altitude record for solar–powered aircraft to , which was also the record for propeller–driven aircraft. On August 6, 1998, Pathfinder Plus raised the national altitude record to for solar-powered and propeller-driven aircraft. On August 14, 2001, Helios set an altitude record of – the record for FAI class U (experimental/new technologies), and FAI class U-1.d (remotely controlled UAV with a mass between ) as well as the altitude record for propeller–driven aircraft. On June 26, 2003, the Helios prototype broke up and fell into the Pacific Ocean off Hawaii after the aircraft encountered turbulence, ending the program. In 2005, AC Propulsion flew an unmanned airplane named "SoLong" for 48 hours non-stop, propelled entirely by solar energy. This was the first such around-the-clock flight, on energy stored in the batteries mounted on the aircraft. The QinetiQ Zephyr is a lightweight solar-powered unmanned aerial vehicle (UAV). As of 23 July 2010 it holds the endurance record for an unmanned aerial vehicle of over 2 weeks (336 hours). It is of carbon fiber-reinforced polymer construction, the 2010 version weighing (the 2008 version weighed ) with a span of (the 2008 version had a wingspan). During the day it uses sunlight to charge lithium-sulphur batteries, which power the aircraft at night. In July 2010 a Zephyr made a world record UAV endurance flight of 336 hours, 22 minutes and 8 seconds (more than two weeks) and also set an altitude record of for FAI class U-1.c (remotely controlled UAV with a weight between ). Vertical flight For a tethered device such as an air observation platform, it is possible to run the power up the tether. In an attempt to create a more practical solution than the clumsy balloons then in use, the Austro-Hungarian Petróczy-Kármán-Žurovec PKZ-1 electric-powered helicopter was flown in 1917. It had a specially-designed continuous-rated electric motor made by Austro-Daimler and received its power up a cable from a ground-based DC generator. However electric motors were not yet powerful enough for such applications and the motor burned out after only a few flights. In 1964, William C. Brown at Raytheon flew a model helicopter that received all of the power needed for flight by microwave power transmission. The world's first large-scale all-electric tilt-rotor was the AgustaWestland Project Zero unmanned aerial vehicle technology demonstrator, which performed unmanned tethered fights on ground power in June 2011, less than six months after the company gave