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Left Wing Inspection Cover

So close to Christmas and it is clear that the left wing will not be done by the 25th.  Work is the main culprit as Tim tried a couple times to connect  with me but I was fighting against a shipment deadline for equipment on ‘critical” project.  I made my own bed and slept in it but I question if in 10 years that it will seem all that critical. Getting this plane in the air and spending time with my family and friends has to be a bigger priority. Something to work on.

Well, today and yesterday were pretty good as far as the getting things done on the plane.  I almost made a mistake today that would have set me back more than a few days.  I’ll get to that  but first the progress.

Yesterday, despite numerous interruptions with honey do list things, I was able to start and finish the inspection cover and the cut out for the tie down in the lower skin. I really like the squeezer that Gary Hall loaned us.  It is really the ticket for installing nut plates.  Tim and I decided to  use nut plates to mount the inspection covers.  While I am behind the decision it turns a 3 minute drill and screw into 3 hours when you want to have the screws countersunk (self tapping screws are what are called out on the plans).  I have a few pictures  but to make sense of what is going on I should explain that buying countersunk nut plates would be faster (and probably smarter) but what we had were a large collection of flat nut plates.  I don’t know the MS number for the nut plates we have but I thought it would be easy enough to just add a small piece of aluminum behind the skin to provide the depth to counter sink for flush mounting rivets and mounting screws.

The procedure is pretty straight forward but it is important to keep track of what holes should be drill first and at what diameter in order to best keep everything aligned.  The procedure I followed was this:

1) drill major inspection hole and make a cover

2) Mark the center line and cross  line for screw holes in cover and skin

3) Drill screw holes with #40 bit in cover

4) Align and match drill screw holes to align cover to skin

5) Cleco nut plate to skin and drill mounting holes with #40 bit.

6) Cleco cover to skin and updrill to #30.

7) dimple cover and skin for screw (this will likely be a #6 dimple die

8) updrill (match drill) previously dimpled holes to #21 (for ample clearance for screws)

9) dimple mounting holes on skin

10) cut small blocks of 0.060″ to mount nut plates.

11) match drill aluminum blocks to nut plates.

12) counter sink aluminum blocks for counter sink depths on skin for mounting rivets and screws.

13) debur and prime mounting blocks and skin.

14) rivet aluminum and nut plates to skin (this is where the squeezer works so well.  Just by measuring the stack up of parts the rivets can be cut to length and the rivet squeezer can be set to the proper compression and it works like a champ)


Only 14 simple steps and you’re done.

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Left Wing Bottom Skin Level And Match Drill

Today was perhaps a good example of how quickly things can move along in the assembly process if all the parts are made (like a kit, instead of scratch building as we are) and if we don’t mess around thinking too hard about stuff.

Tim was busy until around 1:30 and I had a load of issues to attend to with regard to work (I so much for vacation but at least I could take care of it without leaving home).   The morning was spent catching up on email and getting things prepped for dinner (gotta keep the “sweetie” happy).  After all that it was almost 12:30 before I got into the garage to even turn on the heat.  I was in the garage actually doing something by time Tim arrive.  I had been on a conference call and simple kept my headset on while on mute and listening in as i drilled holes in the skin to finish the top side match drilling.

When Tim arrived i had the match drilling pretty much done and while I pulled out the bottom skin Tim cleaned up the rear spar trailing edge to file off any alignment error between the skin and the spar.

We flipped the wing over and Tim aligned the bell crank brackets to the upper skin while I worked to level the then skin by supporting each of the four corners with blocks and shims to insure the wing was flat (not having any wash out or pitch variation from root to tip.  

Left Wing Level Bottom Side Up

The process of squaring and leveling the wing (as mentioned earlier) can be done a couple different ways but the bottom line is that (in my view) you need to have an image in your mind of the process you are involved in.  I spent a good part of my youth working for my “old man” building houses and even did it for a few years before and during my college years.  The process of squaring a wall so that when you stand it up it will be plump is very similar to assembling a wing to be square and not have any wash out. For me it is almost an intuitive process that I know most framing carpenters would find easy.

The process can be broken down into two primary steps.  The first skin must set the wing with regard to square (which is not terribly hard but a bit of a challenge to find a reference).  The second step, once the wing is held square by the first skin, is to insure it is flat (no wash out).

To square the wing it is also a good idea to have it close to level, although not necessary to be exact, it will be needed on the second side skinning so the procedure is good practice.  Once level it is easiest to find four points that define a parallelogram. The first two points on the skin are the wing station 22-3/4″ center line at the center of the main spar and the trailing edge of rear spare at the same 22-3/4″.  These two points will be  marked on the upper and lower skin as the intersection of the center line (where the holes are drilled) and the edge of the skin.  If you cut our skin carefully (as you should) the final width should match the plans and the skin should be square (don’t trust factory cut sheets of aluminum to be square).  Even though the root and the wing tip have very irregular contours, the center line of the first rib in from each end (rib #1 and rib #12) should form a perfect rectangle on the wing skin.  The second two points are the same position on theT #12 rib. The key characteristics of a rectangle is that each of the opposite sides is the same length and the angles where the adjacent sides intersect should form 90 degree angles. The wing skin when laying flat provides a perfect pattern to align the wing box.  The only task that remains is to identify the reference point that make a rectangle on the skin, and mark them on the wing box.

To really describe the above process i need to generate a picture or some sort of graphical layout.  maybe that will be a task for later.

Once the wing is held square by the skin on one side of the wing, attaching the second side will give the wing 3 dimensional rigidity.  Holding the wing flat, or vertical and planar, when skinning the second side will insure that there is no wash out in the final wing structure.

If all of the wording above is confusing, I hope it is because of my poor explanation and not the readers inability to understand the concept of square and flat.  Otherwise, you are doomed.

Wing Skin Drill Jig For Between Ribs

The bottom line for the  night.  The bottom skin is fully match drilled and the inspection hole is cut.  Tomorrow I need to determine if I want to add the fwd ribs and skin or updrill the aft ribs.  it probably does not matter but immediately after the leading edge is skinned I will proceed to cutting in the landing light for the left wing. That could happen tomorrow…

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Bending Forward Wing Skins

(Been a while since I have updated the website)

Dan cut out the top and bottom skins.  Now it was time for the dreaded forward skin with the leading edge bend.    The factory suggested a U shaped wooden channel and a guillitine type press that pivots on one end.  Think of a paper cutter at the office.  This seems kinda drastic but it must work.  We had looked on the internet about the different ways people do this.  Some have used the same wodden U channel but the center piece is actuated down level by two threaded rod jack screws.  Finally there is the vacuum method that uses a pipe at the inside of the leading edge and you wrap the sink in some polymer sheeting and suck the air out with a shop vac.  The pressure drop on the large sides of the skin pulls the metal in.  There are several YouTube videos on this and we liked the result.  So we tried it.  The following pictures on the second side.  We already had the experience of the first.

First we need to mark the sheet.  Sonex provides a set of X-Y points for both ends since these are interesting curves as they wrap around the leadign edge.  I used CAD to make a spline fo the curves and plotted it out.  We aligned the plot with the bearest row of rib rivets and traced the line.  We movd the plot over so we have an offset to cut on.  We can file down to the line later.

Traced Skin Edge

Now marking and double checking the center line of the skin

Marked end with offset:

Cutting out the skin with the electric shears (they are great)

 

There is some technique to the electric shearsyou have to tilt is at the right angle and feed at the right rate, Dan has the golden touch (I think he pratices every morning before breakfast):

Now we lay the skin on top of the poly sheeting:

Since the pipe will lay directly on the centerline we made a mark on either side of the center line of radius of the pipe.  We used 1.5 inch diameter black (gas) pipe schedule (? thick).  We double checked these marks and used a square on the edge of the pipe to line up with the mark:

Dan had tried pipe flange clamp but didn’t like the results so we used muffler clamps.  They seemed really stiff.

Double checking the pipe location by a measurement from the pipe to the outer edge:

Next step is to bring the two long edges together.  This is accomplish slowly using tape by working your way down one side and back again, down and back…  Takes a while but you need to be gentle so the skin doesn’t bend.  Two people makes it go quicker.

Got the top edges touching:

  As you do this you are moving from tape piece to piece.  With hindsight you really want to make sure the two sides are lined up precisely at the top.  Now we folded the poly over and tucked it under, folded the other side over, twisted the ends and tied with wire:

We put the shop vac hose in one end:

We used a smaller shop vac but it worked just fine.  (I wanted to borrow a 3/4 hp industrial blower from work but Dan veto-ed that.)

After taking a deep breath we pulsed the shop vac on and sure enough the poly collapsed and made a beautiful teardrop shape of the skin.  We let the vac run for a little but all the bending was done.   All that prep work for 26 seconds of vacuum forming, (I have a movie of it but need to upgrade this blog to show it).  Here is our unwrapped result (still taped at the top)

Now you have to un-tape it slowly maybe .5 inch a time at each tape strip and work back and forth:

Finally you have a leading edge skin, we are really happy with the process, the relaxed bend is close to the assembled leading edge Dan made in the Sonex workshop.  We didn’t get any wrinkles or kinks which was a huge relief.

Thanks to those that pioneered this method.

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Cutting Out Wing Skins

The wings structures are all together and ribs up drilled to the front and rear spars.

Next step is the wing skins.  We thought we had been pretty clever in our 4′ x 12′ aluminum sheet planning but we discovered once we laid out the wing skins on what is left we will need to buy another sheet for a fuselage skin.  With hindsight we should have cut out the wing and fuselage skins and put them aside.  No biggie.

Dan had cut out the top and bottom skins.  Note that the aluminum sheets are not perfectly square from the mill.  A good framing square will show it.

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