The airflow direction in a crossdraft booth should flow from ‘nose to tail’. An airplane has a preferred way of moving through the air and ‘nose to tail’ is the best and most logical way to design the booth. Eddies are reduced to a minimum when you examine the nose to tail airflow pattern.
Overspray from the paint gun will drop on its journey to the filter wall. In many cases this may cause blemishes if the painter does not cover sections of the aircraft downstream of the spray guns. It is best to work high to low and front to back in crossdraft booths.
It has been said that a downdraft booth is the best booth in which to paint cars, trucks, buses, railcars and farm equipment; in short anything you don’t have to paint the bottom of. Planes have vast areas that are on the underside (about 50% of the plane) and painting these areas positions the painter between the paint gun and the floor. Painters with a small amount of experience will find ways to avoid overspray that is directed toward them. But, paint overspray is always pulled away from the plane toward the floor filters in a downdraft booth.
In any case, the eddies set up by air rolling over the wing and the fuselage will cause problems in controlling overspray. It is best to work high to low when using a downdraft booth.
There is a dramatic difference in the ability to maintain the filters of the two booth types. The crossdraft booth allows for all filter stages to be in one location and you can change the filters from outside the filter house. The only tools needed are a rolling platform to reach overhead filters.
In a downdraft booth the first stage of filters are located in the floor trench under the grating. If the grating is a man load rated grating, then the grates must be lifted off so the filters can be accessed. If the grating is rated for the load of the airplane, it may be necessary to use a hoist to remove the grating because of its weight.
The use of an automatic filter changing system which uses rollers and a support bed can ease the pain of filter change-out as well. These have been used to good success as long as the filters are changed often enough so that the accumulation of paint residue is minimized. The filters in the filter house (2 stages) are handled the same way as the filters in a crossdraft filter house.
Downdraft paint booths are recognized as the state of the art in high-quality finishing applications. Even for airplane painting, downdraft gives a very high quality of paint job. Having said that, Gulfstream is known for the high quality of paint job applied at their completion centers, and they use crossdraft booths. High quality finishes may be obtained from both types of paint booths.
It is apparent that a paint booth will give a better paint job than painting a plane in a hangar with the door open. Controlling the airflow, and the cleanliness of the air is essential to getting a blemish-free appearance.