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Throttle Cable Friction

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DaveG601XL

Joined: 27 Oct 2006
Posts: 351
Location: Cincinnati, Oh

Posted: Thu Jan 31, 2008 11:50 am Post subject: Throttle Cable Friction

I am installing the Jabiru dual throttle system in my 601XL and am trying to work some of the friction out of the system.  Most of the friction is in the solid wire Aircraft Spruce throttles as there are a few bends in the system.   Is there any lubricant that someone can recommend for this push-pull cable application?



Thanks,

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_________________
David Gallagher
Cincinnati, OH area

victorbravo(at)sbcglobal.
Guest

Posted: Thu Jan 31, 2008 1:18 pm Post subject: Throttle Cable Friction

Sorry for the dictatorial rant, but please read this: As I posted 

recently, we lost a 601XL recently from our EAA chapter on the first 

flight. It was sheer luck that the guy walked away. There is a high 

probability that the throttle linkage bent, or "over-centered" or had a 

friction problem or did not overcome the spring on the engine, or 

something of some sort... which caused the engine room to not answer the 

phone when the pilot needed it most.



A quick answer to your throttle friction problem is the use of a flex 

cable instead of a solid wire. This will usually resolve a lot of 

friction issues. BUT you have to be triple-careful, because a flex cable 

will not stay as rigid in compression (pushing) as a wire.



The problem is that too little stiffness in the pushrod causes one 

problem, and too much stiffness causes another. The flex cable is 

fantastic in push and pull when it is inside the outer sheath, but gets 

weak in pushing after it leaves the sheath. Add to this the fact you 

MUST have some "cushion" in the system, meaning that the pushrod system  

has to have at least 10% more free movement than is required by full 

movement of the (carburetor / air control / fuel injection servo / 

engine control arm) that the pushrod is moving.



The bottom line is that you have to play around with your engine 

controls a LOT, make absolutely sure there is no binding or 

over-centering or weakness against a spring, etc., make DAMN sure you 

have that 10% or better cushion, and then you have to TEST it out 

operationally before it flies. Again, sorry for the oppressive tone 

here, but I'm probably saving someone's life.



Have someone sit in the cockpit and operate the throttle while you move 

and bend and pull on every part of it from the instrument panel to the 

engine. You are TRYING to create a failure, or sticking, or binding, or 

over-centering. Hold the throttle arm on the engine and try to RESIST 

the movement of the lever in the cockpit. Pull the pushrod in all 

directions to see if you can make it stick. Hold the engine control 

against and with the throttle movement. Twist and kink the pushrod 

anywhere it can be moved and see what that does. You will probably find 

that you want to tie the pushrod in more places inside the engine 

compartment, and you will probably see that one or more rigid supported 

"stand-off" parts are very well advised.



This test of having someone in the cockpit moving the controls and you 

trying to prevent the controls from working is also necessary on every 

other type of control, like the elevator, ailerons, rudder, steering, 

flaps, canopy/doors, etc. This is life and death stuff here, folks, pay 

attention.



Also, FORGET about using those wonderful little plastic wire ties to 

hold everything on the engine. They can melt, they can crack and they 

can get a little loose over time. Any flight critical tiedown inside the 

engine compartment should be done with an Adel clamp (aircraft loop 

clamp) or good old safety wire. Non-critical wiring and SOME of the 

spark plug leads, engine instrument wires and such... sure, the plastic 

ties are fine.



The Devil is in the details, as they say. These are the details in which 

the Devil hides in an airplane.



DaveG601XL wrote:

 	  Quote: 	
		   



 I am installing the Jabiru dual throttle system in my 601XL and am trying to work some of the friction out of the system.  Most of the friction is in the solid wire Aircraft Spruce throttles as there are a few bends in the system.   Is there any lubricant that someone can recommend for this push-pull cable application?



 Thanks,



 --------

 David Gallagher

 601 XL, tail &amp; wings completed and

 fueslage pretty well done. Working engine and electrical systems.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=161639#161639

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DaveG601XL

Joined: 27 Oct 2006
Posts: 351
Location: Cincinnati, Oh

Posted: Fri Feb 01, 2008 3:59 am Post subject: Re: Throttle Cable Friction

VictorBravo,



You cautions are duly noted.  Especially those about tie wraps.  I have a fair amount of firewall wiring in the vicinity of the throttle torque tube levers.  You are right in that these need to be secured by more than mere plastic straps.



Thanks,

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_________________
David Gallagher
Cincinnati, OH area

goodings(at)yorku.ca
Guest

Posted: Fri Feb 01, 2008 8:53 am Post subject: Throttle Cable Friction

The CHOKE cable on Rotax 912s (mine is a 912S) is notoriously stiff.  We

cured the problem with a product called "Rust-Check" which is sold in

Canada in Canadian Tire Stores.  I presume it is available also in the

U.S.  It is wonderful stuff: a very thin (red-coloured) oil that wicks its

way along the cable wire, frees it up and keeps it free.  We apply it

fairly regularly to the cable ends.  No more problems.



John Goodings, C-FGPJ, CH601HD with R912S, Carp/Ottawa, Toronto/Waterloo.

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