How Electric Hypercar Tech Could Bring Back Supersonic Air Travel (At Last!)

Only 66 years separated the first Wright brothers’ flight and the launch of the supersonic Concorde passenger jet. The engineer/optimist in me is therefore deeply disappointed air travel speeds have only slowed in the nearly quarter-century since the graceful Concorde last flew. Car lovers take pride: After decades of aerospace innovation flowing into automobiles (turbochargers, carbon fiber, aerodynamics, ceramics), the auto world is poised to reciprocate—impressively.

The supersonic Concorde’s real Achilles’ heel was the thirst of its four Rolls-Royce turbojet engines (which could reportedly guzzle 1–2 tons of fuel on the ground prior to takeoff!). This limited the plane’s range, which prevented it ever serving hyper-profitable trans-Pacific routes. How to solve this thorny problem? The way cars can do (kinda): hybridize!

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The McMurtry Spéirling “fan car.”

San Francisco-based Astro Mechanica is working to incorporate Helix electric motors like those powering such roadgoing rockets as the Aston Martin Valkyrie, Lotus Evija, Czinger 21C, and the McMurtry Spéirling “fan car,” not to mention Formula E racers. What does “electrifying” a supersonic aircraft look like?

The motors will power the fan stage of Astro Mechanica’s proposed “Duality” turboelectric adaptive engine (TAE) concept. Conventional jet engines mechanically tie the fan to the turbine, forcing both to operate as a compromise across widely varying flight conditions.

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A decoupled design can independently optimize compression and power generation—especially at high speeds where inlet ram compression contributes significantly to total pressure rise. This reduces wasted work and improves overall efficiency. Electric compressor fans allow the same engine to behave like a turbo fan at lower speeds (today’s state of the art for subsonic flight), a turbojet at higher speeds (Concorde, MiG-21), and somewhat like a ramjet (SR-71, air-to-air missiles) when flying supersonic.

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This very early concept illustration shows the turbo-generator set (center) feeding two propulsor turbines, with compressors powered by Helix motors. Astro Mechanica hints that the current arrangement of parts has advanced considerably.

Where does the electricity come from? While there is a battery on board, it merely serves as a buffer—as in a mild hybrid car. The bulk of the electricity used by the likely four fan motors in two propulsor units is generated on demand by a separate turbine engine powering similar Helix motors working as generators (hence incurring some fuel-to-electricity conversion losses).

At high speed, Duality’s electrically driven compressor stages can potentially be idled. Running them like windmills could generate some energy, but it’s not yet certain this benefit would outweigh efficiency losses due to airflow restrictions. Fuel is primarily saved by avoiding excess compressor work that ram-air pressure is supplying. That said, any buffer battery will be sized to meet all HVAC and power needs on the ground, and it will be able to taxi the plane emissions-free, powering the fans electrically without firing the main turbine. (Founder/CEO Ian Brooke envisions a 40-kWh, 200-pound battery in his initial smaller planes.)

A point of clarification: Actual Helix SPX242-94 supercar motors have been used for proof-of-concept test firings that have already demonstrated supersonic exhaust flow, but bespoke fifth-generation Helix motors based on similar “mass-production” hardware are being hardened for low-temperature, low-pressure, high-altitude service. In thin air it’s easier for electricity to arc—between stator phases or to ground. Preventing this requires more insulation around stator windings. Helix has motors developed for satellite launch vehicles (as primary flight control actuators), so the company already has motors capable of working at -90 degrees.

Finally, although the motors are 98.4–98.8 percent efficient, 2 percent of nearly a megawatt per motor is still a lot of heat to manage, and sustaining high continuous-power ratings demands state-of-the-art cooling of both the stator and the magnets in the rotor, which is handled via multiple cooling circuits. Those motors work hardest during the takeoff and climb.

An interesting note: The motors will drive the fans directly, because the motors and fans are sized such that the motors hit their inertial limit at roughly the same speed as the fan blade tips hit their aerodynamic speed limit.

Astro Mechanica is working to make supersonic travel a reality within a decade—developing large, high-speed, unmanned systems first. But the longer-term goal is supersonic passenger flight priced near today’s coach fares. To accomplish this too-long-awaited goal, Brooke proposes a three-pronged approach.

Duality’s vastly improved efficiency is the first obvious prong. The second will be to fuel Duality with liquified natural gas (LNG). It’s significantly cheaper than jet fuel on an energy basis, offers higher specific energy that can extend range in aircraft designed for it, and produces roughly 20–30 percent less CO₂ at combustion. But implementing an LNG refueling infrastructure will take years if not decades.

A third way Astro Mechanica envisions reducing supersonic travel costs is by employing a business model somewhere between the private-jet-like scheduled small-craft service JSX (formerly JetSuiteX) and an “Uber for air travel” hailing model using small (five- to eight-passenger) supersonic jets operating out of smaller airports.

How fast are we talking, what about the sonic boom, and what’s the skin material? Astro Mechanica targets Mach 2.25–2.70 (1,726–2,072 mph, well up from the Concorde’s 1,354 mph). Its aircraft will be lighter and the shape better designed for distributing lift, which should make the sonic boom cone trailing the airplane much smaller and quieter—especially when heard from the plane’s 60,000-foot cruising altitude.

That is too fast for the Concorde’s aluminum skin (300 degrees max), and the titanium (660 degrees) used for the SR-71 Blackbird is too difficult to form into an ideal aero shape. So Brooke expects to use a titanium structure skinned mostly in carbon fiber in a thermoset resin called Bismaleimide (or BMI—480 degrees), employing titanium only where the surface heat is greatest—like the wings’ leading edges.

Circling back to those motors, Astro Mechanica has a plan to supply Duality engines as well as full airplanes. Helix may end up supplying the motors (and McLaren the silicon-carbide inverters) as they are today, but the company has secured other suppliers, as well.

What lessons might Helix have learned from its aerospace applications that could translate back to land-bound EVs? Chief engineer Derek Jordanou-Bailey points to the triple three-phase architecture as a big one (three inverters per motor, presently the best way to supply sufficient current using today’s 800–900-volt architecture). Helix’s novel high-voltage connection techniques were also crucial to achieving the high continuous-power density Duality requires, and these will likely find their way into motorsports and high-performance road cars. Meanwhile, integrating the motorsport-type cooling system into a more commodity-based motor architecture marks another advance with a potential road car or Formula E payoff.

How soon will you be able to hail a “hybrid” supersonic ride? Brooke expects to be flying planes within the next few years but concedes you won’t hail an affordable LNG-fueled supersonic flight much before at least the mid-2030s.

Of the five companies working on supersonic travel, I’m most impressed with Astro Mechanica’s strategy for boosting efficiency. The fact it is keeping a sharp eye on the “financial engine” needed to fund the company during this development phase is also encouraging—numerous contracts are signed for nearer-term deliverables Brooke was not at liberty to elaborate on.

Having personally traveled more than 3 million miles on Delta, dawdling along at an average speed of 560 mph, I can’t wait to sample Mach-speed flight. Godspeed, Helix and Astro Mechanica!