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yak52
Joined: 25 Oct 2007
Posts: 50
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 Posted: Fri Jul 10, 2009 9:49 am Post subject: Most recent letter from Chris |
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As some of you are not following ZBAG, I thought you might like the response to Jim's recent letter concerning flutter. Those in quotation marks are ZBAG's reply to Jim's statements, and the others are my reply to that.
As recently stated:
"It is my belief that the only FEA models of the 601XL/650 wing prior to the
recently completed tests for the DAeC, are the models developed in conjunction
with ZBAG by Mark Sensmeier and Jim Helbling, and by Stephen Mitchell."
None of those models were validated by GVT, yet were sent to the NTSB. Have the
GVT results supplied by Zenith been applied to those FEA models to re-evaluate
those opinions?
" I have absolutely no doubt that it would be possible to design a
601XL without counterbalances that would be immune to flutter with the
controls disconnected."
Why would you want to have an aircraft designed as immune to flutter with the
controls disconnected? You couldn't fly it. Also, as has been stated by numerous
authorities, an aircraft is supposed to be designed not to flutter within its
flight envelope as properly maintained.
" I believe that Jim is probably correct that the 601XL wing will not flutter
if the cable tension is high enough. However, it is obvious from Mat Heintz'
AvWeb Podcast that the 601XL wing will flutter with slack control cables. And
it is apparent from the same Podcast that, by adding counterbalances, the wing
will not flutter."
Therefore, flutter can be prevented by merely maintaining the cable tensions at
the levels proscribed by the designer without any further design change,
including counterbalances.
" So, while it is obviously possible to design a flutter-free, modern
aircraft without counterbalances, the cost effective solution to the
flutter problem for almost all aluminum skin general aviation aircraft is to
just add counterbalances so that the aircraft meets the criteria of A&E Report
No. 45. And that is why you find counterbalances on the vast majority of small
aluminum skinned aircraft, be they FAA certificated or E-AB's."
How is it cost effective to redesign the aileron control system to meet some
criteria, that it was not designed to meet initially, by the addition of
counterbalanced ailerons and any associated structures, when you agree that the
flutter can be prevented within the aircraft's flight envelope by maintaining
the cable tension as designed?
Also my two cents worth
[quote][b]
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d.goddard(at)ns.sympatico
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| Posted: Fri Jul 10, 2009 10:28 am Post subject: Most recent letter from Chris |
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Very interesting Roger. I have not quoted the entire posting just the one sentence, hope you don't mind.
I think you might be approaching this from the standpoint that you do not want these aileron counterbalance. If you discard that position and look at it instead as a question of will these balances improve the aircraft, or even a more open perspective of will they hurt it you may come away with different opinion of the posting. We appear to be fairly reassured that flutter is not an issue with cables at proper tension, adding balances is not required. On the other hand they need not be heavy or complex and then flutter mitigation would not require a specific cable tension (although flight control would certainly require some tension). If they are added the ailerons would certainly not flutter even with no tension, controls disconnected (the ultimate slack) flutter would then never be an issue, under any circumstances. Now I regard that as an improvement. I don't think the author was advocating for flight minus controls. If such a mod is approved, it should be optional, but any further attempt to vilify ZBAG simply because of this wording will only serve to further split the Zenith community.
Is there anyone here who still believes the XL WILL experience destructive flutter with these cables properly tensioned? That's not COULD, I specifically asked WILL. Further is there anyone here who would object to the existence of an optional mod that would remove COULD from the equation? If the answer to these questions is no, we should surely not be at each others throats over it. If the answer is yes, I'd be surprised, but the attitudes of some list members toward this has already surprised me so no change there!
[quote] ---
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dougsire
Joined: 10 Jan 2006
Posts: 37
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| Posted: Fri Jul 10, 2009 11:29 am Post subject: Re: Most recent letter from Chris |
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Roger,
There is no "ZBAG reply" as you state, "Those in quotation marks are
ZBAG's reply to Jim's statements". There is no global ZBAG headquarters where opinions are promulgated and press releases generated. It is simply a forum for those individuals wishing to discuss 601XL design issues in a civil and intelligent matter. To state otherwise is a misleading statement.
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Doug Sire 601XL
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Juan Vega Jr
Joined: 13 Jan 2009
Posts: 157
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| Posted: Fri Jul 10, 2009 3:08 pm Post subject: Most recent letter from Chris |
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Dave,
i don't understand, whats your point?
Juan
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paulrod36(at)msn.com
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| Posted: Sun Jul 12, 2009 10:33 am Post subject: Most recent letter from Chris |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Not to take a stand on the issue, but, before I hang the wings, I'm planning to strip out the cables, and put in pushrods. Not because I must, but BECAUSE I CAN. They're neat, they don't require tensioning, and RV'ers love them. Same reasoning for the BRS,the LRI, and the Dynon goodies. Come to think of it, same reason why I fly at all. Because I can.
Paul R.
(expecting my crank back from Nitron this week)
[quote] ---
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Gig Giacona
Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA
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| Posted: Mon Jul 13, 2009 5:18 am Post subject: Re: Most recent letter from Chris |
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You do know if you are installing a Dynon it has an AOA function that pretty much does the same thing as a LRI?
| paulrod36(at)msn.com wrote: | <xml><xml><endif> Not to take a stand on the issue, but, before I hang the wings, I'm planning to strip out the cables, and put in pushrods. Not because I must, but BECAUSE I CAN. They're neat, they don't require tensioning, and RV'ers love them. Same reasoning for the BRS,the LRI, and the Dynon goodies. Come to think of it, same reason why I fly at all. Because I can.
Paul R.
(expecting my crank back from Nitron this week)
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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR |
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