![elios prototype 3 elios prototype 3](https://cdn.motor1.com/images/mgl/8oyle/s4/elio-motors-ec1-la-2016.jpg)
Using the traditional incremental or stairstep approach to flight testing, the Helios Prototype was first flown in a series of battery-powered development flights in late 1999 to validate the longer wing's performance and the aircraft's handling qualities. In this configuration, the number of motors was reduced from 14 to ten. The second configuration, HP03, optimized the aircraft for endurance, and used a combination of solar cells, storage batteries and a modified commercial hydrogen–air fuel cell system for power at night. The first, designated HP01, focused on achieving the altitude goals and powered the aircraft with batteries and solar cells. To this end, the Helios Prototype could be configured in two different ways.
![elios prototype 3 elios prototype 3](http://cyrilhuzeblog.com/wp-content/uploads/Elio11.jpg)
The ERAST program had two goals when developing the Helios Prototype: 1) sustained flight at altitudes near 100,000 feet (30,000 m) and 2) endurance of at least 24 hours, including at least 14 of those hours above 50,000 feet (15,000 m). The aircraft's maiden flight was on September 8, 1999. The larger wing on the Helios Prototype accommodated more solar arrays to provide adequate power for the sun-powered development flights that followed.
![elios prototype 3 elios prototype 3](http://i.kinja-img.com/gawker-media/image/upload/s--uaYUcqEM--/c_fit,fl_progressive,q_80,w_636/1289712414727867974.jpg)
The NASA Centurion was modified into the Helios Prototype configuration by adding a sixth 41 feet (12 m) wing section and a fifth landing gear and systems pod, becoming the fourth configuration in the series of solar-powered flying wing demonstrator aircraft developed by AeroVironment under the ERAST project. AeroVironment Chairman Paul MacCready shows a cross section of the AeroVironment/Helios Prototype wing spar.