Caravan Pilots and Mechanics

PLEASE NOTE: You are currently viewing the OLD FORUMS which are working in archived mode. See our NEW FORUMS at this link!

Caravan Pilots

Caravan Pilots from around the World
It is currently Mon Dec 18, 2017 10:03 am

All times are UTC [ DST ]




Post new topic Reply to topic  [ 25 posts ]  Go to page Previous  1, 2
Author Message
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Mon Oct 13, 2008 12:28 pm 
Offline

Joined: Fri Oct 29, 2004 3:13 am
Posts: 56
Location: Niagara Falls Area
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.


 
 Profile  
 
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Mon Oct 20, 2008 5:23 am 
Offline

Joined: Fri Aug 15, 2008 10:43 am
Posts: 14
Location: Thailand
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.


 
 Profile  
 
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Thu Jan 21, 2010 7:44 pm 
Offline

Joined: Thu May 05, 2005 3:49 pm
Posts: 12
Location: Central Asia
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.


 
 Profile  
 
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Fri Jan 22, 2010 10:41 am 
Offline

Joined: Sat Oct 13, 2007 5:29 am
Posts: 8
I think that note was added in Rev 7 of the POH - but don't hold me to that statement.


 
 Profile  
 
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Fri Jan 22, 2010 1:10 pm 
Offline

Joined: Mon Apr 28, 2008 1:16 pm
Posts: 13
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...


 
 Profile  
 
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Sat Jan 23, 2010 1:37 pm 
Offline

Joined: Fri Oct 29, 2004 3:13 am
Posts: 56
Location: Niagara Falls Area
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.


 
 Profile  
 
 Post subject: Re: Prop setting in a cruise climb/descent - Benefits vs Cost
PostPosted: Wed Mar 17, 2010 10:47 pm 
Offline

Joined: Wed Sep 21, 2005 8:39 pm
Posts: 6
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.


 
 Profile  
 
 Post subject: Re:ITT ... " barely measureable variation "
PostPosted: Fri Apr 30, 2010 7:36 pm 
Offline

Joined: Fri Oct 29, 2004 3:13 am
Posts: 56
Location: Niagara Falls Area
* are we to be sure that's always the case in climb ?


Last edited by pdw on Tue Aug 31, 2010 3:36 pm, edited 2 times in total

 
 Profile  
 
 Post subject: "much more tolerance for over torque at 1900 rpm"
PostPosted: Tue Jul 06, 2010 4:51 pm 
Offline

Joined: Fri Oct 29, 2004 3:13 am
Posts: 56
Location: Niagara Falls Area
The high rpm is also best thrust-response when adding power.


 
 Profile  
 
 Post subject:
PostPosted: Thu Aug 19, 2010 7:19 pm 
Offline

Joined: Fri Oct 29, 2004 3:13 am
Posts: 56
Location: Niagara Falls Area
(quickest response when more thrust is needed quick)


 
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 25 posts ]  Go to page Previous  1, 2

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2002, 2006 phpBB Group
[ Time : 0.041s | 14 Queries | GZIP : Off ]