Roee Kalinsky's RV-7A Project

2006.09.17: (1.0) With the fuselage now off the ground, I finally have access to fix a defect that's been nagging me since I first received the fuselage from Van's.  The skin has a conical curvature in the area where the cabin steps penetrate the fuselage.  At the vertex of the cone, the skin has a very tight bend radius and therefore is under considerable stress.  Although a relief hole is called out, it is very common for a stress fracture to develop from the vertex.  I've observed this on many flying RV's, and mine is no exception.  When I inspected the fuselage after receiving it from Van's I noticed a small crack emanating from the relief hole on the starboard side.

Since the crack was still very small, approx 1mm in length, I decide not to drill a stop hole, but rather just enlarge the hole slightly beyond the edge of the crack.  Taking inspiration from my dentist, I put a small grinding bit in my Dremel and went to work.  As best as I can tell, it worked.  I enlarged the hole, deburred it nicely with a needle file, and no longer see any sign of a crack.  Now time will tell.  If ever a crack does develop again, I'll reconsider stop-drilling.

2006.09.18: (1.0) Upon closer inspection, I noticed tiny cracks in the same place on the port side as well.  Gave it the same treatment.

With that out of the way, I can start actually working on the cabin steps.  I marked the 1.5" diameter nominal cutouts on the skins, as well as 1.6" diameter oversized circles to help keep everything centered if I have to enlarge the holes slightly.

2006.09.19: (1.5) Cut the 1.5" hole in the skin for the starboard cabin step.  Used a Dremel with an 1/8" tungsten carbide cutter bit (Dremel p/n 9903) for the initial cut, then cleaned up with a 1" sanding drum in the air drill.  Then did the same to the outboard flange of the F-623 floor rib.  Note that the clearance holes are not really circular because the skin and ribs are not quite at a right angle to the step's torque tube.  The holes have to be made slightly oblong fore-aft.

2006.09.20: (2.0) Did the same as yesterday for the port side.  Then removed material from the inboard flange of the F-623 floor rib.  The Dremel was too wide and short to reach through the hole in the skin, so I used the 1" sanding drum in the air drill all the way.  The "neck" of the air drill is long and slender enough to reach through the hole in the skin, and this worked well.

2006.09.30: (3.5) Cut the clearance holes through the F-725 baggage ribs using a hole saw through the hole in the skin.  I had to use a Harbor Freight 90 degree drill adapter that I had laying around, not because I needed the 90 degree, but because it was the only way I could the hole saw in there.  My air drill is narrow enough to get through the hole in the skin, but its chuck is too small for the hole saw.  My battery powered Makita can chuck the hole saw, but the chuck is too big to get through the hole.  Anyway.  Hole saws are not the most gentle of tools, especially when used at an angle to the material, so I supported the rib by clamping a piece of plywood to the opposite (inboard) side of the web.  It went fine.

I then proceeded to start fitting the starboard step.  First I had to shorten the torque tube by about 3/16" (easily done using the die grinder).  I then had to enlarge the hole in the skin to accommodate not just the tube's diameter, but also the weld fillet where the tube joins the flange.  But before enlarging the hole I carefully marked the flange's position on the fuselage as aligned by the tube through the 1.5" holes, and also again drew an even larger concentric circle around the hole to help keep it centered as I enlarge it.  After enlarging it I could push the weldment all the way in, but the flange doesn't quite conform to the skin's contour, even in the relatively flat areas forward and along the top.  So I started adjusting the flange little by little toward a good fit with the skin.  Used a big adjustable wrench as a lever arm, which worked pretty well.  I was surprised at how easily I could shape the steel flange while cold.  I thought I might have to use a torch to heat it up -- no need.

I then marked a hole pattern, which is slightly modified from that shown on the plans.  Specifically, I carefully repositioned the rivets that go through the F-724 bulkhead to ensure good hole spacing considering the flush rivets already attaching the F-724 to the skin.  So I ended up with four evenly spaced rivets in that column instead of five.  And to center that column with the F-724 bulkhead it also ended up a little forward of where Van's drawing shows it relative to the dimensions of the flange.  I then also repositioned the aft rivet columns for even spacing.  Anyhow, Van's drawings for the step kit are ancient hand drawings that were done for the RV-6A, and they don't exactly match the dimensions of the RV-7A, nor the dimensions of the weldments themselves.  So the instructions and drawings are useful, but not to be taken literally.

2006.10.02: (2.0) Drilled the starboard step to the fuselage using the step's flange as a drill guide.  For now I only drilled the forward holes and the top row.  I still have to finish shaping the bottom aft portion of the flange, which is what I spent most of the evening doing.  I've seen a lot of RVs with a very poor fit in this area.  It's impossible to get a perfect fit the way the weldment is designed, but I want to get as close as I can.

(Hard to see in the photo, but there's actually a lot curvature in this area.  Before shaping the flange, there was more than 1/4" misfit to the skin at the extremes.)

2006.11.14: (16.0) [This entry represents approximately the past 5 weeks.  Being extremely busy with my "day job" lately, work on the airplane has been limited to an hour here and there, and I opted to spend all of that time building rather than logging.  I'll try to capture the highlights.]

Finished shaping the flanges on both steps.  The starboard step came out pretty well with bending alone, but the port side gave me some trouble.  The curvature of the skin in that area was not as neat as it was on the starboard side, having some concaveness toward the F-624 vertical rib in additional to the expected conical convexness aft.  I matched the curvature as closely as I could, but still ended up with a slight gap (approx 0.050" max) between the flange and the skin in the center where the welded tubing prevents bending the flange.  I didn't want to attempt riveting with this size gap in there, so I decided to shim the worst area and then smooth over the rest with filler.  I used some 0.040" 4130 chromoly for the shim (JB Weld'ed to the flange), and JB Weld for the filler around it.  I then sanded it all down and got a very nice fit to the contour of the skin.

I finished drilling the flanges to the skins (temporarily to 3/32") and fitted the plastic blocks at the inboard ends of the tubes and the F-726 ribs.  I then enlarged the clearance holes and cutaways in the F-623 and F-725 ribs to clear the tubes by at least the thickness of a mil-spec Popsicle stick.  This is to ensure that as things twist and flex under stress, the tubes and ribs don't touch and exert force on each other.  I used the alodine pen to treat the cutaway areas.

2006.11.18: (2.5) Prepping the steps for primer.  Beveled the edges of the flange for a smoother transition to the skin.

2006.11.19: (4.0) Alodined the skins where they'll mate with the step flanges.  Sprayed AKZO primer on the skins (the mating surfaces), the step weldments, and miscellaneous other unrelated parts I've had laying around for a while waiting for primer.

[Note: The apparent jaggedness of the cutout in the fuselage skin is an artifact of resizing the photo.  The hole is super smooth!]

2006.11.20: (2.0) Installed the cabin steps to the fuselage.  Garnet came over to help, and did a nice job on rivet gun duty.  [Garnet has been involved with aircraft restoration for the USS Midway museum.  See pictures of a newly restored TBM Avenger here.]  I was on bucking bar duty, and had one slip that resulted in a minor ding in the skin under the baggage floor.  @#$%!  Otherwise, the steps came out really nice.  I'm really happy with the fit in all places except for the bottom aft, which I knew I wouldn't be able to fit perfectly.  Will deal with that later using filler.