ITT question
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ITT question
When turboprop is climbing, should ITT to rise, remain constant or drop?
Is it the same in pt6 and garrett or larger PW engines?
What ITT should read on climb in Citation ?
thanx
Z.
Is it the same in pt6 and garrett or larger PW engines?
What ITT should read on climb in Citation ?
thanx
Z.
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Speaking of a PT6 TP, youŽd be limited by torque in the beginning, way below whatever limit the ITT gives you. In the B200 the red line is 800° - the outfit I fly with limits the ITT to 740°, others I know fly up to 760 and even 780°. So during climb we use max torque UNTIL the ITT gets to the limit (in our case 740°)
DonŽt know about other PWs and Garretts.
What Citation are you talking about ? Most Non Fadec Citations I have flown are more limited by fanspeed than ITT. Essentially the difference to the TP is, that you pull back during climbout to prevent an over the limit N1 in the jet and you push forward in the TP until you reach the templimit.
DonŽt know about other PWs and Garretts.
What Citation are you talking about ? Most Non Fadec Citations I have flown are more limited by fanspeed than ITT. Essentially the difference to the TP is, that you pull back during climbout to prevent an over the limit N1 in the jet and you push forward in the TP until you reach the templimit.
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Hello!
The one I fly has PW535 engines. As already written, the manufacturer states a limit N1 speed for different altitudes and temperatures, not an ITT value. The latter one is limited by the red line only which you will never reach if you observe the N1 values.
However one TRI/TRE who taught me a lot about flying these aircraft told be that it is good to limit the ITT at 600 degrees all the time (the red line is at 700 degrees). This will result in an N1 value of 2 or 3 percent below the permitted value and still give you plenty of power. Even observing this (arbitrary) limitation I have had one catastrophic turbine failure (catastrophic not for me but for the turbine....) and since then I am even more cautious never to exceed that limit.
My turboprop experience is limited to a Garrett powered Metroliner which had a "single red line computer" fitted. This permitted the pilot to always operate the engines at the red line which was not constant, but varied with outside conditions. I have no idea whether or not this is standard with Garrett engines or some fancy extra of "our" aircraft.
The one I fly has PW535 engines. As already written, the manufacturer states a limit N1 speed for different altitudes and temperatures, not an ITT value. The latter one is limited by the red line only which you will never reach if you observe the N1 values.
However one TRI/TRE who taught me a lot about flying these aircraft told be that it is good to limit the ITT at 600 degrees all the time (the red line is at 700 degrees). This will result in an N1 value of 2 or 3 percent below the permitted value and still give you plenty of power. Even observing this (arbitrary) limitation I have had one catastrophic turbine failure (catastrophic not for me but for the turbine....) and since then I am even more cautious never to exceed that limit.
My turboprop experience is limited to a Garrett powered Metroliner which had a "single red line computer" fitted. This permitted the pilot to always operate the engines at the red line which was not constant, but varied with outside conditions. I have no idea whether or not this is standard with Garrett engines or some fancy extra of "our" aircraft.
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Ok, but when one is climbing on turboprop and DO NOT touch the power levers, ITT remains constant ?
And when one is climbing on pure jet, and do not touch the power levers, is N1 constant or falling or rising?
I'm not familiar with engines other than piston and tryin to understand turbines :-)
Z.
And when one is climbing on pure jet, and do not touch the power levers, is N1 constant or falling or rising?
I'm not familiar with engines other than piston and tryin to understand turbines :-)
Z.
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Hello!
That's a somewhat theoretical question as one usually does not leave the thrust levers untouched during climb... (unless the aircraft has FADEC). Again I can talk for the one I fly (PW535 variant): When takeoff thrust is set the ITT will show a certain value. After takeoff during initial climb this value tends to be higher, so there is an initial rise. But I do not think that this is caused by the change in altitude alone, gaining forward speed does have an influence as well. The fuel control unit (FCU) is a very complex (and non-linear) mechanism which has several T and P sensors and constantly adjusts fuel flow to match the changing conditions. There will be certain regimes where a change in altitude will result in an ITT rise and others where it will not. Because one of my tasks as a pilot is to protect the aircraft and it's engines from damage I will manually override the FCU by moving the thrust levers in order to keep the ITT within a comfortable range. Sitting there and watching what it will do on it's own is not an option...
Another Citation which I once flew had JT15 engines. These had the tendency to increase N1 speed with altitude (thinning air) when the thrust levers were not touched. Well beyond 100%. Leaving them alone in order to investigate what the ITT might do would have meant blowing up the engines in a matter of minutes!
Another Citation which I once flew had JT15 engines. These had the tendency to increase N1 speed with altitude (thinning air) when the thrust levers were not touched. Well beyond 100%. Leaving them alone in order to investigate what the ITT might do would have meant blowing up the engines in a matter of minutes!
Last edited by what next; 28th Mar 2019 at 14:39.
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"Ok, but when one is climbing on turboprop and DO NOT touch the power levers, ITT remains constant ?"
Basically the turbine wants to get a certain mixture of air and fuel, constant please. Just like a piston engine, but by other means. So, as you climb the density of the air goes down. Meaning: less fuel will be injected, so the ITT should rather go down. Now, a lot of cooling in the engine is done by the air going through it - which is now less dense. So it wouldnŽt stay exactly the same, but for the task of understanding it, yes it would, but torque (basically the delivered power) goes down. A lot of things do influence the temperature, in the PT6 installations I flew (mostly KingAir, some Cheyenne) you could increase the ITT by 20-30-40° by using anti ice - that would not use bleed air as in most jets, but open doors in the duct to the engine air inlet, basically taking a bit of air off. It also can depend on prop rpm, although usually to a lesser degree and also airspeed and OAT. A turbine engine has a relatively narrow operating range rpm/temperature wise in which it really "feels" well, as a turbine pilot you basically try to keep the engine in that range whilst observing the limits (like ITT, torque or N1/N2). I understand (while not experienced in these, the single shaft engines have narrower bands in respect of operating ranges.
An nice example for the internal cooling is the air condition on the KingAirB 200 - its connected with an electric clutch to the right engine. The KA200 has 2 idle settings (depending on the mounted props the figures differ a bit), something like 63% for low idle and 70% high idle. One should use high Idle when the a/c is on...now one would think the engine runs hotter at a higher power setting, but no sir, it actually runs a lot cooler at high idle, since there is more cooling through the engine (and as well through the oil cooler). To deal with this excess air most engines do have bleed air valves that open and close during engine acceleration, bleeding off excess air when required.
Basically the turbine wants to get a certain mixture of air and fuel, constant please. Just like a piston engine, but by other means. So, as you climb the density of the air goes down. Meaning: less fuel will be injected, so the ITT should rather go down. Now, a lot of cooling in the engine is done by the air going through it - which is now less dense. So it wouldnŽt stay exactly the same, but for the task of understanding it, yes it would, but torque (basically the delivered power) goes down. A lot of things do influence the temperature, in the PT6 installations I flew (mostly KingAir, some Cheyenne) you could increase the ITT by 20-30-40° by using anti ice - that would not use bleed air as in most jets, but open doors in the duct to the engine air inlet, basically taking a bit of air off. It also can depend on prop rpm, although usually to a lesser degree and also airspeed and OAT. A turbine engine has a relatively narrow operating range rpm/temperature wise in which it really "feels" well, as a turbine pilot you basically try to keep the engine in that range whilst observing the limits (like ITT, torque or N1/N2). I understand (while not experienced in these, the single shaft engines have narrower bands in respect of operating ranges.
An nice example for the internal cooling is the air condition on the KingAirB 200 - its connected with an electric clutch to the right engine. The KA200 has 2 idle settings (depending on the mounted props the figures differ a bit), something like 63% for low idle and 70% high idle. One should use high Idle when the a/c is on...now one would think the engine runs hotter at a higher power setting, but no sir, it actually runs a lot cooler at high idle, since there is more cooling through the engine (and as well through the oil cooler). To deal with this excess air most engines do have bleed air valves that open and close during engine acceleration, bleeding off excess air when required.
Last edited by His dudeness; 28th Mar 2019 at 21:02.
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Concerning your Original Question:
In a PT6, everything untouched, yout Torque goes down and ITT stays the same, in climb!
Because you are Torque Limited ( that will be the first Redline you hit), until appr. FL170 in a PT6-42 KA200, you will constantly adjust your Pwr Levers to stay at your desired Torque Setting. With every movement of them ITT rises a bit, until hitting your desired max ITT ( most Operators stay below redline).
From that Moment on you dont touch your Pwr Levers anymore ( more or less) and Torque (Pwr) goes down in climb.
All written before is true as well: You have to watch Torque when adjusting rpm ( Rpm down-Torque up-ITT stays) -- When bleed flow changes ITT rises or falls -- When Ice vanes are deployed your torque falls - ITT rises etc etc. You cant set Redline Torque static on the Rwy, because it will rise 5-10% accelerating to VR.
In Jets you set Pwr by N1. And a very good description was made by Whatnext above. With Fadec, you dial in MCP in climb and relax....
In a PT6, everything untouched, yout Torque goes down and ITT stays the same, in climb!
Because you are Torque Limited ( that will be the first Redline you hit), until appr. FL170 in a PT6-42 KA200, you will constantly adjust your Pwr Levers to stay at your desired Torque Setting. With every movement of them ITT rises a bit, until hitting your desired max ITT ( most Operators stay below redline).
From that Moment on you dont touch your Pwr Levers anymore ( more or less) and Torque (Pwr) goes down in climb.
All written before is true as well: You have to watch Torque when adjusting rpm ( Rpm down-Torque up-ITT stays) -- When bleed flow changes ITT rises or falls -- When Ice vanes are deployed your torque falls - ITT rises etc etc. You cant set Redline Torque static on the Rwy, because it will rise 5-10% accelerating to VR.
In Jets you set Pwr by N1. And a very good description was made by Whatnext above. With Fadec, you dial in MCP in climb and relax....
