The Ultrasport 331 is a development of the Ultrasport 254 and, like that model, is named for its empty weight in pounds. The aircraft was designed to comply with the US Experimental - Amateur-built aircraft rules. It features a single main rotor, a single-seat enclosed cockpit with doors, skid-type landing gear and a twin cylinder, air-cooled, two-stroke, dual-ignition 650NaN0 Hirth 2706 engine.
The aircraft fuselage is made from composites. Its 211NaN1 diameter two-bladed rotor has a chord of 6.71NaN1 and employs an ATI 012 (VR-7 mod) airfoil at the blade root, transitioning to an ATI 008 (VR-7 mod) airfoil at the tip. The ring-mounted tail rotor has a 2.61NaN1 diameter and a chord of 21NaN1. The cyclic control is mounted from the cockpit ceiling, but otherwise is conventional. The horizontal tailplane mounts end-fins for directional stability.[2]
The aircraft has an empty weight of 3300NaN0 and a gross weight of 6800NaN0, giving a useful load of 3500NaN0. With full fuel of the payload is 2900NaN0.
The manufacturer estimated the construction time from the supplied kit as 60 hours.
By June 2014 three examples had been registered in the United States with the Federal Aviation Administration, although a total of six had been registered at one time.[3]
