Category Archives: Prime/paint

More fitting and body work has been associated with the upper and lower cowling. The sequence I used for painting the cowl parts:  cut and fit the cowl as needed, sand/putty for initial prime, attach hinges and fasteners, Smooth Prime, sand/spot putty, prime again, scuff with Maroon scotchbrite, and final paint.  Splitting the lower cowl before final prime to accommodate a three-bladed prop was a difficult process.

Fitting the lower cowl bracket and bending the air outlet louvers were the beginning final cowl preparations.

Holes for the Skybolt camlocks were drilled with a Unibit into the lower cowl where the air scoop will attach.

Superfil was applied to the air inlet ramps of the upper cowl for smooth airflow into the engine compartment.

Sanding the air inlet ramp and application of resin/glass bubbles to secure the Rod Bower scoop inlet piece were also done.

Drilling for the nose connection screws and aft pin retention block were completed on the upper cowl before the final separation.

Fishing line (hard to see in the left photo) provide a trace line for the center cowl center. The lower cowl was held together with a forward custom retaining piece while a curf-less saw started the cowl splitting process from the aft side.

Further splitting of the lower cowl continued with the scoop installed until full separation was achieved. The split process was nerve racking, but seems to have been successful.

On the left, the lower split cowl near the aft section is shown held together with a custom retaining piece. On the right, the side hinges were then riveted using a pneumatic squeezer.

Side piano hinges are shown with intermediate and final rivets.

A thin layer of West System resin and colloidal silica was spread to the upper side hinge rivet lines.  After 24 hours of cure time, the layers were sanded smooth before Smooth Prime was applied.  Another round of sanding in preparation of the final prime coating.

Here the rivet lines on the firewall hinges for the upper cowl are filled, then sanded smooth.

After the first coat of primer was applied, some body work or spot putty was needed in some locations. Those areas were then sanded smooth for another round of priming.

After the initial prime, Skybolt fasteners were applied to the lower cowl halves and the lower firewall brackets.  All the parts were then sanded again and reprimed.

Final prime on cowl parts.

Fitting the Aerosport side cowl pin retention blocks and the Skybolt Camlock pins were the last steps before final paint was applied.

MISCELLANENOUS

The flaps were the first set of completed parts transported from the workshop to the airport for staging in the final assembly operations.

Oil lines were covered with firesleeve, then run from the engine mounted adapter to the remote oil filter on the firewall.

Now that many of the main components have been built, the next steps are prime and paint before final assembly.  The tail section and smaller removable parts were the initial targets for this activity.  I have been priming interior parts throughout the entire build, but this was my first experience with PPG CA7504 primer.  The decision was made to switch to this product, which is specifically designed for airplanes.  This primer is formulated with the elastomers, fillers and other ingredients for the flexibility needed to withstand rapid temperature changes, as compared to general automotive paints. This primer used in conjunction with PPG Aerospace topcoats prevents cracking, improves surface adhesion, and helps the mechanical characteristics of the paint layer.

The effort needed for painting takes considerable time, but is really not worthy of new posts.  I intend to prime all exterior components, then seek assistance from someone to spray the final topcoats.  I can perform the drudge work of preparations due to the time/cost involved, but am not confident enough to shoot a smooth, final surface. We shall see how this strategy goes.

The general steps of surface preparation, mixing and spraying are the same as the previously used on interior parts using automotive PPG DP40LF primer. The new material requires greater attention to mixing ratios, measuring induction time with a Zahn #2 viscosity cup (15-18 seconds) prior to application, and modifying the application technique.

Wing tips, rudder caps, and empennage parts were in the first batch.  The outcome of the initial session were very poor, with runs and fisheyes.  Subsequent attempts after sanding smooth and more rigorous surface preparations were much better.  Additional filters were installed in the pneumatic air lines, and the lines were thoroughly purged of water and debris. Plus using higher quality Techline gun for better atomization and holding the gun further from the surface seemed to help. A few cycles of spray practice on the first batch have improved my technique to eventually yield good results.

Preparation steps include using a maroon (=320 grit)  Scotch Brite pad in a palm sander to scuff the surface, clean with degreaser, condition with Prekote, then apply primer.

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The second batch on rudder and trim tabs worked out well with only one application session.  Next up are elevators, ailerons, flaps and the horizontal stabilizer.  The wings and fuselage will be last. More updates will be forthcoming when significant progress is made.

Rudder (close-up and after second prime)(October)

Ailerons (before and after priming)(October).

Elevators (October)

Oil door opening (November)

Oil door cover (November)

Flaps (November)

Horizontal Stabilizer – tip (November)

Horizontal Stabilizer (November)

COWL HINGES

The upper and lower engine cowlings are attached to the firewall with 1/8″ PIANO HINGE.  The initial sides and bottom pieces are shown.

Fabricated parts ready for fitting.  The right photo shows the initial layout, then match drilling occurs next.

Hand squeezing the side rivets was not so easy.  The angle of the firewall-to-side and interference with the squeezer head was an issue.  An number of rivets were later redone with a pneumatic jaw-type squeezer.

Final results were not great, but acceptable.