Finishing rear bulkhead assembly

All but four of the 100-plus rivets needed to complete the rear bulkhead assembly can be squeezed using one of the two "C" yokes that came with the Cleaveland Main Squeeze rivet squeezer (a dozen or so are of the "pop"-rivet variety).  So I saved those for last, which, in retrospect, was kinda dumb.  Shoulda done 'em first.  The yokes have about a two-inch reach.  To get those last four rivets squeezed requires a yoke with a three-inch reach, which I don't have.  That means it was time to learn how to use a pneumatic rivet hammer and bucking bar.

Remember back in July I borrowed my neighbor's air compressor?  Well, six months later I finally fired it up and tested out the rivet hammer.  To my relief, both worked perfectly.  Here's what those items are:

By this time the rear bulkhead assembly had quite a number of hours invested in it and I didn't want to mess it up when it was so close to being finished so I asked the owner of nearly all of the tools that I've been using, Mr. B, for his assistance bucking those four rivets.  Mr. B was a great sport and came over to help.

First thing we did is select the right bucking bar out of the four or five that came with his rivet gun.  But even the one with the small end on it was slightly too large for the narrow space available to work with, now that all of the other "easy" rivets were in.  So Mr. B took a little bit off the corners of the bucking bar with the bench grinder.

And it worked!  Then Mr. B held the bucking bar and bulkhead steady and I "shot" the rivets with the rivet gun.  Due to my lack of experience (no dry run practice for me, thank you very much) a couple of rivets had to be drilled out, but fortunately we noticed that the top of the rivet wasn't sitting flush before getting too far along.  All part of the learning curve.  A bit later all of the rivets on the rear bulkhead were done.  Thank you Mr. B!

Before we finally get to the actual building of the tail cone skins, there's one last chance to test fit the bulkhead to the stabilator.  See those bearings?  The AN4 stabilator hinge bolts go through those with a washer on each side of each bearing.  AN4 hinge bolts are 4/16ths diameter (1/4" for the fractionally-challenged), which seems a bit wimpy.  But if you do the math you get a bolt shear plane of just under ¼ x ¼ x ¼ π = .05 square inches.  Multiply that by the shear strength of the bolts, about 100,000 psi, and you get almost 5,000 lbs of force required to shear the bolt.  Multiply that times four possible shear planes (two per bearing), and you can deduce that other parts would fail before those bolts will.

Vans has you choose whether to use a thick washer or a thin washer on each side of each bearing, as long as it's symmetrical.  So the choices are:  four thin washers, four thick washers, or two thin and two thick.  You determine which ones give the best fit in the stabilator brackets.  A good fit is snug (no lateral movement between the bulkhead and the stabilator), but not too snug.  Once you select the right washer combo they're super-glued in place onto the stabilator brackets.  That's 'cause, unless you have very small slender hands, those bolts and washers are difficult to place and even harder once the tailcone is assembled.  Having my eight year-old daughter help out really came in handy.  In my case the magic combination is two thin washers and two thick washers.  Perfect fit.  Just hope they don't fall off.

Note for RV builders who are married:  You may want to keep the fact that you're using super glue on the airplane to yourself.  Even though you're just using it to temporarily hold a couple washers in place, it doesn't help the confidence-building with your spouse, if you catch my drift.  Trust me on this one.

Merry Christmas everyone!

 

Skidplate Fabrication Part 2

I went a little bit out of order.  You're supposed to tap out the hole first, and then put it on the rear bulk head to drill the rivet holes in the skid plate.  But since I didn't have a tap handy, I went ahead and did the rivet holes drilling first.  In this case it didn't make any difference.  Next day I borrowed a 3/8" x 16 tpi tap and handle from a guy at work known for having a nice tool collection, drilled out the hole and started threading the hole with the tap.

As you can see, it gets harder as you go, until...

Uh-oh.  Broke the jaws on my friend's tap handle.  What are my options?

Vice grips can do a lot of things, but turning a tap isn't one of them (seemed worth a shot though).

This doesn't work either:

So I went to Home Depot to get a new beefier handle.  I'm sure I'll use it again sometime.

So with lots of turning, unturning (to clear out chips), and turning again, plus a few drops of bike chain oil, I eventually ended up with a nicely threaded one-inch hole in the bottom of the skid plate to screw the rear tie down eye bolt into.  Following day I returned the tap and asked my co-worker if he wanted me to replace the broken tap handle and he said he had extras and not to bother.  We'll see if he lets me borrow any more of his tools in the future.

With the skidplate fabrication done, we're ready to rivet together the bulkhead assembly, and here's what that looks like (well one side anyway):

Note that all 95 (or so) rivets are done except the two on the left and two on the right.  There's no way that the rivet squeezer I have with its two-inch "C" yoke was going to reach those two rivet holes, what with the "ears" for the main stabilator bearings on the reverse side being in the way.  I've mastered (sort of) the hand rivet squeezer.  Now it's time to learn to use the pneumatic rivet hammer.

Skidplate Fabrication Part 1

Page 10-3 has us fabricating a skid plate by taking a section of extruded aluminum, cutting several pieces off of the extrusion, and threading the center hole with a 3/8" tap.  Funny that they would call it a skid plate, since the part will never touch the ground.  But it will provide a place to screw in an eyelet bolt to be used as a rear tie-down point.  I suppose if you were to really over-rotate on landing or take off the eyelet bolt could scrape the runway, but airplanes aren't normally flown that way (sure would wake you up if you did).  Still, it's good to have because eyelet bolts are cheap and easy to replace, whereas runway rash on the rear bottom skins, well, I don't even want to think about what a PITA how difficult that would be to repair.

 Here's the [mostly] unmolested piece with a cut mark on it:

And here it is after a little band saw surgery:

The next couple steps use the drill press, band saw (again), and scotchbrite wheel on the bench grinder to remove additional material at the bottom (right), and to grind out a notch in the side, as shown:

A thin aluminum template is used to locate the notch and drill the first two of 16 rivet holes.  Here's an important builder tip for drilling those first two rivet holes:  After drilling the first rivet hole, cleco the template to the skid plate using that hole.  Guess what happens if you don't.  That's right, your second hole may end up in the wrong location.  Using the magic of Photoshop <not>, here's what that would look like ('cause I would never do anything that stupid):

So remember, cleco the template with that first hole.  You might even consider drilling just one of those two rivet holes now, and the rest when the plate is on the bulkhead.  Cleco each as you go.  That will allow you to precisely center the bottom part of the skid plate (with the threaded hole) between the doubler plate flanges on the bottom of the bulkhead.  Be sure the notch position is okay before you start drilling.

Back in the Saddle

I know.  It's been over a month since I last posted.  Truth is, I just haven't worked that much on the plane.  Lots of yard work and things like that have gotten done on the weekends (with body aches to prove it), but for some reason my enthusiasm for evening work on the plane has wained a bit with the shorter days, despite taking a day or two off to work on it.  I need to get on the ball though.  There'll probably be a scheduled price increase in February on the various kits that Van's sells and I'll want to have my order placed for the RV-12 wing kit before then.  Because of workspace issues I'll also want to have the tailcone finished and stowed away before the big crate full of airplane wing parts arrives at my door.

So what have I done in the last month?  Well, I
 * removed the blue plastic protecting the skins along all the rivet lines,
 * deburred all the rivet holes and edges,
 * bent the edges on the tailcone skins per the plans (not hard, once someone shows you how),
 * fluted the frames to straighten the rivet hole lines, and
 * fastened together the tailcone frame hoops shown in picture.

The large and medium hoops are easy - a few pop rivets and you're done.  The small hoop, the one that goes at the very aft of the tail cone, required the assistance of my neighbor Ken because there's a doubler plate and six-inch angle fastened with #4 rivets that need to be squeezed, and the pieces are too light to secure firmly while operating the rivet squeezer, which is also awkward to use (for me anyway).  In return I promised to help Ken clean out his second-story rain gutters this weekend.

As you can see, I did manage to mess up the first rivet (bottom row left) by oversqueezing it, I think.  Somehow there ended up being a small gap between the doubler plate and the frame after I squeezed the rivet.  So I drilled it out and, since the hole is now enlarged, ordered some #5 rivets from Aircraft Spruce to use in that hole.  They should arrive any day now.  The other 17 rivets went in pretty well because I took my own earlier advice and only gave each rivet a half-squeeze until all 17 were in, then went back and re-squeezed down to spec.  It also helped a lot having Ken hold the frame steady while I manned the rivet squeezer.  With the exception of the first bottom rivet (soon to be fixed), I'm satisfied with it.

December 18 update:  The # 5 replacement rivets came in the mail so I could finish the final rivet in the small bulkhead hoop.  You're not supposed to use a Cleaveland Main Squeeze rivet squeezer on 5/32" rivets but I used it anyway and didn't break anything.  Here's the # 5 "oops" rivet next to seventeen # 4s:

It should be okay.  It's deep in the tailcone and faces aft, so no-one will see it anyway.

You Meet the Nicest People

Step 1 of Section 10 has us "break" the edges on six 8' tailcone skins.   By "break" they mean bend the long edges of the skins a few degrees so that the overlapping edge is flat and snug when the skin is riveted (the clamping pressure of a rivet can cause the edge to lift a little bit).   Due to the geometry of the tailcone (radius is smaller at the back end than the front end) the bend, or "break", increases as you move down the narrow end(s) of the skin(s).  Fortunately there's a handy tool for breaking edges (shown in the picture) that I borrowed from the guy at work.  Apparently it's easy to use once you learn how.  Problem is I don't know how to use it.  Seriously.  Clueless.  Never seen it done before.  The owner of the tool never used it either.  So I put a message out to the Sacramento RVators group to ask for help. 

Right away the group's founder, president, secretary, treasurer, and newsletter editor, Ed Martinson, put me in contact with Kerry Richburg, a retired fellow who flies a beautiful RV-9A he built at Sacramento Executive airport.  Kerry took time out of his morning (he was prepping to fly to Monterey) to introduce me to the edge tool and a few other tools that I'll be needing down the road, including a tube bender and fuel line flaring tool.  The SacRVators group loans them out like a library book so that RV builders don't have to shell out dough for an expensive tool they may only use a few times.  Here's a picture of Kerry and his -9A:

 

Kerry demonstrated proper technique for breaking an edge and gave me some scrap aluminum to practice with (it's not like you can just pick up 2024-T3 0.020" aluminum at Home Depot, and none came with the kit).  He also passed along info about a flying club called DGA (Damn Good Association) located at the other end of the airport.  The club's hangar is open weekends and anyone can drop by and take the nickel tour of some of the club's 10 different airplanes.  At any given time the club is always rebuilding some vintage aircraft, but the latest project acquired by the club is a partially-completed RV-12.  It seems that the original builder became ill (Alzheimer's or Parkinson's or something like that) and was unable to finish.  So the club bought his partially completed -12 for less than the cost of the kits.  The finished parts include the stabilator, vertical stabilizer, rudder, trim tabs, tail cone, wings, flaperons, and most of the fuselage, all very nicely put together.  Here's a picture of the tail cone, which is the part that I'm just now starting:

 

I asked one of the builders there, Mark Z., how long he thought it would take the club to put the -12 together and he said that they would probably have it flying by April.  Holy c*@p!  He also speculated that, with high fuel prices, it would be a very popular airplane for the club.  The good news is that there's at least one CFI (that's FAA-certified flight instructor you land-lubbers) in the club who will be able to provide the necessary transition training in the -12 before it's my turn to once again "slip the surly bonds".

 

November 2014 Update:

Okay I'm back from the future.  The DGA RV-12 was completed and certified airworthy in July 2013.  Club members flew it around, added wheel pants, and recently had it painted.  Here's a picture of N471PD:

 

Congratulations DGA!

Stabilator is Finished

Section 9 concludes with drilling holes and attaching weights to the counter balance arm.  With five pounds of lead weight on the counterbalance arm, the stabilizer now wants to tip forward except that my helpful assistant (out of the picture) is holding down the stab to prevent that.  After picture-taking the counterbalance arm is taken off and stowed away.

And   we    are    done!

With the stabilator finished it's time to move it to make room to start the next piece. The safe place turns out to be in the family room.  Nice place to store it, don't you think?

The vertical stabilizer and rudder are in the corner.  Together these parts should make interesting conversation pieces just in time for Thanksgiving festivities.

Coming up is Section 10: Tailcone assembly.
I have a feeling this part is going to take a while.

Halloween Downpour

Our neighborhood was swarmed last night with ninja warriors, vampires, princesses and trick-or-treaters dressed up as teenagers too lazy to put on a costume.  The problem with having generous neighbors is that ghouls and bandits from miles away are bussed in to collect a share of the loot.  Then at 8:30, after my kid returned with her cut of the action and three large bags of candy were just about gone, a storm front moved in that soaked the area for about five or ten minutes.  You could hear the cries and screams a block away.  Heh heh heh.  A steady drizzle afterwards meant that the Halloween blackmail was over and I could open up the airplane factory for a couple hours.

80 rivets later the aft stab skins are attached and it's time to attach the stab horns.

One of the bolt holes on the lower horn did not line up perfectly with the nut plate inside the spar box so I had to elongate one hole slightly in order to get the bolt in the nut plate without risking a cross-threaded bolt.  Really hated to mar the powder coat finish on the steel stab horns but it was necessary since moving the nut plate was out of the question.  I think it will be okay.  I'm probably not the first one who's done this.  If I had a do-over I would have taken much better care to center the nut plates for the horn bolts exactly before the spar box is riveted together.

The stab counterweight arm is put back on temporarily in order to attach lead counterweights, which I'll do tonight.

Skinning the Stabilator

So moving along last week I drilled holes in the piano hinges for the trim tab.  The drill press I borrowed worked well for that task.  Also finally got around to throwing out the piano hinge that I screwed up on September 12.  The light soft aluminum hinges cut and drill easily and, as you can see, bends easily as well.  Thought about turning it into a Christmas tree ornament but the CFO quickly put the kibosh on that idea upon seeing it sitting on the kitchen counter.

After prepping the hinges it's time to attach the main stabilator skins to the skeleton with clecos and start riveting.  The right skin I did myself but for the left one the assembly was too awkward and bulky so I needed help nudging the forward ribs and skin holes to line up.  Fortunately relatives came over and volunteered to help ("volunteered" - sounds much nicer than "drafted" doesn't it?).

We always start riveting at the leading edge and work our way back.

After a while the rivet tool was getting less and less of a grip on the rivet post and started requiring 7, 8 or 9 squeezes to "pop" the rivet.  Driven to exasperation I disassembled it, sprayed out the barrel with automotive prep clean followed by WD-40, reassembled it and tried it on a rivet.  Better, but it still wasn't getting good bite.  Then I put a washer on the interchangeable nose of the tool and after that it worked perfectly:  squeeze, squeeze, squeeze, POP!

530 pop rivets later the stabilator skins are on!  Keeping things in perspective, however, that's just a dent in the box of 10,000 rivets shipped to me by Vans to build the airplane.

The next step calls for attaching the aft trim tab hinge to the back of the stabilator.  Before riveting I checked to see if the trim tabs would fit by installing the trim tabs and hinge pin.  It was a tight fit but seemed okay so I cleco'd the hinge onto the back of the stabilator with the trim tab still on.  Here's a picture of the control horns where the two trim tab halves meet:

After the test fit the trim tab was removed and the hinge(s) and splice plate were riveted on.  By this point I had "popped" 670 rivets and my hand was sore from all the squeezing on the rivet tool so I took a break from popping any more rivets.

I did, however, cleco on the aft stabilator ribs (4) and skins to see how they would look.  I was concerned with how I would ever get the trim tab hinge pins in once the aft ribs and skins were on.  Reading ahead shows that the hinge pins are sharpened on one end and inserted from the middle by bending it.  The other end is bent into an "L" shape and safety wired in place.  Inserting the hinge pin promises to be a PITA difficult and I wondered why we don't just put the AST trim tab on now while there's still easy access to the hinge pin holes.  Upon further reflection it occurred to me that the inboard aft skin ribs need to be bent over a little to get the rivet tool on the rivets and that would not be possible with the trim tab(s) on.

Stabilator Hinge Brackets

Page 9-7  has us bolting in the stabilator hinge brackets and hinge stops (that's what the 21/32" pieces of alumninum tube were for).  The page has a nice figure that explains everything.  What it does not have, however, is anything reminding you to use a torque wrench.  Apparently you're just supposed to know that you need it.  Indeed, way back on page 5-10 (which also covers topics like canopy protection and scratch removal) it does say to use a torque-wrench on all the bolts.  I suppose I must have read it back in June sometime, but somehow didn't stick in the right brain cell.  At any rate, I've accidently sheared off my share of bolts (including one for the water pump on my truck that bolts into the engine block) so not wanting to break anything or strip any threads I bolted in the brackets and hinge stops to what I felt was a safe place somewhere between "snug" and "tight".  Then, as I cleaned up to go inside and enjoy a nice cold beverage, I remembered reading something about using a torque wrench on these bolts.  Sure enough a quick check of DaveG's 11/24/09 Schmetterling Aviation blog entry showed that a torque wrench was needed at this point, and that the specified torque is 20-25 inch-lbs.

Since page 9-7 of the manual said nothing about using a torque wrench, the revelation caught me by surprise, but okay, no problem.  The guy at work who loaned me the precision calipers, drill press, band saw and all the other airplane building tools I've been using also loaned me his torque wrench.  First thing I wanted to do is to measure how tightly I had torqued the bolts with a regular socket wrench.  Next thing was to re-torque them to spec.  Turns out I had wayyy over-torqued the bolts - about 45 in-lbs or so.  So I backed 'em off to 15 or so and then re-torqued to about 25 as required for AN3 nuts and bolts.  25 inch-lbs is just five pounds of pressure on the end of a five-inch wrench, and really is not very tight at all.

Page 5-10 also says to torque the nut, not the bolt, whenever possible.  If the figure on page 9-7 had the bolts for the hinge stops pointed inward, instead of outward, it would be possible to get a torque wrench on the nut to tighten it.  As it is you have to torque-wrench the bolt head and not the nut because the inboard ribs are in the way.  I just have to trust that Van's has a good reason (yet to be revealed) for pointing the hinge stop bolts in the outboard, rather than inboard, direction.

Skeleton complete

Just in time for Halloween, the stabilator skeleton is done.  (Not a very good costume though.  More strange than scary!)

Stabilator spar box and ribs

Page 9-2 has us separating hinge brackets, spacers, and doubler plates; final drilling holes, countersinking, and deburring.  With the right tool, deburring holes is fairly routine by now and goes quickly.

Didn't have any issues (I hope) following the instructions on pages 9-3 (prepping the spar box) and 9-4 (installing the counterbalance arm bracket); don't have any interesting stories to tell (Chinese curse: may your day be interesting); didn't take any pictures; and I'm behind on my blogging so I'm skipping past those pages.  I just hope that I got the nut plates for the upper and lower stabilator horns riveted in the right place.  If the horns don't bolt in just right, it would be bad.  Really bad.

Page 9-5 has us cut a short piece of aluminum tube into four shorter pieces of aluminum tube.   They'll be used as hinge stops.

It's actually quite a PITA challenge because the prescribed length is 21/32nds of an inch, plus 1/32nd or minus 0/32.  When was the last time you saw a ruler marked in 32nds of an inch?  Since metal is much easier to remove than to add back on the strategy is to cut slightly too long and nibble it ever so delicately down to a target of 43/64ths of an inch (0.672") with a Scotch brite wheel.  At 43/64ths the tolerance range is +/- 1/64th (+/- .016").  The only way to measure that is with precision calipers, which, lucky for me, was included with all the other tools loaned to me by a guy at work.

It was difficult making the ends perfectly square, but the final tube lengths came out to 0.666 +/- .004, 0.674" +/- .003, 0.676 +/- .002, and 0.672 +/- .001.  Two were ground down below spec. (Rats!)  I suspect that's why Van's included two of the tubes in the kit.  They know.

On Page 9-6 Van's suggests that "A great way to form the radius [of the rib tips] is with a fine file." Since there are 8 foward ribs (and, thus, 16 tips to radius), I think they say that to get a laugh, like the instructions to use a metric crescent wrench.  A scotch-brite wheel is wayyy faster and is the one indespensible tool if you want to get the plane done before it's time to move into the old folks home.  Here's the before and after picture:

Attaching the ribs on the spar is encouraging because you know it won't be long 'til the skin goes on, which, in my case, will free up a lot of space on the shop table.  The pop rivets used are fairly dummy proof, but unfortunately the tiny space between the rib and rivet post makes it hard to get a pop rivet tool on the rivet post.

That's what these little wedges are for.  Sometimes you use one, sometimes two.  Sometimes you start with two and then switch to one.  The instructions don't really say.  They help you get the rivet tool on the post, or mandrel, and pull it at an angle till it "pops" (breaks off).  Bending the rib over a little bit helps too.

Speaking of rivet tools, I've been lobbying a coworker to let me "try out" his pneumatic pop-rivet puller for months.  I think I'm finally wearing him down.  Just in time too.  The two stabilator skins use almost 600 pop rivets.  Once he realized that it had a lifetime warranty he seemed a bit less concerned about me borrowing it.  Smart guy.

And now we have a nice rivet in a very hard to get at location.  Whew!  Just 30 more to go...

Trim Tabs Complete

I finished the trim tab a.k.a. AST a.k.a. anti-servo tab a.k.a. Flettner tab last week.  I'm finally getting around to posting the pics.  I also have advice for -12 builders to pass along that didn't get mentioned in my previous posts.

Firstly the CFO picked me up a pair of clamps from Harbor Freight on sale for two bucks apiece.  Do I have an awesome wife or what?!  They came in handy for holding up the trim tabs for final riveting:

And here it is getting all buttoned up with the pop rivets:

And now for the builders advice.  It should be obvious but in case it's not, you should be using this squeezer yoke for riveting on the horns:

and not this one:

I mention it because how I was going to rivet on the AST horn (top picture, right side) was a bit of a head-scratcher 'til I figured that one out.  The other advice I have for riveting the AST horns is to only give 'em a half-squeeze 'til all five rivets are in.  Then go back and squeeze 'em down to final size, but not too hard.  It just seems to work better with the thin aluminum AST rib doing it that way.

And here they are:  Two halves of the AST trim tab, which will eventually go at the back of the back of the plane:

Tah-daah!
Up next:  Section 9: Stabilator

Another AST Oops

Page 8-3 has you disassemble a length of piano hinge by removing the hinge pin and then trimming the two halves to the prescribed length.  Then you drill 33 evenly-spaced holes to match the pre-punched holes on the AST skin and spar.  To drill the holes in just the right place Van's provides a nifty drilling template shown in the picture:

The bottom hinge half is the one I drilled before I carefully read the instructions.  The top hinge half is the way it was supposed to be drilled - with one row of holes, not two. 

Another 15 bucks down the drain.  Sigh.

Warning to other builders:  Before you start on this, use a Sharpie to cross out the upper row of holes on the drilling template.  If you're a tired it's entirely possible to repeat the above "oops" again.  Don't ask me how I know.  And if we ever meet - don't bring it up.  It's embarassing.

I'm trying to decide whether to include the cost of my screw-ups in the cost tally -- it's not really fair to Van's to inflate the airplane building cost.  The CFO says "Yes."  "Definitely yes."

AST Oops

This is an AST trim tab spar.  Nuthin' fancy - just a piece of angle aluminum with pre-punched rivet holes spaced about an inch apart.

Here I'm spraying it with primer "just because".

Here it is leaning inside the garage door track, you know, so it doesn't fall over between the first and second coats:

This is me getting distracted and completely forgetting about the AST spar (wait for it...)

And here's the 150 lb garage door closing on the spar still leaning inside the door track:

OUCH!

Tried to bend it back into shape but it's a goner.  No way the precision-punched holes will match up to the holes on the trim hinge or the skin.  So it's $8 to replace three soda cans worth of aluminum angle + $7 shipping from Van's.