DA-40 Cruise Performance

Flying Viking

Flying Viking

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Flying Viking
I got checked out in the DA-40 G1000 late last year - wonderful little aircraft to fly, and quite the step up from the 38 year old Cessna 172 I trained in...

I have a question on cruise performance - on a recent trip to KHND I flew at 9,500 ft outbound, 10,500 ft homebound. According to the AFM 55% is max power recommended for flights above 9,000 ft...using the performance table the optimal power setting was 19.55 mmIn manifold pressure at 2,200 RPM, leaned out to 50 degrees ROP. This translated to approximately 105 KIAS / 120 KTAS and a fuel flow of about 6.8 GPH.

Is this the best performance to expect at altitudes around 10,000 ft, or am I misunderstanding something? I routinely get 95 KIAS / 110 KTAS out of a 180 hp conversion 172N at the same altitude, and I had expected somewhat better performance from the DA-40...
 
This is an older DA-40 I assume? The POH online from 2001 suggests you are very accurate, albeit with lower than expected fuel burn. The cruise performance chart indicates that 10k pressure altitude, std temperature, 55% power should give you 122 KTAS. How close were you to wide open throttle?

I've only flown them a few times, but also with an older DA-40 and the speed didn't exactly blow me away, either. I don't mean that it was slow, just that it looks like a faster plane than it really is. I know the newer models are supposed to be significantly faster, and there are plenty of owners on here who should be able to chime in.
 
You can certainly get more speed, say, 135 KTAS, by pushing up the power, but that's also going to push the fuel burn to around 10 gph, which is a lot lower mpg than you're getting at 55% power. You might want to ask Diamond why they suggest no more than 55% power above 9000 feet -- that engine is certainly perfectly happy at full throttle at that altitude. Personally, I like to run that engine around 65-70% power as a good balance of speed and economy.

That said, 50 ROP is not really where you want to be with the mixture with this engine. That's pretty much at peak CHT, and that's not usually the best place to be in cruise. I lean the DA-40 to right around peak EGT using the "lean to rough, enrich to smooth" technique recommended by Lycoming for this engine. You'll save some gas, too.
 
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Is that 55% because it's a rental plane or in the actual Diamond DA40 POH? Cruise performance is usually done at 75% power (not sure if the DA40 will pull enough manifold at 10k to even get 75%) so I would have thought at altitude you'd be running full throttle, 2400 on the prop (max continuous I believe)...very surprised at that limitation, only other thing I could think of is some odd vibration???
 
mrkbbd said:
Is that 55% because it's a rental plane or in the actual Diamond DA40 POH? Cruise performance is usually done at 75% power (not sure if the DA40 will pull enough manifold at 10k to even get 75%) so I would have thought at altitude you'd be running full throttle, 2400 on the prop (max continuous I believe)...very surprised at that limitation, only other thing I could think of is some odd vibration???
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When I pulled the generic POH from the interwebs I saw that the cruise table only listed power settings up to 55% for PA greater than 9,000' and wondered if that's what the OP is seeing. I did not see a limitation suggesting you couldn't go beyond that, only a lack of data. But, I won't say that there wasn't a limit I missed, either. I don't have a good explanation for why you wouldn't run that engine WOT at that altitude.
 
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Actually, the long wing will probably get you even higher before you hit peak TAS. Power flow exhaust will help. One thing I think would be neat to try is to take 1/8" drill bit with a gauge stop on the tip to do a full on golf ball dimpling on it.
 
Per the DA40 AFM, page 5-6, if you set MP at 20.7 and RPM at 2400 you'll get 65% power at 9000 ft. Best power fuel flow is 9.8 gph, best economy is 8.5 gph. The DA40 was limited to 2400 with the old MT prop (for noise). New Hartzel props don't have that limitation. For an idea of what the engine will produce at higher RPMs look at the AFM for the DA42 TwinStar WITH IO360 engines (not the diesels).
 
On 10gph I could get 148-150 knots on my 2008 DA-40 with the Powerflow exhaust. Between 8,000 & 9,000 was the sweet spot for best speed. Lean it out to 8gph and you can still go 140+ at those altitudes. Wheel pants and Powerflow make a big difference. I ran at 2,450 RPM and WOT.
 
I did a lot of flying in the summer of 2008 in a DA-40, and I seem to recall the best speed I could get out of it was between 9 and 11K feet, wide open throttle, and about 2550 RPM. I played with a lot of stuff, and that's what I remember working best.
 
Giver some more power, you're renting wet right?

Nothing flys like a rental :wink2:
 
James331 said:
Giver some more power, you're renting wet right?

Nothing flys like a rental :wink2:
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Are you suggesting that running wide open throttle above 8000ft damages the aircraft in some way?
 
Speed versus fuel burn,il take the speed ,you don't buy most airplanes to go slow.
 
frfly172 said:
Speed versus fuel burn,il take the speed ,you don't buy most airplanes to go slow.
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This not only costs one fuel, but cylinders and other maint issues as well. For the record, I am WOT from take off to descent and have no problem turning RPM so long as the prop tips stay <.9M. I do restrict my power though with the mixture handles. I typically would fly the 310 15kts slower than it was capable of. I got 180ktas on 21gph and had CHTs in the 320° range and only white powder in my exhaust extractors and augmenters.

The trick to choosing a traveling plane is find one that does the speed you want to do at a loaf, not a run. Three miles a minute is what I want to loaf at, and then I let it loaf.
 
A big thanks to everyone for your replies. I rent a 2006 DA-40, and was using the same generic AFM that some of you have been citing. Looking at the performance tables, it does not recommend cruise above 55% at altitudes above 9,000 ft, hence the question.

So if I understand correctly, I can run the engine at higher power settings (limiting the prop to 2,400 rpm) without causing damage in the long run? Yes, it's a rental but I still wish to be respectful to the owner and not run the plane at settings where I will cause damage. That being said, I'd happily trade some fuel burn for speed given the hourly rate I pay (I was doing the owner a huge favor cruising at 6.8 GPH...).

Ron - thank you, point taken on the leaning procedure.
 
Flying Viking said:
A big thanks to everyone for your replies. I rent a 2006 DA-40, and was using the same generic AFM that some of you have been citing. Looking at the performance tables, it does not recommend cruise above 55% at altitudes above 9,000 ft, hence the question.

So if I understand correctly, I can run the engine at higher power settings (limiting the prop to 2,400 rpm) without causing damage in the long run? Yes, it's a rental but I still wish to be respectful to the owner and not run the plane at settings where I will cause damage. That being said, I'd happily trade some fuel burn for speed given the hourly rate I pay (I was doing the owner a huge favor cruising at 6.8 GPH...).

Ron - thank you, point taken on the leaning procedure.
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lol very true!
 
Flying Viking said:
A big thanks to everyone for your replies. I rent a 2006 DA-40, and was using the same generic AFM that some of you have been citing. Looking at the performance tables, it does not recommend cruise above 55% at altitudes above 9,000 ft, hence the question.
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Again I have to ask -- does it say that operation above 55% is not recommended?

I really think you're just mistaking a lack of published cruise data as an implied recommendation not to do it. Just because the climb chart for my Tiger stops at something like 10,000 doesn't mean the plane won't or can't go higher. It doesn't even mean that such operation "isn't recommended" as you say. It just means they didn't provide any data.

So if I understand correctly, I can run the engine at higher power settings (limiting the prop to 2,400 rpm) without causing damage in the long run? Yes, it's a rental but I still wish to be respectful to the owner and not run the plane at settings where I will cause damage.
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Learn to use cylinder head temperatures as a starting point, which you should have in that plane. Flying it responsibly as a renter is a great thing, but you are paying by the hour so you don't need to be out there flying at 55% burning 7gph unless you specifically want to fly slow.
 
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dukeblue219 said:
Again I have to ask -- does it say that operation above 55% is not recommended?
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On page 5-5 of the AFM is the second half of the engine performance table containing the 65% and 75% columns. At the bottom of the table it says "The areas shaded grey under each RPM heading are the recommended bands." The boxes at 9000MSL ISA and below have manifold pressure values filled in and some are grey. The boxes above 9000MSL ISA are white and don't have MP values.

I don't have attachment or URL privileges yet, so you'll just have to Google for "DA40 AFM" and find it yourself.
 
asicer said:
On page 5-5 of the AFM is the second half of the engine performance table containing the 65% and 75% columns. At the bottom of the table it says "The areas shaded grey under each RPM heading are the recommended bands." The boxes at 9000MSL ISA and below have manifold pressure values filled in and some are grey. The boxes above 9000MSL ISA are white and don't have MP values.

I don't have attachment or URL privileges yet, so you'll just have to Google for "DA40 AFM" and find it yourself.
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Fair enough, I see that now.
 
asicer said:
On page 5-5 of the AFM is the second half of the engine performance table containing the 65% and 75% columns. At the bottom of the table it says "The areas shaded grey under each RPM heading are the recommended bands." The boxes at 9000MSL ISA and below have manifold pressure values filled in and some are grey. The boxes above 9000MSL ISA are white and don't have MP values.

I don't have attachment or URL privileges yet, so you'll just have to Google for "DA40 AFM" and find it yourself.
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This! Made me take the safe route and just cruise in the recommended range.
 
Flying Viking said:
A big thanks to everyone for your replies. I rent a 2006 DA-40, and was using the same generic AFM that some of you have been citing. Looking at the performance tables, it does not recommend cruise above 55% at altitudes above 9,000 ft, hence the question.

So if I understand correctly, I can run the engine at higher power settings (limiting the prop to 2,400 rpm) without causing damage in the long run? Yes, it's a rental but I still wish to be respectful to the owner and not run the plane at settings where I will cause damage. That being said, I'd happily trade some fuel burn for speed given the hourly rate I pay (I was doing the owner a huge favor cruising at 6.8 GPH...).

Ron - thank you, point taken on the leaning procedure.
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You can run that engine top of the green arcs full time and not hurt it as long as you keep the CHT and oil temp in their range. How much more than 55% power is available at 9000'?
 
Henning said:
You can run that engine top of the green arcs full time and not hurt it as long as you keep the CHT and oil temp in their range. How much more than 55% power is available at 9000'?
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Quite a lot, IIRC.
 
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