Preferred Power Settings

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AJChenMPH

Preferred Power Settings

Post by AJChenMPH »

Hi everyone,

Fairly new PP here (just over 100 hours and about to start my instrument rating), and recently got checked out in the 2005 DA-40 over at Princeton/39N (N412PJ).

Still learning the ins-and-outs of power settings (first CS prop plane I've flown), and I've been using a power settings chart contained within a checklist that I found online:
Image
I took the plane out for my first real cross-country flight in it yesterday (39N to Salisbury/SBY)...based on that chart, I had the engine set to 21.0" and 2400rpm while at 7,500' flying home last night (leaned to about 20 degrees ROP), and was getting about 120-125 KIAS and 135-140 KTAS. (Can't remember exactly what my outbound settings were...something like 22.0" and 2,300rpm or 2,400 rpm at 6,500'.)

Are other folks essentially flying the same settings, or are there other settings I should consider (based on the balance of speed, fuel consumption, wear and tear on the engine, etc.)? Any way to make more power at those altitudes to get a few more knots of airspeed (understanding that I'll burn more gas)? I wasn't too sure I should be experimenting too much with unlisted settings lest I do something undesirable to the engine...

Thanks,

Andy
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Re: Preferred Power Settings

Post by CFIDave »

It sounds like you've got the settings just about right for flying at higher altitudes. You're getting about the expected performance for a non-Powerflow-equipped DA40. At 7000 or above you should be operating wide open throttle (WOT) since you can't hurt the engine with lower manifold pressures up there.

If you're looking for more speed up high, I'd suggest increasing RPM to 2500. This will draw a greater fuel-air mixture into the engine (for more power) to somewhat make up for the lower MP, and you might get 3+ more knots TAS. Of course it will also increase your fuel consumption/hour slightly. But it won't hurt your engine.
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Re: Preferred Power Settings

Post by DavidS »

I've used the same sheet on my '08 XLS and have discovered that airspeeds tended to be a little pessimistic for me. I usually wind up with another thousand feet or so before I hit what the sheet says.

Looking through some photos I've taken of the g1000:
2500', 137ktas, 24.3", 2440 rpm.
11500', 148kt ground, 19.5" WOT, 2460 rpm.
7500', 148 ktas, 23.2" WOT, 2450 rpm. (after annual, they must have gotten the nosewheel adjusted right. :-) )

Last week at 7500' at max gross weight max aft cg we were at 137ktas, but I don't recall the key figures there.
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Re: Preferred Power Settings

Post by Antoine »

Flying with the throttle wide open as soon as possible makes sense.
A partially closed throttle chokes the engine. Compression ratio is decreased and so is fuel efficiency.
I took me a long time to figure out that the RPM limitation to 2400 is an obsolete guideline. In fact, my engine is definitely happiest between 2450-2550.

In my PowerFlow equipped DA40XL, when flying cross country, above 6000 ft DA, the typical setting is 2500 RPM, and peak EGT. Depending upon density altitude this uses 9 GPH +/- 0.3 GPH. Speed is 143-146 KTAS.
AJChenMPH

Re: Preferred Power Settings

Post by AJChenMPH »

Great, thanks for all the replies!

Andy
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Re: Preferred Power Settings

Post by Marc_CYBW »

Most interesting. Most of my flying is at 8,000' to 14,000' (field elevation is 4,000' and we live next the Rocky mountains). Most IFR flying is at 2,400. I'll try 2,500 on my next outing.
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Re: Preferred Power Settings

Post by Antoine »

Marc, I suggest you even test 2600 RPM when MP goes below 20. You'll see a LOT more speed and there is no restriction to how long you can use this RPM setting - only max power is restricted on the IO-360.
My engine seems to give max power at 2600, it declines when going to 2700...
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Re: Preferred Power Settings

Post by Kurt h »

The original poster's chart looks similar to the one from the POH. I never understood why the 75% power setting stops at 5000'? Originally I thought this meant WOT was ok above 5000 (because 75% power could not be exceeded), but did some more research with the attached performance chart from Lycoming:
Lycoming Power Chart.pdf
(484.07 KiB) Downloaded 573 times
It takes some time but I worked my way through the chart to produce this 75% power settings table:
Power Settings.pdf
(10.77 KiB) Downloaded 810 times
You can see the table closely matches the POH up to 5000'. But using the values above 5000' I typically don't reach WOT until about 8000'. Do most of you fly WOT higher than 5000'? If not, what MP/RPM settings do you use? I am flying a 2004 with 2 blade prop and no Powerflow.
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Re: Preferred Power Settings

Post by Rick »

There seems to be general agreement here on the DAN that the max continuous 2400 RPM limitation in the POH no longer applies, but can anyone tell me where I can find something official to "prove" this to some local CFIs? My wife is working on her PPL, and her first CFI made her reduce RPMs to 2400 immediately after lifting off "because it's required by the POH" (I consider this unsafe!). He also states that, per the POH, you should "never exceed 2400 RPMs for any length of time". Apparently that is the prevailing belief here, so without something official that supersedes the POH, I will have trouble making progress with these "by-the-book" guys...

I sure wish Diamond would update their POH to reflect reality!
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Re: Preferred Power Settings

Post by linzhiming »

Rick wrote:There seems to be general agreement here on the DAN that the max continuous 2400 RPM limitation in the POH no longer applies, but can anyone tell me where I can find something official to "prove" this to some local CFIs? My wife is working on her PPL, and her first CFI made her reduce RPMs to 2400 immediately after lifting off "because it's required by the POH" (I consider this unsafe!). He also states that, per the POH, you should "never exceed 2400 RPMs for any length of time". Apparently that is the prevailing belief here, so without something official that supersedes the POH, I will have trouble making progress with these "by-the-book" guys...

I sure wish Diamond would update their POH to reflect reality!
Hi Rick,

It should be in a separate AFM supplement that comes with the propeller STC. I am travelling at the moment so can't scan it in for you but assuming that the AFM supplement was added to the AFM, it should be one of the supplements following the main AFM itself (from memory, it is the first supplement in my AFM binder).

Wolfgang
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