6th March 2010

Primer prep, and a goof caught

Hours: 4.9 | Posted in Center Fuselage, Forward Fuselage

Etched all the fuselage components that are done to date, except for the side and forward bottom skins, and the main longerons.  Those are big enough that they really need to be done outside (the etch solution eats the concrete floor, and they’re too big to fit in the big plastic tray I use for etching parts); we’ll see if the weather is good enough tomorrow to get it done.  Should be able to get the priming done this week.

After tiring of etching, I thought I’d look at the install of the crotch strap brackets.  This is where I discovered a dormant screw-up that I was previously unaware of.  Turns out that when I initially fit the seat ribs to the center section, I got the inboard pair of F-916 ribs reversed.  That is, the inboard F-916-L goes on the right side, and vice versa.  Unlike some other parts of the plane, it’s completely possible to reverse these with no ill effects–the seat pans, bottom skin, and everything else all fit perfectly, so nothing screamed “wrong!”  Until I held the crotch strap brackets in place, when it became very evident what had happened.  The space between the ribs that are spanned by the bracket is about 3/4 of an inch too wide.  Since the center section isn’t yet attached to the tailcone, access to drill out and re-rivet these ribs isn’t a problem, so I drilled both out and put them in the correct orientation.  Easy enough, except for one thing: the 3/16″ holes that were match-drilled from the main spar, where AN3 bolts are inserted, are not in alignment with the line of rivets that runs down the forward flange of the ribs, but rather offset by a small amount.  This means that when the already-drilled ribs were flipped into the correct orientation, those 3/16″ holes are out of alignment by about 1/2-diameter, which would result in ovalled holes if drilled.  I’ve sent an email off to Van’s asking their advice–my guess is that they’ll say it’s fine, put in the bolt and move on, since that rib is also held in by a bunch of rivets.  But better to ask…if the ribs need replacing, it should be easy to do that, too…for $17.73 apiece, plus shipping.  Sigh.  I feel like I’ve made several stupid mistakes lately.

Seat rib installation drawing Moving ribs in center section Relocated rib in center section Misaligned hole on ribs after placing in correct location

(The ribs in question are the third in from each side on the drawing — the inboard “F-916-L/R outboard seat rib”.  Marked by the clecos on the second photo.)

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