The PRO series helicopter ring-type engines are equipped with dual ball-bearings, Schnuerle porting, one ring-type piston / cylinder assembly and two-needles automatic mixture control carburetor. The PRO-Heli series are manufactured by automated computer-controlled machinery, resulting in a product that looks and performs better. The PRO-90H provides the smooth hovering and on-demand power and acceleration required by FAI pilots as well "hot dog" and "3-D" aerobatic fliers. Precision air bleed carburetor makes adjustments simple, and efficient mufflers keep things quiet at the field.