Component-Level Weight Analysis for RBCC Engines

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Olds, John R.
McCormick, David Jeremy
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Rocket-based combined-cycle engines (RBCC) engines have recently received increased attention for use on advanced, reusable space launch vehicles. By combining convention rocket and airbreathing operating modes into an integrated unit, they have given designers a middle ground between the high-thrust, low-I<subscript>sp characteristics for a pure rocket and the low-thrust, high-I<subscript>sp of pure airbreathers. Engine weight (or thrust-to-weight ratio) is a highly sensitive parameter in the design of advanced reusable launch vehicles. While substantial experience exists with ground-test engines from the 1960’s, little parametric data exists to help conceptual designers predict weight for today’s advanced technology, flight-weight RBCC engines. This paper reports a new set of component-level paramedic weight estimating equations for advanced rocket-based combined-cycle (RBCC) engines. These equations are derived from top-down regression analysis of historical data and include variables to account for advanced technologies and materials. Component weight equations are given as functions of engine geometry, internal pressure, flight modes, etc. Taken together, the equations are used to build up an overall RBCC weight estimation model - WATES. This spreadsheet-based model is not intended to replace a more detailed weight analysis, but rather to assist conceptual vehicle designers in assessing the relative advantages of various engine concepts. Sample RBCC engine weight predictions are given.
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