Crew escape systems are an integral feature in combat aircraft. Two main concerns with such systems are their aerodynamic stability, and the potential injury level to which their occupants are exposed.

CFDRC, sponsored by the US Navy and the SBIR program, has been on the forefront of developing CFD technology for escape system aerodynamic analysis, design support and injury reduction. CFDRC engineers have worked very closely with the U.S Navy and major ejection seat manufacturers on developing and applying CFD technology to support major escape system programs including ejection seat upgrades, mishap investigations and design of new systems. Areas of applications include ejection seat and canopy trajectory simulation, windblast protection, stabilization devices, head and neck injury assessment, helmet mounted Display (HMD) and goggles, inflatable restraint systems and rocket plume interference. The developed numerical technologies and related capabilities have been incorporated into the CFD-FASTRAN code.

Our engineers have performed analysis and design support on all major NATO ejection seats in service including the NACES, ACES-II, SIIIS, Martin Baker MK16 seat and their variants.

NASA's vision for Space Exploration will enable humans to pioneer the solar system but before humans can move through the cosmos they must leave Earth safely and return in-tact. The loss of the Space Shuttle Columbia has strengthened NASA's focus on crew protection, abort and overall health and protection. A significant driver in spacecraft design must include an understanding of physiological effects of acceleration loads, stability and control induced loads, and blast induced loads translated through a spacecraft to the crew compartment.

CFDRC has been involved in collaboration with NASA and private industry on the adaptation and application of well-proven aircraft crew escape system simulation technologies for launch vehicle applications. The application of this simulation technology will reduce the complexity and weight that would otherwise be added to compensate for uncertainties in crew abort scenarios. The proper response of the crew abort or escape system (CES) to a launcher failure is critical to the success of any crew exploration vehicle architecture. This simulation technology will make significant contributions in this little-understood area.

The simulations on the left are examples of demonstration simulations that were conducted by CFDRC engineers for NASA and industry partners.

The US Air Force and U.S. Navy, as well as commercial ejection seat manufacturers, are constantly investigating new concepts and devices to stabilize ejection seats and their occupants in high-speed flows. CFDRC engineers have performed computational analyses on a variety of aerodynamic stabilization devices including deployable fins and extendable booms.

CFD plays an integral role in early trade studies and in down selection of potential designs. The data generated from CFD computations includes aerodynamic forces and moments for evaluating the stability and controllability of the seat with and without the stabilization device, and surface pressures for assessing the windblast loads and potential occupant injuries. Additionally, the near-field flow-field solution data can be used to determine the effects that stabilization devices would have on the sensors that are installed in the seat, such as the Pitot tubes.

CFDRC engineers have provided analysis and design support to several programs including the Navy NACES Pre-Planned Product Improvement (P3I) program, The Joint Escape System Program (JESP) and the Navy Stability Improvement Program (SIP).

During egress from an aircraft, the occupant of an ejection seat is exposed to severe windblast effects from the oncoming flow. The US Department of Defense, as well as manufacturers of ejection seats, have been continuously working on developing better ways of shielding the occupants from these effects.

CFDRC engineers have provided analysis and design support during the development and optimization of new windblast protection concepts. CFDRC engineers have investigated ways of stagnating the flow over the helmet region through the use of brim designs. Methods of protecting the occupant's torso have also been investigated. These methods include the use of flow deflectors, and raising of the legs of the occupant towards the torso. The data generated by CFD computations includes aerodynamic forces and moments for use in analyzing the stability of the ejection seat, and surface pressure data for use in determining the head and neck loads, and flow-field information required to determine the readings of on-board sensors.

The presence of a helmet-mounted display (HMD) and night vision goggles adds another level of complexity to the crew escape sequence. Before such devices can be safely used , any harmful side effects they may have must be determined.

CFDRC engineers have used CFD-FASTRAN to analyze the effects of the attachment of various devices to helmet-head configurations. The computations enabled the prediction of the additional loads experienced by the occupant, prediction of the overall effect on the aerodynamic characteristics of the seat, and prediction of the near-field interference effects on the seat control sensors.

Understanding the aerodynamic characteristics and loads on a canopy and an ejection seat during their separation and emergence from an aircraft is necessary to determine the potential for occupant contact with the aircraft canopy. Because of the high costs of escape system evaluation using ground or flight-testing facilities, it has become increasingly cost effective to use computational methods to simulate the actual event. Using CFD-FASTRAN, CFDRC engineers have performed various canopy separation analyses. These analyses combined the CFD flow-solution module with an aerodynamically-coupled rigid-body motion model to yield accurate trajectory predictions.

CFD-FASTRAN capabilities include motion constraints that represent the slides and hinges that control the motion of the canopy during the initial phases of separation, and ockets that are used to force the canopy away from the body of the aircraft. The figure and animation on the right shows the results from an analysis for an F/A-18 rocket-jettisoned canopy. The figure shows the close agreement between the computational results predicted with CFD-FASTRAN and the corresponding hardware test data.

CFDRC engineers have considerable experience in developing and applying CFD technology for analysis and support of a wide range of crew escape systems applications. These include stabilization devices, windblast protection, head and neck injuries, inflatable restraints, rocket plume interference and jettisoned canopy and ejection seat trajectory predictions.

As an ejection seat and its occupant exit an aircraft, the configuration enters a highly complex and transient flow field. Understanding the emergence effects encountered during the initial stages of the ejection sequence requires high fidelity analysis. CFDRC engineers have developed and successfully applied computational simulation tools to model the complex phenomena associated with emergence and full sequence ejection events.

The figure and animation on the right show results from simulations performed by CFDRC engineers using CFD-FASTRAN for an SIIIS seat emerging from an AV-8B aircraft. The simulations utilized the code's overset chimera algorithm and its rigid-body dynamics model. The simulations also utilized the features in CFD-FASTRAN that allow the user to specify motion constraints, and time- and distance-dependent point forces. The data generated included aerodynamic forces and moments for stability and control analysis, surface pressures for determining head and neck loads, and kinematics and dynamics data for trajectory analysis. The head loads predicted in these simulations compared well with the corresponding sled test data.

CFDRC engineers have considerable experience in developing and applying CFD technology for analysis and support of a wide range of crew escape systems applications including stabilization devices, windblast protection, head and neck injuries, inflatable restraints, rocket plume interference, and jettisoned canopy and ejection seat trajectory predictions.

Rocket propulsion systems are an essential part of ejection-seat escape systems. The thrust applied by the rockets propels the seat out of the aircraft, and stabilizes the seat during and after the ejection sequence. CFDRC engineers have provided analysis and support to several programs involving controllable propulsion systems. Some of the problems considered required analysis of the influence of the rocket plumes on the aerodynamic behavior of the seat. CFDRC engineers support efforts by the U.S. Navy, Aerojet and the Boeing Company to develop a controllable propulsion system for the Fourth Generation Ejection Seat program.