Today, almost all aircraft designed to fly much above 450 mph (390 kn; 720 km/h) use a swept wing. Since the inside of the propeller is moving slower in the rotational direction than the outside, the blade is progressively more swept back toward the outside, leading to a curved shape similar to a scimitar - a practice that was first used as far back as 1909, in the Chauvière two-bladed wood propeller used on the Blériot XI. (At the blade root, the blade is actually swept forward into the rotational direction, to counter the twisting that is generated by the backward swept blade tips.)[74] The Hamilton Standard test propfan was swept progressively to a 39-degree maximum at the blade tips, allowing the propfan to produce thrust even though the blades had a helical tip speed of about Mach 1.15.[75]