Fitting the F-902 Bulkheads - 6 hours

Started the morning with drilling the bottom of the F-684 gussets.

Next step I drilled the #19 holes for the nutplates.

Now that I have everything fitted up. I double checked my edge distance on the lower engine mounting brackets and I have about 0.240" edge distance so well within min. requirements.


Next I fitted up the F-902 bulkheads and then I noticed that the F-713 Auxillary longerons do not sit nicely in the cutouts of the F-902 bulkheads. Its like the longerons are too low...




I cleco'd on the F-7101 gear attach web and that too needs to be trimmed along the top in order to sit correctly. I'm really scratching my head on this one. After a bit, It finally dawned on me what I had done... The instructions on page 8-8 have you "draw lengthwise centerlines on Auxiliary Longerons F-713-L&R...". I assumed they meant the backside of the longeron and I drew a line perfectly down the center. It now occurs to me that if I had drawn the centerline based off the inside face(s) of the angle and drilled according to that dimension then I would have the correct fit as the longeron would be offset the 1/16" from where I currently have it placed.

Makes so much more sense now. That's why I was having such edge distance issues on the F-684 gussets, they were being placed 1/16" too high.

What happens if I trim the bulkheads and gear attach web to accommodate the lower longeron where I drilled it?. I did some checking on this. I am going to run into an edge distance issue on the F-796B-L/R tank attach angles.






If I follow the plans, then edge distance for the AN3 bolt is ok (No room for error though). However if I maintain the longeron where I have it...the edge distance is blown. I did up a test piece to see how much material I had to work and its just not enough.

I called Van's and the advice was if I already had it riveted in, then I'd just have to go with it. But since everything is just cleco'd the best option is to redo the F-713 longerons. Crappy, but it is the right thing to do. Order was placed for new parts...we will come back to this another day.

In the meantime...I checked the fit between the F-902 bulkhead and the F-7101 gear attach web and I do have a bit of a gap. Seems this is fairly common among the various builders websites so I too will be making a space for both the Left and Right sides out of 0.063" material.