A successful aircraft with the speed of an airplane and vertical take-off and landing capability of a helicopter was long sought after. Such aircraft tent to be complex. In the 1970s technology had advanced that much that the first modern tiltrotor aircraft appeared. This research vehicle was the Bell 301, designated XV-15 by the military. The XV-15 has a fuselage with large cockpit windows similar to those often found on helicopters. At the end the rear fuselage slopes up, ending in an H-tail. The largest part of the vertical stabilisers is above the horizontal ones, and the vertical stabilisers have a significant sweep angle. The leading edge has a bent, while the trailing edge is straight. The aircraft has a retractable landing gear with double wheels on all legs. The main gear retracts in bulges at the sides of the fuselage. The XV-15 has fairly short wings with big nacelles at the tips. The whole nacelles can be tilted ninety degrees, from fully forward to vertical. They have the circular exhausts at the back. The turbine engines power three-blade rotors/propellers with large, pointed spinners.
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Essentially, the V-22 is a much larger development of the XV-15 research tiltrotor. It has the same basic shape as the Osprey, including H-tail, three-blade rotors and double wheels on all gears. The nacelles of the Osprey are larger and have rectangular exhausts. Also, the vertical stabilisers have a non-swept trailing edge.
This is to be the first commercial tiltrotor. It is about the same size as the XV-15, but with a T-tail and single wheel main landing gears that retract rearward in the fuselage. (photo: pjs2005/WikiMedia)