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Iron Cross Attitude Simulator

The Iron Cross was a pioneering ground-based simulator for testing early reaction controls. It is primarily orbital, suborbital and hypersonic vehicles that require reaction control capability, but it was recognized in the mid-to-late 1950s that the earliest flight evaluation of reaction controls would occur with supersonic research aircraft. It was also believed that the flight research should be preceded by ground-based simulation studies.

DFRC Photo # Photo Date Image Description
  Skip links in main table Iron Cross Attitude Simulator Photo Collection Contact Sheet
E-2633 October 12, 1956 Three axis control stick used on Iron Cross Attitude Simulator
E-2578 September 27, 1956 Iron Cross Attitude Simulator with pilot Stan Butchart
E56-2607 October 8, 1956 Closeup of research pilot Neil Armstrong operating the Iron Cross Attitude Simulator reaction controls simulating the X-15 flight at high altitudes

Additional Information

The pioneering jet reaction (reaction control) simulation work at NACA High-Speed Flight Station, spanned the last years of the NACA organization and first NASA years (mid-to-late 1950s.) A two-phase study was begun; one was a fixed-base setup with an analog computer to solve the equations of motion and the other used a three-degree-of freedom mechanical simulator wherein the pilot experienced motions.

The analog computer simulator represented the airplane in five-degrees-of-freedom with control provided from the pilot's short control stick. The stick was unconventional for its time because it was necessary for the pilot to control about three axes through one control device. The stick pivoted fore, aft, and laterally for pitch and roll control, and lateral thumb movement provided yaw control. For most of the study, the pilot presentation consisted of an oscilloscope trace for pitch and bank angle, and a simple volt meter for angle of sideslip.

The Bell X-1B airplane offered an ideal testbed in 1957 for a trial reaction control installation. In preparation, NACA High-Speed Flight Station technicians built an iron-frame simulator, dubbed the "Iron Cross," which matched the dimensions and inertial characteristics of the X-1B, installing small reaction control thrusters on it and then mounting it on a universal joint so that a test pilot could maneuver it in pitch, roll, and yaw. The universal joint from a truck permitted motion about the three axes. High-pressure nitrogen gas was expanded selectively through the six jet nozzles to provide the reaction forces. Flight-type recorders were used to record control stick position and the various angular rates.

NACA's test pilots "flew" this mechanical ground-based simulator extensively.

Iron Cross movie collection

Last Modified: July 16, 1999
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