As Volante Technologies and Aircar successively completed manned transition flights in the tilt-rotor track, and AutoFlight secured the world's first three airworthiness certificates for an eVTOL over one ton, the industry seems to be forming a consensus: tilt-rotor represents the upper limit of performance, lift-plus-cruise is the shortcut to commercialization, and multirotor is a temporary expedient. However, in this debate over "how to fly in the sky," one technical route has long been underestimated and even misinterpreted—distributed ducted fans.
Its voice is not loud enough. But upon careful examination of urban commuting, the most core and demanding application scenario for eVTOL, the distributed ducted fan may be the answer that truly "adds up."
Constraints of the Urban Sky Are More Ruthless Than the Flight Itself
When discussing the pros and cons of eVTOL configurations, if one only focuses on the range and speed parameter tables, it is easy to draw a simple ranking: tilt-rotor > lift-plus-cruise > multirotor. But this ranking ignores a fundamental premise—eVTOL is not meant to show off at airshows; it is designed for high-frequency takeoffs, landings, and passenger commuting in cities.
The requirements for aircraft in urban commuting scenarios are fundamentally different from those in other scenarios. Tian Yun, Chairman of Yuntu Aviation, has a judgment worth noting: safety, noise, and life-cycle economics—these three constraints must be solved together from the overall configuration stage. If a configuration that is easy to prototype is determined first and then supplemented separately later, higher engineering costs will have to be paid.
Let's talk about safety first. Cities are densely populated with tall buildings. Aircraft must not only rely on the reliability of individual components but also form system safety through power redundancy, fault isolation, and emergency response. The natural advantage of distributed ducted fans lies in the distributed arrangement of multiple small ducted units along the wings or fuselage. When a single unit fails, the remaining units can redistribute thrust through the flight control system to maintain flight. More importantly, the duct structure itself physically encloses the rotor. Even if the blades rupture, the duct ring can prevent debris from flying outward, which is of great significance for safety over cities. Lilium has specifically designed a blade disk structure with retaining elements in its ducted propulsion unit, with the core purpose of solving the risk of high-speed rotating blades rupturing or detaching.
Then there is noise. Whether urban operations can gain public acceptance depends not on a single demonstration, but on the continuous noise level during high-frequency takeoffs, landings, and cruising. The noise sources of open rotors mainly come from blade tip vortices and broadband noise, while the duct structure can shield part of the noise. At the same time, the duct lip combs the airflow, making the rotor run more smoothly and evenly. Germany's Lilium specifically optimized the noise-reducing liners of the propulsion units in the design of its ducted tilt configuration, and even designed a bidirectional drainage network to ensure stable noise reduction performance in any flight attitude. Although the mechanical complexity of the tilt duct brings airworthiness challenges, when it comes to being "quiet," the ducted route has an inherent advantage.
Finally, let's talk about cost. This point is most easily overlooked. The mechanical tilt structure of the tilt-rotor poses extremely high requirements for R&D, verification, and maintenance. The lift-plus-cruise configures two completely independent power systems for vertical takeoff and landing and cruising. Both systems mean extra weight, cost, and maintenance complexity. The solution of distributed ducted fans plus power lift does not rely on mechanical tilt. Multiple power units work in coordination with the wings, completing the transition from hover to level flight through continuous aerodynamic changes. According to data disclosed by Yuntu, on the premise of keeping the airframe structure, avionics, and flight control costs consistent, its power system cost is reduced by about 80% compared to mainstream solutions, and the overall aircraft cost is reduced by at least 40%.
The "Hidden Advantage" of Ducted Fans: Underestimated Aerodynamic Synergy
Another reason distributed ducted fans are underestimated is that the industry's perception of them has long remained at the qualitative level of "low noise and good safety," ignoring the potential system-level improvement they may bring in aerodynamic efficiency.
The ducted fan itself is not a new technology. Its core advantages are high thrust per unit disk area, compact structure, and strong wind resistance. But when ducted fans are combined with wings in a "distributed" form, more complex aerodynamic coupling effects occur. Academic research shows that arranging distributed electric ducted fans near the leading edge of the wing can significantly increase wing lift by utilizing the slipstream of the propulsion system. ONERA's AMPERE concept observed in a 1:5 scale wind tunnel test that the maximum lift coefficient of the distributed ducted fan configuration reached about 2.4 at a 22-degree angle of attack, with a CFD predicted value of about 3, far higher than that of conventional wing configurations. This means that the power system not only provides thrust but also "increases lift" for the wing. Power and lift are no longer two independent ledgers.
This is precisely the characteristic most needed in urban commuting scenarios. The typical flight segment for urban air taxis is very short, with climb and descent accounting for a significant proportion of flight time. Hover efficiency and level flight efficiency are equally important. Pure multirotors have high hover efficiency but low cruise efficiency. Tilt-rotors have high cruise efficiency but complex control during the transition phase. The idea of distributed ducted fans + power lift is to find a smoother transition between the two—no mechanical tilt is needed, nor is there any "dead weight" from two independent systems. The power units participate in both lift generation and thrust generation simultaneously.
There Is No "Ultimate Answer" in the Configuration Debate, Only "Scenario Answers"
It must be admitted that the advantages of tilt-rotors in range and speed are real. The Joby S4 has a range of 250 kilometers and a maximum speed of 322 km/h. Aircar's E20 has a range of 200 kilometers and a speed of 320 km/h. For inter-city travel scenarios, these performance metrics are rigid demands.
But the logic of urban commuting is different. A typical mission for an urban air taxi might be from Hongqiao Hub to Lujiazui, or from Shenzhen Bay to Songshan Lake in Dongguan, with distances between 30 and 80 kilometers. This distance range is exactly the "sweet spot" where multirotors cannot reach, and lift-plus-cruise and tilt-rotors have excessive performance. The range of multirotors is generally between 30 and 65 kilometers, with speeds between 90 and 130 km/h. The range of tilt-rotors and lift-plus-cruise is often over 150 kilometers, with cruising speeds over 200 km/h. For high-frequency, short-segment urban commuting, excessively high speed performance may not translate into operational efficiency, but may instead bring higher energy consumption and more complex maintenance burdens.
The positioning of the distributed ducted fan lies precisely here. It does not pursue the ultimate in range, but tries to find a more balanced solution among safety, noise, cost, and efficiency. As has happened many times in aviation history: multiple configurations coexist in parallel for a long time, gradually converging only after safety verification, cost accounting, and commercial operation. The direction of convergence has never been "the one with the strongest performance," but "the one most suitable for that scenario."
What Will the Second Half Compete On
The eVTOL industry in 2026 is crossing a watershed. EHang has obtained certificates, AutoFlight has obtained certificates, Volant has completed manned transition flights, and Aircar and Volante have entered the deep water of compliance verification in tilt-rotors. "Being able to fly" is no longer news. The next question is: who can truly put aircraft into high-frequency commercial operations with acceptable costs, acceptable noise, and acceptable safety levels.
The distributed ducted fan is not the only answer, but it may be the answer most underestimated by market sentiment. When capital and public opinion rush towards the route with the "highest performance upper limit," the configuration choices derived by working backward from scenario constraints often require more time to prove themselves. But the ledger of the urban sky ultimately calculates not the parameters at airshows, but the safety redundancy of every flight, the noise decibels of every takeoff and landing, and the comprehensive cost per kilometer of range.
This configuration debate is far from over.
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