Tubing Corrosion

[Supermega]

Some of the large auto racing sanctioning bodies use a sonic test to check wall thickness on roll cages and frame members in tech inspections.

I wonder if they can sonic test through fabric. From what Bill said, maybe not?

 

[Cub junkie]

From the way I have seen the test conducted the test probe is placed in a small dolop of what appears to me as dielectric grease. To have fabric in the way even if its tightly wraped around the longeron might give an erroneous test result.

 

[Bill Ingerson]

SuperCub with wood frame

I like this site, it reminds me of fishing, this time I used the wood frame for bait and caught you guys ! What I wanted to talk about was the Sonic test or X-ray of the tubes. For a accurate test you must be down to bare metal for testing. The test sight is about the size of a dime and only on that side of the tube, I would suspect that between the tube and fabric would be a area that would go bad first, because of dirt, water turning to damp mud and trapped between the tube and fabric sets up a possible problem area. I dont think that alot of frames show any pitting corrosion ect. Another way we check boiler tubes is with a bora-scope that looks inside the tube, kinda like a proctologist might use. How ever in boiler tubes the camera magnifies the corrosion so much it makes things look alot worse than they are. I would not want to cut random tubes just for that type of test. Best Idea ! make sure that there is a coating of oil inside and you will be fine. Never weld a tube that has oil in it without drilling a hole in the tube first, a friend had one blow up on him and he was burned pretty bad. Powder coating is a concern for me. I built a new funny car and few of them are powder coated frames. They could hide cracks in the welds. If I used the funny car motor in a SuperCub would 600 H.P. per cylinder be overkill ?

 

[Supermega]

I took all these recent posts to em, and they answered everything. Sonic testing is an option but it does require removal of the fabric. I'm going to go ahead with the x-ray. I'll let you know how it goes.

 

[cubdrvr]

.........and the paint also for ultrasound. PA-25 AD requires it on the wing attach tubing cluster.

 

[CptKelly]

Speaking of "wide bodies" fuselages.....

A wide body fuselage appeals to me due to the increased room. What does this do to the cruise speeds?

Mike in NC

 

[Supermega]

x-rays

Well I had some x-rays taken of my potential purchase. I say "some" because it only took 4 x-rays to see that I was about to buy I big tail tubing repair bill. Bittersweet I guess. Glad I found the problem, but now I have to find a new airplane. oh well.....

 

[Crash]

New Fuselage

A new fuselage adds at least $10K to the resale value of a plane in my books. You can inspect every thing else on a plane, but it is next to impossibe to inspect for rust inside the tubing. Crash

 

[bcone1381]

..... I drill the bottom longerons and put oil in and then use a solid pop rivet with PRC on it. Most of the frames I have repaired show no internal corrosion unless there was a hole somewhere in the tube. Cut a landing gear/strut carry-thru out of a 1949 Clipper this week and it was as clean as the day it was new. Same at the end of the lower longerons. The outside of the tubing was pitted between the rudder post and the first diagonal tube coming down and forward of the rudder post. I cut a section out and found it had a tube inside a tube and was still oily inside. The fuselage drawing did not show this tube inside a tube. Have since found it on other fuselages.

I am building an Experimental from a kit with a 4130 steel tube fuselage. I am thinking that preventative corrosion proofing might be prudent.

-What are your thoughts? Should I do just the bottom longerons?
-What is PRC?
-I assume that the tube filled with oil then drain it out. Is that correct?

 

[Steve Pierce]

PRC is a fuel tank sealant. Oil in the bottom tubes is adequate. AirTractor has holes in each tube at every cluster and the pressurize the fuselage with hot linseed oil at a bungee welded into the firewall tubes and then drain it all out.