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Hobbs input on Ovation w/ G1000


VetRepp

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Hi All,

If anyone knows, I need  'how it works' info...

I have a 2006 M20R Ovation w/ G1000. It also has a Hobbs meter in baggage compartment that has stopped working. The engine time on G1000 works correctly and in testing I completed the circuit on the Hobb's itself which caused it to run fine and keep very accurate time. The Oil pressure is accurate and I have checked that switch. Gear squat switch and stall warnings all appear to be working correctly.

My Question is, Does anyone know where the Hobbs get it's input to start running on my bird. Does it come out of G1000 - or some other source.

Admittedly - not a big deal - but I like to have everything working how it's supposed to be

Thanks in advance for any info provided

Thanks

 Roger

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Ignore this post for further verification....

 

Roger expect that there is a pressure switch on an oil line on or near the engine.  Oil pressure trips the switch and delivers power to the Hobbs meter.

This is the usual for long Bodies...  pretty sure that it is independent of the G1000.

Best regards,

-a-

Edited by carusoam
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From page 7-8 (Section VII) of the AFM:

7. Hour Meter

Hour meter – located on baggage compartment bulkhead indicates actual flight time and is triggered by the airspeed switch.

From page 7-15:

Retraction System

... An Airspeed Safety Switch, located on left fuselage side adjacent to the pilot's left knee and connected to the airspeed indicator is incorporated into the electrical system to prevent landing gear retraction while on the ground and until a safe takeoff speed (approximately 60 +/- 5 KTS) is reached.

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That's what the book says but I'll be damned if there's an airspeed safety switch anywhere on the left fuselage side adjacent to my knee. When working with Joey Cole and testing the landing gear components, I seem to recall him gently blowing into the pitot tube itself to test the airspeed safety and gear warning system. I think the POH is outdated on this.

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Dave & Deb,

Check page 7-7, if you would....?

The part about the hour meter at the bottom.  Indicates that the hour meter is active while the engine is running...

The airspeed switch is set for 60 or so Kias.  It won't collect idle running and taxi time this way...

Looks like I made an assumption that it is using an oilP switch. But can't find any proof of how it actually works...

Best regards,

-a-

 

Edited by carusoam
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Dave & Deb,
Check page 7-7, if you would....?
The part about the hour meter at the bottom.  Indicates that the hour meter is active while the engine is running...
The airspeed switch is set for 60 or so Kias.  It won't collect idle running and taxi time this way...
Looks like I made an assumption that it is using an oilP switch. But can't find any proof of how it actually works...
Best regards,
-a-
 

Notice how it says it records "actual flight time". This is exactly what you want for "time in service" wrt to maintenance usage. No one wants to include the taxing and idle time except for FBO's that are charging rental fees by the hour - in which case they want to charge for every minute the engine is turning - (if not for every minute the master in on). This is where the oil pressure Hobbs meter gets installed as a add on - but they are generally never installed by airframe manufacturers for maintenance time tracking. Most all earlier systems used tachometer time which was based on rpm. Tachometer time is only 1:1 at its intended cruise RPM which is typically less than redline, maybe more like 2450 in earlier Mooneys. The affect is the same as the airspeed switch on a G1000 Mooney since such a low RPM greatly discounts idle taxi time but does not eliminate it.
The modern digital tachs use a threshold RPM. The EI uses 1300 rpm so it too doesn't count any idle and taxi time unless the pilot is using more than 1300 rpm. In contrast the Horizon unit uses 800 rpm (by memory) which is way to low in my opinion which makes their unit an undesirable replacement for the Mooney hour meter IMO since it's an automatic hit on accumulated engine time.


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That's what the book says but I'll be damned if there's an airspeed safety switch anywhere on the left fuselage side adjacent to my knee. When working with Joey Cole and testing the landing gear components, I seem to recall him gently blowing into the pitot tube itself to test the airspeed safety and gear warning system. I think the POH is outdated on this.

You won't be able to see it unless you get your head under the panel back to the brake pedals and look up with a flash light. You'll see the pitot static lines running rough it as well electrical connections. Joey was testing that the red safety bypass switch next to gear illuminated with the gear switch down on jacks at 0 kts and the gear would start to raise without having to push it to bypass the air speed safety switch.The switch is mounted pretty level with mid-height of your panel as he blew into the pitot tube to simulate about 60 kts causing the safety switch circuit to power the gear and unlight the red button.

I go through this in detail with any new owner as part of their transition training so they understand how their gear works and what the emergency procedures are and why.

 

 

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Looks like the POH may be in error.  See the underlined part.  Having it on the back wall makes it challenging to see it operate or not operate from the front seats...

Rev A 10-03... From the O POH...

Page 7-7

25. HOUR METER
Hour meter - located on baggage compartment bulkhead and indicates elapsed time while engine is running. Location may vary depending on installed systems. 

 

Great discussion, thank you.

Best regards,

-a-

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Looks like the POH may be in error.  See the underlined part.  Having it on the back wall makes it challenging to see it operate or not operate from the front seats...
Rev A 10-03... From the O POH...
Page 7-7
25. HOUR METER
Hour meter - located on baggage compartment bulkhead and indicates elapsed time while engine is running. Location may vary depending on installed systems. 
 
Great discussion, thank you.
Best regards,
-a-

Your Pre-G1000 hour meter is entirely different and does not use the airspeed safety switch. It is tachometer based as I described above meaning it's always on but only records 1:1 at its intended cruise rpm. Surely you have noticed it does not match clock time of the engine on but more like a couple tenths less overall per flight?


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Paul,

my O1 only has the hour meter on the baggage compartment wall.  Nothing else to compare with.  The tach is a digital device driving an analog needle.  No engine hour gauge up front.

The first Os were an interesting exercise to modernize and or remove some things...  there is no Fuel pressure gauge it was replaced with FF/totalizer.  The vacuum gauge was added later on. the annunciator panel wasn't good enough for a previous owner.  The voltage gauge is the same as the amp gauge, when you push a button, it reads volts on a scale that is hard to read.

I think I need to work on getting some real updated instruments starting with a JPI 930...

Best regards,

-a-

Edited by carusoam
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Paul,
my O1 only has the hour meter on the baggage compartment wall.  Nothing else to compare with.  The tach is a digital device driving an analog needle.  No engine hour gauge up front.
The first Os were an interesting exercise to modernize and or remove some things...  there is no Fuel pressure gauge it was replaced with FF/totalizer.  The vacuum gauge was added later on the annunciator panel wasn't good enough for a previous owner.  The voltage gauge is the same as the amp gauge, when you push a button, it reads volts.
I think I need to work on getting some real updated instruments starting with a JPI 930...
Best regards,
-a-

My 252 is nearly identical. Iam sure you would find the hour meter in your baggage area is wired off the Mooney tachometer as was mine. It stopped working when the tachometer died since it lost its feed. But I have not checked your schematic. You didn't comment if you have verified yours reads less than 1:1 with engine time?


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Paul,

I'm not sure how it is recording.  I roughly match it to hours flown that get logged by my iPad.  Nothing accurate to measure against...

The assumption I was following was the oil pressure switch sent the ship's voltage to a clock mounted on the back wall.  The clock records time as long as it has electricity.

It sounds like more modern Mooneys are using the airspeed switch to send the ship's voltage to the clock.  That would be the most direct method of measuring engine flight time.

The old Hobbs meter did a nice job of measuring engine hours differently based on an accumulation of the engine's revolutions.  It counted all the revolutions, no matter how fast it was turning.  It just had a weird way of calling it hours when it didn't actually measure time....

Best regards,

-a-

Edited by carusoam
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Paul,
I'm not sure how it is recording.  I roughly match it to hours flown that get logged by my iPad.  Nothing accurate to measure against...
The assumption I was following was the oil pressure switch sent the ship's voltage to a clock mounted on the back wall.  The clock records time as long as it has electricity.
Best regards,
-a-

To my limited knowledge the Mooney hour meter has never been done that way. Nor is it considered suitable for measuring time in service which what our hour meter is for. But what you describe is an add on used on virtually every rental aircraft that is referred to as the Hobbs meter. But it's use was not intended for maintenance time in service.

I do know of a 231 that I instructed in that had the original hour meter replaced with a device that was simply wired to the master switch. Pretty crazy to be racking up engine time before the engine is spinning but his was.


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Btw, I always had one of my GNS430Ws record elapsed time since startup and I would always right down the flight time from it just before shutdown. I did this for the purpose of tracking pilot log book time. There was never a time when the hour meter wasn't at least 0.2 less than actual elapsed time and the difference was bigger if we got delayed waiting for departure.

 

 

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I'll have to go find out what is really powering my hour meter...  The installation matches the POH description.

My BK ADF was the device that would keep two timers.  One for the panel instruments master turning on and a second to record actual flight time.  Only challenge is there is no record once the panel has been turned off... the flight timer had to be turned on.

Best regards,

-a-

 

 

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