In 1940, the British Purchasing Commission approached J.H.
"Dutch Kindelberger, President of North American Aviation
with a proposal to produce Curtis P-40 War Hawks, under license,
for Great Britain. North American's designers, Raymond Rice
and Edgar Schmued, responded with a counter proposal that
they produce instead a brand new airframe that used the same
Allison engine employed by the P-40.
The British agreed, under the condition that the new prototype
be ready in an unheard of 120 days. North American, who had
never even produced a fighter before, designed, manufactured
and flew the NA-73x (P-51) prototype in a truly amazing 102
Despite revolutionary features like a laminar flow wing,
an under the fuselage radiator that provided additional "thrust"
and a slick, aerodynamic shape, the early P-51A models were
hampered by the poor high altitude performance and the mediocre
top speed of the original Allison engine. Although good low
level attack planes, they did not attract much interest on
either side of the Atlantic.
All that changed when the British decided to test a Rolls
Royce Merlin engine (used in the Spitfire) in a Mustang airframe.
The rest, as they say, is history. Top speed leaped past 400
mph and high altitude performance was a revelation. The result
was the P-51B, followed by re P-51C, both of which featured
a Packard built Merlin and the flush patterned cage style
canopy featured in our film.
The definitive wartime Mustang was the P-51 D, which introduced
a new clear "bubble top" canopy (inspired by the
British "Malcom Bubble") that offered an outstanding
field of vision and a new 85 gallon fuel tank located behind
the pilot's seat. The latter innovation was critical to the
Mustang's success as a long range bomber escort fighter because
it could now fly all the way from England to Berlin and back,
something no other fighter could do at the time. It also meant
that P-51's could roam far into enemy territory as a fighter/bomber
to attack roads, airfields, rail lines, depots and communications
to cripple the opposition's ability to respond
It was the Mustang's ability to place at or near the top
in so many categories that made it an outstanding aircraft
and a leading candidate for Best All Around Fighter of World
War II: It was among the fastest piston engine planes of the
war; it had an outstandingly high Mach number and strong construction
so it could out dive opponents; it had a very good roll rate
and could use it's "combat flaps" to turn inside
many opponents; the P-51's great range meant it could fly
farther and loiter longer in the battle zone than it's opponents,
it's six 50 caliber machine guns packed plenty of punch and
the mustang's rugged frame could absorb an unusual amount
of damage. Though not "easy' to fly and requiring that
the pilot pay attention, the Mustang was predictable, with
good stall characteristics and was without any really nasty
habits. About the only shortcoming of the P-51D was it's relatively
heavy weight, which made it only a mediocre climber up to
20,000'. That deficiency would have been more of a draw back
in an "Interceptor" than in the roles the Mustang
was designed for, and that fault was corrected in the lightweight
P-51H, which was produced too late in the War to see action.
Ironically, it was the World War II workhorse, the P-51D,
not the newer "H" model that saw heavy action in
Korea because of an abundance of spare parts.
|North American P-51D "Mustang"
Single seat fighter Power plant one 1,695-hp (1186-kW)
Packard V-1650-7 Merlin liquid-cooled 12 cylinder vee
piston engine, four blade Hamilton Standard propeller
Maximum Speed: 437 mph (clean) 395 mph at 5000 ft (525m)
Initial Climb: 3,745 ft (1059m) per minute Service Ceiling:
41,900 ft (13410m) Range: 2,600 miles (4184 km) with max
Span: 37 ft 1 in ft (11.29m) Length: 32 ft 3 in (9.83m)
Height: 13ft 8 in (4.17m) Wing Area: 235 sq ft (21.83m2)
Weights: Empty: 7,125 lb (3232 kg) Max. Take-off: 11,600
lb (5262 kg)
6 X 0.5 (12.7mm) Browning machine guns Bomb Load 2 X
500 lb (1818 kg) bombs, H149 8 X 5-in (127mm) HVAR rockets
two-seat trainer version of P-51D, Four 0.5-in wing
guns Production: 10 built in Dallas, also several conversions
of existing aircraft
Redesignated TF-51D in 1948
The Rolls-Royce and Packard built Merlin engine is universally
acknowledged as one of the finest piston engines that
has ever been manufactured. Remarkably, over 50 years
have elapsed since the last Merlin engine rolled off the
production line, yet it is still in widespread daily use
in warbird aircraft, not least of all the P-51 Mustang,
Just as North American Aviation would never have envisioned
their Mustangs would still be flying, Rolls-Royce probably
never considered that their beautiful Merlin powerplant
would still be in "front line service" in the
The overall success of this famous engine is built
on one simple fact. By employing technology many years
ahead of its time, fueled by the urgency of war, Rolls-Royce
produced a powerplant that still has no equal as a piston
Ironically, but not untypical of British industrial
practice in the 20th Century, the British government,
through the Air Ministry, declined to fund a new engine
despite the Schneider Trophy success of the early 1930's.
In December 1932 the Rolls-Royce board, in the true
spirit of British entrepreneurship, elected to finance
the engine themselves as a private venture. Thus, early
development of the engine were designated P.V.12 No
one could have envisioned that this step would contribute
so significantly to the allied victory in the air.
Few would dispute the Battle of Britain was won as
a result of the Merlin II and III. Another significant
development was the brilliant discovery, by a scientist
at the Royal Aeronautical Establishment, Miss Shilling,
who designed a most simple system - a small metal diaphragm
in the float chamber of the carburetor - that enabled
the engine to continue running in negative G situations
1938 saw Stanley Hooker join Rolls-Royce. It was Hooker
who concentrated on the development of the Merlin's
supercharger. Even modern day Merlin rebuilders will
tell you the engine's supercharger is the finest of
its type ever produced. Why? It improves the power envelope
from 12,000 to 40,000 feet. This unit is at the heart
of the engines remarkable performance over a significant
At the beginning of World War II and the beginning
of the Battle of Britain, every front line fighter aircraft
was fitted with the Merlin. One of the main Luftwaffe
tactics was low flying and the sea level power of the
Merlin had to be enhanced as a result. Rolls-Royce achieved
a 40% increase in power at sea level due to the supercharger
development and this forced the Luftwaffe to fly higher
to combat air superiority at low level. With the success
of supercharger development the Merlin XX and Merlin
45 were introduced into the Spitfire and Hurricane and
this enabled the Royal Air Force to maintain fighter
During the war years over 150,000 Merlin engines were
manufactured in the U.K. and U.S.A. The Packard Motor
Car Company undertook the latter and it was this version
that was to power the legendary North American Mustang.
However, unrecognized by many are the huge differences
in the Packard built version. Packard manufactured some
57,000 Merlin engines, over a third of all Merlin production.
From its earliest version the Merlin was clearly a precision,
hand built work of engineering art constructed by some
of the best British engineers. Even in its infancy the
powerplant was built in small lots and had a string
of design changes incorporated in an effort to squeeze
performance and increase reliability in combat situations.
The setback was this was not an engine designed for
mass production, so in 1940, when the British Government
turned to Packard for help with production of the Merlin
some provisions had to be made.
In June 1940, Packard was requested to undertake the
production of some 9000 Merlin XX engines. It took just
three days for the company to respond positively but
on that proviso that some modifications would be made
to the powerplant to enable American accessories such
as carburetors, fuel and vacuum pumps to be utilized.
Packard then began the monumental task of organizing
an engineering group to handle drawings and redesign
for American production. In parallel Packard organized
U.S. sources for carburetors, magnetos, spark plugs,
and other accessories. Packard assigned some 200 personnel
to the project and this included the draughtsmen who
would undertake complete revisions of production drawings.
At the outset the Packard engineers ran into problems,
generally due to the fact that the engine was not designed
for mass production. That the project was completed
at all is testament to the determination and skill of
those assigned the task.
After the end of hostilities in World War II, the Merlin
saw extensive commercial service, particularly in Great
Britain and Canada, extending well into the late 1950's.
The Merlin 600 and 700 series were the subject of most
testing and modification until as late as the 1960's.
Since the Merlin emerged there have been three categories
of operator in aviation. The use of the engine in battle
tanks and boats is beyond the scope of this chapter.
Broadly, these can be categorized as the originally
Military operators, commercial (such as airlines) and
right up to the present day, civilian warbird operators.
When commercial operators began using the Merlin cost
became an important consideration. Most airline operators
know the profit is in the last 20%. Civilian operators
logged more TBO (time between overhaul) on their Merlin
engines than military operators by a significant amount
and consequently experienced associated problems military
engineering teams never witnessed. Importantly, it was
not cost effective to replace every component when it
was worn past military service limits, so Rolls-Royce
developed countless repair schemes and legal modifications
to salvage otherwise unserviceable parts. Hence this
extended the running life of parts in the engine. The
repair schemes and modifications were the result of
hours of re-engineering, development, and testing in
the field. As these schemes became available for release,
they had to have approval from Great Britain's Air Ministry.
Many of these repair schemes are still in (legal) use
In the late 1950's the Mustang was released for sale
to the general public. Most airframes sold had low times
and consequently warbird owners enjoyed a period of
three decades where engine overhaul posed little problem,
and very often a spare engine (or two) had been acquired
with the airframe anyway. Overhauls undertaken during
this time were similar to military schedules where the
engines were disassembled, cleaned, and reassembled.
Though new seals and rings were sometimes installed
major rework was just not necessary.
At the time of writing we calculate there are in the
region of 500 Merlin engines (not counting museum static
aeroplanes) in circulation amongst warbird operators
and either installed in aircraft of held as spares.
Some parts are becoming critical and there are a number
of programs being undertaken to manufacture critical
items to enable the Merlin to run for another 50 year,
adding yet more achievements to what is already history.
THE MUSTANG IN CANADA:
Shortly after the war ended in 1945, the RCAF received
100 P-51D Mustangs from the USA. These were placed in
service with the regular squadrons (until being replaced
by Vampires and Sabres during 1949 and 1950) and also
with auxiliary squadrons. The Mustangs served with the
auxiliary units until 1956, when they had all been replaced
by Vampires, and then by T-33s and Sabres. Some were
also flown by the Central Experimental and Proving Establishment
at Rockcliffe and some as fighter-bombers at the Canadian
Joint Air Training Centre at Rivers, Manitoba.
THE POST WAR MUSTANG SQUADRONS
- 400 (Auxiliary) "City of Toronto" Toronto,
- 401 (Auxiliary) "City of Montreal" St.
- 402 (Auxiliary) "City of Winnipeg" Winnipeg,
- 403 (Auxiliary) "City of Calgary" Calgary,
- 411 (Auxiliary) "County of York" Toronto,
- 416 (Regular) "Lynx" Uplands, Ont.
- 420 (Auxiliary) "City of London" London,
- 421 (Regular) "Red Indian" Bagotville,
- 424 (Auxiliary) "City of Hamilton" Hamilton,
- 438 (Auxiliary) "City of Weatmount" St.
- 442 (Auxiliary) "City of Vancouver" Vancouver,
- 443 (Auxiliary) "City of New Westminster"