Roger Lee Posted May 30, 2022 Report Share Posted May 30, 2022 Has anyone ever had a fuel sight tube break in half while flying? I've never heard of such a thing. The fuel in that wing ran everywhere. One just happened to a CTSW down in Florida area. The only thing I can come up with is it was put in under a twisted stress during installation or a bad batch of tubing. The owner was fairly new to that CT and didn't know when the last wing inspection was. The tubes were pretty dark. They may have never been changed? They tried to plug the open ends for the plane to get home, but the tubes just split. If I get more information I'll post it. Quote Link to comment Share on other sites More sharing options...
GrassStripFlyBoy Posted May 30, 2022 Report Share Posted May 30, 2022 Can't say I've heard of that, but dang - sounds like a tense situation. I rented a LS that had nasty tubes real dark, and I thought that was a bad situation - could barely see fuel through them. Could be the clamp created a stress riser, or a nick / cut that stress cracked and let go. I'd like to see a picture of the failure. Quote Link to comment Share on other sites More sharing options...
Tip Posted May 30, 2022 Report Share Posted May 30, 2022 We found this on a recent inspection. A friend bought a 2015 and the site tube was rubbing the bulk head. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted May 30, 2022 Author Report Share Posted May 30, 2022 Hi Tip, This one I can see, but to just have one snap in half in the middle? It just completely broke. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted May 31, 2022 Report Share Posted May 31, 2022 I use C-210 tygon (clear ) , after 2 years still soft. Supercubs have used tubes for over 50 yrs with no issues, just have to maintain them properly. The only issue I have is that there is no reducing orifice at the bottom tube connection like in other aircraft. This would reduce full fuel flow in case of failure. Quote Link to comment Share on other sites More sharing options...
Anticept Posted May 31, 2022 Report Share Posted May 31, 2022 Madhatter that's a brilliant idea. A restrictor would also make it easier to read in bumpy air. Implementing this next time I replace my tubing Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted May 31, 2022 Report Share Posted May 31, 2022 Busted sight tube is one of my worst CT fears. Seems we could make something a little better. Maybe a shut-off valve on the tube fitting you could turn to block the fuel flow if it failed? Of course you'd have to redesign quite a bit to make that work and be accessible. A squared, permanent tempered glass tube behind a sealed plexi cover so fuel could only go down the side of the airplane in a failure is another option. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted May 31, 2022 Report Share Posted May 31, 2022 29 minutes ago, Anticept said: Madhatter that's a brilliant idea. A restrictor would also make it easier to read in bumpy air. Implementing this next time I replace my tubing I've been called a.lot of things but not brilliant. I've been toying with the idea of a better sight tube for about 5 yrs but will have to find a spare end plate to modify. Dakota Cub sells one for the supercub, of which is cleanable in place. It would be along the same principle but different in size and mounting. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted May 31, 2022 Author Report Share Posted May 31, 2022 The clear plastic poly tubing and the Tygon tubing have been used with FD since the beginning. There hasn't been any issues. Probably close to 2K CT's world wide use the stuff. This is just one of those weird explainable incidents and we don't know any history like time in use or under stress due to a poor install. Quote Link to comment Share on other sites More sharing options...
Anticept Posted May 31, 2022 Report Share Posted May 31, 2022 The other idea I was toying with was changing the fuel return line so it doesn't go back to the gascolator, but rather returns with a nylon line back up along the left a pillar tucked under some tape, up to join the left wing sight tube and directed back into the left wing tank. Since there is a restrictor on the return line, and it's very small, it would allow very rapid purging of air in the line, but not a lot of fuel in normal operation, and would probably improve some of the issues with fuel warnings. Was just a tangent related to the fuel sighting tube. Quote Link to comment Share on other sites More sharing options...
Mike Koerner Posted June 1, 2022 Report Share Posted June 1, 2022 I had a sight tube fuel leak very recently which resulted in some surprising observations. At first the cockpit just smelled of fuel. I noticed wetness on the left wing sight tube and tightened the upper clamp. I thought I had solved the problem. Later I filled the plane with fuel for a flight the next day. The next morning fuel was dripping out the junction between the right wing and fuselage. When I pulled the tape off that side a whole mess of fuel, which had been dammed up behind the tape, came pouring out. And yet, the sight tube and fuel fittings on the right wing seemed dry. I thought I had a serious problem. I drained both fuel tanks and pulled the right wing. I then refilled the right wing and was stupefied to find that it was not leaking at all. I scratched my head for hours then came back the next day and refilled the left wing with fuel. The left wing sight tube had a substantial crack on its hidden outboard side, at or near the lower edge of the upper hose clamp. Fuel was pouring out, running along the bottom of the well-taped left wing root, then crossing the fuselage in the wing box and leaking out the right side. Apparently, the tape on the right wing root had not been quite as fuel-tight as that on the left, which had shown no evidence of leakage. Surprising observations: 1) Fuel leaking from left wing sight tube did not pour directly into the cockpit but instead ran back along the wing root toward the lowest point near the spar. 2) The wing root tape on the left side formed an effective (though surely temporary) fuel dam, preventing any visible leakage on that side. 3) The wing box above the cockpit is fuel tight and provided a conduit for fuel that had leaked into the left wing to cross over to the right side. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 1, 2022 Report Share Posted June 1, 2022 Thanks for that breakdown Mike, that's a crazy situation! How long had those tubes been in when the crack developed? Quote Link to comment Share on other sites More sharing options...
D. Spencer Posted June 6, 2022 Report Share Posted June 6, 2022 My CTSW had the attached fuel gauges when I bought it, which are nice to read, but I'm planning to return to stock sight tubes because I doubt FlightDesign would approve this and it has 4 hose ends instead of just 2 that could develop a leak. The upside is that you could use any Standard fuel hose, not just clear, and these gauges don't get cloudy. I haven't been able to find the brand, though. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 6, 2022 Report Share Posted June 6, 2022 Those gauges are interesting, really not a bad solution. There are definitely additional hose connections, but you could use real fuel hose instead of clear that is less durable. If your airplane is SLSA FD would frown on that. My main question is how do you get behind that thing to pop the hoses off for a wing pull? The wing won't slide out without removing the gauge, and there is no room to get behind it. Do you flex the hoses, push one end of the gauge through, then the other? Quote Link to comment Share on other sites More sharing options...
D. Spencer Posted June 6, 2022 Report Share Posted June 6, 2022 Ease of wing removal is one of the reasons I'm considering returning to stock. If someone were to make gauges like this that fully fit into the wing opening, that would be a great alternative. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted June 6, 2022 Report Share Posted June 6, 2022 If you don't kink the sight tube you can put one of these in each tube to make seeing the fuel level easier. https://www.univair.com/piper/piper-pa-11/view-all/u10853-000-piper-fuel-gauge-float-ball/ Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 6, 2022 Report Share Posted June 6, 2022 One could put in two small 90 degree fittings so that the tubes are straight. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 6, 2022 Report Share Posted June 6, 2022 28 minutes ago, Anticept said: One could put in two small 90 degree fittings so that the tubes are straight. You know, that could really solve some problems. Make it easier to get to the clamps on the tubes, eliminate tube kinking as a thing, and prevent a tube cut too long from chafing through on the bulkhead. Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 6, 2022 Report Share Posted June 6, 2022 They would need to be transparent fittings though, which is the drawback, otherwise you won't be able to see it at the bottom level. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 6, 2022 Report Share Posted June 6, 2022 23 minutes ago, Anticept said: They would need to be transparent fittings though, which is the drawback, otherwise you won't be able to see it at the bottom level. You should be on the ground by then anyway! Consider everything below the fitting as "emergency reserve fuel". Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 6, 2022 Report Share Posted June 6, 2022 I do agree, but there's other reasons to be able to see the fuel, such as while doing maintenance and performing flow tests. You won't see it on the stick before the sight tube starts to fill. Alternatively, maybe just the top needs the 90 degree fitting. That alone would reduce kinking significantly. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 6, 2022 Report Share Posted June 6, 2022 The tubes need to be integrated into the end plate and low profile. It can be done but will take some work to get the best design. It will take some machining work but once figured out it should be easy to replicate. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 6, 2022 Report Share Posted June 6, 2022 5 minutes ago, Anticept said: I do agree, but there's other reasons to be able to see the fuel, such as while doing maintenance and performing flow tests. You won't see it on the stick before the sight tube starts to fill. Alternatively, maybe just the top needs the 90 degree fitting. That alone would reduce kinking significantly. Both at 45 degrees. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted June 6, 2022 Report Share Posted June 6, 2022 I haven't had a kinking issue in several years, since I figured out the best length for the tube. I also pre-from the curve by storing the next tube in inventory on some coiled 1/4" aluminum tube. I have a table in the shop marked for the length with a notch. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 6, 2022 Report Share Posted June 6, 2022 I have found the best length for no kinks is as long as possible while still providing 1/16" to 1/8" or so clearance to the bulkhead. YMMV. Quote Link to comment Share on other sites More sharing options...
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