In June of 2000, after we had concluded tests of our proprietary oxygen/alcohol igniter, we set to work on a 160 lbf liquid oxygen and isopropanol engine, which we ran in October of the same year. Following successful tests of this engine, known as the XR-3A2, in November 2000 we started to design and build the regeneratively cooled 400 lbf LOX/alcohol engines that we eventually integrated into a Long-EZ airplane to create our EZ-Rocket aircraft.
The XR-4A3 engines went through multiple acceptance tests before the first flight of the EZ-Rocket on July 21, 2001. Early flights on engines 101 and 102 quickly lead to design improvements, and serial numbers 103 and 104 powered 20 of the 26 flights of the EZ-Rocket.
The flight test program passed its first milestone by flying with both engines for an engine run time of 96 seconds, and a total flight time of five minutes and twenty seconds. Later flights achieved burn times of up to 2.5 minutes, altitudes to 11,500 feet, and the point-to-point distance record for a rocket-powered vehicle.
Specific impulse of this engine is higher than either LOX/alcohol engines in the Bell X-1 and the Redstone.
The fact that two 4A3 engines powered an aircraft safely, reliably, and routinely multiple times proved to us the viability of civilian rocket-powered aviation. Routine operations must be the primary criterion for rocket engine development. Our approach is to build safer and more reliable rocket engines first, then progress to the higher performance needed for orbital launch vehicles.