aircraft_murman

aircraft_murman - 16.885J/ESD.35J Aircraft Systems...

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16.885J/ESD.35J Aircraft Systems Engineering Introduction to Aircraft Performance and Static Stability Prof. Earll Murman September 18, 200 3
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Today’s Topics Specific fuel consumption and Breguet range equation Transonic aerodynamic considerations Aircraft Performance Aircraft turning Energy analysis Operating envelope – Deep dive of other performance topics for jet transport aircraft in Lectures 6 and 7 Aircraft longitudinal static stability
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Thrust Specific Fuel Consumption (TSFC) Definition: TSFC lb of fuel burned (lb of thrust delivered)(hour) Measure of jet engine effectiveness at converting fuel to useable thrust Includes installation effects such as bleed air for cabin, electric generator, etc. . Inlet effects can be included (organizational dependent) Typical numbers are in range of 0.3 to 0.9. Can be up to 1.5 Terminology varies with time units used, and it is not all consistent. TSFC uses hours “c” is often used for TSFC lb of fuel burned Another term used is c t (lb of thrust delivered)(sec)
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Breguet Range Equation • Change in aircraft weight = fuel burned dW ± c t Tdt c t TSPC /3600 T thrust • Solve for dt and multiply by V f to get ds ds V f dt ± V f dW ± V f W dW ± V f L dW c t T c t T W c t D W • Set L/D, c t , V f constant and integrate R 3600 L ln W TO TSFC V f D W empty
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Insights from Breguet Range Equation R 3600 L ln W TO TSFC V f D W empty 3600 TSFC represents propulsion effects. Lower TSFC is better L V f D represents aerodynamic effect. L/D is aerodynamic efficiency L L L V f D a f M f D . a f is constant above 36,000 ft. M f D important ln W TO represents aircraft weight/structures effect on range W empty
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Optimized L/D - Transport A/C “Sweet spot” is in transonic range. 20 waves 1 2 3 Max (L/D) Mach No. Concorde Losses due to 10 shock Ref: Shevell
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8 Transonic Effects on Airfoil C d , C l C d Region I. II. III. M cr M drag divergence 1.0 M M<1 M<1 M>1 M<1 M>1 Separated flow M < M I. 8 cr V M < M < M drag II. cr divergence III. M > M V drag divergence
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Strategies for Mitigating Transonic Effects • Wing sweep – Developed by Germans. Discovered after WWII by Boeing – Incorporated in B-52 • Area Ruling, aka “coke bottling” – Developed by Dick Whitcomb at NASA Langley in 1954 • Kucheman in Germany and Hayes at North American contributors – Incorporated in F-102 • Supercritical airfoils – Developed by Dick Whitcomb at NASA Langley in 1965 • Percey at RAE had some early contributions – Incorporated in modern military and commercial aircraft
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Basic Sweep Concept Consider Mach Number normal to leading edge sin P =1/ M f M f M n P / =M f cos / P = Mach angle, the direction disturbances travel in supersonic flow For subsonic freestreams, M n < M f - Lower effective “freestream” Mach number delays onset of transonic drag rise.
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This note was uploaded on 11/08/2011 for the course AERO 16.851 taught by Professor Ldavidmiller during the Fall '03 term at MIT.

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aircraft_murman - 16.885J/ESD.35J Aircraft Systems...

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