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Cable tensions

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kenhaslett

Joined: 10 May 2010
Posts: 1
Location: Kilrush Ireland

Posted: Tue Sep 21, 2010 6:10 am Post subject: Cable tensions

Folks



I've just got my Bird back into the air after being grounded for nearly 2 years awaiting the 'powers that B' coming up with a fix. I'm on a european register.   I set the aileron and rudder cable tensions as per Zenair but am very unhappy with the result. The aircraft feels heavier than a C182. 



Before the upgrade my aileron cables were set at 12lbs and the aircraft could be controlled very easily using my index finger resting in the 'Y' of the control column. The aircraft had the same feel and response to that of a modern glider. Now I have to hold the control column in my hand and use a lot of force to make a turn. 



Same with the elevator. The trim is not as sensitive, not a bad thing, but once again requiring a lot more effort in comparison with the previous iteration. 



I'm worried that the tension is putting significant loadings on the aileron bushings, bellcrank and supporting ribs.



Anyone else found similar problems and have they found a way round it.



Any help would be appreciated



Ken

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mhubel

Joined: 05 Sep 2009
Posts: 141

Posted: Tue Sep 21, 2010 2:00 pm Post subject: Cable tensions

Ken,

     It would seem that from the flutter analysis that 12 pounds tension 

on the ailerons was determined to be near the edge of stability. As I 

remember, it was just inside the stability window but with little 

margin. Cable tensions that low may have contributed to some of the wing 

failures that caused so many problems. I would not go anywhere near 

there anymore.

     I have always had the tensions set to the current (post update) 

values so I can't say much about before and after but I can say that 

with a bit of lubrication on all contact points, I find the ailerons to 

have very low friction, nothing like a 172 "truck". I will say that 

before I added the lubrication, it was a bit sticky. If you haven't 

greased all points where cables rub on nylon and oiled the pins at the 

cable ends, you might find that doing so will help.

     I do find some friction in the rudder but that is probably from the 

tension of the bungy cord on the nose wheel, not a part of the update. 

The additional friction from the cable tension pulling on the nose 

assembly probably does make it worse. I have some ideas on how to reduce 

this but it is not so bad as to be a major problem in my case.



N708HU

Jabiru 3300

59 hours

On 09/21/2010 10:10 AM, kenhaslett wrote:

 	  Quote: 	
		   



 Folks



 I've just got my Bird back into the air after being grounded for nearly 2 years awaiting the 'powers that B' coming up with a fix. I'm on a european register.   I set the aileron and rudder cable tensions as per Zenair but am very unhappy with the result. The aircraft feels heavier than a C182.



 Before the upgrade my aileron cables were set at 12lbs and the aircraft could be controlled very easily using my index finger resting in the 'Y' of the control column. The aircraft had the same feel and response to that of a modern glider. Now I have to hold the control column in my hand and use a lot of force to make a turn.



 Same with the elevator. The trim is not as sensitive, not a bad thing, but once again requiring a lot more effort in comparison with the previous iteration.



 I'm worried that the tension is putting significant loadings on the aileron bushings, bellcrank and supporting ribs.



 Anyone else found similar problems and have they found a way round it.



 Any help would be appreciated



 Ken





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=313205#313205




	


-- 

Mark Hubelbank

NorthEast Monitoring

2 Clock Tower Place

Suite 555

Maynard, MA, 01754 - USA

mhubel(at)nemon.com

978-443-3955

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_________________
Mark Hubelbank
N708HU
CH601XL
Jabiru 3300
Rotec TBI 40-3 carb
Sensenich ground adj prop.
240 hr TAF
Pictures at photo.hubbles.com

tigerrick(at)mindspring.c
Guest

Posted: Tue Sep 21, 2010 2:26 pm Post subject: Cable tensions

Hi, Mark and Ken,



Using the SWAG method, it sounds to me like Ken may have inadvertently set his tensions too high. I seem to recall that the nosewheel needs to be fully extended to get the rudder cable tensions right, but his issue is with aileron and elevator control response. I have no idea what equipment was used to set the tensions, but on my tensiometer, it's pretty easy to look at the wrong scale!



And in my conversations with the folks at Zenith after the German GVT, they said that they really had to work hard to induce flutter with aileron cable tensions below 5 lbs - and this is without any counterweights.



My advice to Ken would be to confirm the accuracy of his tensiometer, make sure he's using the 1/8 cable scale, raise the nosewheel off of the deck when checking tensions, and try somewhere between 20 to 25 pounds. This is what has served us well on several Zenith 601s, and it shouldn't be a risky proposition assuming he's gone ahead and installed the aileron balance weights.



Having the right tensions still shouldn't result in controls that are hard to move.



Just my humble opinion. YMMV.



Rick Lindstrom

First Light Aviation Grp.

Home of CC#18!



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larry(at)macsmachine.com
Guest

Posted: Tue Sep 21, 2010 3:47 pm Post subject: Cable tensions

Ken,

I use 15 to 25 lbs max cable tension and have never  had a problem with loss

of tension as result. I also think you do damage to the light pivot points

when you overload them. 

Flutter is not the problem and never has been.  If you go much tighter, the

cables will perpetually be undoing tension. 



Larry McFarland 601HDS at www.macsmachine.com



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