28 January 2014

Wings: Fuel tanks. Doing them over.

My fuel tanks tested leak free, both left and right.  But there was one thing that bothered me so much, that I decided to scrap these completed tanks and make news ones:  The skin-to-baffle countersinks.

First issue was that those countersinks were too shallow.  They were just on the hairy edge of being at the 0.006" proud spec for shaving.

I went ahead and shaved them all with my shaver back in October of 2013, figuring I'd probably do the tanks over in the future anyway.

The bigger concern was that the holes in the skin were excessively elongated (they went down to a "knife-edge" but that may be unavoidable with a skin thickness of 0.032") as I wasn't very careful with keeping the drill speed slow.  I hadn't noticed the issue until after I was done sealing the baffle.  So, though I don't know if the corresponding baffle holes also got elongated, I had to assume they were.

Now, the plans initially have you skip countersinking every 10th hole to help keep things aligned.  The holes that you skip get countersunk after the baffle is sealed in.  This meant that I could rummage through my image library and possibly find illustrative images with the non-countersunk holes to see how they compare to the countersunk ones.  Two such images are below.  You can see which holes were skipped (highlighted in red) by their smaller radius.  That's the radius appropriate for an AD3 rivet.  The larger holes were too big. 

The two images of the baffle holes I found (not shown) didn't show evidence of elongation.  Under the assumption that the baffle holes weren't elongated, this is what the squeezed, set rivets would probably look like (pardon my poor computer art skills).

I also wasn't confident that the AD-42H pop rivets holding the tank attach zees were properly pulled.  Here's an image from inside the tank (looking through the filler flange).  The heads didn't look consistent to me.  I may not have been pushing down hard enough on the rivet puller when setting these rivets.

Perhaps I'm being too conservative, however I just wasn't comfortable with these outcomes.  So I shelled out the $1223.90 for replacement tanks.  For the second build, I will:
  1. Dimple, rather than countersink, the skin-to-baffle holes (being deliberate with my sealant use to ensure the baffle seals).  There is successful precedent for this (here is the reason for using the countersink approach).  It would be a stronger joint and avoid the pitfalls of dirty countersinking.  Apparently it's important to use reduced diameter dies on the baffle to avoid distorting the flange.
  2. Rivet the flange bearings last to ensure access to all rivets on the tank/rib assembly.
  3. Avoid missing a dimple.
  4. Avoid needing an AD5 rivet.
  5. Seat the AD6 rivet filling the outboard rib tooling hole so that the adjacent AD4 rivet can be fully set.
  6. This time, I will not use deeper dimple dies.  There's an interesting thread about this
  7. Do a better job routing the capacitive probe wires.  I thought they were too loose.
  8. Do a better job shaping the fuel float wires.  I had to buy a second set on the first run and they ended up with slightly different deflection extrema on each side.
  9. Generally, apply the sealant more cleanly (example of poor aesthetics can be found on the third picture above). A sealant gun should help here (purchased 3-Feb-14).
  10. Continue using the fay seal technique as described here
  11. Update 26-Feb-15:  If I were ever to do a third set of tanks, after sealing the mating surfaces, I would not shoot the rivets wet. I would remove the sealant from the dimple, buck/squeeze the rivet then dollop the shop head.  Apparently even Van's doesn't shoot their rivets wet and doesn't seal in the shop heads in QB kits (read whole page 15).  At least, that's how I construe the conversations in those two links.
Click here to follow my fuel tanks redo in reverse chronological order.

19 January 2014

Empennage: Aft fuselage. Final priming.

The final parts for the aft fuselage have been primed.  Including those I decided to replace

Top side skins.

Top skin and remaining parts.

Now all that remains is some time dedicatd to riveting and the empennage will be completely riveted.  I don't have enough space in my current digs to complete the attachment of the control surfaces and the Fiberglas fairings.  Once this point is reached, the build stalls until new space is acquired.

18 January 2014

Empennage: Elevators. Outboard trailing edges tapered.

The plans call for the outboard edges of the elevator trailing edges to be sanded down, providing a taper to transition between the different thicknesses of the wedge itself and to the elevator tip fairing.  I had just recently purchased a belt sander for this and other aspects of the build.

The left elevator taper didn't turn out as good as the right side, no doubt owing to the fact that I did the left one first.   Here are a few perspectives on the left side.  Not perfect.  Almost a bit of a twist was formed owing to the asymmetry of each side's taper.  But it will do (it's a sort of Catch-22 in that once you're on this trajectory, the more you fix it, the worse it gets).

When the left side is laid across an untapered trailing edge, you can see how it compares.

Now, for the right side.  I did a much better job on this side.

With the right side adjacent to the rib fairing, I think the taper will be okay.

13 January 2014

Shop: Belt sander purchased.

Picked up a Craftsman 21514 4"x36" belt sander today.  Will help me finish the lenses on the wing tips, the rudder stops and later Fiberglas pieces.

12 January 2014

Empennage: Aft fuselage. Bulkheads riveted.

Got all of the bulkheads riveted.  Mostly good work on my part, however I had two outcomes that will result in a lighter wallet.

First they get cleco'd up.

Then they get nailed together.

Horizontal stabilizer front attach bulkhead.   All rivets squeezed.  I actually had to remove and replace the two top rivets on the right attach bar.  On one I mangled the shop head by being off center with the squeezer and the other somehow got a rivet that was 1 mm too short.

Bulkhead with tail tiedown.  All rivets squeezed.  Notice the slight warping of the holes near the #12 screw holes in the bracket.  This was due to my dimpling those holes (per plans) only to realize that they should not be dimpled so I had to flatten them (plans need a revision on 10-07, step 1).  I also dimpled each hole in the web the wrong direction and had to re-dimple in the right direction.  Update 11-Dec-14:  I've decided to replace this bulkhead even though it's already riveted in.  Update 29-Jun-15:  The bulkhead was replaced after installation in the aft empennage.

Horizontal stabilizer rear attach bulkhead.  All rivets squeezed.

Aft bulkhead with rudder cable bracket.  I used the rivet gun to prevent warping such thin parts with the squeezer.

Forward bulkhead.  Again, I used the rivet gun to prevent warping such thin parts with the squeezer.

So now, the big mistakes.

Mistake #1:  I took the picture on the left to be manifested in the physical world as on the right.  How could that happen?  See, I got overconfident on recently finding several rivet sizes in the plans that were inaccurate and decided the AN470AD4-4s called out should be -6s.  Proud of myself for finding another error in the plans, I later found that I was the one in error, but only after squeezing 19 rivets.

I decided I could drill out those 19 rivets to separate the parts and move on.  Which I did.  The holes were slightly enlarged, but not too badly.  However in the end, I decided that I didn't want that part in the plane with the stress introduced by my error.  So I'm going to replace those parts.  The battery angle is $17.  We'll see what the ribs are.  I'm awash in surplus nutplates so I don't need to purchase any more of those.  I'm actually solving two issues at once since I also had a countersink too deep on one of the battery angle nutplate attach rivets.

Also, the plans don't call for the bellcrank rib flanges to be dimpled #40.  They need to be as they will be directly riveted to the skin.

Mistake #2:  On the systems bulkhead, I dimpled not just the nutplate attach holes (the latter highlighted in red), but the screwholes too.  Not a big deal really.  I pressed them out, but because dimpling stretches the metal (especially for #8 screw holes), the part was no longer very planar.  Looking at it, I didn't want it in the plane, so I scrapped it and will replace it.  Also, whilst working on this bulkhead, I found out I was missing MS21055-L3 (a.k.a. K3000-3) nutplates.  Apparently, I'm not the only one.  Wasn't even on my manifest.

Empennage: Aft fuselage. Priming.

Nothing exciting other than priming a whole lotta parts.  For the first time, given the many parts, I used the dimpling table which is usually just out of the time lapse camera's range in the far field.  That table is shown in the bottom row, right side.

As an aside, I tried taking some pictures immediately after priming.  When the flash was engaged, the images came out foggy.  On cleaning the lens, they were still foggy.  I quickly realized it was due to the primer that precipitated out and became airborne.  I hadn't realized that this happened.  This is why I wear a respirator.  Left image, no flash.  Right, with flash.

The next day, I took a picture of all the parts that are primed and ready to go.  First we have what's in the basement...

...then for completeness, what we already have in the guest room.

I don't live in a house any longer.  It seems I'm living in a hangar that has no runway access.

07 January 2014

Wings/Lighting: Landing lights. Wiring complete.

My landing lights, the AveoMaxx Hercules 30,  as received.

Ridicuously bright.  The camera doesn't do it justice:  At midnight, this single light makes it noon.

The wing kit's harness wires are appropriately gauged for the currents they'll carry with the  AveoMaxx Hercules 30.  However, I needed to buy Tefzel wire for the three additional lines beyond the stock kit provisions. 

Here's the wiring of the lights with the wire colors from the wing I'm using overlaid.

Since the AveoMaxx Hercules needs 7 wires as I'm going to use them, the 9 position connectors below worked great.  Also, one of the lights has to be defined as the "slave" (otherwise wig wag would just be a wig and no wag), so I jumpered one wire from ground to the master/slave line.  This was done on the wing wiring side, thus the lights themselves get defined as master/slave by which wing they plug in to.  

All crimps were easily made with a budget crimper then soldered for security.

Here's the right wing connectors, not fully inserted.  You can see the ground jumper since I defined the right wing as the slave side.

Part numbers for the Molex connectors are:


I'll have to pull and reposition several pins on the wing root wiring harness.  For that one needs a Molex pin extractor (formerly Cat. No. 2062447).  I found mine on eBay and it works great.  I originally tried this extractor, but it only works for the male pins, despite manufacturer claims.

Finally, I need to work on the mount.  The mounts that came with my lights don't fit.  Looks like Van's kit isn't quite the PAR36 standard.  This image was taken looking in the landing light cutout directly towards the W-00017 mount.  Update 30-Apr-17:  I completed the landing light mounts.