Hobbs vs. Tach

[A Squared]

As a matter of honor, you should always return a man's equipment in better shape than you found it, w(h)eather you're borrowing it, or renting it. As a practical matter of airmanship, you should always take ownership of an aircraft when you fly it, and treat it accordingly.

Never abuse an airplane. Treat it as though your life depends upon it.

Because it does.

The cracks caused in the vertical stab attach brackets from sideslipping at high speeds may not affect you, but may affect the pilot days or years later when the aircraft fails. The brakes you burn up because you're "not paying for them" will raise the cost of the aircraft and everyone will pay..or they might just fail from repeated overheating and cracking, and hurt someone else. What do you care? You're not paying for it, right?

What you're describing isn't something to brag about. It's a character flaw, and unless corrected, ought to be a source of embarassment to you.

Well said, Avbug. That's what I really meant.

 

[pgcfii2002]

Fly at a reduced RPM, maybe 1800 or so...you'll save some cash that way.

 

[sky37d]

Fly at a reduced RPM, maybe 1800 or so...you'll save some cash that way.

Actually, not the case, unless the rental is dry. If the limit switch reaches the point where it activates the tach, usually somewhere around 1000, or 1200 RPM, then it is just a hobbs meter that isn't going to charge you for taxiing around the field.
Once the tach is activated, it matters not whether you are at 1800 or 2600, it is going to record the same amount of TIME , just like a hobbs meter does.
So there is no TIME savings by flying at 1800.

For a conventional HOBBS meter, it starts recording time when you hit the master switch. The only way to disable it is to turn off the master switch. I can remember in primary, taxiing for 3 clicks of the HOBBS. A tach time rental would not have charged for that time.

 

[avbug]

Actually, not the case, unless the rental is dry. If the limit switch reaches the point where it activates the tach, usually somewhere around 1000, or 1200 RPM, then it is just a hobbs meter that isn't going to charge you for taxiing around the field.
Once the tach is activated, it matters not whether you are at 1800 or 2600, it is going to record the same amount of TIME , just like a hobbs meter does.
So there is no TIME savings by flying at 1800.

What on earth are you talking about? Limit switches, activating tachs, and the like?

A tach is a mechanic device, with no limit switches. The odometer function of the tach records time based on gear movement, period. The slower the gears turn, the slower it records time. The unit is designed to record time accurately at a given RPM. Any RPM lesser than that will record time at a slower rate than is actually occuring.

The tach is "activated" by starting the engine, or turning the engine. You suggested that it will record time at the same rate, regardless of the RPM of the device it measures, but this is exactly incorrect. The tach will record time directly in response to the rate at which the engine turns, and subsequently turns the tach.

For a conventional HOBBS meter, it starts recording time when you hit the master switch. The only way to disable it is to turn off the master switch. I can remember in primary, taxiing for 3 clicks of the HOBBS. A tach time rental would not have charged for that time.

Also untrue.

An electrical hour meter (hobbs, datacon, etc, are brand names) will begin to record the time when it is supplied electricity. Had you read the thread, you'd know that a variety of means are used to accomplish this, only one of which is correlating operation with the position of the battery master switch or relay. Often the hour meter works in conjunction with landing gear or landing gear component switches, such as squat switches or limit switches. In other cases, air pressure switches activate the electrical hour meter by experiencing a particular pressure on the switch; it won't record time until a particular airspeed is reached. Still others use pressure switches from oil, or pneumatic systems to begin recording time. How and when the hour meter begins recording time depends entirely on it's installation, and of course, it's proper function.

A tach will show taxi time, but at a slower rate than it will show flight time. The tach is always recording, so long as it is turning, but the rate at which it does so is entirely dependent upon RPM.

 

[sky37d]

Ok
Disregard all after good morning

 

[avbug]

??

Ah...it's night time. Circadian dyslexia?

 

[pgcfii2002]

I was always told the tach turns at roughly 80% of the hobbs which is why so many flight clubs boast about being "dry tach" when they rent.

 

[avbug]

That would really depend on the speed of the engine at any given time now, wouldn't it?

(It would. And does).

At full speed...they record the same.

 

[check6]

At a flight school I used to work at, the HOBBS would always poop out on us, or just run slow. Our policy was to multiply the TACH difference by 1.2, which accurate in comparison with the HOBBS time if the dang thing worked.

 

[FlyingFisherman]

Boy some folks wouldn't know humor if it bit them on the ass, pointed, grinned and then laughed at them.