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Helicopter Design Methodology by Andrew T. Bellocchio


Book Details

The transformation of Joint forces to be lighter, more lethal, and capable of deploying from multiple dispersed locations free of prepared landing zones will widen acapability gap that cannot be met by the current fleet of Joint aircraft. In order to close this capability gap, a dedicated heavy lift VTOL aircraft must rapidly deliver large payloads, such as the 20 to 26 ton Future Combat System, at extended ranges in demanding terrain and environmental conditions.

Current estimates for a single main rotor configuration place the design weight over 130,000 pounds with an installed power of approximately 30,000 horsepower. Helicopter drive systems capable of delivering torque of this magnitude succeeded in the Russian Mi-26 helicopter’s split-torque design and the Boeing VERTOL Heavy Lift Helicopter (HLH) prototype’s traditional multi-stage planetary design. The square-cube law and historical trends show that the transmission stage weight varies approximately as the two-thirds power of torque; hence, as the size and weight of the vehicle grows, the transmission’s weight becomes an ever-increasing portion of total gross weight. At this scale, optimal gearbox configuration and component design holds great potential to save significant weight and reduce the required installed power.

The presented drive system design methodology creates a set of integrated tools to estimate system weight and rapidly model the preliminary design of drives system components. Tools are provided for gearbox weight estimation and efficiency, gearing, shafting, and lubrication and cooling. Within the same architecture, the designer may add xxiii similar tools to model subcomponents such as support bearings, gearbox housing, freewheeling units, and rotor brakes.

Measuring the relationships between key design variables of these components and system performance metrics reveals insight into the performance and behavior of a heavy lift drive system. A parametric study of select design variables is accomplished through an intelligent Design of Experiments that utilizes Response Surface Methodology to build a multivariate regression model. The model permits visualization of the design space and assists in optimization of the drive system preliminary design.

This methodology is applied to both the Boeing HLH and the Russian Mi-26. Both designed in the late 1970’s, the tandem rotor HLH fails to take full advantage of the tremendous benefits gained by dividing the input torque into multiple, high speeds paths and then recombining the split paths at the final stage. The Mi-26 has successfully employed a split torque gearbox in the field for over 20 years. This study applies the drive system design methodology to compare the split-torque gearbox over a multi-stage planetary gearbox in a single main rotor heavy lift helicopter.




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