NG40 VS IO-360 real user pros and cons appreciated

Any DA40 related topics

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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Rich » Fri Mar 15, 2019 5:10 pm

Just for fun I thought I'd overlay the W&B envelopes for the variants of DA40's: NG, -180, and TDI (AKA Thielert/CD), based on the respective POH's.

1. The red line is DA40 NG. The dashed red line is the max Zero Fuel Weight of same. I assumed all possible MAM's required to reach these limits.
2. The solid purple line is the envelope of DA40-180 with 40 gal tanks and 2646 MTOW option.
3. The dashed vertical purple line is the rearward limit of both a DA40 with 50 gal tanks and the TDI variant.
4. The dashed horizontal purple line is both the Zero Fuel Weight for the DA40/2646 lb, and the MTOW for the TDI variant and the original 2535 MTOW.

There are some plot points which represent TOW and ZFW based on the "sample" NG in the POH and represent the loading of flight I took the year before last. Just ignore for now. These (and indeed the envelopes) are based on an Excel W&B I put together for the NG. I may fiddle with the spreadsheet so one could do comparative loading of these variants for a given flight profile.

Naturally there are more combinations, but I figured these are the most common 3 variants of the DA40.
DA40-NG-180 W&B Envelope.jpg
DA40-NG-180 W&B Envelope.jpg (29.3 KiB) Viewed 302 times
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Don » Fri Mar 15, 2019 6:13 pm

Nice comparison chart Rich. This is the reason, the solid purple lines, that I special ordered my XLS with 40 gallon tanks making it a true four seater.
Last edited by Don on Fri Mar 15, 2019 6:39 pm, edited 1 time in total.
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Rich » Fri Mar 15, 2019 6:39 pm

Don wrote:
Fri Mar 15, 2019 6:13 pm
Nice comparison chart Rich. This is the reason, solid purple lines, that I ordered my XLS with 40 gallon tanks making it a true four seater.
Yep. Looking at it like this, you see that the various DA40's can be very different planes. Planes like mine are the best load-haulers. Others are faster, etc.
the load.jpg
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by CFIDave » Sat Mar 16, 2019 1:34 pm

What's misleading in the overlay of different DA40 W&B envelopes is that the NG is relatively nose-heavy with the cast-iron block Austro engine. So in any typical loading scenario the loaded CG will be more forward than in a Lycoming DA40, and thus the aft CG limit doesn't become a factor for the NG.

I'm guessing the aft CG limit of the NG is located where it is because of the spin testing that was done (winglets were tried and rejected on the Lycoming DA40 XL that failed spin testing back in 2007). Winglets permit the NG to fit into 40 foot T-hangars more easily by shortening the wingspan by about a foot.
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Steve » Sat Mar 16, 2019 2:02 pm

CFIDave wrote:
Sat Mar 16, 2019 1:34 pm
What's misleading in the overlay of different DA40 W&B envelopes is that the NG is relatively nose-heavy with the cast-iron block Austro engine. So in any typical loading scenario the loaded CG will be more forward than in a Lycoming DA40, and thus the aft CG limit doesn't become a factor for the NG.
Understood. But... what about a more typical scenario with two heavy guys up front? Is there any issue with possibly exceeding the forward CG limit? In my airplane (40 gallon) I can take off with 2 - 235 pound guys up front and no baggage, full fuel, and be within the forward CG limit.

Steve

Now, physically fitting 2 - 235 pounders in may be problematic...
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Rich » Sat Mar 16, 2019 2:11 pm

CFIDave wrote:
Sat Mar 16, 2019 1:34 pm
What's misleading in the overlay of different DA40 W&B envelopes is that the NG is relatively nose-heavy with the cast-iron block Austro engine. So in any typical loading scenario the loaded CG will be more forward than in a Lycoming DA40, and thus the aft CG limit doesn't become a factor for the NG.
Actually the rear CG limit can be in play. Here are three W&B overlaid with the same load, representing the load in the picture I posted. The extended baggage is actually required to accommodate the volume of all the stuff. The plane was chock full. In the overlay, the red line is the "sample" NG, the green line the "sample" CD, and the purple line my actual plane. (In reality, the CD probably could not actually carry the real load because it lacks the extended baggage compartment.) The upper part of the line is TOW/CG, the lower is Zero Fuel Weight. Note the NG is, in fact, out of rear CG. I can do this for a "real" NG if anyone wants to supply actual numbers as "sample" airplanes are likely to be heavier, with different CG's. Note that my plane, which is almost as nose-heavy as the NG sample airplane, would have been out of CG if it had the same rearward CG limit as the NG.

It's also worth noting that a most of the Lycoming DA40's would also not be able to carry this particular load, especially the 50 gal ones.

Full tanks (40 gal) assumed in all cases, with 340 lb in front seats, 200 lb. in back seats, 100 lb. baggage in the "Baggage 1" location of the extended baggage.
DA40 Variant W&B.jpg
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by CFIDave » Sun Mar 17, 2019 10:34 pm

The 40 NG only carries 39 gallons maximum with its "extended range" tanks. It doesn't need to carry as much fuel because it only burns 6.5 gph at 75% power in cruise, or 8 gph at 92% maximum continuous power (MCP). The DA40 NG is far more efficient than (and different from) a Lycoming DA40 -- which was quite efficient to start with.

So you typically don't carry as much fuel in the 40NG as you do in an avgas Lycoming DA40, the vast majority of which have 50 gallon tanks. 50 gallon tanks became the norm on Lycoming DA40s way back in 2007 with rare exceptions (such as owner Don here that opted for 40 gallon tanks for W&B reasons).

Again, the W&B overlay diagrams in this thread are misleading when comparing the avgas Lycoming DA40 vs. the DA40 NG.
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Colin » Mon Mar 18, 2019 12:50 am

The fuel burn on the NG is not just less, it is also more accurate for calculations. When I figure 10.8gph combined on my DA42, it *really* burns 10.8gph for the whole flight. When I was flying my Lycoming DA40 for 11 years I used a conservative number because the fuel burn fluctuated depends on my altitude and other factors.
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by Rich » Mon Mar 18, 2019 1:16 am

CFIDave wrote:
Sun Mar 17, 2019 10:34 pm
The 40 NG only carries 39 gallons maximum with its "extended range" tanks. It doesn't need to carry as much fuel because it only burns 6.5 gph at 75% power in cruise, or 8 gph at 92% maximum continuous power (MCP). The DA40 NG is far more efficient than (and different from) a Lycoming DA40 -- which was quite efficient to start with.

So you typically don't carry as much fuel in the 40NG as you do in an avgas Lycoming DA40, the vast majority of which have 50 gallon tanks. 50 gallon tanks became the norm on Lycoming DA40s way back in 2007 with rare exceptions (such as owner Don here that opted for 40 gallon tanks for W&B reasons).

Again, the W&B overlay diagrams in this thread are misleading when comparing the avgas Lycoming DA40 vs. the DA40 NG.
Sorry about that extra gallon. My bad for that 1 lb. relative discrepancy in the misleading graph. There does remain confusion about what a gallon of jet fuel weights, so this comparison uses what's in the POH.

Given the Lycoming DA40's being sold today, you are correct that there isn't much load-carrying capacity advantage, if any, for the Lycoming-powered ones. Between the CG limitation for the 50-gallon unis coupled with the fact that the empty CG's are considerably aft (making the forward part of the envelope essentially moot) the Lycomings DA40's have been somewhat castrated in this particular area of performance. I've added the practical forward CG boundary for 2007+ DA40-180's (based on what I find in the Wiki) to the comparison as the vertical dotted line . But the original portrayal for we lucky few, we band of brothers, who have the older (or 40 gallon), nimbler DA40's the original solid line is absolutely, completely factual. If you find it's misleading, I can't help that. (And FWIW it's been a rare occasion (like maybe 4 times) in 17 years where the 40 gallons of avgas has been an minor inconvenience.)

I would also stand by using full fuel in the calculations. How many pilots actually figure, to the gallon, what they actually need, rather than top off the tanks? Nevertheless, this version shows a problem even with a mere 20 gallons in the tanks. Also note that even the empty-tank scenario is borderline, where amount or density of fuel matters not at all. And this is the "sample" NG, I am confident that every single NG that has actually gone out the door is heavier and likely with a further aft CG than the sample.
DA40 Variant W&B.jpg
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Re: NG40 VS IO-360 real user pros and cons appreciated

Post by CFIDave » Mon Mar 18, 2019 3:43 am

The 2nd diagram is not only misleading, but incorrect with respect to the empty (or full fuel) CG of a DA40NG relative to its W&B envelope.

I can literally "hang on the tail" of a DA40NG with all my body weight and it's nearly impossible to lift the nose wheel off the ground. In contrast, the easiest way to turn around a Lycoming DA40 on the ground is to push down on the tail to lift the nose wheel and turn the plane -- In my experience this can be done with all Lycoming DA40s. DA40 NGs all have a CG that is further forward than Lycoming DA40s due to the heavier Austro turbodiesel engine. (I don't have access to the actual aircraft CG numbers where I am right now, or I'd share them.)

As a result of the more forward CG, I can assure you that there is no W&B "problem" -- the aft CG limit of the DA40 NG isn't a factor in any reasonable loading scenario. In contrast, the aft CG limit *IS* a factor to be considered in Lycoming DA40s with 50 gallon fuel tanks.
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