1,000-lb useful load? +BRS?

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Rich
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1,000-lb useful load? +BRS?

Post by Rich » Mon May 13, 2019 4:47 pm

It has been suggested that the DA40 could be trimmed of excess structural weight and thereby achieve a 1,000-lb useful load without further increasing MTOW. But I contend it would take more than just lowering the empty weight to make the useful load, well, useful.

This is a possible loading of my DA40, which has a 940-lb useful load, extended baggage, 40 gallon tanks, and a forward CG typical of the early Stars:
N40XE W&B.jpg
The seats in this sample loading includes the values I use for myself and my wife, and the equivalent of a hypothetical similar couple in the rear seats. Note this comes within a whisker of the MTOW and aft CG allowed in my plane. To do so requires (in addition to the lighter weight than most of the DA40 fleet):

1. The forward CG. The not-so-obvious orange dot down and to the left is the empty weight and CG.
2. The aft CG limit of 102 in. 50-gallon tanks would be a no-go.
3. The extended baggage option. I use this a lot, and on several occasions it has been required. Without it, the utility of the plane is limited. Herewith a picture taken a day before the 2017 eclipse:
the load.jpg
This trip (Spokane, WA -> Prineville, OR) required all the volume in the plane, though the weight and CG weren't really at the extreme limits shown in the possible loading above.

The 940 lb. available to me will likely never be a real limitation. But a 1,000 lb useful load would be a boon to our 50-gallon folks IF the aft empty CG and aft CG limit were also dealt with. This would not seem to magically happen just by lightening the structure.

It has also been suggested that a BRS (or equivalent) be added to the DA40. I see several challenges with that in the context of this discussion:

1. The BRS system for the weight class of the DA40 is listed by BRS as 79 lb. So it would add yet more challenge to the weight trimming. Some of the DA40's as they are now (with various goodies stuffed within) are well over 1,800 lb empty. So if you're going to get to that 1,000 lb for most of the airframes you'd need to trim more than 150 lbs off the empty weight without adding the BRS. To compensate for the BRS, it'd need more like a 230+ lb. reduction.
2. Where would you put the BRS rocket? The lion's share of the system is the rocket/chute and its mounting hardware. This would be way aft in the airframe, contributing further to the aft CG challenge. It can't be in the passenger compartment, it'd have to be behind what is retained of the baggage compartment. As I said, I've used all existing available volume numerous times and wouldn't want to see that lost.
3. How would you route the chute lanyards? The fuselage structure would have to be reworked to allow for the "zipper" effect needed for chute deployment.

This all sounds like quite a bit of non-trivial redesign to me. I could see it maybe being pulled off with a different airframe altogether, but retaining the same aerodynamic principals as the DA40.
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 Colin » Tue May 14, 2019 2:24 pm

I would attached the chute and rocket to the belly, aiming to the rear. Yes, it's possible you flip over on the way down, but that way you to get look at where you are landing in great detail and you're wearing safety belts anyway.
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Re: 1,000-lb useful load? +BRS?

Post by Steve » Tue May 14, 2019 2:30 pm

Colin wrote:
Tue May 14, 2019 2:24 pm
I would attached the chute and rocket to the belly, aiming to the rear. Yes, it's possible you flip over on the way down, but that way you to get look at where you are landing in great detail and you're wearing safety belts anyway.
Colin: I trust that you are being facetious. All of the passive shock absorption in the DA40 is on the bottom (seat crush blocks, landing gear). You land upside down, even under the chute, and you are in a world of hurt...

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

Post by Colin » Tue May 14, 2019 9:55 pm

I might not be a fan of the 'chute idea on the DA40. Perhaps on a new model that was designed for it. There's been a lot of discussion about it on the board, and my position has always been that a DA40 in full stall descends 700fpm and the SR22 under the chute is 1,500fpm. (Yes, I know there is forward motion with the stall and all of that.)
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Re: 1,000-lb useful load? +BRS?

Post by jb642DA » Wed May 15, 2019 12:19 am

I'd take the DA40 anytime esp compared to the SR20!
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Re: 1,000-lb useful load? +BRS?

Post by Keith M » Wed May 15, 2019 7:24 am

Colin wrote:
Tue May 14, 2019 9:55 pm
my position has always been that a DA40 in full stall descends 700fpm and the SR22 under the chute is 1,500fpm. (Yes, I know there is forward motion with the stall and all of that.)
I don't think you should encourage people to think there is any equivalence between the two, as a full stall into the ground is likely to end up in tears. The SR22 has an aluminum honeycomb structure under its seats, and the undercarriage is designed to progressively collapse, to absorb the impact. The DA40 has neither of those, and the forward motion, as the wheels dig into the ground, will likely result in it somersaulting. As it also doesn't have 4-point seatbelts, the occupants would get much more thrown about and maybe knocked unconscious.
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Re: 1,000-lb useful load? +BRS?

Post by Colin » Wed May 15, 2019 1:51 pm

A number of the DA40's have the seatbelt airbag, which seems even better than four points. I was told the landing gear *is* designed to collapse on impact and absorb the energy of an uncontrolled drop. And I was also told the reason the seats were fixed without reclining ability was so that they were rated for 45g crashes. (Obviously, most of that is from the salesman, who called the seatbelt airbags "An open coffin option." So I never knew how much of his chatter to take as gospel.) I definitely hold that the same pilot in their first 500 hours is a lot safer in a DA40 than an SR22 even with the chute in play.
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Re: 1,000-lb useful load? +BRS?

Post by Keith M » Wed May 15, 2019 2:43 pm

Colin wrote:
Wed May 15, 2019 1:51 pm
I definitely hold that the same pilot in their first 500 hours is a lot safer in a DA40 than an SR22 even with the chute in play.
That's why I bought one. Their primary safety features are better than the SR2x, but Cirrus compensate with secondary safety, apart from their wet wings which have a tendency to catch fire when ruptured. They had airbag seatbelts from the outset, but they were never an option for the DA40D.

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

Post by TimS » Wed May 15, 2019 3:10 pm

Colin wrote:
Wed May 15, 2019 1:51 pm
A number of the DA40's have the seatbelt airbag, which seems even better than four points. I was told the landing gear *is* designed to collapse on impact and absorb the energy of an uncontrolled drop. And I was also told the reason the seats were fixed without reclining ability was so that they were rated for 45g crashes. (Obviously, most of that is from the salesman, who called the seatbelt airbags "An open coffin option." So I never knew how much of his chatter to take as gospel.) I definitely hold that the same pilot in their first 500 hours is a lot safer in a DA40 than an SR22 even with the chute in play.
Colin,

More useful to compare a DA-40 with the SR20. The SR22 is closer in performance/mission to the DA-42 (the pre -VI variants).

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

Post by Rich » 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.

FWIW, of the 7 fatal DA40 accidents in the US, 3 might have been non-fatal had the plane had a chute and it had been deployed in time. The remaining 4 were all some sort of CFIT. One of those 4 might have involved some sort of pilot incapacitation, but he was alone in the plane. It's worth noting that in one of the other 4 (an icing encounter), there were 2 occupants - 1 fatal, one serious injury.

The rationales you most-often hear about having a chute available:
1. Pilot incapacitation. This is a rare event and the chute is not likely to help if the pilot is alone unless it's a partial/temporary event. Not sure if this has ever happened in a DA40, but there are some known among the Cirri.
2. Engine failure. I can find no DA40-180 fatal accidents initiated by engine failure. There have been a few DA40 power loss incidents we've come to be aware of with no injuries. Some have had outcomes so minor they don't make it into the NTSB database. Lots of such SR22 events in the NTSB database have appeared in recent years.
3. Mid-air collision. Very rare in any case, but the only mid-air I could find involving a DA40 was in England. The DA40 landed without injury or incident, though the RV6 pilot was killed. A Colorado mid-air in 2010 involving a SR20 had the successful chute deployment rendered moot due to the aforementioned tendency of the Cirri to catch fire.
4. Caught in mountainous terrain. A DA40 non-fatal accident in Utah in 2007 illustrates the value of doing what you're always taught: Keep the plane under control all the way through, even a collision with trees. 4 occupants, 2 minor injuries, 2 none. Aircraft low-speed handling, cabin structure and pilot maintaining his cool (following a dumb mistake) are all in play.
5. Loss of control for various reasons. Spatial disorientation, can't recover from spin, elevator flying off, etc. Legitimate concerns. The three DA40 fatal accidents arguably fall into this category. That's why I concede these. There are numerous Cirrus events that fall into this category.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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