Aircraft Painting AIRCRAFT PAINTING – WHAT YOU SHOULD KNOW
Inspection and Planning When the aircraft arrives for painting, all surfaces are inspected with the customer to determine the existing condition of skins, composites, windows, landing gear, control surfaces and and plastics. Small dents and wrinkles in the skin that are hardly noticeable under old, chalky or weather-beaten paint will stand out noticeably under a new, shiny coat of high-gloss paint. Any defects that could affect the quality of the exterior painting are noted and discussed with the customer prior to starting work.
Control Surfaces Control surfaces cannot be painted on the aircraft. All primary flight controls (ailerons, elevators and rudder) and any necessary fiberglass or plastic components are removed from the aircraft in our maintenance facility. Flight control rigging data is recorded, then the aircraft and removed parts are moved next door to our stripping and painting facility.
Preparation for Stripping Preparation for stripping is a very time-consuming, and critical step. All windows, fiberglass, brite-work, engine inlets, actuators and all other openings in the aircraft must be wrapped with chemical-resistant foil and tape to prevent any chemical damage. Foil tape is extended onto the aluminum at least 3” past the point where any plastic begins, and over door and baggage compartment openings to ensure that no chemicals leach onto the plastic or door gaskets.
Stripper Application Stripper is applied, and allowed time to work. Usually several applications are required, with pressure-washing and rinsing between each application.
Control surfaces are stripped separately from the aircraft.
If applied correctly, the stripper will begin to penetrate the base coat and primer and break the bond between the primer and the underlying aluminum within 15 minutes.
The paint and primer will actually begin to fall off in sheets. This is very different than the old types of stripper that just ate into the paint and left a gummy residue.
When the finish has loosened to bare metal, the stripper and residue are agitated with brushes. Immediately after agitation, all loosened residue is scraped from the surface with a rubber bladed squeege, and fresh stripper is applied as required.
Stripping Cautions Never allow stripper to dry – it will set up and be extremely difficult to remove. Do not expose the aircraft to direct sunlight during stripping. Never rinse surfaces with water between chemical remover applications as this stops the removal action and causes the residue to set up on the surface. Schedule removal operations so that, once started on an area, they can proceed without interruption through the entire sequence to complete removal to bare metal. If the removal operation is interrupted, extreme difficulty will be encountered completing the operation.
A final pressure-wash removes all traces of the old paint and primer.
Hand-Sanding The chemical-resistant foils and tapes that were used to protect the windows, fiberglass, brite-work, engine inlets, actuators, door seams and all other openings in the aircraft are removed, exposing a considerable area of unstripped surface. The areas that were protected by the foil now have to be sanded, by hand. This easily can take 4 people a week or more to complete on a small single-engine aircraft.
Post-Stripping Inspection When all paint is completely removed from the aircraft, it is inspected for any hidden damage, corrosion and loose rivets. It is possible for corrosion to work unseen for years under an old paint-job. If found, now is the time to correct it before proceeding further in the process. Royal Aircraft Services handles minor repairs as a matter of course. If substantial surface restoration, filling, riveting or sheet-metal work is necessary the customer will be contacted for approval to perform this work.
Basic Body-work Small dents in the skin that are hardly noticeable under old, chalky or weather-beaten paint will stand out noticeably under a new, shiny coat of high-gloss paint. Basic body-work involves filling any major defects with a special 2-part epoxy filler, then hand-sanding the repairs to a smooth finish.
Etch and Alodine Surface preparation for painting is the most important requirement for insuring proper adherence and performance of a paint system. Prior to applying the primer coat, the bare metal is given a final hand-sanding and a special wax and grease remover is used to remove any impurities. The bare aluminum is acid-etched and chemically treated to assure long-term protection from corrosion. Chromate conversion coating material is brushed on and allowed to react with the aluminum surfaces until it turns a brassy iridescent yellowish tint; reaction time is between 3 and 5 minutes. Then the material is blotted off with rags and clean water. No visible coating residue (yellowish color) will remain on the rag after the last blotting action.
Surface Preparation The aircraft is moved from the stripping booth into the paint booth where filtered, forced hot air is used to dry the aircraft. The chromate conversion coating must be allowed to dry for at least 2 hours before taking further action. When the aircraft is thoroughly dry, all windows and other surfaces that are not to be painted are masked-off using a variety of special papers and tapes. All engine openings and door jambs are also masked to prevent any overspray from reaching these areas. Just prior to spraying the primer coat, a final hand wipe-down with a tack-cloth is done to remove any dust or lint that may flaw the final finish.
Primer Application Two-part corrosion inhibiting epoxy primer is applied by sprayer. A final hand wipe-down with tack cloth is done to remove any particles from the surface before priming. The primer must be applied within 48 hours after the application of the chromate conversion coating chemical. The product should never be applied unless the air, the primer, and the aircraft surface temperature is above 50° F (10 ° C) and the surface temperature is at least 5 ° F (3 ° C) above the dew point. Our paint booth is heated prior to application using natural gas radiant heaters, supplemented by a natural-gas fired furnace coupled to our air intake-filtration system.
“ Royal Treatment” The basic body-work performed prior to priming removed any major dents and dings from the surface. For customers who desire a “glass-smooth” finish on their aircraft, we offer the option of applying additional layers of high-build epoxy primer, which is laboriously hand-sanded to an exceptionally smooth finish.
The “Royal Treatment” is usually applied to the entire aircraft, but it can also be applied just to specific “problem areas”, at the customer’s request. The “Royal Treatment” is usually applied to the entire aircraft, but it can also be applied just to specific “problem areas”, at the customer’s request.
Base Coat Painting As with the primer, the base coat can only be applied if the air, the paint and catalyst, and surface temperature of the aircraft is above 50° F (10 ° C) and the surface temperature is at least 5 ° F (3 ° C) above the dew point. It is essential that no more than 48 hours elapse between the application of the primer and the base coat. The bond between the primer and the base coat depends upon a chemical reaction between the two products. After 48 hours the primer becomes chemically inactive and this bond will not occur.
Without the chemical adhesion between the primer and base coat, over time the paint will begin to flake off the leading edges and other surfaces that are exposed to abrasive action.
Paint Application Royal Aircraft Services uses one of two spray methods: High Volume Low Pressure (HVLP) application – Paint is atomized by a high volume of low pressure ( < 20 PSI) air through the spray gun nozzle. A high volume of air is used to push the paint and form a very soft, low-velocity pattern. This soft spray provides a consistent coverage and very good overall finish. Electrostatic Spray - The paint material is charged inside the gun (60,000 volts at about 200 microamps), and is attracted to the grounded aircraft. The combination of the low particle velocity of the airless spray and the electrostatic attraction to the aircraft produces an excellent transfer efficiency rate. Overspray is greatly reduced and hard-to-coat areas such as edges and irregular shapes are more effectively painted.
After painting, temperature is increased in the heated paint booth and the base color is allowed to thoroughly dry, then a two-color painted stripe design, or custom vinyl stripes and numbers are applied (depending upon customer preference) to match the customer's specs and drawings. Registration numbers are then applied (again either painted or vinyl, depending upon the customer's preference).
Inspection Once all colors and vinyl have been applied, all paper and tape is removed and the surfaces are inspected for any imperfections and touched-up as necessary to assure an excellent exterior finish. All necessary detailing is completed at this point, including the application of anti-skid material to any wing-walk areas.
Re-Assembly The aircraft and its newly painted primary flight controls are moved to our maintenance facility for: Balance-check and reinstallation of control surfaces, using the data recorded during the aircraft's disassembly Rigging check Operational inspections of the flight controls, flaps and lights Inspection of gear wells, flap wells, flight control wells, static port, pitot tubes, etc. Inspection of wheel bearings and repacking Gear-retraction test
Painting Problems <ul><li>Rivet head “pops ” – </li></ul><ul><ul><li>Corrosion-X and other corrosion inhibiting materials are great to use inside your aircraft, but not before or after painting. Do not use Corrosion-X for several months before, or after your new paint job. </li></ul></ul><ul><ul><li>Even though the paint is “dry” and the aircraft is flying, solvents will continue to migrate out of the paint for a month or more after painting; the chemical reaction between the paint and the primer is not complete. Solvents like Corrosion-X are designed to weep into microscopic openings, and can find their way around rivet heads and into the still active paint and primer. This causes the paint to “pop” off the rivet heads. </li></ul></ul>
Painting Problems Orange Peel – <ul><li>Occurs when: </li></ul><ul><li>Paint is not thinned enough </li></ul><ul><li>Paint is too cold </li></ul><ul><li>Insufficient air pressure </li></ul><ul><li>Gun stroked too far from surface </li></ul><ul><li>Wrong air cap or fluid nozzle used </li></ul><ul><li>From overspray striking a previously sprayed surface </li></ul>
Painting Problems Sandpaper Finish – <ul><li>Occurs when: </li></ul><ul><li>Incorrectly primed </li></ul><ul><li>Dirty painting area </li></ul><ul><li>Primer not adequately sanded </li></ul><ul><li>Improperly cleaned paint equipment </li></ul><ul><li>Dried overspray: gun too far from surface </li></ul>
Painting Problems Wrinkling – Occurs when: Too thick a coating is applied, preventing uniform drying of the coat. Results in the formation of ridges and furrows.
Painting Problems Lifting – Occurs from: Absorption of solvents by previous partially dried film (coats not allowed to dry/cure for the proper time before recoating) Use of incompatible paint and thinners.
Painting Problems Fish Eyes – Occurs from: Use of waxes or sealants and adhesives containing silicones (improper cleaning and prep) Presence of other types of oils, greases, or hydraulic fluids on the surface. Minute quantities of silicones can cause this film.
Painting Problems Blistering – Occurs from: Oil or grease left on surface Moisture in paint lines Trapped solvents (use of improper thinner)
Painting Problems Pitting or Cupping – Occurs from: Rust under the surface Oil or grease on surface Moisture in the paint lines Trapped solvents (improper thinner proportions)
Painting Problems Crazing – Occurs when: Painting over a hard, glossy coat. A base coat of this condition offers a poor surface adhesion of subsequent coats. In drying, the topcoat slides over the base coat, breaking out in cracks. Also can be caused by excessive amount of catalyst in the paint, causing brittleness. Cracking –
Care of New Paint <ul><li>Washing the aircraft – </li></ul><ul><ul><li>The finished application of paint contains a microscopic coating of resins that rise to the top of the color pigments. This clear coat provides the "shiny" appearance and prevents oxidation and acid rain damage. When washing the aircraft, do not use harsh detergents that may penetrate and wear away this surface coat. </li></ul></ul><ul><ul><li>Do not use “Joy” or “Dawn” or other dishwashing soaps that are designed to remove grease – they will remove the resins from the paint prematurely and dull the finish. </li></ul></ul><ul><ul><li>Improper cleaning agents will also compromise the UV protection designed into the paint. </li></ul></ul>
Care of New Paint <ul><li>Waxing the aircraft – </li></ul><ul><ul><li>Don’t do it – for at least two to three months after painting. </li></ul></ul><ul><ul><li>Just use water and a very mild automotive washing soap for three months (like Meguiar’s Gold Class Car Wash Shampoo and Conditioner) </li></ul></ul><ul><ul><li>When washing or waxing, use the same care that you would when polishing your plexiglass windows. Always use soft rags - no hard brushes, and NO PAPER TOWELS! </li></ul></ul><ul><ul><li>Do not apply degreasing materials to remove grease stains. A mild automotive soap with plenty of water is best. </li></ul></ul>
Proper care will extend the appearance of your aircraft for 10 to 15 years.
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