Tanks and fabric questions

[Tom T]

Well today was an interesting day.

I completed painting a small fabric patch on the right wing in prep for mounting the wings to the fuselage.

These are 2005 vintage wings/tanks built under the builder assist program at SkyStar, covered and painted with Aerothane.

We decided to slosh the right tank for possible release agents and contamination. Mixed a 50/50 solution of acetone and avgas. While sloshing we had a significant leak at the finger strainer fittings. The solution wetted the fabric along the leading edge in the tank bay and some of the lower rib lines, before we could get it cleaned up some of the paint blistered.

Several questions:

Does anyone have a recommended sealant for the fittings, as I'm not too impressed with the Permatex used by Skystar.

These tanks don't have the sump quick drain fittings. Can/should they be added?

The slosh solution damaged the paint (soaked thru from the back side), but I doesn't seem too have much effect on the polytac/polybrush/fabric bonds. Is this a problem?

Thanks in advance for any feedback you can give.

[Dorsal]

"These tanks don't have the sump quick drain fittings. Can/should they be added?"
Tom, Are you saying there is no fitting or no hole, I have the same vintage setup and the threaded holes should be there. If they are just still covered over this may explain your leaking.
Just asking.

[Tom T]

Dorsal,
Thanks for the hint! Yep I found them.

Now that I've found them, I'm surprised they don't have any reinforcement or grommets around them???

I also noted comments from other posts about adding drain grommets in the wings and elevator. These were not installed either and as I've said, that's a little surprising with the fabric painted by the factory....

Live and learn...

[Tom T]

Hey all, I continue to learn from this mistake.

I searched the posts and didn't find any info specific to my issues so here's what I have to date.

As Dorsal pointed out the drains holes were in the tanks, I just plain missed them due to not having built the wings or done the covering (failure to read closely enough :o )

The wonderful tech support at PolyFiber responded today (Sunday) and indicate the solution didn't do any fabric damage :).

It did blister the paint on the wing and we are now discussing options to repair the finish as well as areas for additional grommets....

[HighWing]

Question. Are the tanks of that vintage the new ethanol resistant Vinylester resin? I don't recall when they were introduced. If they are - no issue. If not did the rinse remove a sloshing compound.

[Tom T]

Highwing,
These are the earlier which are not Ethanol resistant...
Thanks for the info

[t j]

I also noted comments from other posts about adding drain grommets in the wings and elevator. These were not installed either and as I've said, that's a little surprising with the fabric painted by the factory....



Chenk your builders manual fabric section to see if you really need...and want...to install drain gromets. In my manual anyhow, it is left up to the builder. It mentions that the factory at that time just used the point of a soldering iron to melt 1/8th inch drain holes in the fabric.

I made a templet out of a small scrap piece of thin sheet aluminum. With a step drill, drill a hole the size you want to make in the fabric. Place it on the fabric where you want to make the hole and poke the needle nose soldering tip through.

[HighWing]

I agree with tj. Gromets are not necessary, but drain holes are a very good idea.

On another note. The tanks are built up in female molds. Any releasing agent would be on the outside. My thinking on the rinse recommended in the service letter.would be to just remove any uncurred resin. I know that Polyester resin is oxygen inhibited. What that means is that the surface resin in contact with air will not cure. Not sure about the Vinyl ester resin, but I suspect the need for the rinse is caused by uncured resin on the internal surfaces, but it is definitely not release agent. One of the guys here at Sun N Fun has a friend who built a Rans S-7 who had plans to put a diesel engine in it so put large fuel filler necks that accommodate Jet A nozzles. He said that he could put his hand into the tank and if the tank had ethanol containing mogas, the surface was rubbery. And then when filled with avgas, the surface would harden right up.

Hate to mention it, but I wonder if the 50% acetone rinse removed any liner. I think the earlier tanks came with a Kreem liner - someone correct.me. When re Kreeming acetone can be used to remove the old Kreem.

[Tom T]

Lowell,
Thanks again for all the additional information.

My tanks have not been kreemed, as far as we can tell. We can see the resin inside the tanks thru the filler and don't see any kind of coating.

You make a good point on not having release agent inside the tank. We were really trying to ensure a clean tank and no fiber release to plug filters, etc.

Fortunately we can get good non-ethanol mogas here (don't know how long though), so I'm resisting a tank coating/liner to protect from ethanol. I may reconsider that now.

[Dorsal]

I have the same gen tanks, no cream and used a pure acetone rinse. The inside of the tanks were sticky before the rinse and not after. As documented in earlier threads I had lots of brown stuff in the first rinse but clear by the third.

[jrevens]

I'm sure I read about this somewhere, but haven't had any luck searching for the answer now... my tanks sit with the top surface just about the thickness of a wing rib cap-strip down from the level of the top surface of the ribs. Is it necessary to fill the top surface area of the tanks with something like Super-Fil so that they are level with the top of the ribs before covering? Will the fabric shrink down & touch the tanks with that much of a gap, if I don't do that? Also, I'm wondering if that will present a problem with the trailing edge of the Laker leading edge if the surface of the tank doesn't touch & support it initially.

[AirFox]

My tanks were level with the top of the rib capstrips. The Laker Leading edge lays right on top of the tank. I used super fill to fether the edge of the laker leading edge.

[HighWing]

John,
I would suspect that the fabric over the tank would lay essentially like it would over any of the other wing bays with the exception of the missing rib capstrip. What I did in that situation was to create a false capstrip using a rib dimensioned plywood strip to fill most of the space, then using Micro to build up to slightly above the capstrip level and then sanding to exact level with sandpaper glued to the center of a wood board. After covering it looked like a normal bay. The only issue might be the filler neck. You might need to glue the fabric to the tank surface there for filler cap clearance.

Back in the day, your situation was my preferred situation because the tank top was not really very flat and it would contact the fabric in random areas. On many airplanes after the Polybrush coat on the fabric, the fabric would bond to the tank top where it touched and there would be a definite marbleized pattern - random adhered areas adjacent to random non adhered areas - that continued to the final finish.

[jrevens]

Thank you, Lowell! That's exactly what I needed to know. I had thought of using the 1" wide strip of plywood , and that will work out just about right. I'll sand as necessary. With the Laker leading edge I'll still have a large area of glued down fabric where I won't be rib lacing, and then I'll also have the trailing edge area laced. I'll feel good about that.

[HighWing]

This might sound a little you know what, but to make the whole thing visibly consistent I cut short - one inch - lengths of rib lacing cord and glued them to the false rib capstrip at the right locations to mimic rib lacing. But that's just me.

[jrevens]

This might sound a little you know what, but to make the whole thing visibly consistent I cut short - one inch - lengths of rib lacing cord and glued them to the false rib capstrip at the right locations to mimic rib lacing. But that's just me.
I know of at least one other builder who did the same thing, & I respect & admire attention to detail like that. Thanks again, Lowell!

[desertfox1]

Bill and I installed the leading edge on the wings for my newest
SS this past weekend. Fortunately the tanks were about level
with the ribs. Will need to use some Superfil to fair every thing
out before cover.

Phil

[Esser]

Phil, Are the scallops on the leading edge for aesthetic reasons? Or do they have a purpose?

[desertfox1]

Mostly aesthetic I suppose, but I think it makes a better transition
for the fabric. Incidently, cutting the scallops took Bill about an
hour or so, maybe 20 minutes longer than a straight line. We use
the Harbor Freight tool, hold the part against something solid (1x4)
otherwise everything vibrates and it doesnt cut. Real advantage
of this tool is lack of clouds of glass dust.

Phil

[jrevens]

That's what I love about this forum, & this group... there's usually always someone who's willing to jump right in & take the time to answer a question to help a fellow builder. Thanks to all who responded to my question!