Hobbs Time and Tach Time: All You Need To Know| 2025 Updated
Do you ever wonder how long your flight will be? There are a few different ways to measure flight time, and in this blog post, we will discuss two of them: Hobbs time and Tach time. Hobbs’s time is measured from when the aircraft starts moving until it stops again.
Tach time is measured from when the propeller or rotor blades start turning to when they stop. Both of these methods have their benefits, so let’s take a closer look at each one!
Measuring flight time is necessary for several reasons. For one, it helps pilots keep track of how long they have been in the air. This information is important for things like filing a flight plan and calculating fuel usage.
Additionally, measuring flight time can help you troubleshoot problems with your aircraft. If you notice that your flight times are shorter than normal, it could be an indication that something is wrong.
There are a few different ways to measure flight time, but the two most common methods are Hobbs time and Tach time. It can be confusing employing both these measuring tools, but luckily we are here to help!
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Table of Contents
What is Hobbs’s time?
Hobbs time was named after John Weston Hobbs, who invented the tachometer. Tachometers are devices that measure the speed of rotating objects, such as aircraft engines. The Hobbs meter is a special type of tachometer that is used to measure aircraft flight time.
Hobbs’s time is measured from when the aircraft starts moving until it stops again. This means that it includes taxi time, take-off roll, and landing roll. Hobbs’s time is a good measuring tool because it is relatively easy to calculate. All you need is a tachometer and a stopwatch.
To measure Hobbs’s time, start the stopwatch when the aircraft starts moving. Then, read the tachometer and note the time when the engine reaches 100% power. Stop the stopwatch when the aircraft comes to a stop.
The difference between these two times is your Hobbs time. For example, if it takes 30 seconds for the engine to reach 100% power and 60 seconds for the aircraft to come to a stop, your Hobbs time would be 90 seconds.
Many pilots and flight schools employ Hobbs time because it is a simple way to measure flight time. However, there are some drawbacks to using Hobbs’s time.
One is that it does not take into account the time spent idling on the ground. Another is that it can be affected by things like wind speed and runway length.
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What is Tach time?
Tach time or tachometer time differs from Hobbs time in that it is measured from when the propeller or rotor blades start turning to when they stop. This means that Tach time does not include taxi time, take-off roll, or landing roll.
To measure the Tach time, start the stopwatch when the engine is started. Then, read the tachometer and note the time when the engine reaches 100% power. Stop the stopwatch when the engine is shut off. The difference between these two times is your Tach time.
Tach time is a good measuring tool because it eliminates taxi time and take-off/landing roll from the equation. This makes it a more accurate representation of true flight time.
Tach time is used for things like billing by the hour and calculating engine wear. Tach time could also be considered “engine time,” as it only measures the time the engine is actually running.
However, there are some drawbacks to using Tach time as well. One is that it can be affected by wind speed and runway length, just like in Hobbs’s time. Another is that it does not take into account the time spent idling on the ground before takeoff or after landing.
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Key differences between Hobbs and Tech time
Now that we have gone over Hobbs’s time and Tach’s time, let’s compare and contrast the two measuring methods.
Hobbs’s time includes taxi time, take-off roll, and landing roll. Tach time does not include any of these things.
Hobbs’s time is measured from when the aircraft starts moving until it comes to a stop. Tach time is measured from when the propeller or rotor blades start turning until they stop.
Hobbs’s time is a good measuring tool because it is relatively easy to calculate. Tach time is a good measuring tool because it eliminates taxi time and take-off/landing roll from the equation.
Hobbs’s time has the following drawbacks: it does not take into account the time spent idling on the ground, and it can be affected by wind speed and runway length. Tach time also has these same drawbacks.
Tachometer and Hobbs Meter Legal Requirements
In the United States, there are no legal requirements for aircraft to have a Hobbs meter or Tach meter. However, the FAA recommends that aircraft have a Hobbs meter or Tach meter installed for measuring flight time.
Aircraft owners and operators can choose to install either a Hobbs meter, a Tach meter, or both.
Hobbs meters are typically used to measure engine run time, while Tach meters are used to measure propeller or rotor blade rotation.
It can also be helpful to have both types of meters installed, as they can provide different types of information about the aircraft.
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So, which measuring tool should you use?
The answer to this question depends on your needs. Hobbs time is a good option if you are simply looking for a way to keep track of how long you have been in the air. However, if you need a more accurate representation of flight time, Tach time is the way to go.
There are a few legal requirements for the Hobbs Meters and Tachometers, respectively. According to the Federal Aviation Regulations (FARs), Part 91.409 and Part 135.427, you are required to have a Hobbs Meter or Tachometer installed to log flight time.
Airplane Rental Fees
Flight schools and airplane rental companies charge you for the time you spend in the air. This is usually calculated using Hobbs time. The hourly rate can vary depending on the type of aircraft but typically ranges from $100 to $200 per hour.
However, there are a few companies that charge you based on the tech time. This is because it is a more accurate representation of the time you spend flying the aircraft. The hourly rate for this type of rental is usually around $150 per hour.
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Conclusion
In conclusion of the article, we can say that measuring flight time is important for a variety of reasons, including billing by the hour and calculating engine wear. Hobbs time and Tach time are the two most common methods for measuring flight time.
Hobbs’s time is measured from when the aircraft starts moving until it comes to a stop and includes taxi time, take-off roll, and landing roll.
Tach time is measured from when the propeller or rotor blades first start turning until they stop turning, and it does not include any of these things.
Both Hobbs time and Tach time have their advantages and disadvantages, so it is up to you to decide which measuring tool is best for your needs. Whichever measuring tool you choose, just make sure it complies with Federal Aviation Regulations. Happy flying!
