WWII

Bristol 188 Burned so Much Fuel it was Retired

The Bristol 188, known as the “Flaming Pencil” due to its distinctive, elongated fuselage, was a British experimental aircraft developed to explore the frontiers of supersonic flight.

Designed primarily to study the effects of high-speed aerodynamics and heat on aircraft materials, it was constructed using innovative materials like stainless steel and titanium.

Despite challenges in achieving its targeted speed of Mach 2 and issues with high fuel consumption, the Bristol 188 provided valuable insights into the thermal dynamics and structural integrity necessary for future supersonic aircraft designs.

Contents

Background

The Bristol 188 was created specifically to overcome the challenges of supersonic flight, particularly focusing on aerodynamics and the use of advanced materials to withstand extreme operational conditions. Conceived during the late 1950s, a time when the aeronautical engineering community was intensely focused on breaking the sound barrier and exploring flight at Mach 2 speeds, the Bristol 188 project was initiated to push the boundaries of what was technologically possible in aircraft performance.

The project was not actually intended to produce a serviceable design, but to help in the development of another aircraft, the Avro 730.

The Avro 730 was a British experimental aircraft, the basic premise of which dated back to the 1940s. At this time, Britain (and other nations) had a desire for a high-speed, high-altitude reconnaissance aircraft.

Avro 730 concept.
Avro 730 concept drawing.

The Avro 730 was the result of this line of thought, with the additional capability of strategic bombing.

Developed by Avro, the same company known for the iconic Lancaster bomber from the Second World War and the later Avro Vulcan, the Avro 730 was envisioned to fly at speeds around Mach 3, with operational altitudes exceeding 70,000 feet.

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Such capabilities were intended to outrun Soviet air defenses, making it a strategic asset in the event of a nuclear conflict. The aircraft design featured a delta wing configuration, similar to other contemporary designs focusing on high-speed aerodynamics, and was to be powered by advanced jet engines capable of sustaining supersonic speeds.

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Because of its extreme specifications, the Avro 730 project faced significant challenges. The technological demands of developing an aircraft capable of sustained Mach 3 flight were enormous at the time. To investigate the many unknowns involved in high-speed flight, a test bed was needed that could reach at least Mach 2.

This test bed was the Bristol 188.

Design of the Bristol 188

The aircraft featured a highly distinctive design, characterized by its slender, needle-like fuselage which earned it the nickname “Flaming Pencil.” This unique shape was meticulously engineered to reduce aerodynamic drag, a crucial factor in achieving and sustaining high speeds. The delta wing configuration further exemplified this focus on high-speed aerodynamics.

Delta wings were known for their ability to handle the shock waves generated by supersonic flight, thus stabilizing the aircraft at speeds close to Mach 2. This wing design not only contributed to better handling and stability but also supported the integration of the aircraft’s complex engine systems.

It was a surprisingly large aircraft, with a length of 79 ft (24 m) and a wingspan of 35 ft (11 m).

Bristol 188 in flight.
The Bristol 188’s fuselage and wings were designed for high speed flight.

Arguably the most important aspect of the Bristol 188’s design was its pioneering use of materials. The fuselage made extensive use of stainless steel, thanks to the material’s ability to resist the high temperatures generated by air friction at supersonic speeds. Stainless steel was employed particularly in areas of the airframe expected to experience the highest thermal loads, such as the leading edges of the wings and the nose section.

Titanium was utilized in parts where its attributes—lightweight and high strength—could be maximized without compromising the structural integrity or heat resistance. These material choices were forward-thinking at the time, representing some of the earliest uses of titanium in aviation, setting precedents for its later widespread use in both military and civilian aircraft.

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The development of the Bristol 188 also involved significant engineering challenges, particularly in terms of integrating these materials with the existing manufacturing technologies. Techniques such as welding and fabricating stainless steel and titanium were still being perfected, and the Bristol 188 project contributed to advancing these techniques.

188 on runway.
The Bristol 188 had a single pilot and no other crew.

Moreover, the integration of its powerplant—the de Havilland Gyron Junior engines—required innovative solutions to manage the heat and stresses associated with their operation at high speeds.

The Bristol 188’s development was not conducted in isolation but was a collaborative effort involving various sectors of the British aerospace industry. The Bristol Aeroplane Company worked closely with government bodies, research institutions, and other industrial partners to pool resources and knowledge.

Gyron Engines

The propulsion of the Bristol 188, vital to its role as a high-speed experimental aircraft, was provided by two de Havilland Gyron Junior turbojet engines. These engines were integral to the aircraft’s entire purpose, which aimed to push the boundaries of speed and explore the upper limits of 1950s aviation technology.

The Gyron Junior was a scaled-down version of the de Havilland Gyron, one of the earliest British turbojets designed to achieve supersonic speeds. However, the Junior version was considered underpowered, so the version used in the Bristol 188 was modified with afterburners.

de Havilland Gyron Junior engine.
The de Havilland Gyron Junior turbojet engine. Image by Nimbus227.

This version was one of the most powerful jet engines available in Britain at the time. Each engine in the Bristol 188 was capable of producing up to 20,000 lbs of thrust. However, despite their advanced design and powerful output, the engines were not without some problems.

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One of the main issues was their high fuel consumption. The engines consumed fuel at an excessive rate, which became a major operational constraint, limiting the aircraft’s range and endurance. This high fuel usage was partly due to the inefficiencies inherent in turbojets of that era, especially under the extreme conditions of near-Mach 2 speeds.

Moreover, the aircraft’s design and its heavy stainless steel construction added to the overall drag and weight, exacerbating the fuel consumption problem.

Bristol 188 underside rear right quarter view.
The 188’s engines were actually less powerful than anticipated.

In practice, the Bristol 188 struggled to reach its design speed of Mach 2, achieving a maximum speed of around Mach 1.88 during its test flights. This was because the fuel consumption was so high, that the engines could not run long enough to reach this speed.

This shortfall was significant, not just for the project’s ambitions but also for the evaluation of the aircraft’s aerodynamic properties and material performance under expected operational conditions. It was meant to fly fast for sustained durations to gather the required data, but it was simply unable to do so. The inability to reach the projected speeds led to partial fulfillment of the project’s objectives and contributed to the eventual discontinuation of the program.

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Despite these limitations, the use of Gyron Junior engines in the Bristol 188 contributed valuable insights into engine performance at high speeds and the challenges of supersonic propulsion. The data gathered from these engines helped to inform future developments in jet engine technology, particularly in understanding the thermal and mechanical stresses that engines endure at supersonic speeds.This knowledge was instrumental in guiding improvements in engine design and efficiency, influencing subsequent generations of more capable and reliable jet engines.

Bristol 188 back end.
The Gyron engine was also in the Blackburn Buccaneer S.1.

Usage

A total of two Bristol 188s were made, with the operational phase of the projecting beginning in 1961 with taxi trials. Its first flight occurred on April 14, 1962. Despite its ambitious technological goals, was marked by a series of challenges that highlighted the complex nature of high-speed flight testing and the limitations of contemporary aviation technology. These challenges, while they constrained the aircraft’s performance and utility, also provided critical insights that contributed significantly to the field of aerospace research.

The biggest flaw of the aircraft was its inability to reach the intended top speed of Mach 2. The aircraft’s maximum recorded speed fell short at approximately Mach 1.88 (1,440 mph). This shortfall was partly due to the limitations of its twin de Havilland Gyron Junior engines, which, while powerful, were not able to get the aircraft up to the required speed for data gathering.

188 ground crew.
Due to terrible fuel consumption, the 188 was never able to reach its design goal of Mach 2.

Furthermore, the engines’ high fuel consumption rate significantly limited the aircraft’s range and endurance, restricting the scope and duration of flight tests. This was a critical issue, as it hindered comprehensive testing under varied and extended flight conditions. The problem was so bad that a majority of the aircraft’s fuel was used just getting to altitude.

The aircraft also had other undesirable performance characteristics, such as its very fast take-off speed of 300 mph.

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Despite these operational challenges, the Bristol 188 made substantial contributions to the fields of aerodynamics and material sciences. The data collected from its flights helped to deepen the understanding of aerodynamic heating, which occurs when the surface of an aircraft reaches extremely high temperatures due to air friction at high speeds.

Bristol 188 on runway.
It was finally retired in 1964.

This research was vital for the development of later high-speed aircraft, including military jets and commercial supersonic transports like the Concorde.

The Bristol 188 also served as a testbed for evaluating the performance of its advanced materials under real-world conditions. The insights gained from observing how stainless steel and titanium behaved under the thermal and physical stresses of supersonic flight informed improvements in materials science, particularly in developing alloys and fabrication techniques that could better withstand the rigors of high-speed travel.

But what about the Avro 730, the aircraft the 188 was a test bed for? Well, that didn’t end well either. After some development, the aircraft was canceled in 1957 due to fears new Soviet anti-aircraft missiles rendered a high-flying, Mach 3 capable aircraft obsolete.

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The two 188 prototypes were meant to be used as range targets, but one airframe, XF926, was relocated to RAF Cosford for educational purposes. The second airframe, XF923, was scrapped. Today XF926 can be seen at the Royal Air Force Museum Cosford in Shropshire.