Project Team: SPENCER BOICE, JONATHAN DEN HARTOG, and SCOTT WISNIEWSKI
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HBEDS HBEDS HELICOPTER BLADE EMERGENCY DETACHMENT SYSTEM Project Team: SPENCER BOICE, JONATHAN DEN HARTOG, AND SCOTT WISNIEWSKI PROJECT SPONSOR: GENERAL DYNAMICS ARMAMENT AND TECHNICAL PRODUCTS, BURLINGTON, VT ENGS290 FINALPatent REPORT Pending MA RCH 2004 0 ©2004 HBEDS EXECUTIVE SUMMARY Despite development efforts conducted by foreign and domestic research agencies, emergency egress systems have not been widely implemented in military helicopters. Proposed egress systems for the UH-1 Huey, AH-1 Super Cobra, and CH-46 Chinook were scrapped in favor of designing more crashworthy fuselages and cockpits that protected occupants upon impact. While the political and economic consequences of military casualties remain, helicopter and aerospace explosives technology have changed considerably since these studies were performed. In consideration of this, the project team has performed a feasibility study and designed a proof of principle prototype for a Helicopter Blade Emergency Detachment System (HBEDS) for military helicopters. The blade detachment system is intended to afford helicopter pilots the ability to quickly remove the main rotor blades in a life-threatening emergency. In- flight activation of the system would provide clearance for pilot ejection or the release of a ballistic helicopter parachute. Alternatively, the system could also increase crew survivability as a standalone feature during hard landing and ditching into water. The team has carried out the project under the guidance and support from the Thayer School of Engineering and General Dynamics Armament and Technical Products, the project sponsor. Risk assessment and project specifications served as the foundation of the feasibility study and subsequent development of the prototype. To begin, numerous risks associated with implementation of the proposed system were identified and organized according to relative significance. Project specifications drawing from these risks were then defined to guide the design and development of the prototype system. A validation test for each specification was also identified to evaluate performance and feasibility. Though the majority of the specifications were evaluated through testing and analysis, the HBEDS team cited military standards as validation tests for explosive stability and durability. Although testing could not be performed by the team, these specifications could be provided to suppliers of aerospace-grade explosives in future development of the system. The HBEDS team identified a representative helicopter platform on which to develop the prototype system. The Eurocopter EC-135 is a helicopter that exhibits modern technology with potential applications in future generations of military helicopters. Its four-blade bearingless rotor system also distinguishes it from aircraft platforms used in previous blade detachment studies, providing unique opportunities for explosive packaging and system integration. Further, ENGS290 FINAL REPORT MARCH 2004 i1 HBEDS access to an EC-135 was conveniently provided by the Dartmouth Hitchcock Advanced Response Team, an emergency service team well versed in the operation and maintenance of the aircraft. The design process involved a series of trade studies regarding the concept, layout, and integration of the system. Decision matrices were used to determine the method and location of blade detachment, the classification of explosive to be used for severance, the signal method and design of the ignition train, and the location of a signal transfer system to link the fuselage to the rotor system. The project specifications provided a framework for assessing the potential for each alternative within the context of the project objectives. On the whole, decisions were largely influenced by the stability of each alternative and its effect on the system’s resistance to inadvertent activation. Specification testing and analysis demonstrated potential for the system to meet the project objectives. Though the prototype failed to meet the cost and weight specification, the system met the requirements imposed by more critical specifications such as stability, clearance time, reliability, and safety. The HBEDS team believes each specification could be met through continued development and refinement of the proposed concept. In conclusion, the team identified a number of recommendations for future HBEDS development. Regarding development of the system itself, the team suggests that full scale tests be conducted to observe the blade exit path and evaluate the reliability and predictability of the explosive severance system. Explosive stability must also be verified by subjecting the system to electrostatic discharge, fire, heat, ballistic shock, and other stresses according to military standards referenced within the project specifications. Finally, risks assessment and dynamics analyses highlighted the need for parallel systems to ensure safe, predictable operation of the system. In addition to an ejection or ballistic parachute system, the team recommends that post- detachment blade containment and tail rotor thrust termination systems be developed to minimize danger to occupants and bystanders following activation. The team would like to thank Jerry Brown, Jon Piazza, Jean Davis, Dean Peterson, and General Dyanamics for their guidance throughout the project. Thanks also go to Dartmouth- Hitchcock Advanced Response Team (DHART) for allowing access to their EC-135 and providing valuable insight concerning its design and operation. We greatly appreciated the assistance from Ensign-Bickford Aerospace and Defense Company and McCormick Selph, Inc. ENGS290 FINAL REPORT MARCH 2004 ii2 HBEDS as we conducted controlled explosives research and from American Eurocopter Corp. as we investigated the specific layout of a helicopter engine transmission. Kevin Baron, Mike Ibey, Leonard Parker, and Pete Fontaine deserve thanks for their excellent support in the Machine Shop. Finally, the project would not have been possible with the support and assistance of the Thayer School Faculty, especially John Collier, Francis Kennedy, and Laura Ray. ENGS290 FINAL REPORT MARCH 2004 3iii HBEDS TABLE OF CONTENTS 1.0 Introduction ...................................................................................................................................................1 2.0 Activation Envelope ......................................................................................................................................3 2.1 Envelope Event Analysis...............................................................................................................................6 3.0 State of the Art...............................................................................................................................................7 3.1 Application Selection...................................................................................................................................10 4.0 Risk Mitigation ............................................................................................................................................12 5.0 Specifications ...............................................................................................................................................15 6.0 Trade Studies...............................................................................................................................................18 6.1 Blade Detachment Method .........................................................................................................................20 6.2 Detachment Location ..................................................................................................................................21 6.3 Explosives Trade Study...............................................................................................................................22 6.4 Signal Transfer Method..............................................................................................................................23 6.5 Ignition Train Trade Study ........................................................................................................................24 6.6 Transfer System Location...........................................................................................................................26 7.0 Design and Development Overview ...........................................................................................................26 7.1 Internal Transfer System Design ...............................................................................................................29 7.2 Transfer System Housing Design...............................................................................................................34 8.0 Concept Prototype Testing .........................................................................................................................37 9.0 Specification Validation..............................................................................................................................39 10.0 Post-Detachment Analysis ..........................................................................................................................46 11.0 Economic and Political Analysis of HBEDS..............................................................................................50 11.1 Economic Effects of Helicopter Accidents.................................................................................................50