Conceptual Model of Aircraft “Chiroptera”

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In the history of world aviation the first attempts to create aircraft were connected with birds flight imitation. The first time the aircraft with a wing like bat’s was created by French engineer Clement Ader (Clément Ader, 1841-1925) ^[9]. His aerostatic machine was a tailless monoplane without vertical fin. Fuselage and wing frames were manufactured of bamboo silk-fabric covered. Aircraft was equipped with two pusher propellers with four blades each of which was fitted with steam engine. He called his aircraft “Eole” in honor of ancient Greek Olympian Eolus. In October, 1890 C. Ader tried to fly on “Eole” which took off and flew about 50 m. However, because of lateral controls absence he failed to perform full flight. But it was the first self-moving flight in the history carried out 13 years prior brothers Wright’s flight.

Aircraft conceptual development starts from creative search stage: choice of style, composite approach, sketch creation, future model draw ^{[10, 11]}. On Figure 1 the sketches of natural bionic forms and variants of creative search are shown. High speed aircraft id assumed to be modeled and therefore as a final variant the construction with extended arrow-headed wing was chosen (Figure 1, left side).

Further the chosen sketch is modified based on aerodynamic, operating characteristics and ergonomic requirements. After that the stage of 3D modeling based on detailed design takes place. In this work graphic modeling system AutoCAD will be used. Nowadays there is a fair number of 3D modeling graphic systems and CAD system. Graphic system AutoCAD enables not only to create and correct drawings, as well it can carry out 3D surface, solid modeling and create realistic rendering. It should be noted that the author has considered the issues of amphibian aircraft 3D computer modeling in his papers ^{[12, 13]}. In the paper ^[12] the issues of amphibian aircraft conceptual design based on bionic forms were described.

3. Modelling Method

To apply Koons method it is necessary to build overall 3D box ^[14]. 3D box is constructed by means of rectangle extrusion to some height. On each side edge of 3D box the curvelinear spline per closed loop is constructed (Figure 2, right side, below). With the help of command Edge Mesh the constructed splines are pointed step by step resulted in smoothed curved surface.

While creating aircraft it is necessary to analyze the commands of surface modeling available as well as possibilities to design components of the object under modeling. We decompose aircraft (based on airframe axis): airframe upper and lower surface, vertical fin surface and engine surface. For better aerodynamic properties the aircraft airframe should be streamlined and for its creation the method of Edge Mesh will be used. Tail unit and engine nozzles can be created with command Ruled Mesh.

Figure 2. Original plane forms of aircraft surface

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With the help of 3D box the half of stream-lined body along its axis is created. To create triangle outline of the body upper part it is necessary to shift one of the closed spline peaks inside 3D box. Using Mirror tool the wing splines mirrored copies are constructed. Original flatness for tail unit and nozzle is constructed in the form of polylines and a spline. The result of preparatory work to create aircraft surface in the form of flat splines and polylines is shown on Figure 2.

Prior performing 3D modeling let’s consider design features of the aircraft model under development. Aircraft aerodynamic configuration pertains to “flying wing” type (without fuselage). As for arrangement it is a monoplane, wing geometry in plan view is a variety of delta wing “ogival” type ^{[15, 16]}. Nowadays monoplane configuration with wing different arrangement is usually used. Delta wing is used mostly for supersonic aircraft. In comparison with straight wings they have a drag at cruise mode and enable to use wing inner volumes more effectively. Aircraft has no horizontal tail (tailless), vertical tail is a twin-finned one. Power plant consists of two turbojet engines located in vertical stabilizer section of the body. Landing gear configuration is supposed to be tricycle nose wheel landing gear.

In order to create aircraft 3D surface the body’s left and right parts are generated step by step with the help of Edge Mesh command. With the help of command Ruled Mesh the tail part and engines nozzles are created. The result of generation in three orthogonal and isometric projections are presented in Figure 3. If necessary the body’s original plane figures can be corrected for aircraft aerodynamic characteristics.

Figure 3. 3D surface model of aircraft in projections

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4. Rendering of 3D Model

Further, in order to create accurate rendering scene it is necessary to assign the materials and determine lighting. The work with materials consists of two stages: adding (creating) new materials to drawing and material binding to scene objects. Creation of appropriate materials is an important part of shading process because the final result considerably depends on this. The material, in its turn, interrelates with lighting, object color affects specular reflection. In AutoCAD graphic system there is a big choice of materials, they can be edited or new one created ^[14].

Notwithstanding that 3D models are more accurate than 2D ones they don’t look like natural, they are lack of real colors, shadows, lighting. Shading enables to generate accurate image of 3D scene based on different optical effects. On Figure 4, Figure 5 rendering scenes of aircraft “Chiroptera” shaded surfaces during cruising flight and target run are shown.

Figure 4. Rendering of “Chiroptera” aircraft conceptual model (cruising model)

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Figure 5. Rendering of “Chiroptera” aircraft conceptual model (target run)

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