The
‘Sabre’ was also a 24-cylinder ‘H’ form engine but it was
horizontally opposed, not vertical as were the Rapier and Dagger, and
water-cooled, not air-cooled. This
engine had sleeve valves, and developed 2,200 bhp.
The radiator and oil cooler were carried in the air intake scoop
below the engine, which gave the aircraft its distinctive ‘chin’.
It was a more powerful engine than its rival the Merlin and was
fitted in the Hawker Typhoon, which was to replace the Hawker Hurricane.
The prototype Typhoon first flew in February 1940.
Although
too late for the Battle of Britain, with its speed of 420miles per hour,
this fighter was more than a match for the new Focke-Wulf 190, to give
the RAF superiority in the air. A
new role was then found for the ‘Tiffy’ as the Typhoon was to become
affectionately called. This
role was for the fighter to be used as a fast ground attack aircraft.
For this purpose it was fitted with four canons and eight
rockets. This gave it more
firepower than a light cruiser. It
became famous for its ability to knock out enemy trains and tanks.
 |
The
HAWKER TYPHOON IB in D-Day
Markings
This
aircraft is fitted with four cannons and eight rockets
|
After
the invasion it was found that there were problems with the engine, when
the aeroplanes were operated from makeshift, dusty airfields.
This was through lack of suitable air filters, allowing the dust
to cause wear in the cylinders. Napiers
reacted swiftly to the challenge. Within
a week they delivered, by air, a new momentum air filter, which fitted
to the aircraft air intakes. This
permitted the Typhoons to be used to achieve the breakout through the
Falaise Gap, which had held up the allied advance from Caen.
 |
The
HAWKER TEMPEST V Fighter Aircraft
|
The Typhoon was superseded by the Hawker Tempest,
which was faster and featured elliptical shaped wings reminiscent of the
Spitfire. Within the wings
were fitted four cannons. For
this aircraft, the Sabre engine was fitted with a four bladed propeller
and the power output had been increased to 2,600 bhp.
This made the fighter the fastest piston engined aircraft in the
world with a speed of 460 mph, which was needed to catch the V1
‘buzz-bombs’. A
development of the Tempest was the Hawker Fury which was fitted with the
Sabre VII engine developing 3,000 bhp, with which it achieved a speed of
490 mph.
 |
Hawker
Fury Fighter Aircraft |
The
Nomad Compound Engine
The
basic fuel efficiency of engines is inherently in their design.
Some design features of different engines within a type may be
altered to make one model marginally more efficient than another, but
for practical purposes the fuel consumption of an engine depends upon
its type and is of the order of the figures shown it the table below.
|
TYPE
OF ENGINE
|
FUEL
CONSUMPTION
|
|
Ram
Jet Engine
|
1.0
lb/hp/hr
|
|
Turbo-prop
Jet Engine
|
0.8
lb/hp/hr
|
|
Petrol
Engine
|
0.5
lb/hp/hr
|
|
Naturally
Aspirated Diesel Engine
|
0.4
lb/hp/hr
|
|
Turbo-charged
Diesel Engine
|
0.38
lb/hp/hr
|
|
Turbo-charged
& Intercooled Diesel Engine
|
0.36
lb/hp/hr
|
|
Compound
Engine
|
0.34
lb/hp/hr
|
The
Nomad engine was a combined diesel and gas turbine engine.
It was designed to have the lowest fuel consumption of any
aircraft engine by utilizing all the heat normally lost from the exhaust
of the piston engine, to feed the gas turbine.
On the earlier model, the diesel drove one propeller and the gas
turbine the other of a contra-rotating system.
Later a continuously variable gearbox was used to couple the two
outputs together. The
engine was demonstrated in flight, at the Farnborough Air Show in 1956,
fitted in the nose of a Lincoln Bomber.
The theory behind the design was for long distance flights, four
tons of engine with one ton of fuel was a more economic proposition than
one ton of engine and four tons of fuel.
The
Nomad engine was designed at a time when simple ram jet engines were
being used for high-speed fighter aircraft.
Lightweight turbo-prop jet engines driving propellers were
replacing piston engines in existing airframes.
The Comet aircraft had not yet flown.
When
the Comet first flew, it was discovered that the great savings in drag
of the aircraft, brought about by high altitude flight, were greater
than the losses through the inefficiency of the jet engine.
Propeller engine aircraft, which could not fly at high altitude,
were overall less efficient regardless of the savings made by them
having low fuel consumption. This
was the end of propeller driven commercial aircraft.
Development of the Nomad engine was, therefore, cancelled.
THE DELTIC ENGINE
Many of our Motor
Torpedo Boats and other high-speed craft were lost during the war
because of the extremely inflammable fuel that they used.
The Germans employed diesel engines in their E-Boats, which were
consequently less vulnerable. The
British Admiralty placed an order with Napier, for them to design and
develop a diesel engine suitable for the post war high-speed craft.
The subsequent design was the Deltic engine.
Although complex in its layout, the Deltic engine is
in fact fundamentally a very simple engine.
It is a two stroke, opposed piston engine, having the inlet ports
in each cylinder, being opened and closed by one piston and the exhaust
ports by the other. There
are neither cylinder heads nor poppet valves, and so no camshaft or
other valve gear. Being
opposed piston means there must be two crankshafts for each cylinder
bank; but by arranging the cylinders in an equilateral triangle means
that only three crankshafts are required for the engine.
There are six cylinders to each bank and three banks to make the
normal engine have 18 cylinders. A
variant having three banks of three cylinders was also built for
generating electricity for magnetic mine sweeping.
 |
SECTION
OF A DELTIC ENGINE |
For the engine proper, the only moving parts are the
pistons, connecting rods and crankshaft.
There is a fuel injection system with one pump per cylinder.
Being a two stroke, the engine needs a supercharger, which is a
gear-driven centrifugal compressor.
As the engine is self-contained it also has the dry sump
lubrication system and water cooling system.
The engine also incorporates a seawater circulating pump and an
ahead and astern gearbox complete with hydraulic clutch.
The engine has aluminium castings for lightweight, with stainless
steel studs and aluminum bronze nuts for high corrosion resistance.
This means that the engine has a very low magnetic weight, which
makes the unit eminently suitable for mine sweeping duties.
 |
Dark Avenger’ one of the Royal Navy’s Short Boats
|
The original engine
developed 2,500bhp at 2,000rpm and was used to power ‘Dark Avenger’
the first of 17 ‘Short Boats’ the ‘Dark’ class of MTBs built for
the Royal Navy. A lower
rating of 1,500 bhp at 1,750 rpm was used for the Coastal Minesweepers.
The first of these was HMS Highburton, this class was originally
powered, some with Mirrlees Blackstone engines and some with Deltics.
The Deltics proved to be so superior in service that the Mirrlees
boats were re-engined with Deltics.
Later versions of the coastal minesweepers had their hulls
constructed of GRP.
 |
HMS
HIGHBURTON the first Deltic Powered Coastal Minesweeper
|
The compact size of the
engine is the reason for it being used for many different vessels.
One of the most successful was the Norwegian ‘Nasty’ class of
MTBs. In addition to
Norway, the USA, Germany and Greece used these boats.
These were fitted with the more powerful turbo-charged version
delivering 3,100 bhp and were capable of 45 knots.
A Japanese Navy fast patrol boat fitted with 3 Deltic CT18-42K
engines delivering almost 3,700 bhp was capable of 50 knots.
Both the nine cylinder
and the eighteen cylinder engines were used for diesel-electric rail
traction. The former was in
a type II locomotive and two eighteen cylinder sets were fitted in the
famous ‘Deltic’ type V. The
prototype Deltic locomotive ‘Enterprise’ is currently on exhibition
in the British Museum. These
were the only diesel locomotives cleared to run at 100 mph.
 |
Type
V ‘DELTIC’ Diesel-electric Main Line Locomotive
|
CONCLUSION
Napier engines were
always very different from others.
With the changing form of the engines from ‘W’ (broad arrow)
‘Lion’, to vertical ‘H’ ‘Rapier’ and ‘Dagger’, to
horizontal ‘H’ ‘Sabre’ and to the triangular ‘Deltic, they
form a unique set not used by any other main engine builder.
However, in different ways they were each a world beater,
squeezing more cylinders into a small volume to give a remarkable power
to weight ratio and power to volume ratio.
It is doubtful if the power to weight ratio of less than 0.75 lb
per bhp of the Sabre engine will ever be surpassed by another piston
engine. Nor will the less
than 4 lb per bhp of the Deltic be beaten by another diesel.
No country in the world
has moved ahead, the speed performance on land, sea and air by vehicles,
as much as Britain. Also,
if the measure of progress is by the number of world records broken,
then D. Napier & Son must rank as the geatest mechanical engineering
company that ever existed.
It is sad that in these
modern times, companies need to be large in order to exist.
It was during the World War II that the Ministry of War
Production brought about the absorption of Napiers into the giant
English Electric Group of Companies, so that Napier lost a great deal of
its individuality. But it
was even sadder when in the 1960s economic forces drove English Electric
to sell off the aircraft engine departments to be lost within the rival
Rolls Royce Company, and for the marine departments to be sold off, then
to be lost within the great David Paxman & Company.
This small company with the great history is now being forgotten.
ACKNOWLEDGEMENTS
The author was employed
by D Napier & Son. from 1947 until 1960, the first four years as a
Student Apprentice and the last seven as a designer working on the
Deltic. During his time
there he had the opportunity to work on the Sealion, Sabre, Nomad and
Deltic engines. He
gratefully acknowledges the help and training he received and the
assistance he obtained from his colleagues.
The photographs and much
of the history of Napiers was taken from Alan Vessey’s grand book
‘Napier Powered’ printed by The Chalford Publishing Company Stroud.
He also wishes to
acknowledge the help given by members of the ‘Napier Power Heritage
Trust’ which is struggling to keep the fame of Napier engineering
alive.
[ Continue to Deltic
History - Page 2 ]
