Was it Any Good? The XP-47H an Experimental P-47

During World War II, the P-47 emerged as one of the most robust and formidable planes amongst the Allied forces. The aircraft was renowned for its superior firepower, credited to the eight .50 caliber guns embedded in its wings, boasting 3,400 rounds.

This aircraft wasn’t only a formidable force in the air; its efficiency was pronounced in ground attacks, with the capability of bearing up to 3,000 pounds of external ordnance.

When fully equipped, the P-47 Thunderbolt could deliver approximately half the payload of a B-17 Flying Fortress, showcasing its versatility and power.


15,600 Thunderbolts

The P-47, designed by Alexander Kartveli and constructed by Republic Aviation (with Curtiss building 354 “G” models towards the end of the war), made its inaugural flight in June 1941.

The Republic P-47, produced between 1941 and 1945
The Republic P-47, produced between 1941 and 1945. It achieved success as a high-altitude fighter and was distinguished as the premier American fighter-bomber, excelling particularly in the ground-attack role during the conflict.

It earned the nickname “Jug,” short for “Juggernaut,” due to its resilience and difficulty to shoot down. Remarkably, owing to its advanced turbocharger, it could reach service ceilings of over 40,000 feet, despite being the heaviest single-engine fighter of the Second World War.

Over 15,600 Thunderbolts were produced between 1941 and 1945, seeing action in every theater of the war and fulfilling diverse roles from bomber escort to close air support.

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They also marked their presence with the British RAF, French Free Forces, and the Soviet Union, underlining their universal appeal and efficacy.

Although its combat debut was in April 1943, the P-47s were extensively deployed, completing over half a million sorties in both Europe and the Pacific.

They are credited with nearly 4,000 enemy aircraft, 9,000 trains, 86,000 trucks, and 6,000 armored vehicles, a testament to their significant role in air-ground missions.

Re-Designated as the F-47,

Post World War II, following Japan’s surrender, the Thunderbolts, now re-designated as the F-47, continued to be in service for years, and in some instances, decades.

While the U.S. withdrew the plane from front-line service in 1949, NATO allies like Turkey, Portugal, and Italy maintained squadrons of Thunderbolts into the 1950s.

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Several Latin American countries operated them until the 1960s, with Peru retiring its Jugs in 1966. This sustained usage underlines the enduring relevance and adaptability of the P-47 Thunderbolt in the dynamic landscape of aviation warfare.

The Republic XP-47H

The Republic XP-47H was another experimental variant of the P-47 Thunderbolt, designed by Republic Aviation to explore the performance limits of piston-engine fighters during World War II.

The XP-47H, much like the XP-47J, was developed with the intention of achieving higher speeds and improved overall performance compared to the standard P-47 Thunderbolt models.

Turbo-supercharger Replacement: Initially, an axial flow supercharger was intended to be connected to the engine, but it wasn’t ready, and a General Electric CH-5 turbosupercharger unit was used as a substitute.

The design of the P-47 was built around a massive powerhouse, the substantial Pratt & Whitney R-2800 Double Wasp radial engine, coupled with a complex turbo-supercharger.

It was this particular configuration that contributed to the Thunderbolt’s distinctive bulky fuselage. The substantial nature of this engine and its accompanying mechanics characterized the design, defining its structure and capabilities.

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In the realm of aviation design, there were instances of successful redesigns wherein aircraft transitioned from radial to inline engines, and vice versa.

However, considering the integral role and substantial nature of the P-47’s powerplant, coupled with the extensive and complex mechanics, envisioning a redesign of the Thunderbolt is challenging.

The concept of removing such a substantial and integral component and its associated mechanics and replacing it with a comparatively streamlined and smaller liquid-cooled engine seems beyond practical feasibility. After all, the engine IS the P-47.

That Engine

In the early stages of 1940, observing the unfolding air combats over Europe, Chrysler anticipated the imminent demand for more potent power plants and embarked on the development of a substantial new liquid-cooled engine, subsequently named the Chrysler XIV-2220.

IV-2220, perhaps a display model (note the cutaway prop).
IV-2220, perhaps a display model (note the cutaway prop). The length of the engine is evident, made even longer by the large accessories section bolted on the left of the block.

The engine, which was envisaged to meet the burgeoning needs of the time, promised a remarkable output of 2,500hp, a feat quite impressive for the 1940s.

In a bid to theoretically simplify the intricate process of constructing such a formidable engine, Chrysler opted to merge two V-8s together inline, crafting an inverted sixteen-cylinder engine spanning ten feet in length.

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Despite the attempt to streamline the design, the endeavor was met with considerable technical challenges, mirroring the complexities encountered in the developments of several counterparts from this era of piston engines.

The ongoing turmoil of the Second World War inevitably impeded the progress, with Chrysler’s industrial capabilities being requisitioned to produce a diverse range of wartime equipment.


This involved the production of a wide range of essential military equipment and materials crucial for wartime operations, encompassing vehicles such as trucks and tanks; components and parts for aircraft; various firearms, ammunition, rockets, and bombs; along with numerous other goods and resources indispensable to the war effort.

Troublesome Engine: The Chrysler engine proved more trouble than it was worth, being unreliable and causing developmental issues.
Troublesome Engine: The Chrysler engine proved more trouble than it was worth, being unreliable and causing developmental issues.

However, by 1943, Chrysler received authorization to test their innovative engine on an aircraft. Consequently, two “razorback” configured P-47Ds were allocated from the production line for conversion and trial.

The integration of this new engine was believed to significantly enhance the performance of the P-47 models in operation at the time, owing to its streamlined design, aerodynamic proficiency, and superior horsepower.

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The meticulous and innovative adaptation was viewed as a substantial step forward in refining the capabilities of the aircraft, aiming to optimize its operational efficiency and effectiveness in the evolving theatre of war.

Big Exceptions – Poor Results

Optimism permeated the expectations for the XP-47H, as despite the substantial size and weight of the XIV-2220 and its accompanying intricate and hefty turbo-supercharger, predictions suggested the aircraft could achieve speeds exceeding 490 mph (approximately 790 km/h).

If realized, this would have positioned it among the fastest piston engine aircraft of the time.

Early Problems

In the initial stages in the design of the XIV-2220, a significant challenge arose due to the unavailability of high-strength aluminum alloys.

Design Aim: The aircraft was envisioned to be one of the fastest piston-engined fighters of the war, with engineers optimistic about achieving a maximum speed of approximately 490 miles per hour.
Design Aim: The aircraft was envisioned to be one of the fastest piston-engined fighters of the war, with engineers optimistic about achieving a maximum speed of approximately 490 miles per hour.

The principal supplier, Alcoa, could only furnish alloys with half the requisite strength. This issue was mitigated by Chrysler through enhanced quality control measures on the production line.

However, the engine still necessitated unusual spacing between the cylinders, extending its length considerably.

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This extension was compounded by the presence of a “gap” that accommodated the propeller gearing situated in the engine’s center and a substantial accessories section at the engine’s extremity.

The IV-2220 was notably immense; to illustrate, the 2,000 hp Rolls-Royce Griffon, having approximately equivalent displacement, spanned 77 inches in length, in stark contrast to the 122 inches of the IV-2220.

Substantial Alterations

The conversion process, executed at Republic, demanded substantial alterations to the fundamental design of the P-47.

Initial modifications involved the removal of armament and military equipment, considered redundant for this iteration—these were the more straightforward adjustments.

One might find it difficult to envision the P-47 being enlarged, but the introduction of the new powerplant necessitated such expansions.

Limited Flight: One of the two XP-47H prototypes never flew for testing and both were soon scrapped, marking the brief existence of the aircraft in aviation history.
Limited Flight: One of the two XP-47H prototypes never flew for testing and both were soon scrapped, marking the brief existence of the aircraft in aviation history.

The newly integrated engine, noted for its elongated structure in comparison to the Double Wasp’s more rounded form, required the incorporation of an extended cowling and propeller spinner for the XP-47H.

Given the inverted installation of the new engine, this modification endowed the aircraft with a distinctive “shark-nose” appearance.

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The extensive modifications underscored the pursuit of creating an aircraft with superior speed and aerodynamic efficacy, pushing the boundaries of piston engine aircraft design during this period.

A quick glance at the P-47 and any model from the XP-47 design, you will soon see this looks more like a P-51 than it does a P-47.

Bloated Belly

The design of the engine necessitated the incorporation of an extensive air scoop along with a plethora of supplementary piping to accommodate the engine exhaust and the newly integrated General Electric CH-5 turbocharger.

It was located towards the rear of the aircraft’s extended undercarriage. This is what gives the XP-47H its rather odd look. Goes against against all the principles of aerodynamics.

Performance Shortfall: It recorded a maximum speed of 414 miles per hour during testing, far short of the expected performance gains.
Performance Shortfall: It recorded a maximum speed of 414 miles per hour during testing, far short of the expected performance gains.

The remaining structure of the aircraft adhered to the original P-47 specifications, maintaining the characteristic elliptical wings and the robust sliding frame canopy, identifiable by its distinctive ridged back.

However, substantial modifications to the fuselage meant the conversion process was intricate and prolonged, executed by a collaborative team from Republic and Chrysler

The path of this venture was anything but smooth, reflecting in the consequent discontinuation of another prospective aircraft, the Curtiss P-60C, which aspired to utilize the same engine.

Became Irrelevant

Despite initial high expectations of superior performance, it appears that the XP-47H quickly transitioned into primarily a test program of secondary significance.

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The shift in focus is attributed to the realization that the prevailing aircraft models, including the P-47, sufficiently met the requirements to secure victory in the war. There was no need to reinvent the wheel.

The emphasis was redirected towards enhancing the performance and reliability of these existing service aircraft over investing efforts and resources in the intricate XP-47H.

Consequently, the aircraft, powered by the Chrysler engine, didn’t experience its inaugural flight until late July 1945. In a succinct testing program spanning a few months, the XP-47H demonstrated that extensive refinements and developments were still needed before it could evolve into a dependable service aircraft.

Did it Hit the Design Brief?

There exist varying accounts regarding the actual performance of the XP-47H, leading to discrepancies in recorded data.

Some sources claim that it indeed reached the anticipated speed of 490mph, while others argue that it was subpar compared to the existing models of P-47 Thunderbolt in service during that period.

However, scrutinizing the efficacy of XP-47H is arguably inconsequential. Even if the XP-47H had exhibited impeccable performance during its testing phase and met all the pre-set expectations, its relevancy was already diminishing.

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The war was nearing its conclusion, the was already over in Europe, and the XP-47H-model did not take flight until July of 1945, just a month before VJ Day. the Japanese surrendered on August 15, 1945, the Pacific War was over.

The emergence of jet fighters signified the impending evolution in air fighter technology. These new models clearly outlined the future of battlefield in the skies.

The P-47 certainly left a legacy, Luftwaffe ace Heinz Bär described the P-47  “could absorb an astounding amount of lead and had to be handled very carefully”

Despite the resilience of the P-47, the North American P-51 Mustang eventually supplanted it in the role of long-range escort in Europe, showcasing advancements in aircraft design and functionality.

Destruction Tally

Between D-Day and VE Day, pilots flying the P-47 Thunderbolt reported the destruction of 86,000 railroad cars, 9,000 locomotives, 6,000 armored combat vehicles, and 68,000 trucks.

During Operation Cobra, near Roncey, the P-47 Thunderbolts of the 405th Fighter Group were instrumental in decimating a German column, comprising 122 tanks, 259 assorted vehicles, and 11 pieces of artillery. It’s reputation was built and sealed.