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Painting Large Aircraft – An integrated approach
Richard Thelen, PE, Global Finishing Solutions
The use of inserts for painting fighter aircraft in the military has a long established and proven record of success. It achieves all of the main objectives of a paint booth. It protects against fires. It contains the VOC’s. It provides the proper environment for the painter. Inserts are standalone paint booths and come complete with their own structural support. Wherever inserts have been used, the paint finishes have been excellent.
Paint Barns are large rooms that have ventilation systems to allow painting in a safe manner. They come complete with their own structural support system. When using an insert, there are two separate structural support systems; the booth’s and the building’s. This paper looks at a new approach that allows the integration of the paint booth insert structure with the building structure.
The use of an integrated paint booth insert for painting large aircraft will meet all of the tests for an effective paint booth including the enabling of a good paint job. The use of paint barns will achieve two of the three objectives but rarely achieves a good paint job. In addition, the paint booth insert will operate at lower costs for energy, be environmentally friendly and have a much lower investment cost.
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Paint Booth Inserts
A paint booth insert is a self-contained enclosure for containing the operations of the painting process. The process considerations are safety, health, and quality.
• Safety: Fire is an ever-present adversary and must be a prime consideration for the designer. The guidelines for design of paint booths are contained in the many Codes and Standards that apply to the industry.
• Health: The effects of volatile compounds and heavy metals on personnel are well known. The protection of the environment is also a prime consideration for the designer. The safeguarding of the health of the employee from the effects of aerospace coatings is very important. Coatings containing metals such as chromates and isocyanates must be carefully dealt with. Some toxic compounds are also frequently used especially in epoxy coating.
• Quality: The overall quality of a paint job is dependent on several factors. Lighting and airflow are very important, as is the quality of the process air introduced into the booth. Dirty or contaminated air will affect the quality of the paint job and increase the need for rework. At times for a large aircraft re-work can amount to several days of extra labor to repair defects in the coating. Defects can be visual and unsightly, but most importantly, defects can be the origin site of new corrosion.
Inserts and paint booths provide good control of airflow and excellent lighting. They also provide a better energy management bargain because airflow is reduced to the absolute minimum required to satisfy the demands of safety, health and quality. The cost of air consumption is very high especially in intemperate climates where replacement air must be heated or cooled. Reduction of airflow is a key energy management tool.
Lighting is a critical and difficult design problem in any paint booth, but in an aircraft paint booth different problems arise than in a typical vehicle booth (for instance). The underside of an aircraft amounts to exactly one half of the aircraft’s paintable surface area, and is the most difficult design problem to accommodate. In a paint booth insert, the very geometry of the insert helps to get lights closer to the surface and directed in such a way as to fully illuminate the aircraft.
Paint booth inserts are completely stand-alone facilities that require little or no structural assistance from the enveloping structure. This feature makes it extremely easy to erect a paint booth insert inside an existing hangar facility. Thus we say the paint booth is “inserted” into the hangar.
The use of paint booth inserts is cost effective. By reducing the overall airflow in a paint booth, the size of the air moving machinery is reduced. Horsepower is reduced and consequential electrical installation costs are saved. Ductwork and duct supports are reduced in size and cost. Accessibility to equipment by use of platforms and storage areas for consumables such as filters are reduced in cost due to reduced area required. Lights are located as close as possible to the aircraft reducing the quantity of lights required. Structural demands are reduced greatly due to the standalone concept and thus steel costs and booth erection costs are greatly reduced.
Paint Barns
A paint barn is a compromise by the designer to accomplish two of the main objectives of a paint booth compromising finish quality (performance) for cost of construction. The designer looks at the design of a proper paint booth and regards as too costly the changes necessary to accomplish a perfect paint booth design. Several considerations are important to the designer is this rationale. One is access to the aircraft, previously done by tele-platforms. Multiple use of a paint facility (such as maintenance) leaand it is ifficult to incorporate them into an insert. Use of fall protection around the top surfaces of a paint booth meant rugged support structures.
The need for fall protection and elaborate access structure in a paint barn means that there are flat spots on the tops of beams and other items that overspray and dust and even pollen in the springtime can settle onto. Once these particles are disturbed, they fall onto the object being painted causing a blemish and reducing quality. Steel beams are a particularly sought after roost for birds and pigeons. While the inner walls of a paint barn can be sheathed with smooth drywall or sheetmetal, the overhead steel and hanging items are another challenge altogether.
Lighting in a paint barn has been uniformly poor in the past designs. Typically the lights are high wattage HID lamps that drop from the ceiling. Electrical classification is also a problem since volatile vapors are ever present.
Airflow is calculated over the entire cross sectional area of the Barn even though the process does not use the air at the ceiling level. To reduce the airflow to a more reasonable level risks the degradation of laminar flow in the center of the plane (the wings) where most of the paint is applied. As the air slows down, and mass is added to the air, the density of the air changes and the laminar flow degrades into eddies. This is visible as a cloud of overspray over the head of the painter.
Large aircraft Integrated inserts
Inserts for large aircraft may take the shape of the booth shown in Figure 1. In this booth the filter wall is located on the rear of the booth (upper right). The replacement air is introduced into the booth through very large doors on the front of the booth (lower left). This design for airflow gives the most consistent laminar airflow possible in a booth of this size. The tail of the plane is located at the rear of this booth.
Figure 1 - Insert Iso View:
 Notice that the difference between the overall height and the sidewall height is significantly different. This has the effect of reducing most of the paint booth ceiling to just barely over the top of the aircraft fuselage. The airflow in the booth is sized for the lower cross-sectional area. Often, this airflow is 50-65% of the airflow required in a paint barn. This very fact helps control the laminar nature of the paint booth airflow.
In an integrated system, all of the best features of an insert are incorporated into the paint barn concept. The booth skin is attached to the girt system of the metal building. This system requires the use of vertical interior sidewall panels. The panels must be smooth on the inside, so the booth is easy to clean and maintain. Overlapping panels and bolted design allows for ease of attachment with no bolt heads visible. Panels are deep enough to allow use of standard Class 1 Davison 2 (enclosed and gasketed) paint booth lights.
Unlike the insert shown above, there is no need for an internal skeleton of structural steel. The ceiling of the booth is suspended from the building steel to form a smooth interior liner that expands and contracts as required with the movement of the building.
Integrating the booth lining with the structural skeleton of the building reduces by many tons the amount of steel required to erect the facility. It also allows the beneficial aspects of a paint booth insert to be a parts of the “paint barn”.
Mechanical equipment
One of the main design efforts for a paint booth is the location of the mechanical equipment. In this case, the low roof of the booth makes an ideal place to store the mechanical equipment. There is plenty of headroom and a wide area available.
Figure 2- Plan view
(Click on image for larger view)
 Notice from Figure 2 that even off-the-shelf air make-up units can be arranged to provide the smaller amounts of airflow that this booth requires. The combined airflow is then ducted to the front plenum filter doors for distribution into the paint booth. The weight of the mechanical equipment and its access platforms is carefully positioned to the very stiff and stable structure of the filter chamber.
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Lighting
Notice the pattern of the lights in Figure 2. It is carefully arranged to get maximum intensity in the area where paintable surfaces are located. In addition it is only 8-10 feet above the fuselage at this point and lighting is extremely good. The large number of lights are also arranged to cast light onto the floor in strategic locations to allow for reflectivity to the underside of the fuselage and wings.
Sidewall lighting further augments to reflected lighting to give a highly visible painted surface at any point on the airplane.
Access & Fall Protection
Access to painting of the aircraft is possible using floor supported devices. While the use of floor supported devices is not feasible for a blast media booth due to buildup of media on the floor, this is not true of a paint booth. If the use of overhead access devices is necessary, the structure of the booth is adequate to support these devices. In addition, since the devices are closer to the painted surface, they are shorter and necessarily stiff reducing wiggling and accidental nicks in the plane surface.
The structural strength of this paint booth allows the easy installation of fall protection devices. These cables or channels used in fall protection designs can be easily attached to the steel beams supporting the roof panels. The booth structure is designed to handle these severe loads and shocks.
Budget costing
We have worked up budget prices for two large aircraft inserts. These sizes can be used to paint many airframes and their overall sizes will be listed.
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Table 1. Paint Booth Budget Pricing
In past installations, it has not been unusual to build these paint barn projects for $22-25 million. Of course that figure includes site work, lockers, offices, and a weather-tight envelope, but the overall cost of a paint project should be much less with an insert than with a paint barn.
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Global Finishing Solutions
12731 Norway Road • Osseo, WI • 54758
P800-848-8738 • F715-597-2193 • info@globalfinishing.com
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