Nine things you need to know about the excellent P-47 Thunderbolt

It was not “best in class” in any category, however, it was very good in just about every category. Fast, long-legged and well-armed, it was also the most survivable fighter of the entire war. In scale and concept, the P-47 was a design outlier, and was different from every other fighter of the war.

Somehow, the unusual Thunderbolt came together in a magical way that resulted its outstanding operational record. Myth and misconception surround the aircraft, and much of this leads to an under-appreciation of what the aircraft actually accomplished. This article will dive into some of those misconceptions and look at the real capabilities of this ferocious flying juggernaut.

The P-47 is the largest single piston-engined fighter ever built. And it is indeed large and heavy! Its empty weight is similar to or greater than every other contemporary single-engine fighter’s maximum weight. It is over twice as heavy as the original Spitfire and Me 109 fighters.

There is a common misconception that large size and weight correlates with low performance. The perception is that a larger aircraft will be slow, lumbering, not very manoeuvrable, and ineffective.

Both manoeuvrability and speed are the key performance qualities of a good fighter.

The second parameter, power-to-weight ratio, states the power of the engine relative to the weight of the aircraft, measured in horsepower per pound or kilowatts per kilogram. This parameter is directly related to the top speed of the aircraft, but also to the takeoff and climb performance.

A high power to weight ratio results in an aircraft that will climb and cruise faster than a competitor with a lower ratio. The bottom line is that size and weight of an aircraft do not determine the aircraft performance. It is quite possible to build a large and heavy high-performance fighter, as long as it has the right sized wing, and a big engine.

The P-47’s designer Alexander Katvelli turned to the new R-2800 twin-row radial engine being developed by Pratt & Whitney as the only viable powerplant. This engine had over 50% more displacement than the Allison, and initially had 33% more horsepower. A problem that plagued US fighters of the day was the lack of sufficient power and performance at higher altitudes.

Most of the contemporary American engines used a single-stage, single-speed supercharger. This design leads to significant falloff in power at altitudes starting around 15,000 feet. The combat experience in Europe was showing that the air battles were often going to be fought much higher than this.

The R-2800 engine had a single-stage supercharger which was integral to the engine. The P-47 design added an exhaust-driven turbo-supercharger to create a second stage. A turbo-supercharger is effectively a variable speed device, being engine exhaust-driven and having a wastegate control system. This allows peak engine power throughout a wide range of altitudes.

The downside of a turbo-supercharger is that the installation occupies a lot of space. Fortunately, the P-47 was already being drawn as a large fighter, and Kartveli was able to squeeze the turbo and even larger intercooler into the belly of the aircraft.

There are at least four aspects that affect what we call “manoeuvrability.” First is the aircraft’s roll rate, or how fast the pilot can bank the wings when choosing to fly in a different direction. The most important manoeuvrability aspect is the turn rate. However, there are really two versions of this: instantaneous and sustained. Instantaneous turn rate is the maximum rate at which you can turn as soon as you roll to a given bank angle and pull back on the stick. The aircraft wing is what determines instantaneous turn rate.

Then there’s maximum sustained turn. As you slow down in a turn, the drag will decrease and eventually you will reach a point where drag matches the thrust your engine can produce, and you can sit here turning until your fuel runs out. A fourth manoeuvrability aspect is the turn rate and turn radius.

Let’s get back to the P-47. How did it rate in the manoeuvrability category? The basic answer is “pretty good.” Many fighters could outturn it, especially at lower altitudes. But the margin was small – small enough that a better pilot in a P-47 could often outturn a lesser pilot in a Bf 109 or Fw 190; it takes a lot of skill to precisely fly a fighter at its maximum turn performance.

The P-47 wing loading was not as low as some of the higher-performance fighters and its instantaneous turning ability was a little less because of this. However, the big R-2800 engine really helped its sustained turn performance.

The range of the P-47 is probably the most misunderstood part of its performance. You often hear about how Mustangs could exclusively escort bombers all the way to Berlin, and thus turned the tide of the war. The real story is much more complicated and steeped in US Army Air Force politics.

The reality is that the P-47 could also escort to Berlin and further much earlier than many people think. Aircraft range is a simple parameter affected primarily by two things. First is how efficient the aircraft can fly at given speed and altitude measured by how much fuel it needs per hour.

Second is how much fuel it can carry. The P-47 does burn a lot of fuel with its large size and weight. However, this larger size also allows it to carry proportionately more fuel. Per the pilot’s manual, the P-47D with maximum internal fuel could fly 890 miles (compared to 1,120 for the Mustang). With two drop tanks (as pictured), the Thunderbolt range increases to 1,360 miles, leaving plenty of margin for the 1,000 mile round trip from England to Berlin.

In level flight, the Thunderbolt top speed performance is much like the rest of its performance envelope. It was not the fastest aircraft at any altitude. But it was very fast and was quite competitive in top speed. This is particularly true at high altitudes, where its engine produces superior horsepower.

PICTURE: P-47s at East Field, Saipan, in 1944

At 30,000 feet, the P-47D was within 7 mph of catching a P-51D, and significantly faster than an Fw 190A-8 or Bf 109G.The final P-47N version was extremely fast, again, especially at high altitude. Its R-2800 engine could produce 2,800 horsepower with water-methanol injection and this resulted in a top speed of 470mph.

Donald Balkeslee, the first Thunderbolt ace is quoted saying “It ought to be able to dive, because it certainly can’t climb.” Just like manoeuvrability, the ability to dive is complex and affected by many parameters. At the beginning of a dive you have to manoeuvre the aircraft into a diving attitude, either by pushing the nose over, or rolling upside down and pulling the nose down.

Once you are in a nose-down diving attitude, the aircraft will accelerate due to the relative balance of aircraft weight, drag, and thrust available. All of these affect the acceleration rate, and your ability to pull away from (or catch) an opponent who is also diving.

The P-47 was excellent in every dive aspects, which makes it one of the best diving aircraft of the period. With its throttle-body fuel injection, the engine did not suffer from negative-g fuel starvation like the early Merlin engines. So a pilot could freely push the nose over to initiate a dive without the fear of the engine cutting out.

Once in the dive, the P-47 accelerated quickly due its engine power and reasonably low drag. Best of all, the Thunderbolt had one of the highest dive speed and Mach limits of any fighter of the era.

The P-47 had eight Browning M2 50-calibre machine-guns, four in each wing, whereas most contemporary fighters had no more than six. The Thunderbolt sometimes gets criticised for not having any larger-calibre cannon. The aircraft certainly could have carried them.

However, for its intended mission of destroying enemy fighters, the 50-calibre round is quite effective, and the combined firing rate of its eight guns meant a much higher probability of getting hits than with a slower-firing cannon. This large aircraft could carry 3400 rounds of ammunition which, for comparison, was 65% more than a P-51.

In addition to the guns, the P-47 could carry a heavy load on its external hard points. Between two wing racks and a belly rack, the aircraft could carry up to 2500 lbs (1136kg) of external weapons. Initially this mostly consisted of bombs. Later, the aircraft was equipped to carry ten “High Velocity Aircraft Rockets” or HVAR (pictured).

These unguided rockets did not have pinpoint accuracy, but were quite effective against larger ground targets. Each had a 45-pound warhead which was equivalent to a 105-mm Howitzer artillery round.

The P-47 had thicker armour in more locations around the pilot than any other contemporary fighter. There were a lot of other features on the aircraft that offered protection and made the aircraft more survivable in a crash landing. With a smooth belly free of cooling features, the aircraft responded well in a gear-up landing with minimal tendency to overturn.

Additionally, the fuselage contained an internal belly skid structure that contributed to survivability in a crash. It also made the aircraft more repairable after the crash. The original razorback P-47 had a substantial roll-over structure behind the pilot. This was omitted in later versions with the bubble canopy due to a low occurrence of roll-over accidents and the added benefit of better pilot visibility.

PICTURE: Flying ace Second Lieutenant John Thornell of 328^th Fighter Squadron in his P-47; he had 17 aerial victories during the Second World War

An aircraft with an air-cooled-engine is generally considered more survivable than a liquid-cooled counterpart. The cooling lines and radiators are particularly vulnerable in that the engine will likely quit soon after a single hit to one of these systems. By comparison, an engine can typically run much longer after a hit to air cooling ducts, or even the turbocharger (at reduced performance).

All of these resulted in a very survivable aircraft. The top-10 Thunderbolt Aces all survived the Second World War. This is a statistic not shared by any other aircraft.

PICTURE: Pilots of the 486th Fighter Squadron, 352nd Fighter Group, with a P-47 Thunderbolt at RAF Bodney air base in March 1944

All of these factors contributed to the P-47 being a very effective fighter in the Second World War, against both air and ground targets. The overall aircraft destroyed and the kill ratio for the P-47 was impressive. By the end of the war, the Mustang had beat the Thunderbolt in both of these categories, by a healthy margin. However, these metrics alone don’t tell the complete story. You have to factor in both how and when the aircraft was used.

The Thunderbolt started flying significant combat missions in Europe in the spring of 1943. This was around nine months before the Mustang arrived. During this time, the Luftwaffe was at the peak of its experience and effectiveness. This provided a very challenging opponent for the Thunderbolt pilots. By the time the Mustang was flying in significant numbers, the establishment of Allied air superiority was setting in, and many of the more experienced Luftwaffe pilots were no longer in the fight.

Additionally, the German aircraft had a more difficult time keeping up with the performance advances of the Allied aircraft due to a shortage of certain materials and high-octane fuel. Before the Allied invasion on D-Day, The P-47 had amassed over three times the combat flight hours of the P-51, and 50% more than the P-38.

PICTURE: An RAF P-47 at Jumchar, India, in 1945; note the B-29 in the background.

A second factor is how the aircraft was used. Due to its superior firepower (and a reduced threat from the Luftwaffe) more P-47 sorties were ground attack missions in the later stages of the war. While these missions were highly effective and greatly appreciated by the ground forces, they don’t contribute to air-to-air statistics, which is how most people judge a fighter’s effectiveness. However, there is much more to the story than these simplified statistics.