The first-generation plane, which was demonstrated at the EAA AirVenture experimental air show in Oshkosh, Wis., was equipped with a kerosene-fueled, pump-fed, 1,500-pound-thrust rocket engine provided by California-based XCOR Aerospace. In contrast, the plane being flown this week at the Oklahoma Spaceport has an alcohol-fueled, pressure-fed, 2,500-pound-thrust rocket engine from Texas-based Armadillo Aerospace.

The engine isn't the only thing that's bigger: The airframe is a modified version of the Velocity XL-5, which is wider, longer and heavier than the Velocity SE that was equipped with the XCOR engine. (One of the league's subsidiaries acquired Florida-based Velocity Aircraft earlier this year.)

If the demonstrations in Oshkosh and Burns Flat were meant as a fly-off, the Armadillo team - led by millionaire video-game programmer John Carmack - came away as the winner.

"The Armadillo engine is going to be the primary engine for the Rocket Racing League," Whitelaw told me. He said five more planes will be built using Armadillo's propulsion system, which is a spin-off from Carmack's years-long quest to win the $2 million, NASA-backed Northrop Grumman Lunar Lander Challenge.

Whitelaw said the planes will be offered to the league's six teams at a cost of $1.25 million each. The Armadillo-powered plane will be painted in the colors of the Bridenstine DKNY Rocket Racer, thus taking on the sponsorship that was announced last month.

"Now that we’ve successfully conducted a test flight with the Armadillo engine, we are looking forward to getting to racing and exhibiting a 21st-century sport for the 21st-century sports fan," Whitelaw said.

XCOR's engine, meanwhile, will be out of the running for the time being, although Whitelaw said he wouldn't rule out using that engine or others in the future if they meet the "specifications that we feel are required for safety, reliability and reusability in a racing format."