- 1. Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns V. High Speed Aerodynamics High Speed Airfoils Critical Mach Number Aerodynamic Heating
- 2. V. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating
- 3. High Speed Aerodynamics As WWII progressed, aircraft flew faster and faster. By mid-war, P51s, Spitfires, and other types were reaching speeds close to that of sound, especially in dives. Pilots began to report control difficulties and unexpected problems which experts determined were due to flying too close to the speed of sound. Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction
- 4. High Speed Aerodynamics In 1940, NACA commissioned the Bell Aircraft Company to build a special research aircraft for the purpose of exploring the speed range near and beyond the speed of sound. It was considered better to do the research using an actual aircraft because the USA had no wind tunnels capable of operating at supersonic speed. Of course, the Germans did. Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction
- 5. High Speed Aerodynamics The research aircraft Bell built was designated the X1. Two operational aircraft were finally built, although they did not fly until the war was over. Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction
- 6. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction
- 7. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction
- 8. High Speed Aerodynamics By the time the war was over, the German research data had been captured and several of the questions the X1 was intended to answer were already known. Nevertheless, the X1 became the first aircraft to exceed the speed of sound in October 1947 when Chuck Yeager flew it to Mach 1.1 . Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction
- 9. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating History and Introduction X1 movie
- 10. High Speed Aerodynamics At subsonic speed (less than Mach 1) air acts as if it’s an incompressible fluid Can change it’s velocity and pressure but not density As long as it can still move, the space between molecules will effectively not change = density remains constant Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Compressibility Effects
- 11. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Compressibility Effects Bernoulli’s Principle: Subsonic: In CONVERGING portion of venturi (Inlet) Air must travel faster to get to other side at same time as bypass air Velocity goes up Pressure goes down
- 12. High Speed Aerodynamics Bernoulli’s Principle: Subsonic: In DIVERGING portion of venturi (Exit) Pressure and Velocity return to original Based on Total Energy being constant throughout Pressure = Potential Energy Velocity = Kinetic Energy Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Compressibility Effects
- 13. High Speed Aerodynamics At supersonic speed (more than Mach 1) air can be compressed and it’s density increased Space between molecules can and is reduced Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Compressibility Effects Link to venturi simulation
- 14. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Compressibility Effects Link to venturi simulation Bernoulli’s Principle: Opposite effects as compared to subsonic Converging: Pressure goes up and Velocity goes down Diverging: Pressure down, Velocity up
- 15. High Speed Aerodynamics Sound is pressure disturbances radiating in all directions from the source Travels @ 661.7 knots (1,116.9 fps, 761.5 mph) under Standard Conditions Speed is directly proportional to temperature (goes down as temp. goes down) Can be calculated (C S = Local Speed of Sound): C S in kts = 29.04 o R C S in fps = 49.022 o R C S in mph = 33.42 o R Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Importance of the Speed of Sound Note: o R = o F + 460
- 16. High Speed Aerodynamics Note that at 36,089 feet the temperature stabilizes at –69.7 and the Speed of Sound also stabilizes at 573.8 kts Also note that above 80,000 feet the temp starts to rise and the Speed of Sound also rises Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Importance of the Speed of Sound
- 17. High Speed Aerodynamics In subsonic flight Sound waves radiate from all points of airframe Can go in all directions as are faster than aircraft Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Importance of the Speed of Sound
- 18. High Speed Aerodynamics In supersonic flight Airplane faster so sound waves “pile up” at nose of airfoil Creates Shock Wave(s) = changes in pressure and velocity of airflow Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Importance of the Speed of Sound Pressure Waves Link (Hide Shockwaves)
- 19. High Speed Aerodynamics Mach # = ratio of True Airspeed of an aircraft to the Speed of Sound at that temperature Subsonic: .75 Mach or less All airflow over aircraft is < Mach 1 Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Realms of Flight
- 20. High Speed Aerodynamics Transonic: .75 to 1.2 Mach Mixture of sonic airflow speeds Some < Mach 1, some >= Mach 1 Aerodynamic center of lift moves to about 50% of chord Shock waves form and move around = large changes in trim & stability (control buffeting) Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Realms of Flight
- 21. High Speed Aerodynamics Supersonic: 1.2 to 5.0 Mach All airflow is > Mach 1 Smooth & efficient flight Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Realms of Flight
- 22. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Realms of Flight Hypersonic: > 5.0 Mach
- 23. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Realms of Flight Hypersonic: > 5.0 Mach Leads to Aerodynamic Heating & other flight problems
- 24. High Speed Aerodynamics Shock waves form when the aircraft (or parts of it) are exceeding Mach 1 in speed Sound waves slower than aircraft speed Air “piles up” in Compression Wave = large changes in pressure, velocity, and density of airflow Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves)
- 25. High Speed Aerodynamics Shock waves form when the aircraft (or parts of it) are exceeding Mach 1 in speed Sound waves slower than aircraft speed Air “piles up” in Compression Wave = large changes in pressure, velocity, and density of airflow Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves)
- 26. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) F18 flyby movie F14 flyby movie
- 27. High Speed Aerodynamics 3 kinds of Shock Waves: Oblique Normal Expansion Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) Pressure Waves Link Show Shockwaves
- 28. High Speed Aerodynamics Oblique Shock Waves Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) Forms on sharp edges with surface changing into the direction of the airflow commonly on Leading and Trailing Edges of airfoil Shock wave forms Oblique Angle with surface and “points” downstream in airflow Angle gets less as speed goes up “ flattens out”
- 29. High Speed Aerodynamics Oblique Shock Waves Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) @ wave: Flow direction is deflected along surface Velocity decreases but STAYS ABOVE MACH 1 Pressure increases Temperature increases Density increases Total energy goes down Energy loss comes from loss of temperature (Heat of Compression) to atmosphere
- 30. High Speed Aerodynamics Normal Shock Waves Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) Forms in front of or on blunt object or one with large included angle
- 31. High Speed Aerodynamics Normal Shock Waves Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) In front: Molecules pile up and create wave detached and in front of the object = “Bow Wave”
- 32. High Speed Aerodynamics Normal Shock Waves Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) On: Attaches to curved portion where airflow speed is just above Mach 1 In Transonic range = form on upper airfoil surface first (at about .75 Mach) then lower surface (at about .85 Mach) NOTE: the indicated Mach numbers vary depending on the airfoil
- 33. High Speed Aerodynamics Normal Shock Waves Supersonic Flow Patterns (Shock Waves) @ wave: Flow direction doesn’t change Velocity decreases TO BELOW MACH 1 Subsonic speed inversely proportional to Mach # entering wave (higher C S going in = lower subsonic speed coming out) Large Pressure, Density, and Temperature increase Large Total Energy decrease (from temp. radiation into air)
- 34. High Speed Aerodynamics Expansion Shock Waves Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Supersonic Flow Patterns (Shock Waves) Form where surface turns away from airflow direction Middle of airfoil Velocity increases Pressure and Density both decrease Temperature remains relatively constant = little or no Total Energy change (is not a compression wave)
- 35. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Below about .75 Mach = all flow is subsonic
- 36. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: At some airspeed ( = Critical Mach Number or M CR ) some airflow will reach or exceed Mach 1
- 37. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: Normal shock wave forms on upper surface where max airfoil thickness is ( = greatest velocity) Causes large increase in drag
- 38. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: Pressure rise through shock wave reduces strength of low pressure area on wing Low pressure usually “sucks” air against airfoil for smooth flow Loss of low pressure = air isn’t sucked down smoothly and SHOCK INDUCED SEPARATION occurs on upper surface = loss of lift and reduced control effectiveness from turbulence
- 39. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: As speed increases closer to Mach 1: Normal wave forms on lower surface and upper wave moves further back towards trailing edge = shock induced separation on bottom, too
- 40. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: At Mach 1: Top and bottom normal waves have moved to trailing edge and form oblique waves there Entire surfaces have supersonic flow = smooth flow Leading edge now has normal wave forming in front of it Known as BOW WAVE Like wave at bow of boat
- 41. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: At Mach 1: Area behind bow wave is relatively slow and called STAGNATION AREA Large energy loss through normal wave creates significant drag Shockwave Link Normal and Oblique Shockwaves
- 42. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number In Transonic speed range: Above Mach 1: Stagnation area gets smaller but energy loss increases Greater change in velocity and pressure through normal wave = greater drag (proportional to speed)
- 43. High Speed Aerodynamics Subsonic Airfoils High Speed Airfoils and Critical Mach Number To increase Critical Mach Number (or delay Shock Induced Separation occurrence): Can use Vortex Generators or Swept Wings
- 44. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Vortex Generators Small, low Aspect Ratio airfoils mounted in pairs at 90 o on wing surfaces Produces strong vortex around end = pulls air back onto wing surface = delays airflow separation Pair mounting = pairs work together for greater effectiveness
- 45. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Swept Wings Swept wings change the THICKNESS RATIO of the wing (also known as Fineness Ratio) Ratio of max. thickness of airfoil to chord Lower Thickness Ratio = thinner wing = less velocity change across wing = higher M CR
- 46. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Swept Wings Unfortunately, this also causes more flow of air in a spanwise direction = stronger wingtip vortices = increased drag overall Also, aft swept wings generally cause the tip to stall first (= potentially loose aileron control)
- 47. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Swept Wings Forward swept wings (I.e. Grumman X-29) have same M CR advantages as aft swept + roots stall first = can do more extreme high angle of attack maneuvers without losing control But needs computer to control as is inherently very unstable
- 48. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Swept Wings Also, at higher speeds the wing will twist due to aerodynamic loading and will tend to wash in Increase angle of incidence = increased lift and drag = increased loads to failure Composite materials make wings light and stiff enough to withstand these forces
- 49. High Speed Aerodynamics Subsonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Movable Hor. Stab. Horizontal Stablizer will also tend to loose effectiveness at Critical Mach Number Can keep it effective by making it’s Angle of Incidence adjustable F86 used this to allow supersonic speeds while maintaining control Was first one to do so
- 50. High Speed Aerodynamics Supersonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number To eliminate Shock Induced Separation in Transonic range = airfoils with max. thickness @ 50% of chord Double Wedge or Biconvex
- 51. High Speed Aerodynamics Supersonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Thin airfoil = no normal shock forms Sharp edges form obliques with tiny bow wave and expansion wave in middle
- 52. High Speed Aerodynamics Supersonic Airfoils Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number All lead to practically zero subsonic airflow (= zero turbulence and drag from energy change) Problem: not good subsonic characteristics
- 53. High Speed Aerodynamics Supersonic Aircraft Configuration Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Wing Planform Low Aspect Ratio & tapered Good strength and weight Sweptback For transonic and low supersonic Straight For high supersonic (Mach 2 +)
- 54. High Speed Aerodynamics Supersonic Aircraft Configuration Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Airfoil Low Thickness (Fineness) Ratio Gradual change in thickness (airfoil shape) Max. thickness @ 50% of chord Sharp leading and trailing edges
- 55. High Speed Aerodynamics Supersonic Aircraft Configuration Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Fuselage & Nacelles Long Slender Fuselage “Wasp Waisted” Decreases overall Form and Interference Drags from interaction of shock waves on various structure areas
- 56. High Speed Aerodynamics Supersonic Aircraft Configuration Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating High Speed Airfoils and Critical Mach Number Tail Surfaces Planform and airfoil similar to wings Generally all movable horizontal surfaces Powered irreversible systems
- 57. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Aerodynamic Heating As speeds increase above Mach 1, the Stagnation Area sees great temperature rises Faster = greater temp rise Less affect at higher altitudes
- 58. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Aerodynamic Heating Increased temps = decreased metal strengths As we near Hypersonic speeds the temps are so high that normal materials will melt Research today is in this area with ceramics and composite materials
- 59. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Future? Lockheed is working on this design slated to fly by 2010 Supposed to disperse the shock waves to allow supersonic flight over populated areas
- 60. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Future? Also, right now “Quiet Spike”
- 61. High Speed Aerodynamics Compressibility Effects Importance of the Speed of Sound Realms of Flight Supersonic Flow Patterns High Speed Airfoils Critical Mach Number Aerodynamic Heating Future? Flew at Mach 9.6 Last year X43 Overview X43 flights