Aircraft Paining and Finishing (Entire Jeppesen Chapter)

What is blushing (in reference to dope)

solvents evaporate due to high humidity, causing a porous and chalky finish

What causes Pinholes in a dope finish?

Dope films that are expose to high heat or excessive wind when they are applied can have pinholes form

What causes Sags and Runs when applying a dope finish?

Slow movement of the spray gun over the surface of the fabric, which causes excess dope to build up on the fabric.

What is Orange Peel and what causes it?

Orange Peel is caused by the surface of the dope drying before the dope beneath it does.

This is typically due to improper spray techniques or air drafts over the surface of the finish

What are Fisheyes? What causes them?

Fisheyes are small spots in the dope that are not dry and are caused by something contaminating the surface, preventing the dope from curing

What is Dope Roping?

Thin trails left from brushing on dope. Fixed by thinning the dope.

Why is polyurethane finish typically not used on doped surfaces?

• poly cracks easier on dope and fabric aircraft

• poly painted surfaces are more difficult to repair

What are the benefits of a smooth, quality paint job?

1. A reduction in drag

2. Protection of the base material from corrosion and abrasion

3 methods for stripping paint

1. Chemical

2. Mechanical

3. Pyrolytic

What is media blasting?

a type of mechanical blasting similar to sand blasting, but uses different forms of media such as glass beads or nut shells

What are the general steps / recommendations for corrosion removal and prevention?

1. Remove finish from structure

2. examine for any corrosion (remove if found)

3. acid etch the surface

4. apply a conversion coating to aluminum, creating an oxide film over it

5. clean the surface before priming/painting

what is the purpose of acid etching prior to painting?

To remove any remaining corrosion

and

Promote paint adhesion

What are the 2 types of primers used today?

1. Wash Primer

2. Epoxy Primers

Which type of primer is prefered today?

Epoxy Primers are better, as they are resistant to skydrol, more protective of the elements, but they are more expensive and more complicated to apply.

List the 3 general types of paint; which one is the most common?

1. Enamels

2. Acrylic Lacquer

3. Polyurethane

Why is Polyurethane the preferred topcoat paint?

Polyurethane is hard, chemically resistant, and durable in harsh environments. Also resistant to Skydrol

List and briefly describe the various types of Special Finishes

• High-Visibility Finish

  • Reflective base coat with colored pigments for safety visibility

• Wrinkle Finish

  • Used on instrument panels, electronics, and other stuff that is subject to rough treatment

• Wing Walk Compound

  • sand mixed into enamel; good non-slip surface

• Acid-Proof Paint

  • for battery boxes, protects against acidic corrosive chemicals

• Fuel Tank Sealer

  • AKA sloshing compound, seals fuel tanks around fasteners/seams

• Engine Enamel

  • High Temp proof, for engines

What is the purpose of retarder?

A type of thinner for dope and fabric that is used in high humidity dope spraying applications

What is Acetone used for?

• Removing lacquer finishes

• clean up after painting

• softening acrylics inside painting equipment

What is Dope Rejuvenator used for?

Softening the old dope and flowing the cracks back together

where should air pressure be regulated for paint spraying?

At the gun itself

List the 3 types of paint application systems.

1. HVLP System

2. Electrostatic Systems

3. Powder Coating Systems

What does HVLP mean? Explain this system.

• High Volume/Low Pressure (HLVP) painting systems use low pressure air delivered at a high volume to atomize and apply paint

• Produce less overspray, but have to hold the gun closer

Explain how Electrostatic Painting Systems work

• paint is negatively charged, and is drawn electrostatically to the part which is grounded.

• This method has little to no overspray

• Uncommon

Explain how Powder Coating works

• AKA “Dry painting”

• dry powdered paint is melted onto surface of ferrous metal

• for use on high stress/high temp/chemically exposed parts only

2 main types of spray guns

1. Suction Feed Guns

2. Pressure Feed Guns

3. (book says 2 main types, fowler also mentioned explicitly “gravity feed” guns)

Explain the operation of a Suction-Feed paint gun

• air flowing out of the gun creates a low pressure zone, pulling the paint out of the cup and into the paint guns air stream (like a carb pulls fuel out)

• used for low volume painting or touch ups

Explain the operation of a Pressure-Feed paint gun

• Paint is delivered from a pot to the gun under a slight positive pressure, then mixed into airstream

• used for high volume painting, large areas

what is the purpose of the wing-ports?

to flatten out the spray pattern by directing air through ports on either side of the atomizing air holes.

What pattern should a correctly adjust spray gun produce?

“A uniform, fan-shaped spray, with the fan perpendicular to the wing ports”

How far away should the spray gun be from the surface?

Roughly 8 inches, or one hand span

What causes this problem: Rough Finish

Dope or paint is too cold

What causes this problem: Fabric Will not Tauten

Fabric put on too loosely

What causes this problem: Blushing

Humidity is too high

What causes this problem: Pinholing

water or oil in spray, or undercoat is still wet

What causes this problem: Bubbles

dope too cool

What causes this problem: Runs/Sags

bad technique, improper thinning

What causes this problem: Dope will not Dry

oil, grease, or wax on surface

What causes this problem: Dull Spots

Porous undercoating, allowing dope or paint to sink in

What causes this problem: Bleeding

Dyes used in undercoats are soluble in the top coat

What causes this problem: White Spots

Water in spray system

What causes this problem: Paint/Primer Peeling

wax'/chemicals from cleaning process still on surface

What causes this problem: Brown Spots

oil in spray system

What causes this problem: Orange peel

spraying with too high pressure

What causes this problem: Wrinkling

reaction between paint and undercoats

What causes this problem: Overspray

wrong spray technique

What causes this problem: Fisheyes

contamination on the surface

When should masking tape be removed? Why?

Tape should be remove when the finish is tacky to the touch, if tape is left on until the paint is dry, the masked line will be rough

Where should registration numbers be located?

between the trailing edge of the wing and the leading edge of the horizontal stab; or on engine pods

How high should registration marks typically be?

12 inches high

How should registration markings be spaced?

no less than one-fourth of the character width apart