Systems Outline

Nick Kraynyk
CFI Ground

1. Pitot Static System.

The pitot static system is a system used in the Arrow for the altimeter, VSI, and airspeed
indicator. The system will use static pressure, and dynamic pressure created from traveling
through the air. By measuring the difference and changes between these two, we can determine
our altitude, airspeed, and rate of climb.

PHAK
The measure of dynamic is pressure is found by finding the strength of the ram air
coming into the pitot tube. In simple terms, as we fly through the air faster, more air will be
passing by and it is the job of the pitot tube to capture some of that air and measure how much
pressure is behind it, also known as its speed

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Air will flow through the hole in the front of the tube and we captured in the pressure
chamber deeper in. The dynamic pressure is then mixed with static pressure to create a total
pressure. This total pressure is then piped to the ASI where it is combined with a second static

pressure to cancel the first static pressure present in the pitot tube. This means only the dynamic
pressure is left to be indicated by the instrument. As the dynamic pressure increases the airspeed
indicator will show and increase in airspeed.
The pitot tube needs to be clear of any contaminates to indicate a correct airspeed. If a
bug gets stuck in the tube and blocks it then we are unable to receive airspeed information. Past
accidents have shown us that icing is a large factor on the pitot tube. As ice builds up and blocks
the ram air input we slowly lose the ability to get any airspeed information. This is why heaters
are installed on the tube itself and are used very often in air carrier aircraft. At the opposite end
of the pitot there is a drain hole which allows any moisture to escape. This allows any ice inside
the tube to be melted and expelled, or any moisture at all to be expelled from the system so we
can receive accurate information.
How do we know if the system is blocked? We can one of two indications, the airspeed
dropping to 0, or the airspeed remains unchanged. If the ram air hole and the drain hole both
become clogged, for example ice as surrounded the tube, the pressure becomes trapped inside the
system and the instrument will not detect any changes, meaning airspeed indicator will not move.
Until we climb or descend and the static pressure changes, as we climb to a higher altitude lower
outside pressure means the trapped dynamic pressure seems higher. Conversely for descents.
Meaning the airspeed indicator will go up when you climb, and go down when you descend.
If the ram air hole is blocked but the drain hole remains open then the pressure inside is
allowed to escape, this means over time dynamic pressure will become equal to the outside
pressure (static pressure), so our airspeed indication will drop to 0.
The ASI is the only instrument to use the static and dynamic pressure so we must
understand how static pressure works as well.

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Static pressure is measured from small holes on undisturbed airflow parts over the
aircraft. As the outside pressure changes so does the static pressure in the lines which allow
pressure to move freely in and out of the system. As we climb, outside pressure will go down and
as we descend outside pressure will increase.

Like the pitot system, this system can be blocked, but unlike the pitot system there is
usually a second static port and system present on the aircraft. This second source is usually
found inside the flight deck, but due to decreased pressure inside the aircraft from the airflow
over the aircraft there can be some errors in reading.

Altimeter will read slightly higher than normal.

ASI indicates a greater airspeed than actual speed.
VSI shows a momentarily climb then stabilizes if altitude is stable.

Another way to create an alternate static source is to punch the glass out of an instrument
using the static system. The best instrument to pick if doing this is the VSI because it is the least
important of all the indications.
The static system is present in all three instruments, and is the single input in the
altimeter and VSI.

Wikipedia.com
This is what the inside of an altimeter looks like. Its job is to measure height above sea
level (more specifically height above a pressure level). The sandwich looking gold things are
called wafers and are sealed with a pressure of 29.92 of mercury. These wafers expand and
contract based on the static pressure surrounding them. As we increase altitude the outside
pressure decreases, static pressure decreases because of that, and the wafers can expand a certain
amount more because of that decreased pressure. This expansion and contraction can be
calibrated and used as an indication in the flight deck to indicate our altitude.

weather.com
In the Arrow, we are able to adjust the setting on the altimeter, and it is important to know
why and what that does. When receiving an altimeter setting from an airport we are able to adjust
the altimeter to match any irregularities in the area. This means this corrected setting is able to
give us the most accurate altitude information. However, we can also really screw up by not
setting the correct setting, or not updating the setting as the aircraft flies along.
Using the picture above we start at airport A with a setting of 30,74 of pressure in the
altimeter window. Therefore, we set our altimeter to that setting take off and maintain the correct
altitude. While we leave the immediate airport area the pressure can change, meaning our
indicated altitude will change even if we are perfectly level. In this example, the aircraft is flying
to an airport 1 in pressure lower than where he departed. This means when he reaches airport B
his altimeter will be adjust for 30.74 still, and be wrong by 1,000ft of altitude. During crosscountries and airport operations, it is important to have exact altimeter settings to allow us to fly
at a correct altitude and remain safe from terrain and other aircraft.

PHAK

The last part of the pitot static system is the Vertical speed indicator, the VSI. It is the
instrument designed to measure the difference in static pressure between altitude 1 and altitude 2.
This measurement can be used to determine the rate of climb of the aircraft.
This instrument functions by having a direct input of static pressure into the diaphragm.
The outside of the diaphragm is also connected to the static line but by a restricted flow,
calibrated leak hole. This means as the aircraft climbs of descends the diaphragm will expand or
contract and indicate a change on the instrument. While the aircraft begins to level out the
calibrated leak will allow the pressure to become equal with the air inside the diaphragm and
allow the indication to return to 0.
Arrow POH.

In the Arrow, the pitot static system provides pressure to the VSI, ASI, and altimeter. Pitot
pressure it picked up by a pitot tube on the left wing. Pitot heat is installed as a de-icing feature.
By adding heat to the pitot system we can prevent icing, or heavy rain from clogging to pitot and
giving us inaccurate readings. This is controlled by a switch in the cabin.
Static pressure is delivered by vents on the each side of the fuselage. Pitot and static
drains and located insider the flight deck on the lower left side. It is important to drain the static
system before each flight as our check list tells us to do to maintain accurate readings on our
instruments.
The Arrow has an alternate static source located inside the cabin. The errors present
above will become factors and must be considered. In the Arrow when using the alternate static
source the storm window and cabin vents must be closed. Cabin heater and defroster must be on.
This is to minimize the venture effect causing a pressure differential inside the cabin. The
altimeter error will be less than 50ft unless placarded.
When parked the pitot tube should be covered, if it becomes blocked it will display
erratic or a zero reading on the ASI.

What is the pitot static system?

How does the pitot system work?
How does the static system work?
What errors can be caused by blocked pitot tube? Using alternate static source?
How does this relate to the Arrow?
What special procedures does the Arrow require when using alternate static?
2. Vacuum System.

PHAK
The vacuum system is designed to spin gyros that give us certain information based on
their characteristics. Before we explore the Arrow system we must understand the basics relating
to a vacuum system.
The point of the vacuum system is to spin gyros. In the Arrow we have three gyros, the
attitude indicator, the turn coordinator, and the heading indicator. Since the turn coordinator is
powered by an electrical gyro, we will focus on the attitude and heading indicator and the
vacuum system related to them.

americanflyers.net
A gyro has two characteristics we use, rigidity in space and precession. Rigidity in space
is the principle that the gyro will always spin in a fixed position. As the picture above illustrates
as the assembly of the gyro rotates around the gyro itself remains spinning at a horizontal
direction. If we set up a gyro to spin at the level of the horizon we can use this stationary
characteristic to measure to degree of deflection upwards, downwards, or the bank the aircraft is
performing.

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Second principle is precession. This is when a force is applied to a gyroscope and when a
force is applied it is deflected 90 degrees In the direction of rotation. This principle allows use to
detect a rate of turn by measuring the pressure on the gyro from changing direction.
For the gyro to work we first need to spin, and keep it spinning. This can be done by
electrical means, or by a vacuum system. In the Arrow our attitude and heading indicator are

powered by the vacuum system, while the turn coordinator is power by an electrical gyro. This is
for redundancy and safety so there is always some source of bank information.

PHAK
Using the same diagram from above we can explain how a vacuum system works. In the
Arrow we have an engine driven vacuum pump, a vacuum regulator, a filter and the plumbing
required. The air first enters through the filter to eliminate any contaminates and keep the filter
safe. It then passes through the instruments and the gyros and forces them to spin. On the gyros
inside the instrument there are small indents that the air will hit and push the gyro around. The
air continues along and passes by the vacuum relief valve which will open if the pressure inside
the system exceeds limits. Finally, the pump will push the air out of the system and allow
continued flow.
In the Arrow the attitude indicator is the only vacuum powered system.

cfi-wiki.net

The attitude indicator is a way to visualize the aircraft and horizon level into an
instrument. As the mini aircraft in the indicator changes its attitude in relative to horizon so does
the real aircraft. The gyro is mounted on a horizontal plane and uses rigidity in space to operate.
The mini aircraft on the instrument is the gyro and remains stationary in space as the aircraft
maneuvers. This means the aircraft rotates around the gyro, while the gyro remains completely
stationary.
The Arrow system is a dry type pump that climates the need for an air/oil separator. A
shear drive protects the engine from any damage. If the pump over speeds and is going to cause
damage to the engine, the shear drive will cut the pump off the accessory case and remove it
from the engine drive.
The pressure in the vacuum system is displayed on the right side of the cabin by the
vacuum gauge. If the pressure in the system is low and decreasing there is a problem with a
system, this can include a dirty filter, vacuum regulator stuck open or a leak in the system. There
is also a low vacuum indication on the instrument panel. Zero pressure on the indication would
indicate a sheared pump, defective pump, or a defective gauge. If the gauge displays anything
out of limits of unnatural then have a mechanic check the system.
In the Arrow, the minimum vacuum pressure is 4.8 and maximum is 5.1 of pressure. A
vacuum regulator is installed to protect the gyros as higher pressures will damage the gyros and
lower pressures will make the instruments unusable.
The Arrow also has an auxiliary vacuum system, which is designed to only be a standby
system. This means if the main vacuum system is defective before takeoff we cannot depart. If
our system pressure drops below 4.8 we must also discontinue flight in IMC conditions. The
auxillary system draws a large load on the alternator, if an electrical failure also occours we must
be aware of the electrical demand on the engine. The auxiliary system is also time limited to 500
hours, or 10 years, which ever comes first.
How does a vacuum system spin the gyros?
What are the gyroscopic principles?
How do the principles give us the indications we need?
What instruments in the Arrow are powered by the vacuum system?
How does the Arrows vacuum system work?
What are some limitations on the auxiliary vacuum system?
3. The Fuel System.

Arrow POH

The Arrow is designed with two 38.5 gallon tanks. With a total capacity of 77 gallons,
and 72 useable gallons. Each tank is equipped with a tab to indicate when there are 25 gallons of
fuel inside the tank. The aircraft can fly with 100 octane (green) or 100LL (blue), although it is
better to fly with 100LL because it is more refined. The fuel tanks are an integral part to the wing
structure and provide structure to the wing. They can be removed easily and repaired as well.
Fuel tanks in aircraft must be equipped with fuel tank vents. The Arrow has a vent for
each tank, but why is this needed? As fuel is removed from the tank and delivered to the engine
air remains trapped inside. Without a vent the air inside will create a low-pressure area and not
allow and fuel to flow out of the tank. By adding a vent, we are allowing the tank to breathe as
the flight, or changing conditions occur. If the fuel heats up and expands the vent allows air to
escape the tank, or if the fuel cools down and contracts air is able to take up the space created
inside the tank. This prevents a vacuum from forming inside the tank that can prevent fuel flow,
or damage the tank itself. Before every flight these vents should be checked to make sure nothing
as trapped itself inside, of they are not blocked in anyway.
Each fuel tank also has a quick drain, or fuel sump, located on the bottom of the wing.
These are designed to allow the pilot to drain fuel at the lowest point on the tank to check for any
sediment or debris inside the fuel tank. If any dirt gets into the cylinders we can seriously
damage the engine so before every flight the tank needs to be drained and checked. Water can
easily get into the tank as well and can destroy an engine quite rapidly if injected into the
cylinders. We also will check that the correct fuel is inside the tanks, if not then we can damage

the engine by detonation or pre-ignition from a low quality fuel. On the nose of the aircraft, the
fuel strainer also has a sump for us to drain before each flight.
Arrow POH

Inside the cabin on the bottom left of the pilots seat a fuel selector is present. This allows
us to switch what tank we want fuel to flow from. In the Arrow, we have three positions as the
picture above shows, right, left, or off. The selector switch points to whatever tank is being
burned, in this picture the right tank is supplying the fuel to the engine. A special latch will
prevent the pilot from accidently switching to off and shutting off fuel flow. One thing to note,
while the selector is off there is still fuel in the lines leading to the engine. This means the engine
can start and run for a short time before it will die of fuel starvation. It is important to know that
switching to off will not immediately shutdown the engine, and starting the aircraft with the
selector on off is possible.
Normally fuel is supplied to the engine through an engine driven fuel pump, but during
maneuvering, takeoff and landings, climbing, or switching tanks we must engage the electric fuel
pump. To turn this pump on we flip a switch inside the cabin. This is a safety feature in case the
engine driven pump fails.
Fuel gauges for both tanks are located near the engine instruments and display quantity of
each tank. These gauges are not accurate, as the regulations only need them to display empty
when they are empty. In between full and empty the gauges can read incorrectly so it is important
to manually check the quantity of each tank before flight. These gauges and measuring devices
are electrically powered. A electrified tube is inside the fuel tanks, as fuel is added to the tank the
resistance to the electrical flow is increased, this increased resistance is used to measure the
amount of fuel in the tank. The higher the resistance the more fuel, the lower the resistance the
less fuel we have.

Arrow POH

Some other information about the fuel system to know is that it is fuel injected. As the
POH diagram shows, fuel first exits the tank and enters the fuel selector. From there whatever
tank is selected has the valve opened and fuel continues on. It then passes through the filter and
drain, which is located on the nose ahead of the firewall and is the same drain sticking out of the
nose that you will drain during preflight. It then passes through both fuel pumps, and comes into
the servo regulator. The servo regular measures the airflow and uses diaphragms to meter the fuel
flow into the engine. With more airflow the more fuel is allowed in. This replaces the carburetor
you will find in the Piper Archer. After the fuel and air mixture is created it passes into the
distributor where it is then discharged into each cylinder.

Lance presentation
The servo regulator works by measuring the difference in impact air and venture air. The
greater the difference the more fuel will flow into the engine. The difference in pressure will
move the air diaphragm, which will increase or decrease the fuel flow into the cylinders. The fuel
is not introduced into the airflow at this point, which means engine icing is almost impossible.
The flower divider is the point where the fuel is delivered into the cylinders. When the mixture is
pulled to idle this portion of the system becomes blocked off trapping fuel in the lines. The fuel
nozzles are pointed directly into the cylinders and the fuel pools inside the nozzles during
operations. When the intake opens a lower pressure exists in the cylinder, which pulls the fuel
inside. By adding the fuel at this point there is not chance of icing since the air and fuel are
meeting inside an already warm engine. However, the engine can boil the fuel in the lines and
turn it into a gas preventing movement, this is called vapor lock.
The benefits of fuel injection are increased efficiency of the fuel, even distribution to all
cylinders, smoother running engine and easier to start the engine, no icing, and easier cold
weather starting. While the downsides are, the chance of vapor lock, the increased complexity,
and increased costs of the system.
How much fuel can the Arrows tank hold? Useable fuel?
Is it fuel injected or carbureted?
What is a servo regulator?
What are the advantages and disadvantages of fuel injection?
What is the purpose of fuel drains?
Why do we need to drain fuel before every flight?

4. The Electrical System.

Arrow POH

The Arrow is powered by a 14-volt, 60amp alternator. This alternator incorporates a

voltage regulator and over voltage relay. The alternator is also able to produce full power at low
RPM meaning electrical equipment functions well and the battery life is increased from less use.

northamericatrans.com
An alternator is designed to supply energy to power all electrical units and recharge the
battery. After the battery starts the engine, the alternator will take over providing power to all
equipment. However it is easy for an alternator to create too much current and damage the
engine.

A voltage regulator is designed to keep the current at a constant voltage. Certain

equipment like avionics can be damaged or destroyed by too much current, this is why this
equipment is installed. The other piece of equipment installed, the overvoltage relay, does just as
the name describes. When the voltage from the alternator exceeds a certain limit the connection
to the equipment is cut off, making the alternator output 0 volts. This protects any sensitive
equipment from too much voltage that can destroy them. These pieces are incorporated into the
alternator itself and are installed in the Arrow. The voltage regulator in the Arrow will keep the
system at 11-14 volts, and the over voltage relay will cut the alternator at 17 volts.

reuk.uk
Secondary power is provided by a 12-volt, 35-amp lead acid battery. This battery is
located behind the cargo section and is used for starting the aircraft, and the primary power
source if the alternator fails. The battery is rated for 35 amps, this means if the alternator failed
35 amps of power is available for one hour. Although, this does not take into account a
magnitude of factors including, the current charge of the battery, the wear on the battery, and etc.
This means a good rule of thumb is to expect that 35 amps for half the time it says on the box.
A lead acid battery is a heavy, but simple system used to store power. It requires less
maintenance and less operational care than a lithium ion battery some more advanced aircraft
might have, and is cheaper to maintain. It is the same battery in your car, and for training aircraft
the best battery to have. Although, at low temperatures a lead acid battery will have poor
performance and may be unable to start the aircraft.

sky-craft.com
To indicate the load on the electrical system, an ammeter is installed. It is important to
know that the ammeter shows load on the system, not the battery discharge. By shutting down
electrical components, the ammeter number will decrease. Normally after start, with no electrical
equipment on the ammeter will show a load of two amps, due to the alternator recharging the
battery.
If the alternator fails, it is important to reduce the load on the electrical system
immediately. This is because the higher the load the faster the battery will be drained. During
normal night flight with both radios, around 30 amps is placed on the system. This allows the
battery to function for close to an hour before dying. By decreasing the load on the aircraft, we
are able to increase battery life when an alternator fails and make it to a repair point, or back
home without losing any equipment.

hedgy.com
Equipment is protected by circuit breakers within the system. These are located on the
right side of the cabin near the copilots legs. Each circuit breaker will be labeled to identify what
it protects. This allows the pilot to pull a circuit if any problems occur, or push the breaker back
in to restore power. Although, if a circuit pops, it popped for a reason. Pushing the breaker back
in after it pops a second time is a bad decision as there is some sort of problem in the system. In

the case of too much voltage by constantly pushing the breaker back you can easily start a fire in
the electrical system.
The Arrows standard equipment are the alternator, electric fuel pump, stall warning horn,
ammeter, and annunciator panel. Optional lights are also included in the system such as cabin
lights, navigation lights, ground recognition lights, landing lights are more. These are all
controlled by switches in the cabin and in the event of an alternator failure, should considered as
the first things to shut down.
The annunciator panel is what will give us any indications of faults in the aircraft
systems. The panel is only a warning telling the pilot that they need to monitor certain engine
gauges to check for irregularities. These should be tested before every flight, and the pilot should
periodically check the panel to make sure no indications are present.
What are the battery and alternator outputs?
What is the standard equipment on the aircraft?
What are some things the electrical system runs?
Is ignition controlled by the electrical system?
How is the equipment protected?
What controls the alternator?
5. The Gear System.

Lancepresentation
The Arrow has a retractable tricycle gear system. It is electrically power and
hydraulically actuated. This means electric power drives the hydraulic pumps, which is what
creates pressure in the system used to raise or lower the gear. To control this pump we use the
gear selector switch located next to the throttle quadrant. Raising or lowering the gear takes
about seven seconds. When the gear is raised, the electric pump maintains a pressure in the
system to hold the gear in place, while the gear is lowered that the pump reverses directions and
releases pressure in the system.
If we move the gear selector switch to the down position, we are forcing fluid into the top
of the cylinders in the picture above. The picture above shows a down and locked configuration
already though. In the Arrow 800 psi of pressure is pumped into the top of the cylinder forcing
the gear down. The gear is also assisted by gravity on extension so less pressure is required than
retraction. The nose gear is also assisted by a spring during extension. When the gear is fully
extended locks will engage and hold the gear in place to prevent it from moving around during
maneuvering and landing.
If we move the switch to the up position now we are fighting spring pressure, gravity, and
the weight of all the parts. This means a much higher pressure is required, 1800 psi to be exact.
The gear is raised into the aircraft, and locked in place. Although, to hold the gear in the up
position we need pressure in the lines. So the retraction pressure stays in the system, and if the
pressure gets low then the pump will be turned on again.
To indicate where the gear is we have three green lights located next to the throttle
quadrant. A red gear unsafe switch at the top of the panel indicates gear unsafe and is illuminated

when the gear is in transit or not locked down or up. There is also a beeping gear unsafe horn that
will sound whenever the gear unsafe light is illuminated. There are 3 conditions that will activate
the gear unsafe light and horn;

Gear up, power reduced below 14 of manifold pressure.

Gear selector up while on ground and throttle idle.
Whenever flaps are extended past 10 degrees and the gear is not down and locked.

PHAK
A basic hydraulic system will look something like this picture above. There will be a
reservoir where the fluid is located, a filter, a valve to control the flow, a relief value, and the
actuator that controls the equipment. In the Arrow instead of a valve, the pump itself is
reversible. This means to actuate the landing gear to a down position the pump will pump the
fluid out of the cylinders. If we want to raise the gear then the pump with reverse directions and
pump fluid into the opposite side of the cylinders piston. This means the cylinder in the Arrow is
a double acting cylinder like in the picture.

slideshare.net
A thermal relief valve is also present in the system and it is designed to relieve pressure
from temperature differences. Like any fluid as hydraulic fluid increases in temperature it begins
to expand and take up more space. When it expands it also increases pressure in the system and
can cause a rupture if expanded too much. It is the job of the thermal relief valve to relieve any
pressure built up in the system from temperature changes. This is most likely to occur while in a
descent to a warmer altitude, or while parked on the ground while the temperature varies over the
day.
A high-pressure relief valve is designed to release fluid back into the reservoir if the
system exceeds a certain psi. This will protect the system from excessive pressures and damages
from a pump control failing and the pump being stuck in the on position.
Up limit and down limit switches are also present in the system. There are three down
limit switches on the aircraft, one on each gear. Down limit switches will shut off the hydraulic
motor, turn off the gear unsafe light, and turn on the three green lights. While the up limit
switches will turn off the gear unsafe light.
We also have a squat switch, which prevents gear retraction while on the ground. On the
ground when weight is on the wheels the circuit is open and the pump will be unable to function.
This prevents the gear from being able to come up. A pressure switch is also present, its function
is to shut off the electric motor after gear retraction. When the gear reaches a certain psi, around
1800, the pump will shut off to prevent damage to itself. If the pressure drops below a certain psi

the switch will sense that, turn the pump back on, and maintain pressure in the lines. This will
keep the gear raised when it is supposed to be raised.
In the event of the gear failing to retract completely, or extend, we have an emergency
gear extension system. To operate this system there is a small lever located between the seats. By
pulling this lever, the pilot is manually releasing all hydraulic pressure in the system. This means
no force is holding the gear in the up position anymore, and the gear will fall downwards due to
gravity. Sometimes the gear is caught and unable to fall into the down locked position, this can
be fixed by yawning the aircraft or putting a load on the airframe. The nose gear is also spring
assisted while being extended.

Lancepresentation
The brake system is independent of the landing gear system but functions using hydraulic
pressure like the gear does. When the brakes are pressed fluid from the reservoir travels into the
cylinders and creates pressure forcing the brake pads closed. This creates friction on the brakes
and allows the aircraft to slow down. We have a parking brake and toe brakes, each is a separate
system, but they share the same reservoir of fluid.
The struts on the Arrow are air-oil type with 2.75 in on the nose and 2.5 in on the mains.
This mixture of oil and nitrogen allows shock absorption. When the aircraft is on the ground the
rudder pedals are the source of steering. The rudder is linked to the nose wheel and when the
nose wheel is retracted, the steering linkage is disengaged.
What do the down and up limit switches do?
How is the aircraft steered on the ground?
What activates the gear unsafe warnings?

Describe the system?

What is special about the hydraulic pump?
6. The Prop System.
The Arrow is equipped with a constant, speed controllable pitch propeller. The control is
located in-between the mixture and throttle on the control quadrant. The propeller is 73-74,
depending on the manufacture, long and is equipped with a low and high pitch stop. The
propeller itself is controlled with the governor attached to the engine. The governor keeps the
propeller at a constant RPM, and is adjusted by the pilot to change pitch angle and RPM.

Lancepresentation
The pilot does not control the propeller in the Arrow, instead he controls what the
governor does. By selecting a certain RPM on the instrument and using the prop control to set
that RPM, the pilot is telling the governor what RPM it should have the propeller hold. By
adjusting the prop control lever you are adjusting the speeder spring and moving the flyweights
up or down. These fly weights are what control the pilot valve, which it turns controls the
amount of fluid into, or out of, the propeller. The governor will also have an oil pump top
increase oil pressure higher than normal engine oil pressure.

Lancepresentation
In the center of the propeller hub lays a hollow piston, which is what the boosted oil will
travel through. This piston is connected to the actual propeller blades. As oil is added to the
system the piston will be pushed aft against the spring force. This will move the blade actuators
and adjust the propeller to a high pitch and low RPM setting. As fluid is released from the piston,
the spring will push the piston back forward and release pressure on the actuating links, which
means a low pitch high RPM setting will happen. The aerodynamic force on the propeller will
also aid is bringing the prop to a low pitch high RPM setting.
In the picture above the aircraft is set to a certain RPM and is on-speed, meaning it is
holding that RPM and the governor does not need to adjust itself. You can tell this by the
flyweights being in a neutral position, and the pilot value shutting off oil flow to, or from, the
propeller. This means the propeller is holding a specific RPM and is not adjusting.
If we increase the speed of the propeller, or pull back on the prop control lever, we are in
an over speed condition. This means the RPM of the propeller is higher than the RPM set in the
governor, so the governor needs to adjust itself to hold the RPM it is set to. In the Arrow, the
governor will lower the RPM of the propeller by increasing its angle of attack. When the over
speed condition is entered the flyweights will be pushed outwards, this will pull the pilot valve
up and allow boosted oil pressure into the shaft of the propeller. This in turn allows the propeller
to increase its angle of attack and lower the RPM back to the set on speed condition it wants.
If the propeller is in an under speed condition, such as a pitch up or an increase on the
prop control, the opposite will happen. The flyweights will be pulled inwards due to less
centrifugal force, this will push the pilot valve down due to the speed spring force and create an
opening for the boosted oil in the propeller to release back into the sump. By releasing oil
pressure, the angle of attack of the blade is decreased, and RPM is increased.
The Arrow has a few limitations on the propeller to be aware of. The high pitch stop is a
27.5 degrees and the low pitch stop is at 12.5 degrees. The pilot must be sure to avoid continuous
operations between 1500 and 1950 RPM below 15 of manifold pressure. This can cause
vibrations and shake the propeller off the aircraft.

When adjusting the prop the best procedure is to adjust the manifold pressure first, then
adjust the RPM setting. This prevents any overpresserization in the manifold and prevents an
over boost in turbo charged aircraft.
During takeoff and landing the propeller will be set full forward, the highest RPM and
lowest pitch. This is where the most power will be created from the propeller, which is needed
during takeoff and go around. Cruise flight is when the prop will be adjusted to a lower RPM
setting, whatever setting was calculated before flight, to increase the efficiency of the propeller
and decrease wear on the engine.
What is a propeller governor?
What is over speed? Under speed?
How does the governor adjust RPM?
How does the hub adjust blade angle?
What are some limitations?
What are some good operation practices on adjust pitch propellers?
7. The Engine System.
The Arrow is equipped with a single Lycoming, IO-360-C1C6 engine. This engine is
rated for 200 horsepower and 2700 RPM at sea level. This engine has four cylinders, direct drive,
normally aspirated, air cooled, and is horizontally opposed.

Toyota.net
The four cylinders are normal 4-stroke cycle, have a compression ratio of 8.7:1 and a
displacement of 361 cubic inches. As the fuel and air are injected into the cylinder, the piston

inside will be descending. The piston will then be pushed upwards by the crankshaft and
compress the fuel/air mixture. Just before it reaches the top of the stroke, the magnetos will
energize the spark plug providing ignition to the fuel/air mixture. As the piston is pushed back
down, the power for the propeller and other cylinders is created. After the piston reaches the max
distance downwards, it is raised again as the exhaust value opens and the combusted mixture is
expelled from the cylinder. The Arrows engine is horizontally opposed as well, which means the
cylinders are laying down on their side inside the engine bay.
A direct drive engine means the crank shaft of the engine is connected directly to the
propeller itself. This means whatever RPM is propeller is spinning at, is how fast the engine
needs to be spinning as well. This means at high RPMs the engine will have a lot of force and a
lot of wear and tear on itself. Although, without a gear box all the power at the crankshaft is able
to be sent from directly to the propeller and not be used to drive other equipment. This means
greater efficiency and power output. Although in the Arrow, we have a few engine driven pumps
such as the engine driven fuel pump, the vacuum pump, the alternator, all of these require power
from the engine, decreasing the available power to the propeller.

Wikipedia.org
The Arrow engine is air cooled as opposed to liquid cooled. This means the airflow from
flight is the airflow that will cool the cylinders, instead of oil or coolant like a car would have.
This creates a lighter and cheaper engine to maintain and build. However, it also requires that a
large airflow be moved, since air is less efficient as dissipated heat than a liquid is. It also can
create a large amount of cooling drag from large openings on the cowling for air to enter and
escape. It is also important that all the cylinders are equally exposed to the airflow to allow even
cooling, this can be a problem in air cooled engines. Air cooled engines will have large fins
spread around the engine to increase surface area, and increase cooling, these are called cooling
fins.
Normally aspirated engines simply means there are no turbo chargers or super chargers
on the engine. The airflow into the cylinders is not adjusted, increased or changed in anyway. If
the aircraft was equipped with a turbo charger, it would not increase the power from the engine,

but it would allow the aircraft to have its max power output at a higher altitude, or nonstandard
days. Although, turbos are expensive, take special operation practices, and are not practical for
training aircraft. This is why the Arrow is normally aspirated.
The exhaust system of the Arrow is a crossover type system. This system reduces
backpressure and increases performance of the engine. It is also equipped with a shroud around
the pipe, which is used to provide heat for windshield defrosting and the cabin heater.
The engine in the Arrow is equipped with a starter, an alternator, an ignition system, a
vacuum pump, fuel pump, propeller governor and a dry induction air filter.
The starter works by injecting fuel directly into the cylinder from the flow divider. This
provides a mixture to ignite in the cylinders and allows the cylinders to fire. Magnetos are what
drive the spark plugs and are independent of the electrical system. They create their own charge
and allow the engine to continue running even if all electricity is lost.
Some limitations on the engine:
A maximum oil temperature of 245 degrees. The engine can be cooled by decreasing
pitch angle, decreasing power, or increasing mixture. It is important to not exceed red line as it
can cause serious damage or failure of the engine.
Oil pressure minimum of 25 psi, maximum of 100 psi. A decreasing oil pressure is
extremely dangerous and may be accompanied by an increasing engine temperature. This can be
caused by a leak in the oil system, not enough oil, or bad quality oil.
Maximum fuel flow of 21.4 GPH/12 psi. And 100 or 100LL fuel only.
Describe the engine?
How is the engine cooled?
What are some limitations on the engine?
Is it high performance?
How is ignition generated?
What are the strokes of the engine?

1.

Pitot Static System

2.

Vacuum System

3.

The Fuel System

4.

The Electrical System

5.

The Gear System

6.

The Prop System

7.

The Engine System