Tells Of Adventures In X-15, Shuttle

by ANN Correspondent Chris Esposito

Major General Joe Engle detailed his adventures in the X-15 and Space Shuttle Projects recently at AirVenture 2007. Engle -- who has amassed 11,000 flight hours, 200 of which were in space -- flew in the space shuttles Enterprise, Columbia, and Discovery. He recounted the advances made with the two aircraft, as well as his personal experiences in them.

The original X-15 used two sets of LR-11 rocket motors; each had four separate chambers "like an over-under shotgun," explains Engle. With a total of eight rocket chambers, the pilot could ignite the fuel all at once, or in stages. The next evolution in the X-15's motor, the LR-99, produced nearly 60,000 pounds of thrust and pushed the X-15 to Mach 6.7. The shockwaves from this speed run caused significant burning of the aircraft's stabilizers and ventral fin, essentially "totaling" the aircraft.

Since there were no solid inertial platforms during the 1950s and early 60s, pilots had to shut down the engine at very specific times to ensure they could manage the X-15's energy enough to make the landing zone, which was typically a dry lakebed. Controlling the descent angle required "all eyeballs out the window." says Engle.

With no approach path aids in the cockpit or at the landing sight, judging distance and glide was very much on the pilot's shoulders. Engle recalls the landing of the X-15 as "very unnatural... No matter what you did with the stick, the nose would slam down," he says.

Control was a problem at high altitudes, particularly after 150,000 feet. To solve this, the X-15's engineers designed two control systems, one using reaction controls powered by oxygen peroxide, and the other using the flight surfaces. Neither control stick was put in the center, as the tremendous G's would mean induced oscillations when the pilot accelerated or decelerated sharply. When the Shuttle program began, the two control systems were combined into one stick that was computer-controlled and would automatically switch between the systems.

"The X-15 really prepared us to fly the Space Shuttle." explains Engle. He described the X-15 program as "one of the most rewarding things I've done in my career." The 300 knot patterns and 195 knot landing speeds of the X-15 meant the test pilots would be well-prepped for Shuttle missions. Engle flew the Shuttle on the initial glide test flights, when the Shuttle was brought aloft by a 747. Originally, the engineers of the Space Shuttle considered putting turbine engines in the payload bay, but discarded this idea after the X-15's many successful flights under no power.

When the explosive bolts detonated, separating the Shuttle from the 747, "we would pop off with pretty good G-force." Engle says. Engle and another pilot would then climb and roll left to assure adequate clearance during separation. Once gliding down, the pilots gathered data on aerodynamics by flying at different angles of attack. Engineers could then calculate lift/drag ratios for different airspeeds and configurations.

As with the X-15, the initial Space Shuttle test flights required pure skill, because the cockpit did not feature an inertial platform for guidance.

"I'm sorry to see us stop flying the shuttle," says Engle, referring to the planned retirement of the fleet in 2010. He prefers the winged approach to spaceflight due to the "stick and rudder" feel.

Looking to the future, Engle sees nuclear power as the only way to extend our reach into the cosmos. The energy produced by such a spacecraft would be "almost inexhaustible," he says.

FMI: www.jsc.nasa.gov/Bios/htmlbios/engle-jh.html