The Lippisch P.13 was a Coal Powered Interceptor

The Lippisch P.13 was conceived during the waning years of the Second World War, this German interceptor aircraft represents a radical departure from conventional aircraft design principles, demonstrating the ambitious vision of its designer, Alexander Lippisch.


Lippisch’s Vision

Alexander Lippisch, born in Munich in 1894, was a pioneer in the field of aerodynamics and aircraft design. His career began with an early fascination with flight, sparked by witnessing Zeppelin airships and the Wright brothers’ exploits.

This passion drove him to pursue engineering, where he quickly distinguished himself as an innovative thinker unafraid of challenging established norms.

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Lippisch’s vision for aviation centred on the potential of the delta wing, a radical departure from the conventional aircraft designs of his time. He believed that delta wings, characterised by their triangular shape and swept-back leading edges, offered superior aerodynamic properties.

This configuration promised reduced drag, enhanced lift, and greater structural strength, particularly at high speeds. Lippisch was convinced that these attributes could revolutionise both civilian and military aviation.

In the 1920s and 1930s, Lippisch’s work gained recognition through his involvement with gliders. His designs, such as the Storch series, demonstrated exceptional stability and performance. These successes validated his theories and solidified his reputation as a leading aeronautical engineer.

An early tailess aircraft designed by Lippisch.
An early tailless aircraft designed by Lippisch.

His gliders, particularly the Delta I and subsequent models, showcased the practical benefits of delta wings, setting the stage for more ambitious projects.

With the advent of the Second World War, Lippisch’s expertise became increasingly valuable. Germany’s Luftwaffe sought to maintain air superiority against advancing Allied forces, prompting a surge in experimental aircraft development.

Lippisch, by then a prominent figure at the Luftfahrtforschungsanstalt Wien (Aeronautical Research Institute in Vienna), was in a prime position to influence the direction of German aircraft design.

Lippisch envisioned an aircraft that could outperform existing models in terms of speed, manoeuvrability, and operational efficiency. The P.13 emerged as a manifestation of this vision. He proposed a design that eschewed the traditional fuselage-wing-tail arrangement in favour of a unified delta-wing structure.

This innovative approach aimed to maximise the aerodynamic benefits of the delta configuration, providing a sleek, efficient, and highly manoeuvrable aircraft.

Central to Lippisch’s vision was the incorporation of cutting-edge propulsion technology. He recognised the limitations of conventional piston engines and jet turbines, which were constrained by their complexity and performance ceilings.

Instead, he advocated for the use of a ramjet engine, a relatively novel concept at the time. Ramjets, designed to operate efficiently at high speeds by utilising the aircraft’s forward motion to compress incoming air, offered the potential for unprecedented velocity.

Lippisch’s foresight extended beyond mere performance metrics. He understood the strategic implications of his designs. An aircraft like the P.13, capable of rapid interception and high-speed engagement, could significantly alter the dynamics of aerial warfare.

A glider mockup of the P.13 to test the delta wing.
A glider mockup of the P.13 to test the delta wing.

Its ability to quickly reach and neutralise enemy bombers would provide a critical defensive advantage, potentially shifting the balance of power in the skies.

Despite the turbulent and resource-constrained environment of wartime Germany, Lippisch remained steadfast in his commitment to innovation. He tirelessly advocated for his designs, collaborating with engineers, test pilots, and military officials to refine and promote his concepts.

His unwavering belief in the potential of the delta wing and ramjet propulsion underscored his visionary approach to aviation.

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In the broader context of his career, the P.13 represented the culmination of Lippisch’s decades-long quest to redefine the boundaries of aeronautical engineering. Although the aircraft never reached production, the principles and insights gained from its development had a lasting impact.

Lippisch’s work on delta wings directly influenced the design of post-war aircraft, including supersonic jets and spaceplanes, cementing his legacy as a true pioneer in the field.

Radical Design Philosophy

Alexander Lippisch’s radical design philosophy for the P.13 was rooted in his extensive research and unwavering belief in the delta wing’s superiority.

This philosophy was a departure from the conventional aircraft designs that dominated the era, reflecting his commitment to pushing the boundaries of aeronautical engineering.

Lippisch’s decision to forgo a traditional fuselage was revolutionary. Instead of the standard arrangement of a fuselage with wings and a tail, he envisioned an aircraft where the wing itself formed the primary structure.

This choice was not merely aesthetic but based on sound aerodynamic principles. By integrating all major components, including the cockpit and the engine, into the wing structure, Lippisch aimed to create an aircraft with significantly reduced drag and increased lift.

This integration also promised enhanced structural integrity, as the wing could bear the loads more efficiently without the additional weight and complexity of a separate fuselage.

The delta wing’s large surface area was another critical aspect of Lippisch’s design philosophy. This expansive wing area provided ample lift, which was crucial for achieving the high speeds and rapid climb rates necessary for intercepting enemy bombers.

A small model of the P.13 A with the ramjet engine if it were put in production.
A small model of the P.13A with the ramjet engine if it were put in production.

The wing’s sharply swept leading edges minimised aerodynamic drag, allowing the aircraft to maintain high speeds with greater efficiency. This design also contributed to better handling characteristics at various speeds and altitudes, making the aircraft more versatile and capable in diverse combat scenarios.

Central to Lippisch’s radical design was the proposed use of a ramjet engine, a propulsion system still in its experimental stages during World War II. Unlike conventional piston engines or early jet turbines, the ramjet promised significantly higher speeds due to its unique operational principles.

The ramjet engine operated by compressing incoming air through the aircraft’s forward motion, mixing it with fuel, and igniting the mixture to produce thrust. This method of propulsion was inherently simple, with fewer moving parts than traditional engines, potentially leading to greater reliability and ease of maintenance.

However, the ramjet’s efficiency was contingent on the aircraft already being at a high speed, as the engine could not produce significant thrust at low velocities. This requirement posed a unique challenge and added complexity to the aircraft’s design and operational use.

Lippisch addressed this by proposing a launch system involving rocket assistance or a catapult mechanism to bring the P.13 up to the necessary speed for the ramjet to become effective. This innovative solution highlighted Lippisch’s ability to think beyond conventional constraints and find practical ways to implement his radical ideas.

Lippisch also considered the aerodynamic benefits of his design for combat effectiveness. The P.13’s delta wing configuration was expected to provide exceptional manoeuvrability, crucial for dogfighting and evasive actions against enemy aircraft.

A replica P.13. Photo credit - Zackcboween CC BY-SA 4.0.
A replica P.13. Photo credit – Zackcboween CC BY-SA 4.0.

The aircraft’s stability at high speeds and its ability to make sharp turns would give it a tactical advantage in intercepting and engaging enemy bombers, which were often escorted by agile fighter planes.

The P.13’s design included a cockpit seamlessly integrated into the wing, providing the pilot with a streamlined forward view while minimising aerodynamic disturbances. The placement of the engine within the wing further contributed to the aircraft’s sleek profile, reducing drag and enhancing overall performance.

Lippisch’s radical design philosophy extended to the material selection and construction techniques. He envisioned using advanced materials to achieve a lightweight yet robust structure. This approach aimed to maximise the aircraft’s speed and agility while ensuring durability and resilience in combat conditions.

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Powering the P.13

The propulsion system of the Lippisch P.13 was one of its most striking and revolutionary features. This choice marked a significant departure from the conventional piston engines and early turbojets that powered most aircraft of the era.

Ramjet engines operate on a principle fundamentally different from other types of aircraft engines. Unlike piston engines, which rely on a cycle of compression, combustion, and expansion within cylinders, or turbojets, which use a turbine to compress air before combustion, ramjets exploit the aircraft’s forward motion to compress incoming air.

This method allows for a simpler, more robust engine design with fewer moving parts, potentially increasing reliability and reducing maintenance requirements.

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The ramjet engine proposed for the P.13 consisted of an intake, a combustion chamber, and a nozzle. As the aircraft moved forward at high speed, air would enter the intake and become compressed due to the aircraft’s motion.

This compressed air would then mix with fuel in the combustion chamber, where the mixture would ignite. The resulting high-pressure exhaust gases would accelerate out of the nozzle, producing thrust.

This process relied on the dynamic pressure of the incoming air, which meant that the ramjet could only operate efficiently at high speeds, typically above Mach 0.5.

A drawing of how the P.13 's ramjet would of worked.
A drawing of how the P.13’s ramjet would have worked.

The primary challenge associated with using a ramjet engine for the P.13 was achieving the initial speed required for the engine to function. Ramjets produce minimal thrust at low velocities, making them unsuitable for conventional takeoff procedures. Lippisch addressed this issue by proposing several innovative solutions to bring the P.13 up to the necessary speed.

One such solution involved using a rocket-assisted launch. This method entailed equipping the aircraft with auxiliary rockets that would provide the necessary thrust for takeoff and initial acceleration. Once the aircraft reached a suitable speed, the rockets would detach, and the ramjet would take over propulsion.

Another proposed method was a catapult launch system. This approach involved using a ground-based catapult to accelerate the aircraft along a track to the required speed before liftoff.

Such a system would eliminate the need for additional onboard rocket systems, potentially reducing the aircraft’s weight and complexity. Both solutions highlighted Lippisch’s ingenuity in overcoming the inherent limitations of ramjet technology.

Once airborne and operating at optimal speeds, the ramjet engine would enable the P.13 to achieve remarkable velocities. Theoretically, the ramjet could allow the aircraft to reach speeds exceeding Mach 2, making it one of the fastest interceptors of its time.

This high-speed capability was crucial for its intended role as an interceptor, enabling it to quickly engage and neutralise enemy bombers before they could release their payloads.


The choice of fuel for the ramjet engine was another critical consideration. Given the resource constraints faced by Germany towards the end of the war, Lippisch explored alternative fuels that could be produced domestically.

One such fuel was coal dust, which was abundant and could be utilised in the ramjet’s combustion process. The use of coal dust required significant adaptations in the engine design to ensure efficient mixing and combustion, further showcasing Lippisch’s innovative approach to engineering challenges.

The ramjet’s high-speed performance also presented aerodynamic challenges that Lippisch had to address. At supersonic speeds, the aircraft would encounter significant aerodynamic heating and stress. Lippisch’s design incorporated materials and structural techniques to withstand these conditions, ensuring the integrity and performance of the P.13 at high velocities.

Furthermore, the integration of the ramjet engine within the aircraft’s delta wing posed additional design complexities. The engine’s placement needed to balance the aircraft’s centre of gravity and ensure efficient airflow through the intake and exhaust systems.

Lippisch’s expertise in aerodynamics and his experience with delta-wing configurations were crucial in optimising this integration.

A Do-217 equipped with a ramjet for testing.
A Do-217 equipped with a ramjet for testing.

Operational Considerations

The operational deployment of the Lippisch P.13 necessitated a thorough examination of several critical factors. These considerations were essential for transitioning the aircraft from a theoretical concept to a functional component of Germany’s defensive strategy during World War II.

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The unique characteristics of the P.13’s design, particularly its ramjet propulsion system and delta wing configuration, presented distinct challenges and opportunities in operational use.

Once airborne, the P.13’s operational role as an interceptor necessitated rapid climb rates and high-speed engagement capabilities. The delta wing design provided the necessary lift and manoeuvrability for such missions, allowing the aircraft to ascend quickly to intercept incoming bombers.

The large wing area and swept-back leading edges contributed to stability and control at high speeds, essential for effective engagement in combat scenarios. Pilots would need to be trained extensively to handle the unique flight characteristics of the delta wing, particularly its behaviour at supersonic speeds.

Fuel efficiency and supply represented another operational consideration. The proposed use of coal dust as a fuel for the ramjet engine, while leveraging an abundant resource, introduced new logistical challenges. Coal dust required specialised handling and storage procedures to prevent contamination and ensure consistent quality.

The infrastructure for fuelling and maintaining the P.13 would need to accommodate these requirements, including equipment for grinding coal to the appropriate particle size and systems for safely loading the fuel into the aircraft.

The strategic deployment of the P.13 also demanded careful planning. As a high-speed interceptor, the aircraft’s primary role would be the defence of critical targets against Allied bombing raids. This role required the establishment of forward operating bases near potential targets to minimise response times.

These bases would need to be equipped with the necessary launch and recovery infrastructure, fuel supply systems, and maintenance facilities to support sustained operations. The positioning of these bases would be influenced by the range and endurance of the P.13, necessitating a balance between proximity to targets and the logistical feasibility of base locations.

Furthermore, the aircraft’s operational effectiveness would be contingent on timely and accurate intelligence regarding enemy bomber formations. Effective coordination with ground-based radar systems and other early warning mechanisms was essential to provide pilots with the information needed to intercept and engage targets.

This coordination required seamless communication networks and well-defined operational protocols to ensure that the P.13 could be deployed swiftly and effectively in response to incoming threats.

Maintenance and repair of the P.13 introduced additional operational considerations. The advanced materials and design features of the aircraft, while enhancing performance, required specialised knowledge and equipment for upkeep.

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Training ground crews to handle the unique aspects of the ramjet engine, delta wing structure, and coal dust fuel system was critical to maintaining operational readiness. Spare parts and repair facilities needed to be readily available to address any damage sustained during missions or routine wear and tear.