As a pilot, it’s important to understand Hobbs time and tach time and how they work. We’ll teach you everything you need to know in this expert guide.
Whether you’re worried about how to keep your logbooks up to date, how engine hours are monitored on an airplane, or how you’ll be charged hourly for aircraft rental, it’s important to know how time is measured in the aviation world. This is where Hobbs time and tach time come in. But what does that really mean and how are Hobbs and tach time different from each other?
Tach time measures the number of hours of wear and tear on an airplane’s engine (engine hours), while Hobbs time measures the actual number of hours that an airplane is operated. Hobbs time should be used in a pilot’s logbook for flight time, and tach time should be used for maintenance.
In aviation, there are two main ways to measure time: Hobbs time and tach time. They both have their own unique benefits and drawbacks, which can be confusing for those who are new to the industry. In this article, we will explore everything you need to know about Hobbs time and tach time. We'll start by discussing both types of time and how they're measured, and then we'll dive into the key differences between Hobbs time and tach time.
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What is Hobbs Time?
Before we can start talking about the differences between Hobbs time and tach time, we need to make sure we explain what they both are. We have to start with one or the other, so let’s first take a look at Hobbs time.
Hobbs time is a measure of time that is used to calculate the amount of use an aircraft has received. In other words, it's the actual number of hours that the airplane has been operated. It is named after John Weston Hobbs and was first used in the mid-20th century after the introduction of the Hobbs meter.
Hobbs time is measured by the number of hours that an aircraft engine has been running. This measurement is usually taken from the time that the engine is started until it is shut down.
Another way to think of Hobbs time is that it's the true measure of flight time. When you're flying and an hour passes on your watch or on the clock on your smartphone, then an hour of Hobbs time has also passed.
That might sound like a silly thing to mention, since an hour is an hour, right? Not quite! As you'll see when we talk about tach time, all hours are not created equal!
How is Hobbs Time Measured?
As briefly mentioned above, Hobbs time is measured using a Hobbs meter. This is a device that's connected to the aircraft engine and records the number of hours that it's been running. The Hobbs meter is often found in the cockpit so that the pilot can easily see how much time has elapsed.
Some newer aircraft are equipped with electronic Hobbs meters, which are able to record and store the data automatically. This can be helpful if you want to track your Hobbs time over a long period of time, or if you want to share the data with someone else (like a mechanic).
The Hobbs meter is usually either wired into the ignition system, put on an oil pressure switch, or hooked up to the airplane's engine in another way to track how many hours it's been used.
What Do Pilots Use Hobbs Time For?
Now that you have a better idea of what Hobbs time is and how it's measured, you might be wondering why it matters. After all, isn't it just another way of measuring time?
Pilots use Hobbs time for a few different reasons. First, it's a good way to track how much flight time they have and is the time that should be used to record the number of hours flown in the pilot's logbook. This is important because pilots need a certain amount of flight time to earn or maintain their certification. If a pilot doesn't have enough flight time, they might not be able to fly passengers or cargo.
Second, Hobbs time is used to calculate aircraft rental fees. When you're renting an airplane, you'll usually pay by the hour. The rate will sometimes be based on the Hobbs time, but we'll get into this in more detail towards the end of this article.
Finally, some aircraft maintenance schedules are based on Hobbs time. This is because certain parts of the airplane will wear out after a certain number of hours of use. For example, the engine might need to be overhauled after a certain number of Hobbs hours.
What is Tach Time?
Now that we've gone into detail about Hobbs time, let's talk about tach time. Tach time is another way of measuring the amount of use an aircraft has received, but it's different from Hobbs time in the way it measures hours and what it's used for.
Tach time is the number of hours that an engine has been running at a certain speed. Unlike Hobbs time, tach time doesn't measure the actual number of hours that an aircraft has been flown. Instead, it's a measure of how much wear and tear the engine has experienced.
Tach time is also known as power-on time or rotor-running time. It gets its name from the tachometer, which is a device that measures the rotational speed of an engine. This is just like the tachometer in your car, which displays the RPM of your car's engine at any time.
A plane's tachometer works similarly, and it typically measures the rotational speed of the plane's propellor (and therefore, its engine).
How is Tach Time Measured?
Tach time is measured using a tachometer, which is a device that measures the rotational speed of an engine. As we mentioned before, a tachometer on a plane is just like the one on your car, except here it's measuring the rotational speed of your airplane's engine. In most cases, this means that it's measuring how many rotations per minute the propellor itself is making.
Tach time is measured in hours, but it's not the same as how many hours pass on your watch or in Hobbs time. Tach time is a measure of how long the engine has been running at a certain speed, and it doesn't necessarily correlate to the number of minutes or hours that have passed.
The only time that tach time will match the actual amount of time that has passed is when the plane is traveling at its cruise speed. This is because the engine is running at a constant speed (which is also the speed that it was designed to operate most efficiently), so the number of hours on the engine will correlate to the actual number of hours that have passed.
What Do Pilots Use Tach Time For?
Tach time is used to track how long the engine has been running. In other words, tach time is used to measure the number of rotations that it has performed, or how many hours of wear and tear are actually on the engine. This information can be used to help maintain the engine and keep it running smoothly.
The Federal Administration Administration (FAA) typically requires that your airplane is inspected every 50-100 hours. This requirement is based on engine hours, which is measured in tach time. That's why it's vital to monitor tach time separately from Hobbs time. Otherwise, you might be getting inspected far more often than you have to (since Hobbs time is often much faster than tach time!).
Tach time is also used to calculate the amount of fuel that has been used. This is because tach time is a measure of how long the engine has been running, and fuel consumption is directly related to how long the engine has been running and at what RPM the engine has been operating. In most cases, an airplane will be most efficient when it's operating at or near its cruise speed.
Key Differences Between Hobbs Time and Tach Time
Now that you have a better understanding of what both Hobbs time and tach time are, let's take a look at the key differences between them:
- Hobbs time is measured using an hour meter, while tach time is measured using a tachometer.
- Hobbs time tracks how long the airplane is operated (engine running), while tach time tracks how many hours of wear and tear are on the engine.
- Hobbs time is measured in hours, while tach time can be measured in hours or rotations.
- Hobbs time should be used for recording flight time in a pilot's logbook, but tach time should be used to monitor the number of engine hours for maintenance.
- Hobbs time will usually be significantly higher than tach time since it starts from the time the engine is started until it's stopped.
- Hobbs time will always match the actual amount of time that has passed, while tach time will only match the actual amount of time that has passed when the plane is at cruise speed.
- The FAA requires that your airplane is inspected every 50-100 hours based on engine hours (tach time), not Hobbs time.
As you can see, there are some major differences between Hobbs time and tach time. While they both may seem similar at first glance, there are actually quite a few key differences between them. So be sure to keep these in mind the next time you're logging your flight hours or getting your airplane ready for inspection!
Are Airplane Rental Fees in Hobbs Time or Tach Time?
Last but not least, let's talk about airplane rental fees. The vast majority of flight schools and airplane rental companies will charge you based on Hobbs time. This is because it's the most common way to measure how long the airplane has been operating since it begins tracking hours as soon as the engine is started.
However, there are some schools and companies that will charge you based on tach time instead. In general, it's cheaper to rent an airplane by the hour if it's based on tach time rather than Hobbs time. This is because tach time will often be significantly lower than Hobbs time (since it doesn't measure the hours in actual time passed unless the plane is at its cruise speed).
So if you're trying to compare prices between different flight schools or rental companies, be sure to ask if they charge by Hobbs time or tach time!
We hope you found this article helpful in understanding the difference between Hobbs time and tach time. It's a bit confusing to think about different ways to measure the time an airplane is operated, but hopefully this article cleared things up a bit!
About THE AUTHOR
After spending years watching every video I could find about flying, I finally scratched the itch and got my pilots license. Now I fly every chance I get, and share the information I learn, here.Read More About Joe Haygood