Friday, October 26, 2012

Advancing Artic Chill Spawns Sense Of Urgency At DOG Aviation

The first advancing arctic cold front of the season is bearing down on northeast Ohio as I type which means cold weather … not good for epoxy primer. The advancing cold front created a sense of urgency at DOG Aviation because the epoxy primer being used requires minimum temperatures of 59 degrees to cure properly and the forecasted highs for the next seven days are in the 40’s with rain every day. This created an all hands on deck call for action to have all wing ribs dimpled prepped and primed before the first throws of winter sets in.

                     All hands on deck at DOG Aviation ready for the necessary long work hours to beat the storm.

The whirlwind of activity and long hours began with the continuation of cutting off flanges from wing ribs. This time it was the W-1210 ribs under the saw having the forward flanges removed from all thirteen of the W-1210-R ribs and a six of the W-1210-L ribs.
                                  Using the band saw to cut off the forward flange of one of the W-1210 wing ribs.

Once the cuts were made and smoothed using the Scotch-brite wheel, it was time to begin a very long dimpling session. Dimpling all of the RV-12’s fifty four wing ribs is a time consuming chore which resulted in almost 2,500 dimples being made in the ribs – thank goodness for pneumatic squeezers!

                   Using the pneumatic squeezer clamped to the workbench to dimple one of the RV-12’s wing ribs.
                                           All 54 of the RV-12’s wing ribs dimpled and ready for primer prep.

Once dimpling of the wing ribs was completed, I turned my attention to the flaperon components. There are twenty four flaperon ribs which needed deburred, plus a few miscellaneous ribs for the leading edge and counter balance assembly. There were also a few miscellaneous brackets and parts that would require primer, so those parts were deburred as well.
                                             Deburring one of the flaperon ribs with the 1” Scotch-brite wheel.

Knowing Thursday was my last full day of 80 degree weather, I found myself confronted with two days of work ... but only one day to do it. Quite a dilemma. Typically, prior to painting I would wash down the parts with either denatured alcohol or acetone to remove oils then scrub with a Scotch-brite pad, followed by wiping the part again with acetone until the rag or towel looks clean then moving on to the next part. There was just not enough time to do all this … I needed to streamline the scrubbing of parts prior to primer.

A quick water test revealed some interesting results. I washed down a rib with solvents (tried both acetone and denatured alcohol) and ran water over it. The water beaded up … not good. Tried the above with the addition of rubbing the part with a Scotch-brite pad .. result, the water still beaded up just not quite as much.

Better living through chemistry! I decided to try using some Alumiprep 33 to see if I could get a break free surface on the ribs without scrubbing with a Scotch-brite pad. I had purchased the Alumiprep 33 (basically a phosphoric acid solution with cleaners) a while back to see if it would help streamline the Sanchem process, but never took the time to test it. Unfortunately, I knew there was just not enough time to Sanchem the parts so that was out of the question … however, thought perhaps the Alumiprep 33 cleaning agent may be useful. YOU BET IT IS!!! Mixed a 1 part Alumiprep to 4 parts of distilled water to make up a solution for testing. Cleaned a rib with Acetone as usual then dropped it into the Alumiprep 33 and watched it bubble and fizz for a minute or so then rinsed it using two water baths. Guess what… the water sheeted off the entire rib!!! Fast and easy, just what I was looking for!
                                  Alumiprep 33 concentrate does a great job of prepping aluminum for priming.

So yesterday morning/early afternoon was spent prepping and washing ribs in Alumiprep 33 and letting them air dry in the 80 degree air followed by primer spraying in the late afternoon/evening. The only places that truly really need primer is where the skins will lay on the rib flanges and where the ribs attach to the spar … the rest is icing on the cake. So to insure as good as possible primer adhesion in those areas, a Scotch-brite pad was used to lightly scuff those areas prior to Acetone cleaning and the Alumiprep dip. I erected a couple drying racks using  a saw horse and broom sticks to hang the ribs on to dry. I would Acetone and Scotch-brite a small batch of 6 to 8 ribs, run them through the Alumiprep 33 acid wash two at a time for a minute or so, place them into a water rinse … plop another two into the Alumiprep, move the rinsed ribs into the second water rinse tub, hang to dry. While those ribs were hanging out drying, I would Scotch-brite and acetone another batch of six or eight ribs and repeat the process. All and all it went far faster than the way I was doing it before. Although, had it not been for a nice breeze and 80 degree temperatures, the drying process may have taken far longer.

Sadly, I did not take the time to photo any of this because it was a full press boogie and I was a man on a mission who lost all sense of time ... and took no breaks until very late afternoon. But at least all the wing ribs, rear spars and miscellaneous parts were painted. There was a little primer left over and some small parts left to prime so I placed the Akzo primer in the freezer for use Friday morning before the cold front hits.