Tach hours vs. real time

Bonchie

Bonchie

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Bonchie
Been renting on Hobbs until I recently passed my check ride last week.

Now looking at all the local options here in DC. I'm looking at joining the faaflyingclub here. They rent a Cherokee for $110 a tach hour + $50 fixed a month.

Out of curiosity, let's say I cruise at 65%. What's a general ballpark figure for how much real time flying I'll get out of a tach hour?
 
It is pretty much airplane specific, but the general rule is 1.2 Hobbs to 1 hour Tach.
 
Well, it's RPM based so what's your RPM with 65%?

The flying club I belong to is tach based. A couple of weekends ago I did a flight from Orlando Exec (KORL) to Umatilla, landed, taxied back, took off, flew to Ocala (KOCF), landed and shut down to have breakfast, took off and climbed up to 5500 (above the forming clouds) and landed at Orlando again. 1.57 Tach time, 2.0 hobbs (and therefore logged).

So that's a 25% savings. I cruised at 2400 RPM.

John
 
jsstevens said:
Well, it's RPM based so what's your RPM with 65%?

The flying club I belong to is tach based. A couple of weekends ago I did a flight from Orlando Exec (KORL) to Umatilla, landed, taxied back, took off, flew to Ocala (KOCF), landed and shut down to have breakfast, took off and climbed up to 5500 (above the forming clouds) and landed at Orlando again. 1.57 Tach time, 2.0 hobbs (and therefore logged).

So that's a 25% savings. I cruised at 2400 RPM.

John
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2400RPM in a Cherokee is closer to 75% power unless you are well up there.

But thanks for the example. That's the kind of real world scenario I'm interested in seeing.
 
When I do pattern work I typically get about .8 tach vs. 1.0 hobbs.

Cross country I typically do better (as you saw above). I did an out, T&G and back in May that was 1.5 Hobbs and 1.2 Tach.

These are C-172 numbers. The first example was C-172 C with the O-300, freshly rebuilt. The examples in this email are a C-172L with the Lycoming O-320.

John
 
My overall average is 1.2 to 1.3 Hobbs to tach,depending on how I fly. Since not renting or building time doesn't make much difference except for overhaul.
 
Like everything in life, it depends. There will be a higher differential if you spend more time on the ground. So flying out of a busy airport like Orlando Executive, you'll see a bigger differential than operating out of Orlando Apopka with short, direct access to the runway.

Anyway you slice it, you'll do better on tach than Hobbs.
 
This kind of information is helping me decide if I should join a flying club that uses Tach instead of Hobbs. Thanks for creating this thread.
 
Different airplanes have different Clock:Tach hour ratios. For the Grumman AA-5-series, it's 1:1 at 2556 RPM. I've seen other planes as low as 2300 RPM. You'd have to look it up in the manuals for your plane (maybe contact the manufacturer or look on the back of the Tach). You also have to remember that RPM for 65% power with a fixed pitch prop will vary with altitude as well as aircraft and prop types. On my Tiger with a 63-pitch Sensenich prop (it's different for the McCauley prop of the same pitch and for other pitches of the Sensenich prop), 75% takes about 2450 RPM at SL, but that increases about 100 RPM every 5000 feet up. So, at 75%, I'd be getting about 1:1 at 5000 feet (about 2550 RPM), less Tach per clock at SL (about 2450 RPM), and more Tach/clock at 10,000 (about 2650 RPM).
 
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Are renters incentivized to treat engines better when they are charged tach vs hobbs?
 
If you can rent with Tach time, and rent it Dry.. You can save a BUNDLE on time building or leisure flights if you just manage the engine properly.

45% power anyone? :)
 
Bonchie said:
Been renting on Hobbs until I recently passed my check ride last week.

Now looking at all the local options here in DC. I'm looking at joining the faaflyingclub here. They rent a Cherokee for $110 a tach hour + $50 fixed a month.

Out of curiosity, let's say I cruise at 65%. What's a general ballpark figure for how much real time flying I'll get out of a tach hour?
Click to expand...

The Hobbs meter reflects how long the Battery or Master switch is on, it's electrical not RPM based. A separate meter runs on RPM, its called 'Engine' time.

Sometimes the meter is run by the oil pressure sender switch, when its active the meter runs (still needs electrical power).

And a few Hobbs are connected to the primary alternator circuit. When the alternator is running, the Hobbs runs.

http://en.wikipedia.org/wiki/Hobbs_meter
 
We fly $70 wet/tach in our club. I flew a short breakfast run Saturday that was 1.0 Hobbs. The tach time was 0.69 Generally speaking though, I figure tach will be around .8 hobbs. That has been true more often than not.
 
CTLSi said:
The Hobbs meter reflects how long the Battery or Master switch is on, it's electrical not RPM based. A separate meter runs on RPM, its called 'Engine' time.

Sometimes the meter is run by the oil pressure sender switch, when its active the meter runs (still needs electrical power).

And a few Hobbs are connected to the primary alternator circuit. When the alternator is running, the Hobbs runs.

http://en.wikipedia.org/wiki/Hobbs_meter
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I'm aware of that. I'm asking about tach rentals.

The Hobbs I currently use is on the master. Because I've always rented Hobbs, I've never ran lower then 75% in cruise. There's just no point.

So I'm mainly curious what kinds of savings you see on the tach at lower power settings. That's why I used 65% as an example.
 
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CTLSi said:
The Hobbs meter reflects how long the Battery or Master switch is on, it's electrical not RPM based. A separate meter runs on RPM, its called 'Engine' time.

Sometimes the meter is run by the oil pressure sender switch, when its active the meter runs (still needs electrical power).

And a few Hobbs are connected to the primary alternator circuit. When the alternator is running, the Hobbs runs.
Click to expand...
The one on the Grumman GA-7 Cougar is hooked to the weight-on-wheels switch, which if you dig in the regs, provides a measurement most like that the FAA says to use for maintenance intervals (takeoff to landing).
 
A great point for renters. Know what runs the Hobbs meter. I was getting checked out in a Warrior and I heard the Hobbs click over. I turned to the instructor and asked if the Hobbs was wired to the master. He said yes. Nothing like paying $12 to preflight the plane.



CTLSi said:
The Hobbs meter reflects how long the Battery or Master switch is on, it's electrical not RPM based. A separate meter runs on RPM, its called 'Engine' time.

Sometimes the meter is run by the oil pressure sender switch, when its active the meter runs (still needs electrical power).

And a few Hobbs are connected to the primary alternator circuit. When the alternator is running, the Hobbs runs.

http://en.wikipedia.org/wiki/Hobbs_meter
Click to expand...
 
Ron Levy said:
The one on the Grumman GA-7 Cougar is hooked to the weight-on-wheels switch, which if you dig in the regs, provides a measurement most like that the FAA says to use for maintenance intervals (takeoff to landing).
Click to expand...

My Navion is the same way (as are most of the later Bonanzas, my engine instruments came out of the Bonanza).
 
I recently joined a club and pay about $100/hr wet based on tach time for a 172. This is good because we are based at a towered airport so there is usually a fair amount of taxiing around and waiting for takeoff clearance. Having to pay on the hobbs for all of that can be really frustrating.

There was another club that I considered that charged about $80 hobbs time for essentially the same plane, but at a non-towered airport. It probably would have worked out to about the same cost. Clubs typically operate at break-even, so either way you end up paying about the same amount. The real difference is in the costs that the rate covers. Hangar vs. tie-downs. In-house maintenance vs. FBO. Social fund vs. strictly flying. New airplane fund vs. normal maintenance fund.

Before I joined a club I was paying a hobbs rental rate of $145 plus sales tax for a 172 from my flight school. Joining a club has saved me a ton!
 
Let me get this straight. Everytime I turn on the Master Switch in my FBO rented C172 the Hobbs is ticking over? I thought I was saving Hobbs time by getting Atis Info with the motor off. LOL. I think I need to looking to Ownership.
 
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evapilotaz said:
Let me get this straight. Everytime I turn on the Master Switch in my FBO rented C172 the Hobbs is ticking over? I thought I was saving Hobbs time by getting Atis Info with the motor off. LOL. I think I need to looking to Ownership.
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Not usually, They stopped doing that when Pilots figured out that the plane flew just fine with the master switch off.

A lot of the new ones run of the oil pressure, if you have the engine running the Hobbs starts.
 
CTLSi said:
The Hobbs meter reflects how long the Battery or Master switch is on, it's electrical not RPM based. A separate meter runs on RPM, its called 'Engine' time.

Sometimes the meter is run by the oil pressure sender switch, when its active the meter runs (still needs electrical power).

And a few Hobbs are connected to the primary alternator circuit. When the alternator is running, the Hobbs runs.

http://en.wikipedia.org/wiki/Hobbs_meter
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Missed one: Our Caravans have the Hobbs hooked up to the pitot/static so they start ticking at 50kts.

evapilotaz said:
Let me get this straight. Everytime I turn on the Master Switch in my FBO rented C172 the Hobbs is ticking over? I thought I was saving Hobbs time by getting Atis Info with the motor off. LOL. I think I need to looking to Ownership.
Click to expand...
Most likely not. The standard is to tick once it senses oil pressure, and it needs electrical power to do that, but it can be rigged differently.
 
evapilotaz said:
Those that have mentioned your in a club paying by Tach do you have a monthly membership fee? Have you consider that in your savings?
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If you're actively flying, unless the monthly fee is seriously out of line it shouldn't have a great impact on your annual costs. In the club I used to belong to it was less than 1/2 hr. of flying. OTOH, when I was training and practicing slow flight and lots of patterns, just the difference between tach and hobbs made up for the monthly nut. After I got my ticket and started doing VFR day trips, even at cruise power, I broke even on the monthly fee vs. FBO rental (plus fuel surcharge, plus non-owned insurance or insurance fee) after flying not much more than than 1+ hrs/month. I also got the greater availabilty, and no daily minimums.
 
I took a short local flight in a mooney, stopped at another airport 15 mi away for a quick landing and taxi back. I ran economy power one way, normal cruise the other. .37 tach, .65 hobbs (stopwatch from start to shutdown). Uncontrolled field and I am pretty efficient.

That should give you an idea.
 
evapilotaz said:
Those that have mentioned your in a club paying by Tach do you have a monthly membership fee? Have you consider that in your savings?
Click to expand...

My monthly fee is $62, which multiplied by all 60 club members covers all fixed costs such as tie down fees, insurance for 3 aircraft, and a small amount for administrative expenses. At least that is how it was explained to me. The tach rate covers all operating costs including fuel, oil, and a contribution to a maintenance fund for any repairs that are required, the annual inspection and eventual engine replacement. The rate is adjusted each month for fluctuations in actual costs. Some clubs set the rate annually, but ours does it every month.

Compared to renting, the only way I don't save money over renting is to not fly at all. If I log just one hour in a month in a club 172 it costs me roughly $142 ($62 club dues + .8 hrs tach time @ $100/hr). One hour rented is $159 ($145/hr + sales tax). Of course the more hours I fly the more I save over renting because the monthly dues are spread over more hours.
 
HighFlyingA380 said:
Most likely not. The standard is to tick once it senses oil pressure, and it needs electrical power to do that, but it can be rigged differently.
Click to expand...
Nope, the standard is it ticks whenever power is applied to it via whatever combination of switches people want to feed it. I've seen it on the master, on an oil pressure switch, on the gear switch (on my plane, for example), on an airflow switch, on the heater switch, etc...
 
flytime said:
My monthly fee is $62, which multiplied by all 60 club members covers all fixed costs such as tie down fees, insurance for 3 aircraft, and a small amount for administrative expenses. At least that is how it was explained to me. The tach rate covers all operating costs including fuel, oil, and a contribution to a maintenance fund for any repairs that are required, the annual inspection and eventual engine replacement. The rate is adjusted each month for fluctuations in actual costs. Some clubs set the rate annually, but ours does it every month.

Compared to renting, the only way I don't save money over renting is to not fly at all. If I log just one hour in a month in a club 172 it costs me roughly $142 ($62 club dues + .8 hrs tach time @ $100/hr). One hour rented is $159 ($145/hr + sales tax). Of course the more hours I fly the more I save over renting because the monthly dues are spread over more hours.
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Thank you for the informative post. This helps.
 
flyingron said:
Nope, the standard is it ticks whenever power is applied to it via whatever combination of switches people want to feed it. I've seen it on the master, on an oil pressure switch, on the gear switch (on my plane, for example), on an airflow switch, on the heater switch, etc...
Click to expand...

So the real test for me is turn on the master switch and see if the Hobbs ticks. What is one tick measured in Time? I don't want to drain the battery by doing this test. :mad2:
 
evapilotaz said:
So the real test for me is turn on the master switch and see if the Hobbs ticks. What is one tick measured in Time? I don't want to drain the battery by doing this test. :mad2:
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Well, the Hobbs is generally in tenths, so 1 hr / 10 = 6 minutes. And it hopefully won't drain the battery; If it does, they need a new battery...
 
evapilotaz said:
So the real test for me is turn on the master switch and see if the Hobbs ticks. What is one tick measured in Time? I don't want to drain the battery by doing this test. :mad2:
Click to expand...
If you're running for any significant amount of time, you'll see something happening on the Hobbs meter. If you're only doing this for 60 seconds or so, it's not going to make a significant difference.
 
Ron Levy said:
If you're running for any significant amount of time, you'll see something happening on the Hobbs meter. If you're only doing this for 60 seconds or so, it's not going to make a significant difference.
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Not on the Oil Pressure activated ones.
 
evapilotaz said:
Those that have mentioned your in a club paying by Tach do you have a monthly membership fee? Have you consider that in your savings?
Click to expand...

The one I am in has a $130/month fixed fee. But $50 of that is flying credit if you fly.

John
 
Actually, by "running" I meant electrical power on to obtain the ATIS before starting the engine. The question I was answering was asking about having the master on to do that before starting the engine, and whether or not the Hobbs would run. I previously said some Hobbs meters work off the master but others off an oil pressure switch. The poster didn't know for sure which way it was on the plane in question, and I was responding saying that if you only have the Hobbs running for a minute or so to get the ATIS, then shut the master off to do the rest of the pre-start checks, that minute wasn't going to be a significant issue on the bill for the flight.
 
When my C 152 was on leaseback in the early 1980s, I was paid on Tach and he charged on Hobbs and as a general rule he got 20 extra hours for each of my 100 hour inspections. Once I got my CFI he would not let me teach in the plane even if I went to another field to teach. It got me started on a bad note with leasebacks.
 
For the OP, Tach Time is supposed to be calibrated to real hours at a specific cruise RPM. If you're making a long trip, your Tach Time will be pretty close to your Hobbs time (and your clock time).

If you are doing pattern work, your running below cruise RPM most of the time, so your TT will be about 60-70% of your clock time.

For the true money-grubbers, note that for fixed prop aircraft, your cruise RPM INCREASES for a given power setting as you climb, but your speed decreases. That means your rental cost is lowest on cross-country flights if you fly a little below the altitude that gives you maximum speed. In C172's a good target is around 7000-8000 ft. You still go fast, but the thicker air slows down the prop so you burn less TT. It's not as fuel-efficient as 10,000 ft, but most rentals and flight-clubs are wet rates per hour.
 
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