Covering Fuel Tank on SQ2 with fabric

I am building an SQ2. The fuel tank does not have an aluminum cover, but is simply covered with fabric. I am to make 3 wood "ribs" to hold the fabric up off the tank.

My question is this: The wood will only be about 1/8" thick. I will not be able to screw or stitch the fabric to these ribs. The tanks are 3" wide. If I can't attach the fabric to any parts above the tank then I will have a 3' span where the fabric will only be glued to the three ribs in this area. The tank basically fills the space below the fabric. Is it OK to just have the fabric glued to the thin wood ribs that are in turn glued to the tank and straps?

Would the 3' span with the fabric only glued to the wood be OK or is there a chance that the glue would not hold the fabric down and it might pull up away from the tank?

The only alternative I can see is to do something like lay nut plates into the bottom of the wood ribs and use short machine screws to attach the fabric.

Is possible to stitch the fabric to the ribs, (using a 4" curved needle) but the ends of the ribs will haft'a be fastened very strong to the spars. It's right in the propwash area & will take a beating. NOT OK to just glue it.
Can't you make tank covers?

NimpoCub said:

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Can't you make tank covers?

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I'm sure they will send me covers if that is what I want. The span is still 3' and thus I assume the aluminum would be rather thick. I would also have to figure out some way to attach nut plates to the leading edge as the wing comes assembled and I can't get to the area that the cover would need to attach to (at least without some dis-assembly of the wing).

What fuel tanks are you putting in?

Brad

Widebody said:

What fuel tanks are you putting in?

Brad

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There are no choices on the SQ2 kit for the main tanks. They are 24 gals each.
http://supercub.com/aircraft-catalog-aircraft-a-accessories/supercuborderforms/mackeysq2info.html

If you can't get to the backside you will probably have to use Rivnuts. I recommend the keyed ones. It only takes a couple of seconds with a file to make a keyway. They are less likely to spin that way. Remember the top of the wing is a low pressure area and as such that fabic is going to be pulling up. You definately need to attach it securely via rib stitches, rivits, etc. I think DW on this site used a carbon fiber for his tank covers. Might look into that option. Unfortunately saving weight is expensive.

Bill

I have more faith in Poly Tak than you do. The fabric will be as secure to the wood "ribs" as the ribs to the top of the fuel tank. I believe Kit Fox fabric is all glued to the ribs without any kind of rib stitching.

This isn't a F-22. If it comes loose, in that 3' section, you will never know the difference.

What ever you are comfortable with...

Don

You certainly could use just glue if you made the false ribs wide enough to give adequate surface area, but then the next question is how are you going to attach the ribs to the tank so that the fabric does not just lift the whole rib up. I considered this as well in an effort to save weight, but finally conceded for lack of good options and also for ease of tank access. I ended up using the std Alum tank covers, but I certainly respect any weight saving efforts and I am interested if you come up with a good solution. I have seen one airplane that uses the top of the tank as the top of the wing. This would solve the problem and save weight but the tanks would have to be redesigned and built for that purpose.

Bill

I went to the hobby store and bought a piece of 1/4" aircraft plywood and layed it flat on top of the tank with it going around the filler cap. I then layed down the reinforcing tape and used the shortest PK screws with fabric warshers to hold the fabric down.
I forgot to mention that I bent up a couple of angles and screw them to each spar to hold each end down on the ply.
It came out perfect and no one notices it was done on my SQ-2.

What covering system are you using?

Jason

jgerard said:

What covering system are you using?

Jason

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I will be using Stewart. I called Stewart and they said that their glue onto 1" ribs will hold just fine and "not to worry". They also suggested that I cover the area as a patch so that if I ever do remove it I won't disturb the rest of the wing.

I was going to say that you'll have absolutely no issues glueing the fabric to the ribs with EkoBond. It has almost 3 times the peel strength of the solvent based glues. The idea of covering the wing and then covering the tank bay is a great way to allow easier access and repair down the road.

Jason