In the early hours of a September morning,
1940, this plane, A Heinkel He 111, was making it’s way towards London, carrying 2 tonnes
of bombs to the densely populated city. It may well have reached its destination,
if not for the early warning systems the British Military Home Defence had created. A network of radar stations, all feeding into
a central operations room where incoming raid information was ratified and mapped on a gigantic
chart of Britain. It was from this room in Bentley Prior that
all RAF commands, during the Battle of Britain, were made. This was a frantic, but precise procedure. Every minute that passed was a crucial minute
stolen from the pilots. Vital time needed to gain altitude to meet
the enemy on a level playing field. This groundbreaking air defence network allowed
Britain's defenders to be in the air, at interception altitude, within 10 minutes of the first sign
of invasion on the radar screens. This would not have been possible without
aircraft capable of quickly gaining altitude to meet their foes. The Spitfire is the icon of the Battle of
Britain, capable of climbing 2500 feet (760 metres) per minute, taking them, at minimum,
4 to 5 minutes to reach their target’s altitude. The Spitfire was a nimple interceptor. A plane that could rapidly gain altitude,
and proceed to fiercely defend its airspace. To do this it needed to be powerful, manoeuvrable,
and capable of packing a punch. Some of the greatest engineers of World War
2 worked on this fighter and the designs they came up with changed the course of the war. This is the insane engineering of the Spitfire. Despite its patriotic fame, the groundbreaking
nature of the Spitfire’s design is difficult to comprehend today. In a world where we are long accustomed to
all-metal low wing fighters, the Spitfire, despite its undeniable elegance, may seem
mundane. However, when the spitfire first swept through
airfields in 1936, the RAF still operated aircraft like the Gloster Gauntlet and the
Hawker Fury Biplanes were the norm for fighters of this
era. The stacked wings increased the lift the aircraft
could generate while making them stronger and better able to withstand the g-forces
of manoeuvres. But they generated a lot of drag. The Spitfire was made possible by new powerful
engines and new revolutionary aged hardened aluminium alloys, freeing the Spitfire’s
chief designer RJ Mitchell to get creative, setting out to create a plane capable of out-running
and out turning any foe. Turn performance is essentially measured by
the minimum turn radius a plane can achieve. A tighter turn radius gives a fighter aircraft
an edge in a dog fight. To understand what effects the radius of this
turn we first need to understand how an aircraft turns. To begin a turn an aircraft will roll in the
direction of the turn, this is called the aircraft bank angle. This splits the lift the plane is generating
into two components: a horizontal component that causes the plane to turn and the vertical
component that keeps the plane in the sky. A steeper bank angle will increase the horizontal
component and decrease the turn radius, while stealing lift from the vertical components. This vertical component needs to equal the
weight of the aircraft, or the plane will lose altitude. To compensate for that the pilot will deflect
the plane's elevators downwards to increase lift, but this increases drag. This increase in drag means the pilot will
also need to increase engine power to maintain speed. The maximum turn possible that won’t result
in loss of altitude or speed is called the sustained turn performance, and it’s affected
by the weight of the aircraft, the excess power available from the engine, and the design
of the wing. To excel in battle the Spitfire needed the
perfect wing, and Mitchell did his absolute best to give it just that. RJ Mitchell had plenty of experience in designing
sleek high performance aircraft, designing the Supermarine S.5 that won Schneider Trophy
race in 1928. There was some deliberation on the shape the
Spitfire’s wing would take, with some early designs, like this one from 1934, showing
a straight taper, unlike the iconic elliptical wing it eventually took. This would have been vastly easier to manufacture,
but the shape a wing takes has a huge effect on performance. In particular, lift distribution, and the
elliptical wing provides the ideal lift distribution to minimise induced drag. Induced drag occurs when high pressure air
from underneath the wing travels to mix with low pressure air above the wing, over the
wing tip. This creates a vortice at the wing tip that
saps kinetic energy away from the plane. This elliptical lift distribution minimises
this effect, but RJ Mitchell is quoted in Alfred Price’s
“The Spitfire Story” saying this: “I don't give a bugger whether it's elliptical
or not, so long as it covers the guns” The reduction in induced drag is often cited
as the sole benefit of the elliptical wing, when in actuality it barely made a dent in
the overall drag characteristics of the plane, which was not worth the added difficulty in
manufacturing. [2] The real benefits of the elliptical wing came
with the planform's slow reduction in chord length. Take a straight tapered wing. Its chord, the width of the wing, steadily
decreases from the root of the wing. Steadily reducing the area near the fuselage
that can be used to fit equipment. The curve of the ellipse on the other hand
maintains the width of the wing close to the fuselage and then drops off more rapidly towards
the wing tips, this provides ample room inside the wing to fit the landing gear, guns, hydraulics,
radiators and wing support structures. The room provided to fit a strong, but lightweight
wing spar is a key benefit that allowed the Spitfire to take daring turns without worry
of structural failure. The engineers of the Spitfire had a delicate
balancing act to perform. Increasing the strength of a wing often requires
adding weight, and adding weight decreases turn performance, climb performance and increases
fuel consumption. The Spitfire’s wing is not perfectly elliptical,
its trailing edge turns inwards more rapidly than the leading edge. This was done primarily for structural reasons. The main structural support of the wing is
the wing spar and in the Spitfire it runs perfectly along the quarter chord of the Spitfires
wing. The quarter chord is located, as its name
would suggest, a quarter of the way up the width of the wing. It is the aerodynamic centre of the wing,
where the overall lift of the wing acts through. If the wing was perfectly elliptical it would
be impossible to place this wing spar along the quarter chord and the overall lift force
would, as a result, be behind the wing spar, instead of directly over it. This would create a twisting motion on the
wing that would require additional strengthening and weight. This is why the trailing edge curves in as
it does, to adjust the quarter chord’s location to be in line with the wing spar. Much was done to minimise the weight of these
support structures. The bending force the wing needs to resist
decreases as we travel down the wing, so the spar can reduce in strength and weight through
the wingspan. Manufacturing this kind of shape was not particularly
easy in the 1940s. Today we can manufacture single parts to shapes
engineers of world war two could only imagine using CNC milling machines. To allow the strength of the wing spar to
decrease, it’s constructed from simple nested square extrusions. The upper and lower spar booms were constructed
from 5 concentric aluminium square sections, which were cut and placed inside of each other
like this. This wing was an engineering masterpiece that
gave the Spitfire incredible handling characteristics. When we compare the Spitfire to the BF109,
its nemesis during the Battle of Britain, we can start to make some real deductions
about the effect this wing had on the plane. The wing area of the Spit is noticeably larger. This affects a performance metric called wing
loading. Which is simply the total mass of the aircraft
divided by the wing area. This affects the turning radius of the aircraft. A heavy aircraft with small wings will have
a large wing loading, and as a result will have a large turning radius. The BF109’s wings were much smaller and
thus it had a higher wing load, and so the BF109 had a larger turning radius than the
Spitfire. [2] While the space afforded by the Spitfire’s
wings allowed it fit 8 Browning machine guns inside the wing, or as later variants featured, 2 larger 20
mm cannon and four of the smaller 7.7 mm Brownings all mounted inside the wing, and outside the propellor arc, which reduced
the engineer effort needed to integrate them. A luxury the BF109 did not have. The engineers at Messerschmitt were forced
to use more complicated designs to integrate armament. Two machine guns mounted above the engine
could fire through the propeller blades with an interrupter gear timing the triggering
to ensure they did not strike the blades. A cannon could be fitted behind the engine,
which would fire through a hollow tube that ran through the inverted V-12 engine and through
the nose of the propeller hub. Later variants attempted to correct the disparity
in fire power by mounting guns inside the wings, but there wasn’t enough room for
ammunition, so a belt feeder was run through a shoot from the fuselage to the guns. This wasn’t a reliable mechanism. Some variants included gun pods mounted below
the wing, which negatively affected the plane's handling. The Spitfire’s primary role was an interceptor. To do this it needed a powerful engine and
light airframe. The most important factor for climb rate is
power to weight ratio. Creating a powerful engine that could fit
into a small airframe required some of the best minds in Britain. The Merlin engine of the Spitfire went through
many iterations over the war, with the constant goal to squeeze more and more power out of
the 27 litre displacement engine. Displacement meaning the volume of the cylinder
swept by each piston. The displacement of an engine has a huge effect
on the total power output. Power is derived from fuel burning to create
heat, which creates pressure on the cylinders to do work. To increase power we need to increase the
amount of heat energy released, but we can’t just add more fuel without adding more air
to burn it. There is an optimum air fuel ratio, about
12-1. 12 parts air to 1 part fuel. This gets even more complicated for aircraft
that fly at various altitudes, because the air pressure decreases as we climb. Air pressure drops by half at 5,500 metres. Which would half the oxygen available to burn
the fuel . To combat this the Merlin featured a supercharger
to increase air pressure. Air began its journey into the Merlin engine
through the air intake located underneath the fuselage. From here it first passes the carburetor where
fuel is mixed into the airstream. The Spitfire utilised a float carburetor. Float carburetors use, as the name would suggest,
a float. The float works similarly to the float in
your toilet cistern, detecting the fluid level and controlling a valve to keep it at the
optimum level in the carburetor tank. This became an issue for the Spitfire when
German pilots learned the engine would cut out in a negative g manoeuvre. A negative g manoeuvre would force the float
down and open the valve, flooding the engine with too much fuel. The BF109 engine utilised direct fuel injection,
a more complicated system that required 12 plungers, 1 for each cylinder, cams to time
the fuel injection, and geared power from the engine. A more complicated solution that allowed German
pilots to perform negative g dives to evade pursuit, while Spitfire pilots needed extra
time to perform a roll before diving, which ensured the dive was made in positive g, giving
German pilots precious time to escape. [3] After passing this carburettor the air entered
the supercharger compressor, where the air was compressed before entering the piston. Increasing the power output of the engine. This system helped the Spitfire squeeze out
extra horsepower from their 27 litre engine, rivalling the power of the 34 litre DB 601
engine fitted into BF109s during the Battle of Britain. However, early Merlin engines featured a single
speed, single stage supercharger. The speed of the supercharger being determined
by the gearing ratio coming from the crankshaft. This forced the engineers to design the supercharger
to work at the optimum speed and compression ratio for a particular altitude. We can see this when looking at power curves
that plot engine power vs altitude. The early Merlin III reached peak power around
10,000 feet, before quickly dropping off. You may notice that power output is actually
lower at sea-level, despite the ambient air pressure being higher here. That’s also a result of the supercharger
speed being fixed, in order to prevent the engine from being over pressured there was
a throttle on the air intake that gradually opened as the plane gained altitude. While the Spitfire had excellent power at
its optimum altitude, its BF109 foes during the Battle of Britain had superior power at
lower altitude. Because they featured an ingenious device
that allowed the supercharger to vary its speed. Their supercharger was placed at a 90 degree
angle and power was transferred to it with a fluid coupling. Which uses a fluid to transfer power from
the engine to the supercharger. The input shaft causes a fluid inside the
coupling to rotate around the casing with a pump, which in turn causes a turbine attached
to the output shaft to turn. This method of power transmission allowed
the supercharger to operate at various speeds, because the amount of oil inside the coupling
was controlled by a separate pump which gradually increased the amount of oil inside the coupling
as the plane gained altitude. [4] This prevented the supercharger from overpressuring
the engine and gave the BF109 engine superior power at lower altitudes. This gave the BF 109 E variant, which was
most widely used during the Battle of Britain, an edge over the Spitfire. While the Spitfire could out turn the 109,
the 109 had a better power to weight ratio, which allowed the 109 to sustain a climbing
turn to out manoeuvre a Spitfire on its tail. British engineers were well aware of this
issue prior to the Battle of Britain and development began on a two stage, two speed supercharger
for the Merlin engine in mid 1940. This allowed the supercharger to operate at
two different speeds via a gear change, but also introduced a second impeller which increased
the compression for even better high altitude performance. This increased compression caused an increase
in temperature of the air that would negatively affect engine efficiency, and so an intercooler
also had to be introduced to cool the supercharged air before entering the piston. This intercooler removed 33% of the heat added
by the supercharger. Removing more heat would have been beneficial
but there is a balancing act here. To remove more heat, the plane needed a larger
radiator to dump that heat to atmosphere and a larger radiator would result in more drag,
which negated the power increase. The radiator design was in fact one of the
chief ways the Spitfire managed to squeeze so much power out of its smaller Merlin engine. German engineers had noted how much smaller
the Spitfires radiators were, and knew exactly why. In one meeting between the chiefs of Germany’s
aviation development Messerschmitt noted that the Spitfires radiators were half the size
of their own, while the head of German engine development explained to an indignant government
official, that to reduce the radiator size would require higher coolant pressure which
their engine couldn’t tolerate without leaking. The British had developed high pressure high
temperature coolant systems for their high speed racing engines to compete in races like
the Schneider Trophy. The Germans were prohibited from participating
in these races by the treaty of Versaille, and so were left behind in the development
of this vital technology. Increasing the pressure of the coolant allowed
the engineers to raise the operating temperature of the coolant without it boiling. An increased temperature difference between
the radiator and the outside air increased the rate heat could radiate away from the
plane, and this allowed the Spitfires radiator to be much smaller. This did require the radiators to be stronger
and thus heavier, but the reduction in drag more than made up for the increased weight. The BF109 and Spitfire were formidable foes
to each other, and the difference between life and death more often than not came down
to the skill of the pilots and the strategic advantages the British had in fighting over
their home soil. The Battle of Britain was won on small margins
and the engineers of the Spitfire did everything they could to give the Spitfire an edge in
battle. But it and the much more numerous Hawker Hurricane
would not have stood a chance without the systems and procedures on the ground that
allowed them to get into the air, day after day. Radar, data processing, mapping, chain of
commands, pilot training and even fuel octane ratings all played a role in winning the battle
of Britain, and I explain it all in our Nebula Original series “The Battle of Britain”. Many of the animated sets, including the custom
made operations room at Bentley Priory, that you saw in this video were created for that
series and that’s the level of quality you can expect from all our Nebula Original series. There are currently 4 episodes available for
you to watch right now, with more on the way, along with our 7 part Logistics of D-Day series. Or you could watch my favourite recent Original
by Wendover Productions covering the history of Wake Island, a tiny remote island in the
middle of the Pacific with a rich history in aviation and world war 2. If you want to support this channel, watch
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