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Flutter Experience

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Terry Phillips

Joined: 11 Jan 2006
Posts: 346
Location: Corvallis, MT

Posted: Sat Jul 05, 2008 8:06 am Post subject: Flutter Experience

With Tom Mim's permission and much trepidation I'm posting an email that I received from Tom describing his experience with flutter in his 601XL. Bill of Georgia has also posted his experience with flutter while passing over an electric plant. My goal is to find out how rare (or prevalent) the occurrence of flutter is in 601XL's. Those are the only two instances of flutter that I recall reading about. If you have experienced flutter in your 601XL, I would very much appreciate receiving as complete a description as possible:   Flight conditions, IAS, altitude, temperature, maneuvers  
Total hours on your aircraft at the time of the incident  
Flight maneuvers taken in response to flutter and the effect, if any, on the flutter 
Any subsequent changes or modifications done to your aircraft to eliminate the flutter  Please respond on- or off-line as you prefer. My goal is just to collect information here, not to start a flame-war. To reach the widest possible audience, I am posting this on both the Zenith-List and the ZBAG forum. Thank you for sharing your experience.

 Terry

  	  Quote: 	
		  >At 02:42 PM 5/9/2008 -0700, Tom wrote:

 >>My KitLog E-mail From: mimsdsl(at)dnet.net

 >>

 >> ... 

 >>

 >>Tom Mims

 >>

 >>P.S. Had wing flutter 2x, Tightened aileron cables, added flap stops, no 

 >>more flutter.  Still worried! 	

 At 06:29 PM 5/15/2008 -0400, Tom wrote:

  	  Quote: 	
		  Terry,

 No objection to sending my email to the list. I read it, just havent't taken the time to figure out how to send messages to it. So far my few attempts have failed. I'm a cumputer dummy.  

 Straight snd level 110 KIAS experienced wing vibration or flutter that seemed to be building or intensifying. Can't be too sure about that though because I reacted quickly by reducing throttle and simultainiously turning left and pulling up (to reduce airspeed.) Flutter stopped immediately w/ the climbing turn and reduced speed.  A repeat test duplicated the experienc at 105 to 110 KIAS. I repeated the same maneuver with the same results.  I wish I could remember for sure, but the Stick may have fluttered ,too. Damn, the whole plane was shaking!  

 On the ground a friend was sure it was because of too much slop in the ailerons - Cables were too loose.

 Another kit builder pointed out that that I had omited the flap stops.

 Both of these problems were corrected. (And I reverseed the main gear because of nose heavy landings.)

 Next test flight, no flutter at all. ZIP, NADA, Couldn't make it do it no matter how fast I went. 120 KIAS was all that I dared to do, though.  

 I'm fairly sure it was the aileron cable slop that was the real cause of the problem.

 The vibration was fairly violent. If allowed to build, I beleive it could easily destroy the center spar carry-through.

 We all know where that would end up.

 I'v downloaded release form. will send $. Sure hope we can nail this thing down.  Thanx for your help.

 Tom Mims N601T

 >

 > 	

 Terry Phillips  ZBAGer

 ttp44~at~rkymtn.net

 Corvallis MT

 601XL/Jab 3300 s .. l .. o .. o .. w build kit - Tail, flaps, & ailerons are done; working on the wings

 http://www.mykitlog.com/N47TP/     [quote][b]

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_________________
Terry Phillips
Corvallis, MT
ttp44<at>rkymtn.net
Zenith 601XL/Jab 3300 slow build kit - Tail feathers done; working on the wings.

Ron Lendon

Joined: 10 Jan 2006
Posts: 685
Location: Clinton Twp., MI

Posted: Sun Jul 06, 2008 4:34 pm Post subject: Re: Flutter Experience

Terry,



I think you might want to know what the cable tensions and hinge play are also.

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_________________
Ron Lendon
WW Corvair with Roy's Garage 5th bearing
CH 601 XLB
N601LT - Flying
http://www.mykitlog.com/rlendon
Corvair Engine Prints:
https://sites.google.com/site/corvairenginedata/

Terry Phillips

Joined: 11 Jan 2006
Posts: 346
Location: Corvallis, MT

Posted: Mon Jul 07, 2008 7:20 pm Post subject: Flutter Experience

Good points, Ron. It may be moot, however, because, so far, no one else has 

come forward who encountered flutter in their 601XL. That suggests that 

flutter may be a very uncommon occurrence--which is good news.



I wanted to post Tom's experience, because I thought there was a lesson 

there for all 601 flyers--check your cable tension regularly. Thank God he 

was  able to get back down to pass along his freshly acquired wisdom.



I have a question--what is "hinge play." And, that brings to mind another 

variable that I should have asked for--piano or flex hinge?



Thanks for the thoughts.



Terry



do not archive



At 05:34 PM 7/6/2008 -0700, you wrote:

 	  Quote: 	
		  Terry,



I think you might want to know what the cable tensions and hinge play are 

also.



--------

Ron Lendon, Clinton Township, MI

Corvair Zodiac XL, ScrapBuilder 


	




Terry Phillips  ZBAGer

ttp44~at~rkymtn.net

Corvallis MT

601XL/Jab 3300 s .. l .. o .. o .. w build kit - Tail, flaps, & ailerons 

are done; working on the wings

http://www.mykitlog.com/N47TP/

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_________________
Terry Phillips
Corvallis, MT
ttp44<at>rkymtn.net
Zenith 601XL/Jab 3300 slow build kit - Tail feathers done; working on the wings.

psm(at)att.net
Guest

Posted: Mon Jul 07, 2008 8:19 pm Post subject: Flutter Experience

Hi Terry,



I think you are selling yourself short a little.  There were two 

really important lessons shown by your story.  The first and most 

obvious one was the story about watching aileron cable tension and 

making sure it is not too slack.



The more interesting lesson was about how to deal with an event when 

the plane starts vibrating like mad.  In your story and in Bill of 

Georgia's story the solution was to do a radical banking 

maneuver.  This makes sense when coupled with the new information 

that the aileron cable tension was loose.  By performing a steep bank 

the tension on one of the ailerons was increased and the vibration 

stopped.  I suspect if the first bank doesn't stop the vibration then 

banking in the other direction will do it.  This makes a great 

"Emergency Procedure" for all XL pilots to perform if they ever get 

into the heavy vibration situation.



I remember reading at least two different accident reports involving 

in-flight structure failure where witnesses heard repeated changes in 

engine speed.  I am guessing these unfortunate pilots experienced the 

aileron vibration and mistakenly guessed it was the engine that was 

stimulating the vibration.  They then moved the throttle in and out 

several times to try to break the vibration.  I just can't think of 

any other explanation for the radical engine noise changes reported 

by the witnesses.



I really appreciate your post of this story.  I am hopeful you have 

found the actual "Smoking Gun" behind the problems.



Paul

XL nearly done



At 08:16 PM 7/7/2008, you wrote:



 	  Quote: 	
		  I wanted to post Tom's experience, because I thought there was a 

lesson there for all 601 flyers--check your cable tension regularly. 

Thank God he was  able to get back down to pass along his freshly 

acquired wisdom.

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klaus(at)utdallas.edu
Guest

Posted: Tue Jul 08, 2008 7:00 am Post subject: Flutter experience

Hi,



A short time ago Philip Welsch told me about a flutter

incidence in his 601XL. He stopped it by reducing power

and pulling up. When I looked at the aileron cables

recently, they seemed properly tensioned.



Happy flying,



Klaus

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