What is a Pitot Tube?

A simple definition for a pitot tube is a device used to measure the speed of a fluid, usually air. Pitot tubes are crucial for aircraft. They feed data to the airspeed indicator, which informs pilots as to how fast they’re flying relative to the surrounding air. A blocked or malfunctioning pitot tube can lead to incorrect readings, which can create serious flight safety risks. Pitot tubes are an important part on every aircraft.

Understanding How a Pitot Tube Works

Pitot Tube on Cessna Skyhawk
On a Cessna 172 Skyhawk SP, a standard pitot tube is placed on the underside of the wing. It collects air pressure as the plane flies, and along with static pressure from the static port, the airspeed indicator shows how fast the plane is flying.

Understanding the Two Key Openings in a Prandtl Pitot Tube:

Front-facing (impact) opening (hole): Also known as the ram air inlet, this measures total pressure (also called stagnation pressure). This is the pressure felt when air is brought to a stop.

Side openings: These measure the static pressure, which is the pressure of the still air around the tube.

By comparing these two pressures, you get the dynamic pressure (also known as “ram air”), which is directly related to the speed of the airflow. The formula used is derived from Bernoulli’s equation:

Dynamic Pressure = Total Pressure − Static Pressure

Some pilots use an online pitot tube calculator by entering two of three required fields: 1) total pressure; 2) static pressure; and/or 3) density. Understanding that a pitot tube measures the flowing velocity of fluids is foundational.

Although a pitot tube itself doesn’t contain a sensor, it’s typically used in conjunction with a pressure sensor to measure fluid velocity by measuring the difference between dynamic and static pressures.

Pitot Tube and Static Port Blockage

Pitot Heat Switch
A pitot tube is heated to prevent ice from forming on it during flight, a potentially hazardous event.

Blockages in the pitot tube or static port can occur when clogged by debris, insects, or ice, which is most common during flight in cold or moist conditions. These blockages can interfere with the airplane’s ability to accurately measure airspeed and altitude. When a pitot tube is blocked, it may give false airspeed readings, making the aircraft appear to be flying faster or slower than it actually is.

Also, if the static port is blocked, it can cause incorrect altimeter readings, leading pilots to believe they are at a different altitude than they really are. Both of these situations can put a pilot in danger, particularly during takeoff, landing, or when flying through bad weather.

False airspeed readings can also trigger stall warnings, even if the aircraft isn’t actually in danger of stalling. This can confuse pilots and cause them to take improper corrective actions.

To help prevent these problems, many aircraft, such as the Cessna Skyhawks here at Epic, use heated pitot tubes. The built-in heating element warms the tube enough to stop ice from forming. This is especially important during high-altitude flights, where temperatures are well below freezing. This heating system helps ensure that the pitot tube remains clear and able to provide accurate airspeed data, which is critical for safe flight operations.

Types of Pitot Tubes

There are several types of pitot tubes, which are suited for different applications:

  • Standard Pitot Tubes – Found in general aviation aircraft like the Cessna Skyhawk SP
  • Prandtl Pitot Tubes – Incorporate both pitot and static ports
  • Dwyer Flow Meters – Used in HVAV and industrial flow measurement
  • Military and Airline Pitot Tubes – Designed for high-speed jets and commercial airlines

Location of Pitot Tube on Aircraft

Standard pitot tubes, such as those on Cessna Skyhawks, are usually found mounted on the outside of an aircraft, typically:

  • On the fuselage, often near the nose
  • Under a wing or on the side of the cockpit
  • Positioned to face directly into the airflow

Their location ensures they measure undisturbed, accurate airflow, away from turbulence caused by other parts of the plane.

Pitot Tube Cover on Cessna
The pitot tube cover protects the pitot tube when the aircraft is on the ramp.

On smaller general aviation aircraft, the pitot tube is a thin metal tube that sticks out. When the aircraft is not in use, it is protected from dirt, bugs, and other debris by a red pilot cover. The words “Remove Before Flight” are displayed on the cover, and removing it is part of the preflight inspection. The most common cause of a clogged pitot tube is bugs, mud daubers specifically here in Florida, because the hole in the pitot tube is the perfect size.

On larger commercial jets, there are usually multiple pitot tubes and static ports. These are typically placed symmetrically on both sides of the fuselage for redundancy and balance.

Does the Stall Horn Work If My Pitot Tube Fails?

The stall horn works independently of the pitot tube. This is because it relies on a static pressure-based Venturi effect rather than dynamic pressure. However, incorrect airspeed readings can lead pilots to misjudge stall conditions.

The stall horn is a warning device that sounds when the plane is getting too close to a stall, a condition where the wings can no longer generate enough lift to keep flying.

Stall horns make a loud, continuous sound that alerts pilots of the angle of attack being too high, putting the aircraft in danger of losing lift. This warning gives the pilot time to take corrective action, such as lowering the nose or adding power in order to avoid an actual stall.

Josh Rawlins Pitot Tube Article

“At Epic, we train both pilots and aircraft mechanics to understand the principles and function of the pitot tube to ensure safe and effective flight operations. You can spot the pitot tube cover to the right in this photo. On the Cessna Skyhawks, pitot tubes are located under the wing.”Josh Rawlins, Chief Operating Officer and Aircraft Mechanic Program Director

What is a Venturi Tube?

A Venturi tube is a specially designed pipe with a narrow throat that creates a change in fluid velocity and pressure as it flows through. It is based on the Venturi effect, a principle discovered by Italian physicist Giovanni Battista Venturi in the 18th century.

What is the Venturi Effect?

The Venturi effect, a principle in fluid dynamics, describes what happens when a fluid flows through a narrow section of a pipe or tube:

“As the fluid enters the narrow section, it speeds up, and its pressure drops.”

This happens because the fluid has to move faster to get through the tight space. According to Bernoulli’s principle, when the velocity of a fluid increases, its pressure decreases.

Venturi Tube and the Pitot Tube

Pitot tubes measure how fast fluid is moving. Venturi tubes measure how much fluid is moving. Although both tubes measure fluid flow, the Venturi differs from the pitot by creating a controlled pressure differential rather than relying on direct stagnation pressure. The Venturi effect is also used in vortex generators and wind tunnel testing. Because they measure the speed and pressure of the airflow, they help us understand the characteristics of objects in a wind tunnel as well as aerodynamic forces.

Fun Fact: In the early days of aviation, some planes had Venturi tubes on the outside of the fuselage. This created suction for the vacuum system for instruments like the attitude and heading indicators.

How Does a Venturi Tube Work?

When air or liquid moves through a Venturi tube, it follows these steps:

  • 1. Enters the wider section – The fluid flows at normal speed and pressure.
  • 2. Passes through the narrow throat – As the pipe constricts, the fluid’s velocity increases due to the conservation of mass.
  • 3. Pressure drops – According to Bernoulli’s principle, as velocity increases, static pressure decreases.
  • 4. Exits through the wider section – The fluid slows down, and pressure begins to recover.

This effect is useful for measuring flow rates, generating suction, and controlling aerodynamics in aviation. See? Pilots need to understand a multitude of concepts.

Venturi Tube Applications

Although we focus on the Venturi tube in aviation (used in some airspeed indicators, carburetors, and pitot-static systems to regulate airflow measurement), it is also used in other fields, such as:

  • HVAC Systems: Used in flow meters to measure air velocity in ventilation ducts.
  • Medical Devices: Nebulizers and oxygen delivery systems use the Venturi effect to mix gases.
  • Industrial Applications: Found in fuel systems, pumps, and water treatment plants.
  • Boats: Also known as pitot probes to measure speed through water (speedometer).

Maintaining the Pitot-Static System

Aircraft Mechanic Pitot Project Board
Aircraft mechanic students learn basic concepts while working on a pitot tube project board.

Maintenance of pitot tubes is an essential part of aviation maintenance. What are some common maintenance issues? In Epic’s FAA Part 147 aircraft mechanic program, our students are trained to:

  • Understand how pitot-static systems work
  • Inspect, clean, and test pitot tubes and static ports
  • Check for blockages
  • Ensure the functioning of the pitot heat system
  • Recognize symptoms of pitot-static failures during flight
  • Ensure accurate calibration
  • Perform leak tests on the system for accuracy
  • Install replacement parts
  • Inspect the differential pressure transmitter
  • Read diagrams and schematics to troubleshoot
Pitot Heat Schematic for Aircraft Mechanics
Aircraft mechanics read schematics like this one in order to maintain the pitot heaters.

This training is vital because pitot-static systems directly affect airspeed indicators, altimeters, and vertical speed indicators, all of which are critical for safe flight. The altimeter relationship with the pitot-static system is through its use of static pressure, but unlike the airspeed indicator, it does not rely on the pitot tube.

Epic mechanics also get hands-on experience with bench testing instruments and using specialized training equipment like pitot-static testers (or “air data testers”) during aircraft inspections. Just one of the benefits of training here – lots of hands-on experience.

Lifespan of a Pitot Tube

The average lifespan of a pitot tube ranges from 5 to 10 years. This varies based on various factors, such as:

  • Aircraft Usage (frequency, altitude, speed)
  • Environmental Conditions (exposure to rain, ice, dust, or salt air)
  • Quality of Material (stainless steel lasts longer)
  • Maintenance and Inspections

That said, pitot tubes don’t usually fail due to age alone. Aircraft mechanics replace them when damaged, clogged, or showing signs of wear during regular maintenance checks. For commercial and training aircraft, they’re inspected frequently and may be swapped out sooner if reliability is a concern.

Pitot tubes, while useful for measuring flow speed, have disadvantages, too. They are vulnerable to clogging, low accuracy, and limited range, especially in low- or high-velocity flows, and there is a potential for vibration damage.

Avoiding Accidents

At Epic, both mechanics and pilots study aviation accidents to learn how to avoid them. For example, Birgenair Flight 301 crashed into the ocean in the Dominican Republic on February 6, 1996 shortly after takeoff resulting in 189 fatalities. The Boeing 757-200 had not flown in 20 days, and someone removed the pitot tube cover 2 days before the flight. Investigators reported a wasp nest built inside one of the tubes blocked the airflow causing pilots to read an incorrect airspeed.

Additionally, Air France Flight 447 crashed into the ocean on June 1, 2009 on its way to France resulting in 228 deaths. The final report found that ice crystals probably blocked the pitot tubes of the Airbus A330-203, causing incorrect airspeed readings and leading the autopilot to shut off.

Anemometer and Pitot Tube Comparison

Anemometer and Pitot Tube
The anemometer on the left measures wind speed in meteorology or weather stations, while the pitot tube on the right measures airspeed on aircraft.

An anemometer is a device used to measure wind speed. They are commonly found in meteorological stations, and they share a similar principle with a pitot tube, which measures airflow speed (airspeed) on aircraft.

Both devices measure the movement of air, but in different contexts:

  • An anemometer typically measures ambient wind speed in the atmosphere.
  • A pitot tube measures relative airspeed as the aircraft moves through the air.

Some anemometers, like pitot-static anemometers, even use the same principle, measuring the difference between dynamic and static pressure to determine wind speed.

Another similar device is the manometer, which measures static pressure. For example, it can measure pressure in pipes and other confined spaces.

Fun Fact: Pronunciation

Although “pitot” looks as though it might rhyme with “pilot,” nothing could be further from the truth!

Future Innovations

Pitot tubes were invented by Henri Pitot in 1732 to measure the water flow velocity. The evolution of this crucial part has led to the current sophisticated pitot-static system described here. Ongoing innovations look toward enhancing accuracy, reducing size, and increasing resistance to operational issues. Pilots also hope for the integration of monitoring in real time along with wireless data transmission for applications such as agriculture, defense, and general aviation.

It may be a small part on the plane, but a pitot tube’s function is instrumental for safe flight operations. This is why pilots inspect it during every pre-flight and aircraft mechanics routinely inspect its functionality.

Watch Our 9-Minute Video on All Things Pitot Tube!

Join the Forum Discussion on Pitot Tubes Below!

Josh Rawlins Author Image

About the Author

Josh Rawlins

Josh Rawlins, a native of New Smyrna Beach, grew up just a few miles from Epic Flight Academy. At age 19, he began working at Epic, sweeping hangar floors and assisting coworkers with various tasks. What started as a humble job quickly evolved into a lifelong career in aviation.

Over time, Josh demonstrated remarkable initiative. While working at Epic, he completed accounting courses, earned his A&P mechanic license, and obtained inspection authorization. These achievements propelled him to Lead Mechanic and, later, Director of Maintenance.

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