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Thoughts regarding Flutter

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sdthatcher

Joined: 13 Mar 2008
Posts: 91
Location: Port Saint Lucie

Posted: Fri Apr 17, 2009 6:03 am Post subject: Thoughts regarding Flutter

I believe the problems that we are experiencing  with the 601XL are not the result of flutter or any other single issue but  instead the result of 4 specific and simultaneous factors that have caused the  wing failures of our aircraft.

  

 First, why not flutter? Because in the instances  that have been reported to be flutter, the time that was required to identify  the vibration and to escape from its destructiveness has been too long (more  than a few seconds).  My opinion is that we are seeing a simple harmonic  vibration of the ailerons that, depending on the tension in the cables, can be  considered as scary enough to cause real concern.

  

 My first theory is that the problem we are seeing  with the ailerons is harmonic vibration, not flutter, and is dependent on the  tension of the cables. In my flight, the cables had loosened to the point that I  could feel a 1-2 inch movement of the stick without any corresponding movement  of the ailerons. As I went over the Valley River Mountains near Andrews, NC, I  could see the ailerons start to vibrate, so I decreased the throttle and the  vibration stopped.  In another case locally, the pilot had loose  cables and, during flights above Va, experienced severe vibration. He  tested this by purposely flying into that portion of the envelope repeatedly  (observing the same type of vibration each time) and then to test it again after  tightening his cables. In his case, the vibration stopped above Va. I  believe that depending on the combination of engine, aerodynamics and cable  tension, the vibration of the ailerons could be seen as mild or severe... but  not flutter.  Another possible instance of severe vibration was a 601  in Georgia that experienced vibration after flying over a power plant  and which required a dive to eliminate the vibration. It is known that to reduce  flutter, you need to reduce airpseed and pray. But in this case the means of  reducing the aileron vibration was to dive at speeds that were close to Vne. Not  the usual way to stop flutter and in any case, the resulting actions took  considerably longer than required to avoid desctruction from flutter. In two of  the three cases mentioned, the vibration was severe enough to apparently cause  movement of the wing, as stated by the pilots.

  

 So, if the problem is just vibration how does that  cause destruction of the wings? My second theory is that the wings of every  aircraft that has failed to date was structurally compromised at some point in  the history of the aircraft.  Recently, I was talking to a gentleman here  in Andrews, NC that was in the Lakeland bound 601 just a week or so before it  lost its wings and was destroyed. He stated that while flying with the pilot  over the mountains near here, they experienced what he described as severe  turbulance. He mentioned to the pilot how really bad the turbulance was and  the pilot stated that "this was nothing compared to a week earlier". Apparently  the turbulance was so bad that the pilot called the experience "bone  crushing".  As for the Yuba City 601, the owner of that aircraft had stated  that there was an indication of "smoking rivets" on the bottom of the wings.  This condition usually is the result of rivets becoming loose and creating a  condition that results in a decrease in structural integrity. The Yuba City  aircraft also (I believe) was flying near or in mountainess areas during its  history.

  

 The third condition that must be met is looseness  of the aileron cables.  I believe that vibration will not occur while the  cables are tight.

  

 And the fourth criteria for these wing failures is  flying above Va (maneuvering speed).

  

 So to summarize, if these 4 conditions are met, the  probability is high for the aircraft to be lost even in mild  turbulance.

  

 Once again, they are:

 1. Aileron Vibrations

 2. Previous structural damage to the  wings.

 3. Loose Aileron Cables

 4. Speeds above Va

  

 I had originally thought that the only way we could  explain the loss of wings on the 601XL was from flutter, however, since 98%  of the fleet has not lost its wings and yet reports continue to surface of  severe vibration, loose cables, etc., it seems to me that there must  be a combination of problems that occur simultaneously that result in  destruction of the wings.

  

 Anyone who has experienced severe turbulance  should carefully look over their wing roots for damage and avoid flight,  especially if they also have loose cables!

  

 Scott Thatcher, N601EL

 601XL with WW Corvair, 25 Hours

 Just finishing first Condition Inspection

  



   [quote][b]

_________________
Scott Thatcher, Port Saint Lucie, FL
601XL with Corvair, Registered as E-LSA
N601EL, EAA203 140 hours and not flying currently.

ciuro

Joined: 02 Oct 2007
Posts: 4

Posted: Fri Apr 17, 2009 7:19 am Post subject: Thoughts regarding Flutter

you should not assume anything at this time.  Assumptions in aircraft accidents are usually wrong'.

--- On Fri, 4/17/09, s_thatcher(at)bellsouth.net <s_thatcher(at)bellsouth.net> wrote:

  	  Quote: 	
		  From: s_thatcher(at)bellsouth.net <s_thatcher(at)bellsouth.net>

Subject: Thoughts regarding Flutter

To: corvaircraft(at)mylist.net, zenith-list(at)matronics.com, zenith601-list(at)matronics.com, ZBAG(at)yahoogroups.com

Received: Friday, April 17, 2009, 9:55 AM

     I believe the problems that we are experiencing with the 601XL are not the result of flutter or any other single issue but instead the result of 4 specific and simultaneous factors that have caused the wing failures of our aircraft.

 First, why not flutter? Because in the instances that have been reported to be flutter, the time that was required to identify the vibration and to escape from its destructiveness has been too long (more than a few seconds).  My opinion is that we are seeing a simple harmonic vibration of the ailerons that, depending on the tension in the cables, can be considered as scary enough to cause real concern.

 My first theory is that the problem we are seeing with the ailerons is harmonic vibration, not flutter, and is dependent on the tension of the cables. In my flight, the cables had loosened to the point that I could feel a 1-2 inch movement of the stick without any corresponding movement of the ailerons. As I went over the Valley River Mountains near Andrews, NC, I could see the ailerons start to vibrate, so I decreased the throttle and the vibration stopped.  In another case locally, the pilot had loose cables and, during flights above Va, experienced severe vibration. He tested this by purposely flying into that portion of the envelope repeatedly (observing the same type of vibration each time) and then to test it again after tightening his cables. In his case, the vibration stopped above Va. I believe that depending on the combination of engine, aerodynamics and cable tension, the vibration of the  ailerons could be seen as mild or severe... but not flutter.  Another possible instance of severe vibration was a 601 in Georgia that experienced vibration after flying over a power plant and which required a dive to eliminate the vibration. It is known that to reduce flutter, you need to reduce airpseed and pray. But in this case the means of reducing the aileron vibration was to dive at speeds that were close to Vne. Not the usual way to stop flutter and in any case, the resulting actions took considerably longer than required to avoid desctruction from flutter. In two of the three cases mentioned, the vibration was severe enough to apparently cause movement of the wing, as stated by the pilots.

 So, if the problem is just vibration how does that cause destruction of the wings? My second theory is that the wings of every aircraft that has failed to date was structurally compromised at some point in the history of the aircraft.  Recently, I was talking to a gentleman here in Andrews, NC that was in the Lakeland bound 601 just a week or so before it lost its wings and was destroyed. He stated that while flying with the pilot over the mountains near here, they experienced what he described as severe turbulance. He mentioned to the pilot how really bad the turbulance was and the pilot stated that "this was nothing compared to a week earlier". Apparently the turbulance was so bad that the pilot called the experience "bone crushing".  As for the Yuba City 601, the owner of that aircraft had stated that there was an indication of "smoking rivets" on the bottom of the wings. This condition usually is the  result of rivets becoming loose and creating a condition that results in a decrease in structural integrity. The Yuba City aircraft also (I believe) was flying near or in mountainess areas during its history.

 The third condition that must be met is looseness of the aileron cables.  I believe that vibration will not occur while the cables are tight.

 And the fourth criteria for these wing failures is flying above Va (maneuvering speed).

 So to summarize, if these 4 conditions are met, the probability is high for the aircraft to be lost even in mild turbulance.

 Once again, they are:

 1. Aileron Vibrations

 2. Previous structural damage to the wings.

 3. Loose Aileron Cables

 4. Speeds above Va

 I had originally thought that the only way we could explain the loss of wings on the 601XL was from flutter, however, since 98% of the fleet has not lost its wings and yet reports continue to surface of severe vibration, loose cables, etc., it seems to me that there must be a combination of problems that occur simultaneously that result in destruction of the wings.

 Anyone who has experienced severe turbulance should carefully look over their wing roots for damage and avoid flight, especially if they also have loose cables!

 Scott Thatcher, N601EL

 601XL with WW Corvair, 25 Hours

 Just finishing first Condition Inspection

 	  Quote: 	

" target=_blank rel=nofollow>http://www.matronics.com/Navigator?Zenith601-List

=nofollow>http://forums.matronics.com

blank rel=nofollow>http://www.matronics.com/contribution

 [quote][b]

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Fri Apr 17, 2009 8:12 am Post subject: Re: Thoughts regarding Flutter

Seeing as how the NTSB notice is based on assumptions as well I think the forwarding of other theories is most certainly in order.

 	  ciuro wrote: 	
		  you should not assume anything at this time.ï¿½ Assumptions in aircraft accidents are usually wrong'.

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Fri Apr 17, 2009 9:08 am Post subject: Re: Thoughts regarding Flutter

Well, I don't understand how you guys think? It's beyond me.



I for a period of time, got to spend right seat time with a now retired 747

captain, who had flown C-46's in WWII over the burma trail. I always

greatly admired him, because his decision making process was crystal 

clear. He would get the info, and regardless of whether it was the answer 

he "wanted" or not, he simply made the decision based on safety.  Never

once did I see him ever say, "well maybe ..." No, he simply accepted that

something wasn't safe and he went with it as called.



Regards,

Jeff

Jeyoung65(at)aol.com
Guest

Posted: Fri Apr 17, 2009 10:39 am Post subject: Thoughts regarding Flutter

Thatcher, Can you tell the older timer what is the difference  between "simple harmonic" and " flutter" ?  Jerry of GA  DO NOT  ARCHIVE

  

  In a message dated 4/17/2009 9:06:46 A.M. Eastern Standard Time,  s_thatcher(at)bellsouth.net writes:

  	  Quote: 	
		  My opinion is that we are seeing a simple harmonic vibration    of the ailerons that, depending on the tension in the cables, can be    considered as scary enough to cause real  concern. 	


 Join ChristianMingle.com® FREE! Meet Christian Singles in your area. Start now!

  [quote][b]

Larry Hursh

Joined: 16 Feb 2008
Posts: 125
Location: Edwardsburg, MI (near Elkhart, IN)

Posted: Fri Apr 17, 2009 4:14 pm Post subject: Thoughts Regarding Flutter

Sorry guys but all of this to me is nothing more than wild speculation.  I am finding all the bantering to be depressing at best.  It's gotten so bad for, I haven't touched a rivet or drill since all of this mess came out.  I honestly don't expect anyone from Zenith Aircraft to step up and work with the NTSB willingly.  Zenith has stated and restated that the problem is wing flutter.  Their claim is its being caused by poorly or improperly maintained tension on the cables tensions.  I think there has been a line drawn in the sand and neither the NTSB or Zenith is going to give one iota.  The NTSB is forcing the issue by posting their statement publicly and asking the FAA to ground all of our aircraft until further notice. Once again, Zenith claims poor tension.  Nothing gives. The next decision will most likely come from the FAA in a formal notice.  If they do ground all 601's (and 650's) this will force Zenith to work with the NTSB.  If Zenith refuses,

 then we, the customers are left out in the cold.  As I said before, I'm finding this all depressing so I am going to STOP reading all these posts and WILL search on the FAA daily for any updates or notices.  I just hope the Heinz family realizes very soon, SOMETHING has to be done - even if its nothing more than to sit down with the NTSB AND the FAA and acknowledge there COULD possibly be a design issue - EVERYTHING has to be ruled out.  It's our lives we are talking about here.  To stand back as Zenith has done and claiming its poor maintenance is a cop out, big time.  Its VERY POOR customer service. I just hope Zenith Aircraft can see this.....Of course this is all my opinion.  Stepping off my soapbox now.



Larry Hursh   

Edwardsburg, Michigan 

Zenith CH650 (N650LM Reserved)  



I hope someday I can be the person my dog thinks I am.....

_________________
Larry Hursh (N650LM Reserved)

"One rivet at a time......one day at a time.."

CH650 (Converted from CH601XL)
1/2 done with fuselage
will be Corvair Powered

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Fri Apr 17, 2009 5:06 pm Post subject: Thoughts Regarding Flutter

Zenith doesn't have to work with the NTSB. The NTSB has absolutely no  

authority in the matter. It's the FAA that has the authority, all the  

NTSB can do is advise. The FAA is free to ignore that advise as they  

see fit. The NTSB notice does not make any mention of the 650 so, so  

far that model is in the clear. The FAA may be able to ground the S- 

LSA version to the 601XL as they have a standard certificate of some  

sort to go after. As far as the E-AB versions of the XL are concerned,  

the FAA would have to ground each airplane on an individual basis,  

because there is no type certificate to take action against. Each is  

considered a one of a kind airplane and the paperwork does not even  

have to contain Zenith or Zodiac or CH 601 XL, the builder can call it  

anything he wants to and many builders probably have done so. The FAA  

doesn't have the resources to track down every homebuilt variant of  

the 601XL to make the attempt to ground them.



On Apr 17, 2009, at 8:13 PM, Larry Hursh wrote:



 	  Quote: 	
		   

 >

 Sorry guys but all of this to me is nothing more than wild  

 speculation.  I am finding all the bantering to be depressing at best.


	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

Larry Hursh

Joined: 16 Feb 2008
Posts: 125
Location: Edwardsburg, MI (near Elkhart, IN)

Posted: Fri Apr 17, 2009 6:25 pm Post subject: Thoughts Regarding Flutter

Bryan, don't try to fool yourself or anyone else on this list.  When I originally purchased my wing kit, it came with the hinge-less ailerons and the new style fiberglass wingtips.  I "converted" my fuselage kit to the 650 within the week of it being introduced at Oshkosh last year.  MY WINGS ARE THE EXACT SAME WINGS AS THE 601.  To "upgrade" them, I added the "L" brackets for the oil canning.  I added the gussets at the first and second rib on the ailerons.  THAT'S IT.  The only major differences (besides the new style rudder) is the angle of the main spar center section.  On the original 601 the angle was set at 9 degrees.  With the 650 the main spar center section is now 7 degrees.  It's for better "forward visibility".  Don't try kidding anyone on here about "being in the clear" Bryan - your NOT in the clear.  Its exactly the same wing with the same flaps and same ailerons because mine WAS a 601.  I know.  You don't, so quit trying to mislead people

 about that on here.  If you doubt me, call Zenith.  You need the number??? 



Larry Hursh   

Edwardsburg, Michigan 

Zenith CH650 (N650LM Reserved)

_________________
Larry Hursh (N650LM Reserved)

"One rivet at a time......one day at a time.."

CH650 (Converted from CH601XL)
1/2 done with fuselage
will be Corvair Powered

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Fri Apr 17, 2009 7:58 pm Post subject: Thoughts Regarding Flutter

I'm not trying to fool anybody, all I said is the CH 650 is not  

mentioned in the NTSB report. We are dealing with buearocrats here,  

nomenclature is everything. If it's not specifically mentioned, it is  

not included. It doesn't matter if it's physically the same.



Don't tell me what I don't know, You don't know what I don't know.

On Apr 17, 2009, at 10:24 PM, Larry Hursh wrote:



 	  Quote: 	
		   

 >

 Bryan, don't try to fool yourself or anyone else on this list.  When  

 I originally purchased my wing kit, it came with the hinge-less  

 ailerons and the new style fiberglass wingtips.  I "converted" my  

 fuselage kit to the 650 within the week of it being introduced at  

 Oshkosh last year.  MY WINGS ARE THE EXACT SAME WINGS AS THE 601.   

 To "upgrade" them, I added the "L" brackets for the oil canning.  I  

 added the gussets at the first and second rib on the ailerons.   

 THAT'S IT.  The only major differences (besides the new style  

 rudder) is the angle of the main spar center section.  On the  

 original 601 the angle was set at 9 degrees.  With the 650 the main  

 spar center section is now 7 degrees.  It's for better "forward  

 visibility".  Don't try kidding anyone on here about "being in the  

 clear" Bryan - your NOT in the clear.  Its exactly the same wing  

 with the same flaps and same ailerons because mine WAS a 601.  I  

 know.  You don't, so quit trying to mislead people

 about that on here.  If you doubt me, call Zenith.  You need the  

 number???


	


-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

tonyplane(at)bellsouth.ne
Guest

Posted: Fri Apr 17, 2009 8:32 pm Post subject: Thoughts regarding Flutter

Additional thoughts, Scott  

  

 Sounds reasonable.  I thought about replacing  cables with push rods, but then thought that the natural freq of a rod would  probably be lower than a tensioned cable and more likely to  resonate.

  

 Today as I was up enjoying the sky in my XL, I  crossed mid-field and broke to down wind and it reminded my of another  reconstructed crash at the crash lab at March AFB during a course I took in  Aircraft Accident Investigation at USC thirty years ago.

 It was an AeroCommander Twin that shed its  wings.  

  

 The physical investigator instructor, (who was  also my undergraduate instructor in Rotary Wing Aerodynamics years prior)  related that he was requested to investigate the wing failure of another Twin  Commander, I believe that occurred in Co.  If I recall correctly, the  Commander made a mid-field crossing and broke to down wind and had a wing  structural failure which was attributed to pilot error causing the  overload.  The instructor related that there were also other  Commanders that had had the same failure.

  

 What he discovered (and I have the plot somewhere  in my class notes, buried ?) was that the stick forces per G went NEGATIVE  at about 4 Gs.  Imagine the yoke coming back in your lap and the wing  fails due to overload, if above Va. (There was an AD issued to require a weight  in the control system to pull the stick under G loading (bob  weights have been  used in many aircraft control  systems).

  

 The reason I bring this up is that I still believe  the XL light stick forces can easily result excessive G loading and are quite  possibly the REAL reason for the wing failures.  Not that light stick  forces are bad, but one has to not be ham fisted above Va. (I previously related  giving an older pilot a ride in my XL during a pretty turbulent day and he  pushed the stick rapidly nose down such that I would have gone through the  canopy without a seat belt.  This happened during climb out  at about  80 - 90kts and the gusty conditions had caused a pitch up.(still can not believe  another pilot would have done that, but possibly his Tomahawk had a much  different elevator response).  

  

 Somehow, some people jumped on the flutter  bandwagon, and as another matronics "inputer" stated - "and so it  was"

  

 What really concerns me is that the NTSB might wish  to make a "Science Project" (Note) over additional flutter testing of the  XL. They evidently do not wish to accept the successful flutter tests  already done by Zenith (see page 6 of the NTSB  report).                                                                 

                                                          Note: 

                A Science Project is where you spend all of your resources but never come  up with a result that is acceptable to the government because additional tests  or analytical parameters are ALWAYS required. ("You only tested (or  modeled) down to -40F.  We require additional testing at -65F  .....and on ....and on ..and ..............").  

  

 Tony Graziano

 Buchanan, Tn

 XL/Jab; N493TG; 483 really great hours in my  XL

  

  

  

 ---

jaybannist(at)cs.com
Guest

Posted: Sat Apr 18, 2009 6:01 am Post subject: Thoughts regarding Flutter

Tony,

 

 I happen to agree with you.  I also think that the elevator is a more likely source of trouble than the ailerons.  Even though the XL that I flew didn't seem to me to have an overly sensitive elevator, I have read and heard comments that indicates that it is troublesome to others. The NTSB letter goes into some detail about the elevator being progressively effective.  It is fairly well accepted that excessive elevator input can overstress an airframe. In the case of the XL accidents, a gross elevator movement could very well have overstressed the wings and made them fail.  The NTSB accident report of the Yuba accident speculated that the first thing to fail was the horizontal stabilizer, in a downward direction.  It seems to me that a max down elevator could have caused that. I did not see any mention of whether the Heintz recommended elevator stop had been added to this airplane. 

 

 This makes me wonder if adding progressive resistance to fore and aft movement of the stick might make sense to defeat the progressive effectiveness of the elevator, ie: bungees or springs. what do you think?

 

 Jay Bannister

 

   

 

   

 

 --

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Sat Apr 18, 2009 8:10 am Post subject: Thoughts regarding Flutter

Another thing to consider is that the CG of the 601XL shifts rearward  

as you burn off fuel. So If you make a long cross country flight in a  

heavily loaded XL, you may discover that the pitch sensitivity has  

increased significantly when it comes time to land. I have had this  

experience myself. I was a little surprised when the plane started to  

porpoise on short final. I realized what was happening and got it  

settled down fairly quickly, but it did get my attention. I sure am  

glad I spent the extra money for the confor-foam seats cushions. I can  

spend four hours in the plane without getting greatly fatigued.



I added a bungee cord to the elevator controls to assist with nose up  

trim. One of these days, I'm going to link it to the flap torque tube  

to provide some automatic trim adjustment with flap deployment.



On Apr 18, 2009, at 9:58 AM, jaybannist(at)cs.com wrote:



 	  Quote: 	
		   Tony,



 I happen to agree with you.  I also think that the elevator is a  

 more likely source of trouble than the ailerons.  Even though the XL  

 that I flew didn't seem to me to have an overly sensitive elevator,  

 I have read and heard comments that indicates that it is troublesome  

 to others. The NTSB letter goes into some detail about the elevator  

 being progressively effective.  It is fairly well accepted that  

 excessive elevator input can overstress an airframe. In the case of  

 the XL accidents, a gross elevator movement could very well have  

 overstressed the wings and made them fail.  The NTSB accident report  

 of the Yuba accident speculated that the first thing to fail was the  

 horizontal stabilizer, in a downward direction.  It seems to me that  

 a max down elevator could have caused that. I did not see any  

 mention of whether the Heintz recommended elevator stop had been  

 added to this airplane.



 This makes me wonder if adding progressive resistance to fore and  

 aft movement of the stick might make sense to defeat the progressive  

 effectiveness of the elevator, ie: bungees or springs. what do you  

 think?




	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

NYTerminat(at)aol.com
Guest

Posted: Sat Apr 18, 2009 10:23 am Post subject: Thoughts regarding Flutter

But weren't some of these accidents straight and level?

  

 Bob Spudis

  

  

  

  

 In a message dated 4/18/2009 12:10:49 P.M. Eastern Daylight Time,  bryanmmartin(at)comcast.net writes:

  	  Quote: 	
		  -->    Zenith601-List message posted by: Bryan Martin    <bryanmmartin(at)comcast.net>



Another thing to consider is that the    CG of the 601XL shifts rearward  

as you burn off fuel. So If you make    a long cross country flight in a  

heavily loaded XL, you may discover    that the pitch sensitivity has  

increased significantly when it comes    time to land. I have had this  

experience myself. I was a little    surprised when the plane started to  

porpoise on short final. I    realized what was happening and got it  

settled down fairly quickly,    but it did get my attention. I sure am  

glad I spent the extra money    for the confor-foam seats cushions. I can  

spend four hours in the    plane without getting greatly fatigued.



I added a bungee cord to the    elevator controls to assist with nose up  

trim. One of these days,    I'm going to link it to the flap torque tube  

to provide some    automatic trim adjustment with flap deployment.



On Apr 18, 2009, at    9:58 AM, jaybannist(at)cs.com wrote:



 	  Quote: 	
		   Tony,



 I happen    to agree with you.  I also think that the elevator is a  

    more likely source of trouble than the ailerons.  Even though the    XL  

 that I flew didn't seem to me to have an overly sensitive    elevator,  

 I have read and heard comments that indicates that it    is troublesome  

 to others. The NTSB letter goes into some detail    about the elevator  

 being progressively effective.  It is    fairly well accepted that  

 excessive elevator input can    overstress an airframe. In the case of  

 the XL accidents, a    gross elevator movement could very well have  

 overstressed the    wings and made them fail.  The NTSB accident report  

 of the    Yuba accident speculated that the first thing to fail was the  

    horizontal stabilizer, in a downward direction.  It seems to me    that  

 a max down elevator could have caused that. I did not see    any  

 mention of whether the Heintz recommended elevator stop had    been  

 added to this airplane.



 This makes me    wonder if adding progressive resistance to fore and  

 aft    movement of the stick might make sense to defeat the progressive     

 effectiveness of the elevator, ie: bungees or springs. what do    you  

 think?




	




-- 

Bryan Martin

N61BM, CH    601 XL,

RAM Subaru, Stratus redrive.

do not  ================================================[b]

	


 

  

 Access 350+ FREE radio stations anytime from anywhere on the web. Get the Radio Toolbar!

  [quote][b]

craig(at)craigandjean.com
Guest

Posted: Sat Apr 18, 2009 11:03 am Post subject: Thoughts regarding Flutter

 	  Quote: 	
		   One of these days, I'm going to link it to the flap torque tube to provide

some automatic trim adjustment with flap deployment.
	




There is a little box that does this (although you might consider it

overkill):



http://www.aircraftextras.com/



-- Craig

tonyplane(at)bellsouth.ne
Guest

Posted: Sat Apr 18, 2009 3:23 pm Post subject: Thoughts regarding Flutter

Jay,

  

 What commonly has been done is to add a  mass to the bottom of the stick assembly, usually Tungsten or depleted  Uranium to save space.  As you change the angle of the stick, the mass  tends to pull the stick relatively straight neutral and the more G loads  the more force exerted by the mass to center the stick relatively  neutral, ----    the more Gs pulled, the more force it takes  to hold back the stick; stick forces per G goes up.  I don't know if the  geometry of the XLs "stick configuration" would permit a mass  addition.

  

 The Yuba City with the stab failure in a down  direction indicates UP elevator.  Once the stab fails, the nose  pitches violently down, and the wing fails in a relatively down direction -  excessive negative Gs.  In a good design, it would be a toss up as to what  fails first under excessive G loading, the stab or the wing.  

  

 I believe the Yuba City wing failure speaks volumes  about an overstress condition caused by stick input

  

 Tony.

  

 ---

Charles3603

Joined: 15 Jun 2009
Posts: 2

Posted: Mon Jun 15, 2009 8:05 am Post subject: Re: Thoughts regarding Flutter

I think all of the problems are true. Airframe & Pilot.

I talked to a builder in Texas that told me that he was flying along, wisling 

dixie, made a accidental push on the stick and the plane re-acted and he re-acted. He went on to say that someone with limited flying experience would have over-reacted and killed themselves.  This plane is very responsive and fast...My suggestion to flutter is to place (2) springs in  

place to make all aileron surfaces return to (0) zero position or neutral. Smile

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