Tach to Hobbs conversion for logging

[Pinecone]

Maybe when you were flying A-10s, but in the C-130 the flight engineer wrote down the time the wheels left the ground and again when we touched down. And that is what was logged. I didn't keep a personal logbook then, but when I left the Air Force, they handed me a computer printout which I consider my first logbook. When I look at it, there is a circle around the total combat hours: 303.6. I transferred that to my first civilian logbook and then realized there would never be a reason to carry that forward.

Not saying we logged from chock to chock, but pointing out that in other than GA flying, the chocks are pulled AFTER engine start.

Yes, my military time was logged from take off to touchdown. No crew chief to do that for the planes I flew, so it was the RSU that captured the times.

I kept a personal logbook (separate from my civilian time) that showed that time, plus 0.3 for ground ops in a separate column, but added to the flight time in the total column. When I entered it all into an electronic log book, I only captured the total time.

Except for LIFT at Holloman AFB. Due to construction, we had to taxi a roundabout path to get back after landing, so ground ops were a bit more.

 

[flyingcheesehead]

OK, was logging my flying over the weekend.

I started with a 6.9 hour XC (Hobbs) that was 6.8 hours tach. Next was a Fight Review flight of 1.8 Hobbes, that was 1.8 tach. Then an IPC at 2.2 Hobbes, and 2.0 tach. Then 7.0 Hobbs back home for 6.9 tach.

Total for the trip was 17.9 Hobbs and 17.5 tach.

So no set ratio/formula to convert. But on it shows that on a long XC, tach and Hobbs are almost the same..

Before this trip was a short triangle that was 0.5, 0.5 and 0.6 Hobbs, but 0.3, 0.5, and 0.4 tach. So short flights have a greater % difference, even though the actual time difference is about the same.

So, IMO, adding 0.1 or 0.2 per flight to the tach time is close to being the actual Hobbs time.

Is that Hobbs on oil pressure, master, airspeed, or other?

That's a much smaller difference than I was seeing when I did the same experiment... Which just points to hacking times probably being a better solution!

 

[EricBe]

The prop is part of the aircraft, right? And it is moving, under its own power?

Regardless, the FAA has long accepted Hobbs time as one of the acceptable ways to log flight time.

I paraphrased; the FAA's definition requires the *aircraft* move. Here's the full text (reference here, emphasis mine):
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; or
(2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.

So, no a mechanised door or a spinning propeller do not count by any reasonable interpretation that I can see.

 

[flyingcheesehead]

I paraphrased; the FAA's definition requires the *aircraft* move. Here's the full text (reference here, emphasis mine):
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; or
(2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.

So, no a mechanised door or a spinning propeller do not count by any reasonable interpretation that I can see.

Yet, the FAA has long considered "rental Hobbs" as a valid method of logging flight time.

Should people be encouraged to let the plane roll a foot immediately after engine start so that they can start logging?

Also, "comes to rest after landing" would seem to indicate that if I stopped on the taxiway just after pulling off the runway to do an after landing checklist that I would have to stop logging right there, whereas if I did the after landing checklist on the roll, I could log it all the way to the hangar. Should that be encouraged?

An airliner being pushed back isn't under its own power, yet airline pilots generally log out to in or brake to brake...

The FAA is not really nitpicky about this stuff, as long as you are consistent about how you do it.

 

[unsafervguy]

I’ll do that from now on, but I’m curious about all the time I’ve logged previously using the 1:1.2 method. Like I say, I’m very particular about making sure I record my experience properly for a future airline job.

the airlines wont care at all, they will not even ask unless something looks out of line.

 

[cowman]

I’ve been using foreflight’s track log feature. Only hangup is if you let it automatically stop/start for you. I once had an 8+ hour flight and when I checked the log it tracked me from my home airport to my destination airport…. then to the rental car, to the hotel, to the restaurant and back to the hotel….

 

[Pinecone]

Is that Hobbs on oil pressure, master, airspeed, or other?

That's a much smaller difference than I was seeing when I did the same experiment... Which just points to hacking times probably being a better solution!

Master, as it is the "Hobbs" in a G3X EIS.

 

[flyingcheesehead]

I’ve been using foreflight’s track log feature. Only hangup is if you let it automatically stop/start for you. I once had an 8+ hour flight and when I checked the log it tracked me from my home airport to my destination airport…. then to the rental car, to the hotel, to the restaurant and back to the hotel….

You can edit the track logs after the fact:

Master, as it is the "Hobbs" in a G3X EIS.

On the G3X EIS, you have "Total Hours" and "Engine Hours". The "Engine Hours", per the manual, is "Counted whenever a valid RPM is detected" and so should be equivalent to a normal oil-pressure Hobbs.

 

[Pinecone]

I am pretty sure you can set it also to show Tach hours, which is RPM based on a baseline RPM. My installer needed that RPM to get up the G3X.

 

[flyingcheesehead]

I am pretty sure you can set it also to show Tach hours, which is RPM based on a baseline RPM. My installer needed that RPM to get up the G3X.

Ah, yes. I see that in the install manual now... But that's what I get for looking in the Pilot's Guide instead!

 

[skyking3286]

A wristwatch and moving the plane a bit while it warms up is so easy I question the overthinking on the thread. Hobbs and tach only work for the dollars on the rental. You can even use a video to document wheels move/wheels stop.