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tigerrick(at)mindspring.c
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 Posted: Wed Jun 03, 2009 12:32 pm Post subject: Putting Flutter Issue to Bed |
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Was it Mark Twain who said something like "Better to say nothing, and let others think you a fool, than to open your mouth and remove all doubt"?
Zenith could have released all sorts of info that essentially said nothing new, but chose not to until the results were in. Not the greatest PR move, but certainly understandable. And no company wants to take on an expensive test regime based soley on speculation from an ad hoc group, but when the evidence suggested that there MAY be some flutter factor involved, it was done.
BTW, I don't think are "sides" in this issue, just a group that has a common goal but way different methodologies. At some point, various personalities became much more invested in being "right" than finding causes, and minds slammed shut.
But I'm pleased that I'll be flying one of the most tested LSAs available, after all of the dust settles.
Rick
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frankroskind(at)HOTMAIL.C
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| Posted: Wed Jun 03, 2009 12:54 pm Post subject: Putting Flutter Issue to Bed |
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In the beginning of this discussion C I suggested that flutter tends to occur at high true airspeeds C often under cases of low density altitude C where calibrated airspeeds tend to be low compared to true airspeeds C because flutter is dependent of true airspeed. I further suggested that was not the place to look I also think that relatively experienced pilots can handle decreasing stick force with greater deflection C although from a human factors design standpoinnt that is not the most desirable arrangement. No one has suggested any kind of divergent displacement or similar instablilty C so the decreasing stick force should not have caused an accident. The pilot would notice the increased g- force in the butt accelerometer long before the wings came off.
I do not think the issue is a design flaw per se. The incidents seem to be more likely to indicate some kind of cracking. The XL has a greater cantilever than the earlier 601's. It stands to reason that an irregularity in the construction of the wing root which causes a small stress riser would be more critical in the XL than those earlier 601's. I wonder if there is an inexpensive way to get non-destructive testing of the wing spars and roots at the connection for a meaningful number of XLs C as I think that even a susceptiblity to cracking would not manifest itself in the vast majority of specimens. A further inidication would be oxidized material near the point of failure in crashed aircraft C and I would like to know if any has been found
I think that owners who are irked by the constant discussion otf the failures have a reasonable point C as the discussion serves to diminish the value of their investments of money and effort. Unfortunately C speculation will continue until a nominal cause is accepted by the general population C and a correction is also implemented. Ironically C were the flutter proponents of ZBAG correct C the answer would have been derived C a solution implemented and the value restored. ZBAG could have served to enhance the value of the fleet. Now we need another hypothesis C and need to verify one at last to restore the aircraft's reputation.
I also think that detractors need to put safety into perspective. A few years back Cessna single engine aircraft were subject to an AD about the seats sliding back. No one at the time pointed out that even with the seat sliding accidents C the 172 was the safest GA aircraft. It would be helpful to put the XL record into a similar perspective. Are competing aircraft really safer C or simply subject to a different set of risks?
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frankroskind(at)HOTMAIL.C
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| Posted: Wed Jun 03, 2009 1:10 pm Post subject: Putting Flutter Issue to Bed |
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Correction C I meant high density altitude C low pressure.
From: frankroskind(at)HOTMAIL.COM
To: zenith-list(at)matronics.com
Subject: RE: Re: Putting Flutter Issue to Bed
Date: Wed C 3 Jun 2009 16:51:36 -0400
.ExternalClass .EC_hmmessage P {padding:0px;} .ExternalClass body.EC_hmmessage {font-size:10pt;font-family:Verdana;} In the beginning of this discussion C I suggested that flutter tends to occur at high true airspeeds C often under cases of low density altitude C where calibrated airspeeds tend to be low compared to true airspeeds C because flutter is dependent of true airspeed. I further suggested that was not the place to look I also think that relatively experienced pilots can handle decreasing stick force with greater deflection C although from a human factors design standpoinnt that is not the most desirable arrangement. No one has suggested any kind of divergent displacement or similar instablilty C so the decreasing stick force should not have caused an accident. The pilot would notice the increased g- force in the butt accelerometer long before the wings came off.
I do not think the issue is a design flaw per se. The incidents seem to be more likely to indicate some kind of cracking. The XL has a greater cantilever than the earlier 601's. It stands to reason that an irregularity in the construction of the wing root which causes a small stress riser would be more critical in the XL than those earlier 601's. I wonder if there is an inexpensive way to get non-destructive testing of the wing spars and roots at the connection for a meaningful number of XLs C as I think that even a susceptiblity to cracking would not manifest itself in the vast majority of specimens. A further inidication would be oxidized material near the point of failure in crashed aircraft C and I would like to know if any has been found
I think that owners who are irked by the constant discussion otf the failures have a reasonable point C as the discussion serves to diminish the value of their investments of money and effort. Unfortunately C speculation will continue until a nominal cause is accepted by the general population C and a correction is also implemented. Ironically C were the flutter proponents of ZBAG correct C the answer would have been derived C a solution implemented and the value restored. ZBAG could have served to enhance the value of the fleet. Now we need another hypothesis C and need to verify one at last to restore the aircraft's reputation.
I also think that detractors need to put safety into perspective. A few years back Cessna single engine aircraft were subject to an AD about the seats sliding back. No one at the time pointed out that even with the seat sliding accidents C the 172 was the safest GA aircraft. It would be helpful to put the XL record into a similar perspective. Are competing aircraft really safer C or simply subject to a different set of risks?
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davgray(at)sbcglobal.net
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| Posted: Wed Jun 03, 2009 1:39 pm Post subject: Putting Flutter Issue to Bed |
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Can someone provide a link to the flap stop drawing. I have not seen it on
the Zenith site.
Gary Ray
davgray(at)sbcglobal.net
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jaybannist(at)cs.com
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| Posted: Wed Jun 03, 2009 1:57 pm Post subject: Putting Flutter Issue to Bed |
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Gary, and Others who have asked,
Here is what my drawings show for the flap gap stop.
On my drawings, dated 04/05 for an XL, this is shown on drawing 6-S-3.
Jay Bannister
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FlapGapStop.pdf |
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planes_by_ken(at)bellsout
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| Posted: Thu Jun 04, 2009 3:37 am Post subject: Putting Flutter Issue to Bed |
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They did some modifications after the first one but that did not do the
job. Cessna's attitude at this point is along the lines of: My God, we
are going to beat this problem or else!
Both had a ballistic chute. The first did not deploy and the pilot
bailed out. The second deployed as advertised.
Ken
Dave wrote:
[quote]
I didn't know that Ken, did Cessna address the issue?
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