Tach time as hobbs etc.

[DonMuncy]

Does anyone keep up with the real numbers relating to their logged time vs tach time showing on the meter. I understand that the tach time reads at a specific RPM (I know I didn't say that right) , and I know it will vary with how much time is spent at low RPM vs high, but I wonder how this relates to most of our flying. I looked back in my log books for the number of hours on the engine since I bought the plane, and compared it to my pilot's log book hours. I know I am fairly generous in rounding up my flight time, but I was amazed at the difference between the two. 

[jaylw314]

Well, to put it in perspective, I've put in about 240 hours of tach time in about 2.5 years, and I've logged about 237 hours in actual time (although I do that by clock, not Hobbs).  On any given flight there can be a big difference--doing pattern work, I can get about 1 hour of flight for 0.7 hours of tach time, but inevitably some amount of time waiting on the ground gets added in, so for me it ends up pretty close. 

And no, I don't calculate or figure out my flight time by using any flight timers, I just look at my watch and estimate to the nearest 10 minutes (for VFR flights, anyway).

[Hank]

I keep all of that in a little notebook in the front seat pocket. Sometimes pax in the right seat look at me funny as I'm digging around under their knee to get it out, but it all becomes clear.

Right now, the notebook is at home while I catch up my logbook. I'll post a photo tonight; going by memory, the tach time is generally pretty close, unless I'm making short, low altitude flights where I run 2300, or doing multiple approaches.

Long term, I've put 657 tach hours on the plane, and I think ~750 in my logbook, I'll double-check that tonight too.

[Mooneymite]

Another source of flight time is the Garmin 430/530.  It records/only that time when the plane is above a pre-set groundspeed, i.e. airborne time, unless you are prone to taxiing real fast.

This flight time is the time that counts against you for TBO on the Lycoming...

I wish I had remembered to reset my 430 to zero when I replaced my engine. 

[Marauder]

Like Hank & Mooneymite, the tach and Hobbs will differ. On the JPI 900 I have a tach and Hobbs time. I also have EI RPM gauge which I use as the official tach time. All 3 don’t agree with each other.

The EI and JPI have different starting RPMs for tach time and the Hobbs time looks to be purely power up time.

Garmin Pilot tracks the “wheels off/on times” and that records at a different rate than all the others.

What I normally see is that my actual “flight” time is roughly 1.2 for every 1 hour of tach time.

And for the definition of “flight time”, from CFR 1.1

Flight time means:

(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing


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[Marauder]

I should add that I also have a clock that I zero when I start the engine and that is what I use to track “flight” time. At a large airport, I may be on the ground for a lot more time taxiing or waiting to launch.


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[1964-M20E]

I have a Davtron that starts timing when the master goes on.  It is good for tank switching and how long the engine has been running for the flight.  The EI tach is for engine and air frame times.  I go back to flight aware for personal log book times and then round to the nearest whatever I feel like it at the time.  IMC time is estimated for each flight based on what I can remember.  I do not keep a flight log on the plane just the maintenance logs.

 

[jaylw314]

1 hour ago, Marauder said:

Like Hank & Mooneymite, the tach and Hobbs will differ. On the JPI 900 I have a tach and Hobbs time. I also have EI RPM gauge which I use as the official tach time. All 3 don’t agree with each other.

The EI and JPI have different starting RPMs for tach time and the Hobbs time looks to be purely power up time.

Garmin Pilot tracks the “wheels off/on times” and that records at a different rate than all the others.

What I normally see is that my actual “flight” time is roughly 1.2 for every 1 hour of tach time.

And for the definition of “flight time”, from CFR 1.1

Flight time means:

(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing


Sent from my iPad using Tapatalk Pro

My CFI said "moving under its own power" included taxiing time for the purpose of training, but I'm just too lazy to try to break it down like that now that I'm not working on a rating...

[steingar]

I just log the tach.  Its probably wrong, but I really haven't anything else dependable and its easiest.  Doesn't matter that much, I'm not climbing ratings are trying to impress anyone.

[carusoam]

Mechanical tach times are geared to assume time based on rpms...

There is only one rpm that matches time with a 1:1 ratio...

That rpm is usually encoded by part number on the case of the tach...

I think @jetdriven Byron has probably detailed what rpm Mooneys usually get with their tachs...

More modern Mooneys May use an oilP switch to turn on the electric hour meter...

The POH has a paragraph that explains how this works in/for really modern Mooneys...

Putting the hour meter on the back wall of the cargo area is a great way of keeping the fear of the Grimm reaper at bay...

Why put a constant reminder of maintenance up in front of the owner...?

Mooney was very thoughtful this way. 

The mechanical tach time is actually counting each revolution of the crank... then converting the count to units of time.

Not a bad way of keeping track of engine maintenance...

PP thoughts only, not a mechanic...

Best regards,

-a-

[carusoam]

Keeping a flight log can be made interesting using an app like CloudAhoy...

it even records flight maneuvers, flight track and time details...  with a waas source it even captures accurate T/O and landing details...

Remembering to turn everything on requires a check list... (for some)

Best regards,

-a-

[skydvrboy]

2 hours ago, DonMuncy said:

Does anyone keep up with the real numbers relating to their logged time vs tach time showing on the meter.

I don't have my plane or log book handy, but at my first oil change, I had 50 hrs on the tach and just over 60 hrs in my logbook.  I'm getting close to my second oil change per tach and now have 114.4 in my logbook.  I know it's going to be different based on the type of flying (short trips, pattern work vs. long cross country), but it seems 1.2 times the tach is about what I'm getting in my logbook, YMMV.

I have a clock on the yoke that I start when I start the plane (part of checklist) and check when I shut down (if I remember) to determine what to put in the logbook.  Don, how far off is your logbook from your tach?

[Vance Harral]

There's a rule of thumb floating around that 1.0 hours of tach time = 1.2 hours of operating time.  It stems from flight schools that operated airplanes with no Hobbes meter, but wanted to charge for time from engine start to engine stop regardless of power setting.

When we first bought our Mooney and everyone in the partnership was doing transition training, we tracked both tach time and "stopwatch time" (from engine start to engine shutdown).  Over the course of almost 100 hours of tach time that first year, the 1.2 multiplier turned out to be spot on.  It's even pretty close for instrument training with lots of long approaches at reduced power.

Obviously the 1.2 multiplier isn't correct for a long cross-country flight, but pretty good for local hamburger runs and training flights.

[David Lloyd]

Tach time is really a rev counter.  Continental used 2566 (think this was the number) RPM to equal 1 hour of time.  Don't remember what Lycoming uses.  I set my electronic tach to count based on 2500 rpm.  Just looked up the actual flight time counter today, it is 424.7 hours versus 432.7 hours tach time. Did not check the hobbs time which is actual hours the engine is running.  Too many choices, I gave up and just use tach time.

[vorlon1]

Good question for me as well. Purchased a C model earlier this year that didn't have a Hobbs meter. I'm so used to having that to assist in recording log time... Never thought I'd miss a Hobbs meter!

[lamont337]

As mentioned it might depend on which tach you have. A previous owner installed a Horizon P1000 digital tach in my plane. Per the manual, real time (1:1) is recorded anytime RPMs are 800 and above. This is less than idle, so I record/log them exactly. 

[RobertGary1]

9 minutes ago, lamont337 said:

As mentioned it might depend on which tach you have. A previous owner installed a Horizon P1000 digital tach in my plane. Per the manual, real time (1:1) is recorded anytime RPMs are 800 and above. This is less than idle, so I record/log them exactly. 

Oh that’s aweful. I’m surprised they're still in business. So all your maintenace has to be done early? Your engine has 10%-20% more hours etc??

-Rkbert  

[EricJ]

I have a JPI EDM900 and I kept my mechanical tach, since the logbook was already consistent with that number and it's a nice backup.     I usually cruise around at about 2500 rpm, so the tach, which records real time at 2400 rpm, runs faster than real time by about 4%. 

I use the Avare EFB, which will log the entire flight and will email me a .kml file of the gps samples starting from when the airplane begins moving until it stops moving, which is consistent with the FAA definition of time.   Loading that file into mymaps.google.com gives me a graphical depiction and I can compare the beginning and end times to get the total loggable flight time.

My EDM and the Avidyne 540 will also log time, but I never remember to use them, while Avare will automatically send me an email with the kml file at the end of each flight.

I wish there was a smoother way.   At some point the airplane avionics will automatically update our electronic logbook every time we fly, but we do not seem to be to that point yet.

 

Edited October 22, 2018 by EricJ

[hypertech]

Just now, EricJ said:

I have a JPI EDM900 and I kept my mechanical tach, since the logbook was already consistent with that number and it's a nice backup.     I usually cruise around at about 2500 rpm, so the tach runs faster than real time by about 4%. 
 

 

The EDM900 includes a setting for what the true speed is for the tach.  My understanding is that it can be set within about 10 hours of the install but after that it would have to go in to JPI to be adjusted.

So, if you every have to send it in, you could ask for that to be changed so that it reads true at your cruise rpm so it stops running unnecessarily fast.

[RobertGary1]

What was wrong with a Hobbs meter? I hooked mine to the alternator indicator post so when the alternator puts out power the Hobbs turns.

-Robert

[EricJ]

Just now, hypertech said:

The EDM900 includes a setting for what the true speed is for the tach.  My understanding is that it can be set within about 10 hours of the install but after that it would have to go in to JPI to be adjusted.

So, if you every have to send it in, you could ask for that to be changed so that it reads true at your cruise rpm so it stops running unnecessarily fast.

Sorry, I wasn't clear but I use the mechanical tach, which is real time at 2400 rpm.   I think the EDM900 defaults to 2400 rpm as real time, but as you mention according to the manual this can be edited, as can the displayed total airframe time, etc.

[Bob - S50]

Don,

I time with a clock from first starting to taxi until shutdown. I find that my tach time is always within 0.1 hours of the same time.

Our EDM730 keeps an hobbs time and it is about 7 or 8% higher than our tach time.

Is that what you were asking?

Bob

[DonMuncy]

Yes Bob. Thanks for everyone's input.

[INA201]

I may be wrong here but I recall renting Cessnas years ago and the HOBBS came on when the master was turned on.  This may have just been set that way for rental aircraft.  The HOBBS can be wired however you want apparently.

[Hank]

My plane has no Hobbs, just a recording tach. Came that way from the factory.   That drives maintenance. A yoke clock provides flight time for my logbook, i just set the red hands over the white clock hands after winding and setting the time, then have to remember to write it down . . . .

Here is my notebook from WV, both times are pretty close except for my IFR Checkride:

This is flying around the SouthEast, some trips of the same length but less Delta-t. Guess there is a price for living in God's Country:

The exercise of adding the "Log" columns and determining the difference between Tach and Clock for each group is left as an exercise for the student. Please report your results here. No partial credit will be given to those who do not show their work . . . . .