Basic Engine Operation
Internal Combustion Basics
It is very helpful to understand the basics of internal
combustion engines. However, it isn't necessary for
playing Targetware.
An airplane needs energy to fly. This energy must
come from the fuel in the form of heat. An engine
is used to extract this energy from the fuel and convert
it into a mechanical force that turns the propeller.
The fuel is made up of carbon and hydrogen, which,
when ignited in the presence of oxygen, produces carbon
dioxide, water vapor, and heat! For all the fuel to
be burned, it must be combined with oxygen in a certain
ratio called the mixture ratio. This ratio is different
for different fuels. Methanol has a different ratio
than octane which is different again from nitro-methane.
The more fuel that can be burned in a given time,
the more power the engine will produce.
Piston Engines
A typical engine is made up of a number of cylinders,
each having a piston that moves up and down in the
cylinder. The linear motion of the piston is converted
to a rotational motion of the crankshaft by a connecting
rod. The fuel is ignited with a spark when the piston
is near the top of the cylinder. The heat released
directly increases the pressure on the piston, creating
a force that pushes the piston down and turns the
crankshaft. There are limits to this system, however.
As the piston moves up, it compresses the mixture,
raising its temperature. If the temperature becomes
too high, the fuel may ignite without a spark, before
the piston reaches the top! If this happens, the force
will slow the piston down and power will be lost.
This is sometimes called pre-ignition or detonation.
For this reason, the compression ratio of an engine
is limited by the properties of the fuel and some
heat energy is lost in the exhaust or transferred
to the engine itself. If temperatures can be reduced
in the cylinder, either by adding water, excess fuel
or by reducing the intake temperature through an intercooler,
then more fuel can be burned for more heat and power.
Engine Operation
A pilot has to manage several controls to operate
his aircraft. The most important of these are:
- Throttle
- Mixture
- Revolutions per Minute
- Propeller Pitch (for variable and automatic prop
pitch aircraft)
- Engine Temperature
- Various Engine Accessories (Boost, Nitrous, etc.)
The Throttle (aka the 'Go' Stick)
The throttle allows the pilot to control airflow
into the engine. That airflow is measured as pressure
and is shown in the manifold pressure gauge. This
may be expressed in PSI (pounds per square inch),
inches of mercury, atmospheres, or other measurements
of pressure. 'Throttling up,' i.e., increasing the
pressure on the engine's combustion cylinders, forces
a greater quantity of oxygen into the piston chambers.
This allows more fuel to be burned. Basically, more
pressure, bigger bang in the cylinders, faster plane.
The greater power from increasing the throttle pressure
doesn't come from simply turning the propeller faster;
the propeller rotation speed is controlled by the
RPM selector. Higher pressure turns the propeller
shaft harder, allowing it to absorb more torque and
the blades to catch more air. Grabbing air, not just
spinning the prop, is what makes the plane go faster.
Increase Throttle = = (equals
key)
Decrease Throttle = - (minus key)
Maximum Throttle = SHIFT + = (equals key)
Minimum Throttle = SHIFT + - (minus key)
Mixture
This is the combination of fuel and air that is ignited
within the piston chambers of the aircraft's engine.
The more fuel there is in the mixture, the more powerful
the combustion will be; the less fuel there is, the
weaker the combustion. A mixture with high fuel is
called rich, while a low fuel mixture is called
lean. At richer levels, the engine will provide
higher performance, but will consume fuel more rapidly.
At leaner levels, fuel is used more sparingly; this
is desirable for cruising over longer ranges, or for
periods of non-combat flight where high performance
is not needed. Of course, a richer mixture will use
more fuel than a lean one. Richer mixture, bigger
bang in the cylinders, faster plane.
Increase Mixture = ’ (apostrophe)
Decrease Mixture = ; (semi-colon)
Maximum (Rich) Mixture = Shift + ‘ (apostrophe)
Minimum (Lean) Mixture = Shift + ; (semi-colon)
Pilots should keep a wary eye on the engine temperature
gauges. Engines run at high performance levels for
long periods of time will tend to overheat, which
could lead to rough operation and seizure. Engines
produce the most heat at their optimal mixture (for
current flying conditions). Both richer and leaner
mixtures will actually run cooler. Richer mixtures
have undetonated fuel that acts as a cooling agent,
while leaner mixtures have a lower energy/heat ratio
per detonation.
Mixture can be manual or automatic. For manual operation
(not implemented yet), the fuel flow will have to
be reduced by 'leaning' the mixture as height is gained
due to lower air density. Failure to do so would eventually
result in the engine cutting out from flooding. For
automatic operation, there is usually an 'auto-rich'
setting and an 'auto-lean' setting. Auto-rich is used
for power settings resulting from supercharging where
manifold pressure is greater than the ambient air
pressure, to provide extra cooling. Auto-lean is the
preferred setting for cruising, providing an ideal
mixture ratio. There is also a 'cutoff' position to
stop fuel flow in order to shut down the engine.
RPMs (Revolutions Per Minute)
RPMs are controlled with a lever on planes that have
a constant speed propeller. This sets the rate at
with the propeller will rotate. It is independent
of the throttle and other settings. The constant speed
prop automatically adjusts the prop pitch to maintain
the RPMs at the rate set. Higher RPMs will draw more
fuel and increase drag.
These are the most elementary controls and understanding
them should allow you to optimize your performance
for different situations. If your goal is to maximize
the range of the aircraft, use a medium throttle setting,
a lean mixture and low RPMs. To go fast and hard when
fighting, use high throttle, a rich mixture, and high
RPMs, but don’t stray to far or you will run
out of fuel before you can return home. With
these simple controls, you should be able to deal
with the average situation. However, there are more
advanced controls that permit more efficient performance,
but they vary by plane type.
Increase RPM = ]
Decrease RPM = [
Maximum RPM = Shift + ]
Minimum RPM = Shift + [
Propeller Pitch (variable and automatic prop pitch
planes only)
The angle at which the propeller blades meet the
air plays an important role in aircraft performance
because it determines how easily the propeller blade
moves through the air.
For variable pitch props, the propeller blade angle
is manually adjusted to give maximum RPM for takeoff
and must be constantly adjusted in flight as speed
and/or altitude changes. While providing better efficiency
for takeoff and climb performance, it greatly increases
the pilot's workload.
With constant speed props, the pilot manually adjusts
the lever to give the desired RPM. The blade angle
of the propeller is automatically adjusted in flight
as speed and/or altitude changes. This is similar
to a variable-pitch prop, but the workload is greatly
reduced. For landing, fine pitch or high RPM is desired
as it adds drag and shortens the landing run. It also
ensures that full power is available by increasing
the throttle, should it be needed as in the case of
a go-around. Both throttle and propeller controls
should otherwise be operated together. When one is
changed, so should the other. Some airplanes even
have interconnected propeller controls with a manual
over-ride, so the pilot doesn't even have to do that.
Increase Prop Pitch = ]
Decrease Prop Pitch = [
Maximum Prop Pitch = SHIFT+]
Minimum Prop Pitch = SHIFT+[
Why are RPMs and Prop Pitch controls assigned
to the same key?
An aircraft is either has constant speed propeller
controls (which controls RPMs directly and automatically
adjusts the prop pitch) or variable pitch propeller
controls (which effect RPMs by manually changing the
pitch of the propeller). Since these controls are
mutually exclusive, it made sense to assign the functions
to the same keys.
Controlling Engine Temperature
For the pilot, there are three main instruments to
watch. The manifold or boost pressure gauge and the
RPM gauge are both a direct indication of power output
(and heat). There will also be a cylinder or coolant
temperature gauge, depending on whether the engine
is air-cooled or liquid-cooled. Cylinder temperatures
should not exceed 260C (500F) and coolant temperatures
usually become critical at 120C (~250F).
There are four methods of controlling the temperature:
- Cooling Flaps
- Increase Speed
- Reduce Power
- Mixture Control
The first method is to open the cooling flaps.
They can be opened or closed in 10% increments for
fine adjustment. Cooling flaps are opened with the
/ (slash) key and closed with the . (period)
key. Keep in mind that opening the cooling flaps will
add drag to the airframe. If that isn't enough, an
increase in airspeed will help to cool the engine
better. Finally, if that's still not enough, power
will have to be reduced with either the throttle (manifold
pressure) or the prop control (RPM) or a combination
of both. If the engine is allowed to overheat, it
will detonate and accumulate permanent damage until
it fails completely, unless temperatures are brought
back under control.
Increase Cooling Flaps = /
Decrease Cooling Flaps = .
Maximum Cooling Flaps = SHIFT+/
Minimum Cooling Flaps = SHIFT+.
Auto Cooling = ALT+/ (this must be enabled
on the server)
Finally, there is a mixture control. The three
settings being cutoff, auto-lean and auto-rich. The
'cutoff' setting shuts off fuel flow to the engine.
This could be important in flight if a dead engine
is wind milling and fuel continues to flow. Auto-lean
is the preferred setting for best power and minimum
fuel consumption. Auto-rich increases fuel consumption
by some 30% but also lets the engine run a little
bit cooler so that higher power settings can be used
without causing any further increase in temperature.
Mixture is controlled with the ; (semi-colon)
key to make it lean or cut it off and ' (apostrophe)
key to make it rich.
It may be possible for a propeller to over-rev in
a high speed dive, or if power is added too quickly.
If the engine over speeds too much, it could result
in a destroyed propeller and a seized engine, making
an emergency landing necessary. However, this is unlikely
to happen under normal circumstances.
If an engine should fail in flight and the airplane
has the ability, the propeller can be feathered.
This
will stop the propeller and minimize the drag.
Feather Engine = SHIFT+E
Note for Jets
Jets do not have to worry about Prop Pitch, RPMs,
or Mixture. They also do not have cooling flaps, blowers,
nitrous or ADI. And they do not suffer from the engine
torque of single-engine propeller driven aircraft.
Engine Accessories
There are several systems for improving basic engine
performance.
Blower
To increase the quantity of oxygen going into the
engine, and efficiency of the fuel burning there,
a Blower is used. Blower is a generic term
that includes compressors and superchargers. Higher
altitudes decrease the amount of oxygen available
because the density of air is lower. Blowers are used
to combat this effect. They increase the air pressure
going into the engine by ‘blowing’ air back
into it. This is done in different ways.
Blower settings should be set appropriately for the
plane’s altitude, if it's on at too low an altitude,
it is a waste because it draws power from the engine
that would otherwise be used for speed. Blowers are
operated in different ways on different planes. On
some planes they are totally automatic, such as the
F-51. Others, like the P-47, have only one setting,
so it isn't difficult to deal with. Yet others have
to be set by the pilot as conditions warrant, like
the F-4U. So, you only have to deal with the blower
on certain planes. The notes on each plane should
indicate what settings are necessary for different
altitudes.
Increase Blower = P
Decrease Blower = O
Auto Blower = SHIFT+P (this must be enabled
on the server)
Note: Turbochargers are distinct from superchargers.
They operate automatically (thus, no pilot controls),
using exhaust pressure to turn a turbine which drives
an air compressor. By comparison, superchargers use
engine power to drive an air compressor.
Boost
Boost is a temporary improvement in engine performance
that comes from exceeding the safe maximum engine
pressure. Planes often had a wire on the throttle
at the maximum safe pressure. The pilot could
get some extra performance by consciously pushing
the throttle through that wire. The added pressure
can overheat and wreck an engine if run too long.
This is sometimes called "dry combat power"
in American literature
In jets that have afterburners, the Boost command
controls them.
Boost = F10
Nitrous Oxide
Nitrous Oxide (N2O), aka “Laughing Gas”
is mostly oxygen (the nitrogen is easily separated).
Using nitrous oxide enriches the oxygen content in
the engine while simultaneously cooling the engine.
Essentially, it allows a plane to have sea level performance
at any altitude. However, if your airplane already
has a supercharger or turbocharger system, nitrous
is only useful above the plane's critical altitude
(the altitude at which the compressor can no longer
generate full manifold pressure, which is what gives
sea level power). Nitrous is stored in a tank somewhere
on the aircraft.
Nitrous = F9
Nitrous Selector = CTRL+\
ADI (Anti-Detonant Injection)
Various Anti-Detonant Injection (ADI) systems were
used in some aircraft to prevent fuel burning while
running at very high manifold pressures. These ranged
from water, to water/methanol mixtures, and other
chemical injections, kept in a special tank. Sometimes
referred to as "wet combat power," these
systems dramatically decrease the engine temperature
because fuel burning (which is what limits manifold
pressure) is controlled by both temperature and pressure.
This temperature drop, in addition to chemical effects
on the fuel, allows higher manifold pressures and
cooler running engines.
ADI = F11
ADI Selector = SHIFT+\
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