Researchers Min Ji Kim, Hyeon Jun Lee and Jae-Woo Lee of Konkuk University in Seoul have unveiled an advanced knowledge-based design framework that transforms the earliest and most consequential phase of aircraft development, the generation and selection of concepts. In conventional practice, a handful of experienced designers sketch out a few candidate layouts, debate their merits, and converge on a favorite through judgment shaped by years of experience. That process has produced the aircraft we fly today, but it carries two structural weaknesses. It explores only a tiny corner of the possible design space, and it depends heavily on the individual designer, which makes outcomes inconsistent and hard to reproduce. When the design space includes hundreds of possible combinations of lift systems, propulsion architectures and fuselage arrangements, human intuition alone cannot map the territory.

The Korean team’s framework attacks the problem on both fronts by integrating five interlocking components: functional decomposition, a knowledge-based database system, systematic morphological analysis, logical concept family grouping, and formal filtering and scoring procedures. Functional decomposition breaks the aircraft down into what it must do rather than what it should look like, generating a neutral list of functions such as lift generation, propulsion, energy storage and passenger accommodation. Each function is then paired with a menu of candidate solution options drawn from a structured knowledge base, ensuring that the concept generation step begins from evidence rather than from habit.

The heart of the framework is the knowledge-based database system, or KBDS, which the team implemented using Obsidian, a networked note-taking platform that allows engineers to link technologies, products and competitors into a navigable web of design knowledge. To populate the database for their case study, the researchers surveyed 67 regional air mobility, or RAM, competitor aircraft, catalogued 102 distinct technologies and compiled 182 product entries. Each entry captures the performance characteristics, maturity level and configuration role of a real-world solution, giving the design team a searchable library of what has already been attempted and how well it works. The use of technology readiness levels adds a practical filter, flagging solutions that are promising on paper but too immature for a near-term aircraft.

With the requirements fixed and the knowledge base assembled, the framework turns to morphological analysis, a method with a distinguished pedigree. First applied to astronomy by Fritz Zwicky in the late 1940s, morphological analysis arranges design problems as a matrix of configuration components and their possible solutions, then exhaustively combines them to enumerate the full solution space. For the RAM case study, the combination of key configuration components and their solution options produced 864 candidate aircraft concepts. That number is precisely the point: no conventional brainstorming session would ever surface 864 distinct, technically grounded alternatives, and many of the most promising ones might never cross a design team’s whiteboard.

Generating hundreds of concepts, however, creates a new problem, namely how to organize and prune them without reintroducing the subjective bias the framework was designed to eliminate. The Korean team’s answer is a statistical clustering technique they call logical concept family grouping. The method measures the configurational similarity of every candidate concept, essentially how closely each one resembles the others in the population across its chosen solutions. Using statistics borrowed from the behavioral sciences, including Cohen’s d effect sizes and contrast ratios, the framework quantifies which solution choices genuinely distinguish one group of concepts from another and assigns each component-solution pairing a family grouping score. The 864 candidates were thereby organized into eight coherent concept families, each representing a distinct and internally consistent design philosophy rather than an arbitrary slice of the list.

Filtering then reduced the field to half of the generated candidates by screening out configurations that violated constraints or duplicated dominant solutions without offering meaningful advantages. The surviving concepts faced a final, multi-criteria evaluation in which figures of merit were weighted using the analytic hierarchy process, a structured pairwise-comparison method that aggregates the judgments of multiple evaluators into a consistent set of priorities. By combining weighted figures of merit with the family structure established earlier, the team narrowed the field to a single final favorable concept for the regional air mobility mission, a result that emerged from a documented, repeatable chain of reasoning rather than from the preferences of any single engineer.

The significance of the work extends beyond one aircraft study. The framework explicitly incorporates AAM-specific features, such as distributed electric propulsion, multi-mode flight capability and urban operational constraints, into the generation process itself, so that unconventional configurations are treated as first-class candidates rather than exotic outliers. Because every step is procedural, from the functional decomposition to the statistical grouping to the weighted scoring, two independent teams applying the same framework to the same requirements should arrive at the same shortlist. That consistency and reproducibility are exactly what regulators, manufacturers and investors need as the AAM industry matures from bold demonstrations into certified, revenue-carrying services.

The timing could hardly be better. Dozens of companies worldwide are racing toward entry into service for electric vertical take-off and landing aircraft, and early design choices, made years before flight test, lock in much of an aircraft’s eventual cost, noise footprint, safety record and certification path. A framework that widens the search while disciplining the selection promises to reduce the risk of betting an entire program on a configuration that a broader exploration would have exposed as inferior. The methodology also aligns naturally with modern knowledge management tools, suggesting a workflow in which an engineering organization’s cumulative experience, captured in a living knowledge base, continuously feeds and improves its concept generation engine.

The researchers acknowledge that the framework does not remove human judgment entirely; evaluators still assign the weights that reflect program priorities, and the knowledge base reflects the scope of the survey behind it. But by converting intuition-heavy steps into measurable, documented procedures, the Konkuk team has moved aircraft conceptual design closer to an engineering science and further from an art. As advanced air mobility fleets prepare to transform how people move through cities, the ideas that take flight first may increasingly come not from a single designer’s sketchbook, but from an exhaustive, statistically disciplined search across 864 futures.

Subject of Research: A knowledge-based design framework for aircraft concept generation and selection in advanced air mobility

Article Title: An Advanced Knowledge-Based Design Framework for Aircraft Concept Generation and Selection

Article References: Kim, M. J., Lee, H. J., & Lee, J.-W. (2026). An Advanced Knowledge-Based Design Framework for Aircraft Concept Generation and Selection. International Journal of Aeronautical and Space Sciences. https://doi.org/10.1007/s42405-026-01296-3

Image Credits: AI Generated

DOI: 10.1007/s42405-026-01296-3

Keywords: advanced air mobility, aircraft design, knowledge-based system, concept generation and selection, design framework, distributed electric propulsion, regional air mobility, morphological analysis, multi-criteria decision-making, eVTOL, Advanced, Knowledge-Based

The review examines electrified aircraft propulsion through four interconnected lenses: propulsion architecture, certification frameworks, system safety assessment methods, and the certification-critical technical challenges that emerge when the two former elements collide. This structure reflects a key insight of the analysis: the way a propulsion system is architected fundamentally determines how difficult it will be to certify. An all-electric design with a single high-capacity battery pack presents a fundamentally different regulatory problem than a hybrid-electric arrangement that couples a turbine engine with electric machines, power electronics, and a transmission network, or a turboelectric concept in which gas turbines generate electricity for distributed motors. Each configuration distributes failure modes, redundancy, and power flows differently, and regulators must evaluate each accordingly.

The authors analyze the major configurations in detail. All-electric propulsion, exemplified by NASA’s X-57 Maxwell program, replaces fuel with batteries and electric motors, promising zero in-flight emissions and radically simplified drivetrains. Hybrid-electric propulsion blends battery and turbine power, offering extended range while retaining some of the operational flexibility of conventional aircraft. Turboelectric systems use generators driven by gas turbines to supply electric motors without onboard energy storage, sidestepping some battery limitations at the cost of added conversion losses. Distributed electric propulsion, or DEP, spreads many smaller motors across the wing or airframe, enabling aerodynamic benefits such as higher lift coefficients and shorter takeoff distances, but introducing complex fault-tolerance questions when any single motor or its power electronics fails. The review shows that certification complexity grows in a strongly architecture-dependent way: DEP, for instance, requires demonstrating that the aircraft can safely tolerate motor failures and power distribution faults across an interconnected network, something conventional single-engine certification rules never anticipated.

On the regulatory side, the review surveys the approaches of the three major airworthiness authorities: the European Union Aviation Safety Agency (EASA), the Federal Aviation Administration (FAA), and the Civil Aviation Administration of China (CAAC). EASA has pioneered special conditions for electric and hybrid propulsion systems, including Special Condition SC E-19 for electric and hybrid propulsion systems and SC-VTOL-02 for small-category VTOL-capable aircraft. The FAA has issued advisory circulars for powered-lift type certification and maintains standards for rechargeable lithium cells and batteries under TSO-C179b, drawing on RTCA’s DO-311A minimum operational performance standards. CAAC has published special conditions for unmanned aircraft systems and, notably, has released airworthiness standards for powered-lift aircraft. These frameworks share a common philosophy: because existing regulations were written around combustion engines, novel propulsion requires applicants to demonstrate, through special conditions and means of compliance, that equivalent levels of safety are achieved even where prescriptive rules do not yet exist.

At the heart of the safety substantiation process lies system safety assessment, formalized in industry standards such as SAE ARP4761A for safety assessment and ARP4754A for civil aircraft and systems development. These methodologies require identifying failure conditions, classifying their severity from catastrophic to minor, and demonstrating that the probability of catastrophic events falls below stringent numerical thresholds, typically on the order of one in a billion flight hours. The review highlights how model-based safety analysis and newer techniques such as System-Theoretic Process Analysis (STPA) are being integrated into this process to handle the systemic and software-driven failure modes that electrified architectures introduce. Digital twin technology, which creates high-fidelity virtual replicas of physical systems, is emerging as a complementary tool, supporting condition monitoring, prognostics and health management, and fleet-level surveillance of battery and electric drivetrain health throughout an aircraft’s service life.

Battery safety emerges from the review as perhaps the single most consequential certification-critical challenge. Lithium-ion cells can undergo thermal runaway, a self-accelerating exothermic failure in which a overheating cell ignites neighboring cells and propagates through the pack. In an aircraft, where batteries constitute a large fraction of the vehicle’s mass and sit close to passengers and critical structure, a thermal runaway event is treated as a design condition that must be contained. EASA has published dedicated guidance on thermal runaway for propulsion batteries, and the review traces the mitigation hierarchy: preventing cell-level failure through cell chemistry and quality control, arresting propagation through physical barriers and thermal management, and ensuring the aircraft can tolerate a complete loss of one battery segment. Recent research on battery thermal runaway prevention and on safety assessment for propagation mitigation, cited in the review, shows that containment design must be substantiated analytically and experimentally, a demanding requirement for packs large enough to propel transport-category aircraft.

High-voltage integration poses its own distinct set of hazards. Electrified aircraft will operate power networks at voltage levels far above those in conventional avionics, in an environment subject to altitude-induced low pressure, temperature extremes, vibration, and electromagnetic interference. Insulation degradation, partial discharge, arcing, and electromagnetic compatibility failures all threaten both the propulsion system and neighboring aircraft systems. The review points to environmental qualification standards such as RTCA DO-160G and software and hardware assurance frameworks including DO-178C and DO-254 as the established means of demonstrating that power electronics, controllers, and cabling can survive the airborne environment and that their software performs to the assurance levels that catastrophic failure conditions demand. Fault tolerance adds another layer: propulsion systems must detect failures rapidly and reconfigure, and in distributed architectures the loss of a motor changes not only thrust but flight dynamics, requiring coordinated control allocation strategies that themselves must be certified.

A recurring theme in the review is that architecture decisions made at the conceptual design stage ripple forward into every certification document an applicant will ever file. Redundancy provisions, segregation requirements, failure detection latency, and the sheer number of system interfaces all scale with architectural complexity. The authors therefore advocate architecture-aware certification strategies, in which certification implications are evaluated early and systematically as part of the design process rather than retrofitted after an aircraft configuration is frozen. They argue that this integration of certification thinking into architecture selection is now the primary challenge facing the sector, more so than improving any individual component, because today’s batteries, motors, and power electronics are increasingly technically viable while the pathway to proving whole-system safety remains immature and expensive.

The stakes of solving this challenge are considerable. International commitments, including the International Civil Aviation Organization’s long-term aspirational goal for international aviation, and the rapid growth of the advanced air mobility sector depend on certifiable electric propulsion. Programs such as NASA’s X-57, which documented its electric aircraft certification and airworthiness approach in detail, offer early lessons on how novel propulsion can be substantiated under existing frameworks, and scaled flight testing of distributed propulsion concepts continues to generate evidence on failure detection and control reconfiguration. But the review’s message is sobering and, at the same time, constructive: electrified flight will reach the market not simply when the technology works, but when the industry and regulators together can demonstrate, architecture by architecture, that it is safe. Bridging that gap, the authors conclude, will require certification strategies designed hand in hand with the propulsion architectures of the future.

Subject of Research: Airworthiness certification and safety assessment of electric and hybrid-electric aircraft propulsion systems

Article Title: Airworthiness certification and safety assessment of electric and hybrid-electric aircraft propulsion systems: architectures, frameworks, and critical challenges

Article References: Wang, X., Cao, A., Liu, Y., Hong, L., Zhou, B., Yuan, X., Liu, B., Bao, W., & Guo, J. (2026). Airworthiness certification and safety assessment of electric and hybrid-electric aircraft propulsion systems: architectures, frameworks, and critical challenges. Aerospace Systems. https://doi.org/10.1007/s42401-026-00526-6

Image Credits: AI Generated

DOI: 10.1007/s42401-026-00526-6

Keywords: electric aircraft, hybrid-electric propulsion, airworthiness certification, system safety assessment, distributed electric propulsion, battery thermal runaway, high-voltage integration, fault tolerance, EASA, FAA, CAAC, digital twin

The physics at stake is deceptively simple to state and notoriously hard to manage. A propeller does not merely push air backward; it spins it. The swirling, pressurized slipstream that washes over the wing behind a propeller changes the local flow speed, the pressure distribution, and the effective angle of attack along the span of the wing. When several propellers operate close together, their slipstreams merge and interfere, and the resulting flow field can either help or hurt the aircraft depending on where each disk is placed. Distributed electric propulsion, the concept that underpins many of NASA’s and industry’s electric aircraft concepts, multiplies these interactions: instead of one wake, the designer must choreograph a dozen or more, each tugging on the wing and on its neighbors.

To untangle this three-dimensional mess, the team led by Xiaolu Wang, Xiaoke Wang, Zixuan Dong, and Ya Su, together with Mingqiang Luo of Beihang University, built a computational fluid dynamics framework in which each propeller is modeled as an actuator disk. Rather than resolving every rotating blade, the actuator disk approach represents each propeller as a surface that injects momentum and swirl into the flow, matching the disk loading and rotational speed of the real rotor. This technique, validated against blade element theory and experimental propeller performance data, captures the dominant propeller-wing interactions at a small fraction of the computational cost of a full rotating simulation. The researchers wrapped the model in a Reynolds-averaged Navier-Stokes solver with shear stress transport turbulence closure, allowing them to resolve wing boundary layers, slipstream contraction, and wingtip vortex formation at cruise conditions.

Seven candidate layouts formed the backbone of the comparison. The configurations differed in the number of propellers per semi-span, their spanwise clustering, their chordwise placement ahead of the leading edge, and their vertical offset relative to the wing plane. Among the labels that emerged from the study, one result stands out: the tip-concentrated layout, designated T2U, which gathers propellers near the wingtip, achieved a lift-to-drag ratio 15.4 percent higher than the least efficient configuration, a root-clustered arrangement labeled R3U. The mechanism is a classic of aerodynamic theory given a new electric-propulsion twist. By injecting momentum and swirl directly into the flow at the wingtip, the outboard propellers energize the very region where the wingtip vortex forms, weakening the vortex and reducing the induced drag that dominates cruise at the modest speeds and low Reynolds numbers where most UAVs operate.

The tip-vortex mitigation, however, came with a trade-off that the study is careful to document. Adding more propellers increases the maximum lift coefficient — the three-propeller root layout R3U produced 8.2 percent more maximum lift than its two-propeller counterpart R2U — because more slipstream means more dynamic pressure over the wing and higher local lift. But every additional propeller also adds nacelle and pylon wetted area, thickens the merged wakes, and spreads the loading in ways that raise induced drag. The net effect, the researchers found, was a 6.4 percent reduction in aerodynamic efficiency and a 5.7 percent reduction in propulsive efficiency when moving from the leaner to the denser layout. In cruise, where the aircraft spends the overwhelming majority of its mission, that penalty swamps the low-speed lift benefit. The message is that the propeller count that looks attractive on a short-takeoff performance chart can quietly erode the range number that determines whether the mission closes.

Not all fixes require giving up propellers. A third design philosophy tested in the study, the non-uniform diameter layout T3N, assigns larger propellers to the outboard stations and smaller ones inboard. This asymmetric arrangement preserves the strong outer-wing blowing that suppresses the tip vortex while shrinking the root propellers, which reduces the flow interference and blockage near the wing root where the fuselage and flow field interact most severely. The non-uniform layout outperformed the uniform three-propeller arrangement F3U, demonstrating that diameter distribution is a genuinely independent design variable — one that previous studies tended to hold fixed while sweeping spanwise and chordwise positions. For designers of high-aspect-ratio electric aircraft, this suggests a richer design space than the uniform rows of identical rotors that dominate current concepts.

The study then went beyond comparing discrete layouts to continuous optimization. The team selected design parameters governing the spanwise and chordwise positions of the propellers and sampled the design space using optimal Latin hypercube sampling, a strategy that fills the parameter space evenly so that a modest number of expensive CFD evaluations covers the relevant combinations. Those evaluations trained a Kriging surrogate model, a statistical interpolator that provides both a predicted performance value and an estimate of its own uncertainty across the design space. A multi-island genetic algorithm then searched the surrogate, evolving populations of candidate layouts in semi-isolated subpopulations that periodically exchange individuals — a scheme known to resist premature convergence better than a single-population genetic algorithm. With the vertical position of the propellers held fixed, this parametric optimization improved the lift-to-drag ratio of the starting configuration by approximately 13.1 percent, a gain achieved purely by repositioning existing propellers rather than changing the wing or the propulsion hardware.

The broader significance of the work lies in its methodology as much as its numbers. Kriging-plus-genetic-algorithm optimization is now standard practice in airfoil and wing design, but applying it to the coupled propeller-wing-wake system requires a validated, affordable way to represent the rotors, and the actuator disk framework demonstrated here offers exactly that. The study’s results align with a growing body of literature on propeller-wing interaction — including prior work on wingtip-mounted propellers for drag reduction and on slipstream effects at low Reynolds number — while pushing further by optimizing multiple positional parameters simultaneously and by comparing lift-to-power ratios that capture the overall system efficiency, not just the wing in isolation. The lift-to-power metric matters because an electric aircraft’s range is set by the energy per unit of thrust delivered, meaning that a layout which helps the wing but burdens the propellers can be a net loss.

For the rapidly growing eVTOL and drone industry, the practical takeaways are concrete. Propellers belong outboard, where they can do double duty as propulsion and as wingtip-vortex suppressors; propeller count should be treated as a cruise-efficiency decision, not merely a takeoff-lift decision; and non-uniform rotor sizing deserves a place in the conceptual design toolbox. Every percentage point of lift-to-drag ratio in cruise compounds over a mission profile, and a 13 to 15 percent aerodynamic improvement from layout alone is comparable to gains that would otherwise demand heavier structure, larger wings, or bigger batteries. As regulators certify the first generation of distributed-propulsion aircraft and operators push for the range and endurance that make cargo and passenger services economical, studies of this kind are quietly redrawing the blueprint — one propeller position at a time.

Subject of Research: Aerodynamic design optimization of distributed electric propeller layouts for cruise-efficient unmanned aerial vehicles

Article Title: Effects of distributed propeller layout on cruise efficiency of unmanned aerial vehicles: a design optimization study

Article References: Wang, X., Wang, X., Dong, Z., Su, Y., & Luo, M. (2026). Effects of distributed propeller layout on cruise efficiency of unmanned aerial vehicles: a design optimization study. Aerospace Systems. https://doi.org/10.1007/s42401-026-00532-8

Image Credits: AI Generated

DOI: 10.1007/s42401-026-00532-8

Keywords: distributed electric propulsion, UAV, propeller-wing interaction, actuator disk, wingtip vortex, lift-to-drag ratio, Kriging surrogate model, genetic algorithm, aerodynamic optimization, eVTOL, computational fluid dynamics, cruise efficiency