We’re really proud of our engineering team. They’ve consistently designed products that raise the bar for the industry in terms of quality and performance, so much so that we’ve almost grown accustomed to their amazing design creations. Every now and then, however, they design something that makes each and every one of us take a step back and say “Wow, now THAT is impressive!”
This was the case back in 2009 when GFS Engineering tackled the issue of designing a better set of doors for use on our massive Aerospace paint booths. These doors are essentially a giant air plenum, complete with ducting and integrated filtration, that must be engineered to precise tolerances to perform above and beyond the requirements of the customer in terms of airflow, filtration, structural stability, durability, and mobility. In addition, they must be capable of withstanding some of the most intense climate conditions on the planet.
One set of such doors was installed at Elmendorf Air Force Base in Anchorage, AK. Here is the report that our engineers put together upon completion of the project:
The exterior weather door is in reality a piece of ductwork or more accurately, a swinging style plenum filter door. The exterior skin matches the architectural skin of the paint hangar in color and style and is insulated with R-12 insulation to reduce heat loss or heat gain during the year round cycle. The door is designed for operation under 60 mph sustained winds, and 100 mph winds while closed. Additionally, it will resist the Anchorage, Alaska seismic forces, a temperature differential of 125 degrees F between inside and outside, building movements and apron slopes.
The door is a nominal 4 feet thick to allow for a good air distribution to a painting area for military aircraft. The interior skin of the door is equipped with filter racks and high diffusion filters to allow a final stage of filtration before entry into the paint booth.
The use of steel HSS and W sections was really the only practical structural solution. Each door leaf is 36 ft wide and 27 ft tall. In addition to allowing airflow through, the need to hold the deflection caused by wind forces low enough to keep the door sealed was the controlling design criteria. The door is configured as multiple cantilevered trusses.
The plenum filter door is powered open and closed with a hydraulic ram and incorporates a separate motor for the drive machinery to permit the door leaf to be operated in a power failure by a 12V DC backup power supply. The ram is located about mid-height of the door to provide for a 10’ clear envelope around the aircraft as it is moving in and out of the booth. The combination of a cylinder at this height with a sliding hinge at the top while the door is open during a 60mph wind creates an uplift condition at the supporting wheels. The addition of 6,000 lbs of concrete to the base at the outer half of the door provides the resistance to eliminate this condition and provide for a stable design. Lightweight structural materials would not have provided any benefit.
Four wheels are required to support the weight of the door and the live loads applied. They are centered at approximately 3⁄4 the length of the door from the hinge point. All of the wheels are located between the door faces with no projections outside of the door. The bottom hinge point is a combination of bearings that allow the door to rotate horizontally and to a lesser degree vertically to account for the apron slope. The top hinge point is actually a sliding mechanism that allows the top of the door to move outward as it is opening but resists the wind forces perpendicular to the door when open or closed. This sliding mechanism also allows the building to move over 3” in line with the doors while they are closed.
The door assembly is equipped with a double row of seals around its entire perimeter to reduce loss of energy when in closed position. A combination of brushes and vinyl/rubber materials are used. The seals at the top are designed to accommodate the deflection of the doors during a design wind.
The interior of the plenum door is designed to contain a positive pressure during operations. This requires that the door be relatively air-tight and construction features are being used to mitigate leakage. The interior surface of the door will be lined with 20 GA sheet metal panels to cover the exterior, insulated liner panel seams. In addition, the joints within the interior liner wall will be sealed with a duct spray sealant.
GFS is proud to say that these doors are working beautifully installed at their Alaskan home. We are also proud to say that the Aerospace Plenum Door is now a standard product offering from GFS, and we can custom-engineer virtually any size door for any size booth, from a small Cessna-size booth to a gargantuan C-17 Globemaster booth. As our engineering team has shown, the sky is the limit!