New Ribs

I had the opportunity today to start the process of fabricating the additional 14 ribs.  Recalling an earlier post, I have decided to replace the leading edge ribs with full ribs.  Though I have more than sufficient material on hand, I need to turn that material into the various small parts that make up a rib. 

The first step is fabricating the rear end blocks.

I decided to build these blocks using the band saw and the sander instead of cutting them out using the router.  I just didn't feel like reconfiguring the shop for the router operation (a big disadvantage of a small shop, things have to be re-arranged for different operations) and I feel confident in my skill with the band saw and sander. 

Task #1, above, is to cut a pattern.  Using a single pattern is preferable so that any variations are not magnified from copy to copy.  The pattern takes particular care to ensure it is accurate. 

The above photo shows the pattern, cut from plain ole 1/4" ply, as opposed to aircraft grade.  All of its dimensions have been checked. 

The photo also shows the outline of the pattern traced onto 1/4" aircraft ply.  I had these squares left over from a previous mistake.  :)

I have found it advantageous to think out the production process, rather than considering fabricating one item at a time, so that all the parts are ready to hand when it comes time to fabricate the rib.  Thinking in terms of production instead of piece-by-piece fabrication really speeds things up and ensures a more uniform finished product.

Next I drew guidelines to cut the square into individual rough blanks.  Even when doing a non-critical cut such as this I find it helpful to draw lines.  It keeps me from making monumental mistakes...most of the time.

Here is the stack of blanks after cutting them apart on the band saw.  There are actually 16 blanks here.  I only need 14, but having two extras gives me the opportunity to make two mistakes without having to cut additional blanks and/or blocks.

The finish cuts are made on the sander.  The straight cuts get done on the disk...

The inside curves are done on the belt. 

A finished end block.

After a couple of hours of work, a stack of 15 end blocks.

But wait.....didn't I say I started out with 16 blanks???  Yep!  A small cutting mistake turned one of the blanks into scrap.  It always pays to plan for mistakes. 

Cooler Temps

Fall has definitely arrived here in the Pacific Northwest, with winter right behind it.  With the cooler weather I have fired up my little kerosene radiant heater to keep the shop comfortable.  It works great.

Obviously, I only run the heater when I am working in the shop.  The result is that the shop gets good and chilly when I am not around.  One result of that is that the T-88 gets really difficult to coax from the bottle. 

Sooo, on days when I am planning to glue, the T-88 goes in front of the heater first thing.

The distance has been chosen so that the T-88 gets warm, but not overly so.  It really improves the flow and decreases the time it takes to mix a batch.

Questions

A friend of mine who is intrigued by this project was confused about how the idea of a steel tube fuselage works:

This is a photo of Mike Finney's fuselage prior to covering.  His airplane is a Wag Aero Cub, rather than the Wag-a-Bond, but the construction approach is identical.

The fuselage is composed of welded 4130 (chrome-moly) steel tube.  It ends up covered in dacron.

Another Change

I just read the excellent article in the EAA Sport Aviation magazine about Mike Finney's shortwing Wag-Aero Cub.  What a beautiful little airplane. If you are not an EAA member, you can access the EAA online magazine "Experimenter" on the EAA website.  There is an article about Mike Finney's plane there, too.  Just go to the EAA website (via Google), go to the Multimedia tab and click on "Newsletters".  You can handle it from there.

I have corresponded with Mike on the Yahoo Groups site for Wag-Aero plans-built aircraft.  With all that, I got thinking.  One of the aspects of his airplane is that there are not leading edge, or "false" ribs.  He built full ribs for those locations instead.  The Wag Aero Cub wing is essentially identical to the Wag-a-Bond wing.

I also got thinking about the history of the Piper Vagabond.  The Wag Aero Wag-a-Bond is essentially an exact copy of the Vagabond. There are some changes.  The Vagabond was one of the first Piper aircraft to use aluminum wing ribs and spars instead of wood.  The Wag Aero wing is, essentially, an exact copy of a  pre-1947 Piper wood wing. 

Post-war (WW2), Piper was struggling financially.  They were building great airplanes, but they were doing so as economically as possible.  So, in all likelihood, the leading edge ribs were necessary for the leading edge of the wing, but an adequate wing could be built without full ribs in those locations.

However, if full ribs are installed in those locations, the result would be a stronger wing, and with more secure attachment of the fabric.  So, the additional ribs result in making an adequate wing better.  The weight penalty is actually pretty small, maybe three pounds.  Ribs really don't weigh very much. 

The downside is about a 70% increase in the amount of materials used, and probably just about double the fabrication time for the ribs, and a substantial increase in labor stitching the wings.

It just so happens that I blew the material takeoff when I ordered the spruce capstrip.  I have well over half of the capstrip I ordered sitting unused.  I also have sufficient material to cut the gussets and aileron rib tail blocks.  The nose blocks, which are needed for the leading edge ribs, are already cut.

So I could build full ribs instead of leading edge ribs at no additional out of pocket cost.  It would mean I am not finished building full ribs (and I have just shy of 100 hours into ribs now) and when covering time came the stitching would require a great deal more labor, but...no, or very little, out of pocket increase in cost.

For a better wing...

I'm gonna do it! 

Short Ribs - Not on the Grill

All of the "normal" sized ribs are complete:

It makes quite a nice pile.  There are 12 aileron ribs and 8 full-length ribs.  Still to fabricate are two tip ribs (slightly smaller cross section), two tail ribs that go behind the fuel tank bay,  two leading edge ribs for in front of the fuel tank bay, two leading edge ribs that match the tip ribs, and 14 leading edge ribs. 

I started the tail ribs today.

These ribs extend from the front of the rear spar to the back of the wing.  Here are the longitudinal members cut and fit.  The steel rule aligns the end of the members exactly with the front edge of the spar.  I also had to add a couple more alignment blocks right at the spar so that the vertical member would not push the horizontal members out of alignment. 

Here is the first tail rib fabricated and glued up.  It sure didn't take long. Now I just need to wait for the adhesive to cure before I can pop this one out of the jig and start on the second one.

I had hoped, dear readers (and there are an astonishing number of you), to treat you to some aerial photos today.  We finally got a small break in the weather and I abandoned work to take advantage of it.  However, when I got airborne I found that a "significant convective event" (thunderstorm) that I thought was stuck up against the mountains, was moving towards the airport.  Not wanting to get shut out of my home field, I circled back and landed after a short flight.  Sorry, no photos.  But I did get to fly.

Another Day - More Ribs

Just for  those of you who think you can't do this because you don't have the space....

This is a photo of about 3/4's of my little shop.  It can be done.  The two cardboard boxes contained the new sander and the little radiant kerosene heater that I bought.  I have kept the boxes for a little while to be sure the products don't have any out-of-the-box problems.

The radial arm saw, being the power tool I use the least right now, has become the catch-all horizontal surface for all the misc. bits and pieces.  Also, the older table saw is serving as a desk.  You can't see it because the plans are draped over it.

Once all the ribs are done and varnished, the two table saws and maybe the radial arm saw will be moved to my hangar to make room for the fabrication table.  My fabrication table will be modular.  The full table needs to be 4' X 14'.  My table will consist of two 2' X 8' modules and two 2' X 6' tables.  That is so I can configure a fabrication table to meet the current need.  For instance, I will only need a 2' X 8' table to build the ailerons, but both the wings and the fuselage will require the full 4' X 14'.

The aileron ribs (wing ribs that include the aileron wells) are complete...

 The closest stack is the pile of aileron ribs...all 12 of 'em.  The further stack contains the completed full length ribs.  I am in the process of building the last two of those...

They are the #10 ribs and are plated with 1/16" ply from the rear spar back.  Building the plated ribs requires a little creativity.

The big challenge is plating the "up" side.  It can't be done in the jig.  In the area that is to be plated the capstrip pieces are end-glued in place.  Grain-end glue joints are very weak, but they serve to hold the pieces in place until the rib can be removed from the jig and the process of fabricating and gluing the plate can begin.

The rib is gusset side down because it is easier for the sizing step.  This rib needs to have the plate installed on the side on which the gussets are already installed. Once the plate has been fabricated, the rib will be flipped over.   The piece of ply is the blank from which the plate will be fabricated.

The outline for the plate is traced onto the blank using the rib as a guide.  Care is needed as those end grain glue joints are very weak.

And the plate is rough-cut on the band saw.  And, yes, I know about the color balance variations.  Live with it!

A check fit, and, sure enough, the plate is just a tad oversize in some areas.  A pencil line is drawn on material that needs to come off.  Note that the rib has been flipped over. 

And the high spots are trimmed off on the sander.

Perfect fit.

And the outline is traced onto another blank for the plate for the other #10 rib (one for each wing).

I cut and fit all the pieces for the second #10 rib, shown here in the jig, before gluing up the plate on the first #10 and the gussets on the second #10.  I have used heavy bolts to hold the plate in place on the first #10 rib.  They apply enough pressure to keep the ply flat, but not so much as to "starve" the joint, a big sin according to SystemThree (the manufacturer of the adhesive).  Once all this is cured, the first #10, the one not in the jig, will be flipped over and the flip side gussets glued in place.   

Applying the plate to the second rib will be easier.  As there is a rib for each wing, the plate will be on opposite sides of each rib.  Note that the gussets have been applied to the rib in the jig.  With the gussets in place, it is a simple matter of pulling the rib from the jig (once the adhesive has cured), flipping it over, and installing the plate along with the flip side gussets.  A piece of cake compared to carefully end gluing the capstrip (making sure the rib doesn't get glued to the jig), and, once the glue is dry, veerry carefully removing the rib from the jig for attachment of the plate. 

Ribs won't be done with these last two full length ribs, though.  I will need to build 18 "false" or leading edge ribs, two partial ribs that install behind the fuel tanks,  and two tip ribs. 

Make a Rib

To try and spice this blog up a bit, I thought I would outline the process of cutting and fitting the rib parts.  I have already discussed my gluing-up process.

I apologize for the varying color balance of the photos.  The primary objective was to get the rib built.  I have various lighting sources in my shop, and the camera was thinking on its own regarding operation of the flash.  I am sure there are adjustments in the camera to force flash on every exposure.  But I was not interested in taking the time to figure it out. 

The very important first step is to clean off the jig.  Usually, the problem is just a bit of dust and wood chips.  It is very important that the capstrip snuggles down flat onto the jig surface.  It is also important to make sure no dried glue drips are lurking where capstrip will go. 

After cleaning things up, it is time to place the blocks.  This rib is an "aileron" rib, so it has both a nose block (shown in this photo) and an end block (shown in the next photo).  It is important to get the block fitted properly in the jig.

Here is the tail block placed on the jig in its proper location.  Due to a minor discrepancy in the jig used to cut these blocks, they all need a bit of adjusting to fit correctly. 

The first longitudinal member to be cut and fit is the bottom one.  It fits into a notch in the nose block at the front end.  The end of the capstrip is carefully marked to match the angle of the notch.

The tail of the longitudinal member needs to be marked for cutting, too.  This is not a critical dimension.  The capstrip just needs to extend beyond the last securing cam beyond the tail block.  The capstrip will be trimmed to final length after the first gusset is in place.

The bottom longitudinal is cut to rough length on my cute little miniature table saw.   This is a handy tool for rough cutting where both ends of the piece are longer than the throat of the band saw.

The angle on the front end of the bottom longitudinal is trimmed to shape on the disk sander.

And the bottom longitudinal is in place.

Just like the bottom longitudinal, the front of the top longitudinal needs to be trimmed to fit into the notch in the nose block.  Marking is a simple process of lining up the capstrip and extending the notch angle onto it.

The next step, after trimming the longitudinal, is to secure it in the jig using the cams.  What you can't see here is that my fingers are pushing the capstrip down firmly onto the jig.  All the capstrip has to be completely flat on the jig.  The tail of the top longitudinal is measured for the rough cut with the capstrip completely installed in the jig to make sure the curve of the top longitudinal doesn't result in cutting the capstrip too short.

I mentioned earlier that the tail block needs some final trimming.  In this photo I am making a pencil line along the bottom edge of the block.  The idea behind a lot of these pencil lines is to serve as an indicator.  By sanding off just to the point where the pencil line disappears, I avoid taking off too much material.  If too little is taken off, I simply make another pencil line and repeat the process.

Here is the tail block being trimmed.  Because the front edge of the block is perpendicular to the bottom longitudinal it makes sense to use the miter gauge. 

Perfect fit!  It is important that these parts are friction fit between the longitudinals without pushing the capstrip out of position. 

Here are the two longitudinals installed on the jig ready for the verticals and the braces.

This is a glimpse of the shelf on my work table.  I keep the hand tools and buckets of gussets handy so that I am not wandering around the shop looking for parts and tools.

Marking the first vertical for trimming.  This is a pretty simple process of lining the capstrip up, sighting down onto the top longitudinal, and marking the vertical-to-be aligned with the bottom edge of the top longitudinal. 

The vertical-to-be is trimmed.  Note the penciled arrow.  I mark parts that have only one orientation with an arrow pointing to the top of the part.  This really helps keep things straight.

The bottom of the vertical is marked to length at the bottom longitudinal.

The vertical is cut to length, at least the first cut, is done on the band saw.  I always make this cut on the waste side of the pencil line.  The part always turns out a little long.  Thankfully.

And, predictably, the vertical is just a bit long. 

I make a pencil line right at the end of the vertical, just a lead-width wide.

And it is trimmed. In these instances I just sand down until the pencil almost, but not quite, disappears.

Still just a bit too long.  So another pencil mark is made and back to the sander.

Perfect fit!  The business card is serving as a shim.  Tony Bingelis recommends that when installing the verticals next to the spars (represented by the 3/4" plywood filler) an allowance of .010 to .015 be made so that the ribs can be slid onto the spars.  The business cards measure out to .013. 

The 1/4-inch shim between the cam and the vertical is there because some of the ribs require double verticals at the spars. 

All of the verticals are cut and fitted using the same process.

Now its time for the braces.  I place a length of capstrip in the location for the brace for marking.  This first mark is aligned with the vertical.

And a second mark aligned with the top longitudinal.

I rough cut the braces to length so that they are easy to handle and the bottom angles can be trimmed on the sander.  The sander works much better for these angled cuts than a saw.

The bottom of the brace is rough cut on the band saw.

On the top of the brace, first one angle is cut...

Then the other.  Again, note the arrow to keep straight which end is the top and which the bottom.  When one is cranking out braces, it can get confusing as to which end is which.

Then the bottom end is aligned and marked for final trimming...

Like so...

And, after a couple of trips to the sander, a perfect fit.  Well, almost. If you look closely, I have made a mistake (not an unusual occurrence)  that will result in my having to make another brace.

That's right.  The shim on the vertical next to the spar is on the wrong side of the capstrip!  I have to watch myself all the time.

The rest of the pieces are simply repeats of these steps down the length of the rib.  Once all the pieces are in place, gluing gussets can begin.