FLIGHT DESCRIPTION

X-15 flights did not begin with a pilot waking up and deciding he wanted to fly that day. Weeks or months before, a researcher would develop requirements for data gathered under specific conditions. One of the flight planners (Johnny Armstrong, Dick Day, Bob Hoey, Jack Kolf, or John Manke, among others) would take these requirements and lay out a flight plan that defined the entire mission. The term "flight planner" does not begin to describe the expertise of the engineers who performed this function. These engineers lived in the simulator and were experts on the airplane. They determined the thrust settings, climb angles, pushover times, and data-gathering maneuvers; they also evaluated stability and control issues and heating concerns. In addition to laying out specific flights, the flight planners performed parametric studies that were not related to a particular flight or pilot training. Some of these included glide performance, peak altitude versus pitch angle, speed-optimization techniques, and reentry trades involving dynamic pressure, load factors, angle of attack, and temperatures.!11!

The flight planners would then present their plan to the pilot selected for the flight. The flight planners and the pilot would spend the next week or month, depending on the complexity of the mission, in the simulator choreographing every second of the flight. After extensive practice with the nominal mission, the pilot flew off-design missions to acquaint himself with the overall effect of changes in critical parameters, including variations in engine thrust or engine shut-down times.!12!

At this point, the primary ground controller (called "NASA-1") joined the flight planners and pilot for additional simulations so that they could all become familiar with the general timing of the flight. After practicing the off-design missions, the team evaluated various anomalous situations, including failures of the engine, stable platform, ball nose, radio and dampers, and variations in the stability derivatives. For instance, the flight planners would insert simulated premature engine shutdowns at critical points to acquaint the pilot with the optimum techniques for returning to the lake behind him or flying to an alternate lake ahead of him. Normally the failure of the velocity or altitude instrument would not affect a flight; however, in the event of an attitude presentation failure during the exit phase of an altitude mission, the pilot had to initiate an immediate pushover from about 30 degrees pitch attitude to 18 degrees so that he could visually acquire the horizon. Failures of the ball nose were usually not terminal since the pilot could still fly the mission using normal acceleration, attitudes, and stabilizer-position indications, but the results were not as precise. Radio failure meant the pilot had to be self-sufficient-an undesirable situation, but not a tremendous problem for most test pilots.-113

A simple flight would encompass 15-20 hours of simulator time, and a complex mission could easily double that. Given that each flight was only 8-10 minutes long, this represented a lot of training. By far, these were the most extensive mission simulations attempted during the X-plane program, and would point the way to how the manned space program would proceed. Although the drill at times seemed tedious and time-consuming to all involved, it undoubtedly played a major role in the overall safety and success of what was unquestionably a potentially dangerous undertaking. All of the pilots praised the flight planners and the simulators, and nobody believes the program would have succeeded nearly as well without it. Milt Thompson later observed, "[W]e were able to avoid many pitfalls because of the simulation. It really paid off. I personally do not believe that we could have successfully flown the aircraft without a simulation, particularly in regard to energy management." Simulation and mission planning are some of the enduring legacies of the X-15 program.[14]