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J U L Y 2 0 1 4 | 5 5 PROTOTYPE UAV parallel to the fuselage) in opposing di- rections, to the hover position, 75° off the fuselage's 0° axis (vertical, in launch position). This wing rotation orients the plane's two propellers in opposite direc- tions, which causes the rotor-wings and upper fuselage to spin while the four- fnned tail unit remains stationary on the ground. When the wings and body motion reaches 60 rpm (1 revolution per sec- ond), the faps (ailerons) are defected down and the aircraft leaps into the air. A small motor in the tail "de-spins the tail" during fight — that is, it maintains the tail's position and prevents it from spin- ning with the fuselage, explains Robert Godlasky, Dzyne's ROTORwing chief en- gineer. Because it does not spin, the tail houses the aircraft's navigation system. Directional control at this stage is pro- vided by defecting the ailerons down on one side of the revolution and up on the other. This tilts the "disk" described by the rotating wings (see graphic on right, p. 56), altering the fight path as request- ed by the pilot on the ground. At a height of 2,000 ft/610m, the wings rotate forward to fight position, the wings and fuselage stop spinning, the tail unit locks into position and the Pathfnder then fies like a conventional airplane at scale speeds between 40 and 100 knots. (Scale speed is the speed the scale model will go in relation to the full size model. In this case, scale speed is about 10 times that of the full-size ve- hicle, or 400+ knots.) To initiate landing, the wings and fuselage are programmed to abruptly pull-up into a vertical climb at full speed and begin the transition back into the rotor wing confguration to allow a vertical landing — enabling the UAV to touch down gently on its tail. "The innovation is that it matches highly effcient, long-endurance fight with vertical takeoff and landing, without needing a giant gear box between the en- gine and the rotor," Page points out. In a conventional helicopter, the gearbox and tail rotor weigh about three times what the engine weighs. This airplane eliminates all that by spinning the wings. "We've got an engine on each wing … like a totally normal twin-engine airplane. The RO- TORwing converts from a helicopter to an airplane using very small gearboxes be- tween each assembly — wings, fuselage and tail — each of which can move inde- pendently of the others." The result is a huge savings in weight. Unusual stressors Godlasky points out that the imposed loads are signifcant during lift-off: "When the wings are spinning one rev- olution per second, that force tries to eject the wings from the fuselage," he says. "In addition to that, you're pulling up to 2Gs momentary thrust to initiate climb. So you have the thrust load in ad- dition to the load from centrifugal force. In addition, there are some smaller loads because the propellers are spinning in multiple axes — rotating about their own axis and being accelerated in a circle around the fuselage. This generates large gyroscopic forces, as well." To determine what materials and de- sign would best handle these unusual fight loads in the prototype airframe, Dzyne used the DS SolidWorks Simula- tion package from Dassault Systèmes (Velizy-Villacoublay, France). Composites were attractive in terms of manufacturing, says Godlasky, because they "allowed us to mold shapes that would otherwise be nearly impossible to manufacture, including the hard edges and small, tight radii we needed." Both carbon fber and aramid fber were con- sidered for the reinforcements. "There are advantages to using aramids in certain applications," Godlasky observes, "but in this vehicle, we were primarily looking for stiffness-to-weight ratio, rather than toughness." Carbon fber composites, at half the weight of aluminum, and one- sixth that of steel, offered the best stiff- ness-to-weight. The prototype airframe was built to Dzyne specifcations by AC&A; (Lake Forest, Calif.), a vertically integrated manufacturer of large, complex compos- ite parts and tooling. AC&A; has onsite capability for 5-axis machining, waterjet cutting, climate-controlled lamination; a 7 ft by 40 ft (2m by 12m) autoclave (ca- pable of 350°F/176.7°C temperatures by donna dawson illustration / karl reque aerial vehicle's helicopter-to-airplane conversion. Pathfinder prototype in airplane mode An artist's conception of the ROTORwing in forward flight, after vertical take-off. Source: Dzyne Technologies 0714hpc FOD-OK.indd 55 6/17/2014 11:13:00 AM