Hobbs vs. Tach

[BizPilot]

I did a search for this topic already, so don't jump all over me. I still couldn't find a good answer.

I am renting an aircraft from an FBO that charges by TACH time. I want to get the most "bang" for my buck. What is the best way to run? (I understand the whole "in the pattern" theory, but I need an answer for long-haul flights)

Do I want to pull the power back to, lets say, 55% power and run a slow Tach?

Or do I want "balls to the wall" and run it at red line?

What is going to give me the best return on my rental dollar?

Thanks!

 

[sky37d]

Tach time is simply that, the time the engine is running, at some predetermined RPM. Hobbs time, typically, happens when the master is on. So, it doesn't matter how lean, fast, etc you run the engine, (unless it is just at idle), it is still going to register time running.
If you are paying by the hour, and you just want to stay in the pattern, it doesn't much matter. If you are doing a cross country, go flat out, below redline of course, make sure it is not to lean.

 

[PacoPollo]

Some freighters,fbo's use Hobbs time on the airplanes.There is usually a switch below the panel that turns the damn thing off.

 

[Flysher]

depending on the plane i think the tach runs off engine speed, so at idle it will turn over less than at full throttle.

Hobbs meter on Cessnas is tied to oil pressure line, Seminoles i flew were tied to the master.

check the POH for the plane and find out i guess.

 

[avbug]

What's going to give you the best return for your rental dollar really depends on what you hope to accomplish with that rental dollar.

If you're renting to actually accomplish something, like go somewhere, then powering back to a minimum power setting won't help you out much.

If you're trying to stay aloft as long as you can and save money, with no particular aim, then yes, flying at a reduced RPM setting will fly you the longest for the slowest turnover on the tach odometer.

If you're just in it to build time, then forget paying for the aircraft and write it in your logbook. If you're in it to build some experience, then go fly maneuvers, approaches, and whatever else you need to do to build your proficiency, and pay for whatever the tach gives you.

A company charging by tach time is giving you a good deal.

Electronic hour meters may be activated in any number of ways, from oil pressure switches to landing gear position switches, air presure switches (based on airspeed), squat switches, electrical direct when the battery master is on, etc.

The tach turns slower at lower RPM's, and the rate at which it records time is slower, too.

 

[FlyingFisherman]

There are several levels of flying style I use based on who's paying the bills.

Private aircraft on business trip. Daily Rate + hourly rate = reduced power settings for passenger comfort and increased fuel efficiency.

Rented aircraft in which I'm the instructor. - "You don't need to fly at 2500rpm in a 172 while in cruise. 2300 is a much better power setting, it's quieter and easier on the engine in the long run."

Rented aircraft in which I am alone. - "Balls to the wall I'm paying for this thing!"

It is absolutely possible to get 165kts TAS out of a 200hp Mooney M20J. You CAN get them slowed down from 160 to 81kts between the outer and middle markers using nothing but the landing gear, prop and a healthy dose of sideslip to do so. They also land in <800' if you want them to and don't mind using someone elses brakes.



If you're trying to build time then renting an airplane while paying for the tach is the best deal going. Log the hobbs and then pay the tach...that's a great deal! Not many places do that and if it's your deal...you've got a good one.

 

[A Squared]

Rented aircraft in which I am alone. - "Balls to the wall I'm paying for this thing!"

It is absolutely possible to get 165kts TAS out of a 200hp Mooney M20J. You CAN get them slowed down from 160 to 81kts between the outer and middle markers using nothing but the landing gear, prop and a healthy dose of sideslip to do so. They also land in <800' if you want them to and don't mind using someone elses brakes.

So if it's somone else's airplane, you don't have any qualms about abusing it. Nice.

 

[Flysher]

Rented aircraft in which I'm the instructor. - "You don't need to fly at 2500rpm in a 172 while in cruise. 2300 is a much better power setting, it's quieter and easier on the engine in the long run."

LOL I'm guilty of that one.

In all seriousness though it does hurt your ears if you goin a long distance.

 

[Mr Wu]

I did a search for this topic already, so don't jump all over me. I still couldn't find a good answer.

I am renting an aircraft from an FBO that charges by TACH time. I want to get the most "bang" for my buck. What is the best way to run? (I understand the whole "in the pattern" theory, but I need an answer for long-haul flights)

Do I want to pull the power back to, lets say, 55% power and run a slow Tach?

Or do I want "balls to the wall" and run it at red line?

What is going to give me the best return on my rental dollar?

Thanks!

Grab the POH and load the profiles into DUATS for the different power settings. Then all you have to do is have it calculate flight time for the different settings and apply rental cost to your answer. Most of these tachs are set for 100% or something close to that. Just use 55% of rental fee for 55% power, etc. Should get you in the ballpark.

 

[avbug]

Rented aircraft in which I am alone. - "Balls to the wall I'm paying for this thing!"

It is absolutely possible to get 165kts TAS out of a 200hp Mooney M20J. You CAN get them slowed down from 160 to 81kts between the outer and middle markers using nothing but the landing gear, prop and a healthy dose of sideslip to do so. They also land in <800' if you want them to and don't mind using someone elses brakes.

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.

 

[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.