Right wing - shell and wing attach pockets

Here's another one of those 2 or 3 line sentences in the plans that you think will only take an hour, but really end up taking a few days or weeks to complete.

Let me start with the FC1 inboard shell cutout... this pocket later houses the aileron bellcranks and other linkages. The plans give us the following sketch with a note stating that the most important cut to maintain the 0.6" dimension is the shear web face.



I made the necessary measurements and marked up the cut lines... top surface...




 bottom surface...





Notice how the cut line ends up being perpendicular to the trailing edge... 


I added a piece of tape to keep the shell from splitting in half after I cut it... since it was already split by the hotwire when Eureka cut the aileron torque tube channel...


I used a simple hacksaw blade to cut this section off... I went really slow and made sure I was staying on line on both sides...


Taaaa-daaaa!



Now to convert it into a shell. I measured 0.60" around the perimeter of the airfoil and made tick marks along the way...


I then connected the tick marks to give me a nice spline on the top and bottom surfaces...


Remember that the most critical cut is the shear web face... this face must be 0.6" thick on this plane. So rather than try to bandsaw around it, I figured the best approach was to shear the face off - to give me a perfectly smooth 0.6" thick plane - and bond it back to the shell later.

My bandsaw at home was too small for this job, so I had to use the one at work.

When I laid the foam flat on the table, I realized the shear web face is not perpendicular to the side plane of FC1. This would not give me the homogeneous 0.6" thick plane that I'm looking for....



So I stuck a scrap metal extrusion that was laying around to prop the shear web face parallel with the bandsaw blade...



With everything aligned and my heart beating like I was running a marathon, it was time to cut...



Four seconds later... it was all over.


Well, not quite... I still had to cut the interior of the shell piece off...


Taaaa-daaaa! Shell piece is cut. The shell gets reattached to FC1 later. But for now, let's move on...



So let's talk about wing attach pockets. The wings get attached to the center section spar (what I call 'the wing box') using 3 bolts per wing. The inboard most bolt is easily accessible inside the shell I just finished cutting out. The remaining two bolts are not so lucky. In order to reach a socket wrench to the bolts, special wing attach pocket depressions are made.

I should note that the plans have us install the jigs and bond the FC sections together at this point; however, I figured it would be a lot easier to make the pockets if I have full control of FC1 and position it wherever I want. So again, I held out on assembling the jigs and bonding the FC sections for now.

Ok, so let's make some pockets!

The plans caution us by stating that the top pocket is of a different depth than the bottom pocket. Studying section B-B on page 19-12 in the plans, it's clear to see why. The top surface of the airfoil has a greater slope... so the relative depth of the pocket will be less than the depth of the bottom pocket. See section B-B below:




Ok, great... so how do I know how deep to cut if my reference plane is sloping? Great question. But before I move on, make a mental note of how the pocket floors are perpendicular to the shear web face.

Follow me here... I started out by making all the necessary measurements as outlined in the plans on page 19-4.



Notice how the LWA4 puck outline is slightly larger than the pocket channel.. this is very important and you will see why later.


If my reference plane is sloping, I figured I needed a flat reference to measure to the pocket floor. Recall that the pocket floor is perpendicular to the shear web face. So I created a small platform (using a 2x1) and shimmed it such that it was square with the shear web face (notice the small foam piece on the aft end of the 2x1 to shim it accordingly).


I then measured the maximum depth of my jig saw...


And made sure the 2x1 gave me the proper elevation I needed...


I then repeated for the other side... notice how I used tape to hold the 2x1 in place...


One last check to make sure the 2x1 platform was perpendicular with the shear web face...


With everything aligned... I used the jig saw to make a few passes....


I then used a knife to remove the notches... notice how I didn't go too far aft with the jig-saw...


I wanted to fine tune the aft end of the pocket with the dremel tool...


I then cleaned it up some more by using sand paper to round all corners and make the surfaces as even as possible...


I placed the 2x1 again (with the proper shim to make sure it was perpendicular with the shear web face) and measured the depth to the pocket floor. The aft end was 2.56"...


And the front was 2.55"... the actual magnitude is irrelevant since I am measuring it to know how sloped the pocket floor is. A 0.01" difference tells me the pocket floor is pretty darn perpendicular to the shear web face... exactly what I was going for!


With the top pocket carved out, it was time to repeat this process for the bottom pocket...


2.53" here....


2.58" here... a difference of 0.05"... again, pretty happy with how "flat" my pocket floors turned out!


With the pockets all milled out... it was time to apply layup #1, a 2-ply BID at 45 in the pocket. So I cut four pieces of BID at 45 (2 pieces for each pocket).


I slurried the pocket...


Added some dry micro to the corners to give me a nice fillet...


Prepregged 2-plies of BID on the bench...


And stuffed it into the pocket...


I trimmed up the edges with scissors to have about a 1" overhang... and used a brush to tuck the prepreg and get rid of as many air bubbles as possible...


Bottom pocket complete... one more to go!


I then flipped FC1 over... notice how I had to place scrap foam pieces to keep the still wet bottom pocket from hitting the table.


Same procedure here... slurried the pocket...


Prepregged 2-plies BID at 45...


And stuffed it in the pocket...




The next day, I trimmed all overhangs with the multi tool...



Now that's a nice pocket!


Next, I had to recess the pocket end so that the LWA4 pucks would be flush with the shear web face. The plans have you do this prior to glassing the pockets... but experience has taught me that if I would follow that procedure, micro would go all over this recess and make things very difficult for me later. So instead, I waited till after glassing the pockets to recess the pucks.

Here I am setting the proper depth on my dremel tool...


I then marked the 0.25" depth onto the pocket end to let me know if I was removing too much or too little...


I then milled away...


0.25" exactly....


Oooooo... nice recess!


Let's test it... looking gooooood!


Now repeat for the other pocket...


Awesome!


Top view...


Remember our shell... with his face cut off?


This made it super easy to lay the face flat on the table and measure out the LWA6 puck (you read it right, that's LWA6... which was not made (nor mentioned) during the other LWA pucks back in the center section spar chapter. Luckily, I still had 2" x 0.25" aluminum bar and made these real quick - a 2" x 2.3" x 0.25" puck). The dimensions and location of this puck is shown on page 19-4, bottom right.


Using the dremel, I milled out the LWA6 section...


Nice and flush!


We are not done just yet. Next I had to make the WI8 shields. These are made out of 0.016" thick aluminum. I cut them 2" wide per plans, but left the tabs extra long so that I could cut them to exact length.


The plans warn us about making sure the plate ends up perfectly flush with the shear web foam surface. So I traced the plate...



And used the dremel to recess the borders. I went really slow and careful here.. hard to judge what 0.016" looks like...


After a few gentle passes... I was perfectly flush with the rest of the shear web surface. Now to cut the extra long ends to size...


First I marked the top lip...


Then the other end...


After a trip to the bandsaw.. the cover plate was spot on...


Test fitting LI8 with LWA4... looking great!


Since some of these pucks will be exposed to the air (not covered in glass or epoxy), I figured I would go ahead and alodine them... here is the before...


Here is the after.


Now that the shell has been cut and the pockets are complete, the next step will be to set up the jig and bond all FC sections together... and reattach the shell back onto FC1.



2 comments:

Dario Zapata said...

Thanks so much for sharing !!

Ary Glantz said...

You're welcome Dario!! I'm glad you are enjoying the blog!