North American P-51 Mustang

Why the P-51 Mustang matters

The P-51 Mustang was the fighter that made daylight bombing of Germany survivable. It could fly with the bombers all the way to Berlin and still fight when it got there.

That range came from a mix of a clean aerodynamic design, a large internal fuel load and a Rolls-Royce Merlin engine built under license by Packard. The record on this page describes the definitive P-51D, which carried six .50 caliber machine guns and a bubble canopy.

The full specification table for the aircraft is on this page. The sections below explain how the numbers came about and what they mean in practice.

A British order that North American turned into a better plane

In 1938 Britain set up a purchasing commission in the United States to buy fighters for the RAF. Few American designs met European standards, and the Curtiss P-40 plant was already running flat out.

The commission asked North American Aviation to build P-40s under license. President James “Dutch” Kindelberger answered that his company could build a better aircraft around the same Allison V-1710 engine, and get it flying sooner than a P-40 line could start.

The commission signed the Mustang project on 4 May 1940 and ordered 320 aircraft on 29 May. The prototype, designated NA-73X, was complete on 9 September 1940, 102 days after the order, and first flew on 26 October 1940.

Laminar flow wing and a clean airframe

The NA-73X was designed by a team led by lead engineer Edgar Schmued. It used a laminar flow wing developed with NACA, which produced low drag at high speed. A wind-tunnel test at the University of Washington showed the new NAA/NACA 45-100 airfoil beating a wing built with NACA five-digit airfoils.

The cooling system was a single duct positioned aft, which cut fuselage drag. Later development showed it could take advantage of the Meredith effect, where heated air leaving the radiator adds a little thrust.

The fuselage was one of the first lofted mathematically using conic sections, which gave smooth surfaces. For production, the airframe was built in five main sections that were wired and plumbed before being joined.

The Merlin engine changed everything

The Allison engine in the early Mustang had a single-stage supercharger, and its power fell away quickly at height. That made the first Mustangs good low-level fighters and tactical reconnaissance aircraft, not high-altitude escorts.

In May 1942 Rolls-Royce test pilot Ronald Harker suggested fitting a Merlin, the engine of the Spitfire Mk IX. Its two-speed, two-stage intercooled supercharger had been designed by Stanley Hooker. The Rolls-Royce Mustang X flew at Hucknall in October 1942, and the US version, the XP-51B, flew in November 1942.

North American began building the P-51B at Inglewood, California, in June 1943. The heavier Merlin meant moving the wing slightly forward to correct the center of gravity. A fuselage fuel tank behind the pilot, added after the USAAF told manufacturers to maximize internal fuel, greatly extended range.

The definitive P-51D used the Packard V-1650-7, a license-built version of the Merlin 66, and introduced the bubble canopy.

The numbers behind the P-51D

The panel lists the engine at 1,720 hp · 1,283 kW. That is the war emergency power rating, a short-term boost. The normal rating, at 3,000 rpm, was lower.

The top speed shown in the panel is 383 kt · 441 mph · 709 km/h. Some sources round the same figure to 440 mph.

The range of 1,434 nm · 1,650 mi · 2,660 km applies with external tanks. That figure depends on the drop tanks. The internal tanks hold 270 gal, and it was the external tanks that let Mustangs accompany bombers from England to Germany and back.

The service ceiling of 41,900 ft · 12,800 m and the climb rate of 3,200 ft/min · 16 m/s show why the Merlin mattered. At the altitude of the B-17 formations the Mustang outperformed the Focke-Wulf Fw 190A.

Flying escort over Germany

The USAAF had assumed in 1942 that tightly packed bomber formations could defend themselves. Heavy losses called that idea into question, and a single-engined fighter with bomber range was thought to be an engineering impossibility.

When the offensive resumed in early 1944, the shorter-range P-38s and P-47s escorted bombers on the first part of a raid and handed over to P-51s when they had to turn back. The Mustang was so clearly better that the Eighth Air Force steadily converted its fighter groups. By the end of 1944, 14 of its 15 groups flew Mustangs.

Mustang pilots also strafed airfields and trains on the way home. The Merlin was liquid cooled, so a single hit to the radiator or a coolant line could end the flight, and strafing losses were much higher than air-to-air losses.

By July 1944 the Luftwaffe fighter force was crippled. Hermann Goering is quoted as saying that when he saw Mustangs over Berlin, he knew the jig was up.

Pilots in all theaters claimed 4,950 enemy aircraft in the war, according to Wikipedia. Lt Col James H. Howard of the 354th Fighter Group received the Medal of Honor for defending bombers near Oschersleben on 11 January 1944.

Iwo Jima and the Pacific

The P-51 reached the Pacific later than Europe, in 1944. From March 1945, Mustangs of the VII Fighter Command flew from Iwo Jima to escort B-29s against the Japanese home islands.

The round trips ran about 1,500 miles, mostly over water, with the engine held at minimum power for long periods. That fouled spark plugs, which had to be changed after each mission.

The P-51s flew 51 missions and 4,172 sorties from the island. The escorts proved less necessary than planned, because Japanese interceptor strength was already fading.

Korea and a long second career

At the start of the Korean War the Mustang, by then redesignated F-51, was the main US fighter until jets such as the F-86 Sabre took over that role. The F-51 then became a ground attack and photo reconnaissance aircraft.

F-51Ds could reach targets in Korea that the short-ranged F-80 jets could not, which kept them flying from bases in Japan.

Other air forces kept Mustangs for decades. The last Mustang shot down in battle fell during Operation Power Pack in the Dominican Republic in 1965, and the Dominican Air Force retired its last aircraft in 1984.

In 1969 a Salvadoran Mustang was shot down by a Vought F4U-5 Corsair in the Football War, the last aerial combat between piston-engined fighters.

P-51 Mustang by the numbers

North American built 15,686 Mustangs. Cavalier Aircraft bought the design rights after the war and remanufactured airframes for the USAF in 1967 and 1972, usually for air forces in South America and Asia. Those rebuilds carried new engines and a taller F-51H-type tail.

Many survive as warbirds and air racers. The type has also had its tragedies. In 2011 a modified Mustang racer crashed at Reno, killing the pilot and at least nine people on the ground.

Frequently Asked Questions

How fast was the P-51D Mustang?

The P-51D reached 383 kt · 441 mph · 709 km/h at altitude. Many sources round this to 440 mph.

How far could a P-51 Mustang fly?

The P-51D flew 1,434 nm · 1,650 mi · 2,660 km with external tanks.

Which was faster, the P-51 Mustang or the Spitfire?

The two shared the Merlin’s two-stage supercharger design. Rolls-Royce test pilot Ronald Harker suggested the Merlin for the Mustang because the Spitfire Mk IX used one. Speed depends on the variant and altitude, so range is the clearer difference: with drop tanks the Mustang could escort bombers from England to Germany and back.

Which was better, the P-47 or the P-51?

In the escort role the P-51 was clearly better. The USAAF used shorter-range P-38s and P-47s for the early part of a raid and handed over to P-51s, and the Eighth Air Force converted most of its fighter groups to Mustangs.

How many P-51 Mustangs were built?

North American built 15,686 Mustangs, according to Boeing Frontiers and AOPA.

Why did the Mustang get a Merlin engine?

The original Allison V-1710 lost power at altitude. A Merlin with a two-stage, two-speed supercharger restored high-altitude performance without costing range.

Is the P-51 still flying?

Yes. After the Korean War, Mustangs became popular civilian warbirds and air racing aircraft, and a number are still airworthy.