Iron Cross Reaction Control Flight Simulator - test in hangar

In the mid-1950s -- after the X-1 had exceeded the speed of sound, the D-558-II had doubled that speed, and the X-2 had flown to a speed of Mach 3.2 (3.2 times the speed of sound) -- the problem of maintaining control of a vehicle at the low dynamic pressures found at high altitudes became real. As the development of larger rocket engines than those used in the X-1, X-2, and D-558-II became a virtual certainty, travel to near-orbital and orbital velocities lay on the horizon. It became natural to investigate alternative means to control an aircraft for low dynamic pressures where aerodynamic controls would be inadequate (even absent for orbital flight outside the atmosphere).

Consequently, the High-Speed Flight Station (HSFS--predecessor of the NASA Dryden Flight Research Center) began pioneering work on simulating and then flying with reaction controls in the last years of the National Advisory Committee for Aeronautics (NACA) and the first years of its successor, the National Aeronautics and Space Administration (NASA). The HSFS began a two-phase study. One phase involved a fixed-base effort with an analog computer to solve the equations of motion needed for simulation; the other used a mechanical simulator in which the "pilot" actually experienced the motions produced by the reaction-control jets.

The "pilot" operated the simulator through a single control stick that -- unusually for the time - controlled three axes with one device. The stick controlled pitch by fore and aft movements, roll by lateral movements, and yaw through thumb movements. The simulator, shown in the video clip, was known as the "Iron Cross." It simulated the X-1B, which was equipped with reaction controls. Although the X-1B flew three missions with reaction controls, it developed fatigue cracks in a propellant tank and had to be retired from flight status. Subsequently, an F-104 equipped with reaction controls flew at relatively low dynamic pressures. Between the simulation studies with both analog computer and the mechanical Iron Cross simulator, on the one hand, and the flights with the F-104, on the other, engineers obtained design guidelines that could be applied to the X-15 research aircraft, which routinely depended on jet reaction controls in its flights to the edge of space. In turn, what was learned from the F-104 and the X-15 experiences with reaction controls was applied to space vehicles in the Mercury, Gemini, Apollo, and Space Shuttle programs.

The 25-second film clip begins with a closeup of the reaction jets in operation, followed by a wide shot of the Iron Cross in full swing with the pilot barely visible on the viewer's right side of the Iron Cross.

   Last Modified: December 9, 2001
   Responsible NASA Official: Marty Curry
   Curator: PAO Webmasters

   NASA Website Privacy Statement