Building, testing and operating an experimental aircraft

HS Front Spar Assembly

30 Dec 2009

After finishing four solid weeks of work, I finally got a chance to get back to building. I picked up a Baldor 111 Buffer as a Christmas gift for Dad, so we could have a dedicated grinder for the Scotchbrite wheels. (I still need to pick up the 3M Light Deburring Wheel from Cleaveland.) I also ordered a bench mount bracket for the Cleveland squeezer, in preparation for riveting the rear spar.

Baldor 111 Buffer Baldor 111 Buffer

Dad had already done a great job of tapering the HS-810 and HS-814 while I was away at work, so we started by filing out the cut marks and cleaning up the edges with the Scotchbrite wheel, then match-drilling them to the HS-702 front spars.

Rivet Squeezer Bench Mount Rivet Squeezer Bench Mount

We then measured the 4 7/16” from the centerline of the 810 and 814, in preparation for bending. We jigged the parts up in the vise, and then just gently bent the six degree angles by hand.

Bending the HS-814 Bending the HS-814

Matched HS-810 and HS-814 Matched HS-810 and HS-814

Although not specifically called out in the instructions, I noticed that other builders had fabricated bend relief holes in the HS-702 front spars prior to bending those. If you look closely at View A-A on DWG 3, you can see these relief holes, but had I not read other builders’ logs, I’d have missed it. We drilled out the holes with the #30 bit directly centered on the bend line, then cut and filed the notches. They’re far from perfect, but I think they’ll do the trick.

HS-702 Bend Relief Holes HS-702 Bend Relief Holes

Next we dimpled and countersunk the four holes for the AN426 flush rivets as called out in the plans. The countersink cage worked flawlessly when mounted in the drill press, and I think that might be the “official” technique from now on. We drilled about ten holes in some scrap angle to dial in the correct countersink depth before moving to the real parts. The new bench mount for the squeezer made accurate dimpling a breeze.

HS Forward Spar Clecoed HS Forward Spar Clecoed

Lastly, we fit and trimmed the HS-404 nose ribs per the plans. However, instead of using the plan’s measurement callouts, we simply test fit the 404s to the front spar.

HS Forward Spar Clecoed HS Forward Spar Clecoed

The idea was to avoid the over-trimming problems noted by other builders. We’ll see how it comes out when we final-drill the parts.

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