North American P-51 Mustang
North American P-51 Mustang
North American P-51 Mustang
The North American P-51 Mustang was a successful, long range fighter aircraft
which entered service in the middle years of World War II. The definitive
version of the single seat fighter was powered by a single supercharged V-12
Merlin engine and armed with six .50 caliber (12.7 mm) machine guns.
Shortly after the war began in 1939, the British government established a
purchasing commission in the United States headed by Sir Henry Self. One of
Self's many tasks was to organise the manufacture of American fighter aircraft
for the RAF. At the time, the choice was very limited. None of the US aircraft
already flying reached European standards, only the Curtiss P-40 Tomahawk came
close. With the Curtiss plant running at capacity already, even that aircraft
was in short supply.
North American Aviation (NAA) President Dutch Kindleberger approached Self with
the idea of selling the British a new medium bomber, the Mitchell. Instead, Self
asked if NAA could manufacture the Tomahawk under licence from Curtis.
(North American was already supplying their Harvard trainer but were otherwise
Kindleberger's reply, however, was that NAA 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 in keeping with
the best conventional practice of the era but included two new features. One
was a new NACA-designed laminar flow wing which was larger than others on similar
aircraft while still having the same drag. This left plenty of room for landing
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 radiator 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 plane made its maiden flight on October 26, 1940, less than nine months
from first being drawn up, an incredibly short period. In general, the plane
handled well and the internal arrangement allowed for a massive fuel load. It
was armed with four 0.5 in (12.7 mm) machine guns and another four 0.3 in
(7.62 mm) guns - a rather light armament load for the era: the contemporary
Focke-Wulf Fw 190 prototype was able to carry four 20 mm cannon and two 7.92
mm machine guns.
It was quickly evident that performance, although good near sea level, was not
up to European standards at higher altitudes. This was due largely to the
mechanically supercharged Allison V-1710 engine. The finer points of supercharging
were very much a British specialty: United States engineers had concentrated
mainly on the turbocharger instead and the Allison suffered in consequence.
About 20 of the Mustang I were delivered to the RAF and made their combat debut
in May, 1942. With their long range and excellent low-level performance they
were judged useful for ground-attack duties over the English Channel, but too
slow at altitude to be used as fighters.
The Mustang Mk.IA removed the 0.3 in (7.62 mm) 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 0.5 in (12.7 mm) guns, dive brakes, and could carry two 500 pound
(230 kg) bombs. Neither of these versions were particularly effective.
P-51B and 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 excellent maneuverability.
Rolls Royce 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 thus considerably better high-altitude performance. 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 astonishing. The high altitude performance and range with the
use of drop tanks enabled the mark to excel as a bomber escort. A license was
sold to Packard to manufacture the Merlin as the V-1650 and production of 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 being manufactured 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 (the southern part of Italy was
under Allied control by late 1943).
The main task for which the plane was used was bomber escort. It was largely due
to the P-51 that daylight bombing raids deep into German territory became possible
in the middle of 1944. Several hundred of the aircraft were also given to the
Allied Air Forces in China, and sold to Australia, under lend-lease.
The P-51D was the definitive Mustang. Armament was increased with the addition
of another pair of the 0.5 in (12.7 mm) guns for a total of six, the inner two
on each wing having 400 rounds and the outer 270. Some aircraft had rocket pylons
added to the undersides of the wings to carry up to ten 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, after the first examples of the P-51D had already been produced,
the D series introduced an improvement consisting of a cut down rear fuselage
and a "bubble" style canopy of new design which offered excellent all-round
visibility. Removing the metal behind the cockpit lowered the longitudinal
stability, so later in the D series a fillet was added to the front of the
vertical stabilizer to improve handling.
The resulting P-51D (and RAF P-51K version which differed very slightly)became
the most produced of all the Mustangs by far. The new version began to arrive
in Europe in March, 1944, just in time to deploy for D-Day combat.
The original NA-73 had been built to the USAAF acceleration standard of 7.33 g
(72 m/sē), which made it stronger but considerably heavier than if it had been
designed for the British standard of 5.33 g (52 m/sē). Both the USAAF and the
RAF were interested in lightening the plane to be more in line with the Spitfire,
which was expected to boost its performance significantly.
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 from
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-1650-9
engine, a version of the Merlin that included automatic supercharger controls
and water injection for bursts of up to 2,000 hp (1,500 kW). With the new
airframe several hundred pounds lighter, the extra power, and a better streamlined
radiator, the P-51H was among the fastest propeller fighters ever, able to
reach 487 mph (784 km/h) at 25,000 ft (7,600 m).
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.
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,
F-51s, though obsolete as fighters, were used as tactical bombers. Because of
its lighter structure and less availability of spare parts the newer, faster
F-51H was not used in Korea in place of the D model. With the planes being used
for ground attack, their performance was less of a concern than their ability
to carry a load.
The F-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. A few of these have been modified for extra speed for competing in air
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 Douhet'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-1930s 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 USAAF reasoned that their bombers' higher altitudes and more powerful
defensive gun load would be enough to turn the tide in favour of the bomber.
The limited numbers of B-17's made large scale operations impossible until late
1943, with only small, well-escorted raids being made in the meantime over
France to shake out the crews and planes.
The numbers had improved enough by late summer of 1943, that the USAAF decided
to attempt large scale operations. Picking the German ball-bearing industry as
a vital choke point of aircraft production, they launched several massive raids
in October that flew deep into Germany. The results were disastrous with over
10% of the planes failing to return to England from each mission and many more
written off due to heavy damage. A few more raids and there would be no bombers
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. The Mustang
changed all that. In general terms, the Mustang was as simple or simpler than
other aircraft of its era. It used a single well-understood and 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 recommenced 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. The numerical
superiority of the USAAF fighters and the flying qualities of the P-51 made
this policy highly effective, and after the Luftwaffe had suffered heavy losses
both in defense of the Reich and in the failed attempt to fight off the Allied
invasion in France, the US, and later British, bombers had little to fear from
German day fighters after the summer of 1944.
P-51s also 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), and even
the Me 163 Komet rocket interceptors and Me 262 jet fighters, though considerably
faster than the P-51, weren't invulnerable. Chuck Yeager, flying a P-51D, was
the first Allied pilot to shoot down a Me 262 when he surprised it during its
The P-51s were deployed in the Far East later in 1944, and operated there both
in close-support and escort missions.
The initial prototype was designated the NA-73X by the manufacturer, North
American Aviation. The first production contract was awarded by the British for
320 NA-73 fighters. This aircraft was name Mustang I by the British. Two aircraft
of this lot delivered to the U.S. Army Air Corps were designated XP-51. A second
British contract for 300 more Mustang Is was assigned a model number of NA-83
by North American.
In September 1940, 150 aircraft designated NA-91 by North American were ordered
under the Lend/Lease program. These were designated by the Army Air Force as P-51
and initially named the Apache although this name was dropped early-on for
Mustang. The British designated this model Mustang IA. A number of aircraft
from this lot were fitted out by the A.A.F. as photo reconnaissance aircraft
and designated F-6A. Also, two aircraft of this lot were fitted with the
Packard built Merlin engine and were designated by North American as model
NA-101 and by the A.A.F. initially as the XP-78, but re-designated quickly
In early 1942, the A.A.F. ordered a lot of 500 aircraft modified as dive
bombers that were designated A-36A. North American assigned the aircraft the
model number NA-97. This model became the first A.A.F. Mustang to see combat.
Following the A-36A order the A.A.F. ordered 310 model NA-99 fighters
that were designated P-51A by the A.A.F. and Mustang II by the R.A.F. A number
of this lot of aircraft were equipped with K-24 cameras and designated F-6B.
All these models of the Mustang were equipped with Allison V-1710 engines except
the prototype XP-51B.
Beginning with the model NA-102 Mustang the Packard built Merlin V-1650 engine
replaced the Allison. In the summer of 1943 Mustang production was begun at a
new plant in Dallas, Texas as well as the existing facility in Inglewood,
California. The model NA-102 was produced as the P-51B in Inglewood while the
NA-103 as the P-51C was produced at Dallas. The R.A.F. named these models Mustang
III. Again, a number of the P-51B and P-51C aircraft were fitted for photo
Reconnaissance and designated F-6C.
The prototypes of the bubble canopy change were designated model NA-106 by North
American and P-51D by the A.A.F. The production version, while retaining the
P-51D designation, was assigned a model number NA-109 by North American. The
‘D’ became the most widely produced variant of the Mustang. A variation of the
P-51D equipped with a Aeroproducts propeller in place of the Hamilton Standard
propeller was designated the P-51K. The photo versions of the P-51D and P-51K
were designated F-6D and F-6K respectfully. The R.A.F. assigned the name Mustang
IV to both the ‘D’ and ‘K’ variants.
Additionally, beginning in 1944, the Australian Commonwealth Aircraft Company
produced some 200 P-51D Mustangs designated CA-17 in a number Marks: Mk.21 the
basic fighter, Mk.22 fitted with F.24 cameras, Mk.23 with newer model Merlin
As the A.A.F. specifications required airframe design to a higher load factor
than that used by British for their fighters, consideration was given to
re-designing the Mustang to the lower British requirements in order to reduce
the weight of the aircraft and thus improve performance. In 1943, North American
submitted a proposal to do the re-design as model NA-105, which was accepted by
the A.A.F. The designation XP-51F was assigned for prototypes powered with V-1650
engines and XP-51G to those with reverse lend/lease Merlin 145M engines. A third
prototype was added to the development that was powered by an Allison V-1710 engine.
This aircraft was designated XP-51J. As the engine was insufficiently developed
the XP-51J was loaned to Allison for engine development.
The final production Mustang, the P-51H embodied the experience gained in the
development of the lightweight XP-51F and XP-51G aircraft. This aircraft, model
NA-126, came too late to participate in World War II, but it brought the
development of the Mustang to a peak which was probably the fastest production
piston engine fighter to see service. With the cut back in production the
variants of the ‘H’ with different versions of the Merlin engine were produced
in either limited numbers or terminated. These included the P-51L and its Dallas
version, the P-51M.
This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "P-51 Mustang".