Magnetorheological (MR) Recoil Damper for the Apache Helicopter Chain Gun

Sponsored by: Army Research Laboratory, Aberdeen Proving Ground, Maryland Industrial Partnerships (MIPS)
Research Team: AITHER, University of Maryland, The Boeing Company (later Alliant Tech Systems), Techno-Sciences Inc.

Medium caliber guns are used on a variety of weapon systems including aircraft (airplanes and helicopters), infantry vehicles (such as the Bradley Fighting Vehicle), and anti-aircraft weapons. Typical of these and larger weapons are high recoil forces that are usually dissipated by large passive fluid dampers. After the gun has recoiled, it is then returned to battery by mechanical springs in time for the next round to be fired. However, passive recoil systems require a trade-off between the amounts of energy dissipated by the recoil dampers, the loads developed on the weapon structure, the available recoil stroke, and the size and weight of the recoil dampers. This is of particular concern for turreted airborne systems, which must compromise between durability and strength of the turret versus added weight. One potential improvement is the use of MR fluid-based dampers to provide a semi-active recoil control system that can be optimized for performance, allowing for a smaller and lighter turret.

During a U.S. Army Phase I SBIR program, AITHER demonstrated the potential for reducing medium caliber gun recoil forces with MR technology. This successful effort led to a Phase II SBIR starting in January 2001. The main goal of the Phase II program was to design, prototype, and test an MR recoil damper for the 30-mm M230 chain gun that is mounted on the nose of the Army’s AH-64 Apache helicopter. To accomplish this goal, AITHER and our team undertook four main tasks: design of a high-speed stroke, high-displacement MR damper, fabrication and testing of the prototype damper, numerical simulations and modeling to facilitate control system design, and full-scale testing on a turreted M230 chain gun.

Before design and prototyping could begin, accurate characterization of the M230’s performance on the Apache turret was necessary. Instrumented firing tests were performed at The Boeing Company’s Ordnance Division (not ATK) test range in Mesa, Arizona. With performance data in hand to guide the design, prototype MR recoil adapters were designed and built. Initial performance of the prototypes was validated on a custom-built pneumatic high-force, high-displacement impulse generator. After impulse generator testing, open and closed loop tests were performed on a fixed M230 to evaluate the prototype’s performance and survivability.

Mathematica and MATLAB’s Simulink modeling environment were used to generate a multi-degree of freedom structural model that accurately simulated the dynamics of the M230 turret as measured during the preliminary testing. With this model, multiple control system designs were developed and tested. dSPACE control system development hardware and MATLAB’s Realtime Workshop were used to host the control system designs. Final evaluations were performed on the M230 with a pair of the prototype MR recoil adapters. These tests proved the feasibility of designing an MR recoil adapter for a medium caliber gun. Significant changes in the recoil cycle were demonstrated between the passive recoil dampers and semi-actively controlled MR fluid dampers.

These efforts have resulted in U.S. Patent #6,694,856, entitled “Magnetorheological Damper and Energy Dissipation Method.”

For more detailed information, please see the following link.