Butt Rib install problem

[Flyboy66]

According to the KF manual, the #1 rib is supposed to be placed 35 1/2" inboard of the #3 rib (center to center, no wing sweep). When I do this, the butt rib, if it would fit, would cover 1/2 of the rear spar pin, and forward spar pin.



I am inclined to move the #1 rib outboard just enough the the butt rib will clear the pins with just enough room to get a socket on the rear pin. The problem with that is that the fuel tanks might be 1/4" wider than the gap that it is supposed to fit into if I do this. My right tank is 34.5" wide at it widest, and the left is 34.125 at its widest. The edge trim job on the fuel tanks isn't strait, and I would like to trim off a little of the edge of the tanks (maybe 1/8th inch each side) to allow the #1 rib to be moved outboard enough to accommodate the Butt Rib.


I measured #3 rib location on both wings and it appears to be correct, so I dont understand why #1 rib cant be placed where it is supposed to be and not have the Butt Rib over the spar pins.

[avidflyer]

Not sure if I'm following you completely, but the spacing has to be right for the flaperon hinges to have something to rivet to. JImChuk

[aviator79]

I would take pictures and contact the factory on this one before you do anything you can't easily undo. As JimChuk said, the spacing is not arbitrary, and an 1/8" off on the rib position may prevent you from being able to rivet the flaperon brackets to the ribs. The hinges have some float, but my #1 and butt ribs were done at the factory and it still took some work to get the flaperon hinges to all align at the same time.

[Flyboy66]

Jim,

I am at the dentist office and don’t have my manual with me.

I believe I am supposed to install rib #1 thirty five and a half inches (center to center) inboard of Rib3, Then I am supposed to locate the Butt Rib inboard of that with a 1/16th inch gap between the two ribs. The problem with that is the butt rib cap strip would have to cover about 1/2 of the spar pin head that holds the wing spar on the spar lugs. So, it is impossible to slide the butt rib where it needs to go without cutting a notch in the cap strip and possibly the Butt Rib webbing.

Is that clear now? If not I can try to take a picture and email it to you.

[jmodguy]

Do NOT move the #1 rib position from the plans. This rib supports a hinge point. I sanded a notch in my butt rib with a dremel tool. This makes the rear spar bolt easy to insert. It will eventually be covered by the skylight.

[Flyboy66]

Do NOT move the #1 rib position from the plans. This rib supports a hinge point. I sanded a notch in my butt rib with a dremel tool. This makes the rear spar bolt easy to insert. It will eventually be covered by the skylight.

Do you have a picture of yours?

I would like to see how the Butt Ribs look installed, so anyone feel free to post a picture.

[Dave S]

Steve,


On our early S7 - I trimmed the capstrip by the rear spar to provide relief for the bolt. If I recall correctly, the front capstrip didn't interfere with the pin; however, my buttribs were made a few years ago and may have had a slightly different length on the capstrips.


The buttrib is not structural to the wing and a little trimming isn't a problem and won't affect the windscreen mounting. As others have mentioned - location of of the wing ribs is very critical.


Sorry, no photos over here of this.