How the PITOT - STATIC system works (Private Pilot Ground Lesson 31)

Summary

This pilot training video delves into the workings of pedostatic instruments, crucial for flight navigation. It explains the function of the airspeed indicator, altimeter, and vertical speed indicator, which rely on air pressure from the pitot tube and static port. The video clarifies the concepts of static, dynamic, and total air pressure, and how these instruments can be affected by blockages or errors in the system. It also offers solutions for dealing with clogged ports, ensuring accurate flight data for safer flying.

Takeaways

• 🌀 The lesson discusses pedostatic instruments, which are the airspeed indicator, altimeter, and vertical speed indicator, using air pressure for flight information.
• 📡 These instruments receive air pressure data from the pitot tube and static port, which are crucial for accurate flight data.
• 🌪️ Air pressure types involved are static air pressure (ambient), dynamic air pressure (impact from air molecules on a moving object), and total air pressure (combination of static and dynamic).
• 📍 Static air pressure is measured in inches of mercury, with an average of 29.92 inches at sea level, decreasing by one inch per thousand feet above sea level.
• 🛫 The altimeter uses static pressure to provide altitude readings, with static ports usually placed on the side of the aircraft to avoid wind influence.
• 🔄 The vertical speed indicator senses pressure differences during climb or descent, providing readings in feet per minute.
• 🚀 The airspeed indicator measures the ram air through the pitot tube and offsets it with static air from the static port to determine airspeed accurately.
• ⚠️ The angle of the pitot tube can affect the airspeed indicator's accuracy, and manufacturers provide correction charts in the Pilot Operating Handbook (POH).
• 💧 The pitot tube has a 'weeping hole' to prevent water from clogging it, and heating elements can melt ice to avoid blockages.
• 🚨 If the pitot tube or static port is clogged, it can cause inaccurate readings in the airspeed indicator, altimeter, and vertical speed indicator.
• 🔄 In case of a clogged static port, newer training aircrafts may have an alternate static source to provide less accurate but usable data.
• 🔮 As a last resort, breaking the glass on a static instrument, preferably the vertical speed indicator, can provide some data in an emergency situation.

Q & A

What are the three primary flight instruments discussed in the script that use air pressure?

The three primary flight instruments discussed are the airspeed indicator, the altimeter, and the vertical speed indicator.

What are the three types of air pressure mentioned in the script?

The three types of air pressure mentioned are static air pressure, dynamic air pressure, and total air pressure.

What is static air pressure, and how is it measured?

Static air pressure, also known as ambient air pressure, is the pressure caused by the atmosphere. It is always present, whether the airplane is stopped or moving, and is measured in inches of mercury.

How does the static air pressure change with altitude?

The static air pressure decreases with increasing altitude, reducing by one inch of mercury for every thousand feet above sea level.

What is dynamic air pressure, and how does it relate to the aircraft's speed?

Dynamic air pressure is the pressure created on an object, like an airplane, as it moves through the air. It is directly related to the speed at which the aircraft is flying.

What is total air pressure, and why is it important for the pedostatic system?

Total air pressure is a combination of dynamic and static air pressure. It is important for the pedostatic system because it helps in accurately measuring the airspeed of the aircraft.

How does the altimeter use static pressure to provide altitude readings?

The altimeter uses a static port to sense the static pressure outside the aircraft. Since the static pressure changes with altitude, the altimeter can provide an altitude reading based on these changes.

What is the function of the vertical speed indicator, and how does it work?

The vertical speed indicator measures the rate of climb or descent of the aircraft. It allows air to escape or come in through a small hole vented through the static port, sensing pressure differences as the aircraft climbs or descends, and provides a reading in feet per minute.

How does the airspeed indicator measure airspeed, and what role does the pitot tube play?

The airspeed indicator measures the ram air that comes from the relative wind through the pitot tube. It also takes static air from the static port to offset any static air that might come in through the pitot tube, ensuring an accurate airspeed measurement.

What could potentially cause errors in the pedostatic instruments, and how can they be mitigated?

Errors in the pedostatic instruments could be caused by the pitot tube or static port getting clogged with bugs, mud, ice, or if water freezes in the pitot tube. These can be mitigated by using a heating element to melt ice or by using an alternate static source if available.

What is the 'weeping hole' on the pitot tube, and why is it important?

The 'weeping hole' is a small drain hole on the back of the pitot tube. It is important because it allows water that enters the front of the pitot tube to drain out, preventing clogging.

What should a pilot do if the static port gets clogged during flight?

If the static port gets clogged, the pilot can use an alternate static source if available, or as a last resort, break the glass on one of the static instruments, preferably the vertical speed indicator, to allow some form of pressure sensing.

Outlines

00:00

🛫 Understanding Aerodynamic Instruments

This paragraph introduces the topic of pedostatic instruments used in aviation, focusing on airspeed indicators, altimeters, and vertical speed indicators. It explains how these instruments rely on air pressure from the pitot tube and static port to provide crucial flight information. The paragraph delves into the three types of air pressure: static, dynamic, and total air pressure, detailing their impact on flight instruments. It also highlights the importance of the pitot tube and static port placement for accurate readings and the potential issues that can arise if these components become clogged, such as inaccurate airspeed readings or frozen altitude indications.

05:01

🚨 Pitfalls of Clogged Aerodynamic Instrument Ports

The second paragraph discusses the consequences of clogged pitot tubes and static ports on the functionality of aerodynamic instruments. It outlines three scenarios that could affect the airspeed indicator if the pitot tube becomes clogged: airspeed dropping to zero, the airspeed indicator freezing at the last reading, or displaying incorrect higher airspeeds. The paragraph also covers the effects on the altimeter and vertical speed indicator if the static port is obstructed, which could result in a frozen altitude reading or a zero indication on the vertical speed indicator, respectively. It provides solutions such as using an alternate static source or, as a last resort, breaking the glass on the least critical instrument to regain some functionality. The paragraph concludes with a reminder of the importance of maintaining instrument accuracy for flight safety.

Keywords

💡Pedostatic Instruments

Pedostatic instruments are a set of flight instruments that utilize air pressure to provide pilots with essential information about the aircraft's performance and environment. In the video, these instruments are the focus, as they are critical for safe and effective flight operations. The term 'pedostatic' is derived from the Greek 'pedon' meaning 'foot' and 'static' referring to the measurement of pressure, indicating the instruments' function of measuring air pressure at rest.

💡Airspeed Indicator

The airspeed indicator is a primary flight instrument that shows the speed of the aircraft relative to the air around it. It is vital for pilots to maintain appropriate airspeeds for various flight phases. In the script, the airspeed indicator is explained as being affected by both dynamic and static air pressures, with the pitot tube and static port playing crucial roles in its operation.

💡Altimeter

An altimeter is an instrument used to measure and display the aircraft's altitude above a chosen reference level, typically mean sea level. It is essential for maintaining safe altitudes and navigating. The script explains how the altimeter uses static pressure from the static port to provide altitude readings, with the pressure changing by one inch of mercury for every thousand feet of altitude gain or loss.

💡Vertical Speed Indicator

The vertical speed indicator, or VSI, shows the rate of climb or descent of an aircraft in feet per minute. It is important for pilots to manage the aircraft's vertical profile. The script describes how the VSI allows air to flow in or out through a small hole vented through the static port, sensing pressure differences to indicate vertical speed.

💡Static Air Pressure

Static air pressure, also known as ambient air pressure, is the pressure exerted by the atmosphere when the aircraft is not moving. It is always present and increases with altitude. The script mentions that static air pressure is sensed by static ports on the side of the aircraft, which are designed to provide accurate readings unaffected by relative wind.

💡Dynamic Air Pressure

Dynamic air pressure is the pressure exerted on an object, like an aircraft, as it moves through the air. It is directly related to the aircraft's speed and opposes its direction of travel. The script explains that dynamic air pressure is sensed by the pitot tube and is a key factor in the operation of the airspeed indicator.

💡Total Air Pressure

Total air pressure is the combined effect of both static and dynamic air pressures. It is important for understanding how the pedostatic instruments work together. The script mentions that total air pressure is considered when explaining the operation of the airspeed indicator, which measures the ram air from the pitot tube while offsetting static air pressure from the static port.

💡Pitot Tube

The pitot tube is a device that protrudes into the airstream and measures the total air pressure, which includes both dynamic and static components. It is essential for the operation of the airspeed indicator. The script describes the pitot tube's placement on the aircraft and how it can be affected by the angle of attack and potential blockages.

💡Static Port

A static port is an opening on the aircraft that allows static air pressure to be measured. It is crucial for the accurate operation of the altimeter and vertical speed indicator. The script explains that static ports are typically placed on the side of the aircraft to avoid being affected by the relative wind and that blockages in the static port can significantly affect the readings of these instruments.

💡Calibrated Air Speed

Calibrated air speed is the airspeed indicator reading that has been adjusted for various factors, such as instrument errors and aircraft configuration, to provide a more accurate representation of the true airspeed. The script mentions that manufacturers account for these errors by providing charts in the Pilot Operating Handbook (POH), allowing pilots to correct the indicated airspeed.

💡Pitot-Static System Blockage

Pitot-static system blockage refers to the obstruction of the pitot tube or static port, which can lead to inaccurate instrument readings. The script discusses the potential consequences of such blockages, such as the airspeed indicator showing zero speed or frozen at the last reading, and the importance of maintaining clear pitot tubes and static ports for accurate flight data.

Highlights

Lesson discusses pedostatic instruments and their function in flight.

Gyroscopic instruments were discussed in previous lessons, focusing now on primary flight instruments using air pressure.

Primary flight instruments include the airspeed indicator, altimeter, and vertical speed indicator.

Instruments receive air pressure from the pitot tube and static port to provide flight information.

Three types of air pressure are explained: static, dynamic, and total air pressure.

Static air pressure is ambient pressure, varying with altitude and sensed by static ports.

Static air pressure is measured in inches of mercury, with standard air pressure at 29.92 inches.

Dynamic air pressure is created by an object moving through air and is related to aircraft speed.

Total air pressure is a combination of dynamic and static air pressures.

Altimeter uses static pressure to give altitude readings, affected by changes in elevation.

Vertical speed indicator senses pressure differences during climb or descent, providing readings in feet per minute.

Airspeed indicator measures ram air from the pitot tube and offsets it with static air from the static port.

Pitot tube and static port placement on the aircraft is crucial for accurate readings.

Angle of attack and aircraft configurations can affect the accuracy of the airspeed indicator.

Clogged pitot tube or static port can cause errors in flight instruments.

Heating elements in the pitot tube prevent ice formation and maintain instrument accuracy.

If the pitot tube is clogged, the airspeed indicator may show zero or freeze at the last reading.

Clogged static port affects the altimeter and vertical speed indicator, potentially freezing or showing zero.

Newer training airplanes may have an alternate static source to maintain instrument functionality.

In an emergency, breaking the glass on a static instrument can provide a less accurate but usable backup.

Transcripts

in this lesson from free pilot training

we'll be discussing the pedostatic

instruments and we'll explain how those

work

in the last few lessons we've been

discussing the gyroscopic instruments

but today we're going to talk about

three of those primary flight

instruments that use air pressure to

give us information these are the air

speed indicator the altimeter and the

vertical speed indicator these

instruments are provided air pressure

from the pitot tube and the static port

and they turn it into information that's

really important for pilots in flight

there are three types of air pressure

that come into play when we talk about

these instruments static air pressure

dynamic air pressure and total air

pressure

static pressure which is also called

ambient air pressure is pressure that's

caused by our atmosphere

this is always present whether the

airplane is stopped or moving

and although it might seem unnoticeable

to you these air molecules push on

everything in our atmosphere

the closer you are to the center of the

earth the more tightly these air

molecules are packed and because they're

packed so tightly at lower elevations

the lower your altitude the higher your

static air pressure is and our airplanes

use static ports to sense this type of

air pressure these are usually placed on

the side so they're not affected by

relative wind static air pressure is

measured in inches of mercury on a

normal standard day at sea level the

average air pressure is 29.92 inches of

mercury now the air pressure isn't

always 29.92 inches of mercury there but

this is about the average so this is

what we call standard air pressure

then every thousand feet above sea level

the pressure reduces by one inch of

mercury in the next lesson we're going

to go into a lot more detail about this

and how the altimeter works so if you

haven't already subscribed please

consider doing so

now anytime an object like an airplane

moves through the air it's impacted by

the air molecules that is traveling

through and this creates a certain

amount of pressure on the object that's

equal and opposite to the airplane's

direction of travel and this is called

dynamic air pressure and in order to

understand how the pedostatic system

works you have to understand that this

pressure is directly related to the

speed at which the aircraft is flying

next we have the total air pressure

and this is a combination of dynamic and

static air pressure and while this may

seem obvious at first you'll see why we

talk about this here in just a minute

now the altimeter uses a static port to

sense the static pressure outside the

aircraft and because the static pressure

changes one inch of mercury every

thousand feet the altimeter is able to

give us an altitude reading because it

senses that pressure now as i mentioned

before static ports are placed on the

side of aircraft

and this keeps the instruments from

being affected by dynamic air pressure

and this keeps the readings as accurate

as possible

the other instrument that uses a static

port is the vertical speed indicator

this instrument allows air to escape or

come in through a small hole which is

vented through the static port

by allowing air to come in or go out

this instrument senses the pressure

differences as we climb or descend then

it gives us a reading in feet per minute

the airspeed indicator is a little bit

different animal it also receives air

from the static pore but not for reasons

you might think

the airspeed indicator measures the ram

air that comes from relative wind

through the pitot tube but this doesn't

give us an accurate measurement because

static air actually makes its way into

the pitot tube as well and this is that

total air pressure we were talking about

earlier

and by taking static air from the static

port the air speed indicator is able to

offset any static air that might come in

through the pitot tube

to keep the air speed indicator as

accurate as possible the people who

designed your airplane usually put the

pitot tube in a spot where it won't be

affected by the prop wash but there is

something that can affect your airspeed

indicator and that's the angle of the

pitot tube in relation to the relative

wind

high angles of attack and different

airplane configurations can affect the

accuracy of your airspeed indicator

and that's because weird angles can make

it difficult for the ram air to enter

the pitot tube

every airplane is different but every

airplane has some kind of error caused

by this and the manufacturers account

for this by putting a chart in the poh

this is what we call calibrated air

speed once you make these corrections

using these charts

something else you could run into that

would cause these instruments to get

errors is if the pitot tube or the

static port got clogged up and there's a

lot of different things that could clog

up these things anything from bugs mud

ice and that's just to name a few one

thing that shouldn't clog up your pitot

tube though is water that's because of

this little drain hole here on the back

i call this the weeping hole this is

there so if water enters the front of

your pitot tube it'll just slide right

out the back here

but if the water freezes in or on the

pitot tube then it can start clogging it

up again but that's what these little

heating elements are for you just turn

the pedo heat on in your cockpit and it

should heat these up enough to melt that

ice

so what happens if these things get

clogged well if the pedo2 gets clogged

the only instrument that's going to be

affected is your airspeed indicator and

if you remember that's because this is

the only instrument that uses dynamic

air pressure to give us a reading for

the airspeed indicator three possible

problems could happen the first would be

if the hole in the front of the pitot

tube for the ram air got clogged

as long as your drain hole doesn't get

clogged what will happen is your air

speed will drop to zero and that's

because the pitot tube is no longer

taking in ram air but the static port

and the drain hole are still both taking

in static air which allow them to offset

each other the second possibility is if

the front of the pitot tube and the

drain hole gets clogged

if this happens any air pressure in the

pitot system will be trapped and your

air speed indicator is frozen at the

last indication it was giving you

from here if the static port is also

plugged you won't see any change but if

the static port is clear then the

airspeed indicator will make minor

changes with altitude i like to tell

students that your airspeed indicator

just turned into an altimeter at this

point the third thing that could

possibly happen is only the static port

gets clogged if this happens the pitot

tube is still taking in the dynamic and

the static pressure from the front of

the pitot tube but the static port is

unable to offset that static air that's

also coming in the front and this means

that your airspeed indicator is going to

give you faster air speeds than what

you're actually going

now because the altimeter and the

vertical speed indicator both use a

static board to get their information if

this gets clogged it's going to affect

both of those too for the altimeter if

the static port gets clogged it's going

to freeze at the last altitude that it

was indicating but the vertical speed

indicator will only display 0 because it

can no longer sense a climb or a descent

if you're lucky enough to have a clogged

static port i do have some good news for

you though on most newer training

airplanes they have something called an

alternate static source

typically this is an alternate static

port that's on the inside of your

cockpit and you can select this

alternate static port by flipping a

switch labeled alternate static on most

airplanes just keep in mind when you use

this alternate static source it's not

quite as accurate as the one on the

outside of the airplane and that's

because the pressure difference on the

inside of the cab is slightly different

than outside now if you don't have an

alternate static source one thing you

can do is you can break the glass on any

of the static instruments

if you do this i recommend breaking the

glass on the vertical speed indicator

and that's because it's by far the least

important of the instruments

and once again if you do this this is

nowhere nearly as accurate as a static

port on the outside of the airplane but

something is better than nothing and in

an emergency this could save your life i

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