
Sergio Ferreira was hired to lead the company’s fly-by-wire flight control system development. Ferreira brings two decades of experience developing, integrating, validating, verifying and certifying fly-by-wire flight control systems. He joined Archer after nearly 10 years with Gulfstream Aerospace, where he most recently was the flight control systems lead for advanced aircraft systems.
Damien Bardon, one of Archer’s earliest employees, assumed the role of Director of Vehicle Management Systems. In this position, he leads the Flight Control and Software team in the development of the essential aircraft components that enable control of the aircraft. Bardon was also a previous Airbus A³ team member, leading the avionics development for Vahana.
Perrine Mathieu, Flight Controls and Avionics Program Lead, accountable for the development and implementation of the fly-by-wire flight control system of Archer’s production aircraft. She brings experience with aviation flight control and vehicle management systems, most recently with Bell Textron, where she was responsible for vehicle management systems. At Bell, Mathieu led the development and implementation of software development, flight controls, avionics, electrical systems and handling qualities across several platforms.
In addition, Dr. Michael Schwekutsch joined Archer as the Senior VP for Engineering, with a background in electric propulsion and high-voltage battery systems. He most recently served as the Senior Director of Engineering at Apple’s Special Projects Group; prior to this, he held a series of positions at Tesla, including as Vice President for engineering. In a LinkedIn post on Dec. 1, Schwekutsch said that he was motivated to move to the Palo Alto-based eVTOL developer because of its team and mission, writing that Archer has a “product and business plan that works with today’s technology.” An Archer spokesperson noted that “He’s an absolute powerhouse in this industry, holding numerous automotive patents and Archer is thrilled to add him to [our] world-class team.”
After the individual components were checked out, they were integrated into the airplane. “So, the first ground testing was low-voltage checkouts — basically making sure everything communicates with each other, you can charge the batteries, you can log data, all the communications between all the boxes are as expected, matching what they’re doing in the hardware-in-the-the-loop simulator.”
The team then began testing the integrated system with high-voltage power on the airplane in the build-up to first flight. “So, this starts really basic, right? You spin one motor at a time… not going to super high RPM. Then you work your way up to the max RPM. We do a lot of system identification [testing]” — such as frequency sweeps on the commands to the actuators for the variable pitch blades on the forward tilting propellers — to make sure the actuator response is “as expected for the dynamics of the system that we’ve calculated and simulated.”
First, all the motors and propellers were checked out individually, and then all together with the complete flight control system. This was initially at low thrust levels and then increased with the vehicle tethered to the ground, working up to the thrust required for hover and beyond. High-power tethered ground testing began in November.
“Then we get into what we call allocation mode,” Bower explained. The flight control laws output commanded forces and moments, and then the control allocation translates them into commands for each of the individual actuators. “It’s not as simple as a conventional airplane or a helicopter where a pitch command goes to an elevator and a roll command goes to ailerons, right? These commands get translated to all the motors,” he explained.
Then the last step of the propulsion system and control system check out prior to first flight is with the inner loops turned on. “First, with the vehicle strapped to the ground, we turn on our roll and pitch and yaw controllers at less than 1g of thrust and see that the vehicle stabilizes itself. And then you do the same thing untethered, as the last test before first flight.” Untethered ground testing began on Dec. 10.
The target date of Dec. 17 had a special significance because Archer’s head of certification, Eric Wright, is a descendant of the Wright brothers’ family. According to the press release, Wright “placed a historic piece of the Wright Flyer in Maker for its inaugural flight to mark the full circle moment.”
The weather in California in mid-December almost unmade Maker’s first flight plans. More than 1.5 inches (about 4 cm) of rain fell on Dec. 14 and more rain was forecasted for Dec. 17 — this was part of a massive storm system from an “atmospheric river” that dumped near-record amounts of rain in the San Francisco Bay Area. But with a break in the rain, first flight was made on Dec. 16.
Bower said the team planned a 20-ft (6.1-m) hover — just high enough to get initial data for steady-state hover controllability. “It’s really to get out of ground effect because it’s hard to predict what’s going to happen there,” close to the ground, because of the airflow and its reflections off the ground and the interactions with the fuselage.
Archer declined to provide many details on the first flight, but confirmed that it flew to about 26 ft (8 m) above ground level — measured from the bottom of its wheels. The video also shows some initial forward velocity at takeoff, followed by a climb to a stable hover, with some pitch oscillations.
The flight test team’s footprint is fairly light, Bower said, with a flight test trailer and the electrical infrastructure for charging the Maker’s batteries. The ground control system has “room for the pilot-in-command, the test director and about five responsible engineers that look at data coming off the airplane from propulsion, flight controls, avionics, flight test instrumentation, [etc]. So, a bunch of people with eyes on data during the tests in good communication” and some spotters outside.
The aircraft, although fitted with two seats and a small display screen at the unveiling, will only be flown uncrewed with pre-programmed flight tasks in “pretty much entirely automated flights,” Bower explained. “The really only inputs the pilot has are to press ‘Takeoff’ and then there are a few contingencies [like] land immediately. When we’re doing operation down the road, they’ll be able to return to home or divert to a pre-designated landing site” in the event of an anomaly.
Following the hover expansion, the team will begin the transition envelope expansion, ensuring that Maker is able to move from hover to forward flight. A second Maker demonstrator is under construction as a risk-reduction asset, though not intended to join the flight test program. In terms of the test plan for the new year, flights will methodically broaden to include hover envelope expansion, verifying Maker’s design and performance. Bower said that it was “a very, very traditional envelope expansion… expanding the speed envelope, the altitude envelope, the endurance envelope.” As part of these tests, “we’ll be doing system identification tests to verify the [control system] plant model, that we’ve got that modeled accurately.” The team will start with hover taxis “at different speeds, probably up to about 20 kt [37 km/h], both fore, aft, left, right and quartering” and then testing with incremental yaw steps.
While expanding the demonstrator’s test flights, Archer also plans to unveil its production-intent aircraft in 2023.
Maker is an 80%-scale demonstrator supporting the development of Archer’s yet-to-be-named production aircraft. “The fuselage cross-section probably won’t inflate when we go to a five-seater, but it’ll stretch and the wing and rotors will roughly scale,” Bower had explained previously (see “Archer Advances eVTOL Commercialization,” Vertiflite, March/April 2021).
Designing, building and assembling Maker was done in record time, leveraging the deep experience of the team. The demonstrator “was all about getting this vehicle built and learning as quickly as we can from it,” Bower explained. “So, we worked with outside vendors to do the structural design and manufacturing, and then the motors and batteries — and a lot of the avionics components — are off the shelf.” Instead, Archer was responsible for writing all the flight software and all the assembly, integration and testing of all the components. However, for the production vehicle, Archer will be developing its own batteries and motors. The primary structural manufacturing may still be outsourced and avionics will likely still be off the shelf.
“Everything we’ve accomplished this year, every milestone hit and partnership struck, was all with one goal in mind: developing both an aircraft and a UAM ecosystem that could scale and change the face of intra-city travel,” said Archer co-founder and co-CEO Goldstein. “With our first hover flight now completed, we’re one major step closer to that goal and have proven that Archer can work at a fast pace without sacrificing safety or quality. Our team stands ready to continue that pace as we work toward launching an aerial ridesharing service in late 2024.”
“As an early investor in Archer, it’s been rewarding to watch Archer grow as a company,” said Marc Lore in the press release, a renowned entrepreneur and the first investor in Archer. “I congratulate the whole team on today’s first hover flight accomplishment and look forward to seeing the way Archer’s unique mode of transportation shapes our cities of tomorrow.”
|Propellers||6 lift/cruise + 6 lift only|
|Weight||3,325 lb||1,508 kg|
|Wingspan||40 ft||12.2 m|
|Range||60 miles||100 km|
|Top speed||150 mph||240 km/h|
|Cruise Altitude||2,000 ft||600 m|
|Hover power||435 hp||325 kW|
Leave a Comment