Joshua's RV-9A Project

Post for reference: this is the diameter of the finished countersinks for #6 and #8 screws.  From Brad Oliver via Mike Bullock (post here / also on VAF here):

#8: 0.365″ – 0.375″ (Fuel Tank Screws)
#6: < 0.3125″ (Inspection Panel Screws)

Finished the day by finishing the ribs.  All are deburred, flanges squared, and fluted.  Next step is match-drilling the skeleton, then prep and prime.  Waiting on a solution to the spar problem, and for my order of primer to arrive.

I test-fit some deburred ribs into the main wing spars today, and I think I’ve discovered a problem. The spar flanges on both spars appear to be bent at the opposite angle of what they should, resulting in the ribs not fitting at all when in the correct orientation, but fitting perfectly when upside down. A photo tour follows, and I’d appreciate knowing how this compares to others — am I crazy and somehow have it all wrong, or do I have spars that are bent wrong? (Click any thumbnail for a full-resolution image.)

First, a photo of the plans section (DWG 11, Section A-A) where you can see that the upper flange should be bent downwards, toward the center of the spar, and that the bottom flange should be bent downwards, away from the center of the spar.

Here’s the ID of the spar I’m working with, clearly marked L, and a picture of the inboard end, to show that I have it clamped to the bench in “flight” orientation–note the angle is on the bottom of the spar. The platenuts for the access panels are on the bottom side, as well.

Here is a shot from the inboard end looking out. The upper flange clearly bends upwards, rather than downwards.

Hold up a rib (since this is the inboard end, this is a W-910-R rib) to the spar…when the forward flange of the rib is parallel to the spar web, the angles of the upper and lower flanges seem to be exactly opposite of the corresponding spar flange. Also, a wider picture to show that the rib is correctly oriented–note the cutout for the J-stiffener; and close shots of the top & bottom.

Flip the rib upside down and you’ll see that it fits into the spar with near perfection…unfortunately, the J-stiffener slot is now on the bottom of the wing, and the holes for the flap hinge bracket are on the top. Not going to work! (In fact, the manual is very specific about not building wings upside-down…)

How’s the other spar? Well, clamp them both upright in mirror-image…same problem.

The situation is the same on the opposite end of the spar. (The L spar is now on the right side of the photo, and the rib pictured is a W-912-R.)

Initally, I did accidentally try to fit the ribs upside-down, since that’s the way they were naturally fitting into the spar; they would only go in one way because of the angles, so I assumed that was the correct way. I found that the bottom spar flange was “gapping” as described in threads here, here, and a more recent one from early July here (links to the related build log: problem and solution). I did try adjusting the angle of the lower flange slightly to close the gap, as was recommended to the builders in those links (and also in the latest RVator…). However, the minor adjusting I did was a) to only ONE flange of the spar (the lower flange, which, as you can see in the pictures, is less off-angle than the upper flange), and b) only a couple 32′nds, not enough to be the cause of this problem. After looking again at the plans and some photos, I realized it was upside-down, and then discovered that there was a major fit problem with the ribs.

Do I have it all wrong? Or is it truly messed up? Comment or email rv9a@pacificrimsound.com

Allison put in another hour on the bench grinder, helping to debur wing ribs.  We’ve made it through more than half the stack — only the large pile of main ribs remains.  Taking a cue from the mini-scotchbrite tool that can be made for the Dremel, I came up with a handy item for deburring the inside flanges of the ribs, especially the little finger bits on the leading edge nose.  I used the top half of a 1″ scotchbrite wheel that had split in half, fit it to the screw mandrel in the die grinder, and shaped it into a wide taper profile by turning it against the 6″ wheel on the ginder.  Just like the Dremel method, on a larger scale.  The secret is that after it’s shaped, unscrew it and put it back on upside down–so the wide part is at the top, tapering inward toward the body of the grinder.  I found this profile worked extremely well for deburring rib flanges, as it allows you to get the “cutting edge” into the bend radius; then you can raise or tip the grinder to debur the slots.  You can also use the blunt end of the wheel for deburring tooling holes and such, like the vent line holes on the tank ribs.  I still used the Dremel device for the corner slots, as the die grinder tool is too big to fit in there.

Shipment from Cleaveland Tool arrived this afternoon with new abrasive supplies, and tie-down parts.  I ordered their set of pre-tapped tie-down bars and power-coated rings–I had made a harmless goof in the fabrication of the tie-down bars and this gave the chance to fix it.  (Be sure which side of the spar is the top side when bolting the match hole in the extrusion…I put them both upside down, which didn’t look like it would be a big deal, it just means the threads would be recessed a bit farther into the wing than intended.  The part I wasn’t sure about was whether the tie-down rings would be able to bottom out, and thus tighten, in the threads before starting to rub on the wing skin.)  In any event, I would have bought the nice red forged rings eventually anyway, so this presented the opportunity to get all that and finx my little oops, plus it means I don’t have to buy a tap-and-die set (which would end up being an extra when I eventually figure out a way to move tools down from home), which probably saves something in the long term anyway.  I’m happy.

I have been enjoying Bob Collins’ Oshkosh coverage, as I’m not able to make it over this year, due to work schedule (someone decided we needed a motivational-speaker “retreat” on one of the days I had hoped to use for OSH), plus unexpected expenses arising from the storm damage.

Spent the evening decompressing in the shop and deburred some wing ribs.  Finished all the lightening holes with assorted 1″ and 2″ scotchbrite wheels in the drill press and die grinder.  Finished the leading edge ribs (non-tank) with the bench grinder and the 6″ wheel.  I used a handy tip I read from another builder about deburring the silly little finger notches — take a section of worn-out 1″ wheel and cut it into quarters, put a piece onto a Dremel screw mandrel, and shape it into a cone against the 6″ wheel on the grinder.  This creates a custom tiny scotchbrite tool for the Dremel–it actually works quite nicely, though the tiny piece wears down after a half-dozen ribs or so, and needs to be replaced.  No biggie, as I have two worn-out 1″ wheels.  More on order from Cleaveland to replace them, along with a bundle of hand pads for primer prep, a #12 bit (I discovered that the #12 slot in my bit set actually held a #11).  I also ordered a batch of Stewart Systems priming supplies from RFS.

Allison helped for an hour deburring ribs on the bench grinder.

Fabricated and drilled the tie-down bars to the front spars.  Drilled & attached the nutplates for the aileron bellcrank brackets.  I used a short bolt stacked with washers to hold a nutplate in place as a jig for drilling.  The bars are off to await priming, which I intend to do as a batch with the rear spar components; they also need to be tapped for the 3/8 bolt threads.

Prepped the rear spar components: drilled, deburred, countersunk and dimpled as appropriate (above the doubler at the inboard end, since these dimples would be nearly impossible once the doublers are riveted in place; their thickness prevents access with the dimple dies).  I need to order some more primer and scotchbrite to move forward on these; now there’s nothing to do besides start prepping wing ribs.

Finally back to the project again, after an insane two weeks. July 10 brought severe weather moving across the area, a tornado 3 miles east of here, and associated straight-line winds. Those winds brought down 5 trees, blew out half the porch windows, and downed our power pole. Five days and one large electrician’s bill later, we were back on the grid. Spent considerable time with a chainsaw cleaning up; thankfully neighbors & friends came by to help out as well. That week was followed up by a 60-hour week on the job, so nothing much was accomplished besides work, eat, and sleep. Today, I was able to temporarily fix up the ignition system on the garden tractor (will need a new coil, but it’s operable), so the light was green for a return to the plane.

So, the front spar prep is basically complete, with the riveting on of the two nutplates at the inboard end of each spar. Van’s sent out the six missing nutplates after I emailed them about the inventory. Next is prep of the rear spars, then the massive rib deburring task begins.

Finished drilling, deburring, countersinking, priming, and riveting the fuel tank attach nutplates to the lower flange of both spars.  Also attached the 24 access panel nutplates.  The next step in the manual is to attach the center section nutplates, which go on the spar web near the inboard end of each spar, two per wing.  These, I discovered, are the K1000-4 nutplates which were omitted from the kit when I received “Q Bag 1923″ instead of the “Bag 1923″ listed on the packing list.  Email sent to Van’s noting the inventory discrepancy.  Beyond that is the fabrication & attachment of the tie-down blocks.  I have no tap to cut the threads, so that might wait for now.  I did drill out the massive spar rivet that had been set in one hole meant for a bolt mounting the tie-down block–I guess someone at the factory just got carried away with the riveting.  For now, I guess I’ll have to get down to business and start prepping ribs.  Which reminds me…I need to order more scotchbrite supplies and some primer.

More drilling, countersinking, and deburring of spars for fuel tank & access plate nutplates. Completed the bottom of the right spar, and about half of the bottom left.  No pictures since it looks the same as yesterday’s work.

Began work on the wing kit today, by drilling and riveting half of the tank attach nutplates. Completed the upper side of both spars. I made a jig for countersinking the #8 screw holes out of a cut-off piece of 1×1 angle by drilling a nutplate to it, and putting a #30 hole (to match the countersink pilot). Clecoing it to the spar didn’t work, as it blocked the countersink cage, but dropping two rivets in the nutplate attach holes, then fixing the jig in place with a clamp, worked well. This reduced the chattering of the countersink cage, since the pilot doesn’t run out of material as it would if you had only the thickness of the spar flange. It produced decent holes.

The process – ream the rivet holes to #40, deburr the bottom, countersink the top. Attach the jig and countersink the center hole for the screw, and debur the bottom. Spot prime with a Q-tip dipped in primer. When dry, cleco one leg of each nutplate, rivet the opposite side, then remove clecoes and squeeze the second rivet.

There are 62 tank attach screws/nutplates on each spar, plus inspection plate holes on the bottoms. I also discovered (looking ahead) that one of the holes that should be open to bolt on the tie-down fixture is filled with a rivet on the left spar. I assume this will just get drilled out, but that’s a massive rivet.