T.I.T Discrepancies

[FAST FLIGHT OPTIONS LLC]

2003 Mooney Bravo here with (perhaps) another stupid question.  My JPI EDM 700 T.I.T gauge reads exactly 90 degrees cooler than my Moritz T.I.T gauge. I operate the engine based on the Moritz T.I.T since it’s the hotter of the two and its certified as the primary.

1) Does anyone else with two T.I.T probes experience this?

2) Why if the Mortiz gauge is indicating 1600 (which is where I run my T.I.T) is the JPI indicating 1510?

3) If the answer is location of the probe than a couple of inches between the two probes could actually mean a 90 degree difference between them?

4)  I want to upgrade to a Garmin EIS or some other primary display but now I’m worried having just one T.I.T probe wouldn’t provide me with assurances I would feel comfortable with regarding my T.I.T. readings.  By that I mean imagine if my current JPI was my only T.I.T. gauge and I ran the engine at 1600 based on the display indication when in fact the turbine was actually operating at 1690 degrees. Do you think my concern is warranted?

5) If I go with a Garmin EIS how could i ensure the T.I.T reading is accurate?

[LANCECASPER]

35 minutes ago, 231-FLYER said:

2003 Mooney Bravo here with (perhaps) another stupid question.  My JPI EDM 700 T.I.T gauge reads exactly 90 degrees cooler than my Moritz T.I.T gauge. I operate the engine based on the Moritz T.I.T since it’s the hotter of the two and its certified as the primary.

 

1) Does anyone else with two T.I.T probes experience this?

 

2) Why if the Mortiz gauge is indicating 1600 (which is where I run my T.I.T) is the JPI indicating 1510?

3) If the answer is location of the probe than a couple of inches between the two probes could actually mean a 90 degree difference between them?

 

4)  I want to upgrade to a Garmin EIS or some other primary display but now I’m worried having just one T.I.T probe wouldn’t provide me with assurances I would feel comfortable with regarding my T.I.T. readings.  By that I mean imagine if my current JPI was my only T.I.T. gauge and I ran the engine at 1600 based on the display indication when in fact the turbine was actually operating at 1690 degrees. Do you think my concern is warranted?

 

5) If I go with a Garmin EIS how could i ensure the T.I.T reading is accurate?

You are correct, the ship's gauge and TIT location is the official TIT temperature and the one to go by for sure. The JPI 700 TIT is just supplementary information and the airplane can't legally be flown without the ship's gauge or another certified primary gauge. 

But the big questions is: When was your ship's TIT probe (that displays on the Moritz gauge) replaced the last time? The heat takes these out relatively fast. If they are even flown conservatively they are usually gone within a few hundred hours . .  and disturbingly, when they fail they read low instead of high. If a previous owner ran hot TITs (1650-1750) it could have conceivably taken the probe out in less than 100 hours.

It would also be interesting to know when the JPI 700 probe was changed last. Depending on time in service they each could be reading significantly low. If your fuel flows are off by the book by much it's usually the probe.

[FAST FLIGHT OPTIONS LLC]

My fuel flows are G2G and correspond to the TIT settings I am using on the Moritz gauge so I am reasonably certain the Moritz probe is working as it should be and the indication is (more) correct than the JPI. I don't suspect any issues there but that brings up a good point about the TIT probe on the JPI.  I may have it replaced to see if it makes any discernible difference.

Edited March 25, 2022 by 231-FLYER

[carusoam]

EGTs change rapidly going down an exhaust pipe…. Related to dP, or change in pressure….

From experience… in a NA exhaust system… millimeters of distance will generate a lot of temp change… with the open ended pipe…

It’s that whole PV=nRT relationship….

What we don’t have a ton of experience with….

Is what the pressure drop from the cylinder, to a turbo inlet, is… 

Which means… we are stuck with putting the TIT sensor in it’s one location…

 

Sooo… the certification work was done with that specific sensor in that specific location… and the POH readings are repeatable this way…

Changing anything may make it more better one way or another… but probably won’t be able to match the numbers printed in the POH…

 

The TIT sensor is in the most harsh environment on the planet…. It gets to experience six blasts of hot exhaust gas in the same amount of time a single EGT sensor sees one blast… this is why the metal erosion is so high in that area…

The EGT sensor will typically be a lower reading than the TIT sensor… as the reading is an average over time…. Average six peaks over time and compare to one peak in the same time… the TIT will read higher…

 

To check the functionality of the sensors… swap their locations, and see if the readings change with sensors or the locations… it’s possible a sensor is starting to go bad…   The JPI sensor is an equally harsh environment and may be going bad at the same time or sooner…

Oddly, both sensors are seeing a similar peak and time relationship… one would expect the one closer to the exhaust valves to read the highest….

Too hard to predict…  make sure you know where the JPI sensor really is…  if it is nearer to one side of the engine… it might be at the end of a three exhaust stream collector… and not after all six streams come together…  we aren’t actually measuring the peak temp… it’s an average over time…

Fun things you learn around MS… 

PP thoughts only…

-a-

[carusoam]

The answer to the question…

1) Garmin EIS is Primary for TIT (make sure this is true)

2) A K type thermocouple is probably the type used in the ship’s current gauge…

3) For the EIS to give you the same data… it would want to use the same location, and probably the same exact sensor…

4) Even sensor construction of where the TC tip really is can be important….

5) This is the basis of being primary… it either is, or it isn’t….

6) Garmin, your installer, and you… have a lot of responsibility to make this happen… or you get stuck with the bill to replace melted fan blades…

 

Essentially, Garmin has to go a really long distance to make sure this is considered primary… before stamping primary in their sales documents…

An example of a TC sensor error….  A TC that pokes into a stream will read the higher temperatures away from the pipe wall…  a TC mounted on the surface of the pipe wall reads the cooler temps of the exhaust gasses cooled by the pipe walls….

PP thoughts only, not a thermocouple engineer…

 

Best regards,

-a-

 

[JohnB]

On 3/24/2022 at 2:15 PM, FAST_FLIGHT-OPTIONS_LLC said:

2003 Mooney Bravo here with (perhaps) another stupid question.  My JPI EDM 700 T.I.T gauge reads exactly 90 degrees cooler than my Moritz T.I.T gauge. I operate the engine based on the Moritz T.I.T since it’s the hotter of the two and its certified as the primary.

 

5) If I go with a Garmin EIS how could i ensure the T.I.T reading is accurate?

I had the EXACT same angst when I upgraded to the Garmin EIS, as I learned if you install an EIS, you are not able to have any other instrument in your airplane measuring the same items as per Garmin's requirements. (I wanted to keep my EDM - 800, but was not allowed). I vaguely remember I had my installer check my EDM 800 tit probe vs the EIS probe and they were pretty much equal before he removed the EDM. I also have noted in flight that fuel flows were the same as my EDM was with the previous equipment TIT settings between 1600-1650.

 

Having said that, and after using the EIS for several years now, it takes a bit of getting used to, but after you do, it is much easier to see alterations of temperatures, gives you more simple visual warnings, and can demonstrate a numeric TIT. However, if you do not feel comfortable with having only one instrument measuring TIT, you can keep the Moritz  and go with whatever engine monitoring system you wish which some people have done.  

[warrenehc]

On 3/24/2022 at 5:16 PM, FAST FLIGHT OPTIONS LLC said:

My fuel flows are G2G and correspond to the TIT settings I am using on the Moritz gauge so I am reasonably certain the Moritz probe is working as it should be and the indication is (more) correct than the JPI. I don't suspect any issues there but that brings up a good point about the TIT probe on the JPI.  I may have it replaced to see if it makes any discernible difference.

I am having the opposite experience based on FF.

Stand Alone JPI TIT reads 1600 when my JPI 900 TIT reads 1500.

Fuel flow is 3 gallons per hour high (based on peak TIT) so I’m guessing I’m about 2 gallons high for running at 1600 on the hotter TIT.

[LANCECASPER]

15 hours ago, warrenehc said:

I am having the opposite experience based on FF.

Stand Alone JPI TIT reads 1600 when my JPI 900 TIT reads 1500.

Fuel flow is 3 gallons per hour high (based on peak TIT) so I’m guessing I’m about 2 gallons high for running at 1600 on the hotter TIT.

Acording to your logs when was the last time the TIT probe was changed? These start reading low as they burn up.

[Fritz1]

Always match fuel flow and TIT, I typically run 30" 2300, 18.5 gph, this typically generates 1580 dF TIT which is about right, TIT probes when operated conservatively have a service life of 300-400h at best, TIT probe and fuel flow transducer rarely fail simultaneously, matching both you will know from experience which one is off, as stated before the TIT probe will read low when it fails which is dangerous

[N201MKTurbo]

You know they say if you have a watch you know what time it is. If you have two watches, you have no idea what time it is.

https://en.wikipedia.org/wiki/Segal's_law#:~:text=Segal's law is an adage,having too much conflicting information.

 

[PeteMc]

Had this issue years ago.  Have the probe tested to see if it needs to be replaced.  If it is good, calibrate, or rebuild, whichever gauge is off.  (Or both of them if needed.) 

My EDM 700 was actually the correct gauge.  The old original gauge was the one that was failing.  

[warrenehc]

900’s was installed 50 hours ago. 
I opened up the cowling. 
The original individual JPI probe is at the inlet of the turbo. (The one running 1600)

The new one on the 900 is back to the right where it looks like it was designed to be installed at..

[Pinecone]

I used to have a JPI 830 and the stock setup in my 252.   There was about a 30 degree difference, with stock setup reading lower. Then it got to be a bigger spread.

Shop changed the stock TIT probe, and the two were reading about 10 degree different.