The upper half portion of the UAV is a ballonet filled with helium gas to provide the main lift. Six arms are attached to the base of the ballonet, and a rotor is attached to the end of four of the six arms. These four rotors provides some additional lift during take-off, but mostly, they provide controls in flight. There are two tiltrotor mounted at the end of the remaining two arms respectively, one on each arm. These two tiltrotor provides the main thrust in level flight, in addition to that provided by the four rotors. According to the designer Mr. Liu Shi-Luan (刘诗鸾), the advantage of this design includes low cost, saving fuel, and heavier payload. Tilt Ducted Fan UAV is an experimental UAV developed by NCHU to explore new ways of achieving VTOL. Tilt Ducted Fan UAV adopts an airframe similar to that of Lockheed Martin RQ-3 DarkStar but with V-tail added. There are a total of four engines, all of which are ducted fans. The two of the three smaller ones are mounted near the wingtips respectively, and the third one is mounted in thenose. These three smaller engines are fixed and provide lift during takeoff and landing. The fourth engine is a large one mounted in the fuselage near the V-tail, and this engine can tilt as needed. During the takeoff, the large engine is positioned just like the remaining three smaller ones providing major lift, and once airborne, the larger engine would tilt 90 degree to provide thrust in level flight. The process is reversed during landing operations. The complete name NCHU gives to this Tilt Ducked Fan UAV is New Type Multifunctional Tilt Ducked Fan UAV (Xin-Xing Duo-Gong-Neng Qing-Xie-Zhuan Han-Dao Wu-Ren-Ji, 新型多功能倾转涵道无人机)  Urban Goblin (Du-Shi Jing-Ling or Dushijingling, 都市精灵) is a VTOL UAV with three ducted fans. What is unusual about unlike most aircraft with ducted fans where all ducted fans are same sized, ducted fans of Urban Goblin are not the same size. Out of three ducted fans of Urban Goblin, two small ones are the same size and attached to the main ducted fan, which is much larger.