1,000-lb useful load? +BRS?

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TimS
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Re: 1,000-lb useful load? +BRS?

Post by TimS » Wed May 15, 2019 6:53 pm

Rich wrote:
Wed May 15, 2019 4:21 pm
My inclusion of the chute in this discussion is because whatever its real merits as a life-preservation device, it's unquestionably a valuable sales tool. At the cost of everyone lugging around an extra 80 lbs or so of equipment that the vast majority will never use.
same for crash cages, and the seat belts. So why have them?

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Re: 1,000-lb useful load? +BRS?

Post by Rich » Wed May 15, 2019 8:17 pm

TimS wrote:
Wed May 15, 2019 6:53 pm
Rich wrote:
Wed May 15, 2019 4:21 pm
My inclusion of the chute in this discussion is because whatever its real merits as a life-preservation device, it's unquestionably a valuable sales tool. At the cost of everyone lugging around an extra 80 lbs or so of equipment that the vast majority will never use.
same for crash cages, and the seat belts. So why have them?

Tim
Seat belts serve an additional purpose experienced sooner or later by virtually every plane out there in the form of keeping you in the seat in an unexpected negative wind shear even some less-than perfect landings.

Crash Cages, seat belts and energy-absorption features provide a particular level of safety in cases where use of the chute is not feasible. Unlike the BRS approach, they do not require periodic expensive maintenance. There are a great many non-fatal accidents experienced every year where the plane is extensively damaged without the use of a chute, whether or not the plane is so equipped. Therefore these other provisions are called into play far more often than chute-pulls. That's true even for the Cirrus models, BTW.
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Re: 1,000-lb useful load? +BRS?

Post by Rich » Wed May 15, 2019 8:28 pm

Incidentally, lest you think this is all about Cirrus-bashing, that is not my intent. Given the chute, and pilots using it when it's called for, the Cirrus line has improved its fatal accident numbers in the last few years. Contrary to a recent Aviation Consumer article I find the SR20 to be doing very well in recent years, with no fatal accidents on the US last year (the 3rd such year in ts history). Of course the DA40 still has crazy low numbers in terms of fatal accidents without having a chute due to its other qualities (and presumably our superior airmanship :) ).
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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Re: 1,000-lb useful load? +BRS?

Post by Antoine » Wed May 15, 2019 9:19 pm

All of this is a matter of positioning. I believe that the DA40 airframe is:
- aerodynamically an amazingly pertinent combination of safety and performance. The slow speed and stall behavior are best in class while drag remains quite low, allowing for excellent efficiency and speed.
- A cabin that is OK for Europe but too small by US standards
- Structurally an example of bad composites engineering. A good example is the Pipistrel Panthera. The DA40 is way too heavy.
- A trainer before being a cross country machine. The landing gear is a compromise that favors robustness at a great cost in every other respect.

A redesign of the DA40 to fix all of the above would require relatively modest investment. The all carbon fuselage design is already done and certified (DA42).
I would definitely add a BRS as an option. Let customers choose what they want and not run to Cirrus because their better half absolutely wants a parachute.
And I firmly believe that 165 KTAS is within reach... This would seriously eat the SR22's lunch...
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Re: 1,000-lb useful load? +BRS?

Post by Rich » Wed May 15, 2019 9:25 pm

Antoine wrote:
Wed May 15, 2019 9:19 pm
A redesign of the DA40 to fix all of the above would require relatively modest investment. The all carbon fuselage design is already done and certified (DA42).
I disagree. The CG problem is not trivial. And putting a chute behind the baggage area complicates it all further. The DA42 has two engines sticking out in front to alter the CG picture, so it's a poor example. And the chute needs a frangible piece in the fuselage to let the rocket easily blast through.

BTW Antoine, your post came out in duplicate.
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Re: 1,000-lb useful load? +BRS?

Post by Colin » Wed May 15, 2019 9:34 pm

In my first 300hrs I *really* needed that robust landing gear.
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Re: 1,000-lb useful load? +BRS?

Post by Rich » Wed May 15, 2019 10:25 pm

Antoine wrote:
Wed May 15, 2019 9:18 pm
- A cabin that is OK for Europe but too small by US standards
- Structurally an example of bad composites engineering. A good example is the Pipistrel Panthera. The DA40 is way too heavy.
- A trainer before being a cross country machine. The landing gear is a compromise that favors robustness at a great cost in every other respect.
Your complaint about cabin design argues for a new airframe. While I don't disagree the US is a country of fatsos this has never presented a limitation in any flight I've made.

Your airframe empty weight complaint needs more validation. How much extra weight? 500 lb, 300? The Panthera, BTW, has a shorter wing, higher wing loading and much higher stall speed. A smaller wing is a good way to save weight. Much of the weight problem in DA40s is not related to airframe structure but all the various options that have come along, giving rise to limited useful load and/or problematic CG situations. (A characteristic that our early ones do not share.) In this we agree that it should be corrected, mostly by lightening up the structure. I just think it's a bigger job than you do. (JSYK, I used to work for managers who didn't appreciate the magnitude of actually implementing their "big picture" ideas.)

Dismissing a "trainer first" characteristic is disingenuous. It seems to denigrate docile handling, robust gear, etc. as suited for toys. Many of us fly these planes all over the country. You seem to say it should be more like a Cirrus, as though that's the gold standard.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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Re: 1,000-lb useful load? +BRS?

Post by TimS » Thu May 16, 2019 1:52 am

I was seriously looking at an experimental plane called a Velocity V-Twin. On one visit, I was discussing carbon fiber instead of fiberglass for the plane. The factory had already calculated the wight savings, just under 100 lbs compared to fiberglass. However, this would have increased the raw material costs by almost 200K, and this was in 2014. No idea on the prices for CF now; but it was coming down at the time.

If you want low stall speed, you need low wing loading. You can get this via complex flaps or big wings.

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Re: 1,000-lb useful load? +BRS?

Post by Rich » Thu May 16, 2019 3:23 am

It's not as if there isn't already quite a bit of carbon fiber in the DA40, if that's the primary expected salvation. The main difference between the DA40 and 42 looks to be in the wing spars (DA40 is part CFRP, DA42 all CFRP) and main fuselage (DA40 is GFRP, DA42 is all CFRP, which precludes internal antennae, FWIW). Wing skin, control surfaces, and horizontal stabilizer look to be of similar construction for the DA42 and DA40. And it isn't as if carbon fiber is completely weightless.

Changing the materials used in the landing gear would yield some savings. But I've held a main gear leg in my hand and they aren't all that heavy. Fairings are CFRP. The use of Cleveland wheels and brakes has the practical benefit of their being ubiquitous and inexpensive to work on.

There are other areas if you're willing to go there:
1. Ailerons each have 4 hinges.
2. Depending on how you count them, the flaps have 6 or 7 hinges apiece.
3. DA40 has internal aluminum fuel cells. Many other aircraft have some kind of wet wing. Not necessarily the best idea in a composite aircraft. Exhibit A: Cirrus.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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Re: 1,000-lb useful load? +BRS?

Post by CFIDave » Thu May 16, 2019 1:05 pm

Keith M wrote:
Wed May 15, 2019 2:43 pm
Incidentally, the DA40s fixed seats may be good for 45g, but maybe not their occupants. Such a vertical force would certainly crush the spine, while horizontally it would break the neck, unless wearing a racing helmet with a HANS device.
The point is not that the kevlar seats themselves will survive a major vertical impact, but that they remain intact while the foam "crush blocks" underneath the seat absorb a vertical impact (up to 26G as I recall) to protect the pilot's spine from injury. As noted above, this is why Diamonds have fixed (non-movable) seats. Newer GA aircraft like Diamond and Cirrus were certified under Part 23, which requires a much higher standard of pilot protection than older planes like C172s (with movable seats) certified under the old Part 3 standards.
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