Can see the 701 wing repair finish line

Sunday was a good day in the shop, and both Ron and I can see the finish line with the 701 wing repair and extension.  Just a few more small items to go.

As Ron gets close to covering his Aeronca Scout with fabric, we've been discussing his plans to make a fabric/pain rotisserie rig for the shop.  You may recall from way back in this blog an engine stand I bought for my Corvair.  With my engine parts in Florida for rework, we're going to modify my engine stand and Ron's engine stand to become the end pieces for the rotisserie.  This rig will allow us to  mount any fuselage, wing or other large parts for priming and painting and being able to rotate them will be very helpful.

The inboard nose skin is ready to be installed.  I clamped the skin in place, lined up along the spar.  To draw the nose skin tight, ratchet straps are used, pulling the skin tight across the ribs.  It's important to place the straps directly over the nose ribs to prevent caving in the nose skin before it is riveted.

Straps are equally tightened until the nose skins lay tight against the nose ribs and spar:

Folded protectors distribute the force across the trailing edge, thin scraps of wood protect the surface skins from the ratchet and strap hooks.

Using the hole duplicator, I matched the new nose skin to the original spar holes on the upper side of the wing.  These were drilled to final size, the nose ribs to A3 until final fitting.  The 3rd rib is drilled, but missing clecos so I can fit the outboard nose skin where it will overlap the slat pickup.

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Once measured up, the outoard skin needs to be slotted to allow the slat pickups to protrude through.  The easiest way to do this is with a trim router and spiral up-flute milling bit.  I laid the outboard skin out on the table and set clamped a straight edge in place as a guide.  Two strips of plywood under the sheet on either side of where the slot will be cut support the thin aluminum sheet and are thick enough to raise the bit above the table

The tool makes amazingly clean cuts requiring very little deburring afterwards.

After cutting all 3 slots perfectly straight, a valuable lesson learned - even if you right down the measurement, that is no guarantee that what you wrote down is correct :(

I measured the first slot as 395mm from the inboard edge, but for some reason I wrote down 595mm.  From that point on, every time I double checked before cutting the slot, I measured/checked it as 595mm.  Bringing the sheet back to the wing, my error was immediately obvious.

Slat on the lower left, slot in the skin above - not where it should be :(

After pacing around the shop wondering how I could have possibly messing up the measurement, Ron told me he could fix the error fairly easily with a simple patch - go ahead and cut the right slot.  This is part of learning and too much sheet metal to start over.

With the correct slot cut, all the slots lined up perfectly with the slat pickups - minor crisis averted.

Kind of a weird look, but the inside of the nose skin reflects the nose ribs before being rolled over.

Holding the skin in place with small spring clips - after all the work I'd hate to drop the skin and ding an edge!

Before working on securing the top side of the outboard nose skin, we thought it best to finish securing the inboard nose skin, that would give us a solid reference point for the outboard skin.  We flipped the wing over and end for end on the bench.  To get the nose skin flat, a thin strip of wood is placed under the ratchet straps.  Once lined up and tight against the ribs, I again duplicated the spar holes and drilled the ribs to A3 size.  Everything lined up excellent.

Even this nose skin, as small as it is lengthwise makes the overall wing so much more rigid. A good sign.

​While waiting to discuss my slotting error I also unrolled my 040 sheet and start marking out the 3 horizontal tail doublers I need.  I was initially really surprised at the amount of tape Aircraft Spruce used to secure the roll, but quickly understood why!  There is a bunch of pent up spring energy in that roll, and I had to be real careful about wrangling it onto the flat floor for measure/cutting.  The longest piece I need from this sheet is 1440mm long, so it was safe to cut that length off the end of the 12 foot long sheet. I marked and rolled the balance back up (that was a task!)  and put it back into storage.

Aircraft Spruce ships all their sheet aluminum with a protective plastic sheet coating on both sides.  Depending on how long the sheet has been on the shelf, room temperature, and other factors determines how easy it is to remove this coating.  I think next time I'll gently warm it with a heat gun or hair dryer - this stuff sticks too good.  For now, I've only removed a few inches from the edge I'm cutting from.

Even cut down to length, this sheet is awkward to put in the bender for scoring, and it's thick enough to making scoring a very long process.  Instead, Ron and I think we are going to try using the router we used on the nose skin slots to accomplish the long cuts.  If this works as we think it will, we'll use the same process for the wing spars (032) and maybe the fuselage sides/tops - anywhere a long straight cut on a large piece of material is needed.  As I said above the tool makes really clean cut edges that require little in the way of deburring.

One other thing I've been doing is adding some of the complex shapes from the plans into CAD.  Like my smaller parts (ribs, plates, etc.), these will be printed out to provide templates.  One example is the wing root nose skin.  I use a free downloadable 2-D CAD program called LibreCAD - it is very simple and more importantly it will accept the X/Y co-ordinate system common in the Zenith plans:

If you like doing things in 2-D CAD, you can download a free copy of LibreCAD here.

For those that have been asking, my finger is healing up nicely :)

More soon, thanks for reading.