skywagon8a
MEMBER
SE Mass MA6
What powers your "Hobbs", oil pressure? That will record more hours than a tach which counts rpms.
Tach is off, who can recalibrate?
- Thread starter RookieCubPilot
- Start date
bob turner
Registered User
No - master switch. We deduct 25%, because almost all flights are .5, and involve 12 minutes of taxi.
Sad, because I went to all the expense of replacing that Mack Truck tach, only to find that I had no space, not even for a 90 degree drive! Win some, lose some.
Sad, because I went to all the expense of replacing that Mack Truck tach, only to find that I had no space, not even for a 90 degree drive! Win some, lose some.
RVBottomly
PATRON
Asotin County Washington (KLWS)
I like that. I have a habit of noting the musical pitch of sounds. Two blades at 2400 rpm is a slightly sharp low E in pitch. Think of the lowest string on a guitar, for instance.
If you are really obsessed (like me), you can use a pitch pipe or fork and count beats to fine tune the calculation....
Charlie Longley
MEMBER
Anchorage, AK
Big difference between signing off a weld and an instrument repair. Look at the regs.
BC12D-4-85
SPONSOR
Fairbanks, AK.
It seems from reading CAR 4 and later 3 that the only instrument that requires limits of accuracy is the airspeed indicator and compass. The rest if required can be accurate or inaccurate to an unspecified degree. Is that true as I might have misread or didn't find a source. If so....what's the big concern about who's checking and maybe improving accuracy if it's poor?
Gary
Gary
supercrow
FRIEND
Smith Pond near Millinocket, Me
Be careful now! Your comments are bordering on common sense. The feds aren't going to have any of that LOL!
wireweinie
FOUNDER
Palmer, AK
What's the difference whether I remove the tach for repair at an automotive shop and reinstall it or go pull one off the shelf/out of a panel for installation? I'm signing that I have checked the unit for proper and safe operation.
The paragraph you cited from Part 65.81 just says I can't perform an instrument repair. If a fed questions me about my tach repair sign off, I will point out that the repair was done at a shop equipped to do those repairs and that I signed off that I checked the tach for safe and proper operation. There are no repair stations that I'm aware of that still work on these (just like the oil pressure, oil temp, and ammeter cluster in Cessnas). The failure of a mechanical tach is not a safety of flight issue. Checking for correct operation of a tach requires no specialized or non standard equipment.
So how is this any different than signing off a repair weld that I or a non A&P welder didn't perform? What reg?
Web
How many of you have had a tachometer recalibrated by a local shop? I’ve replaced a couple of tachs because I was told they couldn’t be repaired. From a practical standpoint I’m happier to replace and fly than remove and wait. The last tach I replaced cost under $300 with range markings and hours set. How much does recalibration cost?
wireweinie
FOUNDER
Palmer, AK
The most accurate tachs are still the electronic types. They use pulses read from the p-leads to calculate rpm so no mechanical parts.
Web
Web
mvivion
SPONSOR
Bozeman,MT
The tach in my 170 took a dump. I sent it in, and had it overhauled. Came back, read 75 rpm off. So, I ordered a new one. Read 100 off right out of the box. Cert. standard says 100 off is within acceptable standards.
Not to me. So, I returned the new one, bought a Horizon electronic tach and never looked back.
Ever wonder why similar airplanes cruise at different speeds and fuel flows but at same power settings? Look no farther than those mechanical tach.
MTV
Not to me. So, I returned the new one, bought a Horizon electronic tach and never looked back.
Ever wonder why similar airplanes cruise at different speeds and fuel flows but at same power settings? Look no farther than those mechanical tach.
MTV
skywagon8a
MEMBER
SE Mass MA6
BC12D-4-85
SPONSOR
Fairbanks, AK.
Mike do you have a link for that "standard" for mechanical tachs? There's a TSO for electric tachs but I can't find anything else. Just curious.
Gary
mvivion
SPONSOR
Bozeman,MT
Gary,
That was told to me by the instrument overhauler that overhauled my old tach, when I called to whine..... They didn't give me a cite from the regs, I just figured since they're instrument overhaulers, they'd know.
MTV
skywagon8a
MEMBER
SE Mass MA6
Not an FAA reg but... https://www.aircraftsystemstech.com/2019/01/aircraft-instrument-systems-maintenance.html
"Tachometer indicators should be checked for loose glass, chipped scale markings, or loose pointers. The difference in indications between readings taken before and after lightly tapping the instrument should not exceed approximately 15 rpm."
This unverified from Canada DOT: https://www.pilotsofamerica.com/community/threads/inaccurate-tach-grounded.26193/
"[FONT="]8. [/FONT]Tachometers The accuracy of mechanical drag cup type tachometers, for fixed wing propeller driven aircraft, shall be checked on site annually, and be accurate to within the tolerances established by the aircraft manufacturer or, where no tolerance has been specified by the aircraft manufacturer, to within +\- 4% of engine RPM at mid-point of the cruise range."
4% of 2400 rpm is 96 rpm. So the number Mike got of 100 rpm sounds reasonable.
"Tachometer indicators should be checked for loose glass, chipped scale markings, or loose pointers. The difference in indications between readings taken before and after lightly tapping the instrument should not exceed approximately 15 rpm."
This unverified from Canada DOT: https://www.pilotsofamerica.com/community/threads/inaccurate-tach-grounded.26193/
"[FONT="]8. [/FONT]Tachometers The accuracy of mechanical drag cup type tachometers, for fixed wing propeller driven aircraft, shall be checked on site annually, and be accurate to within the tolerances established by the aircraft manufacturer or, where no tolerance has been specified by the aircraft manufacturer, to within +\- 4% of engine RPM at mid-point of the cruise range."
4% of 2400 rpm is 96 rpm. So the number Mike got of 100 rpm sounds reasonable.
Wingwrench
Registered User
Lakeland, Fl
No local shops. https://www.centuryinstruments.net/ overhauled mine for $150, took about 10 days. I've been using them since the late 80's for instrument repair. http://keystoneinstruments.com/ will o/h them as well, never used them for tach repair though.
bob turner
Registered User
I have had maybe five done by speedometer shops. They even made new cables and sheaths. Of course I would never use such instruments on a certificated Cub. They even give me an accuracy sheet at sbout six different rpms.
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