Build a Solar-Powered Airplane: Innovative Aeromodelling

In this article, we shall explain the fabrication of a small aircraft fly on solar power. The aircraft is radio controlled using the usual transmitter-receiver pair used in aeromodelling. The aircraft has a wing of span 2.5 m and chord of 30 cm with no tapering or sweep angle. The model weighs approximately 1,500 g out of which 400 g is the weight of the 18 solar cells, which are installed in the plane. The solar cells produce about 50–60 W@9–11 V under normal conditions. For construction of the airplane, balsa wood is used, which is then covered by heat shrunk model aircraft covering. The length of the fuselage is 200 cm which is also completely built of balsa wood and uses trusses to reduce weight and retain strength. The airplane uses a brushless DC motor and a direct drive slow fly propeller for producing thrust. Two-bladed propeller is used for more efficiency. Along with this a system is also developed for emergency landing in case of dim sunlight or to handle any other power failure situation. After fabrication, flights were taken and necessary improvements were done to enhance its performance. The key feature of this design of solar airplane is the solar cells which initially charge a battery and when these cells discharge during flight—these were subsequently made to continuously charge during the flight. It removes the need for using a heavy battery for storage, thus improving efficiency and reducing the weight considerably.

The distinguishing quality of solar aircrafts is the long duration of flight without the need of refuelling. A solar plane theoretically can remain in air for any duration of time that, too, with zero emission. This aeromodel uses electric motor to run a propeller and is powered by several solar cells installed on them which either provide electricity to run the electric motor directly or charge a battery pack that later discharges during flight. A solar plane gains altitude and recharges its batteries during daytime; after sunset it flies on batteries or simply glides until sunrise. The fabrication can be completed in three stages:

Stage-I

In this stage the aircraft was designed, keeping in mind the available resources.

Stage-II

Constructing the ribs and spar; then parts for the fuselage were cut and glued together followed by the tail and fin sections. Then solar cells were soldered and their installation on wing and tail was undertaken and electrical components were installed.

Stage-III

The first flight of the plane has to be taken on battery power so as to check the stability of the plane and to find out its behaviour during take-offs, turns, and landings. Based on this flight, further improvements on the design is to be taken up.

It is advisable to use polycrystalline solar cells, since these cells are comparatively less costly, sufficiently efficient, and have light weight.

• Size: 156×156mm, Thickness: 200µm±30µm
• Power: 4.28 Watts, Voltage: 0.628 V

The airplane requires a minimum of 45–55 W of electricity to remain in a levelled flight under no wind conditions. Considering the available space on the aircraft, 18 solar cells could be placed on wings and horizontal stabilizer (14 on wing and remaining 4 on the tail), which could supply 50–60 W. Since each solar cell produces 0.6 V and 18 solar cells are used, all of which are connected in series, an output voltage of 9–11 V is generated which is then directly fed into the electronic speed controller (ESC), which powers the brushless motor. The following electronic components are used in the aircraft apart from solar cells: electronic speed controller (ESC), small brushless DC motor, 2.4 GHz transmitter and receiver, servo motors, and battery eliminator circuit (BEC). Figure 1 is a block diagram showing the connections between different electrical components.

The most important part of this airplane are wings. They need to be light in weight, must accommodate the required number of solar cells, must have sufficient strength, and most importantly they must produce sufficient lift at very low air speed. NACA 7313-63 airfoil was chosen. This airfoil possesses qualities required for slow flying. Wings of span 2.4 m and chord 30 cm and aspect ratio as 8 and mass of aeromodel is about 1.5 kg. It uses 1400 kV motor which turns a 10-inch propeller. Figure 2 gives the drawing of a solar plane.

Contributed by Mr Ahmed Shams, Part III IDD Civil Engineering, IIT(BHU), Varanasi-221005, Uttar Pradesh, India. Email: shams.ahmed.civ14@itbhu.ac.in