A growing fleet of rocket-powered racers will fly with a liquid oxygen and alcohol engine developed by Armadillo Aerospace, instead of an XCOR Aerospace design used during the Rocket Racing League's public debut earlier this summer.
The league had originally planned to pit a racer with an XCOR engine against a racer with an Armadillo engine in the upcoming Reno Air Races set for Sept. 10-14 in Reno, Nev., but for now will only use the Armadillo engine, said league officials.
"When we feel the XCOR engines meet our standards of safety, reliability, reusability, and performance for a rocket racer, then we may bring them back into the league," Rocket Racing League co-founder and CEO Granger Whitelaw told SPACE.com last week.
The Rocket Racing League formed in 2005 to promote NASCAR-style racing in the sky. The league currently has six teams on its roster under title sponsor DKNY Men, a New York City-based men's sportswear line that is also backing the Bridenstine Rocket Racing Team headed by former U.S. Navy jet pilot Jim Bridenstine.
A rocket racer equipped with the Armadillo engine recently completed seven test flights at the Oklahoma Spaceport in Burns Flat, Okla.
No details emerged about exactly why the league decided to hold off on using the XCOR engine, but the decision leaves open the question of what, if anything, will fly at Reno. As of Sept. 5, the Federal Aviation Administration still had not granted approval for a public demonstration of a racer powered by the Armadillo engine.
The decision also comes despite the league's smooth debut with an XCOR engine-powered racer in late July and early August at the EAA AirVenture air show in Oshkosh, Wisc. Whitelaw called the Oshkosh event "a very controlled flight test," and added that XCOR Aerospace is still running flight and engineering tests.
Meanwhile, the XCOR Aerospace firm based out of Mojave, Calif. continued to express confidence in its engine.
"We still have a few last things to test, but so far the engine is very solid and we're very proud of the performance of the engine," said Douglas Graham, an XCOR spokesperson. He added that that XCOR holds no hard feelings against the Mesquite, Texas-based Armadillo Aerospace firm.
"We have nothing but praise for them," Graham told SPACE.com. "Both of our engines have different performance characteristics and different qualities and different levels of complexity."
A side-by-side comparison of the engines shows some of the differences. The XCOR engine emerged from a program aimed at developing suborbital flight, while the Armadillo engine grew out of a more vertical approach to the Northrop Grumman Lunar Lander Challenge. The liquid oxygen and kerosene engine developed by XCOR maintains steady thrust throughout its burn, unlike Armadillo's liquid oxygen and alcohol engine where thrust drops off as fuel burns off.
Graham emphasized that XCOR Aerospace has a history of safe and reliable development, in answer to any uncertainty that might arise from the league's recent announcement.
"XCOR has performed more than 50 manned rocket flights with no loss or damage to the vehicle," Graham said. "We've fired engines more than 3,500 times in our nine-year history without any time loss for injury because of the operation of a rocket engine. That's a safety record that speaks for itself."
Whitelaw, a racing car veteran of the Indianapolis 500, did not elaborate on any requirements that XCOR's engine might need to meet. But he praised Armadillo Aerospace and its founder, John Carmack, for rapidly responding to the league's specifications throughout a six-month test period.
"John will literally solve the problem, design the part and implement the change in hours," Whitelaw said. "And that's what you have to be able to do with racing."
The league plans to officially start its season with 10 rocket racers, six of which will carry Armadillo engines. The other four racer engines "will be up for grabs," according to Whitelaw.
Rocket racing events may include the Reno National Championship Air Races in Reno, Nev., between Sept.10-14 and Aviation Nation at Nellis Air Force Base in Las Vegas, Nev., on Nov. 8-9.
This story was updated at 11:58 p.m. EDT on Sept. 10.
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