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Republic XP-47J (Superbolt)

High-Performance Single-Seat Fighter Aircraft Prototype

Republic XP-47J (Superbolt)

High-Performance Single-Seat Fighter Aircraft Prototype


Just one of the two contracted XP-47J high-speed fighter prototypes were realized before the project came to an end.
National Flag Graphic
ORIGIN: United States
YEAR: 1944
STATUS: Cancelled
MANUFACTURER(S): Republic Aviation Corporation - USA
OPERATORS: Untied States (cancelled)

Unless otherwise noted the presented statistics below pertain to the Republic XP-47J model. Common measurements, and their respective conversions, are shown when possible.
LENGTH: 33.30 feet (10.15 meters)
WIDTH: 40.78 feet (12.43 meters)
HEIGHT: 14.21 feet (4.33 meters)
WEIGHT (EMPTY): 9,663 pounds (4,383 kilograms)
WEIGHT (MTOW): 16,788 pounds (7,615 kilograms)
ENGINE: 1 x Pratt & Whitney R-2800-57(C) turbosupercharged air-cooled radial piston engine developing 2,800 horsepower and driving a four-bladed propeller unit at the nose.
SPEED (MAX): 505 miles-per-hour (813 kilometers-per-hour; 439 knots)
RANGE: 1,072 miles (1,725 kilometers; 931 nautical miles)
CEILING: 44,997 feet (13,715 meters; 8.52 miles)
RATE-OF-CLIMB: 4,900 feet-per-minute (1,494 meters-per-minute)


6 x 0.50 caliber Browning heavy machine guns (three to a wing).

Series Model Variants
• XP-47J "Superbolt" - Base Project Designation; two prototypes contracted for though only single flyable example was completed.


Detailing the development and operational history of the Republic XP-47J (Superbolt) High-Performance Single-Seat Fighter Aircraft Prototype.  Entry last updated on 7/13/2018. Authored by Staff Writer. Content ©
The classic Republic P-47 "Thunderbolt" fighter of World War 2-fame went through many revisions during its time aloft. Born from the company's work on the P-43 "Lancer", the P-47 entered service with the same "razorback" dorsal spine and large nose-mounted air-cooled radial engine. In time, the "Jug" was advanced to include a bubble-style canopy and higher-performance. Some became true thoroughbreds and excelled at interception duties while others performed exceptionally in the ground-attack role. As either a fighter or fighter-bomber, there were few designs of the war that could match the return-of-investment seen in the American P-47, its design attributed to Alexander Kartveli.

During all this, the U.S. Army was always on the lookout for more of everything and, in November of 1942, contacted Republic to engineer a lighter-weight, higher-performing version of its P-47 (entering official service that same month). This new aircraft would fit an uprated engine in the nose that featured additional cooling and water injection for maximum power at altitude. Weight would be saved wherever possible including armament and fuel. An Army contract issued on June 18th, 1943 covered two XP-47J prototypes.

Engineers returned with a revised form of their P-47 which was designated "XP-47J". The design's engine cowling was refined with a smaller frontal area and this tight cover housed the Pratt & Whitney R-2800-57(C) engine within. The engine outputted at 2,800 horsepower and would drive a standard four-bladed propeller unit. Both the engine and propeller unit were off-the-shelf, in-service products which would aid in mass production of the aircraft. For weight savings, the wing mainplanes were revised to a lighter-constructed form and one of the four machine guns in each wing were deleted (as were some of the internal fuel stores which, in turn, reduced operational ranges). Additionally, some cockpit equipment was removed and the dorsal area aft of the cockpit was cut down. A true bubble-style canopy was not in play as of yet - instead a revised version of the basic P-47 framed canopy was added and this did help in improving vision out-of-the-cockpit for the pilot.

The first XP-47J had its R-2800 engine mounted further ahead in the airframe and the installation was forced-cooled by an intake fan built into in the propeller's spinner. The exhaust ejection system was designed to pull additional thrust from the air flow and the turbosupercharger was aspirated by a new air scoop mounted under the chin of the aircraft.

The second prototype was to feature a true bubble canopy and perhaps a contra-rotating propeller unit to squeeze even more speed out of the design. However, budget issues curtailed its development and it was cancelled in March of 1944.

A first-flight of the XP-47J prototype was had in November 26th, 1943. It did not go airborne again until March of 1944 at which point it revealed itself to be one of the fastest prop-driven aircraft of the period (and the war for that matter) at 500 miles per hour in level flight. During testing on August 4th, 1944, the aircraft - now fitted with the GE CH-5 turbosupercharger - recorded a maximum speed of 505 miles per hour while flying at over 34,500 feet, the fastest speeds ever for a propeller-driven aircraft. Such capabilities gave the XP-47J the nickname of "Superbolt".

Notably, in USAAF hands during testing, the XP-47J is said to never have been able to exceed speeds beyond 493mph.

XP-47J remained a viable fighter development until it was found that another Republic offering, the XP-72 "Ultrabolt" (detailed elsewhere on this site) was showing more promise and more company personnel were appropriately being assigned to this venture instead of the Superbolt. Additionally, Army authorities were put off by the fact that Republic lines would have to be considerably retooled to accommodate mass production for the proposed XP-47J - there was only some 30% commonality of parts between base, in-service P-47 fighters and the proposed XP-47J. As such, this fast fighter prototype born from the P-47 line died before the end of the war in 1945.


Our Data Modules allow for quick visual reference when comparing a single entry against contemporary designs. Areas covered include general ratings, speed assessments, and relative ranges based on distances between major cities.

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Relative Maximum Speed Rating
Hi: 750mph
Lo: 375mph
    This entry's maximum listed speed (505mph).

    Graph average of 562.5 miles-per-hour.
City-to-City Ranges
Graph showcases the Republic XP-47J's operational range (on internal fuel) when compared to distances between major cities.
Aviation Era
Pie graph section
Pie graph section
Pie graph section
Pie graph section
Pie graph section
Useful in showcasing the era cross-over of particular aircraft/aerospace designs.
Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units

  * Commercial Market High belongs to Cessna 172.

  ** Military Market High belongs to Ilyushin Il-2.

Altitude Visualization
Small airplane graphic
Supported Roles
Ground Attack
Aerial Tanker
A2A=Air-to-Air; UAV=Unmanned; CAS=Close Support; ASW=Anti-Submarine; AEW=Airborne Early Warning; MEDEVAC=Medical Evac; EW=Electronic Warfare; SAR=Search-Rescue
Supported Arsenal
Graphical image of an aircraft medium machine gun
Graphical image of an aircraft heavy machine gun
Commitments / Honors
Military lapel ribbon for Operation Allied Force
Military lapel ribbon for the Arab-Israeli War
Military lapel ribbon for the Battle of Britain
Military lapel ribbon for the Battle of Midway
Military lapel ribbon for the Berlin Airlift
Military lapel ribbon for the Chaco War
Military lapel ribbon for the Cold War
Military lapel ribbon for the Cuban Missile Crisis
Military lapel ribbon for pioneering aircraft
Military lapel ribbon for the Falklands War
Military lapel ribbon for the French-Indochina War
Military lapel ribbon for the Golden Age of Flight
Military lapel ribbon for the 1991 Gulf War
Military lapel ribbon for the Indo-Pak Wars
Military lapel ribbon for the Iran-Iraq War
Military lapel ribbon for the Korean War
Military lapel ribbon for the 1982 Lebanon War
Military lapel ribbon for the Malayan Emergency
Military lapel ribbon representing modern aircraft
Military lapel ribbon for the attack on Pearl Harbor
Military lapel ribbon for the Six Day War
Military lapel ribbon for the Soviet-Afghan War
Military lapel ribbon for the Spanish Civil War
Military lapel ribbon for the Suez Crisis
Military lapel ribbon for the Vietnam War
Military lapel ribbon for Warsaw Pact of the Cold War-era
Military lapel ribbon for the WASP (WW2)
Military lapel ribbon for the World War 1
Military lapel ribbon for the World War 2
Military lapel ribbon for the Yom Kippur War
Military lapel ribbon for experimental x-plane aircraft
* Ribbons not necessarily indicative of actual historical campaign ribbons. Ribbons are clickable to their respective campaigns/operations.