Tom, you learn something new every day. Didn't realize there were that many probes involved in measuring ITT. Hello from Fresno!

I don't think the temp will change too much, you are now just averaging 9 probes. The probes are in parallel. My understanding is some probes are in hotter or cooler locations, so if one in a hot location fails the temp goes down some, or it could go the other way.

Is the system smart enough to now divide by 9 instead of 10?

Is the system smart enough to now divide by 9 instead of 10?

I have a mission that is almost exactly 1,100nm that I fly in the M600. I can do it nonstop with IFR reserves as long the the average headwind is less than 50 knots and I have no more than 550 lbs in the cabin. There are not that many passengers willing to sit in an M600 for 5.5+ hours though.

I haven’t gone to school on the design of the thermocouple loop, so the actual construction may be different than I imagine. It is already stipulated that the 10 thermocouples are in parallel. This means their voltage will be averaged as measured between the mutual connection points. So if this were the voltage being measured and marked on a meter as ITT, then what would be the point having 10 probes?

Among other reasons, it’s because the ten probes produce more current. While the probes’ voltage will be averaged, their collective current (ma)output would drop proportional to the number of probes lost. This is where the resistor at T5 comes into play.

Since the resistor value, once trimmed, remains constant the voltage drop across that resistor will fluctuate as the current changes. That voltage drop is what is measured and displayed on a voltmeter marked ITT.

So a loop with 10 probes working will read 50 millivolts and a loop with 5 probes working will still read 50 millivolts. Voltage is not a useful measure in this case.

At 100 dC, the loop with 10 probes working will flow 20 milliamperes and a loop with 5 probes working will flow 10 milliamperes. At 700 dC, the loop with 10 probes working will flow 200 milliamperes and a loop with 5 probes working will flow 100 milliamperes.

The value of that flow is measurable. Put a resistor in that circuit and get a predictable voltage drop, which will move up and down as the temp changes, but will never be as high in relative terms if less than 10 probes are “contributing”.

*** Note, all values pulled from my a$$, just using to illustrate how things might work.

So if this were the voltage being measured and marked on a meter as ITT, then what would be the point having 10 probes?

Among other reasons, it’s because the ten probes produce more current. While the probes’ voltage will be averaged, their collective current (ma)output would drop proportional to the number of probes lost. This is where the resistor at T5 comes into play.

Since the resistor value, once trimmed, remains constant the voltage drop across that resistor will fluctuate as the current changes. That voltage drop is what is measured and displayed on a voltmeter marked ITT.

So a loop with 10 probes working will read 50 millivolts and a loop with 5 probes working will still read 50 millivolts. Voltage is not a useful measure in this case.

Typically, yes - voltage (potential difference really is a better term..) is the usable metric from a thermocouple. When connected in parallel as described, the voltage would be averaged I think. Or perhaps tend toward the highest voltage depending on the rest of the resistance? Per Tom's explanation of the T5 probe, the amperage is measured in this case, but of course the are all explicitly connected. amperage= (Voltage10TCs+VoltT5)/resitanceT5. Where resistanceT5=inherit resistance+ added "trim" resistor. Someone that knows more than me please correct the above

Funny how many planes are advertised to go
* This far
* This fast
* This altitude

* just not at the same time

Just got my M600 back from annual. I don’t normally run max power tables, but they split the engine, because of an anomaly, so I wanted to ring it out and make sure it could deliver book numbers. Here I am at FL250 ISA-5, 20 ft. Lbs below max torque for those conditions, in perfectly smooth air, 281 knots true, which is a full 10 knots above book, burning 20pph below book. This bird is dialed in. A little faster than our last M600, by about 3 knots.

Cuck, I wonder about your fuel temp
-40°C OAT and only -3° fuel temp.?
I would see -32° in my Meridian?

Is there a difference between the M500 and the M600?

Someone should make an stc for these with an auto ice door a la tbm. A 300kt m600 would be spectacular.

Oooo that would be fun, but needs autothrottles so that it can mitigate over torque/over temp when the door closes, no?

New m600 has autothrotrles. They need it for autoland.

Would not surprise me if piper has this in the works. The wing is overbuilt for the current speeds.

Yes. The fuel heater is more robust in the M600. I asked one of the engineers about retroing the heater to the M500. He told me that he had thought of that but turns out the engineering for whatever reason is not practical. I have been at -52 for hours without hitting critical fuel temps, but it does start pushing the heat level in the cabin. .