coloredcoat
Well-Known Member
So this idea isn't original to me at all. But this system is used on many different pieces of equipment from reactor vessels to Blackhawk blade spars. Here's how it works: any closed tubing structure that is welded shut, incorporates a small vent hole. It has to be left open for venting while welding. You see this on aircraft tubing, and some people use that vent hole to inject linseed oil or paralketone. Then that hole gets plugged with a brass rivet or similar.
Anyway, on UH-60 helicopter blades, the spar is made from a long rectangular titanium tube. That spar gets covered with the `nomex airfoil cores and carbon fiber skins and can't be accessed for inspection without major blade deconstruction. So what the designers did was put a small inflation valve stem and a pressure indicator that shows whether the blade is still inflated properly or not. The goal of the thing is to indicate whether the blade has internal damage such as a crack or whatever that would affect the strength of the spar. It works pretty well, and it is very simple.
In the process industry we have laminated pressure vessels, and we use a similar weep hole system of leak detections to measure whether or not the inner lamination has failed somehow. The goal is the same: if it leaks, you have a structural failure of some kind. I intend to use this same system on aircraft tubing structure. Some practical changes would be piercing or drilling holes at each cluster so that the tubes are all on the same pressure boundary. That's probably the biggest change to normal tubing construction. Then when the last tube is being welded, the addition of a valve stem and pressure gage would complete the integrity monitoring system.
The benefits of using this system would be several: It would allow you to purge the interior of your tubing structure of all oxygen and water such that interior corrosion is completely prevented. It would allow an immediate indication of weld cracking not normally caught until major fabric repairs are done, increasing structural safety by a tremendous margin. It would increase the quality of welds on your tubing. Likely even the best looking welds won't be automatically leak free, but you'd have an achievable goal with this pressurized tubing test.
In my previous thread on using stainless steel tubing, many builders did not seem to be using anything like dye penetrant or X-ray inspection on their welds. While not 100% the same as either of those other inspection methods, this pressurized integrity testing system would achieve something much better than purely visual inspection.
Has anyone ever worked with or seen this system used on aircraft structure before?
Anyway, on UH-60 helicopter blades, the spar is made from a long rectangular titanium tube. That spar gets covered with the `nomex airfoil cores and carbon fiber skins and can't be accessed for inspection without major blade deconstruction. So what the designers did was put a small inflation valve stem and a pressure indicator that shows whether the blade is still inflated properly or not. The goal of the thing is to indicate whether the blade has internal damage such as a crack or whatever that would affect the strength of the spar. It works pretty well, and it is very simple.
In the process industry we have laminated pressure vessels, and we use a similar weep hole system of leak detections to measure whether or not the inner lamination has failed somehow. The goal is the same: if it leaks, you have a structural failure of some kind. I intend to use this same system on aircraft tubing structure. Some practical changes would be piercing or drilling holes at each cluster so that the tubes are all on the same pressure boundary. That's probably the biggest change to normal tubing construction. Then when the last tube is being welded, the addition of a valve stem and pressure gage would complete the integrity monitoring system.
The benefits of using this system would be several: It would allow you to purge the interior of your tubing structure of all oxygen and water such that interior corrosion is completely prevented. It would allow an immediate indication of weld cracking not normally caught until major fabric repairs are done, increasing structural safety by a tremendous margin. It would increase the quality of welds on your tubing. Likely even the best looking welds won't be automatically leak free, but you'd have an achievable goal with this pressurized tubing test.
In my previous thread on using stainless steel tubing, many builders did not seem to be using anything like dye penetrant or X-ray inspection on their welds. While not 100% the same as either of those other inspection methods, this pressurized integrity testing system would achieve something much better than purely visual inspection.
Has anyone ever worked with or seen this system used on aircraft structure before?
