The International Cessna 170 Association

During this years annual I spent a lot of time running wires under the floor, and whilst laying underneath looking up at the cables I noticed a shinny mark on the RH brake pipe where it crosses the fuselage. I exercised all the controls and found that the elevator cable moved through an upward arc and at maximum aft control the cable touched the pipe. In fact it rested in the recess it made. The act of getting it to touch left some grease in place and made it much harder to spot. There was a rubber pipe over the aluminium but it stopped about one inch short.

When removed, the pipe appeared to be crudely made and had not seen a tube bender. I made a new pipe and changed the geometry so that the pipe sat higher away from the cable. The new pipe sat much nicer in place and there is now plenty of clearance. New rubber hose now protects against all cables.
The new pipe

Good catch!

One matter of which to be aware when designing/replacing pipes/hoses is to avoid upper bends/curves in which air bubbles may collect. A high bend or point (^)in the routing can allow air to congregate and make bleeding the brake line difficult.

Fuel lines have the opposite problem. A low-point (U)in a fuel line may allow water to settle and remain, resulting in difficulty to properly drain.

Did the cable suffer any damage?

Good one Kevin, thanks for showing us.

Good find. I've always disliked the lack of clamping or support on that line.

Yep. good catch. I would hate to discover that the other way. At annual I try to look and/or feel for this kind of stuff on every inch of all brake and fuel lines.

I had that problem in a car one time. Rear brake line (flexible part) came out of its support clip. Slowly and silently rubbing in the accumulated grit on the rear axle until it failed rather dramatically late one night.
Decades have passed but I still tend toward paranoia about inspecting my brake lines.

George

As you can imagine the elevator cable had a very close physical and visual inspection, and did not have any damage. Fortunately the aluminium pipe is much softer than the cable / swaged fitting that was making contact.

Kevin Pearce wrote:George

As you can imagine the elevator cable had a very close physical and visual inspection, and did not have any damage. Fortunately the aluminium pipe is much softer than the cable / swaged fitting that was making contact.