Aviation Powerplants Essay, Research Paper
Aviation Powerplants
Aviation has reshaped modern life and has provided for extreme convenience for
traveling businessmen, vacationers, and thrillseekers alike. It also plays a key role in
military operations of all kinds. Although aircraft design progression plays a predominant
role in advancing speed, agility, utility, and entertainment; none of these would be
possible without powerplant development, refinement and modification.
Aviation powerplants originated with the Wright flyer and its small 2 cylinder
inline engines of a mere 45 horsepower. This style engine dominated aviation well into
the First World War. They were generally placed in pushing positions (rear-facing) and
produced a relatively low number of revolutions per minute (2500 RPM redline). There
was little need for new engine development at this time because aircraft design
progressed slowly.
Rotary engines became popular around 1910 and powered many fighters and
bombers in The First World War. These engines are placed in a radial pattern around the
crankshaft. These produced respectable horsepower numbers in the category of up to
185+. They were used in such famous aircraft as the Sopwith Camel and Moth. A
variation of the rotary engine was used in the most famous aircraft of the war: The
Fokker Dr.1 Triplane flown by Baron Von Richtofen. A unique feature of these engines
is that they had no throttle, but ran at a constant speed. Also the cylinders were not fixed
in place as one might expect. They instead rotated around a fixed crankshaft. The
propeller was attached to the cylinders. The advantage of this configuration was lowered
production time and elimination of a costly and vulnerable cooling system. Speed control
was gained by cutting the fuel supply and thus shutting down the engine. The engine
would retain enough momentum to allow the pilot to simply turn back on the fuel system
and restart the engine to get power.
Rotary and small inline engines soon gave way to the large Radial engines of
World War 2. These were configured in a radial pattern similar to that of Rotary engines.
They, however do not have a fixed crankshaft but instead directly spin the propeller from
a moving crankshaft. Throttles are included here to slow down for combat while still
staying out of a stall. The Radial engines produced immense amounts of horsepower.
One example of this is the 18 cylinder dual layer Pratt & Whitney R-2800 (from the P-47
Thunderbolt, also the best aircraft of the war). Stock, the engine produces 2100+
horsepower. This engine, when coupled with a Turbo-Supercharger (for altitudes above
20,000 feet) it produces 2500+ horsepower. The radial engines also boast survivability
far beyond that of inline or V-configurations. One 18 cylinder Radial was found with 17
30mm cannon shells imbedded in the engine block. The radial engine is a great package:
survivability, durability, reliability, power, and acceleration.
Inline water-cooled engines were also available during World War 2. These are
similar to the ones in standard cars, except they are larger (12 -24 cylinders) and develop
more horsepower (up to 1600). The drawbacks to using inline engines include:
vulnerability due to the necessity of a radiator; and a head on 30 mm cannon shot can
take out numerous cylinders and physically stall the engine.
Horizontally opposed engines are still used today in small private aircraft
(Cessna, Bonanza, etc.). These, however, do not use the distributors or computers used to
control the spark as do the newer cars. They instead use magnetos and spark plugs
because these technologies have been proven and used for nearly 100 years. Also, no fuel
injection is used but instead carburetors are the standard. They are standard FAA
approved equipment and will not likely be replaced soon.
In late 1945, the first turbofan engine was used in an active combat aircraft. The
turbofan provides enormous amounts of thrust (35,000 lbs. without afterburners, upwards
of 60,000 maximum with afterburners). The turbofan works in six stages:
1)Air is sucked into the intake and compressed in stages by turbine blades that spin
3/1000ths of an inch from each other. 4-6 stage compression.
2)Compressed air is injected with high explosive jet fuel and moves into the combustion
chamber
3)Air fuel mix is incinerated and the resulting superheated gases move into a second set
of fan blades.
4)Here the hot gasses (1800-2500 degrees) drive turbine blades that create energy to
augment the first compression stage’s effectiveness.
5)The gasses then move into an optional augmentor (more commonly known as an
afterburner) where raw jet fuel is forced into a second combustion chamber and is burned
immediately due to high temperatures.
6)Gasses escape from an exhaust nozzle and provide thrust.
The turboprop and turbojet engines follow the same principles as the turbofan but
with a few variations. The turboprop is simply a turbofan with a geared-down prop
attached to the main shaft of the fan blades. The turbojet compresses about 10% of the
incoming air and the rest bypasses the combustion chamber(s) and is used to cool the
blades, compressors, and generators.
A new experiment in propulsion is the ramjet. The ramjet is in principle one of
the simplest possible flight propulsion units. It is essentially a duct open at front and rear.
At high speed in flight, air is rammed into the front of the duct, whose shape immediately
reduces the air’s speed, compressing and heating it. In a combustion chamber, fuel is
injected into the airstream, which is ignited. Extremely high temperatures can be reached
and very high fuel efficiencies achieved. The intensely hot exhaust gas then exits in a
propulsive stream through a discharge nozzle. Unlike gas-turbine jet engines, the ramjet
can be used only to propel vehicles already in flight. Applications have been confined
mainly to missiles, where a ramjet takes over after a rocket has propelled the missile to
supersonic speeds. The experimental SCRAMJET (supersonic combustion ramjet) will
propel vehicles at hypersonic speeds (above Mach 6) with gases moving through the
combustion chamber at supersonic speeds.