Gas Turbine Engine Types, Jet Turbine Engines, Auxiliary Power Units
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Almost all electrical power on Earth is produced with a turbine engine of
some type. Today, very high efficiency gas turbines harness about 40% of
the thermal energy, with the rest exhausted as waste heat. A gas turbine engine extracts energy from a flow of hot gas which is produced by combustion of gas, oil fuel or any other fuel producing gas, in a stream of compressed air. It has an upstream air compressor (radial or axial flow) mechanically coupled to a downstream turbine and a combustion chamber in between. "Gas turbine" may also refer to just the turbine element. |
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Energy is released when compressed air is mixed with fuel and ignited in the combustor.
The resulting gases are directed over the turbine's blades, spinning the turbine,
and mechanically powering the compressor.
Finally, the gases are passed through a nozzle, generating additional thrust by
accelerating the hot exhaust gases by expansion back to atmospheric pressure.
Energy is extracted in the form of shaft power, compressed air and thrust, in any
combination, and used to power aircraft, trains, ships, electrical generators, and
even tanks.
Jet Turbine Engines
Airbreathing Jet Turbine Engines are gas turbine engines optimized to produce thrust from the exhaust gases, or from ducted fans connected to the gas turbine engines. Jet engines that produce thrust primarily from the direct impulse of exhaust gases are often called turbojets, whereas those that generate most of their thrust from the action of a ducted fan are often called turbofans or (rarely) fanjets.
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A Jet Turbine Engine is an engine that discharges a fast moving jet of fluid
to generate thrust in accordance with Newton's third law of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets and pump-jets. But in common usage, the term generally refers to a gas turbine Brayton cycle engine, an engine with a rotary compressor powered by a turbine, with the leftover power providing thrust. |
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Jet Turbine Engines are so familiar to the modern world that gas turbine engines
are sometimes mistakenly referred to as a particular application of a jet engine,
rather than the other way around. Most jet engines are internal combustion
engines but non combusting forms exist also.
Jet Turbine Engines can be dated back to the first century AD, when Hero
of Alexandria invented the Aeolipile. This used steam power directed through two jet
nozzles so as to cause a sphere to spin rapidly on its axis. So far as is known,
it was little used for supplying mechanical power, and the potential practical applications
of Hero's invention of the jet engine were not recognized. It was simply considered
a curiosity.
Jet propulsion only literally and figuratively took off with the invention of the
rocket by the Chinese in the 11th century. Rocket exhaust was initially used in
a modest way for fireworks but gradually progressed to propel formidable weaponry;
and there the technology stalled for hundreds of years.
In Ottoman Turkey in 1633 Lagari Hasan Çelebi took off with what was described to
be a cone shaped rocket and then glided with wings into a successful landing winning
a position in the Ottoman army. However, this was essentially a stunt.
The problem was that rockets are simply too inefficient at low speeds to be useful
for general aviation. Instead, by the 1930s, the piston engine in its many different
forms (rotary and static radial, aircooled and liquid-cooled inline) was the only
type of powerplant available to aircraft designers. This was acceptable as long
as only low performance aircraft were required, and indeed all that were available.
However, engineers were beginning to realize that the piston engine was self-limiting
in terms of the maximum performance which could be attained; the limit was essentially
one of propeller efficiency. This seemed to peak as blade tips approached the speed
of sound. If engine, and thus aircraft, performance were ever to increase beyond
such a barrier, a way would have to be found to radically improve the design of
the piston engine, or a wholly new type of powerplant would have to be developed.
This was the motivation behind the development of the gas turbine engine, commonly
called a "jet" engine, which would become almost as revolutionary to aviation as
the Wright brothers' first flight.
The earliest attempts at jet engines were hybrid designs in which an external
power source first compressed air, which was then mixed with fuel and burned for
jet thrust. In one such system, called a thermojet by Secondo Campini but more commonly,
motorjet, the air was compressed by a fan driven by a conventional piston engine.
Examples of this type of design were Henri Coandă's Coandă-1910 aircraft, and the
much later Campini Caproni CC.2, and the Japanese Tsu-11 engine intended to power
Ohka kamikaze planes towards the end of World War II. None were entirely successful
and the CC.2 ended up being slower than the same design with a traditional engine
and propeller combination.
The key to a practical jet engine was the gas turbine, used to extract energy
from the engine itself to drive the compressor. The gas turbine was not an idea
developed in the 1930s: the patent for a stationary turbine was granted to John
Barber in England in 1791. The first gas turbine to successfully run self-sustaining
was built in 1903 by Norwegian engineer Ægidius Elling. The first patents for jet
propulsion were issued in 1917. Limitations in design and practical engineering
and metallurgy prevented such engines reaching manufacture. The main problems were
safety, reliability, weight and, especially, sustained operation. In 1923, Edgar
Buckingham of the US National Bureau of Standard published a report expressing skeptism
that jet engines would be economically competitive with prop driven aircraft at
low altitude and the airspeeds of the period.
In 1929, Aircraft apprentice Frank Whittle formally submitted his ideas for a turbo-jet
to his superiors. On 16 January 1930 in England, Whittle submitted his first patent
(granted in 1932). The patent showed a two-stage axial compressor feeding a single-sided
centrifugal compressor. Whittle would later concentrate on the simpler centrifugal
compressor only, for a variety of practical reasons. Whittle had his first engine
running in April 1937. It was liquid-fuelled, and included a self-contained fuel
pump. Whittle's team experienced near-panic when the engine would not stop, even
after the fuel was switched off. It turned out that fuel had leaked into the engine
and accumulated in pools. So the engine would not stop until all the leaked fuel
had burned off. Whittle was unable to interest the government in his invention,
and development continued at a slow pace.
In 1935 Hans von Ohain started work on a similar design in Germany, unaware of Whittle's
work. His first engine was strictly experimental and could only run under external
power, but he was able to demonstrate the basic concept. Ohain was then introduced
to Ernst Heinkel, one of the larger aircraft industrialists of the day, who immediately
saw the promise of the design. Heinkel had recently purchased the Hirth engine company,
and Ohain and his master machinist Max Hahn were set up there as a new division
of the Hirth company. They had their first HeS 1 engine running by September 1937.
Unlike Whittle's design, Ohain used hydrogen as fuel, supplied under external pressure.
Their subsequent designs culminated in the gasoline-fuelled HeS 3 of 1,100 lbf (5
kN), which was fitted to Heinkel's simple and compact He 178 airframe and flown
by Erich Warsitz in the early morning of August 27, 1939, from Marienehe aerodrome,
an impressively short time for development. The He 178 was the world's first jet
plane.
Auxiliary Power Units (APU)
Auxiliary power units (APUs) are small gas turbines designed for auxiliary
power of larger machines, such as those inside an aircraft. They supply compressed
air for aircraft ventilation (with an appropriate compressor design), start-up power
for larger jet engines, and electrical and hydraulic power.
These are not to be confused with the auxiliary propulsion units, also abbreviated
APUs, aboard the gas-turbine-powered Oliver Hazard Perry-class guided-missile frigates.
The Perrys' APUs are large electric motors that provide maneuvering help in close
waters, or emergency backup if the gas turbines are not working.
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An Auxiliary power unit (APU) is a device on a vehicle whose purpose is to
provide energy for functions other than propulsion. Different types of APU are found on aircraft, as well as some large ground vehicles. An aircraft APU is a relatively small gas turbine used to produce shaft power to start the jet engines, usually with compressed air, and to provide electricity, hydraulic pressure and air conditioning while the aircraft is on the ground. |
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In many aircraft, the APU can also provide electrical power in the air through a
generator installed on the gearbox.
A gasoline-petrol piston engine APU was first used on the Pemberton-Billing P.B.31
Nighthawk Scout aircraft in 1916. The Boeing 727 in 1963 was the first jetliner
to feature a gas turbine APU, allowing it to operate at smaller, regional airports,
independent from ground facilities.
Although APUs have been installed in many locations on various military and commercial
aircraft, they are usually mounted at the rear of modern jet airliners. The APU
exhaust can be seen on most modern airliners as a small pipe exiting at the aircraft
tail.
In most cases the APU is powered by a small gas turbine engine that provides compressed
air from within or drives an air compressor (load compressor). Recent designs have
started to explore the use of the Wankel engine in this role. The Wankel offers
power-to-weight ratios better than normal piston engines and better fuel economy
than a turbine.
APUs are also fitted to some tanks to provide electrical power when stationary,
without the high fuel consumption and large Infrared signature caused by running
the main engine.
Some commercial vehicles now mount Auxiliary power units of their own. A
typical APU for a commercial truck is a small diesel engine with its own cooling
system, heating system, generator or alternator system, and air conditioning compressor,
mounted to one of the frame rails of a semi-truck along with an internally mounted
inverter in some cases. This unit is used to provide climate control and electrical
power for the truck's sleeper cab and engine block heater during downtime on the
road.
In the United States, federal Department of Transportation regulations require 10
hours of rest for every 11 hours of driving. During these times, truck drivers often
idle their engines to provide heat, light, and power for various comfort items.
Although diesel engines are very efficient when idling, it is still financially
and environmentally costly to idle them like this, from a fuel consumption and an
engine wear perspective.
The APU is designed to eliminate these long idles. Since the generator engine is
a fraction of the main engine's displacement, it uses a fraction of the fuel; some
models can run for eight hours on a US gallon (≈ 4 litres) of diesel.
The generator also powers the main engine's block and fuel system heaters, so the
main engine can be started easily right before departure if the APU is allowed to
run for a period beforehand. An APU can save up to 20 gallons (Cat 600 - 10 hours
downtime @ 2 gallons per hour idling) (≈ 76 litres) of fuel a day, and can extend
the useful life of the main engine by around 100,000 miles (≈ 160,000 kilometres),
by reducing non-productive run time.
Some vehicle APUs can also use an external shore power connection for their heating
and cooling functions, thus eliminating fuel consumption during rest periods altogether.
Many truck stops already provide shore power connections in their parking areas.
On some older diesel engines an APU was used instead of an electric motor to start
the main engine.
These were primarily used on large pieces of construction equipment. As an alternative
to the diesel units, APUs using an auxiliary battery system or hydrogen fuel cells
as a source of power have also been designed. Freightliner has shown a demonstration
model of a fuel cell APU, run on a tank of liquid hydrogen mounted to the truck,
on one of their Century Class S/T road tractors.
Gas Turbines for Electrical Power Production
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Industrial gas turbines range in size from truck-mounted mobile plants to enormous,
complex systems. They can be particularly efficient——up to 60%——when waste heat from the gas turbine is recovered by a heat recovery steam generator to power a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration. A cogeneration configuration can be over 90% efficient. |
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The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600
rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox.
Such engines require a dedicated enclosure.
Simple cycle gas turbines in the power industry require smaller capital investment
than either coal or nuclear power plants and can be scaled to generate small or
large amounts of power. Also, the actual construction process can take as little
as several weeks to a few months, compared to years for base load power plants.
Their other main advantage is the ability to be turned on and off within minutes,
supplying power during peak demand.
Since they are less efficient than combined cycle plants, they are usually used
as peaking power plants, which operate anywhere from several hours per day to a
couple dozen hours per year, depending on the electricity demand and the generating
capacity of the region.
In areas with a shortage of base load and load following power plant capacity, a
gas turbine power plant may regularly operate during most hours of the day and even
into the evening.
A typical large simple cycle gas turbine may produce 100 to 300 megawatts of power
and have 35–40% thermal efficiency. The most efficient turbines have reached 46%
efficiency.
Turboshaft Engines
Turboshaft Engines are often used to drive compression trains (for example in gas pumping stations or natural gas liquefaction plants)and are used to power almost all modern helicopters. The first shaft bears the compressor and the high speed turbine (often referred to as "Gas Generator" or "N1"), while the second shaft bears the low speed turbine (or "Power Turbine" or "N2"). This arrangement is used to increase speed and power output flexibility.
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A Turboshaft Engine is a form of gas turbine which is optimized to produce
shaft power, rather than jet thrust. In principle a turboshaft engine is similar to a turbojet, except the former features additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power. Ideally there should be little residual thrust energy in the exhaust and the power turbine should be free to run at whatever speed the load demands. |
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The general layout of a Turboshaft Engine is similar to that of a turboprop,
the main difference being the latter produces some residual propulsion thrust to
supplement that produced by the shaft driven propeller.
Another difference is that with a turboshaft the main gearbox is part of the vehicle
(e.g. helicopter rotor reduction gearbox), not the engine. Virtually all turboshafts
have a "free" power turbine, although this is also generally true for modern turboprop
engines. At a given power output, compared to the equivalent piston engine, a turboshaft
is extremely compact and, consequently, lightweight.
The name turboshaft is most commonly applied to engines driving ships, helicopters,
tanks, locomotives and hovercraft or those used as stationary power sources.
The first true Turboshaft Engine was built by the French engine firm Turbomeca,
led by the founder, Joseph Szydlowski. In 1948 they built the first French-designed
turbine engine, the 100shp 782. In 1950 this work was used to develop the larger
280shp Artouste, which was widely used on the Aérospatiale Alouette II and
other helicopters. The distinct whine of the Artouste is familiar to all those who
have watched a 1967 UK television series The Prisoner, since an Alouette was featured
in many of the episodes. Note that Artouste is also the name of an unrelated English
design, the Blackburn Artouste.
Major efforts were underway in the United States and the United Kingdom to build
similar engines. In the US Anselm Franz followed the same principles of simplicity
that he used to develop the Jumo 004 in Germany, producing the T53 engine at Lycoming
in 1953, and following this with the larger T55. General Electric beat his design
into operation with their T58 series.
Today almost all engines are built so that power-take-off is independent of engine
speed, using the free turbine stage. This has two advantages:
1. It allows a helicopter rotor or propeller to spin at any speed instead of being
geared directly to the compressor turbine.
2. It allows the engine to be split into two sections, the "hot section" containing
the majority of the engine, and the separate power-take-off, allowing the hot-section
to be removed for easier maintenance.
This leads to slightly larger engines—compare the Pratt & Whitney PT-6 and similar
models from Garrett Systems, for instance—but for the speed ranges served by these
engines it is considered to be unimportant. Today practically all smaller turbine
engines come in both turboprop and turboshaft versions, differing primarily in their
accessory systems.
Some vehicle APUs can also use an external shore power connection for their heating
and cooling functions, thus eliminating fuel consumption during rest periods altogether.
Many truck stops already provide shore power connections in their parking areas.
On some older diesel engines an APU was used instead of an electric motor to start
the main engine. These were primarily used on large pieces of construction equipment.
As an alternative to the diesel units, APUs using an auxiliary battery system or
hydrogen fuel cells as a source of power have also been designed. Freightliner has
shown a demonstration model of a fuel cell APU, run on a tank of liquid hydrogen
mounted to the truck, on one of their Century Class S/T road tractors.
Radial Gas Turbines
In 1963, Norway, Jan Mowill initiated the development of the Radial Gas Turbine
at Kongsberg Våpenfabrikk. The turbine had a unique, all radial configuration, originally
rated at 1,200 kW. The turbine proved very successful and was generally sold in
electric generating packages. The major markets for the units were in the maritime,
offshore oil and gas and communications industries.
During the following years, more than a thousand units were delivered world wide.
Kongsberg Våpenfabrikk was privatized, split up and sold off in the late nineteen
eighties and development of the original turbine business was discontinued under
the new ownership. As a result, Jan and Hiroko Mowill founded OPRA in Hengelo
in 1991.
Consequently the first 1.6 MW OP16 was designed as a single shaft, all-radial machine.
NOx emissions were developed to a very low level for both diesel fuel and natural
gas. This was achieved with a unique, patented fuel and air pre-mixer in connection
with an annular combustor.
The current production model, OP16-3 features both single and dual fuel operation
as well as low emissions on natural gas. For improved maintenance and serviceability,
a four can combustion systems was favored rather than the annular combustor used
on the prototype.
For a single stage radial turbine the pressure ratio of 6.7: 1 is relatively high,
which entails a high turbine impeller tip speed of 700 m/s (equal to the velocity
of a rifle bullet).
Since this is nearly the same as the velocity of the gas entering the impeller tip
from the nozzle guide vanes, an "impact" between the hot gas and the turbine impeller
is avoided.
It could be said that this phenomenon constitutes "dynamic" cooling gaining about
100°C compared to a temperature increase in an axial turbine. OPRA's radial turbine
is able to take this high tip speed due to it's "Eiffel Tower" shape with a strong
base and a thinner blade tip region with low stresses. Having low stresses in the
hot tip region and higher stresses in the cold, "fat" hub region makes OPRA work
with nature rather than against it.
The OPRA radial turbine stage has an advanced aerodynamic design with an efficiency
of 90% from the inlet of the guide vanes to the exhaust diffuser exit.
The efficient centrifugal compressor has a very good "match" with the turbine as
their optimal running speeds are similar.
Since both compressor and turbine are close coupled via a Hirth-type teeth connection,
an overhung rotor suspension is possible. This system provides balance integrity
despite the differential thermal expansions between the compressor and turbine.
A ball bearing is placed in the front of the rotor support housing taking the combined
thrust- and radial load. The rear, tilting pad bearing takes the main radial load.
The cantilever, or overhung suspension of the rotor places the bearings in the cold
section of the engine, avoiding oil supply to hot bearings. This system has considerable
positive impact on engine reliability and maintenance.
A flexible coupling connects the turbine to the two stage planetary gearbox, reducing
the turbine speed from 26000 to 1500 or 1800 rpm, depending on generator speed requirements.
The OP16-3 has an ISO rating of 1.9 MW. The engine efficiency of nominally 27% is
at the highest level in the below 2 MW power range. Past competitors (no longer
active) in this range have been at the 23–25% level.
Utilising proven radial gas turbine technology, the OP16 gas turbine is a compact,
efficient and reliable industrial gas turbine designed for supplying power generation
applications to both the Oil and Gas and Industrial markets.
The OP16 generator sets can be provided in a variety of configurations to meet customer
specific requirements. The engineering design, component selection and maintenance
accessibility of the generator sets enhance high reliability and long product life.
The generator sets can be provided with low emission and dual and multifuel capabilities.
Single or multiple OP16 units can effectively cover installations from 1.5 to 10
MW electric power demand.
OPRA provides gas turbine generating sets for customers world-wide within the oil
& gas and industrial sectors. OPRA's 2 MW class OP16 gas turbine is of an industrial,
all-radial design which provides robustness, reliability and class leading efficiency
and emissions. Dual fuel and off-specification fuel options are also available.
Complete gas turbine generating sets are engineered to meet customer specific requirements
both for land based and offshore applications.
Scale Jet Engines
Also known as miniature gas turbines or micro-jets.
Many model engineers relish the challenge of re-creating the grand engineering feats
of today as tiny working models. Naturally, the idea of re-creating a powerful engine
such as the jet, fascinated hobbyists since the very first full size engines were
powered up by Hans von Ohain and Frank Whittle back in the 1930s.
Recreating machines such as engines to a different scale is not easy. Because of
the square-cube law, the behaviour of many machines does not always scale up or
down at the same rate as the machine's size (and often not even in a linear way),
usually at best causing a dramatic loss of power or efficiency, and at worst causing
them not to work at all.
An automobile engine, for example, will not work if reproduced in the same shape
at the size of a human hand.
With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one
of the world's first Micro-Turbines, the FD3/67. This engine can produce up to 22
newtons of thrust, and can be built by most mechanically minded people with basic
engineering tools, such as a metal lathe.
Its radial compressor, which is cold, is small and the hot axial turbine is large
experiencing more centrifugal forces, meaning that this design is limited by Mach
number. Guiding vanes are used to hold the starter, after the compressor and before
the turbine, but not after that. No bypass within the engine is used.
Microturbine Engines
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Also known as:
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Microturbine Engines are becoming wide spread for distributed power and combined
heat and power applications. They range from hand held units producing less than
a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts.
Part of their success is due to advances in electronics, which allows unattended
operation and interfacing with the commercial power grid. Electronic power switching
technology eliminates the need for the generator to be synchronized with the power
grid. This allows the generator to be integrated with the turbine shaft, and to
double as the starter motor.
Microturbine Engine systems have many advantages over reciprocating engine
generators, such as higher power density (with respect to footprint and weight),
extremely low emissions and few, or just one, moving part. Those designed with foil
bearings and air-cooling operate without oil, coolants or other hazardous materials.
Microturbine Engines also have the advantage of having the majority of their
waste heat contained in their relatively high temperature exhaust, whereas the waste
heat of recriprocating engines is split between its exhaust and cooling system.
However, reciprocating engine generators are quicker to respond to changes in output
power requirement and are usually slightly more efficient, although the efficiency
of microturbines is increasing. Microturbines also lose more efficiency at low power
levels than reciprocating engines.
They accept most commercial fuels, such as natural gas, propane, diesel and kerosene.
They are also able to produce renewable energy when fueled with biogas from landfills
and sewage treatment plants.
Microturbine Engine designs usually consist of a single stage radial compressor,
a single stage radial turbine and a recuperator. Recuperators are difficult to design
and manufacture because they operate under high pressure and temperature differentials.
Exhaust heat can be used for water heating, drying processes or absorption chillers,
which create cold for air conditioning from heat energy instead of electric energy.
Typical microturbine efficiencies are 25 to 35%. When in a combined heat and power
cogeneration system, efficiencies of greater than 80% are commonly achieved.
MIT started its millimeter size turbine engine project in the middle of the 1990s
when Professor of Aeronautics and Astronautics Alan H. Epstein considered the possibility
of creating a personal turbine which will be able to meet all the demands of a modern
person's electrical needs, just like a large turbine can meet the electricity demands
of a small city. According to Professor Epstein current commercial Li-ion rechargeable
batteries deliver about 120-150 Wh/kg. MIT's millimeter size turbine will deliver
500-700 Wh/kg in the near term, rising to 1200-1500 Wh/kg in the longer term.
Advances in Technology
Gas turbine technology has steadily advanced since its inception and continues
to evolve; research is active in producing ever smaller gas turbines. Computer design,
specifically CFD and finite element analysis along with material advances, has allowed
higher compression ratios and temperatures, more efficient combustion, better cooling
of engine parts and reduced emissions.
Computational fluid dynamics (CFD) is one of the branches of fluid mechanics that
uses numerical methods and algorithms to solve and analyze problems that involve
fluid flows. Computers are used to perform the millions of calculations required
to simulate the interaction of fluids and gases with the complex surfaces used in
engineering.
However, even with simplified equations and high-speed supercomputers, only approximate
solutions can be achieved in many cases. More accurate software that can accurately
and quickly simulate even complex scenarios such as transonic or turbulent flows
are an ongoing area of research. Validation of such software is often performed
using a wind tunnel.
On the emissions side, the challenge in technology is actually getting a catalytic
combustor running properly in order to achieve single digit NOx emissions to cope
with the latest regulations. Additionally, compliant foil bearings were commercially
introduced to gas turbines in the 1990s. They can withstand over a hundred thousand
start/stop cycles and eliminated the need for an oil system.
Foil bearings are a type of air bearing. A shaft is supported by a compliant, spring
loaded foil journal lining. Once the shaft is spinning fast enough, the working
fluid (usually air), pushes the foil away from the shaft so that there is then no
contact. The shaft and foil are separated by the air's high pressure which is generated
by the rotation which pulls gas into the bearing via viscosity effects. A high speed
of the shaft with respect to the foil is required to initiate the air gap, and once
this has been achieved, no wear occurs. Unlike aero or hydrostatic bearings, foil
bearings require no external pressurisation system for the working fluid, so the
hydrodynamic bearing is self-starting.
On another front, microelectronics and power switching technology have enabled commercially
viable micro turbines for distributed and vehicle power.
Advantages and Disadvantages of Gas Turbine Engines
Advantages of Gas Turbine Engines
- Very high power-to-weight ratio, compared to reciprocating engines (ie. most road
vehicle engines);
- Smaller than most reciprocating engines of the same power rating;
- Moves in one direction only, with far less vibration than a reciprocating engine,
so very reliable;
- Simpler design;
- Low operating pressures;
- High operation speeds;
- Low lubricating oil cost and consumption.
Disadvantages of Gas Turbine Engines
- Cost is much greater than for a similar-sized reciprocating engine (very high-performance,
strong, heat-resistant materials needed);
- Use more fuel when idling compared to reciprocating engines - not so good unless in continual operation.
These disadvantages explain why road vehicles, which are smaller, cheaper and follow a less regular pattern of use than tanks, helicopters, large boats and so on, do not use gas turbine engines, regardless of the size and power advantages imminently available.
Business Tips
Some tips on how to avoid business failure:
- Don't underestimate the capital you need to start up the business.
- Understand and keep control of your finances - income earned is not the same as
cash in hand.
- More volume does not automatically mean more profit - you need to get your pricing
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- Make sure you have good software for your business, software that provides you with a good reporting picture of all aspects of your business operations.
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