Detailed Design

Through a series of iterations and analysis, we were now able to model the final design of the aircraft. Based on the results and analysis of the previous discussion, the following dimensional parameters were finally selected for fabrication.

5.1 Dimensions

5.2 Structural Characteristics

Till this moment, we had decided the specifications of the different parts of the aircraft and finalized the dimensions as mentioned in the above table. The prime specifications are the choice of the fuselage, high wing configuration and selection of conventional tail while taking into account the mission requirements and weight reduction to achieve the optimum flight performance. Furthermore, the design also needed to be easily detachable and assembled so as to provide assistance in transport. All these parameters are discussed in detail following sections.

5.2.1 Wing

The airfoil selected for wing is customized airfoil MH 114 that has rib structure as shown in fig 5-1. The wing span is 60 inches and has chord of 12 inches. It is fabricated such as to assemble and detach on and from the fuselage effectively. This was achieved by using screws that were inserted in fuselage through the wing. The rib structure greatly reduced the weight of the wing as well as provided the necessary strength to the wing and fuselage. Rib structure was covered by a thin sheet of mono-coat to make it a solid model.

5.2.2 Fuselage

The fuselage configuration best suited for our mission specifications is single boom configuration. The fuselage had a maximum width of 5.5 inches and a length of 45 inches. 2 Different types of woods that is Balsa and Plywood with varying thickness are used in different parts of the fuselage to provide the necessary strength to the structure. Large sections were removed from the walls of the fuselage to reduce weight. The whole body was covered with a mono-coat to provide a solid model look.

5.2.3 Tail

Tail of the aircraft is also made with Balsa wood and has a rib structure. As mentioned earlier, weight reduction being the prime objective while designing, the rib structure is carefully selected with proper thickness so it does not fail under the given stress conditions. It is made to assemble on the fuselage easily.

5.2.4 Elevators & Rudders

Elevators and rudders extend throughout the width of the horizontal and vertical tail and are capable of movement controlled by servo motors attached. The material used is balsa wood.

5.3 System and Subsystem Design

5.3.1 Propulsion

Outrunner Brushless motor is selected for propulsion since it has high torque. But the outrunner motor has one disadvantage and that is low RPM. This was overcome by using a large diameter propeller. The high torque provided by the outrunner motor can easily rotate large diameter propeller, providing the necessary acceleration required to take off within the 60ft specified distance.

5.3.2 Controls

“HITEC Standard HS-325HB” servos are used to control flaperons, elevator and rudder of the aircraft. They have excellent response to the signal and delivers the torque efficiently even at higher speeds of the aircraft. The choice of the servos is based on the efficiency of the servos, their availability in the market and economic factor

5.3.3 Radio Control

“HITEC OPTIC 6 Channel Digital Proportional Radio Control system” is used for remote control of the servos and speed control. This Radio control system has 6 channels that operates at 2.4 GHz. A total of 5 channels are needed to control the aircraft including the 4 servos and a speed controller. Our choice is based on the number of channels required and economy factor.

5.4 Weight & Balance

Initial weight of the aircraft body kit without the motor, servos, receiver, battery packs and any other payload is about 4.40lbs as calculated by SOLIDWORK software by using mass property tool. The actual weight of the aircraft may vary.

The initial approximation of CG is also performed using the same software while later on, its actual position is determined by simple balancing technique. The variation in the position of CG is explained as follows.

5.4.1 Without Internal Payloads

The CG of the aircraft body without any internal payloads is near the trailing end of wing which positions it at about 30% of the fuselage from the tip.

5.4.2 With Internal Payloads

After mounting the motor, servos, receiver, battery packs and the mentioned payload i.e. 500ml water bottle, the CG shifted towards the leading edge at almost 50% of the wing chord from the leading edge and at about 27% of the fuselage from the tip.

5.5 Drawing Package

This section of the chapter contains a detailed CAD package that demonstrates the design of the aircraft. Drawings for the aircraft dimensioning, structural arrangements system layouts and payload accommodations for the aircraft can be seen in the figures.