Riveting – A Day Long Over Due

Finally a day of solid production at DOG Aviation setting all the rivets that makes up the vertical stabilizer skeleton and rudder hinge brackets.

                                                        The first rivet set … one down 9,999 left to go.

                                                           Finished upper and lower rudder hinge brackets.

Builder Tip:

Test all platenuts. Based on first hand experience helping my friend Pete put together his RV-9A, it is a good idea to make sure the plate nuts are not to tight. We found ourselves in a situation where some of the installed platenuts had to be drilled out because they were so tight they totally damaged the threads on the screws. Most were OK but some were unusable. After that bad experience, I plan on testing each platenut prior to riveting it on the airplane.

An easy way to test the platenut is drill a hole in a piece of wood, place the platenut over the hole and pound a couple of rivet mandrels or finishing nails through the rivet holes. This will keep the platenut from turning while a screw is worked in and out of it. Using a little Boelube dosen’t hurt either. For lots of platenuts use a power screwdriver.

Priming – A Comedy Of Errors

Today was a mixture of the Good, Bad and downright Ugly as the DOG Aviation paint department utilized the new Eastman spray gun, digital regulator and the DeKups disposable painting cup system by DeVilbiss. The primer of choice is a two part epoxy primer made to Boeing specifications by Akzo Nobel.

First the good … The parts primed today turned out marvelous and the spray painting box worked great… but getting there was nothing less than a miracle.  The entire morning was a perfect day for spray painting … not breathtakingly hot and humid, no wind ... almost a dead calm with an occasional swirl of air. Mixed up a batch of the Akzo and let it sit the 30 minutes required mixing occasionally. OK good to go!

The Bad - While the primer was sitting the required 30 minutes the shiny new spray gun was removed from the box, digital regulator attached, followed by a water separator and connected to a 50’ 1/2” hose. ( Eastman recommended only using a max of 25’ hose which just was not long enough so I figured if one were to use a 1/2” hose there would be less restriction to the air flow). So far so good ... maybe. Next tried to adjust the pressure regulator at the gun to the required 29 PSI … think the best I could get was 19 PSI so I turned up the regulator at the compressor to 120 and that got it up to 22 PSI. Decided to remove the water separator and that got the pressure up to 26 PSI. Close enough, so decided to put paint in the gun.

The Ugly – The primer was mixed in the disposable DeKups liner, liner placed in the cup, on goes the locking ring … good to go. Turned the gun upside-down, attached the assembly to the gun, pulled the trigger and nothing … no paint, no collapsing paint bag. ( Pulling the trigger with the HVLP gun upside down is supposed to bleed the air out of the paint cup by collapsing the bag until there is no air in the bag making upside down painting possible). Now at this point I know there is something wrong, but I haven’t connected the dots just yet. So I decided to move on … figuring I’m not planning to paint upside down, so I’ll just use the cup as a gravity feed .. right? WRONG! When I turned the spray gun upright I pulled the trigger and was looking at the pressure gauge so did not notice the paint pouring out of the fitting where the DeKups locking ring attaches to the gun. The gun is just covered with dripping epoxy primer!!!

More Ugliness - Then to add insult to injury, when I disconnected the gun from the air hose the quick release valve broke … air was just hissing full blast out of the hose so I had to run back, disconnect at the compressor and find a replacement quick connector.

After changing over to the paint cup that came with the spray gun, the job got finished and the results were encouraging. I was able to lay down a nice thin coating of primer on the parts with no runs. I was never able to get the regulator pressure up to 29 PSI but the gun seemed to work well at 26 PSI. At this point not sure if the digital gauge is reading low or if I just can’t achieve 29 PSI at the gun even though a hose with a larger diameter was used.

While cleaning up the winds kicked up so began transferring parts inside. The small parts hanging were OK but one rib hit the ground. Fortunately it was dry enough not to have any grass stick onto it.

                                       Cleaning up the aftermath of the mess still wondering what went wrong.

A Senile Delinquent moment … After literally spending hours trying to scrub off dried Akzo from the gun and all the accessories (no easy task with Akzo primer) and wondering why all the paint had leaked out in the first place, the dots finally got connected. Could the metal adapter have been machined wrong or perhaps the plastic locking ring was molded incorrectly (it did not look like a tight fit) or could there have been a rip in the liner. Nope … just didn’t know what the issue was. Anyway, while cleaning things up, I discovered there was an unopened box on the table … an unopened box of lids. Yes, you read that right LIDS!!!!  In my over exuberance to get painting I forgot one very important step … putting a disposable lid on the disposable liner BEFORE placing the liner in the cup holder and putting the locking ring on it!  DUH!!! Won't be making that mistake again!!!

Alchemy – Turning Aluminum To Gold

The ancient practitioners of Alchemy chemistry who got caught up in wasting their time trying to turn lead into gold were apparently using the wrong process and metal. DOG Aviation with the help of chemicals from the Sanchem Corporation successfully turned aluminum to gold earlier today.

Prior to priming, all the aluminum airframe parts will be treated with Sanchem CC-6100 which is a cold conversion process similar to Alodine but without the nasty environmental and personal hazards. The process converts molecules of aluminum near the surface into a corrosion resistant form which will then be protected  with an epoxy primer. For the start of the RV-12 project Sanchem CC-6100 will be used but DOG Aviation’s R&D department is looking into switching over to Sanchem CC-3400 for the wings where there are lots and lots of parts.

                                           Sanchem CC-6100 treated rib is on the left .. untreated rib on the right.

In an effort to not waste the chemicals I did not mix up a large batch … only mixed around a cup or so. First the parts are cleaned with a part C cleaner using a Scotch-brite pad and rinsed in distilled water. Next the part is exposed to the CC-6100 solution for 60 seconds and rinsed in distilled water. I noticed that small parts which could be kept submerged turned out looking better than parts having the solution brushed on. The golden finish was more even looking … the longer parts which were brushed with the solution tended to have streaks. I suppose if I were not priming and leaving the metal bare, I would not be pleased with the overall look of the brushed parts ...  but since I plan to epoxy prime it is not a big deal. That said, if I don’t switch over to the CC-3400 for the wing ribs I will try to make a tray just large enough for the ribs and mix enough solution to make sure the ribs are totally submerged.

The CC-6100 and CC-3400 processes each have their own advantages and disadvantages but the end results are the same. Both products require a wash/activation which uses a mild cleaner that is scrubbed onto the part with a Scotch-brite pad until a break free surface is obtained. (Break free means the water sheets evenly on the surface of the part and does not bead up). CC-6100’s downside is once mixed (50-50 part A and part B), it has a shelf life of only 8 hours meaning … mix only what you can use up because any leftover solution should not be stored more than 8 hours. Upside, mix it at room temperature and it is ready for use by either immersing the part into the solution or wiping the part with a brush, sponge or rag. The conversion happens in seconds. The CC-6100 solution also neutralizes any cleaner left over from the cleaning/scrubbing phase.

Sanchem CC-3400 is a bit more involved and more suited for manufacturing environments because there are temperature requirements. There is an Alkaline cleaner bath that requires being kept at 100 to 120 degrees F and the CC-3400 solution requires being kept at 135 to 140 degrees F. The upside is there is not a shelf life on the mixture so you can keep using it over and over again until the chemical is depleted and no longer converts the aluminum. Another upside is one gallon of CC-3400 makes 11 gallons of solution.

Dimples-O-Plenty

This afternoon the two 120 degree female dies that Bob Avery of Avery Tools made custom for DOG Aviation were delivered by UPS. Both dies were cut down a little on a lathe so they don’t interfere with the inside corner of the bend on the ribs at the web to flange transition.  One die has the standard shank for inserting into a rivet squeezer or C-frame dimpler. The other die is the type that has a hole drilled in the center for use in close quarters with the hand pop rivet puller.

As you can see the new female die now clears the web to flange transition although just barely, which is what I wanted.

I used the pneumatic squeezer all evening and dimpled all the ribs, spars and miscellaneous parts of the vertical stabilizer. The new dies Bob Avery custom made worked marvelously and left no mars on the inside corners of the parts.

                                     About to make the first dimple using the new custom female 120 degree die.

Note: Setting the pneumatic squeezer over edge of the work bench and clamping it down is a good way to use the squeezer when making lots and lots of dimples. The pneumatic squeezer gets heavy when doing lots of squeezing.

                                 All the internal parts of the vertical stabilizer dimpled and ready for primer prep.

All the vertical stabilizer parts are now ready to be sent off to the paint department for metal prep and a light coat of primer before final assembly.

With This Dimple I Christen Thee EAB

As mentioned earlier, it has been decided flush rivets would be a nice touch for the RV-12. In order to utilize flush rivets, all the holes on the skins will need to be dimpled as well as the corresponding holes in the ribs underneath.  However, that change will constitute a deviation from Van’s plans and change how the aircraft needs to be certificated.

                          About to start the dimpling of the vertical stabilizer skin with the C-frame. Note the
                          use of the noodles (the pool toy variety) to keep the skin level with the C-frame.

                     The noodles as you can see are just about the same height as the lower die in the C-frame. The noodles
                     keep the skin from becoming scratched plus allow the skins to be moved easily across the C- Frame.

So what does the title of this Blog mean? Well, in a nut shell the RV-12, as sold by Van’s, is to be certificated as an E-LSA (Experimental – Light Sport Aircraft). When building an E-LSA aircraft from a kit, the builder is required to use all the parts the manufacturer supplies and make no changes what so ever … essentially you are building an exact carbon copy of the original Van’s RV-12. The main advantages include a relatively short phase one flight testing requirement, professional building assistance is permissible and annual inspections can be made by subsequent owners after passing a 16 hour course. The big disadvantage is no changes can be made until after the aircraft is registered and flight testing is completed.

In the case of an airplane certificated as EAB (Experimental Amateur Built), a category that has been around since the late 1940’s, the FAA has strict restrictions. The true intent of EAB is solely for the builders own education and recreation. Strict requirements are placed on what is called the 51% rule … a rule that requires the builder to be able to prove he or she did at least 51% of the work on the aircraft (this includes taking into consideration parts prefabricated by the kit manufacturer) and the practice of farming out parts to a professional for assembly is prohibited. Lately, the FAA has been scrutinizing kits closer to make sure they truly comply with the 51% rule. To Van’s credit, Van’s petitioned the FAA to have the RV-12 evaluated and it has passed the evaluation and is now on the FAA’s list of aircraft kits that qualify under the 51% rule. The main advantage of building the RV-12 under EAB rules is the ability for the builder to make changes to the RV-12 during the build … so if a better radio, GPS or neat gizmo were to come along, the builder can incorporate the new technology during the build rather than waiting until after the build when it is much harder to make changes. The biggest disadvantage is the phase one flight testing requirement is far longer, typically 40 hours. The builder can apply for maintenance privileges which will allow the builder to do the annual inspections … however subsequent owners of the airplane must use a certified A&P mechanic to perform the annual inspections.

For a complete tutorial on the subject of E-LSA vs EAB there is a well written article on the Experimental Aircraft Association’s WEB site at the following link:

http://www.eaa.org/experimenter/articles/2010-10_darside.asp

Another Small Bump In The Road Less Traveled

Why is it always late in the week when I discover problems that can’t be resolved over the weekend? Case in point, I thought I had the dimple die issue totally resolved until I felt it prudent to see how the new dies would work with the wing and vertical stabilizer ribs. Previously, I tested the fit of the dimple dies using the vertical stabilizer’s rear spar and there were no clearance issues. Much to my surprise, when  testing the clearances using the wing and vertical stabilizer ribs, I discovered the radius of the dies were about 1/32" or so to wide. If one were to dimple using them, the female die would mar the area on the rib where the transition is made from the web to the flange.

 Here one can see when the female die (top) is squared up with the hole in the wing rib the female portion of the die would deform the web/flange transition when squeezed … not good.

Bob Avery to the rescue … Late in the afternoon on Friday I called Avery Tools and described the issue to Bob who suggested a few fixes. Sure, I could just remove some of the metal from one side of the female die on a grinder or bevel the base of the die … but then it becomes yet another thing to keep an eye making sure the die does not rotate with use. The decision was made to have Bob turn down the female dies decreasing the radius by 1/32” or so on a lathe … no need to turn down the male dies since only the female dies are used on the underside where the clearance issue is. Glad this is all getting sorted out now and is only a small speed bump. There are plenty of metal parts to prep so progress can still be made while waiting for the dies.

R&D Delays Finally Resolved

Yet another delay was encountered last week. Decided it prudent to test the standard 120 degree dimple die set that will be used with the C-frame my friend Pete (owner of the RV-9A I helped build) loaned me for the project.

                                              120 degree dimple die set that was discovered to be slightly off.

                                              C-frame with dimple dies installed. The plunger is pulled down

                                              until the centering pin on the male die goes through the hole in the

                                              material to be dimpled. Next the plunger is whacked with a mallet

                                              to make a dimple in the material.

There was some scrap metal available that was removed from the vertical stabilizer ribs so decided to test the 120 degree dimple dies with the C-frame. Much to my surprise, the dimples were not deep enough and the rivets were standing a little proud … not good! I’m not going to mention the manufacturer of the dies because all the other dies and tools purchased from them are of good quality and appear to be fine so this must be an anomaly, although I will try to get credit for the dies.

Based on the perfect dimples the custom made Avery dimple dies made, DOG Aviation’s procurement department placed a rush order for the Avery version of the standard 120 degree dimple dies. They just came in today and were immediately tested in the C-frame. Results … perfect dimples.

                                         One can clearly see the rivet on the right is sitting proud and not flush.

Clicking on the photo to enlarge it will show the rivet on the left is setting in the dimple made by the new Avery 120 degree dimple die set. Perfect ... not at all proud. The rivet on the right is setting in the dimple made with the problem dimple die set.  Is it really that big of a deal? Probably not, but quality control is the responsibility of the builder. A flush rivet is called a flush rivet for a reason … it is supposed to set flush.

Builder Tip:
If it does not look right, then most likely it is not right. Examine parts and workmanship closely. The photo above is a clear example of the need to keep a keen eye on the way parts fit together.