Primed Ribs

     I really am smiling behind that mask. After much deliberation I have finally primed my ribs. So I am happy to have the job done. I am still not sure that I really needed to prime. But I have. Maybe some day I will live by the ocean, and I will still have this plane.

     In the above photo you can see what I used to prime the ribs. There is a Harbor Freight HVLP detail spray gun. Attached to the paint gun is a water separator that I picked up at a local discount store. A frame covered with hardware cloth holds the small pieces and sawhorses with two by twos hold the ribs. In the garage there is a lightweight aluminum table that I used to “Rand-Prep” the parts before painting. Of course there is the paint mask, I am not sure of the effectiveness of the mask so I used a fan to keep the fumes downwind.

     What is not shone in the above photo is a glass mixing cup. I had borrowed my wife’s mixing cup. When she went to make cookies the next day she could not find it. I confessed, then instead of making cookies she went shopping. I had mixed the two part Randolph primer by volume in the cup. I had to fill my little detail gun many times. I guess I should have gotten the larger gun.

Setting Wet Rivets

     What you see above are the tools I used for setting wet rivets. A brush, mixed primer and MEK in a glass cigar tube for cleaning the brush. To dispense the primer into the bottle I would use eyedroppers. The backdrop is the vertical stabilizer skin.

     I am setting most of my rivets wet. What I am doing is painting the inside of the hole with primer, then before the primer dries I set the rivet. This will squeeze the primer around the rivet and into any cracks.

ARRGGGHHHH, The Start of My Primer Story

     When it comes to RV building I am not sure if anything causes more debates than primer. The primer debate can be broken up into two major categories. The first is whether to primer or not. The second would be what kind of primer to use.

     I hope to be 50 when this plane is finished, then I plane on keeping it. So I suppose I could say that the life expectancy of the craft would be 30 years. Normally a plane should survive 30 years without any primer. When I first started to build I thought that I would like to put the RV on floats. Putting an aircraft on floats should not be taken lightly. More power is needed, I probably could not do the float thing on the O-235 that I planing to install. I had thought of using a cetificated prop off of a Cessna 152 to provide the thrust nessisary. Something to ponder. So even if I do not put the plane on floats I will probably spend some time near the ocean. So I may need primer some time in the future.

     Because I believe in dreaming (no other reason) I decided to prime the RV. Now the next question is what type of primer to use. Having no experience with any type of primer, I did a few searches on the Matronics e-mail lists and came up with what I thought the best primer is Randolph. It is two-part zinc chromate epoxy Mil-spec primer used by the military.

     I chose the yellow color. My dad says that it looks like the primer on theP-51s that he used to build so long ago. He used to build the fire extinguisher door for the pilot. He would wonder why they were so fussy on the rivet quality for a non-structural door.

     Being nasty stuff I brought all of my empanage parts down to a local hot rod painter and had him paint the parts. I was reasonably happy with the job that he did, but the paint was much too thick. Instead of .0005 inches thick the primer was .002 inches thick. I worried about the weight and balance. I then weighed a stiffener that had paint and compared it to a stiffener that did not have paint.

     The primed stiffener weighed 16.917 grams the unprimed stiffener weighed 15.797 grams this would be 1.12 grams of primer on the stiffener. Or an increase of  just over 7% weight on the .024 inch thick stiffener. On the thicker parts the weight increases would be proportionately less. I would give a rough caculation of one or two pounds of excess weight in the tail. If I were to do it over again I would put the primer coat on thinner.

Stiffner Weight Update

     After painting some stiffeners myself, I weighed them. The weight of my self painted stiffeners averaged about 16.3 grams each, plus or minus about .03 grams. So the weight savings of self priming works out to just over .6 grams or better than 50%! So self prime and be frugal. Save weight and the cost of the primer! Here I am thinking how I will do the primer thing next time around. Hmmm, my wife says just one plane though.

Well, I guess I am ready to set the first rivet.