16885J/ESD35J-oct1,2002 Optimized l/d- Transport A/C Sweet spot' is in transonic range osses due to shock D Concorde waves Mach no Ref Shevell
16.885J/ESD.35J - Oct 1, 2002 Optimized L/D - Transport A/C “Sweet spot” is in transonic range. Losses due to shock waves Ref: Shevell Max (L/D) Mach No. 1 2 3 10 20 Concorde
16885J/ESD35J-ct1,2002 Transonic effects on airfoil c. c 1.0 M<1 M<M M<1 I Mcr<M<Mo M<1 divergence
16.885J/ESD.35J - Oct 1, 2002 Transonic Effects on Airfoil Cd, Cl Cd M cr Mdrag divergence M 81.0 M < M8cr V 8 V 8 Region I. II. III. I. II. III. M > Mdrag divergence 8 Mcr < M < Mdrag divergence 8 M<1 M<1 M>1 M>1 M<1 Separated flow
16885J/ESD35J-0ct1,2002 Strategies for mitigating transonic effects Wing sweep Developed by Germans Discovered after Wwll 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 upercritical airo Developed by dick Whitcomb at NASA Langley in 1965 Percey at rae had some early contributions Incorporated in modern military and commercial aircraft
16.885J/ESD.35J - Oct 1, 2002 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
16885J/ESD35J-ct1,2002 Basic sweep concept Consider Mach Number normal to leading edge sinμ=1/M M=M.cosA u=Mach angle the direction disturbances travel in supersonic flow For subsonic freestream M.<M.- Lower effective"freestream Mach number delays onset of transonic drag rise For supersonic freestream M<l,A>H- Subsonic leading edge M>1,A<H- Supersonic leading edge Extensive analysis available but this is gist of the concept
16.885J/ESD.35J - Oct 1, 2002 Basic Sweep Concept • Consider Mach Number normal to leading edge • For subsonic freestreams, Mn < Mf - Lower effective “freestream” Mach number delays onset of transonic drag rise. • For supersonic freestreams – Mn < 1, / > P - Subsonic leading edge – Mn > 1, / < P - Supersonic leading edge • Extensive analysis available, but this is gist of the concept sin P=1/ Mf P = Mach angle, the direction disturbances travel in supersonic flow Mf Mn=Mfcos/ P /
16885J/ESD35J-oct1,2002 Wing Sweep Considerations Moo>1 Subsonic leading edge Can have rounded subsonic type wing section Thicker section pper surface suction More lift and less drag Supersonic leading edge Need supersonic type wing section Thin section Sharp leading edge
16.885J/ESD.35J - Oct 1, 2002 Wing Sweep Considerations Mf > 1 • Subsonic leading edge – Can have rounded subsonic type wing section • Thicker section • Upper surface suction • More lift and less drag • Supersonic leading edge – Need supersonic type wing section • Thin section • Sharp leading edge