If you were to pack an electric plane with batteries so that it would also be sufficient for medium or even long-haul routes, there would be hardly any space left for freight or passengers. The Californian start-up Magpie Aviation has now presented a crazy-sounding but not entirely implausible alternative: electric tow planes that pull conventional cargo or passenger planes a bit behind them.
The principle is nothing new. As early as the Second World War, cargo gliders were brought to their destinations with tow planes. “F-tow” is also a common take-off method in gliding. However, the tow rope is latched to the ground and both machines start together. Magpie’s concept, on the other hand, envisages that the aircraft to be towed take off under their own power and only latch onto the tow rope in the air. That makes things even more complicated. But the start-up has already demonstrated an automatic coupling that allows the two machines to be connected in flight.
The model was the refueling of military jets in the air. The tanker aircraft pulls a hose behind it, which is stabilized by a small parachute. The jet now has to fly into the funnel-shaped coupling of the hose with its tank nozzle, where it is automatically locked.
First towing from a glider
Magpie has now expanded this process to include electronic aids. Optical sensors and GPS with so-called real-time kinematics allow the clutch parts to be positioned with centimeter precision. The coupling on the tow cable is automatically guided to the counterpart on the nose of the aircraft with baffles. “The pilot just has to approach the tow plane at the right speed,” Magpie CTO Andrew Goessling told Aviationweek. “The device takes care of everything else – vertical and horizontal alignment.” That’s why docking is easier than air refueling in the military, which requires “considerable flying skills” from the pilot.
With this construction, the Magpie succeeded several times in test flights in connecting a glider with a tow plane. A first in aviation history, according to Aviationweek. Magpie chose a glider primarily for cost reasons. But it also increased the difficulty of the tests. “After all, there is no throttle to control the distance,” says Goessling.
The tow rope for these trials was about 100 meters long. For later assignments with larger machines, Magpie talks about rope lengths of 500 to 1500 meters. This should sufficiently decouple both machines from turbulence. By 2030, the start-up hopes, it will be possible to tow machines the size of a turboprop regional aircraft in everyday operation. Single-aisle jets will also follow later. The towed machines themselves can be powered electrically, conventionally or hybrid.
Vision: Entire fleets of towing aircraft
Initially, the flying tractors are only intended to help bring aircraft to cruising altitude shortly after take-off. In the future, according to the vision, entire fleets of tow trucks stationed at low-cost regional airports along the flight route could replace each other like in a relay race, thus enabling electric routes of more than a thousand kilometers. The towed machines should always have enough energy on board to be able to land at an alternative airport if the handover doesn’t work out.
The whole thing sounds like a huge effort. After all, for each long or medium-haul flight, several launches of tow planes have to be coordinated. And the system only makes sense if it really works continuously with sufficient reliability so that machines do not regularly have to land somewhere unexpectedly due to a lack of connecting tugs. The start-up shows a graphic on its website, according to which its system is slightly more expensive to operate than conventional passenger aircraft, but still cheaper than climate-neutral fuel or hydrogen. In addition, the start-up argues, the concept can also be used for (partial) electrification of the existing fleet.
But maybe it doesn’t have to be the big vision: after all, an airplane uses up most of its energy during take-off and ascent. Once it has reached its cruising altitude, further locomotion is relatively economical. With an additional starting aid on the ground, for example in the form of a winch, and a tow plane for the first ascent, it is possible to realize quite slim e-aircraft with a usable range.
“It sounds crazy, but we couldn’t find any reason why it shouldn’t work,” said CEO Vander Lind at the launch. According to its own statements, the start-up has already contacted the US aviation authority FAA for approval of the process.
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