PT6driver

It's my understanding that this engine was derated from 1,600SHP to 1,200SHP (5 minute limitation) and then to 1,000SHP continuous.

How was this derating achieved? ITT limit? TQ limit? Both?

I ask because some of my coworkers run the engine well below it's maximum continuous ITT limit for climbs and cruise and I just don't understand the justification behind it other than, "we only have one so we'll take it easy" and, "this is the way "everyone" else runs it."

In the Series 9, Max. Continuous ITT is 760*C. We run it at 720*C.
In the NG, Max. Continuous is 820*C. We run it at 780*C.

It's also my understanding that Pratt & Whitney says you don't need to observe any specific TQ values in cruise so long as you stay under the Max. Continuous ITT. Pilatus provides a maximum TQ chart in cruise and have heard this is only a CYA move by Pilatus for liability reasons. I run the engine exactly as I've been taught but I just don't understand the "why" aspect of it all.

Why are we being taught to be easy on an engine that is already derated? I don't do well with "just run it this way." I need to understand the reasoning behind it.

JamesNoBrakes

So are you saying you run it above the maximum in this chart, or you want to?

Yoda2

I don't really have the time to answer your questions properly, though the airframe manufacturers info generally takes precedence. An engine manufacturer might state certain capabilities and limitations of an engine, though all might not be prudent to utilize regarding a particular application. Also keep in mind "that" airplane, especially an NG, pretty much records everything...

PT6driver

Neither.

Is there going to be unnecessary damage incurred if the engine is run up just below its max continuous ITT? Where did this lower ITT setting stem from? If you're a PC12 driver, do you just use the max continuous charts provided to set cruise power?
I understand that the aircraft manufacturers info takes precedence. Im aware of the recording as well. I don't actually go and make my own power settings. I'm just looking for the logic behind why we run ours a particular way. My coworkers don't have any good reasons.

PT6driver

Looks like I found the discussion I was looking for.

-You can, but you don't need to. Interesting point about the ITT probes. Looks like the 720 came about from a company who first started leasing the aircraft and was paying for their own overhauls.

AVCANADA ? View topic - PC-12 cruise power setting?

bozobigtop

I was always taught to use a cruise power setting on the PT-6 engines, that would be somewhere at the top of the green range for your engine. The only time I ever used Max Continuous is in a simulator while training usually during emergencies such as windshear, icing, and falling out of the sky. I have well over 9000 hours flying airframes with PT-6 engines. As a A&P/IA Max Continuous means you have an emergency and it means just what it says and is not necessarily limited if you need the power.

JohnBurke

All damage is unnecessary. You are not going to incur damage by operating within limitations. You will not achieve the maximum life from the engine, however, and in turbine engines, a small reduction in ITT/EGT can provide a substantial increase in service life and or a significant reduction in wear. Heat in the turbine is the enemy.

When I run a PT6A-67, I run it at the max continuous EGT as long as I need it there, which is during the extended climb, because that's what the engine is rated to do for that period of time. Derating is irrelevant.

Derating the engine allows the engine to be operated at it's maximum rated shaft horsepower to higher altitudes, rather than running into limitations early on and having a torque or temp curve to respect.

I don't operate a PC-12, but I do operate the -67 quite a bit. The max continuous ITT for our operation is 800, which I'll use until in cruise, and reduce to whatever value is needed to run at the top of the green/bottom of the yellow. It's typically in the 750 range, torque in the 3000 ft/lb range. I'll generally leave the prop at max 1700 if I'm heavy, and wont' retard it until I'm empty in cruise, then back to 1,500. We're derated substantially. I run up against torque limits at lower elevations, temp limits at higher elevations, as one does with a turboprop.

I don't have limitations other than max for the aircraft I'm flying, but in any aircraft, I observe the most restrictive of the engine or airframe manufacturer limitations.

PT6driver

Max. continuous ITT is the top of the green arc for me in cruise.

*reference picture*

I'm assuming you're in a multi. The limitations you posted correspond with what I see here on the EIS, but the POH for the Series 9 PC-12/45 states that Max. Continuous is 760*c which is represented by the top of the green/bottom of the yellow arc.

**Leaving for a few minutes and I'll finish up my post when I get back.**

JohnBurke

Don't assume. You'd be wrong.

Again, if you have limitations prescribed by your particular airframe, follow them.

The PT6 has a variety of limitations that are applicable, and they vary not only with the dash number of the engine, but also with the propeller and airframe installation.

PT6driver

Figures.

I was working on editing the previous post but I have my limitations and they will be followed. Thanks for the answers.