HALE (high altitude long endurance) aircrafts are small airplanes used in weather and atmosphere monitoring. They are unmanned aircrafts. They are remotely controlled from the ground. Having flight durations that last many days, they require a consistent energy source.
Most HALE aircrafts have a standard propulsion system (propeller engines) which is their main thrust source. However during long missions this has been a setback as the aircrafts would need to come back to Earth to refuel. This setback is time consuming and not very cost effective.
So in order to overcome this obstacle of refueling and the obvious irony of monitoring an atmosphere and desecrating at the same time, engineers have found a solution (THEY ALWAYS DO). An environmentally friendly solution. A cost and time effective solution. (If you remember from my previous post I talked about square panels called "solar panels"). YES, solar panels. Engineers decided that they needed alot of flying time and they needed to save the environment at the same time so they decided to use the Sun as an energy source. Hence, a HALE aircraft with solar panels spread out through its very long sing span. The solar panels get energy from the Sun to power the propellers used on the aircraft, and if we're lucky we would use it to power the onboard weather monitoring equipment and avions of the aircraft. This has not proven to be a big challenge for now as HALE aircrafts are very light and don't require much thrust force for take-off or maintaining level flight. In the future I suppose the developments of more efficient and cheaper solar panels could see this technology being used on everyday civil aircrafts. Until then, we would have to breathe in more and more carbon dioxide and nitrous oxide everyday. But have faith, because as I said earlier, ENGINEERS ALWAYS FIND A WAY. (an example of a HALE aircraft using solar panels is shown below, courtesy of http://www.qinetiq.com/).