Cheyenne Itt

[mjrhealth 3]

Just wondering, as i am trying to understand ITT temps. I usually ignore and just fly the plane by the numbers but someyimes that means the ITT is redlined which usually means an engine failure i believe if left that way. Flying the Cheyenne 2 at FL 180 with torque at 1100 and rpm at 1900 ( if i remember correctly ) the ITT is at red line I have to reduce torque to about 950 to get ITT into green, of course this means a lower airspeed but not a major issue. of course ITT gets higher as i climb so have to back off more. Am i correct in this. Please explain,

Thanks in advance

[Shaun Fletcher 570]

Hello mjrhealth,

Maybe a search of Google how the engines etc work may yield some answers.

Unless someone on the forum can explain how these all go together.

[pbearsailor 9]

The Cheyenne's PT-6 engine depends on air to make power. As you climb, just like in a normally aspirated piston powered plane, as the air gets thinner, power goes down. Most turboprops will reach a point in the climb where you can no longer maintain torque at the redline and must then use ITT as your limit with the power levers. True airspeed is usually almost as high up in the flight levels as it would be at 10,000, and your fuel burn is much much lower, so most of the planes in this class operate best from around FL180 up to FL270 or so. The other limiting factor is pressurization as you want to maintain a cabin alititude below 10,000 feet for passenger and crew comfort. I've flown the King Air and C-441 a lot and Cheyenne only a little, but it's pretty normal on all of them to be flying on ITT at FL210 or so with a cabin alititude around 7 or 8 thousand. The C-441 in particular could really climb and we could often get it all the way up to FL350 with a really low fuel burn. The Twin Otter, with the same basic engine as the Cheyenne, lacks cabin pressurization and will usually be flying lower than 10,000.

Overtemping, unless it's by a big margin, is most likely going to lead to heat damage of internal engine components and a shorter time between hot section inspections or overhaul. Cool is good on ITT and many operators tend to limit ITT to something less than the actual redline ITT limit, say 30 or 40 degrees cooler.

Hope that helps.

cheers,

steve

[alehead 126]

You shouldn't redline the ITTs at all, it seriously affects the engine's life (OK in the RW, not in the sim...)

I fly the Cheyenne on a combination of torque settings and ITTs, but always keeping the ITTs at least 50°C below redline...

Cheers to Steve for the explanation

Andrew

[mjrhealth 3]

Well I tend to Keep ITT in the green. I enjoy the take off though, having to throttle up a little then let is settle then throttle up a litle more so it wont red line, Landing a plane on steroids is fun but i do get it down. Thanks for input though I was sort of on the right track.

Regards