Rudder cables without levers and pulleys

[Chris Fox]

Hello everyone, my first post here. I've recently picked up a fairly complete Long Ez, with strakes as the next task.

Forward brake master cylinders have been fitted, so the lever/pulley rudder controls due to be fitted on the firewall seem over complicated.

I am hoping to route the nylaflow conduit in pretty much a straight line from the rudder pedals to just beyond the fuel tank blister, then a gentle curve through the fuselage/under the spar to then align with the rear face of the spar and aim towards the wing conduit. Extending the contour back from the blister to fair it in smoothly.

Has anyone got experience doing this, and does it seem sensible?

Regards,

Chris

[Marc Zeitlin]

1 hour ago, Chris Fox said:

I am hoping to route the nylaflow conduit in pretty much a straight line from the rudder pedals to just beyond the fuel tank blister, then a gentle curve through the fuselage/under the spar to then align with the rear face of the spar and aim towards the wing conduit. Extending the contour back from the blister to fair it in smoothly.

Has anyone got experience doing this, and does it seem sensible?

Folks have done similar installs with either nylaflow or AL tubing. It can work, but there are a couple of possible issues, one of which I've seen multiple times.

First, the SS cable will wear the tubing as it goes around the bend. How long with the tubing last? Hard to say. I suppose it depends on how much and how hard you use the rudders at speed. Nylaflow DOES wear - I've seen it worn through at the exit to the belhorn at the winglet, where it wears a groove in the nylaflow. But a totally enclosed tube is less prone to wear. AL will wear as well, but it might take 10 years or it might take 1000 years.

Secondly, and this is the issue I have seen, is that unless the tubing is extremely rigidly mounted where it passes through the firewall and where the SS cable exits to go to the wing, it will flex and you will lose rudder deflection motion. And the rigid mounts need to allow for tubing replacement in case of damage to either the cable or the tubing.

My $0.02.

[Chris Fox]

Hi Marc, thanks for the prompt reply!

Would you think using a PTFE liner to the nylaflow would help? Also, would an aluminium/stainless steel tube outer to form the bend and set the direction at the outboard firewall mitigate the second issue?

Cheers,

Chris

[Marc Zeitlin]

6 hours ago, Chris Fox said:

Would you think using a PTFE liner to the nylaflow would help? Also, would an aluminium/stainless steel tube outer to form the bend and set the direction at the outboard firewall mitigate the second issue?

Friction isn't the issue - wear is (or MIGHT be). If you can find something that doesn't get worn by SS cable (and in turn, doesn't wear the cable, which is just as bad), then that might be a good liner. Or you might be fine with a 20 year lifetime and a note in the logs that after 20 years, it's time to replace the cable and the guide. Don't know.

AL/SS tubing would still need to be fixed securely at both ends. One plane that I've worked on for the past 11 years has AL tubing as a guide, and every couple of years we've got to re-bend and secure it, as rudder throw continually gets lower and lower over time. Fix it well at both ends and this problem goes away.

[Chris Fox]

Thanks for the input Marc,

I'm hoping regular inspection and scheduled replacement of the conduit will work out less effort over the years than inspecting and lubricating elbows and pulleys. Plus it will leave less clutter on the firewall.

I'll look at keeping the ends firmly in place: the curved aluminium tube would be embedded in glass/foam, so shouldn't go anywhere, with a stainless tube stub exposed in the fire protected area behind the spar with a clamp at the end where the cable exits. Are rubber bellows a good idea at the exposed ends?

Cheers,

Chris

 

[Marc Zeitlin]

31 minutes ago, Chris Fox said:

I'm hoping regular inspection and scheduled replacement of the conduit will work out less effort over the years than inspecting and lubricating elbows and pulleys. Plus it will leave less clutter on the firewall.

Belcranks and pulleys take approximately zero maintenance. 15 seconds at the CI to make sure they're still attached, and never lubricated, since they have sealed bearings. The fact that people have installed these tubing guides does not imply that they were fixing a problem.

32 minutes ago, Chris Fox said:

I'll look at keeping the ends firmly in place: the curved aluminium tube would be embedded in glass/foam, so shouldn't go anywhere, with a stainless tube stub exposed in the fire protected area behind the spar with a clamp at the end where the cable exits. Are rubber bellows a good idea at the exposed ends?

Never seen them and can't imagine why they would be required.