18x5.5 Tubes

[JimC]

These have been talced. I'll upload photos of the tube later today. There's no wear on the outside; it's a manufacturing failure. I'll also cut it open to look at the inside.

Even if you don't talc it, the wear should come under the tread, not on the sidewall.

I found Goodyears for sale at Aircraft Spruce Europe (but they won't ship to the US) and here: $389!!!! These are bent valve stems; the Aero Classics are straight valves.

https://www.aircraftsupply.com/302-339-300.html

[JimC]

Here are three areas of degredation on the same tube. Note the lack of wear on the exterior of the tube. The interior is unremarkable.

The defect that is completely contained within the ribs is the one that actually failed, although it's clear the others were on their way.

We could not find anything on the interior of the tire that could possibly cause this.

[mshac]

Those pics are very disconcerting, to say the least.

Here's a theory, a SWAG if you will:

The damage to the tubes is due to heat emanating from the brake caliper. Say you use the brakes hard, then park. The caliper will be pretty hot, and the tube area nearest the caliper will get heat transferred through the tire.

It would explain the damage being on the sidewall, because that's closest to the caliper. Also, most stories have the tubes failing after a landing, when the tires and brakes are hottest.

Any other theories besides "Manufacturing error"? Which it still may be, because the tubes should be more heat resistant then that.

[JimC]

Nope. That heat has to go through the tire, which is MUCH thicker and shows no sign of wear. Enough heat to fail the tube would cause the tire to actually melt. The heat would transfer much faster through the steel wheel. Also, the brake pads are much larger than the small areas of defect. The defect areas seem to have tight boundaries.

And the most definite reason that's not it: For this failure, all three areas are on the valve side of the tube - away from the brakes. I didn't save the tube from my earlier failure.

[JimC]

We have a new theory from another board, and it fits the facts:

The tube & tire are new. The tire may have come with 3 rectangular stickers on the inside that the A&P removed. The adhesive residue remained. The adhesive is corrosive to the tube rubber but not the tire rubber. That's why they're all the same shape.

A poster on another board said that my failures looked liked ones he had that he was able to conclusively track to stickers on the inside of the tire.

[mshac]

Originally Posted by JimC

We have a new theory from another board, and it fits the facts:

The tube & tire are new. The tire may have come with 3 rectangular stickers on the inside that the A&P removed. The adhesive residue remained. The adhesive is corrosive to the tube rubber but not the tire rubber. That's why they're all the same shape.

A poster on another board said that my failures looked liked ones he had that he was able to conclusively track to stickers on the inside of the tire.

Your theory makes perfect sense. I was wondering why the failed areas were so symmetrical.

I guess the take-away is leave the stickers on inside the tires, or remove them and thoroughly clean any residue with Goof-Off or such!

[Learjetter]

Possible tire (& tube?) source:

Wilkerson Aircraft tires in Virginia.

Www.wilkersonaircrafttires.com