frankroskind(at)HOTMAIL.C
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 Posted: Sat May 10, 2008 7:49 pm Post subject: Zenith Builders Analysis Group -- "I'm in" responders... |
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If flutter were the answer, then the You-tube shots of the Brazilian aircraft doing high-speed passes in situations very prone to flutter would have likely shown a plane encountering flutter. They videos do not show anything likely to indicate flutter. Further, the Brazilian aircraft apparently entered a spin as a prelude to crashing. I have not read much correlating spin and flutter. In fact, spins usually involve relatively low airspeeds in which flutter is relatively rare. I also think flutter would make it less likely a spin would flatten, not more likely. Flutter is an interesting phenomenom, but I find it hard to relate to the crash in Brazil. It may have something to do with the crashes where there were structural failures, but even there it seems like an odd choice of failure mode.
Does anyone have NTSB reports which do involve flutter as the original cause of failure on some other airplane, where witnesses reported seeing the wings fold? What were their descriptions like?
I think the commenter who suggested that it is unlikely that a "smoking gun" will be found is probably right. In order to have the data necessary to really find out what caused the failures we would need a mass of records, and I am pretty sure none of us want to maintain such copious and burdensome records.
Nevertheless, there may be some measures which would do no harm, which might prevent an accident. I thnk it is relatively benign to take steps to make the control surfaces more resistant to flutter. Certainly it is a great idea to adjust cable tensions carefully, and also a great idea to make sure that you have balanced your control surfaces in accord with the design, or with a modification approved by a knowledgeable engineer.
There may be other steps which would be relatively benign which might make it easier to avoid in-service faiures. If we can discern which points on the wing failed, especially the spar, we can try to make those points easy to inspect. An inspection window, assuming one can be added without affecting structural inegrity, near the attachment points would be useful. I also think it would be easier to inspect for cracks if the spar were painted a color likely to show a crack. A white primer might make cracks easier to see. Perhaps some other color would be even more effective. We can also be extremely careful to avoid stress risers in the vicinity of bolt holes, and make sure bolts are clean when inserted. Maybe it would be useful to check the bolt holes and surrounding areas with dye penetrant before painting. None of these would seem to be harmful to the design.
In operation, we can be very careful to describe hard landings, and to describe and perform appropriate inspections after hard landings. Perhaps a low cost g-meter can be added, with some kind of maximum g force indecation, and exceeding a certain value can trigger some very detailed inspection.
Some of the heroic measures suggeseted seem likely to add risks as rapidly as they reduce other risks. Some would add to the structure, not knowing whether they are creating more or less potential for crack inititation. Some have decided to abandon their projects, but this seems hasty. Unless those abandoning projects also intend to abandon aviation, they would seem to be reducing one type of risk and substituting an unknown risk. From all accounts the 601 is easy to fly. There are a lot of competing aircraft which are more challenging. To name one example, suppose our bold aviators switch to early model Yankees, which had a reputation for squirrely handling. It isn't hard to get a Yankee too slow and get into trouble. Stall/spin accidents seldom have happy endings. Whatever change of course you decide to engage in, a reasonable precept would seem to be "do no harm."
From: Afterfxllc(at)aol.com
Date: Sat, 10 May 2008 22:42:08 -0400
Subject: Re: Re: Zenith Builders Analysis Group -- "I'm in" responders...
To: zenith-list(at)matronics.com
| Quote: | I think now we have 4 reports of aileron flutter and the pics we have show the aileron dislodged from the hinge and the only part of the hinge that pulled away from the pin and separated was at the outboard section and that section has I believe 6 rivets close together. No one has answered the question as to where the aileron was in conjunction to the wings. I am with Andy and think flutter is the smoking gun. And I would be willing to bet the farm that most do not use a tensi o meter to tighten the cables correctly. I have never looked in the plans but I don't think (and I might be wrong) that the proper tension is listed anywhere. I go by the book as far as cable size tension so if it's there I just haven't seen it. BTW who's airplane is being used for these tests? Are you simply using the plans? It would seem to me a retest of the wings is in order but who is willing to sacrifice their wings and center section for this test. I agree with the other persons post that a inspection of the wrecks is a much better way of finding answers but that would mean you would have to wait and most want answers now but I don't think anything fruitful will come of this other than something is being done right now.
Jeff
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