AE-705: Introduction to Flight Pressure & Airspeed Measurement - PowerPoint PPT Presentation

AE-705: Introduction to Flight Pressure & Airspeed Measurement Part-II Siddharth Joshi Mechanical Engg. Department VIT Vellore AE-705 Introduction to Flight Lecture-06 Capsule-03

Outline  Altitude & ROC/ROD Measurement  Errors in Pneumatic Measurements  Measurements in Compressible Flows  Non-Pneumatic Measurements AE-705 Introduction to Flight Lecture-06 Capsule-03

Using pneumatic instruments ALTITUDE MEASUREMENT AE-705 Introduction to Flight Lecture-06 Capsule-03

ALTIMETER used to measure the altitude of an object above a fixed level is supplied with P static from the static ports altimeter shows the pressure directly as an altitude above mean sea level Source: http://cormsquare.com//Images/Product/20160316062658667/_03162016062658667_58d0dc8a-08b0-4bfe-b52b-c441dca78856.jpg Source: https://s-media-cache-ak0.pinimg.com/736x/2f/b2/d0/2fb2d079d23f32df9574b6c02eec46ab.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

ALTIMETER a stack of sealed aneroid diaphragms expand and contract as the pressure rises and falls Kollsman window used to calibrate the instrument to the local altimeter setting A pointer moves on the Source: https://www.americanflyers.net/aviationlibrary/instrument_flying_handbook/images/Chapters%201%20to%207_img_80.jpg barometric scale giving the reading AE-705 Introduction to Flight Lecture-06 Capsule-03

VARIOMETER (VSI) Measures the rate of descent or climb of the aircraft detects the change in air pressure as altitude changes VSI is used to ascertain that level flight is being maintained Source: http://sarasotaavionics.com/images/productimages/UMA/T8-310.jpg Source: https://s-media-cache-ak0.pinimg.com/736x/2f/b2/d0/2fb2d079d23f32df9574b6c02eec46ab.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

VARIOMETER has a thin sealed diaphragm connected to the static port VSI dial returns to zero to show level flight Sealed instrument case Calibrated leak to control P static Source: https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Faa_vertical_air_speed.JPG/220px-Faa_vertical_air_speed.JPG AE-705 Introduction to Flight Lecture-06 Capsule-03

Leading to wrong readings / Crashes ! ERRORS IN PNEUMATICS AE-705 Introduction to Flight Lecture-06 Capsule-03

ERRORS IN PITOT STATIC SYSTEMS If the pitot tube becomes blocked, the system will give frivolous reading Contaminants in the pitot tube Source: https://i.stack.imgur.com/imdrz.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

ERRORS IN PITOT STATIC SYSTEMS If the static port becomes blocked and the pitot tube remains operable, the airspeed indicator will barely work and readings will be inaccurate The altimeter will freeze in a place where the blockage occurred VSI will indicate zero Blocked static port Source: http://i.imgur.com/ptfYbcV.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

One of the aircraft's three pitot tubes was blocked by a wasp’s nest Source: http://www.computerweekly.com/news/1280096929/Crash-One-Birgenair-Flight-301 The left engine quit first, and then the Source: http://www.airlive.net/onthisday-in-1996-birgenair-flight-301-crashes- shortly-after-takeoff-from-puerto-plata-dominican-republic/ Auto-pilot system calculated that the airliner went into a full stall and plane was travelling too fast crashed into the Caribbean Sea Auto pilot raised the nose to slow it down Birgenair Flight 301 Crash Animation AE-705 Introduction to Flight Lecture-06 Capsule-03

High Subsonic, Transonic and Supersonic Flows COMPRESSIBLE FLOWS AE-705 Introduction to Flight Lecture-06 Capsule-03

INCOMPRESSIBLE FLOW A flow can be assumed to be incompressible if its velocity is less than 30% of its sonic velocity 𝟑 𝟑 𝐖 𝟐 𝟑 + 𝐐 𝟐 ⍴ + 𝐡𝐚 𝟐 = 𝐖 𝟑 𝟑 + 𝐐 𝟑 ⍴ + 𝐡𝐚 𝟑 𝑨 1 = 𝑨 2 For Stagnation Pressure ↔ V=0 𝟑 𝐐 𝐭𝐮𝐛𝐡𝐨𝐛𝐮𝐣𝐩𝐨 − 𝐐 𝐭𝐮𝐛𝐮𝐣𝐝 𝐖 = 𝛓 AE-705 Introduction to Flight Lecture-06 Capsule-03

SUBSONIC COMPRESSIBLE FLOW 𝛅 𝐐 𝐭𝐮𝐛𝐡𝐨𝐛𝐮𝐣𝐩𝐨 𝟐 + 𝛅 − 𝟐 𝛅−𝟐 𝟑 = 𝐍 ∾ 𝐐 𝐭𝐮𝐛𝐮𝐣𝐝 𝟑 Mach number of free stream Source: http://www.efunda.com/designstandards/sensors/pitot_tubes/images/Pitot_tube_Mouth.gif Velocity can be calculated using : 𝛅−𝟐 𝐐 𝐭𝐮𝐛𝐡𝐨𝐛𝐮𝐣𝐩𝐨 𝟑𝛅 𝐐 𝐭𝐮𝐛𝐮𝐣𝐝 𝛅 𝐰 = − 𝟐 𝛅 − 𝟐 𝛓 𝐭𝐮𝐛𝐮𝐣𝐝 𝐐 𝐭𝐮𝐛𝐮𝐣𝐝 Source: http://nptel.ac.in/courses/101103004/module7/lec6/3.html AE-705 Introduction to Flight Lecture-06 Capsule-03

SUPERSONIC COMPRESSIBLE FLOW The characteristic feature of a supersonic flow is the formation of a shock wave P stagnation,probe > P stagnation,freestream introduction of a Pitot probe leads to a detached bow shock Source: http://nptel.ac.in/courses/101103004/module7/lec6/images/23.png AE-705 Introduction to Flight Lecture-06 Capsule-03

SUPERSONIC COMPRESSIBLE FLOW Rayleigh-Pitot formula for supersonic flows stagnation pressure of the normal shock 𝛿 𝛿 − 1 𝛿−1 𝑁 ∾ 𝑄 2 02 = 1 𝑄 ∾ 𝛿 + 1 𝑁 ∾ − 𝛿 − 1 2𝛿 𝛿−1 𝛿 + 1 Free stream static pressure Source: https://s-media-cache-ak0.pinimg.com/736x/2f/b2/d0/2fb2d079d23f32df9574b6c02eec46ab.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

SUPERSONIC COMPRESSIBLE FLOW The Rayleigh-Pitot formula represented graphically Source: http://nptel.ac.in/courses/101103004/module7/lec6/3.html AE-705 Introduction to Flight Lecture-06 Capsule-03

FOR SUPERSONIC AIFRCRAFT Why are pitot tubes shaped like this? Source: https://thumbs.dreamstime.com/x/d-pilot-thinking-render-50306654.jpg Source: https://s-media-cache-ak0.pinimg.com/736x/2f/b2/d0/2fb2d079d23f32df9574b6c02eec46ab.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

SUPERSONIC COMPRESSIBLE FLOW position error → P static, local – P static, ambient An “aerodynamic - compensation” pitot tube has a contoured shape Masud J ., Performance characteristics of flush angle-of-attack measurement system integrated on a pitot tube , Engineering Applications of Computational Fluid Mechanics, 2010 Jan 1; 4(4):549-57 AE-705 Introduction to Flight Lecture-06 Capsule-03

SUPERSONIC COMPRESSIBLE FLOW Angle of attack (AOA) sensors measure P static difference between top and bottom surfaces Employed in supersonic fighter aircraft AOA Source: https://www.researchgate.net/profile/Imran_Afgan/publication/269062238/figure/fig2/AS:392309884637187@1470545373346/Figure-2-Computational-mesh-in-the-vicinity-of-the-Pitot-tube-oblique-view-only.png As AOA ↑ ↔ P static difference ↑ AE-705 Introduction to Flight Lecture-06 Capsule-03

SUPERSONIC COMPRESSIBLE FLOW AIR DATA MODULES Converts air pressure from a Pitot tube or a static port into numerical information System connected together with a data bus ADM → Flexible and modular can be installed anywhere Source: Moir and Seabridge, Aircraft systems, Pneumatic systems AE-705 Introduction to Flight Lecture-06 Capsule-03

Current Developments NON PNEUMATIC INSTRUMENTS AE-705 Introduction to Flight Lecture-06 Capsule-03

PITOT PLATES Direct air through a plate with a hole Measure the amount of air constricted by an obstruction Used in F-22 Raptor and B2 stealth bomber Source: http://www.wermac.org/images/orificeflow.gif How do they work ? Answer via Moodle ! Source: http://images01.military.com/media/equipment/military-aircraft/f-22-raptor/f-22-raptor_009-ts600.jpg AE-705 Introduction to Flight Lecture-06 Capsule-03

LiDAR for Airspeed Measurement  NESLIE (2009) NE w S tandby L idar I nstrument E xperiment   DANIELA (2011) D emonstration of AN emometry I nstrum E nt based on LA ser  Verbeek, M. J., and H. W. Jentink. "Optical air data system flight testing. NLR-TP-2012-068, 2012 AE-705 Introduction to Flight Lecture-06 Capsule-03

NESLIE & DANIELA AE-705 Introduction to Flight Lecture-06 Capsule-03

Now you have to answer a Quiz ! THANKS FOR YOUR ATTENTION ! AE-705 Introduction to Flight Lecture-06 Capsule-03