(page 17-06) Wingtip close out

I had dreaded starting on the wingtip close out, because with all those tabs to be bent to all those different angles, I figured there would be lots of trial-and-error fitting.  A wooden tool was required to be built, which greatly facilitated the physical bending of the tabs, but the amount of the bend was

left up to the eyeball.  As can be seen in the picture, the amount each tab needs to be bent is specified to one degree.  At first I took this to be more Oregonian humor, but decided it's the perfect angle that the CAD model spit out, and the builder is to come as close as he or she can to this ideal.  Fortunately, close is good enough.  The tabs can easily be bent with the fingers to fine tune everything during installation.






I sketched the angles in five degree increments on a piece of cardboard cut from a white paper plate  (shown on the second pic) and eye-balled it as best as I could.  Worked great.  The only two tabs to

require a bit of fiddling were the forward-most two (left in the first pic), with one being a bit greater than 90 degrees.  I straightened and re-bent those two a couple of times, finally lining the holes up with the ice pick enough to insert clecos.









Overall, this was nowhere near as bad as I expected.  The cleo insertion was fairly typical, requiring the usual tools (ice pick, 1/8th inch punch

used as a reamer and, on a couple of holes, the hand held #30 drill bit mounted in an old chuck).  Now, the only thing left on the right wing is the strobe light fairings and electrical connectors.  The fiberglass fairing has to be bonded and riveted to the aluminum.  Doesn't look like fun. Then I get to do it all again on the left wing.

Service Bulletin 14-11-03: Wing Skin Doubler

One of the Mothership's higher time RV-12s used as a demonstrator was found to have a few "smoking" rivets on the lower inboard wing skin.  This condition arises when a rivet loosens and allows fretting corrosion (very small scale relative motion between mating surfaces due to vibration) and subsequent oxidation of the resulting aluminum dust which is produced.  The loosening was no

doubt a result of the high stress in the skin at this location.  Putting on my engineer's cap for a moment, I'd say this location has the highest skin stress of the entire airplane.

The fix involved installing a rather robust (0.04 inch thickness rather than 0.03 inches for the wing skin) doubler plate with four different rivet types, eight of which are 5/16th inch rather than the usual 1/8th inch diameter rivets.  I was thinking "Wow, it's great that I received the kit for this service bulletin before I installed the wing skins.  Now I won't have to drill out 20 rivets per side like many builders are having to do because their skins are already on!"  Then I proceeded to install all the rivets in the right wing skin, then had to drill out the aforementioned 20 rivets.  This required the invention of several new, stronger swear words since I have essentially worn out all of the customary ones during previous mistakes in this project.  I won't (I hope) make the same mistake with the left wing.  I'm astonished at the strength and complexity of this fix (four different rivet types!), considering that the fix isn't mandatory.

The plans call for final drilling the holes for the 5/16th rivets with a #22 bit, which I did using a bit from my new #1-through-#60 bit set, obtained from Amazon rather than Spruce or one of the other "name brand" aircraft suppliers.  The rivets would not fit into the holes.  Upon measuring the bit diameter I discovered that the #22 bit was considerably smaller than spec, and that the #21 bit in the set had a smaller diameter than a proper #22.  You get what you pay for!  I had checked the bits with a go/no-go gauge, but that didn't catch it.

At last, a valid reason for making no progress on the RV-12

All of my other lame excuses pale compared with this one.  On September 27th, while riding my bicycle in the rain (first act of stupidity for that day), I fell while crossing a railroad track and broke my femur into three pieces.  The railroad track runs at about a 45 degree angle to the road, simply requiring that I slow down and steer the bike so that I'm crossing the rails at a 90 degree angle.  Cycling 101, right?

Instead, as is my usual habit (second act of stupidity), I attempted to bunny hop over the track and fell as if smacked down by the hand of god (I said smacked, not shmacked -- even if I do spend part of the year in Boulder). This resulted in a new titanium rod in my leg, extending from my knee to my hip.  The titanium structure below the knee is a result of a car wreck in 2005, and extends from ankle to knee.  In all future bike crashes, I'll try to fall on that side since it would be difficult to break it again with all the titanium in there.  I suggested to the Spousal Unit (my beautiful Ironman wife, Karen) that when she has me cremated she should retrieve all the titanium and put it on the mantle over the fireplace.  She didn't see the humor in that.

The good news is that after going from a walker to two crutches to one crutch, I'm now able to stand long enough to actually make progress on the airplane.  I still can't stand for long periods, but it's a start.

I ordered the finishing kit (a deceptive name since when it's finished I'm nowhere near finished with the airplane). The kit arrives in one month, which means the wings have to be finished and on the wing stand before the finishing kit arrives.  The right wing requires only that I finish the wing tip, then I have to repeat the entire skinning process for the left wing (except for the landing light, thankfully -- anyone who installs a landing light in both wings is a glutton for punishment).  Looking ahead, it seems that money will be the limiting factor in the completion of the project.  When I look at what I've built, it seems that I'm way more than half way done.  From a cost standpoint, however, I'm not.  The engine kit and avionics kit are horrendously expensive.

(Page 40-xx and 17-yy) Wing miscellaneous

After enduring the pain of installing the landing light I can say with some certainty that no one ever did this installation after the wing was built.  The build manual for the lighting kit is written for a person adding the kit to a completed airplane.  No way. 

Even without the wingtip installed, allowing access to the back of the light, starting the bolts into the sides of the light was difficult.  It was with trepidation that I applied 12 volts to the power wire for the light, my big fear being, of course, that the light would not illuminate.  This would require removal of the light, which I sincerely hope to never do.  It worked!

Cosmetically, the landing light is, by far, the worst thing I've done.  The primer on the upper surface of the wing is a result of scratches I inflicted on the aluminum during the numerous trial fittings.  The lens fits the opening poorly, though it's not immediately obvious to the casual observer.  Close inspection reveals a slight gap between the Plexiglas and the aluminum at some points.  The problem arises from drilling using the paper template which appears in the build manual.  If I ever build another -12, I'll devise another way.  I blindly followed the manual, which is usually a good procedure.  A little more thought before drilling would have helped.

Wing Stand

Even though I haven't finished the right wing (much less the left), I figured it would be a nice break to so some carpentry and build the wing stand.  I built the standard EAA wing stand, complete with

castors. 

Even though I evicted the car which used to share the garage with the airplane, I'm back to having a space problem, with a wing on each work table and the fuselage between them.  There's nowhere to put the stand once a wing is on it.

Update:  Turns out that the length of the carpet strips was too great, allowing the wings skins to come very close to the plywood gussets.  A lot of wood had to be removed from the gussets to make everything clear.  I also should have centered the carpet strips on the center of the horizontal 2X4s and probably should have made the strips wider.  Additionally, I should have bought higher quality castors with larger diameter wheels.  When pushing the stand around in the shop, the wheels frequently (usually) won't self-align, causing me to have to align them manually, an unnecessary PITA.  We live and learn.

(Pages 17-02 through 17-04) Gimme some (wing) skin, part deux

I cleco, therefore I am -- a new philosophy called Existential RVism

After the exercise in frustration that involved cutting the hole for and installing the landing light, skinning the right wing (I did that one first rather than the left as shown in the manual so I could see just how bad the landing light looks) was a walk in the park.  As was the case when I skinned the stabilator and rudder, I was surprised when all the rib holes lined up with the holes in the skin,

considering how much straightening and fluting had to be done to the ribs.  I was always able to pull the holes into alignment with an ice pick and awl, allowing clecos to be inserted.  The key seemed to be starting at the leading edge and going hole by hole with the alignment tools.  As I've always done, I primed the mating surfaces before joining. 

The pneumatic rivet squeezer has always been my favorite tool, and I made ample use of it (my first one wore out after the first few thousand rivets, found a great but cheap one on the aviation aisle at Harbor Freight).  I also bought from Aircraft Spruce their new design for cleco pliers which has the handles rotated up ninety degrees from the jaws.  This works much better on the horizontal wing surfaces, keeping the wrist in a natural position.

The bottom and top skins went on surprisingly easily (with the exception of the landing light), it's just quite tedious when you consider the process: align the holes, insert the clecos, remove the clecos, insert the rivets (about 70% of which require running a 1/8th-inch punch through the holes for final alignment/reaming), pull the rivets, repeat a few thousand times.

If you've ever been in my office, you'll probably notice a resemblance between my office and my shop in the first picture.  I use the same organization scheme in both.

(Page 40-02) Bad hole locations using template

As mentioned in the previous post, drilling holes in the wing skins using the templates in the build manual doesn't work well.  I followed the plans exactly, realigning the template for the top then the bottom holes, marking the hole centers with an awl, then drilling.  This resulted in several holes which were misaligned with the holes in the pre-punched landing light ribs, sometimes by more than a half diameter.  This required slotting the holes in the landing light ribs.  Two holes in the plexiglass had to get the same treatment.  This is a cosmetic rather than a structural problem, but I'm not happy about it.  This could have been done better.

There also appears to be an error in the build manual on page 40-04 step 9.  I believe it should read "Wire to the W-1223B-R" rather than W-1223B-L.  I've reported it to the Mothership.

(Page 40-01) Cutting holes for the lighting kit

I'm beginning to seriously question my decision to install the lighting kit: way more time than anticipated.  I'd probably skip the landing light if I had it to do over.  All three holes have full-size templates included in the build manual.  First step was to photocopy these and double check that the copies overlaid exactly on the originals.  I have in the past encountered copies which were slightly bigger than the originals.

I also think that paper expands or shrinks a bit with changes in atmospheric moisture, not good when the rivet holes shown on the templates have to match up with pre-punched holes in the hardware (landing light).  The holes for the wing-tip strobes are not critical since they will be covered by the fiberglass fairings which the strobes actually attach to.  In fact, the large hole specified could be replaced with a 3/4-inch hole easily done with a step drill.  A large hole is specified because the write up for the entire lighting kit assumes that the kit is being installed on a completed airplane and there's a need to reach in to the wing tip enclosure.  This job is made considerably easier when done during the build process.  In fact, it's hard to imagine doing the landing light installation after the fact.  The strobes wouldn't be a problem.

I cut out the cross-hatched areas in the template with an Exacto knife, taped the template to the aluminum, marked the hole with a Sharpie, then cut out the metal with an abrasive disk in a Dremel tool.  The last cutting pass was with an abrasive drum in the Dremel, followed by a 2-inch Scotch Brite wheel in a die grinder.  If I were doing it over, I'd put the Scotch Brite wheel in a drill since the die grinder has the potential do damage owing to the high speed.  Although the build manual doesn't say this, the template obviously must be flipped over when going from left wing to right wing.

I followed the same procedure with the landing light cut out.  This required temporarily clecoing the appropriate wing skin to the ribs, then making the cut.  I once again used the Scotch Brite wheel in a cordless drill for final smoothing, and was quite pleased with the results.  The problems arose after I drilled the rivet holes, which have to match up with stiffeners which have the holes pre-punched to accept nut plates (to be detailed in a following post).

The cut was tedious, the good thing being that there's only one of them.

The Scotch Brite wheel can be seen in the cordless drill.  I should have ordered one of these small wheels much earlier in the build.  From the start of the build I have made extensive use of a six-inch Scotch Brite wheel in a drill press for deburring, but access is limited for large parts.
                                                                                                                                  

Pilgrimage to Mecca complete for 2015

My 27th trip to Oshkosh ended with me in my usual happy/sad state.  Can't believe it's over for a year, but my daily routine of getting up at 4:00 am in order to be at the show when the gates open at 6:00 has worn me down.  I'm toast physically, but mentally I'm fired up to work on the -12.  Great photo gallery here: https://www.flickr.com/photos/eaaairventureoshkosh/    From that link, a P-51, P-38 and F-35 fly in formation.

The highlights of the week were getting my 5th flight in an RV-12 and attending every forum Burt Rutan gave.  Burt officially presented his latest (and last, he says) design, the SkiGull.  He had planned to fly it to the show, but didn't quite make it.  Can't wait to see it next year.  The plane will, according to Burt, land on snow, dirt, pavement and water, with water being its preferred habitat.  It uses a pneumatically actuated pair of skis which pop down during the take-off run, lifting the hull clear of the water.  The skis are extended for water landing to absorb shock.  Apparently, it will handle ocean landings, allowing the owner to land, then taxi up onto a beach.

On the builder front, the big news is that the Mothership has given their blessing to using a split bulkhead behind the baggage compartment.  Van did this on his personal RV-12 and most people building E-AB did it, but until now those of us building SLSA couldn't.  Without this, the builder must remove the fuel tank for each yearly condition inspection.

The RV-12 shown is one of the most beautiful I've seen.  The builder has a Cobra painted the same color.

SB 14-12-06 completed

Complying with this SB involved drilling out ten pulled rivets, six of which are through relatively thick aluminum plate.  The accepted method of removing this size pulled rivets (LP 4-3) is to drive out the center mandrel with a 1/16th punch, then drill out the rest with a 1/8th bit.  Problem is, in order to drill out the rivet without enlarging the original hole requires that the drill be exactly perpendicular to the plate containing the hole.  Even with my trusty Tight Fit Drill Kit I couldn't make this work.  Not enough distance from the rivet centerline to nearby structure.

I've always used a different procedure, when possible, for removing pulled rivets, one which eliminates the possibility of enlarging the original hole.  I carefully drill off the manufactured head with a 1/8th or #30 bit, then either pull the rest out by grasping the shop head with needle-nose pliers or drive it out with a 1/8th punch.  In this case, the metal was too thick for this method to work without modification.  I drilled off the manufactured heads, drove out the mandrels (lacking a 1/16th punch I used the shank of a 1/16 bit, worked great), then drilled out the remainder of the rivets with the right-angle attachment (shown next to the drill in the pic).  For the two which were too close to adjacent structure, I used an old drill chuck (shown between the right-angle attachment the drill) and turned it by hand.  The chuck was still a bit too fat for perfect alignment, so I used a smaller bit and went through at a slight angle.  This loosened the rivet enough to be pulled out with pliers.

Free advice for other people building airplanes.  Don't lose momentum in the build by going for long periods with no work.  Getting back up to speed is a huge waste of time.  Example:  yesterday I had to reacquaint myself with the tool and procedure for properly crimping Molex connectors.  Had to go to EweTube (they're a bunch of sheep politically) and watch a couple of instructional videos, then destroyed the first connector I tried.  I'm taking a solemn vow to never again take a break from the project.

The completed part for the SB is shown at left.

Off topic - or how I've learned to love the carburetted 912.

Partial explanation for why I've made no progress lately.  Read this only if you're interested in antique cars.

Said car has consumed a substantial chunk of my time (and an even larger chunk of my money) for the last year.  With the engine installed the car can actually propel itself down the road, though much work remains to be done with the engine management software.  Full throttle operation is awesome

(borderline scary), but anything else leaves a lot to be desired.  It's making 544 hp and 500 ft-lbf on the engine dyno, numbers that this chassis was never meant to handle.  Next step is to put it on a chassis dyno and try to  improve the drivability with the help of noted engine gurus Luke Woroniecki and Wes Kiser.

It says Chevrolet on the valve covers, but nothing in the engine, including the block, was made by Chevrolet.  100% aftermarket.  I used a vertical throttle body (costing horsepower) to give it an old-school, carbureted look (the barrels even open progressively, like the carbs of my youth).  If I'd had any brains I would have actually used a carburetor, where the spark map is controlled simply by flyweights on a spinning shaft and manifold vacuum.  If ever there was a mature technology, it's the four-barrel carburetor.  In fact, this experience has caused me to completely re-think the carburetor vs. fuel injection question for the Rotax 912.  I was initially unhappy that the 912is was not being made available for the RV-12.  In fact, I think that earlier in this blog I opined that I had assumed that the four carbs on my Honda motorcycle were the last carbs I'd ever have to balance.  Now I say bring'em on.

Work resumes tomorrow on the RV-12.  First up is SB 14-12-06.  I'm completely out of excuses.  The spousal unit (my beautiful and super-fit wife, Karen) is spending the summer in Boulder, CO training for the Boulder Iron Man (2.4 mile swim, 110 miles on the bike, 26.2 mile run, all at altitude in mountainous terrain).  My plan is to finish this airplane by the end of next summer (Voice from the Future: Boy, was I naive, bordering on stupid, to think I could finish that soon).  Oshkosh is in two weeks and will consume a week of my time, but I will more than make up for the time loss with the inspiration and enthusiasm I'll bring home from the show.