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C90 takeoff power settings

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340drvr

Well-known member
Joined
Feb 10, 2003
Posts
454
Here's a question for anyone with C90 experience, specifically older models with the -20 (not -21) engines.
The book says max power for takeoff, 5 minute limit is 1315 ft lbs. and an ITT of 750, then cruise climb to ITT 725. It's been suggested that to "baby" the engines, you would set t/o power less than max. Sorry, I don't know the exact settings used.
I've only had experience with -21 engines, we always used max allowable power limits for takeoff, usually temp limited, but sometimes torque limits on colder days.
I don't like the idea of less than full power for t/o, just for the sake of a few extra hours before overhaul, and that won't count if you run off the end of the runway, (we're talking Rocky Mts. here) and the whole thing sounds like one of those old-wives-tales, but maybe that's how the -20's need to be operated, I just don't know. Anybody know the real story? Thanks for any info.
 
340drvr said:
I don't like the idea of less than full power for t/o, just for the sake of a few extra hours before overhaul, and that won't count if you run off the end of the runway, (we're talking Rocky Mts. here) and the whole thing sounds like one of those old-wives-tales, but maybe that's how the -20's need to be operated, I just don't know. Anybody know the real story? Thanks for any info.

Can't say much about the KingAirs, but the Saab 340 is routinely operated at reduced power takeoffs. We calculate our data based on accelerate-stop distance, and climb and obstacle clearance assuming an engine loss at V1. Our data supports this operation without having to worry about running it off the end.

I've seen enough weird stuff happen with these engines that I feel safer babying them than I do running them up to max every time.

LAXSaabdude.
 
It's not uncommon to use less than max TO power on takeoff (at least on our PT-6's).

At the airline I work at we are only required to use max TO power on the first flight of the day. On each flight thereafter we use the assumed temperature take off power setting. Basically, this is the minimum power setting that will meet all performance requirements based on your weight. This way you are still getting book performance by using a lower power setting which is easier on the engines.
 
One thing I forgot to mention, but Illini and I both alluded to, make sure you have the numbers to back up your power settings. The only turboprops I have any significant time in have been with the airlines, and my company has developed an FAA approved performance program allowing reduced power takeoffs.

Conversely, all of the piston aircraft I have flown previously had performance charts predicated upon maximum available power used for every takeoff.

Whatever you decide to do, make sure that you can back up your performance calculations. Don't just wing it, use the book numbers.

LAXSaabdude.
 
The procedure you speak of must be company policy. I have some time in B and C90s with -20s and never used reduced power for takeoff. My C90 manuals and checklists make no mention of it. There are no performance tables in the POH outlining performance data for reduced power takeoffs, either.

Guess that makes you a test pilot. Let me know how it goes.
 
"Guess that makes you a test pilot"

Bart, that's kinda what I thought, too. The manual for -21 c90's has a Minimum Takeoff Performance chart, with torque numbers for different PA/temp situatuions, but I've not seen that for the -20's.
 
laxsaabdude said: "Conversely, all of the piston aircraft I have flown previously had performance charts predicated upon maximum available power used for every takeoff."

Since you brought it up, it sounds like piston partial power takeoffs is a bad idea mechanically for the engine...(from avweb)

Partial Power Takeoffs

In recips, they're dumb, dumb, dumb, no matter how you look at them (jets are a different subject, not covered here). But maybe if you do them, you haven't really looked at them, and have just listened to some ABM ("Airport Big-Mouth") spout off. Without thinking about them, you may very well fall for the Old Wives Tale "Gee, why beat up the engine, when I don't need to?"

First, any partial-power takeoff will leave you lower and slower, for a longer time. This does not enhance safety. If you are flying a twin, a partial power takeoff enormously complicates the engine-out case, because not only do you have the engine loss to handle, you must get the remaining engine(s) up to full power to get any climb performance at all. But there is more, when it comes to "high-performance" engines (big-bore flat sixes, and big radials).

To the best of my knowledge, all these engines have some sort of method or device to greatly enrich the mixture at full rated power, for cooling. On some, it's called a "Power Enrichment Valve" and it's a straight mechanical device. Others may call it by different names, and it's done a little differently on the big radials, but the purpose is the same, to cool the engine with excess fuel. Look at the exhaust from any of these engines at full power, and you'll see a dirty, sooty stream of unburned "stuff" coming out.

If you don't pull enough power to activate that device, you are pulling very high power, without the enriched mixture for cooling. Some engines may tolerate that better than others, but it's hard on all of them.
 
Well, I don't think I explained this very well in my first post but when we use lower than max power for TO, we have FAA approved performance charts to reference. If your AFM doesn't have the performance charts to back up your power settings, then don't use a power setting less than what is called for in the AFM. Doing so would, like bart said, make you a test pilot.

Sorry I wasn't a little clearer the first time.
 

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