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 Post subject: Cruise performance charts
PostPosted: Tue Apr 15, 2008 5:20 pm 
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Joined: Sat Apr 05, 2008 3:26 pm
Posts: 1
This may be a stupid question but here it goes.

What are the values in the cruise performance charts based on? If the chart says that I have to set power below the torque limit why is that? If red line is 1865 then why can't I set that power (assuming ITT and Ng are within limits are well)?

Thanks in advance


 
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 Post subject: Re: Cruise performance charts
PostPosted: Tue Apr 15, 2008 8:44 pm 
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Joined: Thu Jan 31, 2008 11:59 pm
Posts: 15
When you get the chance, shoot me a PM, I'll do my best to answer this one for you.


 
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 Post subject: Re: Cruise performance charts
PostPosted: Wed Apr 16, 2008 11:24 pm 
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Joined: Thu Jan 31, 2008 11:59 pm
Posts: 15
30,
Did that help??


 
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 Post subject: Re: Cruise performance charts
PostPosted: Mon Oct 20, 2008 5:00 am 
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Joined: Fri Aug 15, 2008 10:43 am
Posts: 14
Location: Thailand
It seems that the POH recommended pressure alt/temp/torque/prop values keep the ITT temp below 700 during cruise (based on my own observation). While the maximum continuous figures can be set and the engine is designed to deal with it, it may not help the engine components pass the 1800 hour hot section inspection. Expensive wear items there make us want to throttle back whenever possible and take care of these components to see that the hot section life will be extended, if it remains in good condition. Most of the wear on the hot section seems to occur during starting, when the ITT peaks above the green arcs on the gauge, so during cruise where you do have control over the temp by power setting, the POH gives recommended figures to make the best of the economy and engine health.

The benefit of "redline" values is only 5-10 knots from the recommended POH settings, so the benefit vs. cost doesn't seem to justify redlining (or greenlining).

Hope this helps,


 
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 Post subject: Re: Cruise performance charts
PostPosted: Wed Dec 17, 2008 11:21 pm 
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Joined: Fri Oct 29, 2004 3:13 am
Posts: 56
Location: Niagara Falls Area
Dirty30 wrote:
This may be a stupid question but here it goes.

What are the values in the cruise performance charts based on? If the chart says that I have to set power below the torque limit why is that? If red line is 1865 then why can't I set that power (assuming ITT and Ng are within limits are well)?

Thanks in advance


Re: "set power below torque limit"

If that's climb power ... could this be in part because of how speed changes affect it ? With higher ambient temps and loading this is a likely place where things get heated very quickly when they do ...


 
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 Post subject: Re: Cruise performance charts
PostPosted: Thu Dec 18, 2008 9:40 am 
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Joined: Thu May 05, 2005 3:49 pm
Posts: 12
Location: Central Asia
The reference for this is not in the POH. It is the Pratt and Whitney Service Information Letter (PT6A-125) Jan 2004

The main verbage states:

"It is essential to use the correct power setting procedures to assure the integrity of the engine. [b]Engines operated regularly beyond the reccomended power settings of the POH, but still below the defined temperature redline settings and engin maintenance manual over temperature chart limits, may experience accelerated CT Blade creep.[/b] This effect is cumulative and could likely leed to reduced CT Blade life or CT Blade fracture and total loss of engine power occuring prior to the blade inspection interval stated in the maintenance manual or overhaul manual."


 
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 Post subject: Re: Cruise performance charts
PostPosted: Thu Jan 21, 2010 7:34 pm 
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Joined: Thu May 05, 2005 3:49 pm
Posts: 12
Location: Central Asia
Recently I came across some Caravan pilots setting cruise power settings to fuel flow, and I see some other people in this thread talk of setting to ITT.

One needs to refer to the P&W Know your PT6A Handout, downloadable on their website.

It states....

"The power lever should be set to the position that produces the desired TORQUE! All other engine parameters such as ITT and NG are monitored only to ensure they are within acceptable limits. Operating the engine IAW the POH/AFM by using torque as the primary setting parameter will achieve optimum reliability while minimizing operating costs."

That about sums it up.


 
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