Fast But Unreliable – Curtiss XP-37

The XP-37 originated from Curtiss-Wright’s efforts to improve upon their earlier successful design, the P-36 Hawk. The U.S. Army Air Corps expressed interest in a high-altitude fighter, leading Curtiss to modify the P-36 design.


The XP-37 was a Better P-36

The XP-37 originated from the United States Army Air Corps’ pursuit of advanced fighter aircraft. In response to this demand, Curtiss Aeroplane and Motor Company, a prominent name in aviation, initiated the development of a new fighter design.

The project, led by renowned aeronautical engineer Don R. Berlin, aimed to enhance the performance of the existing P-36 Hawk by incorporating a supercharged engine and a more aerodynamic design.

Similarities can be seen between the XP-37 and Curtiss' later aircraft.
Similarities can be seen between the XP-37 and Curtiss’ later aircraft.

The Curtiss P-36 Hawk and the Curtiss XP-37 share a significant relationship in the realm of military aviation history, particularly in their development lineage.

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The P-36 Hawk, a successful fighter aircraft in its own right, was known for its traditional air-cooled radial engine. However, as the quest for higher performance and more advanced fighter aircraft became paramount in the late 1930s, Curtiss engineers sought to upgrade this platform. This led to the development of the XP-37, which was an attempt to incorporate a more powerful and efficient propulsion system into the basic design framework of the P-36.

The most notable change in the XP-37 compared to its predecessor was the replacement of the P-36’s radial engine with an Allison V-1710 liquid-cooled V-12 engine.

The P-36 used an aircooled radial engine. Photo credit - Alan Wilson CC BY-SA 2.0.
The P-36 used an air-cooled radial engine. Photo credit – Alan Wilson CC BY-SA 2.0.

This was a radical change, as liquid-cooled engines were not as common at the time. The engine in the XP-37 was positioned behind the pilot, a design decision aimed at enhancing aerodynamic efficiency. This change necessitated an elongated nose, which distinguished the XP-37 visually from the P-36.

However, this modification brought its own set of challenges, including issues with pilot visibility due to the rearward placement of the cockpit and the long nose.

Water Cooling

The V-1710-21, like other engines in the V-1710 series, is a liquid-cooled V-12 engine. This design was a departure from the more commonly used air-cooled radial engines of that era.

The choice of a liquid-cooled configuration allowed for more efficient cooling of the engine, which was crucial for maintaining performance and reliability, especially under the demanding conditions of high-speed flight and combat.

This engine was notable for its horsepower output, which marked a significant improvement over previous models and contemporaneous engines. Its enhanced power output was a result of both its advanced design and the use of high-quality materials and manufacturing techniques.

This made it capable of propelling fighter aircraft to higher speeds and altitudes than previously possible, contributing to the advancement of aircraft performance during the war.

The Allison engine used to power the XP-37 and the subsequent P-40.
The Allison engine used to power the XP-37 and the subsequent P-40.

The V-1710-21 also featured improvements in terms of reliability and serviceability. Allison’s engineers focused on making the engine more robust and easier to maintain, understanding the importance of these factors in military operations.

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The design allowed for quicker and more efficient field maintenance, a critical aspect in wartime conditions where rapid turnaround and high availability of aircraft were essential.

Additionally, the V-1710-21 was part of the broader V-1710 series’ legacy in pioneering the use of fuel injection over carburetion. This advancement led to better fuel efficiency and performance, particularly at high altitudes where carbureted engines often struggled.

Performance at the Cost of Everything

The flight performance of the Curtiss XP-37, although it showed initial promise, ultimately revealed several significant challenges that hindered its operational effectiveness.

When the XP-37 took to the skies for its maiden flight in 1937, it displayed impressive speed and climb capabilities, a direct result of its innovative design choices, particularly the Allison engine.

Curtiss' creation was fast, but at the cost of almost everything else.
Curtiss’ creation was fast, but at the cost of almost everything else.

Despite these advancements, the XP-37’s operational performance revealed critical shortcomings. Pilots reported significant issues with the aircraft, primarily related to visibility and handling. The elongated nose and rearward placement of the cockpit, necessary to accommodate the new engine layout, severely restricted pilot visibility.

This was a critical flaw, especially in combat situations where visibility is paramount. Additionally, the aircraft’s handling characteristics were found to be less than ideal. Pilots faced difficulties in controlling the XP-37, particularly during the takeoff and landing phases.

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The cooling system for the liquid-cooled engine also proved to be a problem. The XP-37 struggled with engine overheating, a critical issue in high-performance aircraft.

Effective cooling is essential for maintaining engine performance and reliability, and the XP-37’s system was inadequate for its needs. This not only impacted the aircraft’s endurance and reliability but also raised concerns about its suitability for prolonged combat scenarios.

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Maintenance challenges further compounded these issues. The extended drive shaft from the engine to the propeller was prone to vibrations, leading to increased wear and maintenance requirements. In a military context, where reliability and ease of maintenance are key, these issues were significant drawbacks.

Issues with the watercooling would have made dogfights even more terrifying.
Issues with the water-cooling would have made dogfights even more terrifying.

Influence and Legacy

Though the XP-37 did not advance beyond the prototype stage, its development had a lasting impact on aircraft design. The lessons learned from the XP-37 influenced the design of subsequent Curtiss fighter models, most notably the P-40 Warhawk.

The Warhawk retained the Allison V-1710 engine but addressed many of the XP-37’s flaws, becoming one of the most iconic fighters of World War II.

In designing the P-40, the engineers optimised the placement of the cockpit for better pilot visibility and improved the aircraft’s overall handling characteristics.

They also addressed the cooling issues that had plagued the XP-37 by designing a more effective cooling system for the liquid-cooled engine. These improvements ensured that the P-40 did not suffer from the same operational limitations as its predecessor.

The shark mouth is synonymous with the P-40.
The P-40 was an excellent aircraft that owed its success to the failures of the XP-37. Photo credit – Jeff Sorenson CC BY 2.0.

Furthermore, the P-40 featured a more conventional and practical design compared to the ambitious but flawed XP-37. This made it a more reliable and maintainable aircraft, suitable for the rigours of wartime service.

The Warhawk combined the high performance of the XP-37’s engine with improved practicality and usability, a balance that was crucial for its success in various combat theatres during the Second World War.

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In essence, the XP-37’s experimental design served as a stepping stone in the evolution of the P-40 Warhawk.

Success in Failure

While the XP-37 was not a commercial or military success, played a crucial role in the evolution of fighter aircraft. It stands as a symbol of innovation and experimentation, embodying the spirit of an era marked by rapid advancements in aviation technology. The XP-37’s story is a reminder of the challenges and triumphs of aircraft design, contributing to the rich tapestry of aviation history.