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 asked about purchasing the Curtiss P-40 Warhawk, but Curtiss was running full out for other customers, namely the USAAC.

He then asked North American (NAA) about bulding the Warhawk under license. NAA was already supplying their training aircraft, known to the RAF as the Harvard, but was otherwise underutilized. 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, ammunition and fuel, all completely inside the wing and well streamlined. Another was the use of a new radiator design from Curtiss, that used the heated 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 cost-free to the USAAC.

The plane made its maiden flight on 26 October 1940, under nine months from first being drawn up. In general, the plane handled well and the internal arrangement allowed for a massive fuel load. It was armed with four 0.50" (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 quickly evident that the performance of the plane was simply not up to European standards. This was due largely to the unacceptable supercharging of its Allison V-1710 engine. The USAAC 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 with whom they made their combat debut on 10 May 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 30 call 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 ordered as the A-36 Apache which included two more 50 cal guns, dive brakes, and could carry two 500 pound bombs. Neither of these versions were particularily effective.

P-51B, P-51C

About the same time, however, the Mustang was looked over by Rolls Royce engineers and test pilots. They were impressed by the great fuel capacity of the aircraft and its aforementioned armament.

Rolls was at that point starting production of the Merlin 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 Merlin 68 engines to four Mustang Mk.IA airframes.

The result was a plane of unbeatable performance. Simply put the plane could outfly anything in the air including the latest British fighters, and could do so at great distances from England. A license was sold to Packard to manufacture the Merlin as the V-1650, and production pf the Mustang with this engine was started immediately.

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 also given to the Allied Air Forces in China and Australia.

P-51D

The only other shortcomings with the aircraft were soon 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 per plane.

The only other major concern was the very limited visibility to the rear, a problem the British had complained about. 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 the metal behind the cockpit lowered the logitudinal stability, so a fillet was later added to the front of the vertical stabilizer to improve it.

The resulting P-51D (and RAF P-51K version which differed very slightly) 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 P-51F (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 production version would be the P-51H, using the new V-1659-9 engine, a version of the Merlin that included automatic supercharger controls and water injection for bursts 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 487 mph at 25,000 feet.

It was planned that the H model would become the standard fighter for the USAAF for the invasion of Japan, replacing all other models. 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 (P for pursuit) was changed to F-51D (F for fighter) because of a new designation scheme throughout the USAF. 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, their performance was less of a concern than their ability to carry a load.

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). The last Mustangs were discarded by the USAF in 1957. Many remain airworthy across the globe, in private hands.

Effects of the P-51

The US effort to launch massive bombing raids into Germany took some time to build up. 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.

A number of air forces had already tried this, including both the RAF and Luftwaffe. They found, contrary to Dohey's thesis, that the single engine fighters were more than able to catch a multi-engine bomber, and outgun it easily. The RAF had worried about this before the start of the war, and had decided in the mid-1930's to produce an all night-bomber force, but when the war started they had these planes operate during the day. Both forces lost so many planes during initial operations that they quickly switched to night operations.

The USAAC thought it knew better. They reasoned that their higher altitudes and more powerful defensive gun load would be enough to turn the tide in favour of the bomber. Although the limited numbers of B-17's made large scale operations impossible until late 1943, with small well escorted raids being made over France to shake out the crews and planes.

But the numbers had improved by the late summer of 1943 that the USAAF decided to attempt large scale operations. Picking the German ball-bearing industry as a vital "choke point" for their aircraft production, they launched several massive raids deep into Germany in October. 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 Lockheed 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 from the skies and the US, and later British, bombers were free to roam over Germany at will during daylight hours. Desperate efforts on the part of the Luftwaffe eventually delivered huge numbers of planes needed to regain control, but most of their better pilots had been killed and the replacements had little experience.

P-51s distinguished themselves while fighting against advanced enemy rockets and 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, 555 built at Inglewood

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