The Curtiss H-1640 Chieftain, a distinctive American 12-cylinder radial aero engine, was designed and constructed by the Curtiss Aeroplane and Motor Company in the mid-1920s.
Unlike the common multi-row radial engines of the time, which featured staggered cylinders for improved airflow and cooling, the Chieftain employed an inline radial configuration.
This unique arrangement positioned the cylinders one behind the other, enabling pairs of cylinders to share a cast cylinder head and camshafts. Although the Chieftain saw some application in the 1920s, it was quickly overtaken by more advanced designs.
The Curtiss H-1640 Chieftain engine represents a unique chapter in the history of aviation engineering, reflecting both the innovative spirit and the technical challenges of the 1920s and 1930s.
Development and Design
This 12-cylinder, air-cooled radial engine was developed by the Curtiss Aeroplane and Motor Company, a pioneer in the American aviation industry. While it did not achieve widespread success, the Chieftain engine’s design and development offer insights into the technological advancements and challenges of its era.

The development and design of the Curtiss H-1640 Chieftain engine in the mid-1920s marked a bold foray into the realm of aviation technology by the Curtiss Aeroplane and Motor Company.
This period in aviation history was characterized by rapid innovation and a drive towards more powerful and efficient aircraft engines. The Chieftain was Curtiss’s response to this challenge, embodying a blend of daring design choices and engineering ingenuity.
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At the heart of the Chieftain’s design was its unique 12-cylinder radial configuration. Radial engines were common at the time, but Curtiss’s approach was unconventional. Most radial engines featured multiple rows of cylinders arranged in a staggered formation to optimize airflow and cooling.
However, the Chieftain deviated from this norm by adopting an inline radial arrangement. This meant that the cylinders were aligned directly behind one another, a design decision that was quite rare for radial engines.
This inline arrangement was not just for novelty; it had practical implications. By aligning the cylinders in this manner, the Chieftain allowed for pairs of cylinders to share a single cast cylinder head and camshafts.
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This design was intended to streamline the engine’s construction and potentially improve its efficiency. Sharing components between cylinder pairs could reduce the overall number of parts required, thereby simplifying manufacturing and maintenance. Moreover, this configuration was expected to contribute to a more compact engine design, which would be beneficial for aerodynamic efficiency and aircraft design.

Another key aspect of the Chieftain’s design was its focus on power and performance. Curtiss aimed to create an engine that would offer superior power output without significantly increasing weight or complexity. The use of advanced materials and innovative manufacturing techniques was central to achieving this goal. The engine was built to be robust yet lightweight, an essential consideration for aircraft performance.
Despite its innovative design, the Chieftain faced several challenges during its development. Cooling, a common issue with air-cooled radial engines, was a particular concern.
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The inline arrangement of the cylinders posed unique cooling challenges, as the rear cylinders received less airflow than the front ones. Curtiss engineers needed to devise effective cooling solutions to prevent overheating, especially under high-stress operating conditions.
The development of the Chieftain also took place against the backdrop of a competitive and rapidly evolving aviation industry.
During this era, engine reliability, efficiency, and performance were paramount, not just for military applications but also for the burgeoning commercial aviation sector. As such, the Chieftain was not just a technical exercise; it was Curtiss’s attempt to assert its prowess in a highly competitive market.
Technical Specs
Designed as a 12-cylinder radial engine, the Chieftain was distinct in its configuration and technical attributes, setting it apart from its contemporaries.

Central to the Chieftain’s design was its unique cylinder arrangement. Unlike traditional radial engines with staggered rows, the Chieftain’s cylinders were arranged in an inline radial format. This meant that all twelve cylinders were aligned in a single row, positioned directly behind one another.
This design was primarily aimed at reducing the engine’s frontal area, thereby decreasing aerodynamic drag, a critical factor in improving aircraft performance.
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The Chieftain’s cylinders were noteworthy not just for their arrangement but also for their shared components. Each pair of cylinders shared a single cast cylinder head and camshafts, a feature that was intended to simplify the engine’s design and maintenance.
This approach was innovative, as it reduced the number of individual parts required, potentially enhancing the engine’s reliability and ease of service.
In terms of displacement, the Chieftain was sizeable, with an approximate displacement of 1,640 cubic inches (about 27 liters). This large displacement was indicative of the engine’s power potential. Furthermore, the engine was air-cooled, a common choice for aircraft engines at the time due to its simplicity and reduced weight compared to liquid-cooling systems.

However, the air-cooling presented its own set of challenges, particularly in terms of ensuring adequate and even cooling across all cylinders, especially given the inline arrangement.
The engine’s power output was another significant aspect. Rated at around 600 horsepower, the Chieftain was among the more powerful engines of its era. This high power output was crucial for the increasingly large and fast aircraft being designed in the 1920s and 1930s.
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The engine’s power-to-weight ratio was also a critical factor, as Curtiss sought to maximize power output while keeping the engine as light and compact as possible.
Additionally, the Chieftain employed advanced features for its time, such as a supercharger. The inclusion of a supercharger was indicative of the growing recognition of the importance of engine performance at higher altitudes, where thinner air could significantly reduce power output.
By compressing the incoming air, the supercharger allowed the engine to maintain a more consistent performance regardless of altitude.
Challenges and Performance
While the engine’s design was innovative, it encountered several hurdles that impacted its overall performance and adoption in the aviation industry.
One of the primary challenges faced by the Chieftain was related to its unique inline radial configuration. This design, while innovative in minimizing frontal area and drag, posed significant cooling difficulties. In radial engines, effective cooling of the cylinders is paramount, as uneven cooling can lead to significant mechanical issues, including overheating.

The inline arrangement of the Chieftain’s cylinders meant that the rear cylinders received significantly less airflow than those in front, making them prone to overheating. Curtiss engineers grappled with this issue, trying various modifications to improve airflow and cooling efficiency, but the problem remained a persistent drawback.
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Another challenge was the engine’s complexity. The Chieftain’s design, featuring shared cylinder heads and camshafts for pairs of cylinders, was advanced for its time but also led to a more complicated engine structure. This complexity had implications for maintenance and reliability.
In an era where ease of maintenance and operational reliability were crucial, especially for military applications, the Chieftain’s intricate design was less appealing compared to simpler, more established engine configurations. This complexity potentially limited its attractiveness to aircraft manufacturers and operators who prioritized straightforward maintenance and servicing.

In terms of performance, the Curtiss H-1640 Chieftain had both strengths and weaknesses. On the positive side, its power output was impressive. Rated at around 600 horsepower, the engine was capable of providing the significant thrust needed for the larger and faster aircraft designs emerging at the time.
The inclusion of a supercharger also meant that the engine could maintain better performance at higher altitudes, a valuable feature given the expanding operational envelopes of aircraft.
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However, the engine’s overall performance was marred by the cooling issues and the maintenance challenges associated with its complexity. These factors limited its operational efficiency and reliability, key metrics for any aircraft engine’s success. As a result, the Chieftain struggled to find widespread acceptance in the highly competitive aviation market of the late 1920s and early 1930s.
Legacy
The Curtiss H-1640 Chieftain engine’s legacy is a mixed one. On the one hand, it was an example of innovative engineering, pushing the boundaries of what was possible in aircraft engine design at the time. Its inverted radial configuration and advanced features like the supercharger were ahead of their time and influenced later engine designs.
On the other hand, the engine’s technical challenges and limited commercial success serve as a reminder of the difficulties inherent in aviation engineering. The Chieftain’s story illustrates how a promising design can struggle to find its place in the market, overshadowed by more reliable, if less advanced, alternatives.