JPI EDM 900 Initial Setup OfTach Time

[Candy man]

Need some advice

We just installed a JPI 900 in our 1970 Mooney C. We recalibrated the tach to read an hour of flight equals an hour of time at 2500 rpm vs the factory setting of 2400 rpm. What we ant to do and can’t find anywhere is how to set the tach to match the total time on the airplane. Any ideas? Thanks in advance.

 

Lawrence 

 

[Tom 4536]

20 minutes ago, Candy man said:

Need some advice

We just installed a JPI 900 in our 1970 Mooney C. We recalibrated the tach to read an hour of flight equals an hour of time at 2500 rpm vs the factory setting of 2400 rpm. What we ant to do and can’t find anywhere is how to set the tach to match the total time on the airplane. Any ideas? Thanks in advance.

 

Lawrence 

 

Pilot Guide, Page 48, Tack Time, "Edit to Change Airframe/Hobbs Time". Manual is available on-line if you didn't get one with your EDM-900.

[PT20J]

This brings up an interesting point. I believe Mooney mechanical tachs are calibrated at 2300 rpm. If you replace it with a tach calibrated higher, it won’t record time at the same rate at other Mooneys with the original tach. The effect when you go to sell it is the same as if you had kept the original tach and rolled the odometer back. I guess it’s kind of an ethical issue. 

[Jim Peace]

8 hours ago, Candy man said:

Need some advice

We recalibrated the tach to read an hour of flight equals an hour of time at 2500 rpm vs the factory setting of 2400 rpm.

 

why?

[Candy man]

I was trying to do the correct thing. In another thread on Mooneyspace it claims that mooney uses 1 hr of flight at 2500 rpm to generate an hour of time. If someone can clarify this I’d like to know the correct answer and set the tach up properly.

 

 

20 hours ago, Jim Peace said:

why?

 

[carusoam]

I found a good description for tach time...

It gives the key words used when looking for a tach...

The one for your Mooney may be different...

This is just a common tach used in aviation...

The 2566rpm set point is probably a funky relationship of all the gearing from the spinning cable to rolling time wheels...

One more tooth on the gear or one less tooth would make a stepwise change in the accumulation of tach time...

In the end... it’s a nice way of saying tach time doesn’t mean very much over the long haul...

The engine is much sturdier than the hours on the tach indicate...

Sooo.... to test your tach time for hour accuracy....  set your rpm to 2566.... turn your timer on...

Wait 6minutes to compare...  did 0.10 hours elapse on your tach time?

PP thoughts only, not a mechanic... or mathematician...

Best regards,

-a-

Mitchell 3 1/8" Recording Tachometer, 2566 RPM Cruise

Important Note: Removal of the glass bezel will void the factory warranty

Mitchell mechanical recording tachometers are specified accurate to within 25 RPM. Range marking material included. Two year factory warranty.

• Average Cruise/Record Time: 2566 RPM
• 3 1/8" Mechanical Recordin
• Range 0-3500 RPM
• Clockwise Rotation
• Stewart Warner P-551-TA
• AC Type RT-11
• FAA-TSO Approved

[PT20J]

The IPC lists a Mooney part number rather than the manufacturer’s part number (probably because of the custom range markings) so that’s no help. Perhaps @M20Doc knows. Chief and Spruce list a 2300 rpm tach for Mooney. You could also email the factory.

[carusoam]

From a 65 M20C....

Keep in mind the colored ranges have been updated over the years...

Getting with an instrument shop to get the dial re-screened would be very worthwhile... for a forever-plane...

Note the red stripe taped to the plastic lens exterior...  red probably isn’t the right color anymore... 

Best regards,

-a-

 

[Guest]

I’m not certain, we don’t use tach time to record airplane total time, we use a journey log book to record all flights and total times.

Clarence

[Joris]

I've mailed Mooney some time ago asking for the "Hobbs calibration" for a M20J 205 tach counter. They've replied with the image below.

[Jim Peace]

On 6/6/2021 at 6:27 PM, Candy man said:

I was trying to do the correct thing. In another thread on Mooneyspace it claims that mooney uses 1 hr of flight at 2500 rpm to generate an hour of time. 

My JPI is set to 2400 and I read someplace that for my 1964C 2400 equated to one hour of flight time.  I thought they were all like that sorry....

Now I need to find my source again for the 2400.....

 

[PT20J]

7 hours ago, Joris said:

I've mailed Mooney some time ago asking for the "Hobbs calibration" for a M20J 205 tach counter. They've replied with the image below.

Is that for the B&D electric tach.? That’s what I have in my 1994 M20J MSE which seems pretty accurate when I cruise at 2500 rpm. My 1978  M20J had a mechanical tach and it always ran faster than actual time at 2500 rpm. Pretty sure the mechanical tachs were set for 2300.

Skip

[Marauder]

23 hours ago, Candy man said:

I was trying to do the correct thing. In another thread on Mooneyspace it claims that mooney uses 1 hr of flight at 2500 rpm to generate an hour of time. If someone can clarify this I’d like to know the correct answer and set the tach up properly.

 

 

 

According to JPI there is suppose to be a 1:1 when your RPM and the set RPM are the same.

https://www.jpinstruments.com/FAQCategory/tach-time-and-hobbs/

One interesting observation. I have both the JPI 900 and the EI RPM in my plane. The JPI is always running faster than the EI. I can't remember exactly how much faster but it was noteworthy. I think it has to do with when these units begin recording time. Something like the JPI starts at 800 RPM and the EI at 1200 RPM.

[Joris]

@pt20j I believe so. I asked Mooney for the calibration numbers for a tach with part no: 880035-507.

[danad]

Mine is set at 2400 but no indication in my logs as why that RPM was chosen.