UK start-up Sora Aviation is progressing towards critical milestones on its 30-passenger S-1 electric tiltrotor, with ground tests of its full-size propulsion system due to begin next year.
That will be followed around two years later by first flight of a full-scale demonstrator of the S-1, says co-founder and chief executive Furqan Afzal.
“We don’t see a lot of value in building a half -scale demonstrator,” he says. “We would spend a lot of time and money proving something the size of Joby’s aircraft could fly.”
Preliminary design activities on the hexrotor S-1 concluded during the early summer, he adds.
While other electric vertical take-off and landing (eVTOL) developers are building aircraft capable of transporting small numbers of passengers on routes of up to 86nm (161km), Sora is thinking bigger.
Its S-1 will accommodate up to 30 passengers in a high-density layout or 24 in an airport shuttle configuration, including their baggage allowance. Range will match that of its eVTOL competitors, he claims. Maximum take-off weight will be in the region of 11t.
Afzal says a “much higher number of passengers is needed” to bring ticket costs down “otherwise we risk exacerbating social inequalities by catering to only high-net-worth individuals and VIPs”.
But the choice to rely on battery power alone for such a relatively large aircraft will raise some eyebrows.
Afzal argues that it is a “misconception” to see batteries as unsuitable for larger aircraft, even with the limitations of current cell power densities.
“You can fly the same range as a small electric aircraft for a given speed,” he says, “but you can’t design for long range or high speed on batteries alone.
“Our belief is that any flight that can be flown on batteries should be flown on batteries.”
Sora’s design sees the batteries stored in the wing “like fuel is today”, allowing for the design of a lighter structure and offering a “better vent path” in the case of thermal runaway.
While the configuration is not without challenges – notably the need to protect the wings from the effects of thermal runaway and to incorporate a thermal-management system – both Joby and Archer Aviation have opted for the same location for their batteries, he points out.
Many of those challenges will be addressed through BatWing, an Aerospace Technology Institute (ATI)-funded project led by Sora and involving the University of Bath which kicked off earlier this year.
“We are comfortable with the design of the battery system, [and] we have a cell solution that we like.” Assembly of a prototype battery pack will take place in 2026.
Each of the S-1’s electric propulsion units will deliver around 0.5MW at take-off power, driving a proprotor that is around 5m (16ft) in diameter – roughly the size of the propellers on the Airbus Defence & Space A400M.
Six electric propulsion units were required for redundancy, he says, with two located on the front wing and four on the rear in a staggered arrangement. The S-1 has no vertical tail, however, instead relying on active yaw control in cruise flight, maintaining both stability and control by adjusting thrust across its proprotors.
Despite the relatively large size of the proprotors, the S-1 is still compact enough to fit into a standard H2 24m-diameter helipad, says Afzal.
Supplier selections for the programme will take place next year, in line with a critical design review scheduled for late 2026 or early 2027.
First flight of the pre-production prototype should take place towards the end of 2028, he says, leading to service entry around 2031.
“It is an ambitious timeline, but we think it warrants us being ambitious and trying to push the boundaries,” he says.
Much of the design draws on work he and Sora’s chief technology officer Malcom Foster performed at GKN Aerospace, where they developed the “mass transit eVTOL” Skybus concept.
Sora is currently in its Series A funding phase, and Afzal believes the S-1 can be brought to market “for under $1 billion if it is done in a lean way with a dedicated focus on a single product ”.
UK company records show to date the firm’s backers are two investors based in Singapore.
Afzal spoke to FlightGlobal at the ATI conference in Newport on 4 November.
