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Republic XP-72 Ultrabolt

United States (1944)
Picture of Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor
Picture of Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor Picture of Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor

The Republic XP-72 Ultrabolt would have been an exceptional fighter but the Allied advance in both Europe and the Pacific derailed its promising development.


Detailing the development and operational history of the Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor.  Entry last updated on 12/26/2016. Authored by Staff Writer. Content ©www.MilitaryFactory.com

The Republic XP-72 Wasp Major-powered "Super Thunderbolt" (or "Ultrabolt") was being developed in the latter part of World War 2 (1939-1945) as the ultimate incarnation of the war-winning P-47 Thunderbolt fighter/fighter-bomber (also produced by Republic). The XP-72 incorporated largely the same airframe with the massive, experimental Pratt & Whitney R-4360 "Wasp Major" series engine rated at 3,450 horsepower. As promising as the high-altitude fighter was becoming, the changing nature of the war ultimately found little need for such an aircraft. No more than two prototypes were produced.

As an expediency, the XP-72 made use of both the proven fuselage and wings of the P-47 before it. Some alterations to accommodate the large Pratt & Whitney were made to the airframe and this included a revised lower cowling to allow for proper aspiration of the engine. A large-diameter, four-bladed propeller unit was affixed to the powerplant. The aircraft was indeed considered the "Super Thunderbolt" when compared to the original P-47 offering.

Developed as soon as the P-47 was entering service, the Republic team focused on two preliminary designs that were to take the beneficial design qualities of the existing P-47 and improve upon it wherever possible. The United States Army Air Force (USAAF) accepted both initial designs, one being an XP-69 mated with a Wright R-2160 radial engine and the other the XP-72 with its Pratt & Whitney. As the designs progressed, the XP-69 design - complete with high-altitude features including a pressurized cockpit and armament of 2 x 37mm cannons and 4 x 12.7mm machine guns - was dropped on May 11th, 1943, in favor of the more promising XP-72. Two XP-72 prototypes were then ordered on June 18th, 1943 with the air war in full swing over both the Pacific and Europe.

The first XP-72 prototype flew on February 2nd, 1944 (with a basic four-blade propeller) and development was very much unlike other aircraft of the period in that the program actually exhibited few delays as it progressed. The first prototype flew through the air with ease - even with the turbocharger off - at a very exceptional speed of 480 miles per hour (though neither XP-72 prototype would ever exceeded 500 miles per hour in flight testing). The aircraft proved quite responsive at the controls and pilots commented on it as being "a joy to fly". With the XP-72 achieving success in its early development, the aircraft was envisioned to rival the high-speed, high-altitude performance found in the latter series of British Supermarine "Spitfire" fighters while at the same time offering the operational range that the Spitfire lacked. Indeed, the XP-72 might have been a good candidate for V-1 rocket interception duty over the South of England than the Spitfires already charged with the task.

The second prototype was given an Aero Products contra-rotating propeller arrangement (a pairing of three-bladed units to a single engine, equaling six total blades) and an estimated maximum speed of 550 miles per hour. Primary armament was to become an array of 6 x 12.7mm (.50 caliber) machine guns mounted in the wings (a reduction from the 8 x 12.7mm machine guns in the original P-47 Thunderbol). An alternative weapons loadout built into the contract was to allowed for 4 x 37mm autocannons in place of all of the machine guns. As secondary armament, the aircraft was to carry high-explosive rockets, 2 x 1,000lbs bombs, or 2 x fuel droptanks as needed at hardpoints under each wing.

Despite the performance gains and relatively easy development process, the conditions in the latter years of the war were such that all-new high-altitude fighters / interceptors were in little demand as existing types were more than enough to fulfill the role. The simple truth became that the XP-72 was no longer a needed commodity in the grand scope of the war - particularly with prop-powered aircraft reaching their technological apexes and turbojet technology beginning to take hold. As such, the two XP-72 prototypes were dropped from further development and scrapped by war's end along with cancellation of a production contract for 100 of the type. The XP-72 "Super Thunderbolt" would go down as just another of World War 2's "what-if" programs that failed to materialize any tangible fruits by war's end - leaving to the imagination what impact, if any, such powerful aircraft would have had if promptly adopted into operational service.


Picture of the Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor
Picture of the Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor



Any available statistics for the Republic XP-72 Ultrabolt Prototype High-Altitude Fighter / Interceptor are showcased in the areas immediately below. Categories include basic specifications covering country-of-origin, operational status, manufacture(s) and total quantitative production. Other qualities showcased are related to structural values (namely dimensions), installed power and standard day performance figures, installed or proposed armament and mission equipment (if any), global users (from A-to-Z) and series model variants (if any).






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.

Image of collection of graph types

Relative Maximum Speed Rating
Hi: 500mph
Lo: 250mph
    This entry's maximum listed speed (490mph).

    Graph average of 375 miles-per-hour.
City-to-City Ranges
NYC
 
  LON
LON
 
  PAR
PAR
 
  BER
BER
 
  MOS
MOS
 
  TOK
TOK
 
  SYD
SYD
 
  LAX
LAX
 
  NYC
Graph showcases the Republic XP-72 Ultrabolt'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
2
2


  * Commercial Market High belongs to Cessna 172.

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


Altitude Visualization
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  Compare this entry against other aircraft using our Comparison Tool  
National Flag Graphic
Origin: United States
Year: 1944
Type: Prototype High-Altitude Fighter / Interceptor
Manufacturer(s): Republic Aviation - USA
Production: 2
Global Operators:
United States (cancelled)
Historical 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 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 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
* Ribbons not necessarily indicative of actual historical campaign ribbons. Ribbons are clickable to their respective campaigns/operations.
Measurements and Weights icon
Structural - Crew, Dimensions, and Weights:
Unless otherwise noted the presented statistics below pertain to the Republic XP-72 Ultrabolt model. Common measurements, and their respective conversions, are shown when possible.

Operational
CREW


Personnel
1


Dimension
LENGTH


Feet
36.61 ft


Meters
11.16 m


Dimension
WIDTH


Feet
40.91 ft


Meters
12.47 m


Dimension
HEIGHT


Feet
16.01 ft


Meters
4.88 m


Weight
EMPTY


Pounds
11,473 lb


Kilograms
5,204 kg


Weight
LOADED


Pounds
17,491 lb


Kilograms
7,934 kg

Engine icon
Installed Power - Standard Day Performance:
1 x Pratt & Whitney R-4360-13 28-cylinder air-cooled radial piston engine developing 3,450 horsepower.

Performance
SPEED


Miles-per-Hour
490 mph


Kilometers-per-Hour
788 kph


Knots
425 kts


Performance
RANGE


Miles
1,200 mi


Kilometers
1,931 km


Nautical Miles
1,043 nm


Performance
CEILING


Feet
41,998 ft


Meters
12,801 m


Miles
7.95 mi


Performance
CLIMB RATE


Feet-per-Minute
5,000 ft/min


Meters-per-Minute
1,524 m/min

Supported Weapon Systems:

Graphical image of an aircraft medium machine gun
Graphical image of an aircraft heavy machine gun
Graphical image of an aircrat automatic cannon
Graphical image of an aircraft conventional drop bomb munition
Graphical image of an aircraft external fuel tank
Armament - Hardpoints (2):

PROPOSED STANDARD:
6 x 12.7mm machine guns in wings

ALTERNATIVE STANDARD:
4 x 37mm cannons in wings

PROPOSED OPTIONAL:
2 x 1,000lb bombs, Rockets, OR Fuel Droptanks under the wings.
Variants: Series Model Variants
• P-47 "Thunderbolt" - Production Series Designation of base P-47 design on which the XP-72 was built upon; 8 x 12.7mm machine guns.
• XP-72 "Ultrabolt" - Prototype Series Designation; two examples constructed; 6 x 12.7mm machine guns; 1 x Pratt & Whitney R-4360-13 Wasp Major engine of 3,450 horsepower.