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Flutter Once Again
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s_thatcher(at)bellsouth.n
Guest

Posted: Wed Feb 13, 2008 5:47 am Post subject: Flutter Once Again

I know, it's been beat to death. But here is my last (hopefully) reflection 

on what caused the last WING flutter case in Forida several month ago.



As you may recall (search archives for flutter for an exhausting display of 

comments and suggestions), there were two 601XL's that experienced either 

flutter or severe torsional or vertical vibrations that appeared to be on 

the verge of destroying the aircraft, but were saved from that fate by luck 

or pilot intervention.



The last one that was reported was in Florida and after talking with the 

mechanic who was repairing the aircraft, this is what happened.



During a descending turn to the right, the entire aircraft began to shake 

violently at which time the aircraft was landed at the nearest airport and 

inspected (no information was provided on how they stopped the vibrations). 

Damage was noted to the flap bearing material that showed the nylon had 

severe elongations in and around the pinion of the flap actuator. The rudder 

had severe damage.



So what caused the "flutter" to occur?



It appears that a previous hangar accident caused one of the ribs in the 

rudder to be bent. The owners then repaired the rib and purchased new skin 

to replace the damage. To strengthen the rib, either wood or metal (I don't 

remember which) was used as a doubler on the rear portion of the rib.



It is thought that the addition of the doubler to the rib affected the mass 

balance of the flying rudder, thus directly contributing to the flutter 

condition (in the tail)! This was then transferred to the wings and appeared 

to be coming from them. It was also thought that the pilot may have 

contributed to the "flutter" by exacerbating the situation in an attempt to 

stop the "flutter."



So, it appears that as long as we follow the construction methods outlined 

by Zenith, we should not have any problems. If you deviate from the plans, 

be sure you know the consequences of your actions. Even the slightest change 

can cost you your life... especially when they occur on control surfaces. 

Always call Zenith. They always will provide you with the help and expertise 

you need to make that repair.



I am in no way faulting the pilot in Lantana for the repair work or actions 

during the flight. Sometimes our reactions are just that and none of us are 

immune from making similar mistakes. But hopefully, we all can learn from 

those mistakes.



Scott Thatcher, Palm Beach Gardens, FL

601XL with Corvair, Registered as E-LSA

N601EL

daveaustin2(at)primus.ca
Guest

Posted: Wed Feb 13, 2008 6:42 am Post subject: Flutter Once Again

Scott's information on the possible cause of flutter in the 601 from Florida 

pushes me to detail a rudder flutter that I experienced back some 11 years 

ago which Don Chapman can attest to.  The a/c is a trike.

Flying straight and level with some air induced bumps of low level, the a/c 

started to vibrate at a very low frequency, maybe twice a second.  I'd 

describe this vibration as very concerning but not panic inducing.  I 

immediately reduced power, to no effect, raised the nose to reduce speed, to 

no effect.  Then realized it was the rudder fluttering.  So I pushed hard on 

the rudder pedals in an attempt to tighten the control cables and this 

stopped the vibration.

On ground checking found that the rudder cables were too loose.  Long 

brainstorming came to the conclusion that I had adjusted the cable tension 

with the nosewheel on the ground taking weight and had allowed too much 

slack for when the wheel was unladen when flying.  That 80 degree angled 

firewall could kill you.

I jacked the nosewheel off the ground and set the cable tension to spec in 

flying position and have never had the problem re-occur.

FWIW.

Dave Austin  601HDS - 912, Spitfire Mk VIII

Jeyoung65(at)aol.com
Guest

Posted: Wed Feb 13, 2008 7:37 am Post subject: Flutter Once Again

Dave, what cable tension did you use. I am building a 601HD and do not  recall any cable tension called out. This sounds like a good idea for setting  the tension.  Jerry of GA

  

  

  In a message dated 2/13/2008 9:43:54 A.M. Eastern Standard Time,  daveaustin2(at)primus.ca writes:

  	  Quote: 	
		  -->    Zenith-List message posted by: "Dave Austin"    <daveaustin2(at)primus.ca>



Scott's information on the possible cause    of flutter in the 601 from Florida 

pushes me to detail a rudder flutter    that I experienced back some 11 years 

ago which Don Chapman can attest    to.  The a/c is a trike.

Flying straight and level with some air    induced bumps of low level, the a/c 

started to vibrate at a very low    frequency, maybe twice a second.   

	




The year's hottest artists on the red carpet at the Grammy Awards.  AOL Music takes you there.

  [quote][b]

steerr(at)bellsouth.net
Guest

Posted: Wed Feb 13, 2008 7:56 am Post subject: Flutter Once Again

I didn't save the original post, so don't have the exact wording, 

but...  Since the firewall is slanted back, the cable tension will be 

less when the plane is on the ground and the nose gear is compressed, 

won't it?  With the plane in the air, and the nose gear at the bottom 

stop (i.e., the steering rod attachment points, and therefore the rudder 

pedals, more forward), the cable tension should be higher.



Am I missing something?



Bill

Jeyoung65(at)aol.com wrote:

 	  Quote: 	
		   Dave, what cable tension did you use. I am building a 601HD and do not 

 recall any cable tension called out. This sounds like a good idea for 

 setting the tension.  Jerry of GA

  

  

 In a message dated 2/13/2008 9:43:54 A.M. Eastern Standard Time, 

 daveaustin2(at)primus.ca writes:



     

     <daveaustin2(at)primus.ca>



     Scott's information on the possible cause of flutter in the 601

     from Florida

     pushes me to detail a rudder flutter that I experienced back some

     11 years

     ago which Don Chapman can attest to.  The a/c is a trike.

     Flying straight and level with some air induced bumps of low

     level, the a/c

     started to vibrate at a very low frequency, maybe twice a second.

daveaustin2(at)primus.ca
Guest

Posted: Wed Feb 13, 2008 9:48 am Post subject: Flutter Once Again

Bill, you are correct.  But I recognized that and decided to leave some 

slack with the nosewheel on the ground so that the cables would not be too 

tight in flight mode.  I gave a bit too much allowance.  Hence the advice.. 

adjust the tension with the nosewheel off the ground.

Dave Austin  601HDS - 912, Spitfire Mk VIII

amyvega2005(at)earthlink.
Guest

Posted: Wed Feb 13, 2008 9:55 am Post subject: Flutter Once Again

Bill,

the tension is not impacted whether on land or air, since you have control rods, (a solid itme) from rudder pedals though the fir walll the Nose whell.   Stiff rudder cables are not as a concern as the Aileron and Elevator cables, which would be around 30 #.  or 4 Inch #.

Tight enough to not bind the movement and still be smooth.

Juan



--

daveaustin2(at)primus.ca
Guest

Posted: Wed Feb 13, 2008 10:04 am Post subject: Flutter Once Again

Jerry,

 It was a long time ago and I cannot find the specs  for cable tension.  I would say however, that I would not tighten to the 30  to 40 lbs as given for the elevators and ailerons as in another msg on  this.  If I recall I used "just snug".  Very scientific!

 Dave Austin  601HDS - 912, Spitfire Mk  VIII

    [quote][b]

steerr(at)bellsouth.net
Guest

Posted: Wed Feb 13, 2008 10:14 am Post subject: Flutter Once Again

Ok, I'm with you.  Thanks.



Bill



do not archive

Dave Austin wrote:

 	  Quote: 	
		   



 Bill, you are correct.  But I recognized that and decided to leave 

 some slack with the nosewheel on the ground so that the cables would 

 not be too tight in flight mode.  I gave a bit too much allowance.  

 Hence the advice.. adjust the tension with the nosewheel off the ground.

 Dave Austin  601HDS - 912, Spitfire Mk VIII

steerr(at)bellsouth.net
Guest

Posted: Wed Feb 13, 2008 10:26 am Post subject: Flutter Once Again

I respectfully disagree with your first sentence.  It is PRECISELY 

because there are solid rods between the rudder pedals and the nose gear 

that the tension varies as the nose gear moves vertically.  Note that, 

due to the angle of the firewall, it isn't pure vertical movement; it 

also moves horizontally.  When the nose gear is at the bottom stop, the 

rod attachment points are farthest forward and thus the rudder pedals 

are farthest forward, thereby pulling harder on the rudder cables.  When 

the nose gear is off the bottom stop, as when it is on the ground, the 

rod attachment points move back, thereby causing the rudder pedals to 

move back, thereby causing less tension in the rudder cables.



Bill

Juan Vega wrote:

 	  Quote: 	
		   



 Bill,

 the tension is not impacted whether on land or air, since you have control rods, (a solid itme) from rudder pedals though the fir walll the Nose whell.   Stiff rudder cables are not as a concern as the Aileron and Elevator cables, which would be around 30 #.  or 4 Inch #.

tjs22t(at)verizon.net
Guest

Posted: Wed Feb 13, 2008 11:16 am Post subject: Flutter Once Again

>the tension is not impacted whether on land or  air, since you have control rods, (a solid item) from rudder pedals though the  fire wall the nose wheel.   

  

 +++ Beg to  differ.  When the nose gear compresses on the ground, the steering rods  move backward very, very slightly (~13 degree slant of firewall).  As  they are a solid link as you pointed out, the rudder pedals will also move  rearward a bit.  Since the cables to rudder are mounted to the pedal tops,  a minor lessening of tension in the cables will result.  The "tension"  (distance) between the pedals and nose gear will not change as it's a fixed arm,  the distance/arm between the pedals and rudder horn will change as nose gear  extends, as in flight, or compresses, as on the ground.

  

 >that I would not tighten to the 30 to 40 lbs as  given 

 	  Quote: 	
		  for the elevators and ailerons as in another msg on  this.

  
	


 Dave, the cable  tension from page 29 of our old Construction Manual is for all control  surfaces, not just aileron and elevator.  I went to the manual and checked  - I would not make the statement if it were not factual.  As you said,  "It was a long time ago and I cannot find the  specs for cable tension."  If it's true that Chris said  25 to 30 pounds then that should be good enough for those who have access to a  tensionometer.

  

  

 Respectfully 

 Jeff  Small    HDS/3300

    [quote][b]

amyvega2005(at)earthlink.
Guest

Posted: Wed Feb 13, 2008 1:11 pm Post subject: Flutter Once Again

Bill,

 I respect your position, though I think you are over thinking it. question though, when is flutter appraent, when in the air or land, or during the transition? set the tension so as not to impede motion, thats it.  Secondly if the rods go through their full movement, then someone is landing way to hard. We are not building x-15 rocket ships here,  set it to feel solid, but not to impede movement, if that does not help, sorry.



Juan



--

planejim(at)bellsouth.net
Guest

Posted: Wed Feb 13, 2008 2:14 pm Post subject: Flutter Once Again

Hey Listers,



When building my 601HD 12 years ago I asked ZAC about this same perceived 

problem ( rudder cable tension changes as nose gear moves up and down). At 

that time Nick stated that it had not been reported as a problem. It turns 

out that then cable tension lessens upon landing when the gear goes up and 

aft. In reality the gear doesn't move all that much as seen by the marking 

on the grease on the gear. I set my cable tension for "in flight" when the 

gear is at the bottom of it's travel. I used about 20 to 25 lbs. tension.



No problem over the past 575 hours.



Rudder flutter could be serious and perhaps "loose" cables, along with 

"unbalanded" rudder could lead to it. The "all flying" rudder on the Zenith 

may be different. I'm not a engineer so I don't know.



I just know that I've had no problem with  my 601HD.



do not archive



Jim Hoak

---

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Wed Feb 13, 2008 3:23 pm Post subject: Flutter Once Again

As long as you build your plane with no "slop" in the controls, you  

are not going to see any signs of flutter in a Zenith airplane within  

the designed speed limits unless you've deviated from the design in a  

MAJOR way. I have test flown my Zodiac to 200 MPH IAS during the phase  

I test period with no evidence of flutter. I didn't calculate the TAS  

for that flight but it was probably close to 210 MPH. Based on my test  

flights, I felt confident setting my Vne at 180 MPH as per the info I  

got from ZAC. I just tightened my turnbuckles until the cables felt  

snug with no slack and called it good.

On Feb 13, 2008, at 5:09 PM, Jim Hoak wrote:



 	  Quote: 	
		   



 Hey Listers,



 When building my 601HD 12 years ago I asked ZAC about this same  

 perceived problem ( rudder cable tension changes as nose gear moves  

 up and down). At that time Nick stated that it had not been reported  

 as a problem. It turns out that then cable tension lessens upon  

 landing when the gear goes up and aft. In reality the gear doesn't  

 move all that much as seen by the marking on the grease on the gear.  

 I set my cable tension for "in flight" when the gear is at the  

 bottom of it's travel. I used about 20 to 25 lbs. tension.



 No problem over the past 575 hours.



 Rudder flutter could be serious and perhaps "loose" cables, along  

 with "unbalanded" rudder could lead to it. The "all flying" rudder  

 on the Zenith may be different. I'm not a engineer so I don't know.



 I just know that I've had no problem with  my 601HD.




	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

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

Tim Juhl

Joined: 21 Mar 2006
Posts: 488
Location: "Thumb" of Michigan

Posted: Wed Feb 13, 2008 5:31 pm Post subject: Re: Flutter Once Again

Scott,

Thanks for bringing us up to date with the FL flutter incident.  I was wondering what was discovered.



I found it interesting that the holes on the nylon bearings in the flaps were elongated.  When I built my flaps I was a little concerned that they were only backed up  by the thin material of the rib so I added a doubler made of 0.040 to the inside of the rib. Whether doing so was a good idea remains to be seen.



Tim

_________________
______________
CFII
Champ L16A flying
Zodiac XL - Jabiru 3300A
Almost done! It'll fly in spring!

jmcburney(at)pobox.com
Guest

Posted: Thu Feb 14, 2008 8:22 am Post subject: Flutter Once Again

Greetings, all,



When tensioning cables using the "scientific" "just snug" method, be very

careful.  Loose cables are easy to see, but when you get the tension in, the

cables don't SEEM to get very tight, because the "give" of the structure

begins to come into play.  A tensionometer is recommended, but if that's not

possible (Yeah, they're $$$$$), always approach the tension from the slack

side, in small steps, till JUST snug.

Re: rudder cables loosening when weight is on the nosewheel; in the 801 they

get VERY slack as the nosewheel retracts, so they must be set with it fully

extended.  Zenith says this isn't a problem, though, as the bungee should

keep the nosewheel extended except during a bad pitchdown after landing or

when hitting a hard bump when taxiing.  My experience flying the Zenith demo

bears this out.



Blue skies and tailwinds



Jim

CH-801

DeltaHawk diesel

Augusta GA

90% done, 90% left

craig(at)craigandjean.com
Guest

Posted: Thu Feb 14, 2008 8:56 am Post subject: Flutter Once Again

When you tension your cables don't forget Larry McFarland's cheap tension

gauge. Go to http://www.macsmachine.com/ and click on "Tools, Jigging &

Handling" in the left column. Then choose "Cable Tools".



Here is a good overall shot:

http://www.macsmachine.com/images/tjh/cabletools/full/tenscalbrate.gif



-- Craig



--

Gig Giacona

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

Posted: Thu Feb 14, 2008 9:37 am Post subject: Re: Flutter Once Again

Maybe I'm missing something but how would you get all that into the areas where the cable was located?



 	  craig(at)craigandjean.com wrote: 	
		  When you tension your cables don't forget Larry McFarland's cheap tension

gauge. Go to http://www.macsmachine.com/ and click on "Tools, Jigging &

Handling" in the left column. Then choose "Cable Tools".



Here is a good overall shot:

http://www.macsmachine.com/images/tjh/cabletools/full/tenscalbrate.gif



-- Craig



--

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

steerr(at)bellsouth.net
Guest

Posted: Thu Feb 14, 2008 9:55 am Post subject: Flutter Once Again

That was his calibration rig.  The tool itself is fairly small, shown at 

the top, with the three rollers.  Take a look at his web site.



Bill

Gig Giacona wrote:

 	  Quote: 	
		   



 Maybe I'm missing something but how would you get all that into the areas where the cable was located?

craig(at)craigandjean.com
Guest

Posted: Thu Feb 14, 2008 11:37 am Post subject: Flutter Once Again

That is the gauge in the calibration jig. The little device with the three

pulleys is the actual gauge. Navigate Larry's site to see the individual

pieces.



-- Craig



--

Gig Giacona

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

Posted: Thu Feb 14, 2008 12:34 pm Post subject: Re: Flutter Once Again

Oh OK. Never mind.

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

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