After reading the instructions about how to position and drill the horizontal
stabilizer to the fuselage, I was still unsure of the correct hole location. The
instructions say to center the hole 5/16 inch from the edge (not vertex) of the longeron.
However, since this will be drilled for an AN3 bolt, shouldn't the edge distance be
3/8 inch? I called Van's about it and spoke with Gus. He indicated that the reason
for deviating from the standard 2X diameter edge distance is because the washer would
interfere with the radius of the longeron. I decided to drill a piece of scrap to
see how it worked out. Here's the scrap angle with two holes. One is 3/8 inch from
the edge (i.e. centered on the angle) and the other is 5/16 from the edge.
With a bolt temporarily installed in the 3/8 edge distance hole, you can see that the
washer doesn't sit down tightly and the bolt is tipped somewhat.
However, with the bolt installed in the 5/16 edge distance hole, everything seats down nicely.
After thinking about this, it occurred to me that in the fuselage this washer won't actually be
seated against the longeron. There's a doubler on the top edge of the F-710 bulkhead which
rests against the underside of the horizontal leg of the longeron angle. Thus the radius won't
be a problem. That said, if I use the 3/8 spacing on the longeron, the edge distance on the
F-710 angle will be only 1/4 inch. So I still think it's better to use the 5/16 edge distance
for the longeron. I'll end up with 5/16 edge distance on the F-710 angle as well.
It took a bit of searching to locate these spacers which go under the forward spar of the horizontal
stabilizer.
After a lot of thought about how to locate the hole which will go through
the lower angle of the horizontal stabilizer forward spar, the spacers, the aft deck, the longeron,
and the F-710 angle I decided I needed to make a drilling jig. The idea is to have this jig fit
through one of the lightening holes in the aft deck and reference off the edge of the longeron.
Then it will extend above the aft deck and over the lower angle of the horizontal stabilizer forward
spar where there will be a pilot hole. Confused? You'll see. Here are a couple parts. The bottom
plate is 2 inch x 3.5 inch. Since I didn't have any 2 inch wide bar stock, I hacked off one flange
of some 6061-T651 square corner angle I had laying around leaving the other 2 inch wide flange.
I also fabricated a 0.063 inch thick football shaped spacer to transition the drilling jig
from below the aft deck to above the aft deck.
Here's the (nearly) completed drilling jig. The football shaped piece is sandwiched between
the 2 inch wide plate and the 1 inch wide bar where the three rivets are. Next step is
to accurately locate the pilot holes.
I started by drilling a hole in a piece of scrap angle exactly 5/16 inch from the vertex.
For transferring the first hole, it only took me two tries to get the position of this hole
correctly located from the vertex. For the second transfer, It took about six tries. A
milling machine could have made this much easier.
...then clamped the angle to the edge of the 2 inch wide plate and also to the face
of the cross bar and drilled through the pilot hole. Now the hole in the cross
bar is exactly 5/16 inch from the edge of the 2 inch wide plate. The process
was repeated for the other side.
Here's the completed jig. You can see the two #30 pilot holes in the cross bar.
...and here's how it works. Just reach through the lightening hole and bias the edge
of the 2 inch wide plate against the edge of the longeron. The pilot hole is now
positoned correctly ready for drilling. I think I'll wait until tomorrow to actually drill
this though. I've got to position the horizontal stabilizer and clamp it in place beforehand
anyway.
By the way, if anyone would like to use this drilling jig, you're welcome
to it. Just pay for shipping both directions.