9A Center Section

Hi all,

I'm working on the center section of my 9A fuselage. Couple of questions:

I have drilled the 1.5" diameter hole for the step in the F-725 baggage floor stiffener. The plans say to notch out the F-623 corner ribs. Should the should the part of the step that goes through the 1.5" diameter hole in F-725 be held perpendicular to F-725 while marking for the notches in F-623?

On page 8-6 it says - Rivets at the intersection of the spanwise row across the forward F-904 bulkhead... a smooth inside surface will help fit the stiffeners properly.

Can someone help me understand that that paragraph is saying???
Sorry for being so dense...

Thanks,

Tom

Tom,

I think 7's and 9's are pretty much the same in this area. I too spent a lot of time recently figuring out what this step was trying to say.

After looking at all the build logs I could find, I've concluded that these holes (the 11th and 19th, starting from outboard IIRC) should not be dimpled so the floor stiffeners (extruded, undrilled aluminum angles installed lengthwise between the forward flange of the main spar bulkhead and the lower angle across the firewall) will fit in their exact final location for match drilling through the bulkhead flange. If the bulkhead is dimpled here, it will be difficult to clamp the angles in place for drilling properly.

I hope this is a better explanation than what is in the manual. If not, then my apologies.

Are you talking about the notch in 623 for the step to clear? Not to detailed in the destructions, but it is just quick work with the die grinder and tool of choice to make the happy C in that rib!

I used a couple of popsicle sticks around the step tubing to center it, then drilled the block in place. I think you do need to cut some relief for the tube on the corner rib. Not a great photo, but is this what you are describing?
Exterior view:

Interior view:

Thanks

Thanks everyone... Bruce, is your step tube at right angles to the F-725 baggage floor rib? Looks to be in the photo.

T.

Av8torTom said:

Bruce, is your step tube at right angles to the F-725 baggage floor rib? Looks to be in the photo.

T.

Click to expand...

I can't tell you for sure, since the baggage floor is riveted in place. The benefits of taking lots of photos. I wish I had taken a LOT more during the build.

Av8torTom said:

Thanks everyone... Bruce, is your step tube at right angles to the F-725 baggage floor rib? Looks to be in the photo.

T.

Click to expand...

IIRC, it is not - I want to say it is perpendicular to the F-726 rib. Here are a couple shots of mine.

F-623 notches

Thanks Greg,

Those pictures are helpful. My main reason for asking is so I know where to notch the F-623 rib - or is there a bit of latitude there?

T.

Av8torTom said:

Thanks Greg,

Those pictures are helpful. My main reason for asking is so I know where to notch the F-623 rib - or is there a bit of latitude there?

T.

Click to expand...

I tried to notch mine ahead of time according to the drawings for the step kit, and ended up butchering it anyway on the left side. I learned from that, and on the right side it looks much better. My suggestion to you is to not notch the rib at all, until you've got the hole cut in the side of the fuse for the step leg. Now go on the inside of the fuse and mark a line on the floor perpendicular to the 726 rib to that sidewall hole where it will mount, this will give you a "topdown" look at exactly where the step tube will lie on the ribs. Now you can partially insert the step tube along that line and see the interference points and notch the 623 rib much more accurately than you can by reference to the drawings alone.

It doesn't matter if the line you draw is exactly in the center of the tube, as long as it's parallel to the tube (with a little offset fore or aft) you can still be sure the tube is straight and perpendicular to the 726 rib.

Agreed

Thanks Greg - I also decided to wait and notch the ribs later - makes sense.

T.

Sorry to revive this but I have a related question.

My construction manual says to use a 1-5/8" hole saw using the prepunched hole in the F-725 baggage rib (pg 8-6, 3rd paragraph.) My Plans say to use a 1-1/2" hole saw (dwg 22, section A-5.)

Which one is it? 1-1/2" or 1-5/8" hole?

Here's what I wrote in my journal way back in 2005:

DWG 22 EXPLODED VIEW calls for a 1 1/2" hole but the manual says to use a 1 5/8" hole saw. Since the step tube is 1 1/2" diameter, I opted for the larger hole.

http://www.aclog.com/rv-9a/index.php?c=3#652

I used 1 1/2" for mine and then opened it up a bit more with a sanding drum on my Dremel as needed to dry fit the the step through the hole. The skin will get a slight bend to it afterwards, but it wasn't enough to need the hole opened up any more. I doubt I added more than 1/16", so it will be tighter than a 1-5/8" hole.

The step tube is 1.5 dia. The hole in the fuse needs to be somewhat larger to clear the weld bead so the step flange sits flush against the fuselage.