content_image/588426.jpg
If the gun is not working properly, use the following information to troubleshoot the problem: 

• A pulsating, or spitting, fan pattern may be caused by a loose nozzle, clogged vent hole on the supply cup, or the packing may be leaking around the needle. 

• If the spray pattern is offset to one side or the other, the air ports in the air cap or the ports in the horns may be plugged. 

• If the spray pattern is heavy on the top or the bottom, rotate the air cap 180°. If the pattern reverses, the air cap is the problem. If it stays the same, the fluid tip or needle may be damaged. 

• Other spray pattern problems may be a result of improper air pressure, improper reducing of the material, or wrong size spray nozzle. 

## Sequence for Painting a Single-Engine or Light Twin Airplane 

As a general practice on any surface being painted, spray each application of coating in a different direction to facilitate even and complete coverage. After you apply the primer, apply the tack coat and subsequent top coats in opposite directions, one coat vertically and the next horizontally, as appropriate. 

Start by spraying all the corners and gaps between the control surfaces and fixed surfaces. Paint the leading and trailing edges of all surfaces. Spray the landing gear and wheel wells, if applicable, and paint the bottom of the fuselage up the sides to a horizontal break, such as a seam line. Paint the underside of the horizontal stabilizer. Paint the vertical stabilizer and the rudder, and then move to the top of the horizontal stabilizer. Spray the top and sides of the fuselage down to the point of the break from spraying the underside of the fuselage. Then, spray the underside of the wings. Complete the job by spraying the top of the wings. 

The biggest challenge is to control the overspray and keep the paint line wet. The ideal scenario would be to have another experienced painter with a second spray gun help with the painting. It is much easier to keep the paint wet and the job is completed in half the time. 

## $^{ }$Common Paint Troubles 

Common problems that may occur during the painting of almost any project but are particularly noticeable and troublesome on the surfaces of an aircraft include poor adhesion, blushing, pinholes, sags and/or runs, “orange peel,” fisheyes, sanding scratches, wrinkling, and spray dust. 

## Poor Adhesion 

• Improper cleaning and preparation of the surface to be finished. 

• Application of the wrong primer. 

• Incompatibility of the topcoat with the primer. [Figure 8-13] 

• Improper thinning of the coating material or selection of the wrong grade reducer. 

• Improper mixing of materials. 

• Contamination of the spray equipment and/or air supply. 

Correction for poor adhesion requires a complete removal of the finish, a determination and correction of the cause, and a complete refinishing of the affected area. 

## Blushing 

Blushing is the dull milky haze that appears in a paint finish. [Figure 8-14]  It occurs when moisture is trapped in the paint. Blushing forms when the solvents quickly evaporate from the sprayed coating, causing a drop in temperature that is enough to condense the water in the air. It usually forms when the humidity is above 80 percent. Other causes include: 

• Incorrect temperature (below 60 °F or above 95 °F). 

• Incorrect reducer (fast drying) being used. 

• Excessively high air pressure at the spray gun. 

If blushing is noticed during painting, a slow-drying reducer can sometimes be added to the paint mixture, and then the area resprayed. If blushing is found after the finish has dried, the area must be sanded down and repainted. 

<img src='content_image/588426.jpg'>

