The Piper J-4 Cub Coupe is a two-place side-by-side aircraft. It was built between 1938 and 1942 by Piper Aircraft. It was Piper's first model with side-by-side seating; combined with docile low-speed handling.
The fuselage of the J-4 is wider than the J-3 and the aircraft had an enclosed rear deck. The first J-4s had a Continental 50 hp A50 engine, an open cowl, oil and spring landing gear, a modified tail wheel system, and many modifications relative to the J3. The early J-4 had a comfortable cockpit but was slower than most side by side aircraft of the day.
The 1940 J-4A incorporate an enclosed cowl, a Continental 65 hp A65 engine, and aft auxiliary fuel. The J-4B was fitted with a 60 hp Franklin 4AC-171 engine. The final version was the 1941 J-4E which sported a 75 hp Continental engine and redesigned interior. The main fuel tank was moved to the wing along with its header tank. Performance was now on par with similar contemporary types, but the attack on Pearl Harbor sealed its fate as all civilian aircraft manufacturing came to a stop.
Some J-4s had another unique feature in the tail construction: the stabilizer was made of stainless steel tubing, riveted together with gussets.