North American P-51 Mustang

The North American P-51, nicknamed Mustang, was a fighter aircraft that was developed by North American Aircraft in the United States during World War II. It is sometimes considered the paragon of piston-engined plane development.

First versions, NA-73, P-51A, Mustang Mk.1, A-36

Just after the start of the war in 1939, Sir Henry Self was posted to New York to see about purchasing US build aircraft for use by the RAF. On one of his trips he approached North American (NAA) about building the Curtiss P-40 Warhawk under license. At the time Curtiss was running full out for other customers (namely the USAAC), and North American was building their trainer aircraft for the RAF already. But Kindelberger at NAA replied that they could have a better aircraft with the same engine in the air in less time.

The result was the NA-73 project from March 1940. The design was fairly standard for the era, but included two new features. One was the use of a new NACA designed laminar flow wing design, which was larger than others on similar aircraft while still having the same drag. This left plenty of room for gear, guns, ammo and fuel, all completely inside the wing and well streamlined. Another was the use of a new radiator design from Curtiss, that used the now-hot air exiting the radator as a form of jet thrust.

The USAAC could block any sales they considered interesting, and this appeared to be the case for the NA-73. An arrangement was eventually reached where the RAF would get its planes, in exchange for NA providing two more for free to the USAAC.

The plane made its maiden flight on October the 26th, 1940. In general the plane handled well, and the internal arrangement allowed for a massive fuel load. It was armed with four .50" (50 cal) machine guns and another four 30 cal guns, considered to be a fairly heavy arms load for the era (the contemporary Spitfire had eight 30 cal).

It was evident that the performance of the plane was simply not up to European standards, due largely to the unacceptable supercharging of its Allison V-1710 engine. The US industry had concentrated mainly on the turbocharger instead of the supercharger, so this isn't very surprising. About twenty aircraft were handed to the Royal Air Force where they made their combat debut on May the 10th, 1942. However they were not deemed useful because of their lacking performance, and used mainly for short range ground-attack duties over the English Channel.

A derivative version, the Mustang Mk.IA, was made by the removal of the lighter guns in an effort to improve performance. At the same time the USAAC was becoming more interested in ground attack planes and had a new version constructed as the A-36 Apache which included two more 50 cal guns, dive breaks, and could carry two 500 pound bombs. Neither of these was particularily effective.

P-51B, P-51C

About the same time, however, the Mustang was checked by Rolls Royce engineers and test pilots. They were impressed by the great fuel capacity of the aircraft and its aforementioned armament. Rolls was currently building the Merlin engine Series 60 of about the same power, size and weight as the Allison, but with far better supercharging and considerably better altitude performance as a result.

Taking it on their own initiative, Rolls engineers did the obvious, and fitted a new Merlin 68 engine to four existing airframes. The result was a plane of unbeatable performance, simply put the plane could outfly anything in the air including the latest British fighters, but do so at huge distances from England. A license was sold to Packard to manufacture the Merlin as the V-1650, and production with this engine was started emmediately.

The pairing of the P-51 airframe and the Merlin engine was designated P-51B/C (B was built at Inglewood, California, and C at Dallas, Texas). The new version was used in 15 fighter groups, that were part of the 8th and 9th Air Forces in England, and the 12th and 15th in Italy (which had been liberated by that time).

The main task for which the plane was used was bomber escort. It was mainly due to P-51 that deep bombing raids became possible in the middle of 1944. Several hundred of the aircraft were given to the Allied Air Forces in China and Australia.

P-51D

The only other complaints about the aircraft were quickly fixed.

The gun-load had been lightened in the Mk.IA, and now it was beefed back up with the addition of another pair of the 50 cal guns for a total of six, the inner two on each wing having 400 rounds and the outer 270. They also added rocket-rails to the undersides of the wings to carry up to eight rockets.

The only other major concern was the very limited visibility to the rear, a problem the British had complained about, and then fixed, on their own designs. Many pilots took to fitting the canopy from later model Supermarine Spitfires to their Mustangs in order to improve the view. However the new model cut down the entire rear area of the fuselage and fit a "bubble" style canopy of new design which offered excellent all-round visibility. Removing this metal lowered the logitudinal stability, so a fillet was added to the front of the vertical stabilizer to improve it.

The resulting P-51D (and RAF P-51K version which differed very slightly) model was to become the most produced of all the Mustangs by far. The new version began to arrive in Europe in March of 1944, just in time to deploy for D-Day combat.

P-51H

The original NA-73 had been built stronger than the British requested. At the time they asked for planes stressed to loads of 5.33g, but the NA-73 was built to the tougher US standard of 7.33g which made it heavier. Both the USAAF and the RAF were interested in lightening the plane to be more in line with the Spitfire, which should boost its performance considerably.

This would result in what was basically an entirely new plane, and it gained a new name, the NA-105. Several prototypes were built with different engines as the F (same engine as the D), G (Merlin 145M) and J (Allison V-1710-119) models.

However none of these would go into production. Instead the final version would use the new V-1659-9 engine, a version of the Merlin that included automatic supercharger controls, and water injection for busts of up to 2,000hp. Combined with the fact that the new airframe had shed several hundred pounds and included a better streamlined radiator, its no surprise that the new plane was fast. In fact it is likely to be the fastest propellor fighter ever, able to reach 437 mph at 25,000 feet.

Production was just ramping up with 555 delivered when the war ended. Additional orders already on the books were cancelled.

F-51D

In 1946, the designation P-51D was changed to F-51D because of the new USAF naming convention. During the Korean War, P-51s, though technically obsolete as fighters, were used as tactical bombers. You may wonder why the P-51H was not used in Korea in place of the D model, but this was due to its lighter structure. With the planes being used for ground attack, the performance was less of a concern than their ability to carry a load. The last Mustangs were discarded by the USAF in 1957.

The P-51 was adopted by many air forces; the Israeli Air Force used them in the War of Independence (1948) and in Operation Kadesh (1956).

Effects of the P-51

The US effort to launch massive bombing raids into Germany took some time to build up. Throughout 1942 the numbers of bombers was quite limited, and the crews were new to their planes. Efforts didn't really get underway until 1943, and then only in limited form over France.

Based on the pre-war concept that "the bomber will always get through", their doctrine was to send in huge numbers of bombers flying in tight formation with heavy defensive gun loads. The RAF had done the same earlier in the war (albiet with lighter gun loads) and had found it largely impossible, switching to night raids.

But the USAAF pushed on anyway, launching several massive raids deep into Germany in late 1943. The result was a disaster, with well over 10% of the planes never returning to England, many more being written off after making it - per raid. A few more raids and there would be no bombers left.

It was clear that the bombers required fighter escort, but no fighter had anywhere near the range of the bombers. The existing P-38 Lightning came close, but this was a very expensive plane to construct and maintain. But the Mustang changed all that. In general terms the Mustang was as simple, or more simple, than other aircraft of its era. It used a single well-understood and increadibly reliable engine, and had internal space for a huge fuel load. With the addition of external fuel tanks it could protect the bombers all the way to Germany and back.

Numbers were available when the 8th and 9th Air Forces had re-grouped over the winter of 1943/44, and when the raids re-commensed in February 1944 things changed dramatically. Bomber losses prior to that point had been primarily (in percentages at least) from rocket-firing twin-engine designs, and these were chased from the skies.

However the Luftwaffe pilots learned how to avoid the US fighters by grouping in huge numbers well in front of the bombers, then attacking in a single pass and leaving. This gave the escorting fighters little time to react. But in May a new policy was instituted which allowed the fighters to roam away from the bombers and attack the German planes wherever they were found. This became a straight one-on-one fight, which the Mustang won almost every time.

By the summer of 1944 it was all over. The Luftwaffe had been swept clear from the skies and the US, and later British, bombers were free to roam over Germany at will during the day. Desperate efforts on the part of the Luftwaffe eventually delivered huge numbers of planes needed to regain control, but most of their pilots were already killed and the replacements didn't have any experience.

P-51s distinguished themselves while fighting against advanced enemy aircraft, be it V-1s that were launched into London (a P-51B/C with high-octane fuel was fast enough to catch up with one), Me 163 Komet interceptors or Me 262 jet fighters. General Chuck Yeager, flying a P-51D, was the first Allied pilot to shoot down a Me 262. The P-51s were deployed in the Far East later in 1944, and operated there both in close-support and escort missions.

In some ways the P-51 was the right plane at the right time. Both British and German designs of a few months later would outperform it in most ways. But that makes little difference, the effect of the P-51 is as great, or perhaps greater, than any aircraft of WWII.

Fact sheet

The technical information is relevant to the P-51D.

• Length: 9.8m
• Height: 4.17m
• Wingspan: 11.3m
• Wing area: 21.8m²
• Empty weight: 3175Kg
• Gross weight: 4173Kg
• Max weight: 5487Kg
• Range: 1610Km
• Cruise speed: 238 knots
• Maximal speed: 380 knots
• Ceiling: 41,800 feet
• Powerplant: Rolls-Royce (Packard) Merlin V-1650-7, rated at 1650hp

Produced versions

• P-51A, 310 built at Inglewood, California
• P-51B, 650 built at Inglewood
• P-51C, 3,750 built at Dallas, Texas
• P-51D/K, 6,502 built at Inglewood, 1,454 built in Dallas. A total of 7,956.
• P-51H,

Total number: 15,675, among American aircraft second only to the P-47 Thunderbolt.