insulation of the gondolas. Although the Mission Team was monitoring the flight closely, there was no way to decrease the temperature for the remaining duration as each daily cycle requires an ascent to 28,000 feet and descent for optimal energy management.
The damage to the batteries was not a technical failure or a weakness in the technology but rather an evaluation error in terms of the profile of the mission and the cooling design specifications of the batteries. The temperature of the batteries in a quick ascent / descent in tropical climates was not properly anticipated.
To avoid the batteries overheating again, engineers upgraded the whole battery system and integrated a cooling system.
Flying over 35,000 km The Solar Impulse’ s motors have an average power over 24 hours of a small motorbike( 15 hp) with a maximum power of 70 hp( four 17.5 hp engines).
Four brushless, sensorless motors, each generating 17.4 hp, were mounted below the wings, and fitted with a reduction gear limiting the rotation speed of a 4m diameter, two-bladed propeller to 525 rpm. The entire system is 94 % efficient, setting a record for energy efficiency.
Solar Impulse can fly at the same speed as a car, between 36 km / h( 20 Kts) and 140 km / h( 77 Kts). At sea level, minimum speed is 45 km / h( 20 Kts) and maximum speed 90 km / h( 49 Kts). At maximum altitude, speed can pick up to between 57 km / h( 31.5 Kts) and 140 km / h( 77 Kts).
Being as a light as a feather … or a car The engineering team managed to build the entire structure proportionately 10 times lighter than that of the best glider. Every gram added had to be deducted somewhere else, to make room for enough batteries on board, and provide a cockpit in which a pilot can live for a week. In the end, it had the weight of a small van or 2,300kg, using a combination of ultralight materials: carbon fibre weighing 25 g / m2( three times lighter than paper) and alveolate foam in the form of a honeycomb. These two materials, assembled in a sandwich, are used in the whole frame of the plane: fuselage( body of the plane), cockpit and spars( central beam representing the spinal column of the wings).
Robustness The upper wing surface of the plane is covered by a skin consisting of encapsulated solar cells, and the lower surface by a high strength, flexible skin. A total of 140 carbon fibre ribs spaced at 50 cm intervals give the wing its aerodynamic crosssection, and also maintain its rigidity.
To be resistant to wind, water, mold and large temperature variations, chemists and engineers invented especially light insulating materials. These included a rigid polyurethane foam( insulation made of alveolate foam) for protecting the cockpit and the pods housing the motors and batteries; high performance polycarbonate sheets( derived from plastic) for the windows, and an ultrathin polymer film( a kind of resin) to protect the photovoltaic cells from water and UV radiation, and allow them to adopt the curvature of the wings without breaking.
Energy efficiency The systems on the airplane for collecting and storing energy were designed to minimise energy loss. The solar cells, batteries and motors have record beating energy efficiency: 23 % for the solar cells, and 97 % for the motors, which only lose 3 % of energy against 70 % for standard thermal motors.
With so many technical innovations on board, Borschberg described the Solar Impulse as“ a flying laboratory full of clean technologies”. These technologies are now opening up new industrial markets and offering an opportunity for economic development and job creation.( see Table 3).
Many hearts and minds have been captivated by Solar Impulse’ s flight around the world this year. Although commercial aviation powered by the sun is still far way, the plane has inspired innovations and pushed the limits of solar energy and energy efficiency.“ If an airplane can fly several days and nights in a row with no fuel, then clean technologies can be used on the ground to reduce our energy consumption,“ Borschberg explains. He believes that clean technologies, such as the ones developed and tested for Solar Impulse, could cut energy consumed on a daily basis by 50 %. – Inforeach
REFERENCE
www. solarimpulse. com Wikipedia
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