Gear up switch starts Tach time?

[Hengelo]

I've been listening to five hour ground school vidoes in the background (as one does, don't look at me funny) and this one mentioned that for a Piper Seminole (2:17) the tach meeter starts when the gear reads as up. I've heard similar from a local A&P but I thought it was just some jankey home-brew engineering... now I'm not so sure.

This seems like a controversial practice, but I'm neither an A&P nor a regulator.

 

[Initial Fix]

hard to comment without knowing the context of the video

But. A tach is always running. A HOBBs is often used on rentals and starts running with the battery switch as they want every possible second to count for $$$

 

[RussR]

I've been listening to five hour ground school vidoes in the background (as one does, don't look at me funny) and this one mentioned that for a Piper Seminole (2:17) the tach meeter starts when the gear reads as up. I've heard similar from a local A&P but I thought it was just some jankey home-brew engineering... now I'm not so sure.

This seems like a controversial practice, but I'm neither an A&P nor a regulator.

Not when the gear itself is up, but when the wheels leave the ground. It's a squat switch. Pretty typical for twins. It's considered a perfectly valid measure of "time in service". In fact, it's the same way many maintenance intervals are calculated for the turbines at work - time off the ground.

Nothing home brew or janky.

 

[Hengelo]

So does that mean twins share a tach number? What happens when one engine is swapped - how are things like 50 & 100 hour managed after that?

 

[Dana]

So does that mean twins share a tach number? What happens when one engine is swapped - how are things like 50 & 100 hour managed after that?

No different from any other plane where the engine was swapped and the tach wasn't, or vice versa, you keep track of the actual time in the logbook.

 

[Magman]

Z
Hourmeters and tachs differ.

Many Steam Gage Tachs record time at a particular rpm ie 2310.

So you run 1 hr at 2310 = 1 hr on tach

OR 4 hrs at 600 = almost 1 hr tach.

It records how many times the engine has rotated ; somewhat like

an odometer.

The hour meter functions bin a different manner and records how long

a system is activated. Common activation is via oil or fuel pressure,

Master switch,airspeed switch squat switch. Recording cabin heater use is

another application.


Tach Time x 1.2 will generally equal,Hobbs Time

 

[Hengelo]

The numbers guy in me is getting hives. Two engines, started in whatever order, run up & down however many times, and a single shared tach starts & stops on the squat switch? How does that work? If I run one engine in flight a little harder than the other, which one is having it's RPM counted?

but, but but... these beans are not being counted!

 

[bradg33]

The numbers guy in me is getting hives. Two engines, started in whatever order, run up & down however many times, and a single shared tach starts & stops on the squat switch? How does that work? If I run one engine in flight a little harder than the other, which one is having it's RPM counted?

but, but but... these beans are not being counted!

View attachment 154401

Each engine has a separate tach with a separate tach time. Some/most twins also have a single hobbs meter for "flight time" that is triggered, typically, off of a squat switch (when the weight is off the wheels, the squat switch opens or closes (depending on installation style) and that activates the Hobbs meter.

In airplanes with mechanical tachs, the time is usually only accurate at a certain RPM as stated above. In airplanes with digital tachs, they usually just start at a pre-set RPM level. On my Duke w/ CGR-30P engine monitors, the "tach" time starts for each engine when that engines RPM exceeds 1300rpm.

 

[Hengelo]

That would make sense, but aren't people saying this twin has one tach, activated by squat switch? That's my entire question.

Each engine has a separate tach with a separate tach time. Some/most twins also have a single hobbs meter for "flight time" that is triggered, typically, off of a squat switch (when the weight is off the wheels, the squat switch opens or closes (depending on installation style) and that activates the Hobbs meter.

In airplanes with mechanical tachs, the time is usually only accurate at a certain RPM as stated above. In airplanes with digital tachs, they usually just start at a pre-set RPM level. On my Duke w/ CGR-30P engine monitors, the "tach" time starts for each engine when that engines RPM exceeds 1300rpm.

 

[Bell206]

This seems like a controversial practice, but I'm neither an A&P nor a regulator.

Time in service (TIS) is the official method to track maintenance requirements and is defined by Part 1.1 regulation below. Flight time has a different definition as shown below. And while an owner can use any method to track flight time and time service time, wheels off ground and wheels on ground is the most accurate for TIS. No controversy needed.

Two engines, started in whatever order, run up & down however many times, and a single shared tach starts & stops on the squat switch?

The tach, like your watch, or hour meter are merely time recording devices to record the usage intervals for the required mx records per 91.417. Each engine must have a TTIS and TSO record separate from the time recording method you use. Same happens if you change a recording tach or hour meter but start at zero. If that makes sense.

 

[Hengelo]

Huh. Who woulda thunk it. So for everyone whose tach starts before takeoff is effectively overstating their engines TTIS? Safer, I suppose.

 

[bradg33]

That would make sense, but aren't people saying this twin has one tach, activated by squat switch? That's my entire question.

I don't think anyone is saying the airplane has a single tach that's activated by a squat switch. That's just not how a tach works. A hobbs, yes, a tach no.

And some airplanes have a single tach that displays both engines, but doesn't have an hour meter on it. In those cases, you just go based on the hobbs and track each engine separately using hobbs time. My old 50s Twin Bonanza was setup that way (single tach for both engines, no meter on it).

 

[Hengelo]

That's precisely what anyone is saying. Which is why I asked.

 

[Doc Holliday]

A lot of airplanes have no recording tach or hobbs meter. Each flight is logged with TO and landing time.

Several older airplanes I've owned never had recording tachs as each flight was logged.

 

[dmspilot]

Dunno about the tach time in the Seminole but it's hard to take a course seriously when they are proponents of the oversquare myth.

2:01:44 "Well, now your manifold is on top because 25 is greater than 23. You're going to overstress the engine."

 

[Bell206]

So for everyone whose tach starts before takeoff is effectively overstating their engines TTIS? Safer, I suppose.

Not safer so much as it is wasteful especially if you fly an aircraft with finite life-limits like a turbine engine. If you go strictly off a hobbs or tach that starts before take-off for those life limited parts you could easily erase up to 10-20% of its life for no reason. A gear mounted squat switch to a hobbs is standard install in some cases or you simply use your watch and mark each take-off and landing as mentioned above.

 

[MauleSkinner]

Not when the gear itself is up, but when the wheels leave the ground. It's a squat switch. Pretty typical for twins.

I’ve flown some piston twins where it was raising the gear that started the Hobbs, not a squat switch.

 

[RussR]

I’ve flown some piston twins where it was raising the gear that started the Hobbs, not a squat switch.

Really?! Sounds like a great way for a renter to get free flight time. Or cut down on maintenance expenses. 100-hour coming up? Just fly with the gear down!

 

[flyingron]

My plane used to have the hobbs on the gear switch. Maintenance time in service is the time the airplane is OFF the ground. That works very nicely with the definition.

 

[MauleSkinner]

Really?! Sounds like a great way for a renter to get free flight time. Or cut down on maintenance expenses. 100-hour coming up? Just fly with the gear down!

they were charter airplanes, because t I won’t tell you how I figured it out.

 

[Magman]

I have a great personaL story re disabling airspeed sensors and ethics.

Little long to retype for me.

 

[Dan Thomas]

I have a great personaL story re disabling airspeed sensors and ethics.

Little long to retype for me.

Maybe a year ago we had a thread on it. Some guy wanted to know how to disable the Hobbes meter so he could get some free flight time. Things got pretty hot for a while here.

 

[M20K]

ot when the gear itself is up, but when the wheels leave the ground. It's a squat switch. Pretty typical for twins. It's considered a perfectly valid measure of "time in service". In fact, it's the same way many maintenance intervals are calculated for the turbines at work - time off the ground.

Just to clarify, you're talking about the Hobbs starting with the squat switch, not the engine Tach time. I've never heard of an Tach Time not starting and ending with the engine start/stop. (Sort of what it is there for. )

 

[Magman]

I’ll shorten:

A certain Part 135 310 would fly numerous flights over long distances with

little change in TIS. That means no required Inspections, AD’s , overhauls

etc. The IA mentioned during Fed visit to take a long look. They discovered

the blocked vane and confronted the Owner. Owner marched out and

fired the IA on the spot who had to tell his bride of 3 weeks that he had

lost his employment. No whistleblower protection.


The reaction in the Aviation Community was very positive and he had no

problem finding a job. Ultimately this led to a career with DoD and

involvement with TIFS, X-22, F-22, F-35. He was honored for his actions

with the Space Shuttle. His boss got his “ hand slapped” for trying to

find out involve in “ Black Projects”.


Word gets around in the Aviation Community.

The initial action showcased his integrity that he could not be bought.

Good warning for the younger techs to keep in mind.

 

[RussR]

Just to clarify, you're talking about the Hobbs starting with the squat switch, not the engine Tach time. I've never heard of an Tach Time not starting and ending with the engine start/stop. (Sort of what it is there for. )

Yes, I guess I am talking about Hobbs, but I kind of suspect that's what the video was talking about too.

Lots of planes don't have a tach time meter. In fact, the Seminole I used to teach in, a typical 6-pack airplane, did not. It did have three Hobbs meters, though - one for "engine running" time (linked to an oil pressure switch on the right engine), a "time in service" Hobbs which was on the squat switch, and then a "heater" Hobbs. Of course, billing was from the "engine running" Hobbs and maintenance was on the "time in service" Hobbs.

The airplane in the video is a G1000 airplane. So it doesn't have a separate tachometer with an integrated hour meter like a 6-pack airplane might have for tach time. I believe the G1000 has a display named "Engine Time", which of course serves the same function as, and is the replacement for, "tach time". I suspect the video is calling it "tach time" (possibly in error or to draw a comparison) and it could certainly be activated by the squat switch, in fact that's what I'd expect.

 

[M20K]

Lots of planes don't have a tach time meter.

My Mooney didn't when i got it. Original tach failed and I opted for a digital, which had Tach Time.

 

[Clip4]

You will also find some chronometers in complex aircraft with the elapsed time activated by the squat switch.

 

[Dan Thomas]

Just to clarify, you're talking about the Hobbs starting with the squat switch, not the engine Tach time. I've never heard of an Tach Time not starting and ending with the engine start/stop. (Sort of what it is there for. )

Lots of planes don't have a tach time meter. In fact, the Seminole I used to teach in, a typical 6-pack airplane, did not. It did have three Hobbs meters, though - one for "engine running" time (linked to an oil pressure switch on the right engine), a "time in service" Hobbs which was on the squat switch, and then a "heater" Hobbs. Of course, billing was from the "engine running" Hobbs and maintenance was on the "time in service" Hobbs.

Yes, the FBOs and flight schools will bill from the time the engine starts until it stops. The maintenance, including inspections, ADs, engine overhauls and all the rest is by time off the ground. This annoys a lot of people paying for that airplane, but if it wasn't done that way the FBO/School would have to raise the prices to meet the actual costs and still leave some room for profit. They would ignore the engine start/stop times and just bill for TIS. It would not save the customer any money. It might save the airplane from the guys that taxi too fast or take off with a cold engine to save a few bucks.

Airplanes cost money, lots of money, to buy, insure, feed, maintain, shelter, and all the rest. Many people have tried to reduce those costs, and if there were easy solutions, we'd be using them. We can blame regulations, but regulations come about because too many people simply will not behave themselves and use some common sense. We already have too many ignoring the regulations, as in the "inexpensive" annuals. The buyers of such airplanes end up with the first-annual bill shocker. The painful cost of cheating eventually comes due for someone.

 

[flyingron]

When I changed out the engine in the Navion, I got one with 9 hours from Tradewinds (Bonanza turbine conversion shop). All my instruments including the tach was from the A36 that the engine came out of (had to have a 14-to-24 volt converter). I switched to a Hobbs on the gear for the TIS. When I redid hte panel the last time, I put in an MVP50 and use its idea of TIS now. The only goofy thing is that the guy who installed it, set to time to the old Hobbs time. One of these days I'm going to fix it to read the airframe TIS (about 4000 hours different).