No EGT on CT7 Engine, how come?
 

Hello everyone,

I am reading the type certification document of the CT7 engine, and I am surprised that there is no exhaust gas temperature limit listed among Operational Limits. Instead Maximum Gas Generator Inter-Turbine Temperature (T4.5/ITT) is given. I am curious to know how the pilot interprets this value or is there some hardware which reads and displays warnings based on the T4.5?

Thank you,

Paul

In general terms: EGT, ITT, TIT, T4, MGT, etc basically indicate what position on the engine the temperature is taken. Most exhaust thermocouple locations are determined by type of turbine engine, manufacture design, etc.

You'll find most free-turbine turboshaft engines (rotorcraft) will monitor the temperature in the middle of the engine (ITT, T4) whereas in a turbo-jet engine (fixed wing) they'll monitor the temp at the ends (TIT, EGT).

The Arriel 2C also has T4.5, the Astazou has T4, the RR Gem has T6 and the Gnome has PTIT.

As long as you have a gauge in the cockpit with indications (and limits) for the hot part of the engine, it doesn't matter what it is called.

CT7-8A in the S92 displays T4.5 as TGT

I don't understand the question - pilots are presented with displays for whatever the manufacturer thinks is important, and then given associated limits to observe.

To put the question in reverse would be like saying "I'm reading the CFM-56 series data sheets and notice that they don't list ITT/T4.5 limits, only EGT (T49.5). I am curious to know how the pilot interprets this value or is there some hardware which reads and displays warnings based on the EGT"

212man, I do sympathise with the OP in one regard, in that we have numerous terms to denote one thing that is of importance, temperature. While the terms T5, EGT, ITT might mean something particular to some one with an engineering background, to a pilot it's immaterial, could we change it to "T" for example. Similar with the Ng, Nf, N1 etc.

Sometimes it's just a case of not thinking about things. Just learnt last night that looking at the moon from the N and S hemispheres you see a reverse image. Obvious when you think about it.

I agree - I think that was what I was trying to say (although Nf is not the same as N1 and Ng....)

Because that's not the best place to measure temperature on that engine for performance and health monitoring. That's why. For that engine, measuring the T where it is measured provides better data, both in the cockpit and for the maintenance functions. (The CT7 is in the same family as the T700, with which I had some experience). It's about 25 years ago, but in our ground training as pilots the "where you find the probe for that temp" was part of our course as was "why it is measured there." One of the neat features of the T700 is the history recorder. (As I recall the T4.5 is one of four parameters tracked, but I'll need to check my old notes later on).

If I can dig up an old training slide on that I'll add it in.

For 212man and others who suffered under the UK CAA licensing system where we learned all manner of crucial trivia that contributed nothing of real value in our later years of actual flight....but did fill the coffers of the Crats....what does it matter where and what is being measured?

If there is a gage with appropriate markings and we know how to apply the indications in an appropriate manner then that should be enough.

Anyone care to explain how a Cereral Bowl Compass work after all we spent plenty of time answering questions on them! As an example!

SAS, I agree - the gauge should have the limits, not the pilots’ brains. Once they’re in it’s hard to forget. Makila 1A Ng limits - 34,900; 34,000; 33,200; 32,500. Always comes in useful after 30 years! Plus the main gear tyre pressure of 7.2 bar.....

I used to fly multiple types at the same time...I used to hate when I would accidently incorrectly refer to engine turbine temp as T4 or EGT or ITT or TOT instead of whatever the actual name was and the "one type wonder" in the other seat would say "It's not ITT it's T6.3 or whatever. I would reply "OK Thanks ...I will endevour to keep Mr. Needle from exceeding Mr. Redline" LOL

Sorry if I implied that, the comment was in regard to a lack of common nomenclature for a particular N eg N1 = Ng.

Thank, your replies very really helpful. Megan is right, coming from an engineering background, I was tempted to understand why the engineers have decided to measure and display T4.5. It makes sense now.