WWII

The Northrop YB-49 was a B-2 from the 40s

The Northrop YB-49, an experimental jet-powered heavy bomber developed in the late 1940s was spearheaded by Jack Northrop and his team at Northrop Corporation, the YB-49 featured a radical flying wing configuration that eliminated the traditional fuselage and tail, showcasing a glimpse into the future of aviation.

Development

The Northrop YB-49 emerged from a period of intense innovation in aviation, driven by the Second World War.

Jack Northrop, an aviation pioneer known for his bold designs, envisioned a new type of aircraft that would revolutionize the bomber category. His concept centred around the “flying wing” design, which promised unparalleled aerodynamic efficiency and performance.

 



Jack Northrop and his team at Northrop Corporation initially developed the XB-35, a propeller-driven flying wing bomber, during the early 1940s. The XB-35 represented a radical departure from traditional aircraft designs, integrating all the major components—engines, crew, payload—into the wing structure itself.

It is easy to similar the similarity between the XB-35 and YB-49.

This design aimed to reduce drag, improve lift-to-drag ratio, and enhance overall performance. However, the XB-35 encountered significant technical challenges, particularly with its complex contra-rotating propeller systems. These issues delayed the project and created doubts about the viability of the flying wing concept.



As the Second World War drew to a close and jet propulsion technology began to mature, Northrop saw an opportunity to address the shortcomings of the XB-35. He proposed converting the existing airframe to accommodate jet engines, which promised higher speeds and better performance.

This conversion led to the development of the YB-49, a jet-powered version of the original flying wing bomber.

Piston to Jet Power

In 1946, the U.S. Army Air Forces (which later became the U.S. Air Force) approved the conversion project. Northrop’s engineers undertook the significant task of redesigning the aircraft to house eight Allison J35 turbojet engines.

This conversion required extensive modifications, including reinforcing the airframe to handle the increased stresses associated with jet propulsion and redesigning the control systems to ensure stability at higher speeds.



The first prototype designated YB-49, was rolled out of the Northrop plant in Hawthorne, California, in 1947. Engineers and technicians worked around the clock to prepare the aircraft for its maiden flight.

Jack Northrop himself supervised many aspects of the development, ensuring that his vision of a streamlined, tailless bomber would come to fruition.

The early Northrop YRB-49A with a pair of engines hanging below the aircraft.

The YB-49 featured a wingspan of 172 feet and a length of 53 feet, with a distinctive, sleek silhouette that set it apart from conventional bombers of the time.



The YB-49’s design integrated several advanced features. The wing structure housed all eight turbojet engines, four in each wing. These engines provided a combined thrust that enabled the aircraft to achieve higher speeds than its propeller-driven predecessor.

The wing itself was an all-metal construction, designed to maximize strength and minimize weight. Engineers incorporated advanced hydraulic systems to control the aircraft’s elevons and rudders, which were essential for maintaining stability and manoeuvrability without a traditional tail assembly.

Test pilots prepared to take the YB-49 on its maiden flight, recognizing the potential and the risks of such an innovative design. On October 21, 1947, the YB-49 took to the skies for the first time, marking a significant milestone in aviation history.

The aircraft demonstrated impressive speed and agility, validating many of Northrop’s design principles. However, the flight also revealed areas that required further refinement, particularly in terms of low-speed stability and landing characteristics.

There are many advantages to flying wings and the YB-49 laid the foundations for aircraft such as the B-2.

Despite these challenges, the development of the YB-49 continued with a series of test flights and modifications. Engineers and test pilots collaborated closely, making iterative improvements to the control systems and addressing any structural concerns.



The YB-49’s performance during these tests showcased its potential as a strategic bomber, capable of high-speed, long-range missions.

The development of the YB-49 did not occur in isolation. It unfolded against the backdrop of post-war military reorganization and budgetary constraints. The U.S. Air Force, newly established as a separate branch of the armed forces, faced decisions about its future strategic bomber fleet.

While the YB-49 showed promise, it competed with other emerging designs, such as the more conventional Boeing B-47 Stratojet, which ultimately won out due to its perceived reliability and ease of maintenance.

Allison Engines

The Allison J35 turbojet engine powered the Northrop YB-49, marking a significant step in jet propulsion technology during the late 1940s.

This engine, developed by the Allison Engine Company, represented one of the first axial-flow turbojet engines produced in the United States, reflecting the rapid advancements in aviation technology at the time.

An Allison J-35.

Development of the Allison J35 began during World War II when the U.S. military recognized the need for high-performance jet engines to keep pace with advancements in aircraft speed and altitude. The design process focused on creating a powerful and reliable engine capable of meeting the demanding requirements of military aviation.



The J35 featured an axial-flow compressor, which differed from the earlier centrifugal-flow designs used in other engines like the British Rolls-Royce Welland. The axial-flow design allowed for a more compact engine with a higher thrust-to-weight ratio, making it ideal for installation in various aircraft, including the YB-49.

The J35’s core design included an eleven-stage axial compressor, a nine-can combustor arrangement, and a single-stage turbine. Engineers selected this configuration to optimize the engine’s efficiency and performance across a range of operating conditions.

The compressor stages progressively compressed the incoming air, significantly increasing its pressure before it entered the combustion chambers. In the combustion chambers, fuel mixed with the compressed air and ignited, producing high-temperature, high-pressure exhaust gases.

These gases then passed through the turbine, driving it and subsequently powering the compressor and other engine accessories.



In the YB-49, engineers installed eight J35 engines, four in each wing. Each engine produced around 4,000 pounds of thrust, providing the combined power necessary to propel the flying wing bomber to its impressive speeds.

The YB-49 was significantly larger than even a 737 from today!

Placement is Important

The placement of the engines within the wings required careful design considerations to ensure optimal airflow and cooling, as well as to maintain the structural integrity of the aircraft.

The J35’s performance in the YB-49 demonstrated the engine’s capabilities and limitations. On the positive side, the engine provided substantial thrust, enabling the aircraft to reach speeds of up to 500 miles per hour and an operational ceiling of approximately 45,000 feet.

These performance metrics represented a significant improvement over propeller-driven bombers, highlighting the advantages of jet propulsion in terms of speed and altitude capabilities.

However, the J35 also presented several challenges. Early versions of the engine experienced issues with reliability and durability, common problems in the early days of jet engine development. Engineers continually worked to refine the design, addressing issues such as compressor stalls and turbine blade failures.

The engine’s maintenance requirements also posed difficulties, particularly in the context of the YB-49’s unique airframe, which integrated the engines into the wings, making access for repairs more complex.

The later aircraft integrated all eight engines into the wing.

The Allison J35 played a crucial role in the evolution of jet engines and laid the foundation for future advancements in turbine technology. Despite its initial teething problems, the J35’s successful deployment in various aircraft demonstrated the feasibility of axial-flow turbojets and provided valuable lessons for subsequent engine designs.

The experience gained from the J35’s development and operational use informed the creation of more advanced engines, contributing to the rapid progress in jet propulsion during the mid-20th century.

Flight Testing

The flight testing phase of the Northrop YB-49 marked a critical period in the aircraft’s development, providing valuable insights into its performance, capabilities, and limitations. This phase began with the YB-49’s maiden flight on October 21, 1947.

On that day, test pilot Max Stanley took the controls, lifting the revolutionary flying wing off the runway at Northrop’s facility in Hawthorne, California. This initial flight, while brief, demonstrated the basic airworthiness of the aircraft and set the stage for a series of more comprehensive tests.

Throughout the flight testing program, the YB-49 exhibited both promising performance characteristics and significant challenges. The aircraft’s jet propulsion system, powered by eight Allison J35 engines, enabled it to reach speeds previously unattainable by its propeller-driven predecessors.

Test flights frequently achieved speeds of around 500 miles per hour, a considerable improvement over the XB-35. The YB-49 also demonstrated a service ceiling of 45,000 feet, showcasing its ability to operate at high altitudes.

Despite these impressive performance metrics, the YB-49’s flight testing revealed several critical issues that needed addressing. Stability at low speeds and during landing posed a major challenge.

The aircraft’s unconventional flying wing design, which lacked a traditional fuselage and tail, created unique aerodynamic properties.

The sleek silhouette is very similar to modern bombers.

Pilots found the YB-49 to be particularly prone to pitch and yaw instability at lower speeds, making landings difficult and often dangerous. To address these issues, engineers worked on refining the aircraft’s control systems and adjusting the elevons and rudders to improve stability and control responsiveness.

Another significant challenge encountered during flight testing was the aircraft’s structural integrity. The YB-49’s large, thin wings experienced considerable flexing and stress during high-speed manoeuvres and at high altitudes.

Not Plane Sailing

On several occasions, test flights had to be aborted due to concerns about potential structural failures. Engineers conducted extensive analyses and reinforced key components of the wing structure to enhance durability and safety.

This iterative process of testing, identifying issues, and implementing fixes was crucial in pushing the YB-49 closer to operational readiness.

During one test flight on June 5, 1948, a catastrophic structural failure led to a tragic accident. The aircraft, piloted by Major Daniel Forbes and Captain Glen Edwards, broke apart in mid-air, resulting in the loss of both pilots and three other crew members.

The investigation into the crash revealed that the failure originated in the wing structure, which had been unable to withstand the stresses encountered during the flight. This incident highlighted the inherent risks of pioneering such a radical design and underscored the importance of rigorous testing and structural analysis.

The YB-49 made several successful test flights. However, the design was not perfect.

In addition to structural and stability challenges, the YB-49’s flight testing also addressed issues related to the integration of its propulsion system. The placement of the jet engines within the wings required careful management of airflow and cooling.

Engineers conducted numerous tests to ensure that the engines operated efficiently without overheating or experiencing compressor stalls. These tests involved various configurations and modifications to the engine nacelles and intake ducts, ultimately improving the reliability and performance of the propulsion system.

As flight testing progressed, pilots and engineers developed specialized training programs to familiarize crews with the YB-49’s unique handling characteristics. The aircraft’s tailless design and advanced control systems required a different approach to piloting compared to conventional bombers.

Pilots underwent extensive training in simulators and on modified aircraft to gain the necessary skills to operate the YB-49 safely and effectively. This training was essential in mitigating the risks associated with the aircraft’s unconventional design and ensuring that test flights could be conducted with a higher degree of safety and precision.

Despite the progress made during the flight testing phase, the YB-49 faced increasing scrutiny from the U.S. Air Force. Budget constraints and shifting strategic priorities led to a reassessment of the flying wing program.