Cracked plastic fuel tank

[Bluey]

I've got an XT912, 2009 model and I detected a slight fuel leak by accident today. Not sure how long its been there for since no drips have ever been noticed. I only detected it because I needed to replace my starter battery today. While in the process of removing the battery, I noticed a slightly damp area just above the battery. This turned out to be fuel! When I moved the seatbelt strap I saw the crack. It's about 10cm long and sits above the 45litre mark in the tank. This is the second crack detected in a trike fuel tank at YWOL in the last few months. The last one was on a two year old trike with only 29hrs. Mine has 692hrs but is 4 years old and I don't know how long the leak has been there. At the time it was detected I had 65 litre of fuel in it (just filled it).

 

Bluey

 

 

[Head in the clouds]

This is a big concern Bluey.

 

I recently conducted some research into 'plastic' fuel tanks because I am considering using them for the later (production) version of the 'Cheap 2 Seater' biplane that features as my avatar. I've heard of some general resistance in the market to seat tanks - some people have a bit of an issue with sitting on all that flammable fuel. At the same time it's a very convenient place to put the fuel, usually being on the CG and in a place which you can't use for much else. It's also easily accessible for filling and the use of cheap and reliable site gauges (or physically see the fuel level via see-through translucent material) rather than electric fuel gauges.

 

My research wasn't exhaustive by any means but in a half day of googling I couldn't find a single instance of a crash causing a ruptured fuel tank, of tanks that were made the way (and of the material) I intended to use. The majority of those type of seat tank are/were used in gyros and the method and material is the standard for plastic 'jerry cans' which have to withstand a test drop (full) of 30m/100ft (IIRC).

 

Those tanks are made by rotational molding and from cross-linked polyethylene and made properly seem to be almost indestructible in the kind of use (and crashes) that might be experienced by gyros or trikes.

 

Discovery of a crack such as you describe quite likely indicates the use of inferior material i.e. not cross-linked (google it if you're not familiar, there are lots of explanations), or the material is not polyethylene, or the molding process was not conducted properly in which case it's not so much likely to be a crack as a molding flaw where the material has not melded as it meets while being 'sloshed' around, possibly due to contaminants and or molding temperature deficiencies.

 

Most molding companies in Australia seem to produce good quality product from good quality materials although the raw material is expensive here due to a shortage of polyethylene which is a by-product of the gas industry, and the gas industry in Oz is small compared to the demand for polyethylene. Tanks made in USA are also usually of very good quality. Unfortunately the more recent general trend has been to get goods made as cheaply as possible these days and most of those come from China of course. Within the molding industry there is considerable anecdotal mention of poor materials being used there, poor molding technique and QA, cheap materials being deliberately substituted contrary to the customer spec and high rates of product rejection. These comments circulate within the molding industry but it should be noted that they are mostly made by local competitors.

 

Nonetheless my reason for posting is that if you happen to have a tank made from the wrong material it could be affected by UV and become very brittle or it could be brittle from the outset in which case it might rupture in event of a mishap, a circumstance we could all do without. If it is well molded and the right material and has a crack for some good reason then they can, I believe, be successfully welded, again there is plenty of info on the net about that.

 

Good luck with it, and I'd refer it to the manufacturer in any case and from a safety viewpoint I'd imagine that other owners might appreciate being informed of your experience in case there is an inherent problem.

 

 

[Bluey]

First thing I did when I got home last night is generate a defect notice through the HGFA website and SMS one of the owners at airborne. They replied pretty quickly and are now aware of the problem. It looks as though a replacement is the only solution. This will mean probably shipping the trike back to the factory. As this is the second instance of a an identical fault, it could be a bad batch of tanks in which case all owners of similar vintage will need to do immediate inspections.

 

Bluey.

 

 

[Air Creation]

Here is the SB from Airborne.. good one Bluey to get the news out there.

 

See attcmt here...

 

SB-016issue1.pdf

 

SB-016issue1.pdf

 

SB-016issue1.pdf

[Bluey]

I did the fuel tank replacement with a friend today and it took about 2 hours. It could be done on your own quite easily.

 

On closer inspection of the old tank, it's quite obvious from the staining that the slow leak has existed for some time, possibly before I took delivery of the trike. I would always take a look at the fuel level at the end of each days flying. Sometimes I would notice that it was slightly lower by a few litres after a week or so. I always thought it was a little odd but never took much notice as I assumed I'd simply forgotten the true level or that I'd incorrectly measured it in the first place. Or, that I'd lost a little due to evaporation. The point is: always investigate when you get that nagging feeling something doesn't quite seem right.

 

Bluey.

 

 

[Russ]

Previously I,ve used a 2 pack silicon, made by 3m, works a treat. Will chase up the tubes and get that info