Caravan Pilots
http://www.caravanpilots.com/phpBB3_archive/

Prop setting in a cruise climb/descent - Benefits vs Cost
http://www.caravanpilots.com/phpBB3_archive/viewtopic.php?f=1&t=722
Page 2 of 2

Author:  pdw [ Mon Oct 13, 2008 12:28 pm ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

Having a pristine engine in your bird, the ITT is less-likely to spike on you as your fuelflow increases there .... as comparing to one nearing an overhaul-requirement.

Burning hot-enough reduces unburned emmissions ... which would increase power a bit too. The crucial thing is to focus in on the proven guidelines that work best to keep from stumbling into the too-hot range ... which is avoided by heeding ALL the failsafe strategies outlined in that detailed 'Handbook'.

One big item is still the range in weights that are carried; another is the 'lift-expectation' itself ... whether that is lift-lost in icing or from hot&high power reductions.

Author:  bassman [ Mon Oct 20, 2008 5:23 am ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

Thanks for your explanations on this topic. If we have a long runway and aren't worried about liftoff/ASDA it probably wouldn't hurt to throttle back a bit and keep the numbers lower for the climbout too. Something to think about, but safety first would dictate the needs to push the engine to the max and for how long.

Author:  pgt066 [ Thu Jan 21, 2010 7:44 pm ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

Interesting that in this whole thread, nobody mentioned the NOTE in Chapter 4 of the POH which states

"ITT which exceeds 740 Degrees can reduce engine life" (Maybe not exact, since I don't have it in front of me)

We limit ourselves to 740 ITT in climbs after 1000ft AGL because of this note. We can still use 765 if we really need to, but don't make a habit of it. We operate hot and high (6000'MSL).

If you stay at 740, you will be below any max power setting for climb in the climb chart.

Author:  werbil [ Fri Jan 22, 2010 10:41 am ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

I think that note was added in Rev 7 of the POH - but don't hold me to that statement.

Author:  MACWHO [ Fri Jan 22, 2010 1:10 pm ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

It has been danced around during all the posts; but, All PT6 applications use engine Tq as the primary power setting parameter. Cessna uses that philosophy in the POH. As long as ITT and Ng are in limits then you get what you get. The following is the P&W philosophy as well; PT6 engines WILL produce power Tq with ITT below 700 degrees and Ng below its max limit. The margin WILL gradually decrease during the service life of the engine...

Not too much else to say on this... The experienced pilots here are the best source for the very first posted question...

Author:  pdw [ Sat Jan 23, 2010 1:37 pm ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

Lower prop rpm setting for descent was discussed in another post, where someone mentioned one operator's restriction was to stay out of the 500 to 1500 rpm range on approach (climb cruise or descent). The idea was protecting the NG Valve from extra wear.

As for reducing fuel flow coming/going off the long (hot-day) runway, ... the limiting thing there is an increased potential for an escape (rise) in ITT ... esp where there's a spike in the demand for more torque across a 'decrease performance' (windshear) while in that flatter descent/climb attitude with max load. The leaner power setting will bite you there when least expected.

Author:  capt. Slow [ Wed Mar 17, 2010 10:47 pm ]
Post subject:  Re: Prop setting in a cruise climb/descent - Benefits vs Cost

Lower ITT for the win, pure and simple.
I fail to see the connection between prop rpm/itt as the itt is a direct result of the gas generator section of the engine. As I see it, what happens past the compressor turbine has very little to do with anything. The mass flow through the engine is really dependent on the gas generator side of the engine. Consider the power turbine and whatever speed it happens to be rotating at as an after thought.
I was told if you look at the over torque charts (as in gee, like a dummy, I forgot to bring the power back in my long decent, and now look, I got lower and am over redline on torque) there is much more tolerance for over torque at 1900 rpm vs. 1600 rpm. So guess where the prop lever stays 100% of the time?

* not to say that power section has NO effect on ITT, just that it is a pretty small, barley measurable variation.

Author:  pdw [ Fri Apr 30, 2010 7:36 pm ]
Post subject:  Re:ITT ... " barely measureable variation "

* are we to be sure that's always the case in climb ?

Author:  pdw [ Tue Jul 06, 2010 4:51 pm ]
Post subject:  "much more tolerance for over torque at 1900 rpm"

The high rpm is also best thrust-response when adding power.

Author:  pdw [ Thu Aug 19, 2010 7:19 pm ]
Post subject: 

(quickest response when more thrust is needed quick)

Page 2 of 2 All times are UTC [ DST ]
Powered by phpBB © 2002, 2006 phpBB Group
http://www.phpbb.com/