The Soviet Yak-15, known by its NATO reporting name “Feather”, is a strangely pretty aircraft built by the Soviets at the end of the Second World War during the desperate rush to field an operational jet fighter. They managed to do this by cramming a Me 262 engine inside a Yak-3 fighter.

This aircraft served as a bridge between the propeller-driven fighters of the past and the advanced jet fighters of the future. It wasn’t a very fast machine, having been converted from a propeller aircraft, but it served as an ideal trainer, being a nice middle ground for pilots transitioning into jets.

Contents

• Background
• Yak-15 Design
• Service History
• Fate

Background

Post-War Soviet Aviation Context

At the conclusion of the Second World War, the Soviet Union found itself both a military superpower and in dire need of modernizing its armed forces. The rapid development and deployment of jet-powered aircraft by its Allies and foes, particularly the British Gloster Meteor and the German Messerschmitt Me 262, had started the process of rendering the propeller-driven fighters obsolete. Recognizing the strategic disadvantage, the Soviet leadership prioritized the development of jet technology.

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Despite fighting on the side of the Allies during the war, this friendship was only really out of convenience and soon soured once the war was over. This turned the former allies into enemies, marking the beginning of the Cold War.

One of the defining traits of the Cold War was the relentless development of technologies, in an attempt give themselves an edge over the other should war break out. Jet aircraft sat alongside nuclear weapons in importance, and the USSR was desperate to field both.

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A crucial factor in the Soviet Union’s early jet aircraft development was the capture of German aeronautical technology and expertise. As the war ended, Soviet forces secured a significant amount of advanced German aircraft and technical documentation.

More importantly, they were able to take German scientists and engineers into custody, including those who had worked on the revolutionary turbojet engines that powered the Luftwaffe’s jet fighters. Among the captured technology was the Jumo 004 turbojet engine, which would become a cornerstone in the development of the Soviet jet program.

Developed by Germany during the war, the Jumo 004 famously powered the Messerschmitt Me 262, the first operational jet-powered fighter. It was an axial-flow design, a departure from the more common centrifugal-flow turbines of the era.

The engine consisted of an eight-stage compressor, six combustion chambers, and a single-stage turbine. It was capable of producing approximately 900 kilograms of thrust (thrust output varied between models). However, the 004 could be an unreliable engine if not cared for properly, and required frequent maintenance.

The Yakovlev Design Bureau Initiative

The Yakovlev Design Bureau, led by Alexander Sergeyevich Yakovlev, was one of the premier design teams in the Soviet Union, responsible for some of the most successful Soviet fighters of the Second World War.

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Given the Bureau’s proven track record, it was naturally entrusted with developing one of the Soviet Union’s first jet fighters.

Development Philosophy and Strategy

Instead of designing a jet fighter from the ground up, Yakovlev and his team opted for a more pragmatic approach. They chose to adapt the existing Yak-3 fighter aircraft, which was known for its excellent performance and handling characteristics.

By using an existing and successful airframe, the development time for the jet-powered aircraft could be significantly reduced. The Soviet Union was in the process of rebuilding its economy after the devastating effects of the Second World War, so utilising an existing design allowed for more efficient use of limited resources.

In addition, it was a matter of national prestige to quickly introduce major technologies such as these to maintain parity with other countries. But using a pre-existing airframe had another major benefit: crew training and maintenance.

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Transitioning to jet-powered was a large step for pilots and maintainers. By maintaining the general layout and handling characteristics of the familiar Yak-3, the transition for pilots could be smoother, reducing the training time and increasing operational readiness.

Mechanics could were also familiar with much of the aircraft, and many of the same parts could still be used.

From Piston to Jet Engine

The key to transforming the Yak-3 into a jet-powered aircraft was the adaptation of the RD-10 engine, a Soviet-built version of the captured German Jumo 004. This required significant modifications to the Yak-3’s airframe, including the integration of the jet engine and the redesign of the aircraft’s fuselage to accommodate the new propulsion system.

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Originally, the Yak-3 was powered by a 1,300 hp Klimov VK-105 V12 piston engine. This was able to get the aircraft up to a speed of 400 mph and an altitude of 34,000 ft.

The nose of the aircraft, previously housing the piston engine’s propeller and air intake, was replaced with a metal cone to direct air into the jet engine, and the cockpit was moved further back to maintain the aircraft’s center of gravity.

Despite these changes, the Yak-15 retained the general layout and many components of its piston-engine predecessor.

Yak-15 Design

The heart of the Yak-15 was, of course, the RD-10 jet engine, a Soviet-manufactured derivative of the German Jumo 004 turbojet. The RD-10 was capable of producing approximately 900 kg of thrust (2,000 lbs) propelling the Yak-15 to speeds up to 490 mph (790 kph) at sea level.

The integration of the RD-10 into the Yak-15’s design was a great achievement, given the young state of jet engine technology and the lack of prior experience in the Soviet aviation industry.

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The engine was actually mounted underneath the fuselage, with its exhaust exit located under the belly of the aircraft. This area was reinforced with steel plating to protect it from the heat emitted from the exhaust. This engine location gives the Yak-15 a very distinct profile, particularly from the side, with a thick, low hanging nose and a thin boom at the rear.

It also permitted the placement of a fuel tank and guns in the nose. Additionally, the fuel system and cockpit were redesigned to accommodate the requirements of jet flight, with special attention to pilot safety and comfort under the new flight conditions.

The Yak-15 maintained the general aerodynamic profile of the Yak-3, including its straight wing design, which was not optimized for high-speed jet flight but provided a good balance between speed, agility, and ease of handling.

The rudder had to be slightly increased in size, but the rest of the flight surfaces were the same. One thing quickly noted during testing was the rear wheel would be melted by the jet engine’s exhaust due to being a taildragger. This was rectified with a solid wheel.

Despite its conversion from a piston-engine design, the Yak-15 exhibited commendable flight characteristics. Its jet propulsion allowed for rapid acceleration and a significant increase in top speed compared to its piston-engine counterparts. However, the aircraft’s performance was limited at high altitudes due to the relatively low thrust-to-weight ratio and the aerodynamic limitations of its straight wings.

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Overall the Yak-15 measured only slightly larger and heavier than the Yak-3, with a length of 8.7 meters (versus 8.5 m) and an empty weight of 2,100 kg (versus 1,850 kg). Interestingly, this makes it the lightest jet fighter to enter service.

The Yak-15 was equipped with two 23 mm NS-23 cannons, mounted in the nose above the air intake. This armament configuration was effective for air-to-air combat, allowing the Yak-15 to engage enemy aircraft with considerable firepower.

Prototype Testing and Challenges

The prototype of the Yak-15 took to the skies for its maiden flight in April 1946. It was competing against the MiG-9 at the time, another Soviet jet fighter in development. The story goes that Yakovlev and Mikoyan-Gurevich settled the decision on which would be the first Soviet jet to fly with a coin toss. MiG won, and so the Yak-15 was the second Soviet jet to take to the air.

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The testing phase was crucial, not only to evaluate the aircraft’s performance but also to refine its design based on flight data. One of the major challenges encountered was the high temperature of the jet exhaust, which necessitated better heat-protection for the belly and rear fuselage.

The aircraft was found to be slow compared to other jet aircraft with a top speed of only 490 mph. The Me-262, which had first flown years before, could reach well over 500 mph, while the competing MiG-9 could fly at 540 mph.

But the prototype tests were largely successful, demonstrating the aircraft’s potential as a fast and agile jet fighter. Test pilots noted that the Yak-15 handled very well and, thanks to its Yak-3 basis, was easy to master.

Following the successful completion of prototype testing, the Yak-15 entered production.

Service History

The Yak-15 was introduced into service with the Soviet Air Force in 1946, at a time when the air force was keenly feeling the need to modernize its fleet with jet-propelled aircraft. The Soviet Union was in a race to catch up with the jet technologies being developed in the West, particularly by the United States and Great Britain.

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The Yak-15, being one of the Soviet Union’s first operational jet fighters, was central to these efforts, despite its somewhat makeshift design. However, one of the Yak-15’s biggest flaws relegated it to being a short-term solution.

This was in regards to its range. It wasn’t unusual for early jet engines to have poor fuel efficiency, but the Yak-15’s range was simply too low to be practical. At only 300 miles, the aircraft was severely limited in what it could do. And, because of the low thrust emitted by the RD-10 engine, it would become sluggish and unwieldy when carrying large loads of fuel to compensate.

As a result, the aircraft was only used as a trainer. Over the course of 1946 and 1947, a total of 280 Yak-15s were built.

Training and Transition

While being a trainer is not the most glamorous role for an aircraft, the Yak-15 was perfect for Soviet pilots transitioning from piston-engine fighters to jet-powered aircraft. The Yak-15’s handling characteristics, while certainly different from those of its piston-engine predecessors, were not as drastically different as those of more advanced jet designs.

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This made it an ideal platform for familiarizing pilots with the nuances of jet flight, including higher speeds, different handling and landing techniques, and the management of jet engines.

The aircraft’s operational parameters allowed pilots to experience the increased performance and potential of jet propulsion without the steep learning curve associated with more advanced jets. Consequently, the Yak-15 served as a critical step in the training regimen, preparing Soviet pilots for the next generation of jet fighters, such as the MiG-15, which would become a staple of Soviet and allied air forces around the world.

Fate

The service history of the Yak-15 was brief, largely due to the rapid development of more advanced jet aircraft in the late 1940s and early 1950s. As newer, more capable jet fighters like the MiG-15 entered service, the Yak-15 was gradually phased out. By the early 1950s, it was only serving in secondary roles, before being retired from active service altogether.

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Despite its short operational life, the Yak-15’s legacy is significant. It represented a critical transitional phase in Soviet aviation, facilitating the shift from piston-engine to jet-powered flight. The lessons learned from the development, deployment, and operation of the Yak-15 were directly applied to the design and implementation of future Soviet jet aircraft.

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