What was designed first on the P-47?

The starting point wasn't the airframe: instead of drawing it and then looking for an engine to fit, Kartveli started with the powerplant, the huge 18-cylinder, turbosupercharged Pratt & Whitney R-2800 Double Wasp. The air-flow system was designed first, and the fuselage structure was built around it. That twin-row radial produced up to 2,000 hp (1,500 kW) and drove a four-blade, constant-speed Curtiss Electric propeller 146 in (3.7 m) in diameter.

Kartveli placed the General Electric turbosupercharger in the rear fuselage, not on top of the engine. It was mounted inside the fuselage, about 22 feet behind the propeller, with the exhaust gases carried from the engine to the turbine through jacketed ducts under the fuselage. Exhaust from the 18 cylinders was routed rearward to spin the turbine, and the compressed air returned forward through an intercooler to the carburetor. The ducts, fitted with waste gates, ran along both sides of the cockpit and glowed red at their forward ends at full power, while the turbine spun at 21,300 rpm. An oil-operated regulator governed those waste gates and automatically adjusted turbine speed to maintain the manifold pressure chosen by the pilot.

To accommodate the large-diameter propeller without sacrificing wing armament or structural efficiency, Republic developed a telescoping main landing gear that extended 9 in (23 cm) when deployed and folded inward into compact wheel wells when retracted. That mechanism also reduced the size and weight of the gear legs and allowed the machine guns to be mounted in the wings. The armament consisted of eight .50 caliber (12.7 mm) Browning AN/M2 machine guns, four per wing, staggered to feed from adjacent ammunition boxes holding 350 rounds each, with a combined rate of about 100 rounds per second. The self-sealing main and auxiliary fuel tanks sat beneath the cockpit, with a total capacity of 305 US gallons (254 imp gal; 1,155 L).