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W-1201A Doubler warning

hamblin10

Active Member
Does the warning on page 17-02 make sense about protecting the LH wing spar caps from being drilled to #20 by inserting a steel strip? If you do not drill through the stack and open the holes then how are you going to install the BSPQ-5-2 rivets? Thanks!
 
Does the warning on page 17-02 make sense about protecting the LH wing spar caps from being drilled to #20 by inserting a steel strip? If you do not drill through the stack and open the holes then how are you going to install the BSPQ-5-2 rivets? Thanks!

The purpose of the metal protector strip is so that once the drill bit has drilled through the skins and spar flange (to enlarge the holes for the 5/32" rivets) the drill bit doesn't damage the edges of the spar cap strips that are just a bit further inside the wing.
 
Thanks Scott! It was just strange how it was worded about protecting between the skin and spar cap.
 
Thanks Scott! It was just strange how it was worded about protecting between the skin and spar cap.

In technical terms (at least in regards to our naming conventions at Van's), the spar cap is the heavy structure material (in the case of the RV-12, the laminated layers of bars) along the top and bottom edges of the spar.
The spar flange is the flanged portion of the spar channel, that the skins rivet too.

On some aircraft the spar flange and spar cap are the same thing, but that is not the case on any RV wing spar (prior to the RV-15 at least ;))
 
Double-checking

I’m about to do this step, and just want to double-check… I don’t think I’m correctly visualizing where the strip has to go to protect the spar cap while still allowing me to enlarge the flange holes.

I’ve got the doubler clecoed to the skin and spar flange, all the holes lined up and everything looks right. However, on the left wing the drill bit will emerge almost an inch from the spar web aft face, and nearly parallel to it; on the right wing it’s much closer, ~1/8”, but there’s still no danger to the spar cap (the bottom of the web, right?) if I drill perpendicular to the doubler/skin/flange.

I don’t see how the steel strip will help, since it has to be pretty narrow to avoid blocking the (enlarged) holes aft of the spar that I’m enlarging, as well as the ones fwd of the spar that I’ve filled with clecos. If I do put the steel strip in place on the right wing and drill 10 or so degrees off perpendicular, the point of the bit will still miss the strip before it scratches the aft side of the spar web (or those fat pre-set rivets). It would only save me if I accidentally started a new hole forward of the holes I’m enlarging.

Does this sound right?

(I’m asking partly because neither I nor my local big-orange-box hardware store have any <.040” steel sheet handy, and I don’t want to take more time searching for it unless I know where to put it that’d help protect me.)

Thanks!
 
...on the left wing the drill bit will emerge almost an inch from the spar web aft face, and nearly parallel to it; on the right wing it’s much closer, ~1/8”, but there’s still no danger to the spar cap (the bottom of the web, right?) if I drill perpendicular to the doubler/skin/flange.

Bryan - I had the exact same confusion, glad I'm not alone! :)
 
A little too much free time this morning, so...
 

Attachments

  • 17-02 Spar Doubler Final Drill #20 Warning.jpg
    17-02 Spar Doubler Final Drill #20 Warning.jpg
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I used those spring-ed collars on the drill bits so the bit only went so far.
No biggie. Seems like the spar was pretty far away from the drilling, if I remember correctly.
 
I remember being confused regarding this caution note when building my wings four years ago. This note was originally necessary when attaching the doubler to the older wing kits when there were no pre-existing holes and the #30 holes were match drilled above the spar cap (ref. RV-12 service bulletin 14-11-03, pg. 3).
I really don't see why thiis caution note is still in the instructions.
 
Thanks for posting the question & replies -- I'm glad nobody's time clock has been running during the (too many) times I've been trying to figure out this instruction! EchoJuliet's comment about the historical context for match-drilling the doubler & skin explains why this comment used to make sense.
 
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