[NSRCA-discussion] Elevator trim change

[DaveL322 at comcast.net]

The vinyl coated kevlar (kevcord) from ACP is great stuff - and I've never experienced stretching with it - the cables do have a break-in period on new planes - it is the vinyl jacket crushing, the knots tightening (or crimps settling into the cable) - but that can happen with any cable system.

I've had several planes hit 1,000+ flights with my own versions of the DEPs system (which I've been using in various forms since 1988) and no pushrod maintenance was required at any time.  Weight is minimal when integrated with the airframe structure from the beginning.  I think Hebert and Harrison could share similar experiences (as well as a few others, including Troy).  The COE is an issue, but it is very consistent and predictable, and only an issue with rather substantial temp changes.

Regards,

Dave Lockhart
DaveL322 at comcast.net

-------------- Original message -------------- 
From: "Nat Penton" <natpenton at centurytel.net> 

George I agree with your comments with one exception. The Sullivan controll line kevlar is the best of all worlds for our hookups. There is no stretch, no weight, no electromagnetic problems. It is unidirectional with, probably, a low COE like carbon.
----- Original Message ----- 
From: george w. kennie 
To: NSRCA Mailing List 
Sent: Tuesday, May 09, 2006 12:50 PM
Subject: Re: [NSRCA-discussion] Elevator trim change


Sorry Guys, I have some thoughts and opinions on this that are based upon my own logic, however flawed,and which may or may not coincide with someone else's logic.

Anytime you have a control system that is based on a system that incorporates an oscillatory motion (fore/aft up/dn) the ultimate result of this motion will generate wear somewhere within the system and wear translates to slop.

I think my contention would be that Lance had it right in the first place and was ill-advised by some well intentioned souls who may have had what they assumed to be good results, but failed to base their conclusions on really long-term experience(who really knows for sure?)

I have long felt that pull-pull cables (vinyl-coated steel) present the most reliable connection for the elevator and rudder inputs.They do not require that the horns be expensive ball-bearing units, they are the lightest by far and due to the fact that they are always under tension the generated wear manifests itself against only one wear surface instead of the two in the push-pull set-up. If the installation can be modified in such a way that the servo can be mounted just ahead of the stab the COE of the fuse can be rendered virtually inaffective. 

With time, you may experience some slight lessening in cable tension (very slight) which can quickly be rectified by disconnecting the clevis and spinning the eye a half turn at each connection.

I have used Kevlar thread and continue to do so, but not on two-meter projects.Kevlar stretches for quite a period of time before settling to it's final length.

Just my $.02
G. 





----- Original Message ----- 
From: Lance Van Nostrand 
To: NSRCA Mailing List 
Sent: Monday, May 08, 2006 8:55 PM
Subject: Re: [NSRCA-discussion] Elevator trim change


This rots.  I've used pull pull forever and switched to the deps system due to heavy promotion by Mike Harrison and Bryan Hebert.  They say it will be more precise.  Can anyone corroborate this?  I'd hate to switch to a system that has more downside than upside.
--Lance
----- Original Message ----- 
From: Gray E Fowler 
To: NSRCA Mailing List 
Sent: Monday, May 08, 2006 10:51 AM
Subject: Re: [NSRCA-discussion] Elevator trim change



Fiberglass laminate CTE = 6 X10 -6/in/in/F 

CF pushrod CTE = 1 X 10 -6 /in/in/F  ....could actually be 0 if fiber vloume is > 58% an all uni fibers 






Gray Fowler
Principal Chemical Engineer
Composites Engineering 



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