DA-42 warts

TangoWhiskey

TangoWhiskey

Touchdown! Greaser!
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Feb 23, 2005
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3Green
I sure like the lines on the Diamond DA42. With the Lycoming engine package, it looks great. Those cowlings on the Austria Turbo diesel version, however, look like warts on a beauty queen. See the new AOPA Pilot. Is it just me?
 
Yeah, that kind of is ugly and asymmetrical.

Biggest wart is the slow speed. :( I sure hope they come out with a DA52 - Pressurized and fast. :yes:
 
If they work and are the most efficient design, I don't care what they look like.
 
The article said something like 176 kts on 8gal/side with the Mercedes engines which is faster than the old plane. That's pretty good speed for that burn. My biggest problem with this plane is that you get strapped with maintaining a twin for no more room/load than comparably priced singles.
 
PittsDriver said:
The article said something like 176 kts on 8gal/side with the Mercedes engines which is faster than the old plane. That's pretty good speed for that burn. My biggest problem with this plane is that you get strapped with maintaining a twin for no more room/load than comparably priced singles.
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That's pretty much the same for any new light piston twin, isn't it?
 
PittsDriver said:
The article said something like 176 kts on 8gal/side with the Mercedes engines which is faster than the old plane. That's pretty good speed for that burn. My biggest problem with this plane is that you get strapped with maintaining a twin for no more room/load than comparably priced singles.
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171 knots at 6.5 a side (13gph total), but that's at 12,500 feet. Even at 8,000 feet, it only goes 162kt at 80% power and 7gph per side. It appears that most of the speed comes from going up high with the turbos, which means you'll spend more time climbing at a slower airspeed. Sea-level ROC is 1180 fpm, Vy is 90 knots. Figure a cruise climb might get you 800 fpm and 105 knots.

So, if you were to go on a 100nm flight for example (I picked that number because it's about as far as I'd be flying today if I had a plane!), if you go to 8,000 feet, you'll spend 10 minutes climbing at 105 and 16 minutes descending (500fpm) at 165 on average, spending 17.5 miles climbing and 44 miles descending, leaving you to cruise at 162 for just 38.5 nm or 14 minutes. Total trip time: 40 minutes.

Say I go to 12,000 instead, spend 15 minutes (26.25nm) climbing and 24 minutes (66nm) descending, that leaves only 7.75nm to cruise at 171, which would take about 2 minutes and 40 seconds. Total trip time: about 42 minutes - Longer time and more fuel burned despite the "faster" cruise speed.

Here's a couple more distances/times:
200nm, 8000, 1:17:18
200nm, 12000, 1:16:48 (ooo, a 30-second savings!)
300nm, 8000, 1:54:20
300nm, 12000, 1:51:54 (2:26 faster)
400nm, 8000, 2:31:22
400nm, 12000, 2:26:59 (4:23 faster)
500nm, 8000, 3:08:24
500nm, 12000, 3:02:04 (6:20 faster)

If we extrapolate in the other direction, we can assume that at 4000 feet we'll be doing roughly 153 knots on 15gph total, and my 100nm joy flight today would take 40:09, actually 6 seconds faster than the 8,000 foot time. On a 500nm trip, it'd take 3:17:01, only 8:37 slower than the 8,000 foot time.

So yeah, you can go high and make the bird seem fast, but when it comes down to it, you spend so much time climbing and descending to get that fast cruise speed that you're not really going that fast - A normally aspirated Cirrus would kick your butt. :frown2:
 
flyingcheesehead said:
171 knots at 6.5 a side (13gph total), but that's at 12,500 feet. Even at 8,000 feet, it only goes 162kt at 80% power and 7gph per side. It appears that most of the speed comes from going up high with the turbos, which means you'll spend more time climbing at a slower airspeed. Sea-level ROC is 1180 fpm, Vy is 90 knots. Figure a cruise climb might get you 800 fpm and 105 knots.

So, if you were to go on a 100nm flight for example (I picked that number because it's about as far as I'd be flying today if I had a plane!), if you go to 8,000 feet, you'll spend 10 minutes climbing at 105 and 16 minutes descending (500fpm) at 165 on average, spending 17.5 miles climbing and 44 miles descending, leaving you to cruise at 162 for just 38.5 nm or 14 minutes. Total trip time: 40 minutes.

Say I go to 12,000 instead, spend 15 minutes (26.25nm) climbing and 24 minutes (66nm) descending, that leaves only 7.75nm to cruise at 171, which would take about 2 minutes and 40 seconds. Total trip time: about 42 minutes - Longer time and more fuel burned despite the "faster" cruise speed.

Here's a couple more distances/times:
200nm, 8000, 1:17:18
200nm, 12000, 1:16:48 (ooo, a 30-second savings!)
300nm, 8000, 1:54:20
300nm, 12000, 1:51:54 (2:26 faster)
400nm, 8000, 2:31:22
400nm, 12000, 2:26:59 (4:23 faster)
500nm, 8000, 3:08:24
500nm, 12000, 3:02:04 (6:20 faster)

If we extrapolate in the other direction, we can assume that at 4000 feet we'll be doing roughly 153 knots on 15gph total, and my 100nm joy flight today would take 40:09, actually 6 seconds faster than the 8,000 foot time. On a 500nm trip, it'd take 3:17:01, only 8:37 slower than the 8,000 foot time.

So yeah, you can go high and make the bird seem fast, but when it comes down to it, you spend so much time climbing and descending to get that fast cruise speed that you're not really going that fast - A normally aspirated Cirrus would kick your butt. :frown2:
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Agree completely. I did that analysis with the Centurions, and it came out just about the same.
 
bbchien said:
Agree completely. I did that analysis with the Centurions, and it came out just about the same.
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How's it work out on the Seneca? ;)

I originally wrote a spreadsheet for this to play around with numbers for the Turbo Twinkie (unfortunately, without real-world numbers 'cuz I don't have an airplane. :(). What I came up with for a rule of thumb was that for the fastest time you should climb 1,000 feet per 18nm of distance on the trip, while for the best fuel economy at the same power settings it was closer to 1,000 feet per 20nm.

So, anything less than about 200nm, it didn't pay at all to have the turbo. However, on something like a trip to the FlyBQ (655nm), it could save almost a half hour and several gallons of fuel. But if you're not going long, it really doesn't pay. :no:
 
On a side note about the diesels, which I'm assuming have CS props on them, how do you tell engine power? Diesels can't have a manifold pressure gauge since there is hardly any vacuum.
 
i did a similar bit of math once on the 421. i seem to remember that i needed to gain 2 knots of speed for every 1000 feet of altitude or else it wasn't worth it to climb. this was based purely on minimizing fuel burn.
 
bigred177 said:
On a side note about the diesels, which I'm assuming have CS props on them, how do you tell engine power? Diesels can't have a manifold pressure gauge since there is hardly any vacuum.
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It's all FADEC-controlled, and there's a percent power readout on the G1000:

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The engines are actually at full "throttle" all the time, and power is controlled through the FADEC by changing the length of the fuel injection pulse. Pretty different than our old-school "normal" aircraft engines!
 

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That's interesting. It really is amazing how different diesels are than gasoline and still be similar. We were dealing with a diesel engine for a project in one of my senior classes and I never knew half of how they worked. So it's computer controlled as a percentage of total possible fuel to be delivered since the air intake is not "metered". Crazy.
 
bigred177 said:
So it's computer controlled as a percentage of total possible fuel to be delivered since the air intake is not "metered". Crazy.
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Computer control is relatively new. You should check out a diesel with a mechanical governor and mechanical fuel injection. Pretty ingenious stuff.


Trapper John
 
I am the proud new owner of a 1996 Dodge 3500 Cummins diesel with mechanical everything. I was blown away with what I've learn't so far. And still have a long way to go.
 
The whole climbing high and having turbos thing only makes sense if you're going on a long trip anyway. Your 100 nm pleasure trip example doesn't work out very well, because for that it doesn't make sense to use much more than a 172 or a Cherokee. For me to fly from Williamsport to Philadelphia takes pretty much the same amount of time in the Archer, Aztec, or Dash 8.

If you're doing a 400+ nm trip, then the altitude will make more sense. But as you know, a lot of other factors go into which altitude you choose. For me, the primary ones are wind and what gives me the most favorable weather conditions. On last weekend's trip, I flew west at 4000 ft most of the way (except in areas where they had to climb me for terrain), and flew back east at 11,000. Why? Headwinds were the least problem at 4,000, and the tailwind/TAS sweet spot worked out at 11,000. Turbos would have given me more flexibility in that I could have gone higher and gotten better tailwinds heading back east, and that would have been worth it. Not to mention performance in the mountainous areas where I had to be higher. That said, I'll also climb higher if it gets me above an icing layer, even if it means more headwinds.

I would rather have the flexibility of having the turbos. Sure there are compromises, just like with everything else, but wouldn't you rather have the ability to take advantage of that extra capability rather than not have it to take advantage of in the first place? You'll always end up being slower at lower altitudes anyway, so you just plan accordingly for the mission.
 
Ted DuPuis said:
I would rather have the flexibility of having the turbos. Sure there are compromises, just like with everything else, but wouldn't you rather have the ability to take advantage of that extra capability rather than not have it to take advantage of in the first place? You'll always end up being slower at lower altitudes anyway, so you just plan accordingly for the mission.
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No doubt at all there... I'm just saying, it's only a 170-knot airplane to the marketing guys.
 
flyingcheesehead said:
No doubt at all there... I'm just saying, it's only a 170-knot airplane to the marketing guys.
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Well, my Aztec was a 210 mph airplane to the marketing guys. Good luck on that one...
 
I actually read this article in AOPA pilot the other day. These things ARE ugly. They look like NASA refrigerators bolted onto the wings.
 
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