<< Val Baganza,Italy, AUG-20-2024 >> F-35 : Origins Part III- The Boeing X-32 TDM NOTE: In the following article we tend to use acronyms STOVL and VTOL interchangeably. Technically they are slighly different in meaning. Also, the engine used in the JSF contenders is often called the F-135. Actually it was a a modified F-119 engine from the F-22. This would eventually evolve in to the F-135 engine for production F-35s. The Team Boeing Design Philosophy It is remarkable how two different contractors, working under the same set of comprehensive and clearly defined requirements, were able to develop such distinctly different solutions. From the outset, Boeing adopted a strategy that prioritized cost-effectiveness over maximizing performance. Rather than striving to exceed the specified performance benchmarks, Boeing focused on meeting the requirements precisely—no more, no less. This deliberate approach allowed the company to channel its efforts into creating a design that emphasized simplicity, which in turn reduced the complexity of design, fabrication, and assembly processes. By doing so, Boeing aimed to significantly lower overall program costs.In the following sections, we will examine these competitive strengths in greater detail and explore how they influenced Boeing’s overall approach to the project. In addition to this cost-driven design philosophy, Boeing also brought several other competitive advantages to the table. First among these was its extensive expertise in lean design and manufacturing—a capability honed over decades of experience in the commercial aviation sector. As the dominant producer of commercial aircraft such as the widely successful B-737 and B-777, Boeing had developed highly efficient mass production techniques. The scale and consistency required for manufacturing these aircraft had enabled Boeing to refine its processes to a high degree of efficiency, giving it a substantial edge in producing high-quality products at reduced costs and within tight timelines. The second advantage, Boeing had already built a production VTOL (Vertical Take Off and Landing) aircraft.One of the most technically demanding aspects of the program was the requirement for Vertical Take-Off and Landing (VTOL) capability. This feature enables aircraft to take off, hover, and land vertically without the need for traditional runways—making it ideal for operations from confined areas such as aircraft carriers or forward operating bases. To meet this requirement, contractors had to develop innovative propulsion solutions, one of which is known as the “direct lift” concept. Unlike conventional aircraft that generate lift through aerodynamic flow over wings, VTOL aircraft using direct lift generate vertical thrust directly from the engine, allowing the aircraft to rise and descend vertically. In a direct lift system, engine thrust is directed downward to produce the vertical force needed for takeoff, hovering, and landing. This can be accomplished through vectored nozzles, dedicated lift engines, or mechanically driven lift fans. Once airborne, the aircraft transitions from vertical to horizontal flight—a complex phase requiring precise control and synchronization of propulsion and aerodynamic forces. A successful direct lift design must balance raw thrust, stability, and control while maintaining manageable weight and mechanical simplicity. The challenge lies not only in achieving sufficient lift but in doing so reliably, safely, and within tight weight and cost constraints. Boeing brought valuable prior experience to the VTOL domain through its involvement with the AV-8B Harrier program. As a partner in the production and support of the Harrier—one of the world’s most successful operational VTOL aircraft—Boeing had firsthand knowledge of the complexities associated with direct lift systems. The AV-8B relied on a vectored-thrust turbofan engine that could redirect thrust downward for vertical flight and rearward for conventional flight. Through years of supporting and refining this platform, Boeing gained a deep understanding of the unique aerodynamic, thermal, and structural challenges involved in integrating vertical lift into a combat aircraft. This background positioned Boeing well to approach the new VTOL requirement with practical insight and proven methodologies. Consistent with its overall design philosophy, Boeing applied this experience to develop a VTOL solution that emphasized simplicity, cost-effectiveness, and manufacturability. Rather than pursuing an exotic or overly complex system, Boeing focused on meeting—rather than exceeding—the performance requirement in a way that would minimize development risk and production cost. Their design aimed to reduce moving parts, streamline assembly, and leverage modular systems wherever possible. The result was a VTOL concept grounded in operational experience and industrial pragmatism—a reflection of Boeing’s commitment to delivering a practical and affordable solution for next-generation aircraft requirements. The McDonnel (now acquired by Boeing) AV-8B Harrier II. This gave them unique experience with "direct lift" VTOL systems. A third key advantage for Boeing was its practical, hands-on expertise in the production of large, single-piece carbon fiber composite structures. This capability was not just a matter of technical know-how—it represented a strategic differentiator in both manufacturing efficiency and aircraft performance. Boeing had developed and refined advanced composite fabrication techniques through years of experience on commercial programs, such as the B-777 and future 787 Dreamliner, where the use of large integrated composite components became a cornerstone of its design and production strategy. The use of large, complex, single-piece composite parts offers multiple benefits. First and foremost, it significantly reduces the amount of fabrication and assembly time required. Traditional aircraft construction often involves assembling numerous smaller components, each requiring individual tooling, labor, inspection, and fastening. By consolidating these into fewer, larger structures, Boeing was able to streamline production processes, reduce the number of fasteners and mechanical joints, and improve overall build quality. This consolidation translated directly into lower labor costs, fewer opportunities for error, and shortened assembly timelines—a major factor in reducing total program costs. Beyond the economic and logistical benefits, the use of large composite parts also enhances the aircraft's performance characteristics, particularly in terms of stealth. Every joint, seam, and fastener on an aircraft can potentially act as a radar reflector, compromising its radar cross-section and undermining its low-observability profile. By minimizing the number of joints through integrated composite construction, Boeing was able to improve the aircraft's stealth characteristics without the need for extensive radar-absorbing coatings or complex edge treatments. This structural simplicity offered a cleaner, more seamless airframe that naturally reduced radar signature and improved survivability in contested environments. Moreover, Boeing’s proficiency in producing these advanced components was backed by an existing industrial base, established supply chains, and a deep understanding of the material behaviors of carbon fiber composites. This allowed them not only to design with confidence but to scale production efficiently and with reduced risk. In high-stakes military development programs where cost, schedule, and performance must all align, this kind of manufacturing maturity gave Boeing a substantial edge over competitors who may have relied more heavily on emerging or less-proven composite manufacturing techniques. A fourth critical advantage for Boeing was its extensive and mature expertise in the use of Computer-Aided Design (CAD) tools. Boeing had long been a leader in adopting and refining digital design technologies, using them not only for basic geometry creation but for fully integrated 3D modeling, simulation, and digital engineering. This deep familiarity with advanced CAD systems allowed the company to streamline its design processes, reduce the need for physical prototypes, and accelerate development cycles—all while maintaining a high level of design fidelity and accuracy. Unlike traditional design methods that often relied on 2D drawings and manual conversions to physical models, Boeing’s use of CAD tools allowed for the creation of fully detailed 3D digital mock-ups of entire aircraft systems. These models incorporated every structural, mechanical, and electronic component, enabling engineers to identify potential interferences, optimize component placement, and validate system integration before a single part was physically manufactured. This approach reduced costly design errors, minimized rework, and ensured that components fit and functioned as intended during assembly. Beyond static modeling, Boeing leveraged CAD tools to conduct extensive simulations that supported performance analysis, structural validation, and manufacturability assessments. Engineers could simulate airflow over surfaces using computational fluid dynamics (CFD), test structural loads using finite element analysis (FEA), and even simulate the effects of thermal stress or vibration during flight. This digital validation process enabled Boeing to explore a wider range of design alternatives, make informed decisions early in development, and confidently meet the program’s stringent requirements for performance, durability, and safety—all without relying solely on physical testing. Moreover, Boeing’s integration of CAD tools with other digital manufacturing systems provided a powerful foundation for end-to-end digital thread capability. Designs could be directly transferred to manufacturing teams and suppliers, reducing translation errors and improving consistency across the entire production chain. Assembly sequences could be modeled virtually, and tooling could be designed concurrently with the aircraft. This holistic approach, often referred to as model-based engineering (MBE), allowed Boeing to bring a level of digital precision and collaboration that few competitors could match. As a result, the company was better positioned to deliver high-complexity aerospace systems on schedule, at lower cost, and with fewer downstream integration challenges. One of the most distinctive and immediately recognizable design features of the Boeing X-32 was its large, monolithic, top-mounted composite delta wing. This delta wing configuration was not just a stylistic choice—it was a deliberate engineering decision intended to optimize certain aspects of the aircraft’s performance. Delta wings are known for their ability to carry a substantial volume of internal fuel, which extends operational range and endurance. Additionally, they offer favorable characteristics at high speeds, particularly in the supersonic flight regime, due to their low drag and structural simplicity. However, delta wings also come with notable aerodynamic trade-offs. They tend to exhibit sluggish handling at lower speeds and suffer from high energy loss during tight maneuvers, commonly referred to as "bleeding speed" in a turn. These limitations reduce their effectiveness in close-range aerial combat, making aircraft with pure delta configurations less than ideal in traditional dogfighting scenarios. Historical examples such as the Convair F-102 Delta Dagger, Convair F-106 Delta Dart, and Saab Draken highlight this trend. While these aircraft were exceptionally fast and capable long-range interceptors, they were not optimized for high-agility air-to-air combat engagements. In contrast, several modern European multi-role fighter aircraft—such as the Eurofighter Typhoon, Dassault Rafale, and Saab JAS 39 Gripen—have addressed the maneuverability shortcomings of pure delta wings by adopting a more advanced aerodynamic configuration: the cranked delta wing paired with forward-mounted canards. The canards, which are small, movable control surfaces placed ahead of the main wing, significantly enhance the aircraft’s pitch authority and agility, particularly at lower speeds and during high angle-of-attack maneuvers. While the addition of canards improves handling and combat effectiveness, it also introduces its own set of challenges. Canards can negatively impact an aircraft's radar cross-section, thereby compromising stealth—an essential requirement for fifth-generation fighters like those envisioned under the Joint Strike Fighter (JSF) program. Furthermore, canard surfaces can be mechanically complex and increase maintenance requirements over the operational lifespan of the aircraft. Due to these drawbacks, particularly the degradation of stealth characteristics, the use of canards was deemed unsuitable for the X-32’s design objectives. Ultimately, the X-32's reliance on a delta wing without canards represents a compromise that favored range and supersonic performance over high agility and stealth-neutral maneuverability enhancements. This decision, among others, played a role in the evaluation and eventual outcome of the JSF competition. Boeing X-32 Vertical lift system The X-32B, utilized a direct lift system to achieve vertical takeoff and landing (VTOL) capabilities. Unlike the lift-fan system later used by the Lockheed Martin F-35B, the X-32’s direct lift approach relied on vectoring engine thrust downward through its main engine exhaust. This method simplified the aircraft's design by avoiding the need for additional lift mechanisms, but it also presented challenges in maintaining stability and performance during vertical operations. While effective in demonstrating basic VTOL capability, the direct lift system was ultimately less efficient and offered reduced flexibility compared to more advanced solutions. Boeing knew how to do this because of its work on the AV-8B. The direct lift system hS Pros and Cons. These are discussed below. To manage its orientation and stability during hover and transition phases, the X-32 employed a specialized attitude control system composed of air plenums and vectoring nozzles. These components were essential for directing small bursts of thrust to counteract unwanted rotations and maintain precise control in all three axes—pitch, yaw, and roll. The system functioned by channeling compressed air from the engine through ducts to strategically placed nozzles on the aircraft’s wingtips and nose. By modulating the airflow through these nozzles, the aircraft could adjust its attitude even while in a stationary hover, providing critical control during VTOL maneuvers. The engine position in the Boeing X-32 played a pivotal role in both the aircraft’s performance and its VTOL capabilities. Centrally mounted within the fuselage, the engine was strategically located to allow for efficient thrust vectoring during direct lift operations. This central positioning helped balance the aircraft during vertical flight by aligning the thrust line close to the center of gravity. However, this configuration also constrained the overall design of the airframe, influencing factors such as intake placement, internal layout, and maintainability. The engine's location was a key design compromise, balancing the need for vertical thrust with aerodynamic and operational considerations. One of the major drawbacks of the direct lift system used by the X-32 was the issue of exhaust gas ingestion, a problem that significantly affected the aircraft’s hovering efficiency and engine performance. During vertical lift, the jet exhaust is directed downward, creating a turbulent cushion of hot gases beneath the aircraft. In certain conditions, especially during low-altitude hover or near-ground operations, this hot exhaust could be re-ingested into the engine’s intake. This phenomenon led to a decrease in engine thrust, overheating, and reduced airflow quality, which compromised both safety and stability. Exhaust ingestion also posed serious limitations on operational envelope and efficiency, particularly in confined or hot environments. This drawback was a key factor in why alternative VTOL systems, such as the lift-fan approach used by the X-35 and F-35B, were ultimately favored in the JSF program. Boeing X-32 Details Boeing X-32 / X-32B – Specifications General Characteristics Feature X-32 / X-32B Crew 1 Length 43 ft 6 in (13.26 m) Wingspan 35 ft (10.67 m) Height 17 ft 6 in (5.33 m) Wing Area ~615 sq ft (57.1 m²) Empty Weight ~22,000 lb (9,979 kg) Gross Weight ~29,000–30,000 lb (13,154–13,608 kg) Max Takeoff Weight ~50,000 lb (22,680 kg) (estimated) Propulsion Feature X-32 / X-32B Engine 1 × Pratt & Whitney YF119-PW-614JS Thrust (Dry) ~28,000 lbf (125 kN) Thrust (With Afterburner) ~43,000 lbf (191 kN) STOVL System (X-32B) Direct-lift with thrust-vectoring nozzle and roll nozzles (no lift fan like the F-35B) Performance (Estimated / Projected) Feature X-32 / X-32B Maximum Speed ~Mach 1.6 (~1,200 mph / 1,930 km/h) Range ~600 nmi (1,100 km) Combat Radius ~450–500 nmi (835–926 km) Service Ceiling ~50,000 ft (15,240 m) Rate of Climb Not officially released (est. high) Armament (Planned) 1 × internal cannon, internal weapon bays (AAMs, bombs) Some Notes on X-32B STOVL Variant: The X-32B was the STOVL demonstrator. Unlike the F-35B, which uses a lift fan, the X-32B used direct lift by rotating its engine nozzle downward (similar to the Harrier). To accommodate STOVL, Boeing had to significantly alter the air intake design and reroute airflow, resulting in a slightly bulkier midsection in the X-32B. The X-32B successfully demonstrated vertical landing and short takeoff, but its STOVL system was deemed less efficient and flexible compared to Lockheed Martin's lift fan system on the X-35B. As we will see later, it was the X-32s mediocre STOVL performance and the other design compromises it created that doomed it in the fly off. One advantage of the design was there wasnt much difference between the CTOL and the STOVL models. Again, boeing looking to cost and increase production efficiency. SUMMARY Boeing’s approach to the Joint Strike Fighter (JSF) program was shaped by a strong emphasis on cost-effectiveness, manufacturing efficiency, and leveraging existing technological strengths. Rather than attempting to exceed the JSF’s performance benchmarks, Boeing made a deliberate decision to meet the requirements precisely, focusing its efforts on simplicity, affordability, and production scalability. This philosophy permeated all aspects of the X-32’s design—from its use of a direct lift vertical takeoff and landing (VTOL) system based on previous experience with the AV-8B Harrier, to its integration of advanced single-piece composite structures and highly refined digital engineering practices. Boeing's extensive background in commercial aircraft production, particularly with models like the B-737 and B-777, gave it an edge in applying lean manufacturing techniques to the military domain, with the goal of reducing cost and development risk without sacrificing mission capability. Additionally, Boeing capitalized on several strategic advantages that distinguished its proposal in the JSF competition. Its VTOL system, derived from direct lift rather than a more complex lift-fan, demonstrated operational competence but faced limitations such as exhaust ingestion and constrained flexibility. Nonetheless, Boeing’s familiarity with the challenges of vertical flight, combined with its mastery of carbon fiber composite fabrication and advanced computer-aided design (CAD) tools, positioned it as a formidable contender. These capabilities enabled Boeing to produce a stealthier, more integrated airframe while streamlining design validation through digital simulations. However, the trade-offs embedded in the X-32’s design—particularly the STOVL system’s comparative inefficiency and the aerodynamic compromises of its delta wing configuration—ultimately impacted its competitiveness. We will see how both contenders STOVL performance and design compromises weighed VERY heavily in the final selection. Now onto the Lockeed X-35. References Barret & Carpenter. Survivability in the Digital Age : The Imperative for Stealth, The Mitchell Institute for Aerospace Studies, Air Force Association, July 2017 Burbage,Clark, & Pitman. F-35 The inside story of the Lightning II. SkyHorse Publishing, 2023. https://www.secretprojects.co.uk/threads/mcdd-northrop-bae-astovl-mrf-jast-jsf-studies.2392/- accessed 10-DEC-2024 https://en.wikipedia.org/wiki/McDonnell_Douglas_X-36-accessed 10-DEC-2024