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jmaynard
Joined: 27 Feb 2008
Posts: 394
Location: Fairmont, MN (FRM)
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 Posted: Tue Jun 16, 2009 7:34 am Post subject: Forwarded: Re: [ZBAG] Re: Link to Zenair GVT Report |
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I don't know if Gig saw this before he was removed from the ZBAG list, and
the comments apply here.
----- Forwarded message from Jay Maynard <jmaynard(at)conmicro.com> -----
Date: Mon, 15 Jun 2009 15:13:13 -0500
From: Jay Maynard <jmaynard(at)conmicro.com>
Subject: Re: [ZBAG] Re: Link to Zenair GVT Report
To: ZBAG(at)yahoogroups.com
On Mon, Jun 15, 2009 at 07:27:40PM -0000, gig_jess wrote:
| Quote: | Anti ZBAG hysteria? Really? I think it is a matter of those of us that are
willing to take "No, there isn't a problem" for an answer as opposed to
those who only request more evidence once they get the evidence they asked
for and it doesn't fit in their preconceived idea of what the problem is.
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I think there's not enough overall evidence to be able to definitively say
"no, there's not a problem" yet. Unlike some folks, I do accept that there's
not a flutter issue with aileron cables that have any tension at all on
them. (I do think we'll wind up with balance weights anyway, however, to
satisfy the government.) Has every suspected failure mode been analyzed yet?
I'll be satisfied that there's not a design flaw when all of the theories
that explain the observed facts have been tested, and none show a design
issue. Until then, "pilot error" is just too pat an answer.
| Quote: | Go back and reread the messages in this forum. Everybody was sure it was
flutter. The GVT was demanded by those on this list. Got it, results were
NO and it didn't change a thing. Well, that's not true there were several
new threads with lists of additional half-baked ideas for modifications
for imagined problems.
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I think most folks here do indeed accept that flutter is not the answer. We
seized on it as an explanation because 1) it explained the observed
failures, 2) it was indeed a possibility, and 3) nobody had ever run real
tests on it before. GVT was needed to confirm it or rule it out. Well, since
it's ruled it out, we need another explanation.
| Quote: | And Jay, I'm a little disappointed in you. I asked you in a conversation
in Matronics if you could reproduce the G induced elevator issue and if so
is it something that you could train someone to deal with. I never got an
answer to that.
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I apologize; I saw your message, made a mental note to reply when I could
sit down and explore the question, and then real life intervened.
As I understand it, the issue is that the elevator stick force gradient
curve gets shallower, not steeper, above about 3.2 G. The curve under
discussion is a relation between how much force the pilot applies to the
stick and how many Gs the aircraft is pulling. Normally, the stick force
required to pull more G increases monotonically as the G force on the
aircraft increases. The NTSB claims that the stick force required to pull
additional G becomes less, rather than more, at 3.2 G positive. I have never
reached that condition, because I've never even pulled 2 G in my airplane,
and have no intention of doing so. (Positive Gs make me urp. Spin training
for my CFI-SP was a struggle.) The curve never goes negative, so the
aircraft is not divergent in pitch (if it were, there would be some point at
which the stick would not work as the pilot expects, and things go quickly
pear-shaped then).
Could I train someone to deal with it? I doubt I could, personally, simply
because I couldn't get into that situation in the first place without
becoming seriously airsick. Could a generic CFI do so? Probably; the big
problem is recognizing you're in that situation and dealing with it
correctly. Frankly, though, I don't see anyone pulling more than 3 G in a
Zodiac unless they're doing aerobatic maneuvers...and we all know how much
of an aerobatic airplane the Zodiac is not. It's a condition the NTSB
mentioned, and so will likely get some form of addressing. I don't think
it's a condition the average pilot will ever see. I also don't think it's
the proximate cause of Zodiac accidents.
--
Jay Maynard, K5ZC, PP-ASEL, CFI-SP http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (KFRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC http://www.tronguy.net/N55ZC.shtml
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_________________
Jay Maynard, K5ZC
AMD Zodiac XLi N55ZC |
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d.goddard(at)ns.sympatico
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| Posted: Tue Jun 16, 2009 9:07 am Post subject: Forwarded: Re: [ZBAG] Re: Link to Zenair GVT Report |
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Hi Jay; I don't think I'd go quite that far. The flutter analysis via GVT
was worthwhile and to be honest I think the proof rather than the assurances
of the designer were needed. But to test for and exhaust ALL theories might
be a little too long-reaching. I'd be ok with casually exploring any
"reasonably likely" scenarios and flutter certainly seemed to fit the bill.
I think at this point some likely scenarios have been stopped with the small
recommended modifications that are now part of the design. Maybe the
accidents will now stop. I would have a hard time buying into the pilot
error reason in any big way, it's just too easy and if it were truly the
case it should have affected other aircraft to a similar degree as there's
no reason to think XL pilots as a group are any more careless than the
general population.
---
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