The pilot of the unregistered airplane reported that he departed with 3 gallons of fuel and that he was flight testing the airplane by flying it low up and down a private, grass airstrip. He added that, about 1 hour 15 minutes hours into the flight, he "neglected to carefully check the fuel remaining" before taking off to conduct a teardrop maneuver. Once airborne, about 50 to 75 ft, he performed a climbing left turn and noticed the "engine was no longer producing power." He leveled the wings and pushed forward on the control stick. He began the landing flare for a forced landing in a field, and the airplane landed hard and nosed over. The airplane sustained substantial damage to the fuselage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The pilot recommended as a safety recommendation to "fill the fuel tank!"