Tach vs Hobbs
- Thread starter Frankh
- Start date
- Status
- Joined
- Mar 23, 2005
- Messages
- 13,226
From our lastest EMS Pilot's users guides, available on our website:
The Tach Timer keeps track of engine time (normalized to the user-configured cruise RPM).
The Hobbs Timer records the duration of time engine oil pressure is at 15 PSI or higher.
The Tach Timer keeps track of engine time (normalized to the user-configured cruise RPM).
The Hobbs Timer records the duration of time engine oil pressure is at 15 PSI or higher.
Tach Time
I´d like to know the advantange to read "Tach Time". Is it used to figure out the future fuel comsumption? Or, is it used to guide maintenance? May be the best value to guide preventive maintanence is Hobbs meter time. Isn´t it? JC - Aracaju - Brasil
I´d like to know the advantange to read "Tach Time". Is it used to figure out the future fuel comsumption? Or, is it used to guide maintenance? May be the best value to guide preventive maintanence is Hobbs meter time. Isn´t it? JC - Aracaju - Brasil
meljordan
Active Member
Tach time is a derivative of the old mechanical style tachometers used in all aircraft prior to the electronics developments. In fact, it is more a total rpm counter than a timer, in that the time it records is directly related to the rpm of the engine. An assumption was made by the manufacturer as to what engine rpm was to be used to equal on minute (the industry standards are 2310 or 2556 revolutions equal one minute), so for example, Mooney may say that 2310 RPM would be the standard, so the Tach would be designed that each 2310 revolutions of the engine would drive the clockwork gears to produce a one minute change in the tach timer. Thus 1155 revolutions would produce a change of 30 seconds, even though this may take over a minute in real time to occur. So in reality, you could take the tach time in minutes, multiply this by the gear ratio of the tach and calculate how many revolutions the engine has made. This is probably the best indicator of engine wear possible.
Tach time is the industry accepted way to determine the amount of use that an engine has recieved. TBO and maintanence schedules are all based on tach time. Hobbs time is a "real" clock and is most frequently used to determine flight times to charge on rental aircraft. I have set my Dynon EMS for a tach time of 2450, as this is my normal cruise RPM, so at cruise it records tach and hobbs times at an equal rate.
Best Regards,
Mel Jordan
Tach time is the industry accepted way to determine the amount of use that an engine has recieved. TBO and maintanence schedules are all based on tach time. Hobbs time is a "real" clock and is most frequently used to determine flight times to charge on rental aircraft. I have set my Dynon EMS for a tach time of 2450, as this is my normal cruise RPM, so at cruise it records tach and hobbs times at an equal rate.
Best Regards,
Mel Jordan
Martin_Sobel
New Member
- Joined
- Jul 21, 2007
- Messages
- 5
Flight time is defined as when the aircraft leaves earth until it lights again on terra ferma.
This is the time that should be used for maintenance.
Block time is when the aircraft taxies under its own power until it is parked. This is the time you log in your flight logbook.
Certainly the Dynon should have the smarts to use an airspeed of 30 kts to start the flight timer. This is what real EFIS aircraft use.
Traditionally,the hobbs meter is used for Block Time, and the recording tach for maintenance. However, with the digital and electronic instations, there is no recording tach installed on the airplane.
I believe this is an important function. It should not be considered "nice to have."
This is the time that should be used for maintenance.
Block time is when the aircraft taxies under its own power until it is parked. This is the time you log in your flight logbook.
Certainly the Dynon should have the smarts to use an airspeed of 30 kts to start the flight timer. This is what real EFIS aircraft use.
Traditionally,the hobbs meter is used for Block Time, and the recording tach for maintenance. However, with the digital and electronic instations, there is no recording tach installed on the airplane.
I believe this is an important function. It should not be considered "nice to have."
lucaberta
New Member
Agree with all the above, with one point which is important for me.
I fly a motorglider, and shutting down the engine is a feature and not a "bug" in the engine itself... ;D
So I'd really like to have an "airspeed above 20KIAS" timer as well as an "oil pressure above 15PSI" timer, as they might differ quite a bit in the good days (definition of a "good day" is the one applicaple to gliders, that is... I doubt that power pilots consider a good day one where their engine all of a sudden makes no noise!)
And of course, all the timers shall be independant of each other.
Ciao, Luca
I fly a motorglider, and shutting down the engine is a feature and not a "bug" in the engine itself... ;D
So I'd really like to have an "airspeed above 20KIAS" timer as well as an "oil pressure above 15PSI" timer, as they might differ quite a bit in the good days (definition of a "good day" is the one applicaple to gliders, that is... I doubt that power pilots consider a good day one where their engine all of a sudden makes no noise!)
And of course, all the timers shall be independant of each other.
Ciao, Luca
Maintenance on certified aircraft (especially part 135 operations were all components have life limits) and 100 hour inspections need only to be based on actual flight hours (time actually airborne). The installation of an “air-hobbs” can decrease this expense significantly (as much as 30% in training aircraft). It also has the benefit of increasing the re-sale value of the aircraft by limiting the “total-time” of the airframe and components.
“Oil-hobbs” was an invention of the FBOs as a way to separate more $ from the wallet of customers but does track most closely the time the FAA allows pilots to log as flight time.
True “tach-time” is probably the most accurate way to gauge maintenance intervals on the engine and components (as it counts revolutions of the engine) but I’m not sure that’s true the way Dynon does it (a preset RPM that goes from low to high recording).
“Oil-hobbs” was an invention of the FBOs as a way to separate more $ from the wallet of customers but does track most closely the time the FAA allows pilots to log as flight time.
True “tach-time” is probably the most accurate way to gauge maintenance intervals on the engine and components (as it counts revolutions of the engine) but I’m not sure that’s true the way Dynon does it (a preset RPM that goes from low to high recording).
- Joined
- Mar 23, 2005
- Messages
- 13,226
We basically do it the same way as the real thing, but we offer a little bit of configurability not normally available with the physical gauge. Our tach counts revolutions (well really pulses, but you put in the pulses/revolution factor to compensate). You then get to set a cruise rpm that represents the rate at which you want tach time to increment in "real time". Then, slower and faster or faster engine speeds result in faster or slower incrementation of the tach timer. Behind the scenes though, we are counting every pulse.
- Joined
- Mar 23, 2005
- Messages
- 13,226
A flight timer (based on airspeed) is on our wish list. As we always say with features that are not yet being worked on, no promises when it will show up in the software (if ever), but we do understand that there is a demand for it.
And as described above, we're fairly unique in the industry in calculating ACTUAL tach time, not just oil pressure above X time.
And as described above, we're fairly unique in the industry in calculating ACTUAL tach time, not just oil pressure above X time.
Martin_Sobel
New Member
- Joined
- Jul 21, 2007
- Messages
- 5
You may think that you are doing the same thing...counting pulses, but you are not. Whatever number is selected is a guess. On the other hand, selecting a speed such as 20 or 30 kts will be off by seconds at the most. Again, this is what Collins and Honeywell use.
Tach Time is the best we had in an ANALOG world. But we are now in a DIGITAL world and I can not understand why you can't see the difference and simplicity of using airspeed as the trigger point. By using tach time, you are emulating an old technology. Why do you want to do this when there is a simple solution to the problem?
Tach time means nothing. It is a guess. We used it to maintain general aviation aircraft because it was the easiest thing to use. We could also use our own log of off time to on time.
When I flew commercially, we used to feel that the flight was sucessful (tongue in cheek) if we remembered to start the timer when we took off. (Somethiing I forget to do to this day.)
The hobbs clock is not a rip off. It is a close measurement of Block Time, the time used in our flight logbooks.
Tach Time is the best we had in an ANALOG world. But we are now in a DIGITAL world and I can not understand why you can't see the difference and simplicity of using airspeed as the trigger point. By using tach time, you are emulating an old technology. Why do you want to do this when there is a simple solution to the problem?
Tach time means nothing. It is a guess. We used it to maintain general aviation aircraft because it was the easiest thing to use. We could also use our own log of off time to on time.
When I flew commercially, we used to feel that the flight was sucessful (tongue in cheek) if we remembered to start the timer when we took off. (Somethiing I forget to do to this day.)
The hobbs clock is not a rip off. It is a close measurement of Block Time, the time used in our flight logbooks.
- Joined
- Mar 23, 2005
- Messages
- 13,226
Martin, Tach time is a measure of how many times an engine turned over. It's a pretty decent measure of wear on an engine. Are you saying an engine gets the same amount of wear no matter if it's at 1200 RPM or 3000 RPM as long as the airspeed is 30 knots or above? And it gets no wear at all as long as it's on the ground? I think Lycoming would disagree with you.
As we said, the feature is on our list, but insulting us about not understanding the difference between tach and flight time is not a way to get what you want. What more do you want from us then to say we hope to do it in the future?
One thing to seriously consider- the *EMS* measures Tach time. Flight time is an *EFIS* thing. Of course we understand these are not the same thing.
As we said, the feature is on our list, but insulting us about not understanding the difference between tach and flight time is not a way to get what you want. What more do you want from us then to say we hope to do it in the future?
One thing to seriously consider- the *EMS* measures Tach time. Flight time is an *EFIS* thing. Of course we understand these are not the same thing.
Martin_Sobel
New Member
- Joined
- Jul 21, 2007
- Messages
- 5
Look:
I've been around this business for 48 years and have well over 24,000 hours. I have flown and taught professional grade EFIS from Collins to Honeywell since 1984.
I am saying that maintenance on an aircraft is based upon Time In Service. Time In Service is defined as when the aircraft leaves the ground until it alights back on earth. If I taxi out for takeoff, but return to the ramp and shut down, there is no Time In Service. None. Zippo. Nadda.
There is no definition in the regulations for tach time.
Tach time is something we used to get with a recording tach. It was better than the oil pressure activated hobbs time for maintenance because it is generally less than hobbs time since engines average less than the rpm's that equal one hour of operation. Many LSA's equipped with Rotax engines do not have recording tach's.
Besides all that, I want to set up a maintenance schedule based upon what the regulations require. If it appears that the schedule is not enough, then I will decrease the intervals (still based upon flight time).
A simple trip log will solve the problem: Out/Off/On/In. In-Out will give the pilot his Flight Time. On-Off will give Time In Service. Only problem here is that one must now start a clock for take off, which is a bad time to divert one's attention to the task at hand. (I seem to forget to do it anyway.) Flight Time goes in his log book (and his pay records). Time In Service is sent to Maintenance to schedule preventative maintenance or required inspections.
There are other considerations beside the engine that require inspections, like the airframe, brakes, etc. These items don't particularly care how fast the engine is turning. There are other considerations as far as engine wear is concerned than engine speed, particularly break-in periods and use of leaded fuel.
You say that "we understand the difference" but you keep reverting to something that does not exist. I defy you to find "tach time" in the regulations. And of all people, a manufacture of glass instruments and solid-state gyros, you should be looking at the future...not what we did in the past.
Your choice to use tach time to determine Time In Service was an error that should be fixed, and it complicated what should be a simple calculation. I'm sorry if I hurt your feelings.
After all, how many years have we been flying airplanes thinking that we are held in the air because of Bernoulli’s Principal. Now we finally have learned that a barn door will produce as much lift as a wing...what holds us up is primarily the deflection of air in a downward force.
To save you some time, here is the definition of Time in Service from the regulations:
Title 14: Aeronautics and Space
PART 1—DEFINITIONS AND ABBREVIATIONS
TIME IN SERVICE, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.
I've been around this business for 48 years and have well over 24,000 hours. I have flown and taught professional grade EFIS from Collins to Honeywell since 1984.
I am saying that maintenance on an aircraft is based upon Time In Service. Time In Service is defined as when the aircraft leaves the ground until it alights back on earth. If I taxi out for takeoff, but return to the ramp and shut down, there is no Time In Service. None. Zippo. Nadda.
There is no definition in the regulations for tach time.
Tach time is something we used to get with a recording tach. It was better than the oil pressure activated hobbs time for maintenance because it is generally less than hobbs time since engines average less than the rpm's that equal one hour of operation. Many LSA's equipped with Rotax engines do not have recording tach's.
Besides all that, I want to set up a maintenance schedule based upon what the regulations require. If it appears that the schedule is not enough, then I will decrease the intervals (still based upon flight time).
A simple trip log will solve the problem: Out/Off/On/In. In-Out will give the pilot his Flight Time. On-Off will give Time In Service. Only problem here is that one must now start a clock for take off, which is a bad time to divert one's attention to the task at hand. (I seem to forget to do it anyway.) Flight Time goes in his log book (and his pay records). Time In Service is sent to Maintenance to schedule preventative maintenance or required inspections.
There are other considerations beside the engine that require inspections, like the airframe, brakes, etc. These items don't particularly care how fast the engine is turning. There are other considerations as far as engine wear is concerned than engine speed, particularly break-in periods and use of leaded fuel.
You say that "we understand the difference" but you keep reverting to something that does not exist. I defy you to find "tach time" in the regulations. And of all people, a manufacture of glass instruments and solid-state gyros, you should be looking at the future...not what we did in the past.
Your choice to use tach time to determine Time In Service was an error that should be fixed, and it complicated what should be a simple calculation. I'm sorry if I hurt your feelings.
After all, how many years have we been flying airplanes thinking that we are held in the air because of Bernoulli’s Principal. Now we finally have learned that a barn door will produce as much lift as a wing...what holds us up is primarily the deflection of air in a downward force.
To save you some time, here is the definition of Time in Service from the regulations:
Title 14: Aeronautics and Space
PART 1—DEFINITIONS AND ABBREVIATIONS
TIME IN SERVICE, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.
Hi - very interesting - Today you say Flight Time is an *EFIS* thing. (as I had on my wishlist in Dec.)
But in Reply #4 - Dec 1st, 2006, 1:24pm you said:
.... if we do this, it would be on the EMS, not the EFIS. The EMS is the product where we keep track of flight times, hobbs time, and tach time.
TIME IN SERVICE is absolutly that what I want too. But If you are realizing this feature one day, is it possible to record the the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing? Only for the last flight - that´s enough! We are paying the aircraft exactly for this time :
Regards, John
The differences in type of flight time was covered in my response (#6) which I will quote again.
"Maintenance on certified aircraft (especially part 135 operations were all components have life limits) and 100 hour inspections need only to be based on actual flight hours (time actually airborne). The installation of an “air-hobbs” can decrease this expense significantly (as much as 30% in training aircraft). It also has the benefit of increasing the re-sale value of the aircraft by limiting the “total-time” of the airframe and components.
“Oil-hobbs” was an invention of the FBOs as a way to separate more $ from the wallet of customers but does track most closely the time the FAA allows pilots to log as flight time.
True “tach-time” is probably the most accurate way to gauge maintenance intervals on the engine and components (as it counts revolutions of the engine)."
Just because the FAA doesn't define it (tach time), doesn't mean it doesn't exist (or have a use). Counting revolutions of the engine is my preferred way to keep track of maintenance for my engine.
I would like to see Dynon add an flight timer function to their products even though my GPS (Garmin 496) already has that function but I definately do not see having a true "tach-time" function as a mistake but rather as very insightful.
You can set up your maintenance based on the FARs, I'll base mine on real world physics were things like revolutions of the engine are what matter.
Martin_Sobel
New Member
- Joined
- Jul 21, 2007
- Messages
- 5
In the real world, engine operations at low power settings do not matter. If they did, the FAA would factor that time into the maintenance equation. A recording tach would be a mandatory instrument.
Time In Service inspections of the engine do not use time as a measurment other than specify when an inspection is required. What is measured is metal in the oil (oil analysis), compression, ignition timing, spark plugs and other signs of wear. Some parts are time limited. But the FAA defines the time as Time In Service.
You have no data to prove your being correct, only your "gut" feeling, that if the engine is running, something must be going on.
What about the fact that if an engine does not run for an extended period, you are creating more damage? Where do you factor that into your equation?
Aviation is not a precise thing. You are trying to measure with a micometer but are hitting it with a sledge hammer.
Nuf Said!
Time In Service inspections of the engine do not use time as a measurment other than specify when an inspection is required. What is measured is metal in the oil (oil analysis), compression, ignition timing, spark plugs and other signs of wear. Some parts are time limited. But the FAA defines the time as Time In Service.
You have no data to prove your being correct, only your "gut" feeling, that if the engine is running, something must be going on.
What about the fact that if an engine does not run for an extended period, you are creating more damage? Where do you factor that into your equation?
Aviation is not a precise thing. You are trying to measure with a micometer but are hitting it with a sledge hammer.
Nuf Said!
Just had to have the last word didn't you...
So you're saying that as long as I never take off, my engine will last forever and never need maintanence (spark plugs, oil, filters etc.) no matter how long I run it at ANY power setting. WOW! who knew? (sic)
Ah.. DUH!, if the engine is running, there most certianly is something going on even if the FARs seams to think that nothing is happening (as long as you have an air-hobbs and not a recording tach).
Oh, and you're wrong. The FAA mandates things like OVERHAUL (not just inspections) of engines based on Time in Service (part 135. part 121) But that's a moot point as a Dynon product wouldn't be installed in a Part 135 or Part 121 aircraft since it's not TSO'd.
Martin, if you're so sure that the FAA way is the only way, why the heck are you here debating the merits of an NON-FAA APPROVED product? Your precious FAA (the end-all-be-all of aviation in your mind) hasn't "approved" of thier products at all.
You'll get very little support for an opinion based solely on the FARs on this forum as these are people who are trying to use technology to do things BETTER than the monolithic dinosar called the Federal Aviation Administration...
By The Way, you're analogy makes no sense...
- Joined
- Mar 23, 2005
- Messages
- 13,226
We generally don't close threads, but we're going to apply a tourniquet to this one since it seems to be heading towards flame territory.
- Status