Fitting butt rib, #1 rib and fuel tank.

[Frontier Fox]

I am reached the point in my build where the wings have been installed on the fuselage and it is time to bond the number one rib. The directions say to bond the rib 35 1/2” from the number three rib, center to center. That spot has been marked and then I thought, just out of curiosity, will there be enough room for the butt rib to fit 1/16” from #1 rib. Also will there be room for the fuel tank. Negative on both accounts. With the number one rib in place there is no way for the butt rib to fit as described. Plus the fuel tank edges where they meet the number three and number one ribs are not parallel to the ribs. That is, they are not square.
So what to do? Trim the edges of the fuel tanks so they are parallel to the ribs, squaring them up.
I searched the forum and didn’t see anyone else bring this up and it is not addressed in the assembly manual.

Any thoughts appreciated.

[Esser]

The butt rib can move in and out. I may be missing what you are saying but are you saying your tank is too large to fit between the rib spacing? Confirm that the rib spacing is the same as the distance between the #3 and #5 rib.

[Brandon Petersen]

Hi Joe!

Here's a couple quick tips that may help you....

1) Some of the butt rib brackets get cut down. The front bracket will be full length, the second one to the rear gets cut to 1.625", the third gets cut to 1.5", and the rear brackets cut to 1.375". If your rear post that those brackets slide onto is not already shorter than the rest, shorten it by 1/4". That will allow your butt rib to fit nicely with the 1/16" gap. The #1 rib is a fixed dimension that must be 35.5" on center from rib#3 or your flaperons won't fit.

2) you can sand the edges of the tanks to true them to the ribs but leave as much flange as possible and always pressure test them again after trimimimg or grinding on the edges. It helps in hose and fitting clearance to hold the tanks toward rib 3 as much as possible. And if you plan to rib lace your fabric, leave yourself a needle width gap between rib 3 and the tank.

Hope that helps....

Brandon

[Frontier Fox]

Brandon

That is exactly the information I need.

I am going to trim a little on the outer flanges of the fuel tanks, just enough to true them with the ribs. This will free up a little space so I can bond rib #1 at 35 1/2”. Good tip on double checking for leaks after trimming!

I was not aware that the butt rib flanges needed to be trimmed, so that solves to mystery of getting the 1/16” gap.
In talking with other builders I’m told that the aft end of the butt ribs are trimmed so they don’t interfere with the spar anchor bolt. Was not aware of that either.

One other mystery I think I have solved and that has to do with how the windshield glass is attached to the butt ribs. Is it true that on earlier model 7’s the glass was attached on the inner edge of the butt rib cap strips?
Unless I misunderstand it looks like the windshield on the current 7 is attached to the outer edge of the cap strip, where the reinforcing piece of aluminum is bonded to the underside. Do I have this right?

Thank you for the help, again.

Joe

[aviator79]

Brandon

Unless I misunderstand it looks like the windshield on the current 7 is attached to the outer edge of the cap strip, where the reinforcing piece of aluminum is bonded to the underside. Do I have this right?

Joe

You've got it.
https://lh3.googleusercontent.com/ACdAfxQpM80Zjzgv6WSMOQnXq1DpmCkwFsJUYiX_ZnPj6zwJM0 eGxb2UTi7OV3qsH2ZUQxTYzYQXobgatYxpjiQhgStWlT-xtscT5Odi0Bg2abkAiW2aLx1G1bdTUEtR-acLaRnfS1Y=w500

[Maverick]

In reviewing my book, it tells me that I need to put the fabric on the butt ribs before proceeding with the next step of installing them and putting in the rivets on the brackets. I don't recall putting fabric on the butt ribs on my last build (20 years ago). Is fabric necessary on the but ribs?

Also, I bought the gap seals from the KF factory. Does anyone have any good pics of how these are installed. I didn't get any documentation with the gap seals.

Thanks,
Fred

[efwd]

my butt ribs don't have fabric. I just filled in the holes in the web, with the exception of the center one, and painted. beyond the installation, all else is for aesthetics. not sure what your referring to when asking about gap seals. If your talking about the sheet metal that closes out the gap at the top of the doors to the wing then I will say I simply used silicone sealant to adhere them to the door frame. You will need to trim a bit of material so that it will fit around the door hinge as well as the trailing edge so that it isn't too long to fit in the door frame. Speaking of the airframe not the actual door.

[Meyer]

I think the technical term for those is butt rib closeout. Some pics in the link below.

https://teamkitfox.com/Forums/threads/5264-Butt-Rib-Close-Out