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Chris' Last Letter

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yak52

Joined: 25 Oct 2007
Posts: 50

Posted: Sat Jul 11, 2009 5:13 am Post subject: Chris' Last Letter

"We appear to be fairly reassured that flutter is not an issue with cables at proper tension,

adding balances is not required."

  

 Agreed.

  

  

  "On the other hand they need not be heavy or complex"

  

  

 Agreed with the proviso that some real engineering would be necessary, including the possibility that additional GVT testng would be necessary. See the recomendations at the end of the GVT report done by Zenith's contractor.

   

 " 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. "

   

  

 Flutter mitigation, within the flight envelope, and a properly maintained airplane is already not an issue without adding additional structures. As there would have to be a specific cable tension maintained,  even with mass balanced ailerons, that would have to be checked as part of your maintainance schedule, you have gained nothing by the addition of the balanced ailerons except redundancy.

   

 "Now I regard that as an improvement. I don't think the author was advocating for flight minus controls. "

  

 Actually the author is on record as demanding that Zenith's  GVT testing be done with the control cables without tension. Try to imagine flying the Zenith without tension between the stick and the ailerons. Your problem would not be flutter if the cables loosened to zero in flight.

   

 "If such a mod is approved, it should be optional,"

  

 Agreed, but who will design and approve it.

  

  

 " but any further attempt to vilify ZBAG simply because of this wording will only serve to further split the Zenith community"

  

 ZBAG is a group of adults who sent the results unverified computer models to virtually every government regulating aircraft insisting that flutter was the cause of the crashes. They also haven't used the GVT testing rsults from Zenith to verify their model. They are big boys who should be able to stand their statements being analyzed. 

  [quote][b]

psm(at)att.net
Guest

Posted: Sat Jul 11, 2009 6:03 am Post subject: Chris' Last Letter

Hi Roger,



This one little part of your post caught my attention.



At 06:11 AM 7/11/2009, you wrote:

 	  Quote: 	
		  you have gained nothing by the addition of the balanced ailerons 

except redundancy.


	




I think my view of this situation would be better stated if you 

changed the word redundancy to robustness.



We all know that the Zodiac XL is basically a very sound design that 

meets not only the specific criteria of ASTM LSA standards but also 

is desirable enough to have sold hundreds or thousands of copies to 

builders and flyers.  It has passed static load testing multiple 

times.  It has passed ground vibration testing.  We don't know the 

results of the other "Engineering design studies" since some have 

been kept secret from the general public, but I think we can assume 

there have been no "Smoking Guns" found to explain the real world 

structure failures.



Nearly everyone who flies a Zodiac XL has a great experience with 

it.  However there have been enough fatal accidents involving 

structural failure in flight that there is cause for alarm.  So the 

nature of the "Problem" with the XL is it lacks sufficient robustness 

to have a great safety record instead of a pretty good one.



The XL design works fine in most cases.  Some times in some unknown 

set of conditions it fails to hold up.   Stated differently:  We need 

to have more robustness in this design rather than a fix for a part 

of the design which is broken.



The latest round of discussion of the aileron controls seems to 

suggest that complete loss of aileron control due to slack cables is 

an unthinkable situation.  This is simply not true.  Aileron control 

is not required to allow for controlled flight.



There are three cables in the aileron control system.  If any one of 

them were severed then the tension in the system would be 

removed.  If it were the balance cable then the control stick would 

still activate one of the ailerons when moved in either direction and 

the pilot would be able to control movement about the aircraft's roll 

axis.  If either of the other cables (the ones going directly to one 

wing) were severed, roll in one direction would still be controlled 

and the other direction would be uncontrolled - as far as the aileron 

system is concerned.  However, roll in that direction and turning in 

general would still be controllable through the rudder.  Indeed if 

the stick had no connection at all to the ailerons the rudder could 

still be used to get the plane to fly in the direction desired by the 

pilot.  Yes, it would be uncoordinated flight, but that would only 

make it a little bit uncomfortable for the occupants of the plane.



Put together this adds up to a robust system.  Even complete loss of 

aileron control leaves you with a controllable and flyable plane.



If loss of aileron cable tension leads to flutter and wing 

separation, then the aileron cables become a critical system for 

flight.  Adding balance to the ailerons seems to change this by 

removing any possibility of flutter when the aileron cable tension is 

lost.  This addition would restore some of the robustness to the 

design that should have been there all along.



Paul

XL grounded

d.goddard(at)ns.sympatico
Guest

Posted: Sat Jul 11, 2009 9:44 am Post subject: Chris' Last Letter

It may be issued  as a result of OTHER gov't's  demands, it doesn't look like the U.S. gov't has much interest. If it isn't  issued and or approved it would be fine with me if any individual designed their  own and self-evaluated the result. If it works well other builders could use it.  If Zenith saw no harm in it that would likely be the extend of factory approval  but we'll see. Frankly i think flutter is now a dead issue, doesn't mean the  airframe can't be improved. I would regard these balance as desirable but not  high priority. 

  

 I see ZBAG as a bunch of interested and engaged  owners, not an enemy. I don't believe they had much influence on the Gov't and I  don't believe they've grounded anything. They MAY have had a very small part in  getting a very small and so far unenforced recommendation made by a safety  agency. I believe the actions of foriegn gov'ts and the accidents will have had  much more influence. All in all I see ZBAG as exactly what they say they are, a  group of interested builders. Mostly irrelevant to the rest of us, certainly not  worth all the electrons and angst required to hate their guts the way most  of the zenith builders have decided to. I would certainly analyse any  "statement" made by the group as a whole as an official statement, but there has  been none and unless they find something definitive I would not expect that. Any  statements by a person who happens to be a member would hold no more weight than  any other of the vast array of opinions I've read here. I encourage ZBAG to do  their thing, so far I percieve them as irrelevant. I'm unsure who the author who  wants the GVT done with slack cables is, but he's free to want anything. I want  the accidents to stop, after that I want to understand the reason this airframe  appears to have a disproportionate rate of failure. I bet my wish happens  before his. 

  

 [quote]   ---

JohnDRead(at)aol.com
Guest

Posted: Sat Jul 11, 2009 1:55 pm Post subject: Chris' Last Letter

How about we bag the Zbaggers and get on with life? Personally I have had  it with their unfounded accusations of the 601.

  

 John  Read

CH701 - Elbert CO - Jabiru 3300



Phone: 303-648-3261

Fax:  303-648-3262

Cell: 719-494-4567   

  



 Looking for love this summer? Find it now on AOL Personals.

  [quote][b]

jmaynard

Joined: 27 Feb 2008
Posts: 394
Location: Fairmont, MN (FRM)

Posted: Sat Jul 11, 2009 2:57 pm Post subject: Chris' Last Letter

On Sat, Jul 11, 2009 at 05:57:51PM -0400, JohnDRead(at)aol.com wrote:

 	  Quote: 	
		   How about we bag the Zbaggers and get on with life? Personally I have had  

 it with their unfounded accusations of the 601.


	


If I thought there was no foundation for the concerns, I wouldn't have sent

in my money to support the effort. Do you think that we're doing this out of

a desire to harm the Zenith family of companies? Why on earth would that be

something Zenith owners and builders would want to do?

-- 

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

_________________
Jay Maynard, K5ZC
AMD Zodiac XLi N55ZC

Juan Vega Jr

Joined: 13 Jan 2009
Posts: 157

Posted: Sat Jul 11, 2009 3:11 pm Post subject: Chris' Last Letter

Dave,

Of all the accidents,  There were two, out of all that may have been remotely based on some flutter,  but totally unproven.  Look at each accident and prior to people seeing the wings fall off, something else occured,  crap weather, engine quits, pilot buzzing the field,  Even the one in Texas,  the witness heard the engine quite,  THEN something about the wing failing.  The only one that is complete unknown, is the one at Sun N FUn.  The rest had something happen right before the claimed flutter.  ZBAG latched on to the flutter issue like a Pissed off pit bull.  Because some guy claimed he saw flutter over flying a power plant,  then couldnt repeat it.    1000 zodiacs flying,  and maybe 2 accidents that arte maybe  a flutter issue.



Where is the disproportionate failure issue? check out the number of accidents of other aircraft.  2 out of how many zodiacs?  PULL EVERY NTSB Zodiac accident,  and label the ones that were possible flutter or design issue!   Maybe 2! And trhe tests and nath can't find it!



Build it right, fly it right , maintain it right,  its a great plane.



Juan  

--

d.goddard(at)ns.sympatico
Guest

Posted: Sat Jul 11, 2009 3:15 pm Post subject: Chris' Last Letter

John, I am not clear that they have made any accusations. I believe they  have some areas of concern that they are investigating. Any absolute accusations  might well have come from a member, or from someone else. Let them do their  thing. So far I don't believe they have harmed anyone, on the other hand,  unexplained failures have. I hope they keep looking, maybe they'll help find an  answer. 

 [quote]   ---

d.goddard(at)ns.sympatico
Guest

Posted: Sat Jul 11, 2009 3:22 pm Post subject: Chris' Last Letter

I don't believe they are out to harm anybody Jay, I believe you/they are 

doing their best to satisfy themselves that their aircraft are as good as 

they can be. Not sure how ZBAG got tagged an enemy that must be attacked at 

every turn, miht be that old "If yer not with us, yer agin us us!!" crap.



---

jmaynard

Joined: 27 Feb 2008
Posts: 394
Location: Fairmont, MN (FRM)

Posted: Sat Jul 11, 2009 3:31 pm Post subject: Chris' Last Letter

On Sat, Jul 11, 2009 at 08:22:17PM -0300, Dave wrote:

 	  Quote: 	
		   I don't believe they are out to harm anybody Jay, I believe you/they are 

 doing their best to satisfy themselves that their aircraft are as good as 

 they can be.


	


I can't speak for everyone involved, but that's certainly my motivation.



 	  Quote: 	
		   Not sure how ZBAG got tagged an enemy that must be attacked at every turn,

 miht be that old "If yer not with us, yer agin us us!!" crap.


	


I don't know either, but I'm getting goddamned tired of it.

-- 

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

_________________
Jay Maynard, K5ZC
AMD Zodiac XLi N55ZC

tonyplane(at)bellsouth.ne
Guest

Posted: Sat Jul 11, 2009 3:34 pm Post subject: Chris' Last Letter

IRT "some guy claimed he saw flutter over flying a power plant,  then 

couldnt repeat it."

See below from my archives;

Tony Graziano; XL/Jab N493TG w 510 hrs to date

-

Hi Bill,Glad everything came out OK. Looks like you ran into some really 

weird turbulence from the power-plant, giving you an "E" ticket ride.  If 

you were really experiencing wing or control surface flutter, your diving 

and picking up speed should have exacerbated the problem with the amplitude 

going divergent very rapidly, until something(s) bends or more likely breaks 

off. Only saw this once in a film of a dynamic model in a wind tunnel - once 

flutter started the entire model was gonzo in a second or two.  Do you 

recall experiencing any feed back in the stick/rudder?In 199 hours in my XL, 

I have had some bumpy rides and the airplane has handled it ok - just glad I 

always have my seat belt tight.  I have also had some GREAT*, almost I would 

have believed, GOOD*, landings and I agree the airplane is tough. *GREAT 

Landing - Airplane is still flyable.  GOOD Landing - You can walk away from 

the airplane.Please let us know if you find anything after your in-depth 

inspection. I kind of suspect you will not find anything amiss, but if you 

do it would be a good data point for all of us for tailoring our structural 

inspections. Tony Graziano  XL; N493TG--------Ben, maybe I did not explain 

well, but it was not control flutter. The

aileron did not move independent of the wing. What occurred is the whole 

wing

fluttered with aileron moving with it., best regards, 

Bill-------------------------  Dear Thread Friends, I went flying this 

afternoon. Took a fellow with me and

just wanted an hour in the clear blue. Conditions were perfect, clear, cool

and only a slight wind. The only big thing around much to see nearby is Lake

Juliette which has a big coal fired power station in the middle. Three huge 

steam



towers that look like a nuclear power station. We flew around the lake about

two miles away at 5000 feet so my pal could get a good look see. On the down

wind side we flew into an invisible killer. We were doing above 140 when we

flew into it. Instantly the left wing fluttered at a fast pitch, aileron and 

all



and it looked to be moving maybe two inched up and down. I figured a couple

seconds would break it off. I didn't have time to look around the passenger 

to



see if the right wing was fluttering, but I suspect it was. I chopped power 

and



did a hard diving wing over to the left and out of it. The flutter sound was

great even over my Lightspeed AN system and the whole thing probably last

maybe 5 or 6 seconds. I regained control out of the snap dive, maxing above 

170



and flew slow and easy back to the field before I tested the controls.

Everything felt okay and I could see no wrinkles in the top skin so I 

landed. Didn't



really have much choice. Upon inspection I found no sign of stress, no skin

deform, no paint cracked around rivets, nothing. I will take off all 

inspection



panels for a close inspection this weekend and check bolts, controls, etc., 

but



I cannot believe such a prolonged violent movement of the wing did not 

damage

something other than my pride. Two things learned. Don't fly anywhere near a

power station. Even at 5000 feet and miles away the invisible heat rises and 

is



most extreme. Maybe intensified in cold weather. The other thing is the XL 

is

very, very tough. Oh, there is a third thing. How could I have been so 

stupid

not to know the first thing !!  I am interested though in knowing why the

wings fluttered in this thermal? What theory of air dynamics would cause 

this

extreme reaction? Was is just the level of heat and speed the invisible air 

was



streaming past? This was my 90th flight in her and she made me proud again.

Best regards to you all,

Bill of Georgia

N505WP

601XL-3300

---

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