Authored By Dan Alex (Updated: 3/20/2016):
Though not too pretty to look at, the Thunderbolt had "it" where it counted - through her stressed metal skin, robust airframe and powerful engine. Her weight never made her a prominent close-up dogfighting champion but this drawback allowed her to excel in "dive and zoom" attacks against enemy fighters while proving her equally adept at ground strikes accomplished through the battery of eight heavy machine guns, 5-inch rockets and conventional bombs. In the end, this unsung hero of World War 2 proved that she played second fiddle to no one - regardless how sexy a design she was up against. The P-47 proved such a fearsome foe that Axis infantrymen on the ground dreaded the day they would have to encounter the "Fatty from Farmingdale" coming out of the skies with her eight machine guns ablaze. The Thunderbolt served in every major combat theater of World War 2.
Alexander de Seversky
Alexander Nikolaivitch Prokofiev de Seversky was born into a wealthy aristocratic family in Tiflis, Georgia, then part of the Russian Empire. Though thousands of miles away from any American city, this family name would help to one day bring about the creation of the fabled P-47. As no one thing was out of reach for such a family, one of the prizes under Seversky ownership became one of the first airplanes in the country of Russia. As such, Alexander Seversky learned to fly at an early age and a passion for all things flight and an equal passion for all things mechanical soon evolved from within. Seversky was then enrolled in military school by age 10 and went on to graduate from the Russian Imperial Naval Academy in 1914. By the time of World War 1, he was stationed aboard a destroyer as a sailor with the Russian Navy in the Baltic Sea but his first passion remained flying - and he was quite good at it. Shortly after 1915, he transferred out of the Navy and attended the Military School of Aeronautics only to return to the Russian Navy - this time as a pilot.
After his re-assignment, Seversky was installed into one of Russia's burgeoning flying squadrons. He was charged as pilot of a two-man bombers with a comrade - the observer/rear gunner - in the second cockpit. Seversky took to the air in what may have felt like a "routine" (if there's anything routine about combat) mission against German destroyers. During the initial attack, his aircraft took serious ground fire, foiling the attack and forcing the aircraft into the sea. To add insult to this mishap, the unexploded ordnance under the wings now detonated, instantly killing his observer and severely mutilating Seversky's leg. While eventually rescued, Russian doctors were forced to amputate the damage leg and Seversky's flying career was all but over.
Recovered from his wounds and now fitted with a wooden leg, Seversky set out to reclaim his former position as a flyer with the Russian air service. While his superiors balked at such a notion, Seversky illegally took to the skies in an aircraft during an aerial exhibition complete with high ranking Russian military officials in attendance. While his airborne actions proved him a sound pilot still, Seversky was promptly incarcerated for his actions but later pardoned by Czar Nicholas II. Seversky was then granted his flight status once more and was airborne in 1916. From there, Alexander Seversky went on to become the Russian Navy's leading combat ace, accruing somewhere between 6 to 13 kills (sources vary widely on this account). Leg or no leg, Seversky was going to fly as long as his heart was beating.
This is Pure Bolshevik!
In 1917, Seversky was part of an envoy sent to the United States to study aeronautical practices and construction techniques throughout the country. America was home to the assembly line and it seemed the perfect place for any developing industrial powerhouse to take notes. However, 1918 saw Russia fall to the Bolsheviks, putting Seversky - with his wealthy aristocracy origins - in jeopardy and dissolved any notion of returning safely to his motherland. As such, he elected to remain in the United States where his combat background and engineering talents were put to use with Curtiss Aeroplane. Seversky served as both test pilot and aeronautical engineer for the firm eventually having his hard work rewarded by a promotion to Major in the US Army Air Corps Reserve.
An entrepreneur at heart, Seversky was quick to protect his innovations when it came to aircraft development. While securing a patent for an early air-to-air refueling technique, he also made headway in the development of a bombsight system which he developed with help from the Sperry Gyroscope Company, also netting Seversky a patent to protect this work. The US military purchased the rights to the bombsight system in 1923 for the large sum of $50,000 and this proved a sound financial ground for which Seversky could begin his own company - aptly named the Seversky Aero Company. However, the financial Crash of 1929 did this first venture in.
Undeterred, Seversky persevered and, netting additional funding from outside parties, began Seversky Aircraft in 1931. He tapped former fellow Russian (Georgian) engineer Alexander Kartveli who had made his home in Paris after the fall of Russia to the Bolsheviks in 1918. The firm found some early success with their new SEV-3 Sport Amphibian aircraft. The three-man aircraft was capable of landings on land and water and garnered a US military contract for production as the BT-8 trainer.
Motivated by the success of the BEV-3, Seversky pursued more advanced designs. His firm moved to Farmingdale, Long Island, to a more spacious outcropping in an effort to build their Army BT-8 trainers. A new competition netted another contract for the Seversky P-35. The P-35 was hardly a burner at 260 miles per hour, but more "modern" fighters with enclosed cockpits and stressed metal skins were needed by the US Army nonetheless. Developments in Europe by this time far outclassed American aircraft by what seemed like leaps and bounds. Regardless, the P-35 entered service in 1938 but were sorely out of date by the time of the Japanese attack on Pearl Harbor on December 7th, 1941.
The P-43 Lancer
A new Seversky demonstrator was already in the works, this fitted with a General Electric supercharger coupled to a Pratt & Whitney R-1830 radial piston engine and designated by the company as the AP-4 - essentially an improved form of the P-35. The Army liked what it saw and granted a contract for 13 evaluation models to be designated as the YP-43 "Lancer". By the end of 1939, Seversky himself went off to England to try and sell his products with the hope of netting more lucrative wartime contracts from desperate European nations looking to match up to the might of the German war machine. It was during this time that the Seversky company Board of Directors delivered a no-confidence vote for Alexander Seversky and ousted as company president. The firm was reformed under the Republic Aviation name and retained the services of Alexander Kartveli as chief engineer for the firm. Seversky himself was out of the picture.
Work on the Lancer continued. The YP-43 was fitted with 2 x .30 caliber machine guns and 2 x 50 caliber heavy machine guns but did not feature self-sealing fuel tanks nor protective armoring for the pilot. The P-43 Lancer entered limited production but did not prove an answer for the US Army. An improved form of the aircraft emerged as the P-44 "Rocket", to which the US Army became quite enthusiastic about, but unfolding events in Europe quickly deflated such enthusiasm. As the Army looked to the air war ongoing over France and Britain, it realized that even the "Rocket" could not accomplish in combat what the nimble fighters over in Europe were doing. These aircraft sported sleek designed frames with relatively powerful in-line, liquid-cooled engines and equally powerful armament to boot. The Army made out a wish list for their next fighter and found that it required an interceptor capable of at least 400 miles per hour at 25,000 feet with an armament of at least 6 x .50 caliber machine guns, long range and protection for the pilot and fuel tanks for extended ranges.
With war inching ever closer, time was of the essence. A new Republic design centered around the Allison V-1710 liquid-cooled V-12 in-line piston engine - closely resembling the powerplant found on the streamlined Bell P-39 Airacobras, Curtiss P-40 Warhawks and the Lockheed P-38 Lightnings. The design took the company designation of AP-10 and, by 1939, Kartveli had completed drawings for the aircraft consisting of the smallest possible airframe. He added some impressive performance estimates that saw the new aircraft hit speeds of 415 miles per hour (in theory). The experimental section of the US Army, based out of Wright Field, took a closer look and offered some subtle changes that included a slightly larger overall airframe with added weight and more surface area. Two hardpoints were set under each wing and armament was a strange pairing of 1 x .30 caliber machine gun and 1 x .50 caliber machine in the upper cowling.
Sensing good things from the preliminary design and, more importantly, still in dire need of modern fighters, the US Army rushed to get the AP-10 into production under the prototype designation of XP-47. The program would begin development in two complete airframes - the XP-47 and the XP-47A. The XP-47 was a full-fledged offering complete with combat armament while the XP-47A would be a flight test model sans combat options but intended to test out the design's validity in controlled experiments. The program was given a window of nine months to produce the end products.
Further review of the XP-47 design by the US Army funding department (those in control of the money) forced yet more revisions. The wing surface area - deemed too small on the original design - was enlarged and an additional .30 caliber and .50 caliber machine gun were added. Self-sealing fuel tanks and armoring were also now included. These options of course drove up the overall weight of the aircraft that was intended to be an interceptor - if an interceptor could not climb within reason, it was no longer considered an interceptor.
Back to the Drawing Board - the XP-47B: the True Thunderbolt Prototype
By this time, the war in Europe was changing on a monthly basis as were the tactics and technology. Pratt & Whitney unveiled their R-2800 Double Wasp, two-row, 18-cylinder air-cooled radial piston engine and rated their massive product at 2,000 horsepower. Though more fuel-thirsty than the original Allison in-line to be used, the Double Wasp promised much more in the way of output and performance over her predecessor. Kartveli tried a second design attempt to fit this new engine into an applicable airframe as the diminutive AP-10 was much too small to handle such a powerplant. The stout new design emerged with 6 x .50 caliber machine guns fitted to the wings, adequate armor protection, self-sealing fuel tanks, large surface areas and an operational weight of 12,000lbs. This new design was given the designation of XP-47B while the XP-47 and XP-47A quickly fell into oblivion, the two ultimately cancelled in full. The US Army was smitten with the prospect of this large 400 mile-per-hour beast and quickly placed a 773-strong production order for the XP-47B on September 6th, 1942 - this before a single prototype was even made available. Amazingly, only one XP-47B would be built while no service test models (YP-47Bs) were ordered - quite the departure for the careful, though now desperate, US Army.
What a Turbosupercharger (or Turbocharger) Actually Does
High altitude performance was a necessity in the new design as dogfights cared little of operational ceilings. As such, a large and complicated turbosupercharger (also known as a turbocharger) was deemed a must for such activities. The turbosupercharger essentially provided for sea level-rated operations at altitudes up to the engine's critical altitude - that is - the maximum altitude an engine could sustain its rated horsepower output at without seeing a decrease in performance. The turbosupercharger featured a turbine that was driven by exhaust gasses from the engine as well as a compressor with a high-speed impeller that pressurized the incoming air. The resulting action produced high-pressure, high-density air which was then re-delivered to the engine to maintain an applicable output at higher altitudes.
Republic engineers placed this system behind the cockpit in an effort to maintain a proper center of gravity and improve stability. The turbosupercharger would then require ductwork to run to and from the engine/turbosupercharger to deliver the gasses for the required boost in performance. Once implemented, this duct system forced the XP-47B to take on a "deep" look fuselage and gave the P-47 its universally identifiable profile but, at the same time, added much-needed room for internal fuel stores to power the thirsty Pratt & Whitney.
The fuselage was affixed to two elliptical wing assemblies complete with rounded edges. The wings would contain the primary standard armament, applicable ammunition stores and main landing gears. The tail surfaces were encased in fabric covering for the time being while the rest of the body was of all-metal stressed skin. The Pratt & Whitney powerplant needed a quality propeller system to make the most out of the horsepower output and, as such, a 12 foot, 2 inch diameter four-blade propeller system was selected to cap the nose of the XP-47B. A new problem quickly arose, however, in implementing such a large diameter propeller blade. The tall propeller system needed clearance along the ground during take-off and landing. Rather than produce an ungainly looking bird with obscenely long landing gear legs, a telescoping landing gear leg system was devised where the assembly could extend out to 9 inches when lowered and retract that length when the leg was pulled up. This issue was not unlike the issue forced onto the designers of the Vought F4U Corsair fitting their own large three-blade propeller. In that particular case, the engineers elected to use an inverted "gull" wing to offset the need for height. Ingenuity for the Americans seemed to come naturally at this time. Unlike production P-47s, the XP-47B featured a canopy that was hinged over to the side with an automobile-style entry/exit door. This would later be replaced after the system was prone to jamming and proved too cumbersome during emergency exits via parachute.
Flight Testing of the XP-47B
The XP-47B was finally constructed to the new specifications by Republic to which the name of "Thunderbolt" was officially assigned (the US had not been in the habit of naming its military creations until the British did so with American Lend-Lease tanks and aircraft). The XP-47B achieved first flight over Farmingdale, Long Island, on May 6th, 1941 and - at the time - became the largest piston-powered single-engine fighter aircraft to fly (not to mention the most expensive). The XP-47B was flown to a US Army base at Mitchel Field for a perfect landing. By all accounts, the large aircraft was a winner despite some oil falling burning off of the turbosupercharger and consequently filling the cockpit with black smoke. After the first flight, some further recommendations bought about more fine tuning including the use of a pressurized ignition harness, wing stiffeners to combat flutter and a new type of engine oil lubricant.
One of the biggest items of note to come out of further testing of the XP-47B was the diving prowess of the airframe. One such power dive netted a speed of 550 miles per hour, pulling off the fabric covering over the tail surfaces in the process. Other items of note included the need for vast amounts of runway required to help the "Heavy" take off as well as a "control freeze" situation encountered by the control surfaces during steep dives - both could prove fatal to the untrained Thunderbolt pilot if not respected.
The P-47B is Delivered
Four early-production Thunderbolts (their hinged cockpits replaced in favor of a rearward sliding "greenhouse" type) soon emerged and, after similar power dive incidents involving torn fabric on the tail surfaces (one such incident leading to the death of a Republic test pilot), the surfaces were covered over in all-metal stressed skin. The first operational-level P-47B was officially handed over to the US Army on May 26th, 1942. In an effort to test out the new aircraft while at the same time garnering valuable experience to new pilots, the US Army formed the 56th Fighter Group squadron at Farmingdale to defend the northeast American coast from the fears of German bombers encroaching across US airspace. The learning curve for these lads was not a light-hearted affair for the squadron would lose up to half of their delivered Thunderbolts to accidents (13 pilots killed while 14 airframes were lost).
One hundred seventy-one P-47B production Thunderbolts were produced at the Republic Farmingdale plant in a short 6 months. The P-47C underwent extensive flight trials with the US Army who then ultimately deemed it clear for operational combat. In practice, the P-47 proved to have a tremendous roll rate, better than that of any current US fighter, and offered many exceptional qualities considering her size. No doubt the "greenhouse" canopy, raised fuselage spine and massive engine mounting curtailed pilot vision but, in all, she was a fantastic creation from the people at Republic. Her range was shorter than anticipated no thanks to the Pratt & Whitney powerplant and her rate-of-climb clearly put her out of the interceptor category altogether but she was something that no current US fighter could match.
Production was already underway at the Republic plant at Farmingdale but demand was such that a new plant was opened up at Evansville, Indiana and Curtiss-Wright was also enlisted to license-produce the type at their Buffalo, New York facility. With production ramping up and the US Army ready for action, the P-47C Thunderbolt was crated up and shipped by boat to England for final assembly and squadron training. The first shipment arrived on the British Isle on December 20th, 1942.
The Thunderbolt's stout appearance makes her one of the most memorable American warplanes of World War 2. Her size was necessitated by the addition of the turbosupercharger and all her applicable ductwork, causing the deep fuselage to take shape. The turbocharger helped to balance the design and featured large diameter ductwork running from charger to engine and back. The large air-cooled Pratt & Whitney Double Wasp engine was contained in the extreme forward of the fuselage, which itself was more elliptical in shape - almost an upside down egg when viewed from the front - than one might realize at first glance. A four-bladed Hamilton-Standard propeller (later refitted with a Curtiss Electric unit) was fitted to a simple spinner at the opening of the engine and intake duct openings were readily present just under the engine face. Wings were of the monoplane type and low-mounted, somewhat forward, along the slender streamlined fuselage. The cockpit was placed just above and slightly ahead of the wing trailing edges. The main wings themselves - another distinguishable characteristic of the P-47 and purely a Republic trademark - were elliptical in shape, sporting rounded edges with a straight leading edge and tapered trailing edge while showcasing some dihedral in the forward profile. The cockpit was situated at about the midway point of the fuselage and early Thunderbolts maintained the "razorback" spine that contoured into the top portion of the empennage. The empennage was dominated by a small-area vertical stabilizer and a pair of horizontal stabilizers. The fuselage progressively tapered down to a rounded cap at the base of the tail.
The keen observer will note the P-47s outward resemblance to Seversky's/Republic's earlier design attempts in the Seversky P-35 and Republic P-43 Lancer respectively.
Both Axis and Allied pilots having the pleasure of flying the P-47 noted the type's exceptionally roomy interior. The cockpit (P-47D) sported clean lines and clustered major dial groups that were well-placed. The pilot sat in what was sometimes termed a "lounge chair" by some and air conditioning was standard. The forward instrument panel was dominated by the top-mounted K-14A gunsight. All major in-flight readings (navigation, altitude) were situated along the upper half of the panel while engine and fuel controls took over the lower half. Bomb/tank selectors were clustered on a panel along the lower left side of the forward instrument group with the throttle to the pilot's left-hand side. The throttle contained a rotating handle to adjust the scale of the gunsight in an effort to keep important controls within reach at all times. Overall control of the aircraft was accomplished through a conventional flight stick with integrated trigger. Rudders were set under the forward instrument panel at the pilot's feet and could be folded down for long flights allowing the pilot to stretch his legs some.
Vision from the cockpit was remembered as adequate to good. Considering the pilot's seat was situated well behind the large engine, this was expected. The large-area main wings also obscured downward vision and the "razorback" raised spines in early-form Thunderbolts didn't help vision to the "six". The implementation of a British-based "teardrop" bubble canopy alleviated the latter problem and much of the heavy framing of the early "greenhouse" canopies was lost in the process. Test pilots of the new canopy were elated at the refreshed vision out of the cockpit. The new canopy slid rearwards (as opposed to the early side-opening ones) to allow for pilot entry/exit and was first utilized on a modified P-47D-5 (as the XP-47K) in the summer of 1943.
The undercarriage was typical of the time and categorized the P-47 as a "tail dragger". The arrangement consisted of two single-wheeled telescoping main landing gear legs (one to a wing) and a diminutive tail wheel under the base of the empennage. The main legs recessed inward under the wings toward the fuselage centerline while the tail wheel was equally as retractable at the base of the empennage. When at rest, this configuration gave the Thunderbolt a noticeable "nose-up" appearance and made for very poor vision out of the cockpit when taxiing into position. The large diameter four-blade propeller necessitated the use of long legs to help the aircraft clear a runway without the blades hitting the surface of the pavement.
The Thunderbolt's wings were constructed with two major spars running nearly the length of the each wing. Spars were charged with the handling of flight loads when airborne and the carrying the wing's weight when on the ground . Republic engineered each Thunderbolt wing assembly to fit 4 x M2 Browning air-cooled .50 caliber heavy machine guns in a staggered arrangement. The P-47 was the only American fighter aircraft to wield this many machine guns (20mm cannon armament was considered early on but dropped from contention). The staggered formation of these machine guns allowed for effective feeding of the systems from four separate ammunition holds. The power of these combined eight machine guns could effectively engage fighters and bombers while being of equal value when tackling ground-based targets. A single burst was enough to down most any aircraft. Such armament could output a staggering 13lbs of blazing hot ammunition on a target per second.
In addition to its formidable machine gun battery, the P-47 made a living under the clouds for German troops a pure hell. With underwing mounts, she could field up to 2,500lbs of conventional drop bombs or 10 x 5-inch unguided HVAR rockets useful against ground- and water-based targets. Drop tanks could be carried in place of munitions and situated along the fuselage centerline (x1) or underwing (x2).
One known conversion of a P-47 attempted to mount 2 x underwing Oldsmobile 20mm cannons. While an awesome prospect in theory, the fitting proved a disappointment in practice, adding unnecessary drag and thusly lowering the Thunderbolt's top speed by 50 miles per hour. This single P-47 was eventually converted back to her base operating form with standard armament.
The Variants (In Alphabetical Order)
The XP-47B was fitted with a Pratt & Whitney R-2800-17 radial piston engine of 2,000 horsepower attached to a 12 feet, 2 inch diameter Curtiss Electric four-blade propeller. The aircraft sported an empty weight of 9,189lbs and a gross weight of 12,700lbs. Maximum speed was listed at 412 miles per hour at 25,800 feet with a maximum range of 1,150 miles at 10,000 feet. Five hundred rounds of .50 caliber ammunition were afforded her 8 x guns.
The P-47B mounted the Pratt & Whitney R-2800-21 series radial piston engine of 2,000 horsepower and entered production in 1942 with deliveries to the USAAF in England beginning in early 1943. At least 171 P-47B production models were delivered. Many B-models were eventually relegated as trainers to get the young pilots use to these large and heavy mounts - truly no American aircraft before it could match the qualities (and drawbacks in some cases) of this heavy hitter from Farmingdale. The P-47B maintained a maximum speed of 429 miles per hour with a range of 550 miles. The service ceiling was listed at 42,000 feet with a rate-of-climb equaling 2,560 feet per minute. A "one-off" reconnaissance form was built with the designation of RP-47B.
While essentially similar to the B-models before them, the P-47C brought about a more powerful engine series in an lengthened fuselage as well as implementation of a droppable belly fuel tank (or bomb if need be). The external fuel tank finally allowed for sorties to Berlin and back. The fuselage was extended by a full 8 inches which allowed engineers to move the engine forward some and improve the Thunderbolt's center of gravity. The addition of the centerline hardpoint added ground attack capabilities to the Thunderbolt's toolbox. The tail section was further strengthened to counteract the resulting stress of those power dives and a 30 gallon water tank was added to "fuel" the water injection system of R-2800-59 engined Thunderbolts. The first 112 P-47C models were fitted with the Pratt & Whitney R-2800-21 radial engine of 2,000 horsepower as the R-2800-59 series engines (and their respective water-injection systems) were not yet available. As such, only later versions carried the improved radials with the increase of almost 300 horsepower. At least 602 C-models were produced.
P-47C models sported an empty weight of 9,900lbs with a maximum weight of 14,925lbs. Maximum speed was 420 miles per hour at 30,000 feet with a service ceiling of 42,000 feet and a range of 835 miles at 10,000 feet. 300 to 425 rounds were afforded to her 8 x .50 caliber machine guns.
The All-Important D-Model...
The P-47D entered production from early 1943 onwards and proved the definitive Thunderbolt in the family line, arriving in Britain in April. A more powerful engine with water injection (known as "War Emergency Power" or "WEP", used for short enhancements of performance) greeted the design. The turbocharger was revised through better ductwork providing for improved efficiency. The pilot's position was granted more protective armoring and engine controls were simplified while landing gear tires were fabricated as "multi-ply" to take on the roughest of airfields. Three drop tanks could now be fitted and underwing hardpoints (the P-47D-15 and on) could now sport a 1,000lb bomb (one to a wing) or 10 x 5-inch rockets (5 to a wing). While an impressive armament load, this often meant that ammunition counts for the machine guns had to be reduced to compensate for the added weight. In some cases, a pair of machine guns were eliminated altogether. Later production D-models fitted the all-important bubble canopy which did away with the raise fuselage spine, improving pilot vision to his "six" ten-fold. It was not uncommon for D-models to be shipped unpainted from Republic factories, these appearing in their all silver bare metal finish, and saw a slight increase to performance. A mind-boggling 12,602 D-models made their way out of the factory doors and production constituted four large batches.
The P-47D was powered by the Pratt & Whitney R-2800-59 Double Wasp 18-cylinder air-cooled radial piston engine of 2,535 horsepower (or R-2800-21W of 2,300 horsepower with water-injection). She operated with an empty weight of 9,950lbs and a maximum take-off weight of 17,500lbs. Performance included a top speed of 433 miles per hour, a service ceiling of 41,000 feet, a rate-of-climb equal to 3,200 feet-per-minute and a range of 1,900 miles with three drop tanks in tow. The maximum external ordnance weight limit was approximately 2,500lbs. Standard armament included the 8 x wing-mounted M2 Browning air-cooled heavy machine guns.
...With a Few Test Developments In-between
The XP-47E was generated for the final P-47B. This developmental model came complete with a hinged canopy, Hamilton Standard propeller and pressurized cockpit used to trial the Pratt & Whitney R-2800-59 radial engine.
The XP-47F model was plucked from a P-47B and modified as a test-bed for laminar-flow wings. Testing revealed that the new wings would not improve performance much and the aircraft soldiered on in other related flight tests thereafter. She was officially lost in a fatal accident on October 14th, 1943.