How important is this?

[Esser]

How important is it to fill the gap between the tank flange and the #1 and #3 rib? Is it for aesthetics? Or is it structural some how?

[Dave S]

Esser,

You will likely get various opinions on this one.

One point to consider is what will happen with the #1 rib after the fabric is attached and the shrinking takes place???? Recall that the outboard rib has two braces between the main spars to prevent the fabric shrink from pulling the rib in at the middle and the #1 will have nothing at the rib cap if the gap is not filled/bridged.

Another point to consider is if any motion occurs in the narrow gap between the tank and ribs where the fabric or paint on the fabric may be subject to fatigue....don't know for sure.

I don't know what all the issues might be with the #3 rib except to say that if the whole works is bonded with the tank lip it is probably stronger....like with a monocoque design in a car or other applications where a core is laminated and bonded to a skin.

For sure, there are some aesthetic advantages to filling the gap......other opinions and experiences may shed more light on the option you are asking about. I don't recall this question coming up before so you might be on new ground that has not been explored much.

FWIW....I did bond #1 & #3 to the tank....also drilled holes for the rib lacing at #3 adjacent to the tank.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp Drive

St PAul, MN

[Esser]

I think I will bond them. I was just curious. Either way I will be rib lacing the number one and three so I will have to drill some #40 hole. What is the best way to epoxy this? Tape the top and fill in? Or tape the bottom and trowel it in for a smooth finish?

[Dave S]

Esser,

I am sure this has been & can be done either way. I recall that I used a strip of masking tape on the backside, hysoled the gap then sanded and finished off with superfil.....maybe a bit AR but I wanted it to look smooth.

Sincerely,

Dave S

[AirFox]

Josh, You will need a larger hole than #40 to get your curved lacing needle through. Don't ask me why I know! Good luck.

Scott

[Dave Holl]

I did the same as Dave S and it worked very well.:)
Dave

[JohnB]

On mine, I left just a large enough gap between the tank and #3 rib to get a rib lacing needle through (about 1/8") and then filled just the forward and the aft couple of inches of the gap with Hysol.

My reasoning (hopefully not flawed) is that the combination of the short bits of Hysol at the #3 rib and the wood spacer blocks between the #1 rib and the tank should keep everything secure and still allow access for lacing the #3 rib. Everything still looks good after covering and heat tightening.

[ken nougaret]

I did the same as johnb. ken

[Esser]

So John and Ken, you put nothing between the #1 and the tank? I was thinking along the same lines of the blocks should keep everything straight.

[HighWing]

Thoughts on this. I think it is aesthetically driven. With the long span of the tank bonded to the spars, the drag / antidrag function for that section of wing is pretty much set. What I discovered over the years with my Model IV is that on cold mornings - noted mostly in the days of our Idaho back country tours, the fabric would wrinkle significantly in that area. It was occasionally a topic of discussion as I was not the only one who noticed it. Warm up a bit and it was back to normal

I think the issue arises because with temperature changes there is significant movement overall and only a small area of fabric to accommodate the movement. In a more outboard wing bay, there is a lot of fabric to share the dimensional changes.

[ken nougaret]

That's correct esser. I can't imagine the #1 rib moving with the 4 blocks in place. I've only heated to 250 so far. But lowell makes a good point. ken

[Esser]

Half the reason I am thinking about this is because i installed the blocks and forgot about this step and now it will be harder to apply the hysol.

And correct me if I am wrong, but with an under cambered wing like we have, can't we only heat to 250?

[ken nougaret]

In appendix c of the polyfiber manual it explains how to do a concave bottom. 2 coats poly tak on bottom of ribs, cover bottom, 50/50 mix poly tak and mek through the covering to hold onto ribs, shrink to 250. After putting on top covering, heat to 250, and then rib stitch. Now that you have it rib stitched it can be heated to 350. ken

[jiott]

Yes it can be heated to 350 if you do as Ken said-folow the manual. But also don't forget to reinforce the trailing edge, as it says in the Kitfox manual or as some others have done with different methods.

Jim