Solar Power Aeroplanes by the 21st Century?

AeroVironments Inc. with assistance from Nasa’s Dryden Flight Research Center have succeeded in creating and testing a long range, high altitude, solar electric aircraft – The Helios Prototype. Helios was built to test Solar Power capabilities for unmanned aerial vehicles (UAV’s), also dubbed ‘Atmospheric Satellites’ because it’s hoped that the eventual production craft will be able to fly at ultra high altitudes for period of perhaps six months at a stretch, behaving much like any other satellite, while conducting either commercial or science based missions.

The upper wing surface is covered with more than 62,000 bi-facial solar cells providing the solar power. Each cell is silicon-based with approximately 19 percent efficient converting solar energy into electrical power.

The Helios Prototype was the 4th generation of aircraft harnessing Solar Power. It was aimed squarely at two major goals of Nasa’s Environmental Research Aircraft and Sensor Technology (ERAST) project. These goals are:

1. Sustained high altitude solar power flight. Sustained meaning 100,000 + feet.
2. Non-stop solar power flight for 24 hours, including a minimum of 14 hours flying time above 50,000 feet.

The solar power design is of a flying wing with a wing width of 8 feet and an awe inspiring wingspan of 247 feet, that’s 32 feet greater wingspan that the largest 747 ‘Jumbo-jet’ commercial airliner. Helios had to have an ultra-light construction using composites like carbon fibre, Kevlar®, styrofoam, graphite epoxy adhesives, with wing coverings made of a transparent plastic skin. The main carbon fibre wing spars have been wrapped with a combination of Nomex® and Kevlar for additional strength and rigidity.

Solar Power for Helios Prototype

Solar Power ‘Atmospheric Satellite’.

That’s a picture of the solar power or solar-electric Helios Prototype flying over Hawaii during an early test flight using just solar power driving 14 brushless electric motors of just 1.5 kilo Watts or (2 hp) per motor.

Each propeller has been constructed using advanced composite materials, following a design with laminar-flow to increase efficiency during any high altitude flights.

The Helios solar power aircraft achieves an avarage cruising speed of just 25 mph, with an equivalent speed similar to a bicycle during take-off and landing.

Relying on Solar Power for ’round-the-clock’ endurance flight.

It became obvious that during sustained night operation the number and weight of batteries needed would be respectively too many and far too heavy, whether these rechargeable batteries were of NiCad or Lithium technology.

The Helios design team turned to Fuel Cell technology using a Polymer Electrolyte design. The recent technological advances in Fuel Cell technology have been largely due to automotive industry efforts. It must be said that Nasa are not the only people chasing the solar power aircraft dream. To read a previous posts about green solar power being used for aircraft power ‘click’ here.

With a Fuel Cell now being used to provide supplimentary electrical power for sustained night flights, the solar power is only needed for daytime flying. These technological advances are unlikely to influence commercial airlines in the forseeable future but solar power UAV’s will be flying high within a decade! Well that’s my guess anyway, solar power from the current solar cell technology is just a bridge too far, for now.