Aircraft Innovation Trends Enabling Advanced Air Mobility

Abstract

This study presents a comprehensive exploration of vertical take-off and landing (VTOL) aircraft within advanced air mobility (AAM), examining the crucial challenges of integrating these innovative technologies into transportation systems. AAM promises transformational social change by enhancing transportation energy efficiency, safety, and operational effectiveness. This research utilizes a methodical approach that juxtaposes a systematic review of patents with an extensive analysis of the academic literature to map the innovation landscape of VTOL technology. This dual analysis reveals a dynamic progression in VTOL advancements, highlighting significant strides in aerodynamic optimization, propulsion technology, and control systems. The novelty of this study lies in its dual-method approach, combining patent analysis with the academic literature to provide a holistic view of VTOL technological evolution. The patent analysis reveals that companies have been most productive on innovations relating to VTOL aircraft transition efficiency, control enhancement, and energy management. The literature review identifies key trends such as the rise in electric propulsion technologies and the integration of AI-driven control mechanisms. These results provide new engineering knowledge that can guide future VTOL development and policy formulation. The original contributions include a detailed mapping of VTOL innovation trends, identification of key technological advancements, and a predictive lens into future directions. These findings offer a valuable resource for aerospace engineers, policymakers, and urban planners. This study contributes a detailed assessment of both theoretical foundations and practical applications, fostering a holistic view of the challenges and innovations shaping the future of AAM. By connecting research and practical development, this study serves as a critical tool for strategic decision making and policy formulation towards advancing the integration of VTOL aircraft into sustainable urban transportation networks.

1. Introduction

The rapidly growing field of advanced air mobility (AAM) represents a transformative frontier in modern aviation, which is anticipated to redefine logistic frameworks. Central to this movement is the environmentally friendly vertical take-off and landing (VTOL) aircraft that does not need a large runway area [1]. VTOL aircraft, a hybrid between quiet helicopters and winged aircraft, offer solutions for reducing urban congestion [2] and enhancing environmental sustainability [3]. This research is motivated by the critical design challenges these aircraft present, including energy efficiency [4], transition fluidity between hover and cruise [1], and the overarching imperative for safety [5]. These challenges have significant implications for sustainable development and the integration of AAM into the global transportation network.

The current scholarly discourse has illuminated various aspects of VTOL technology, outlining advances in propulsion systems [6], aerodynamics [7], and control mechanisms [8]. However, a void persists in comprehensively synthesizing these disparate threads of innovation to understand the interplay and convergence of a wide variety of technological domains. The academic literature often discusses design results based on aeronautical and theoretical principles or the results of simulations, resulting in insufficient practical insights that full-scale testing of commercial aircraft can provide. The proprietary nature of aircraft development and the desire to maintain a competitive advantage by keeping trade secrets has left a void in knowledge. Without insights into the remaining design challenges and current technological capabilities to resolve them, it becomes impractical to forecast a realistic timeline for VTOL commercial deployments. This research aims to close this gap by systematically reviewing and classifying patents to discern trends and trajectories in VTOL innovation.

The goal of this study is to map the innovation landscape of VTOL aircraft, identifying key trends and assessing their potential impact on AAM. Through a detailed analysis of patent data from 2018 to 2023, this study illuminates the evolving focus of VTOL research and development, providing insights into the shifting priorities and emerging themes within the field. To achieve this goal, this research employs a systematic patent review (SPR) through a workflow comprising preprocessing, screening, and classification stages, encompassing robust statistical analysis to ensure the precision of trend identification. This methodological rigor allows for a high-resolution snapshot of VTOL innovation, capturing the multifaceted dimensions and complexity inherent in patent filings.

The contributions of this study are manifold. First, the study presents a granular, data-driven examination of technological advancements, contributing to the academic body of knowledge with a comprehensive overview of the state of VTOL innovation. Second, by delineating the connections between different areas of development, the study provides a multidimensional perspective on how various technological improvements converge to advance the field. Last, the work offers a predictive lens into the trajectory of VTOL technologies, serving as a framework for industry stakeholders and policymakers in aligning strategic priorities with technology developments.

The structure of the rest of this paper is as follows: Section 2 reviews the recent literature on AAM and VTOL aircraft design. Section 3 describes the SPR workflow developed and employed to conduct this study. Section 4 discusses the results, including visualizations to aid observing patterns in the patent objectives. Section 5 engages in a detailed discussion about the findings. Section 6 concludes the research and suggests future directions.

2. Literature Review

The subsections of this literature review begin with a review of the broader topics within the AAM landscape before delving into more narrowly focused topics within the realm of VTOL aircraft design, the main topic of this research.

2.1. Advanced Air Mobility

AAM represents a paradigm shift in transportation, promising a future that integrates air travel into population centers [1]. AAM is inherently multifaceted and complex, characterized by its breadth of dimensions [9], ranging from the dynamic demand of air mobility services to integration into smart cities [10]. The significance of AAM lies not only in its technological innovations but also in its potential to offer a new layer of mobility that complements traditional ground transport systems in both urban and rural settings [11].

AAM will unlock the vertical space and offer a fluid, on-demand mobility system that contrasts sharply with the fixed schedules of conventional aviation [12]. With urban air traffic management lagging behind VTOL aircraft development, research into seamless and safe airspace integration is a crucial challenge [13]. Additionally, the public perception of drones, which is most skeptical with regard to their commercial applications, highlights the importance of fostering a positive societal view of AAM technologies [14]. Positive attitudes towards technological innovations strongly correlate with the intention to use these services [15]. For instance, the clear benefits of using VTOL for aeromedical transport can help to spur its adoption ahead of broader use cases involving regular passenger transport [16]. For this reason, identifying the optimum location of vertiports to enable aeromedical transportation becomes paramount [17].

While the public may be warming to drone usage, the larger scale and visibility of AAM raises new concerns regarding risk perception, technological reliability, and perceived benefits over existing transport options [3]. The technological advancements in AAM, such as new propulsion technologies and sustainable aviation fuels, offer environmentally friendly alternatives but require behavioral adaptations from consumers, including the choice of efficient options and carbon offsetting [3].

Analysts anticipate that AAM will play a significant role in the development of future smart cities [18]. Studies have recognized that the benefits of AAM for society and the environment are substantial, outweighing its costs [19]. However, stakeholders must address numerous integration challenges, including control challenges in dense urban settings [8]. Moreover, the design of airspace for urban air mobility is still in the conceptual stage, with most proposals focusing on maximizing safety and capacity without fully considering ground-level factors such as noise and privacy [5]. The operational considerations for AAM are multifarious, encompassing infrastructure design, operational planning, the identification of operational constraints, and competitiveness with other transportation modes [20]. The diversity of operations using VTOL with different levels of autonomy and technologies presents unique challenges to integration into the National Airspace System [21].

Ground-based infrastructure, including networks of vertiports, maintenance facilities, energy supply, and navigation and communication capabilities, forms the backbone of AAM [22]. Additional considerations include fleet procurement, maintenance, pilot training, and dynamic route planning [23]. Given the breadth of AAM and the vast spectrum of associated research challenges, this study will focus on the specific domain of VTOL aircraft design challenges. VTOL aircraft are central to the AAM vision, representing a critical innovation in diversified transportation, and necessitating focused attention on their unique technological, infrastructural, and operational challenges [24]. Addressing the design challenges of VTOL aircraft will contribute to the field and provide a critical foundation for future research addressing other facets of AAM.

2.2. VTOL Design Challenges

Johnson and Silva (2022) summarized that efficient VTOL capabilities require technological advances in rotor noise reduction, emission reduction, resilient lightweight structures, advanced automation and control, and enhanced efficiencies in propulsion, energy generation, and energy storage utilization [6]. Despite anticipated commercial deployments this decade, limitations persist in many dimensions, including flight endurance, flight speed, and payload-carrying capability [25]. The paragraphs below discuss the design challenges under the specific categories of architecture selection, advanced materials, control systems, battery technology advancements, airspace integration, autonomy, and cost.

Architecture: VTOL aircraft designs include both wingless and winged categories, with each further categorized based on how they transition between vertical and horizontal flight modes [1]. Wingless VTOL designs have one or more rotors, akin to helicopters. Additional rotors provide more degrees of control and fault tolerance [26], but they also consume more energy and add complexity [27]. Rotary aircraft are more suitable for missions below 10 km (6 miles) due to their inefficiency in cruise flight resulting from the lack of a wing to provide lift [28]. Winged designs include either fixed position or tiltable rotors to enable vertical flight. Fixed rotors that park during cruise mode increase aerodynamic drag unless a mechanism can retract them into the airframe. There is also a tradeoff in rotor designs that maximize efficiency during vertical versus horizontal flight modes [29]. Tiltable rotors contribute both vertical and forward propulsion, but their tilting mechanisms can add weight and increase control complexity during flight mode transitions [30]. Fixed rotors on tiltable wings offer a tradeoff by eliminating tiltable rotors, but the wing tilt mechanisms can also add weight and complicate control stability during flight mode transitions [31].

Several strategies have emerged to reduce design complexity and reduce rotor noise. An innovative design referred to as the tail-sitter can avoid tilting or retracting rotors by landing the aircraft on its tail and rotating its body while transitioning between vertical and horizontal flight modes [32]. Ducted thrust emerged as a strategy to enhance efficiency and reduce noise by placing the fan inside a duct or cylindrical shroud to reduce blade tip losses and reduce drag during cruise mode [33]. Focusing on blade tip modifications appeared to be an effective strategy for reducing both tonal and broadband noise [34]. Overall, each configuration has advantages and disadvantages in terms of power consumption during cruise versus hovering, design complexity, noise in hovering, range, speed, and ride comfort [35].

Material: There has been a gradual departure from heavier metals in favor of lighter, more resilient composites which directly contribute to increased aircraft endurance by reducing the overall weight and thus enhancing energy efficiency [36]. Electrification further compounds the thermal challenges for airframe materials and heat sink capacity [37]. Composite materials offer superior strength-to-weight ratios, corrosion resistance, and greater flexibility in aerodynamic shaping, which are critical properties for VTOL aircraft that require agility and sustained flight [7]. Despite these advantages, the high costs associated with producing and shaping composite materials have so far hindered their mass adoption within the AAM ecosystem [36].

Control: Mohsan et al. (2023) highlighted how rapid advancements in control, miniaturization, and computerization have led to more robust and cost-efficient designs [38]. Nevertheless, the complex aerodynamic coupling between the systems that enable both vertical and horizontal flight modes can lead to unforeseen issues during transitions [39]. Buildings and other urban structures can channel turbulent air flows and gusts that affect aircraft steadiness and stability [40]. Consequently, advanced control strategies are necessary to ensure that VTOL aircraft have the stability and agility required for complex flight dynamics [41]. Some manufacturers have attempted to avoid these tradeoffs by adapting the aircraft design to mission-specific requirements. For instance, Ozdemir et al. (2014) presented a tradeoff study to accommodate interchangeable payload pods and wings of different sizes, allowing VTOL aircraft to be adapted to different mission types based on unique requirements for hover, endurance, and cruise speed [42].

Battery: In contrast to hybrid propulsion, all-electric designs can reduce costs by simplifying the drive train and lowering the operating temperature [43]. However, the estimated battery energy density requirement is 600 Wh/kg to satisfy most regional flight range specifications [44], with current battery technology capable of only up to 250 Wh/kg [43]. All-electric designs require careful temperature management, including temperature prediction and safety diagnosis to provide early warning of potential battery fires [45]. To boost endurance while providing the peak power density necessary for lift, researchers found that there is some benefit to combining hydrogen fuel cells with lithium-ion batteries, albeit at the cost of added complexity [46]. Hydrogen fuel cells are of interest because the byproducts are only water and heat; however, high production costs and the need for bulky hydrogen tanks hinder integration into aircraft [47]. Another solution is battery swapping, but this approach requires investment in multiple batteries and charging stations [48]. Aside from increasing energy density, designs must also aim to reduce charge time and increase the maximum number of recharge cycles [49]. More recently, rechargeable metal-air batteries [50] and liquid hydrogen [51] have emerged as potential solutions.

Airspace: The integration of VTOL aircraft into the commercial airspace and traffic control system remains a significant challenge [52]. Current air management tools cannot seamlessly adapt to enable the safe operation of these new types of aircraft [53]. Consequently, VTOL aircraft certification challenges persist [54]. Technologists have been turning to artificial intelligence to inform intelligent traffic control strategies through modeling and simulation [55]. Al-Rubaye et al. (2023) suggested that the lack of wireless coverage in congested cities and rural communities can further challenge airspace integration and traffic management [56]. One study suggested that a combination of terrestrial and aerial base stations could help to provide more robust wireless communications, albeit at a higher cost [57]. With wireless communications come the significant challenge of assuring trustworthy and secure communications as technologies continuously evolve through different generations [58]. For instance, 5G wireless communications will soon transition to 6G as AAM developments evolve [59].

Autonomy: An emerging view is that autonomous navigation capabilities will become necessary for the successful integration and operation of eVTOLs in urban environments [2]. More than 150 companies were developing prototypes in 2023 [60]. However, a myriad of challenges remain [60]. Autonomous flying requires systems to accurately sense flight parameters like airspeed and angle of attack to control stability, especially when subjected to wind gusts [61]. Autonomous navigation capabilities encompass enhanced perception, intelligent planning, and advanced control [32]. Systems must precisely track aircraft trajectory to optimize flight paths for efficiency and safety while considering changing environments [4]. Autonomous landing is particularly difficult when using image sensors to locate landing markers [62]. Additional challenges in automation include maintaining reliable communication links for data transmission and control [63], accurately detecting and identifying objects in the environment [64], and handling sensor failures and unexpected situations [65]. Developers have been evaluating artificial intelligence to enable autonomous navigation, object recognition, and predictive maintenance [66].

Cost: Price estimates for VTOL aircraft are scarce because of the absence of commercial operations and the proprietary nature of their development. Based on announced provisional orders by major commercial airlines, one analyst estimated the price tag of an eVTOL capable of range exceeding 100 miles and a maximum cruise speed of 200 mph to be USD 4 million each [67]. A report by Deloitte Research estimated the price range to be between USD 1.2 million and USD 4 million, which is on par with or lower than many helicopters [68]. An academic study estimated that a design capable of carrying 500 kg (1102 pounds) a distance of 500 km (310 miles) at a speed of 207 km/hour (128 mph) will have a price tag between USD 14 million and USD 18 million [69]. However, as with most hardware technologies, economies of scale dictate that prices will decline over time as manufacturing ramps up.

3. Methodology

The primary database used for the patent analysis in this study is the United States Patent and Trademark Office (USPTO) database. The objective of the methodology is to effectively identify, process, and analyze all USPTO-issued patents to yield insights into technological advancements and thematic shifts in VTOL aircraft design and functionality. The focus on the USPTO is justifiable for several reasons. First, the USA dominates in VTOL patents issued, accounting for more than 40% of global development efforts [70]. Second, inventors in other countries, particularly in the United Kingdom, Europe, and Asia, file their more significant inventions at the USPTO, claiming priority dates from their domestic filings.

Figure 1 illustrates the structured methodological workflow of the SPR developed in this study. The SPR methodology provides a replicable framework for assessing innovation over time, which is critical for understanding the evolution of VTOL technologies. The SPR workflow comprises three main stages: preprocessing, patent screening, and classifying objectives.

The following is a detailed description of all the steps in the SPR workflow:

Preprocessing: This initial stage prepared the USPTO data for analysis. It begins with text cleaning that converted all characters to UTF-8 encoding and converting all letters to lowercase for processing consistency. The “Patent Filter” procedure extracted potentially relevant patents by using Boolean logic on specific keywords. The patents must contain all the keywords specified in the “AND” list and may contain any of the additional keywords in the “OR” list. The “AND” keyword list was [aircraft, vertical, electric]. The OR keyword list was [VTOL, UAV, drone, vertiport, autonomous, battery, aerial, vehicle]. These terms captured a wide spectrum of innovations without bias towards any specific organization or entity, providing a comprehensive overview of the technological landscape. The similarity function removed redundancy by excluding patents with a similarity score of 95% or higher, which removed duplicates from the dataset. This step required vectorizing the text to apply a cosine similarity function, a common method employed in natural language processing (NLP) [71].

Patent screening: The second stage of the workflow filtered the patents to identify relevant documents for detailed analysis. The “Relevance Measures” procedure collected statistics on term frequency and the position of terms within the documents. The “Filter 1: Frequency” procedure removed patent summaries with term frequency less than or equal to two, meaning that further review considered only patents with terms that appeared more frequently. This threshold was set based on empirical observation of patent relevance during the preprocessing stage. The “Position Outlier” and “Filter 2: Position” procedures utilized the Tukey method to remove patent summaries with keywords first appearing beyond an outlier threshold, γ, as determined by the equations based on the interquartile range (IQR) and the third quartile (Q3). The rationale is that irrelevant patents will have the important keywords appear statistically late in the patent narrative.

Classifying objectives: The final stage involved classifying and assessing the innovations described in the patents. The “Category Labeling” procedure used the author, a subject matter expert (SME), to classify patents based on their objectives. The “Theme Visualization” procedure produced a word cloud of the most frequent bigrams (adjacent words) within each of the categories to visualize the quality and consistency of the SME classifications and themes. In preparation to produce the word clouds, the “Text Normalization” procedure used lemmatization to reduce words to their base or dictionary form, and stop word engineering to remove common words that did not add semantic value. The word cloud generator utilized the bag-of-words technique in NLP to identify the top keywords and bigrams [71]. The “Objective Validation” procedure provided further validation of the SME classification by depicting the frequency distribution of keywords for patents within each of the classified domains. The “Theme Assessment” procedure added a succinct SME statement of the innovation in terms of the specific problem that the invention addressed.

4. Results

The subsections that follow discuss the results from the SPR workflow.

4.1. Systematic Patent Review

Table 1. SPR workflow results.

SPR Stage	2018	2019	2020	2021	2022	2023
Original	310,568	357,790	355,647	330,645	326,228	314,794
Contains AND/OR keywords	160	197	215	227	267	406
Remove duplicates	158	197	213	225	267	403
Remove 95% similar	152	194	213	217	262	375
Freq (all) ≥ 2	21	36	39	42	48	83
“aircraft” ≤ pos	17 (229)	31 (304)	32 (173)	33 (184)	44 (138)	73 (101)
“vertical” ≤ pos	14 (1058)	28 (1370)	30 (519)	26 (338)	37 (649)	66 (774)
“electric” ≤ pos	12 (3121)	25 (1451)	29 (1828)	25 (1663)	32 (856)	61 (873)
SME classification	8	22	25	21	32	50

presents a summary of the results from each stage of the SPR for each year of the patent database. Altogether, the SPR initially extracted 1472 patents related to VTOL design, identified from a total of 1.9 million patents. This represented less than 0.1% of the patents issued during the six-year period. The multilayered filters produced a final set of 184 patents total. For the outlier position filter, the table shows the word position threshold for each AND keyword in parenthesis. The SME review and classification removed 26 irrelevant patents from this set, resulting in a total of 156 relevant patents. Further in-depth review of these patents revealed that the USA accounted for 82% of the patents, whereas Germany and France accounted for 8% and 3%, respectively. Other countries represented included Italy, Japan, Malaysia, Spain, Sweden, Korea, Portugal, and the UK.

4.2. Classification of Objectives

Figure 2 shows the distribution of VTOL aircraft patent categorizations from 2018 to 2023. The distribution shows a progressive increase in the total number of patents filed each year, indicating a growing innovation rate within the VTOL sector. A marked uptick in patents related to transition efficiency emerged in 2020 and continued to rise, reflecting a focused innovation drive to enhance the switch between vertical and horizontal flight modes. Interestingly, patents relating to both thermal and energy management showed modest representation in earlier years, with a marked increase in 2023 suggesting a more recent focus on safe energy utilization from batteries. There was a consistent presence of patents relating to safety enhancement through the years, aligning with the strong focus on safety in aviation.

Figure 3 provides a complementary view of the information in Figure 2 by highlighting the number of patents within each category in ranked order of count. Patents relating to transition efficiency dominated, further validating the concentrated effort on improving the efficiency of transitioning between flight modes. Patents relating to control enhancement followed as the second most prolific category, with a notable presence across the years emphasizing a focus on VTOL operational control systems. Patents relating to adaptable systems accounted for one of the smallest portions, indicating less emphasis in this area. Nevertheless, the variations in patent counts year by year within each category suggest the ebb and flow of research and development focus. Overall, the distribution illustrates a diversified innovation strategy that targeted a broad spectrum of technological improvements in the industry.

The word cloud in Figure 4 provides a visual representation of the most frequent terms within each category, quickly highlighting key themes and trends. The keyword distribution of Figure 5 complements the visual summary by offering a detailed and precise account of the top 10 keywords, ensuring clarity and specificity. Together, these visualizations enhance the reader’s understanding by providing both a broad overview and specific details of the keyword frequencies. In the word cloud for adaptable systems, terms such as “wing”, “lift generation”, and “configuration” suggest a focus on the flexibility of system assembly to achieve different mission objectives. The cloud for control enhancement features keywords such as “control”, “fuselage”, “propeller”, and “actuator”, pointing to advancements in flight control systems and airframe integration. The keywords “rotor” and “reinforcement” stand out in the cloud for safety enhancement, highlighting the need for rotor safety and the development of safer structural features.

The cloud on transition efficiency frequently shows “wing”, “rotor”, and “thrust producing”, indicating significant attention to the elements that produce lift and forward flight during mode transitions. The cloud on drag reduction emphasizes words like “structural member”, “airframe”, and “surface”, implying innovations aimed at reducing airflow friction across the larger aerodynamic surfaces of the aircraft. The cloud on thermal management prominently features “heat transfer”, “battery cell”, and “battery module”, reflecting the critical challenge of managing the heat in electrically powered aircraft components, especially batteries.

The Figure 5 subchart on adaptable systems shows that “wing” and “element” are among the most frequently occurring terms, suggesting innovations focused on wing design as a modular component. The chart on control enhancement has “control” as the dominant term, reinforcing its importance in the operation and maneuverability of VTOL aircraft. The chart on propulsion efficiency features “motor” and “propulsion” as key terms, highlighting areas crucial for efficient power delivery and aircraft movement. The chart on safety enhancement has “control” and “rotor” as the most frequently mentioned keywords which, as expected, are associated with the integration of control systems to enhance the safety of external rotor operations. The chart for transition efficiency reveals “wing” and “rotor” as predominant, indicating that transition performance between flight modes relies heavily on these components. The chart on drag reduction shows a focus on “rotor” and “flow”, highlighting the aerodynamic tradeoff in using rotors for both vertical and horizontal flight. The keywords “power” and “electrical” are dominant in the chart on energy management, pointing to the significance of electrical power systems in VTOL innovation. Finally, the chart on thermal management emphasizes “battery” and “cell”, which is expected due to the thermal challenges in managing high-density energy storage in VTOL aircraft.

In analyzing the distinct categories of VTOL aircraft patents, one can discern a web of intricate interrelationships among these themes. For instance, the category of energy management also relates to thermal management. That is, efficient energy management in VTOL aircraft not only concerns the optimal use of power but also the dissipation of heat generated by high-capacity batteries and electrical systems. Effective thermal management systems are crucial to ensure the longevity and safety of these energy systems, particularly in compact airframes where heat accumulation can pose significant risks. Similarly, reducing drag has a complex association with propulsion efficiency and transition efficiency. Reducing drag contributes directly to propulsion efficiency by enabling the aircraft to use less energy in forward flight, thus extending its range and endurance with the same energy expenditure. As for transition efficiency, which concerns the shift from vertical to horizontal flight, reduced drag can minimize the power spikes and control issues during this critical phase, thereby contributing to a smoother and more energy-efficient transition.

These interrelationships highlight that advancements in one technical domain can have cascading effects on others, suggesting that innovation in VTOL aircraft is synergistic instead of siloed. The interplay between energy and thermal management is a clear example of how solving a challenge in one area can unlock efficiencies or create new challenges in another. In the broader scope of VTOL development, acknowledging and harnessing these interdependencies is key to creating holistic and integrated aircraft systems that excel across all performance parameters.

5. Discussions

The subsections that follow extend the discussion on the significance and trends of the patent objectives discovered, assess the intertwined trends, and discuss the limitations of this study.

5.1. Categorical Trends

Table 2. Categorical trends and key findings.

Category	Key Findings
Transition Efficiency	Aerodynamic optimizations, including adjustable wings and variable-pitch rotors. Advancements in electric propulsion and integration with aircraft aerodynamics. Sophisticated control systems employing AI to manage flight dynamics.
Control Enhancement	Development of advanced control algorithms using machine learning. Integration of multisensor arrays for real-time feedback. Mechanical innovations in control surfaces, including variable-geometry wings.
Energy Management	Innovations in high-capacity battery systems and energy storage solutions. Smart energy routing and adaptive energy distribution systems. Exploration of renewable energy integration, such as solar panels and hybrid systems.
Safety Enhancement	Structural enhancements for increased resilience and fail-safe mechanisms. Emergency response systems, including automated parachute deployment. Advanced sensor arrays to detect obstacles and monitor critical components.
Propulsion Efficiency	Novel designs for propulsion systems, such as counter-rotating propellers. Integration of lightweight, high-strength materials. Energy distribution optimization across propulsion units, including regenerative energy.
Drag Reduction	Aerodynamic design modifications, including streamlined fuselage shapes. Surface treatments to reduce skin friction. Adaptive systems capable of altering shape or surface characteristics in real time.
Adaptable Systems	Modular design approaches for customizable aircraft components. Adaptable propulsion systems, including variable-pitch rotors. Configurable flight control systems for dynamic optimization of flight parameters.
Thermal Management	Advanced cooling systems using liquid cooling and phase-change materials. Use of thermally conductive composites. Integration of thermal management solutions into overall aircraft design.

captures the categorical trends and the significant findings, providing a concise summary for easy reference, followed by subsections that provide further details of each.

5.1.1. Transition Efficiency

This category of patents showcased a spectrum of innovative approaches aimed at enhancing the transition between vertical and horizontal flight. These innovations broadly fall into the categories of aerodynamic optimizations, propulsion system advancements, and control system enhancements, each addressing the unique challenges as follows:

Aerodynamic optimizations: A significant number of patents detailed structural and design modifications to improve aerodynamic efficiency. These included adjustable wings and rotor systems that adapt to different flight phases, reducing drag and increasing lift during transition. Innovations such as retractable wings, variable-pitch rotors, and shape-adjustable fuselages harness aerodynamic principles to smooth the transition phase and minimize energy consumption.

Propulsion system advancements: The trend in electric propulsion reflected a broader movement toward sustainability and efficiency. The relevant patents introduced novel configurations of electric motors and batteries designed to provide reliable power for both vertical and horizontal flight. Notably, the aims were to integrate these systems seamlessly with the aircraft’s aerodynamics, highlighting a holistic approach to design that considered propulsion as integral to the aircraft’s overall aerodynamic efficiency.

Control system enhancements: These patents employed sophisticated software and hardware solutions, including artificial intelligence, to manage the complex dynamics of the transition phase. These include advanced flight control algorithms, automation systems, and sensor arrays that continuously monitor and adjust the aircraft’s flight parameters. This category aligns with the ever-increasing role of digital technologies in enabling the next generation of aircraft.

Evaluating the patents in the transition efficiency category across the years revealed an evolving landscape of innovation. Early patents tended to focus more on mechanical and structural solutions such as innovative wing and rotor designs. More recent filings shifted towards electric propulsion and sophisticated control systems, reflecting broader themes in transportation relating to environmental concerns and the advancement of digital and computational tools.

5.1.2. Control Enhancement

Patents in this category encompassed a broad array of innovations focused on improving the precision, stability, and responsiveness of aircraft control systems. The following key approaches emerged:

Advanced control algorithms: A significant portion of the patents emphasized the development of sophisticated control algorithms to maintain stability and respond to pilot inputs or autonomous control signals. These algorithms leveraged modern computational techniques, including machine learning and AI, to predict and react to dynamic flight conditions. These patents aimed to enhance the aircraft’s adaptability to changes in the environment and flight dynamics, including enabling various levels of autonomous navigation [2].

Sensor integration and data processing: A prevalent approach involved the integration of advanced sensors and data processing capabilities to enhance control systems. These innovations used multisensor arrays to provide real-time feedback on various flight parameters, such as altitude, velocity, and attitude. The integration of this data into the control system enabled more informed decision making, enabling finer control adjustments and more stable flight, especially during the transitional phases.

Mechanical innovations in control surfaces: Some patents focused on the mechanical aspects of control enhancement, introducing novel designs for control surfaces and actuation mechanisms. These innovations included variable-geometry wings, tiltrotors, and adaptive surfaces that can change shape or orientation in response to control inputs. By physically altering the aircraft’s aerodynamic profile, these mechanical innovations provide pilots and automated control systems with more degrees of freedom to manage flight dynamics and directly influence the aircraft’s behavior.

There was a clear annual trend of innovations in this category. While earlier patents tended to focus more on mechanical innovations and basic electronic controls, more recent filings emphasized complex algorithms, artificial intelligence, and integrated sensor networks. This shift reflected broader technological advancements and a growing emphasis on automation and data-driven decision making in transportation.

5.1.3. Energy Management

Patents in this category encompassed a range of innovations aimed at optimizing the use and management of energy resources to enhance aircraft performance, efficiency, and sustainability. The main approaches were energy storage and battery technology advancements, energy distribution and management systems, and renewable energy integration. These areas reflected efforts to address the significant energy demands of VTOL aircraft as follows:

Energy storage and battery technology: Many patents focused on innovations in battery technology and energy storage solutions. This included the development of more efficient, higher-capacity battery systems that can store more energy in a lighter, more compact format. Advancements in battery chemistry, cooling systems, and energy density were key themes, aimed at extending the operational range of VTOL aircraft while minimizing weight and maximizing safety.

Energy distribution and management systems: These systems optimize the flow of energy between the aircraft’s various systems and components, ensuring that energy use is efficient throughout flight phases. Innovations in this area included smart energy routing, real-time energy consumption monitoring, and adaptive energy distribution algorithms that can dynamically adjust to flight conditions and battery status. These systems emphasized efficiency enhancement for both the energy source and energy utilization.

Renewable energy integration: A smaller subset of patents explored the integration of renewable energy sources into aircraft operations. This included the use of solar panels to supplement battery power or hybrid systems that combine electric propulsion with more traditional fuel sources to increase efficiency and reduce emissions. While still emerging, this approach reflected a forward-looking perspective on energy sustainability and the potential for VTOL aircraft to leverage renewable energy for enhanced operational efficiency and environmental impact.

Patent trends in this category over the years indicated a clear trajectory toward more sophisticated and integrated energy management solutions. Early patents tended to focus on fundamental improvements in battery technology and basic energy distribution systems. However, more recent filings revealed a shift towards comprehensive energy management systems that incorporate advanced algorithms, real-time monitoring, and renewable energy sources. This evolution indicates a maturing field where the focus has expanded to optimizing every aspect of how the aircraft manages and uses energy.

5.1.4. Safety Enhancement

The innovations in this category broadly fell into the areas of structural enhancements, emergency response systems, and advanced safety features, each aimed to address different aspects of flight safety as follows:

Structural enhancements: Several patents focused on physical and structural improvements, aiming to increase resilience and reduce the risk of critical failures during flight. These enhancements included the development of more robust fuselage materials, the implementation of fail-safe mechanisms for critical flight systems, and the design of aircraft structures that inherently improve stability and durability. Such innovations indicate a foundational approach to safety, emphasizing the more general importance of physical integrity and reliability in aviation.

Emergency response systems: The inventors designed these systems to take immediate action in the event of a malfunction or crisis situation, such as automated parachute deployment for controlled descent, or advanced fire suppression technologies tailored for electric propulsion systems. These patents focused on mitigating the consequences of potential emergencies, ensuring safety through proactive measures.

Advanced safety features: This category included a range of technological advancements aimed at preventing accidents before they occur. These innovations include advanced sensor arrays for obstacle detection and avoidance, integrated systems for real-time health monitoring of critical components, and enhanced cockpit instrumentation for improved situational awareness. Such features represented a more pre-emptive approach to safety, leveraging technology to identify and mitigate risks dynamically.

A review of patents from the earliest to the most recent in this category revealed a trend towards increasing sophistication and integration of technology to enhance safety. While earlier patents focused more on structural enhancements and basic emergency response mechanisms, more recent filings exhibited a shift towards leveraging advanced electronics, software, and materials science to create comprehensive safety solutions. This evolution mirrors broader trends in aerospace and technology, reflecting growing expectations for safety in an increasingly complex and automated aviation landscape.

5.1.5. Propulsion Efficiency

Advancements in this category are crucial for extending the range, improving the performance, and enhancing the sustainability of VTOL aircraft. Although overlapping with other categories, the main focus of these patents was on propulsion system design, advancements in propulsion materials and technologies, and innovations in energy utilization.

Improvements in propulsion system design: A significant portion of the patents in this category outlined novel designs and configurations of propulsion systems aimed at maximizing thrust efficiency and reducing energy consumption. These include counter-rotating propeller systems, integrated propulsion systems that minimize drag, and optimized blade designs for rotors. Such designs aimed to achieve a balance between the power required for take-off and the efficiency needed for sustained cruise flight.

Advancements in propulsion materials and technologies: Innovations in this area included the use of lightweight, high-strength materials that reduce the overall weight of the propulsion system, as well as the implementation of electric and hybrid propulsion mechanisms.

Innovations in energy utilization: Although overlapping with the main category of overall energy management, the focus of these innovations was on optimizing the distribution and use of power across multiple propulsion units. Methods included recovering and reusing energy, such as that which occurs in regenerative braking systems adapted for aerial use.

Examining the patents from earlier to more recent filings revealed a clear trend towards the integration of electric and hybrid technologies, reflecting a growing emphasis on sustainability and efficiency. Similar to other categories, early patents focused more on mechanical and aerodynamic optimizations while more recent filings focused on electrical propulsion and smart energy management.

5.1.6. Drag Reduction

Approaches to drag reduction included aerodynamic design modifications, surface treatments, and adaptive systems as follows:

Aerodynamic design modifications: A significant number of patents focused on the physical design and configuration of aircraft components to reduce drag. These modifications included streamlined fuselage shapes, optimized wing and rotor blade shapes, and the integration of components in a manner to minimize air resistance. Innovations in this area often involved computational fluid dynamics simulations to identify and mitigate sources of airflow impedance, demonstrating a blend of theoretical modeling and practical engineering.

Surface treatments: These innovations included the use of coatings or textures designed to reduce skin friction, as well as the implementation of materials that can alter their properties in response to varying flight conditions. Such technologies aimed to create surfaces that are less susceptible to air resistance, contributing to drag reduction.

Adaptive systems: Several patents detailed adaptive systems capable of altering the shape of the aircraft or surface characteristics in real time to optimize aerodynamic performance across different flight phases. These systems involved movable wing sections, variable-geometry fuselages, or active surface controls that adjusted to minimize drag during take-off, transition, and cruising phases. The emphasis was on flexibility and adaptability, enabling aircraft to maintain optimal aerodynamic conditions throughout the flight envelope.

An analysis of the patents in this category, from earlier filings to more recent ones, indicated an increasing emphasis on adaptive systems and advanced materials. While initial patents focused primarily on static design modifications for drag reduction, newer patents reflect a growing interest in dynamic, responsive solutions that can adjust to changing flight conditions. This trend towards adaptability and smart materials suggests a shift in the aerospace industry towards more sophisticated and versatile drag reduction strategies, aligning with broader advancements in materials science and aerodynamics.

5.1.7. Adaptable Systems

Inventors designed systems in this category to allow the aircraft to modify its configuration or functionality in response to different mission requirements or environmental conditions. These innovations included modular design approaches, adaptable propulsion systems, and configurable flight control systems as follows:

Modular design approaches: Several patents emphasized the importance of a modular design, allowing users to easily swap, reconfigure, or upgrade components such as wings, propulsion units, or payload systems. This approach supported a wide range of applications, from cargo delivery to passenger transport, by enabling customization for specific tasks, thereby enhancing the utilization of the base aircraft. Modular designs also facilitate maintenance and upgrades, ensuring that the aircraft can evolve with emerging technologies.

Adaptable propulsion systems: Another subset of patents detailed propulsion systems that can adjust based on flight mode or operational demands. These systems included variable-pitch rotors, engines that can shift orientation, or multimodal propulsion units that combine the benefits of different propulsion technologies. The objectives of some patents in this category overlapped with those in the propulsion efficiency category, although these inventions focused more on adaptability.

Configurable flight control systems: Inventors designed these systems to adapt to changes in the aircraft’s configuration or operational mode. This involved software that can recalibrate for different weight distributions, control surfaces that adjust based on flight conditions, or autonomous systems capable of dynamically optimizing flight parameters. Although overlapping with the objectives of patents in the control enhancement category, these patents focused more on the adaptability aspect with respect to varying mission requirements.

Similar to other categories, trends in this category exhibited a shift towards increasing integration of digital technologies and automation in adaptable systems. While initial patents focused on mechanical adaptability and modularity, later filings increasingly incorporated advanced sensors, software, and artificial intelligence to enhance the adaptability and responsiveness of systems. This shift reflected broader trends in aerospace towards smart, connected aircraft capable of autonomous decision making and real-time adaptation to complex operational scenarios.

5.1.8. Thermal Management

The patents in this category reveal several distinct approaches to managing thermal loads, including advanced cooling systems, material innovations, and integrated thermal management strategies as follows:

Advanced cooling systems: A significant portion of the patents describe advanced cooling systems designed specifically for the unique demands of VTOL aircraft. These systems leveraged liquid cooling, phase-change materials, or air cooling in innovative configurations to efficiently remove heat from critical components such as batteries, motors, and electronics. The emphasis was on systems that can operate effectively in both stationary and in-flight conditions, ensuring consistent thermal management across all phases of flight.

Material innovations: Another area of focus was the development and application of materials with superior thermal properties. This included the use of thermally conductive composites or coatings that can dissipate heat more effectively across the aircraft’s structure. Such materials not only contributed to cooling but also enhanced the overall structural integrity of the aircraft by mitigating the risks associated with thermal expansion and contraction.

Integrated thermal management strategies: Several patents highlighted the integration of thermal management solutions into the broader design of the aircraft, resulting in a holistic approach to addressing thermal challenges. This involved the strategic placement of components to facilitate natural heat dissipation, the use of structural elements such as heat sinks, or the integration of thermal management systems with other aircraft systems to optimize efficiency. The goal was to create a seamless, system-wide solution to thermal management that supports the aircraft’s overall performance and reliability.

An analysis of the patents from earlier to more recent filings revealed an increasing emphasis on integration and advanced materials. While initial patents focused more on discrete cooling systems, more recent innovations demonstrated a trend towards incorporating thermal management considerations into the overall aircraft design, including the use of advanced materials and integrated systems. This evolution reflected a growing recognition of the complex interplay between thermal management and other aspects of aircraft performance, as well as advancements in materials science and cooling technologies.

5.2. Intertwined Trends

The innovation trends in VTOL aircraft are distinct and yet interconnected. Each category, from transition efficiency to thermal management, encapsulates a facet of VTOL aircraft evolution, driven by a necessity to address complex multidimensional challenges. For instance, energy management and thermal management are intricately related because the efficiency and safety of energy storage and conversion depend on the ability to manage heat dissipation. High-density energy storage solutions, essential for VTOL endurance and performance, generate significant heat, which the design must mitigate to preserve the integrity and performance of the aircraft. Similarly, the reduction of aerodynamic drag directly influences both propulsion and transition efficiency. By minimizing air resistance, the aircraft can use energy more effectively, which is vital for maintaining power during the critical phases of take-off, transition, and landing. Enhanced aerodynamics also aid in smoother transitions between flight modes, emphasizing the synergistic nature of these categories.

These trends aligned with broader technology progression, where initial innovations concentrated on mechanical and structural elements, subsequently evolving toward integrated, system-wide solutions embracing computational, material, and environmental considerations. This progression mirrors the maturation of the aerospace sector at large, indicating a shift from singular, often isolated, improvements to holistic design approaches that synergize diverse technological advancements.

The interrelationships among the categorized innovations highlight a comprehensive approach to VTOL aircraft development. The findings highlight that these innovations do not exist in silos, but weave together in a cohesive fabric of technological progress. This interrelated approach signifies the aerospace industry’s concerted efforts to realize a new era of AAM that is safe, efficient, and responsive to the growing needs of contemporary transportation. The literature review section has already provided a comprehensive overview of existing research, and these findings align with previous studies. For example, the significant advancements in electric propulsion technologies identified in the patent review align with the trends reported by Johnson and Silva (2022) in their analysis of NASA concept vehicles. However, the present study goes further by uncovering specific patent data on AI-driven control mechanisms, which the existing literature has not extensively covered. Additionally, the detailed mapping of VTOL innovation trends in the present study provides a unique perspective that complements the broader analyses found in similar reviews.

A comparison of the results from the literature and patent reviews revealed distinct focal points and insights. The literature concentrated mostly on theoretical frameworks, conceptual advancements, and simulation results that emphasize the foundational principles of aerodynamics, propulsion, and energy efficiency. This discourse highlights the vital role of these principles in overcoming the enduring challenges of VTOL design, such as enhancing energy utilization, reducing noise pollution, and ensuring seamless transition phases between flight modes. In contrast, the patent review unveiled a pragmatic shift towards tangible solutions, with a marked emphasis on specific technological innovations aimed at practical application and commercial viability. The patents delineated a trajectory of innovation that progressively addressed the most important challenges highlighted in academic discussions, presenting solutions that ranged from improved propulsion systems and advanced materials to novel approaches for thermal and drag management. The present research not only illustrates the industry’s response to theoretical challenges, but also signals a move towards integration and system-level optimizations, with inventions aimed at enhancing the operational efficiency, safety, and environmental sustainability of VTOL aircraft.

This juxtaposition of the literature and patent review findings paints a comprehensive picture of the VTOL innovation landscape. While scholarly articles lay the theoretical groundwork and present a broad overview of challenges and potential directions, patents offer a lens into the applied research and development efforts, revealing how developers translate theoretical principles into technologies that they can commercialize. This dual perspective highlights a dynamic interplay between conceptual understanding and practical application, with each domain enriching the other. As the field of AAM evolves, the insights gleaned from both the literature and patents are instrumental in guiding future research directions, informing policymaking, and shaping the trajectory of technological advancement towards the realization of efficient, sustainable, and widely accessible air mobility solutions.

5.3. Limitations

The research, while pioneering in its systematic approach to mapping the VTOL innovation landscape through patent analysis, had several limitations. Firstly, the reliance on patents as a primary source of technological trends may not fully capture the breadth of ongoing research and development activities. Patents inherently represent a subset of innovations that organizations consider commercially viable or strategically significant enough to protect, potentially omitting emerging or speculative technologies still in the conceptual or early developmental stages. This selection bias might lead to an incomplete view of the innovation ecosystem, particularly in areas where open collaboration and academic research play pivotal roles. Secondly, the methodological focus on USPTO data, though justified by the prominence in VTOL development in the United States and filings by other countries, may inadvertently overlook significant contributions from other regions, given the global nature of AAM. Such geographic bias could skew the understanding of innovation dynamics and regional technological strengths.

The stated scope of focusing on aircraft design challenges, while crucial, may underrepresent other critical factors influencing the adoption and success of AAM, such as regulatory frameworks, public acceptance, and infrastructure development challenges. These non-technical dimensions are vital for the holistic advancement of AAM but fall outside the direct scope of this work. Finally, the rapidly evolving landscape of VTOL technology, coupled with the lag between invention, patent filing, and publication, suggests that the insights from this study, though current, may not fully reflect the latest advancements or shifts in research and development priorities. Understanding these limitations within the broader discourse on AAM can inform future studies to address these gaps, ensuring a more comprehensive understanding of the VTOL innovation ecosystem.

While this research provides a comprehensive exploration of VTOL technological advancements through systematic patent and literature reviews, it does not include controlled experiments or scenario-based simulations. Such empirical studies, although crucial for practical validation, fall outside the scope of this work, which aims to map the current innovation landscape and identify key trends and challenges. However, the insights gained from this study can significantly inform the design and parameters of future experiments and simulations. By identifying critical areas of innovation and technological gaps, this work lays the groundwork for subsequent empirical research that will further validate and extend its findings. Future studies should build upon this foundation to conduct controlled experiments and scenario-based simulations, leading to a more thorough and complete understanding of VTOL integration into transportation systems.

6. Conclusions

The following are the enumerated conclusions of this work:

• Scientific novelty: This research addressed a critical juncture in modern aviation and urban transportation by illuminating the field of VTOL aircraft, a crucial pillar of AAM. Through a meticulous synthesis of the academic literature and an expansive review of patent filings, this study presented a landscape of VTOL innovation, encapsulating the complex interplay between theoretical foundations and practical technological advancements. The systematic patent review, complemented by a comprehensive analysis of current scholarly discourse, enabled a multifaceted understanding of the sophisticated technological trajectory and innovation patterns characterizing VTOL development.
• Applied significance: The findings highlight a significant evolution in VTOL technology, marked by an increasing emphasis on energy efficiency, safety, and operational effectiveness. These innovations, spanning aerodynamic optimizations, propulsion advancements, and control system enhancements, emphasize the industry’s concerted efforts to overcome the complex challenges inherent in VTOL design and operation. The dual approach of juxtaposing patent insights with academic perspectives offers a multidimensional view of the innovation ecosystem, revealing both the current state and prospective directions of VTOL technology.
• Structured framework: This research provides a structured framework for tracking, analyzing, and forecasting technological innovations in the VTOL sector. It offers stakeholders such as aerospace engineers, policymakers, and urban planners a grounded basis for strategic decision making, policy formulation, and future research aims. By closing the gap between theoretical research and applied technological development, the study fosters a deeper comprehension of the intricate dynamics driving innovation in AAM.
• Future prospects: Future research will focus on the continued monitoring and analysis of emerging VTOL technologies, with particular attention to advancements in energy storage, autonomous control systems, and integration into urban air mobility frameworks. Additionally, exploring the socio-economic impacts and regulatory challenges of VTOL deployment will be crucial for facilitating their widespread adoption.
• Recommendations: By unveiling the broader themes of safety, efficiency, and sustainability, the study not only informs immediate technological and regulatory endeavors but also contributes to the global discourse on future transportation paradigms. The methodological approach presented, characterized by its analytical rigor and adaptability, offers a blueprint for future work, including generalization for application to other emerging technologies within the expansive domain of transportation. The author recommends continued interdisciplinary research and collaboration among industry stakeholders to ensure the successful integration of VTOL aircraft into sustainable urban transportation networks.