AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyIntroduction to PerformanceFlight Mechanics is the study of the motions of bodies (aircraft and rockets),through a fluid.Stability and Control Aerodynamic Performancethe science of designing for steadyand controllable fight characteristicsspeedrate of climbrangefuel consumptionmaneuverabilityrunway length requirementsAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyWhy Study Performance?AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Anatomy of the AirplaneAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAirplane ConfigurationsSource: Shevell, Fundamentals of FlightAnhedralAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAirplane ConfigurationsSource: Shevell, Fundamentals of FlightAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAirplane ConfigurationsSource: Shevell, Fundamentals of FlightAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Standard AtmosphereWhy do we need to know about the atmosphere?The performance of aircraft, spacecraft, and engines depend on the atmosphere inwhich they operate, primarily density and viscosity.Density and viscosity, inturn, are functions of altitude.Density, , varies with pressure, p, and temperature, TViscosity, , varies only with temperature, TThe standard atmosphere is defined from the equation of state of a perfect gas: p = RTPerfect Gas LawAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Standard AtmosphereRemember: R = F + 459.7K = C + 273.15For our purposes, the atmosphere can be regarded as a homogenous gasof uniform composition that satisfies the perfect gas law.p = pressure in lb/ft2 or N/m2 = density in slugs/ft3 or kg/m3T = absolute temperature in Rankine (R) or Kelvin (K)R = gas constant = 1718 ft-lb/slugR or 287.05 n-m/kgKAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyEffect of Water Vapor on AtmosphereWhen there is a significant amount of water vapor in the air, the density ischanged, but by a very small amount. = 0.002243 slug/ft3dry air = 0.002203 slug/ft3100% humidityAlthough the effect of water vapor on air density is very small, water vapordoes have a significant effect on engine performance and supersonicaerodynamics.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyInternational Standard AtmosphereTo allow for comparison of the performance of airplanes, as well as calibrationof altimeters, standard properties of the atmosphere have been established bythe International Civil Aviation Organization (ICAO).The ICAO and the U.S. Standard Atmosphere are identical below 65,617 feet.This standard atmosphere is representative of mid latitudes of the northernhemisphere.Standard sea level properties are:g0 = 32.17 ft/s2 = 9.806 m/s2P0 = 29.92 in Hg = 2116.2 lb/ft2 = 1.013 x 105 N/m2T0 = 59 F = 518.7 R = 15 C = 288.2 Kr0 = 0.002377 slug/ft3 = 1.225 Kg/m3AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyRegions of the AtmosphereExosphere-rarefiedIonospherePositive Temperature GradientStratosphereZero Temperature GradientTroposphereNegative Temperature GradientTropopause ( 36,089 ft)300 ~ 600 mi50 ~ 70 mi5 ~ 10 miIn subsonic airplane aerodynamics, only the troposphere and stratosphereare important.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyTemperature Variation with AltitudeBelow 36,089 ft, we assume there is a constant drop of temperature from sealevel to altitudeT = T1 + a ( h - h1)a = lapse rate = -0.00356616F/ft in the standard atmosphereT1 and h1 are reference temperatures.For sea level, T1 = T0 and h1 = 0Above 36,089 ft in the stratosphere, the standard temperature is assumedconstant and equal to -69.7 F.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyPressure/Density Variation with AltitudeBelow 36,089 ft(relative to standard sea level values)TT0= = 1 + h = 1 - 6.875 x 10-6 h aT0pp0= = 5.25610= = 4.2561AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyPressure/Density Variation with Altitudepp00= 0.2234 exph-36,08920806.7= 0.2971 expAbove 36,089 ft(relative to standard sea level values)h-36,08920806.7T = constant = -69.7 FAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyPressure/Density Variation with AltitudeSo, now you can calculate the temperature, pressure, and density at any point inthe troposphere or stratosphereORYou can use the nifty tables in the back of Andersons book (Appendices A, B)Be careful which units you are using...AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyViscosityViscosity varies primarily with temperatureThere is a strong relationship between air viscosity and boundarylayer behavior.This will be discussed more when we reviewaerodynamics.Kinematic Viscosity = /R = VlReynolds NumberAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAltimetersProperties of the standard atmosphere can be used to calibrate altimeters.An altimeter translates barometric pressure into a display of elevation in feet.known referencepressure insideAs the airplane climbs and descends, the aneroids expand and contract,which is reflected by the altimeter readingAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAltimetersHowever, unfortunately, atmospheric pressure changes not only with altitude butalso with fluctuations in the weather.To account for these changes, thealtimeter must be set to the current altimeter setting, which is the current sealevel barometric pressure, in inches of mercury.The adjustment knob is used to set the altimeter and this adjustment is shown inthe Kollsman window.A change of 1 inch of mercury on the Kollsman windowresults in ~ 1000 foot change in altitude on the display needles.Pilots obtain current altimeter settings from an airplane control tower or a FlightService Center.If this information is unavailable, the altimeter can be set to thefield elevation of the airport.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAltimetersThree point altimeterDrum altimeterAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyErrors in AltimetersScale error - at lower altitude, errors due to the aneroids not assuming theexact size corresponding to altitude is on the order of plus/minus 50 feet.Athigher altitudes, these errors can be as much as plus/minus 200 feet.Friction error - due to friction of the mechanical parts.Usually the vibration ofthe airplane overcomes the friction, or the pilot can tap on the glass.Hysteresis - due to the imperfect elasticity of the wafers.After long flights athigher altitudes, the wafers can become set.Errors on the order of 100 feetare not uncommon.A few minutes at the new altitude will reset the altimeterAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyTypes of AltitudePressure Altitude - defined as the reading on an altimeter when the Kollsmanwindow is set to 29.92 inches of mercury (standard sea level pressure).Thisis the altitude used in performance calculations and for flights above 18,000feet (where pressure altitudes are called flight levels).True Altitude - is the true height above mean sea level (MSL).Sea level isassumed fixed, therefore MSL altitudes do NOT change with atmosphericconditions.Realize that a properly functioning altimeter will indicate truealtitude ONLY if it is operating in a standard atmosphere, which rarely ornever occurs.Indicated Altitude - is what the altimeter reads at any given time.Absolute Altitude - is altitude above ground level (AGL).AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyTypes of AltitudePressure = 29.92 inches of mercuryAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyWeather and the AltimeterIf the pilot does not reset the Kollman window in flight, what happens?The pilot will be flying at a line of constant pressure.If s/he flies from highpressure weather to low pressure weather, the true altitude will show adescending flight path.To remember this phenomena, use the following rhyme:from a high to a low, look out belowfrom a low to a high, youre high in the skyThis also works for temperature fluctuationsAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyWeatherand theAltimeterAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyPitot-Static TubeRam air, or pitot air, is captured in a hollow tube that projects from the aircraft.The pitot tube is placed in such a way as to capture impact air with minimaldisturbance from the rest of the airframe.The static port measures local atmospheric pressure.The static port is usuallyplaced perpendicular to the airstream so as to negate any pressure caused frommotion.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Airspeed IndicatorThe airspeed indicator subtracts the static pressure from the total pressuresupplied by the pitot tube.This difference is called dynamic pressure, and is ameasure of the airplanes forward speed.Recall Bernoullis Equation:pt = p + 1/2 V2total pressure static pressuredynamic pressureAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Airspeed IndicatorThe chamber is flooded with static pressure.The diaphragm expands orcontracts due to pitot (total) pressure.How much the needle deflects isan indication of the difference between the two pressures (dynamicpressure).AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Airspeed IndicatorAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyAirspeed Indicator LimitationsThe airspeed indicator may fail or reflect an incorrect speed primarily dueto pitot tube blockage:the pilot forgets to remove the protective cover from the pitotbefore takeoffice accumulationforeign object blockage such as dirt or insectsAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyTypes of AirspeedsIndicated Airspeed (IAS) - is the direct reading from the airspeed indicator.This represents the airplanes speed through the air, NOT necessarily its speedacross the ground.Calibrated Airspeed (CAS) - is the indicated airspeed corrected for instrumentposition and instrument error.This is a function of each unique aircraft and theposition of its pitot tube.There is no direct reading of CAS in the cockpit!Thepilot must refer to the Pilots Operating Handbook for a table corresponding tothat particular aircraft.True Airspeed (TAS) - because an airspeed indicator is calibrated for standardsea level conditions, when the airplane is flying at altitude, the airspeed is notcorrectly reflected.The amount of error is a function of temperature andaltitude.TAS can be approximated by increasing the indicated airspeed by 2%per thousand feet of altitude.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyVertical Speed IndicatorThe vertical speed indicator, or VSI, registers the rate of change of staticpressure and converts this to an indication in feet per minute.airtight caseAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Pitot Static InstrumentsAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Magnetic CompassMagnetic Compass - indicates the direction the airplane is heading with respectto magnetic north.The difference between this and true north is called variation.magnets fixed to compass cardliquid in the compass stabilizes and damps the motionAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyGyroscopic InstrumentsA gyroscope is a mass spinning rapidly about an axis.A spinning gyroscopeexhibits two fundamental properties:Rigidity in space - a spinning gyroscope will tend to maintain itsorientation in space an resist any forces that tend to displace it.Precession - when a gyroscope is displaced by a force, such as friction,the reaction generated by the gyroscope is called precession.Thisreaction acts 90 degrees from the applied force, in the direction of therotation of the rotor.The instruments that depend on gyroscopic motion are powered instruments,using either electricity, air pressure, or vacuum.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Attitude IndicatorThe attitude indicator, also called the artificial horizon or gyro horizon,provides the pilot with a visual representation of the airplanes flight attitudewith respect to the horizon.The gyro is universally mounted on a vertical spin axis.It is attached to anattitude sphere, which remains rigid when the airplane manuevers.Aminiature airplane is free to rotate with the airplane.attitude sphereAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Attitude IndicatorAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Turn CoordinatorThe turn coordinator actually contains two instruments.An airplane symbolindicates the airplanes rate of turn once a constant bank angle is established.The ball in the tube, called the inclinometer, provides information about thequality of the turn.The gyroscope in the turn coordinator is installed with fore and aft axis of themounting canted slightly with respect to the airplanes longitudinal axis.Thegyroscope senses motion about the roll and yaw axis.Any pitch related motionis restricted.The airplane symbol reacts directly with the aircraft.The inclinometer is a ball in a curved liquid filled tube.The position of theball is determined by centrifugal and gravity forces of the turn.AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Turn CoordinatorAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyThe Heading IndicatorThe heading indicator is also called the directional gyro (DG).It displays theairplanes heading from a gyroscopically rigid platform.It must be set prior toeach flight or during straight and level flight to agree with the magneticcompass.Precession caused by friction in the bearings can cause the gyro todrift, so it must be periodically reset in flight (approx. every 15 minutes).AE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologyStandard Instrument Panel LayoutAE 3310 PerformanceLecture 1- May 14, 2002Dr. Danielle SobanGeorgia Institute of TechnologySources for Lecture 1Shevell, Richard S., Fundamentals of Flight, 2nd Edition, Prentice Hall,NJLan, Chuan-Tau Edward and Roskam, Jan, Airplane Aerodynamics and Performance, Roskam Aviation and Engineering Corporation, KSGlaeser, Dennis et al, An Invitation to Fly- Basics for the Private Pilot, 4thEdition, Wadsworth Publishing, CAKershner, William K., The Student Pilots Flight Manual, 7th Edition,Iowa State University Press, Iowa