Archer Aviation has resumed test flights with its Maker eVTOL technology demonstrator aircraft six months after the subscale model made its first short hover flight in mid-December. In a June 21 blog, chief engineer Geoff Bower reported that flights restarted last week with what he said was the first use of the two-seat aircraft’s new tilt propeller system (TPS) that is deployed for hover control.

According to Archer, the availability of the TPS clears the way for it to expand the flight test envelope as it seeks to achieve a full transition from vertical to horizontal flight by the end of 2022. In April, the California-based company told shareholders it will unveil the first full-sized “production-intent” example of its planned four-passenger eVTOL in 2023. Archer had previously indicated this would be achieved by the end of this year.

In his blog, Bower explained that the TPS “is a system of actuators, sensors, and software that can move the angle of the forward six propellers relative to the wing in order to control the aircraft from hover through transition to wing-borne flight in cruise.” He reported that initial assumptions about how the system would perform have been validated since test flights resumed.

The test flight campaign will now be stepped up to build on extensive ground testing conducted since last year. Archer said it will be focusing on data related to the following items: flight mechanics model validation (such as trim motor RPMs and power draw as a function of airspeed); control system stability margins; improvements to simulation models for vehicle aerodynamics, battery performance, and motor efficiency; vibration and thermal environments for future airborne equipment qualification; and acoustics.

Data from the flight and ground testing is being used to complete detailed design work on the full-scale eVTOL vehicle. Archer has formed an advisory committee with key investor and prospective customer United Airlines to review the design to take account of factors such as making it easy to maintain.

In May, Archer told its financial analysts that it is on track to meet its goal of certifying its production aircraft and starting commercial air taxi services by the end of 2024, which is now just 30 months away. By then, the start-up will also have to have secured a Part 135 air operator’s certificate.

To advance plans for commercial operations, Archer recently appointed Tom Anderson as its chief operating officer for urban air mobility. He was previously COO of Breeze Aviation and also has management experience with airlines including JetBlue, Azul, and Virgin America. In addition, he has worked for regional airliner manufacturer ATR, as well as Airbus and Boeing, in customer support and sales roles.