They're out there among us...

[Rich]

Rich,
I’m confused. I think you write that I can reduce my fuel by 15 gallons and increase my passenger/luggage load by 101 pounds. That would be 680 pounds. Fiddling with Foreflight I can go to zero fuel and that very much exceeds the ZFW. Now, there is a very real chance I’m doing this wrong, but with full tanks (39) I can carry 580 pounds. With empty tanks I can do 585. ZFW is the limiting factor - not gross weight.

I had a long talk with my instrument DPE about this. He taught me about how this ZFW relates to the wing’s ability to support the fuselage.

I hope I’m confused. But every manipulation still results in a red ZFW warning at the top of the page. See attached. At 590 and 0 fuel I’m in w&b but exceed zfw. At 585 and full tanks I’m in w&b but at limit. At 580 with full tanks I feel good about it. Am I wrong?

I was trying to point out that even if the ZFW limitation weren't a specific number, there's a practical limitation on how far one can take trading off fuel for cabin load and that the limitations in the DA40's isn't that big aa deal.

[Rich]

The person I quoted in the original post talks about 200 lb over max, but doesn't state whether it's against the 2535, 2646, or 2883-ish numbers. So simplistically this means flying at or beyond 2735, 2846, or 3083 lb. Note that all variants of the DA40 have similar horsepower and pretty much the same basic aerodynamic characteristics.

There is also no mention of CG. But unless it's one of the early airframes like mine it's likely out of aft CG constraints, even if you consider it valid to extrapolate the aft CG beyond the MTOW value. It's actually more correct to use the POH graph in section 6.4.12 which shows the limits as permissible moment, which is, for example, 269,762 lb-in. for the 2646 lb case (most common) and is easily exceeded at 2846 lb for most Lycoming versions.

As we've come to say about this sort of thing: "This works until it doesn't."

[dant]

One of the things that makes people a bit more risky is that there are several alleged instances of aircraft limits being put in place due to regulation rather than any physical property. I think I saw someone on here comment that the yellow line on the airspeed indicator isn't due to frame stressing but due to the relation to the stall speed. Light sports are certified to 1320# not because of the plane but because then they aren't regulated as light sports. You see similar things with the airway fees in the EU. I've heard it said that the rear cg limit for the 50g DA40 is because of spin recovery times... which if you don't spin seems hardly worth worrying about.

If one were to believe these tales of when the limits aren't actually due to safety, it's easy to understand how such a person might take them so flippantly.

[mhoran]

I've heard it said that the rear cg limit for the 50g DA40 is because of spin recovery times... which if you don't spin seems hardly worth worrying about.

If one were to believe these tales of when the limits aren't actually due to safety, it's easy to understand how such a person might take them so flippantly.

I think this is an important point. As pointed out by Rich: "This works until it doesn't." I don't think anyone intentionally stall / spins their plane into the ground -- but it happens. In the accident involving my former flight instructor, the high weight plus density altitude resulted in misunderstanding of the situation at hand -- he suggested to the student pilot that the plane was not "making power", before he stalled and dove into the ground. If he'd realized what was really happening, and continued a slow but steady climb out and circle back to land, he likely would have survived.

While yes, there are safety margins built into the certification and you *may* be able to push those limits, they are there for a reason (not just because someone wanted to limit the utility of your plane.) *If* you do get into this situation where you are right on the edge -- are you going to make every perfect decision? Or will you make mistakes, and those mistakes add up until you've burned through that safety margin.

[Rich]

One of the things that makes people a bit more risky is that there are several alleged instances of aircraft limits being put in place due to regulation rather than any physical property. I think I saw someone on here comment that the yellow line on the airspeed indicator isn't due to frame stressing but due to the relation to the stall speed. Light sports are certified to 1320# not because of the plane but because then they aren't regulated as light sports. You see similar things with the airway fees in the EU. I've heard it said that the rear cg limit for the 50g DA40 is because of spin recovery times... which if you don't spin seems hardly worth worrying about.

If one were to believe these tales of when the limits aren't actually due to safety, it's easy to understand how such a person might take them so flippantly.

The yellow area is a consequence of the design load factor being reached at a particular speed assuming specified gust loads. It's not arbitrary unless you assert that the certification gust load is hypothetical. Of course it is. You could say every single thing about certification is arbitrary, therefore overly onerous and can be ignored.

[Rich]

Ignoring or even intentionally testing limits is a fairly common sport. In Australia I have seen cases where intentional spins in DA40's are being routinely included in flight training. One knows of this because reports show up in the predictable places.

In the early days of the SR22, there were two guys who took their new SR22 up and intentionally spun and recovered several times. In a classic demonstration of "it worked until it didn't" they successfully recovered N-1 times.

[dant]

The yellow area is a consequence of the design load factor being reached at a particular speed assuming specified gust loads.

This was my understanding as well - however someone else heard differently. I think it was on this board that I read it. IIRC As a result they regularly fly well in to the yellow.

I should have left the spin CG one out of my examples as it's clearly related to safety, but I wanted to demonstrate that the failure mode that caused the limitation might not be one that folks encounter in their day to day flying, which can cause a mindset that the limitations aren't relevant to your style of flying. I think folks usually think that a CG limitation causes a loss of control in reasonably normal flight due to e.g. insufficient elevator authority, which in reality it's something more eccentric.

[Rich]

The yellow area is a consequence of the design load factor being reached at a particular speed assuming specified gust loads.

This was my understanding as well - however someone else heard differently. I think it was on this board that I read it. IIRC As a result they regularly fly well in to the yellow.

I should have left the spin CG one out of my examples as it's clearly related to safety, but I wanted to demonstrate that the failure mode that caused the limitation might not be one that folks encounter in their day to day flying, which can cause a mindset that the limitations aren't relevant to your style of flying. I think folks usually think that a CG limitation causes a loss of control in reasonably normal flight due to e.g. insufficient elevator authority, which in reality it's something more eccentric.

The yellow zone is not a prohibited area of the envelope. It just has the limitation of "in smooth air" - whatever that means. Many folks regularly fly in the yellow. I do as well. But the further into the yellow, I figure the smoother it better be. My normal max cruise at normal altitudes lies at the top of the green, but yellow it is when keeping speed up on descent or cruising at lower altitudes.

The 50-gallon CG limitation is clearly a spin-recovery limitation. This is demonstrably so. Compare it to an otherwise identical DA40 with 40 gallon tanks. It probably results from testing wherein when spun in conformance with certification requirements it couldn't reliably be recovered in the requisite rotation limit. But there's a point where having your moment too far to the rear (and you don't know what "too far" is if you ignore aircraft limits) will result in not having the necessary nose-down authority to get you out of trouble.

[dant]

Am I being super unclear? I feel like my point isn't getting received. I'm not arguing in favor of these things, I'm explaining how given a certain point of view it's not surprising that folks push the limits, and instead I'm getting a bunch of corrective comments for stuff I already know.

[Rich]

... a bunch of corrective comments for stuff I already know.

It was not my intent to correct you, but to expand. What you know, others may not. We have folks with all sorts of levels of experience here. Sorry if I came off otherwise.

I live amongst those with the point of view of which you speak. This applies to some pilots around around here as well as the larger community.