Wing Men

In early May, Davidson traveled to Pope Air Force Base in North Carolina and took walk-around photos of another full-size A-10 for reference, and Selby dug up a book of photos of Johnson’s A-10. He also unearthed schematics and official guides to markings and heraldry. In the “static” part of the Top Gun competition, a team of judges meticulously checks the model’s lines, markings and weathering against photos of the actual plane, right down to the scratches and dings. It must be an exact copy of that moment in the A-10’s career. “If there’s a defect on the real plane,” Tiano says, “you’d better have the same defect on your model, or you’re going to lose points.”

Small but Powerful

Selby’s model will be the first A-10 to fly in competition, and probably the largest jet ever to fly at Top Gun. About 85 percent of Top Gun competitors build from kits, but Selby designed and built nearly everything on Johnson’s A-10 from scratch in his 1,500-square-foot workshop, just off the parking deck of his 30-story apartment building. The shop is a tech geek’s dream, outfitted with a laser-cutting machine, computer numerical control mill and lathe, 3-D laser scanner, and plastic vacuum former.

A scale modeler’s biggest challenge is building a functional model that will look like the real plane, while using different materials and construction techniques, and keeping thrust-to-weight and lift-to-weight ratios within practical limits. “A plane with an overloaded wing will fly like a powered brick,” Selby says. “In low-speed situations, you can run into stalls and control problems, and the sink rate on the plane is quite high.”

Starting with Davidson’s photos and the original Fairchild Republic drawings of the A-10’s wing, Selby scaled the wing down and modified the control surfaces, using design and airfoil-analysis software. The A-10’s fuselage, wing and control surfaces are made of lightweight fiberglass, carbon fiber and Kevlar. To make the skin look authentically weathered, Selby bound pastels into the paint and then rubbed it with steel wool—a particularly impressive feat considering that he’s partially color-blind.

Real A-10s are equipped with turbofan engines, which drive a fan that feeds extra air into the burner, but to stay aloft, model jets typically use lighter and simpler single-stage axial turbines. Unfortunately, most single-stage turbines take several seconds to accelerate from idle to full throttle. This lag time can sometimes make the difference between being able to abort a landing, and crashing.

Selby and Saechour’s Bangkok-based scale-jet company, PST Engines, boosts its miniature jet engines’ acceleration by adding extra vaporizers in the combustion chamber and sophisticated digital fuel controls. Built out of heat-resistant superalloys and kitted out with full ceramic bearings, the A-10’s engines rev up to 120,000 rpm and develop up to 29 pounds of thrust—more thrust for their weight, Saechour claims, than anything else on the market. With both wings attached, Selby’s 5.5:1-scale A-10 stretches 10 feet across and weighs 65 pounds at takeoff. Inside the fuselage, carbon fiber snakes like spaghetti around five Kevlar fuel tanks, which hold 8.5 liters of jet fuel, enough for about 15 minutes of flight.

Selby designed the plane’s electrical system with enough redundancy to make NASA proud. A power box distributes signals from the two radio receivers to 24 servo motors, which operate the control surfaces. The redundant radio system calculates which receiver has a stronger signal and constantly switches back and forth. Two separate electrical systems run the microswitches and small microcomputers that handle sequencing, and backup lithium-polymer batteries guard against catastrophic loss of power.