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On G2066 I have a plastic fuel tank, it has always weeped around the outlet and a crack at the 30 litre top bolt that holds the fuel level indicator line. It is not only annoying, but also a fire risk both on ground and in flight. I"m speaking to Gerry Goodwin about a replacement seat tank to remove the issue. The existing tank is not a Goodwin tank, just to be clear.On the basis that I was going to chuck out the old one I decided to investigate the issue.I worked out the length of the cast in ferrule and drilled through the plastic to it at mid height, the idea being to inject silicone form-a-gasket into the crack and seal it off. When the drill bottomed on the metal two things came out - dust & metal. So, there is corrosion occuring and this is what has split the tank, I imagine the corrosion grows in volume, stretching the plastic until it fails. I am disappointed that the manufacturer didn"t take this issue into account and make use of 316 stainless steel ferrules instead of aluminium, condensing moisture is always a problem and should be catered for.I drilled 4 holes and used a 3ml disposable syringe to inject the silicon.. the hole drilled was 4ø to fit the syringe. The silicone will have cured tomorrow & I hope to test it out tomorrow for leaks.The crack at the 30 litre bolt was fixed (maybe) using a soldering iron... I"ll test it tomorrow as well and let you know..
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Is it a silicon that will handle petrol?Aussie Paul.
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Paul,I was looking at my truck full of plumber"s roof & gutter sealant....-tempting.... but found instead my black RTV form-a-gasket silicon and used it, yes - it is fuel resistant, but I thought the tank was supposed to be too :-( Time will tell.
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Hi guys,I have written the Tech Manual draft part on fuel systems to NOT allow for any repair attempts on seat tanks, and very strongly urged that a damaged seat tank is to be rendered completely unserviceable by cleaving or cutting in two with a grinder rather than on-sold to an unsuspecting buyer. The section further prohibits the use of fabricated polyethylene seat tanks or cube tanks in any circumstance - by fabricated I mean plastic-welded. It"s stating the obvious, but the plastics industry long ago found out that while incredibly robust plastic tanks can be made by spun injection molding, welded tanks are unsatisfactory (and dangerous) because of seam leak and failure issues. In other words, there"s a reason why you don"t see welded plastic and PE fluid tanks on the market - only spun injection molded ones.The Tech Manual start date has necessarily slipped back to 1 Jan 16 because it is so difficult and extremely time consuming researching what the various standards and practices are for materials and methods used in gyro construction.Cheers,Mark R
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Mark,Thank you for the commentary, it makes the decision pretty easy.Now to the question of the replacement... since I don"t want a repeat of the failure of the ferrule, and if no plastic tank is fitted with a stainless ferrule, I shall use a metal tank. Are there any construction standards for those?Thanks,Nic.
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Is it a silicon that will handle petrol?Aussie Paul.Yes.......3m make it, 2 pak epoxy silicon, can"t remember the product name, but call Rod T, I sent him 2 tube paks.1080 I think it was, 1040 maybe ??
If you aim for nothing, you'll hit it every timeComment
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Oye Nic......why not bolt on a Goodwin 70L tank.......comfy too
If you aim for nothing, you'll hit it every timeComment
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Russ,Yes, spoke to Gerry as noted prior. $600 for 40ltr, $650 for 70ltr, the extra $50 is well worth it. He"s still moving house and says they"re buried in the back of his container and it will take 2 weeks to dig them out. Paul B says they"re comfortable too.. and you don"t have to fill them up every time, do you?I worry though that the ferrules may be the same - aluminium, hopefully his ferrules are stainless steel or silicon bronze. I will be asking about this as I don"t want to buy the same problem again. If they are I will be thinking long & hard about a fabricated metal tank.
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Hi Nick,That"s a good point about are there any construction standards for spun polyethylene seat tanks. Short answer is no - not here, nor in BCAR-T (UK) or the ASTM (USA). The philosophy behind mandating a strict approach to seat tank repair attempts came after I researched why there were no fabricated (plastic welded) tanks of any kind on the market. It"s actually a fascinating area of inquiry because it overlapped the intriguing issue of why aluminium welding is frowned upon in structures, yet appears to be standard in fluid tanks. Eventually I arrived at 2 conclusions -For cross-linked polyethylene: ANSWER: there is no consumer-level equipment available on the market for plastic welding (and I"m not talking about heat seal machines for sealing bags or packets - I"m talking about technology that could produce consistent reliable and perfect 6mm+ thick welds).
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Mark,Thank you for the response, most illuminating. It is funny that I can ring up and ask for a seat fuel tank, buy one and find it has "not for fuel" stamped into it... sort of defies the trade practices act a little... I think mine has something to the effect that it is for water storage only.As to the police, etc being amazed that we"re strapped onto the fuel tank.. what is the difference between being 3" from 60 litres of fuel on fire or being 3" from 60 litres of fuel on fire... none.. in fact the 3" may be the more dangerous of the two, at 3" you can reach the fuel tap to turn it off.The business of plastic welding is interesting, as noted a fabricated plastic tank is no match for a one piece unit.. there is no issue with variance in compatability, fewer chances of inclusions and the linearity of the polymer chains is likely to be better in a one piece. I wonder though if you may be a little harsh in this unrepairable issue. I think the issues may be the same as for welding metals with relation to weld strengths, where it fails because of the loss of the homogenous nature of the parent metals, so post repair heat treatment may be required to reinstate the uniformity of the material, much as you do when welding excavator tynes after they"ve been broken. The preparation is full bevel and 100% penetration welding with preheating before welding and then post heating after welding with an extended cooling period. This is difficult to do with plastic fuel tanks due to their size, etc.
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Let me report a pleasant surprise here... the silicon injection worked.
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Yeah Nick -You"re spot-on about aluminium tanks not needing to be 6061-T6.
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Mark,I was curious to know whether your technical manuals require any CAD illustrations?
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Let me report a pleasant surprise here... the silicon injection worked.I guess the words are, "for now"...Aussie Paul.
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Yep,Until I next have to clean the brass mesh filter in the seat tank.....
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