飞行力学全册配套最完整精品课件(英文版).ppt
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1、飞行力学全册配套最完整飞行力学全册配套最完整 精品课件精品课件(英文版)英文版) I Principles of straight and steady level flight 1. Straight and steady level flight Lift Z V Velocity vector X Drag Thrust F Weight mg Thrust balances drag An airplane has : wings to generate lift, engines to balance drag. Lift balances weight 1. Straight an
2、d steady level flight Expressions for lift and drag : Lift : V2 S CzDrag : V2 S Cx V2 is the kinetic pressure, also noted q is the air density (in kg/m3) V is the air velocity (in m/s) S is the wing reference surface (in m2) Cz and Cx are lift and drag coefficients Drag is parallel to the velocity v
3、ector and opposed to velocity (Cx is always positive) Lift is normal to the velocity vector (upwards when Cz is positive) 1. Straight and steady level flight Symmetrical flight Wings leveled (zero bank angle) Zero lateral force (zero sideslip angle) Straight and level flight : velocity vector is hor
4、izontal Lift balances weight Steady flight : Constant speed : thrust balances drag Moment equilibrium is achieved by flight controls deflections 1. Straight and steady level flight V Velocity vector Angle of attack, , is the angle between the velocity vector and the airplane longitudinal reference.
5、Lift and drag coefficients are functions of angle of attack. Angle of attack and pitch attitude Horizontal plane In straight and level flight, the velocity vector is horizontal : angle of attack equals pitch attitude : = Pitch attitude, , is the angle b e t w e e n t h e a i r p l a n e longitudinal
6、 reference and the horizontal plane. Flight controls Thrust levers Aerodynamics PropulsionWeightInertia Moments Ma/G +MF/G = dt d ( I . W W k) ForcesRa +F + gm= dt d (mVk) 1. Straight and steady level flight Flight mechanics equations Flight controls are used to control attitude Forward/aft stick (o
7、r control wheel) controls pitching moment through elevator Left/right Stick (or control wheel) controls rolling moment through ailerons (and spoilers) Rudder pedals control yawing moment through rudder 1. Straight and steady level flight 1. Straight and steady level flight Lift equation mg = V2 S Cz
8、lift balances weight Propulsion equation F = V2 S Cxthrust balances drag To maintain straight and steady level flight : Angle of attack is controlled by elevator deflection in order to maintain lift equilibrium (lift = weight) Thrust is controlled by thrust levers in order to maintain thrust equilib
9、rium Equations for straight and steady level flight 2. Pressure and altitude : the altimeter Note : 1 ft = 0.3048 m Pressure (hPa) 0 20 40 60 80 100 120 2004006008001000 Altitude (X 1000 ft) 0 1013.25 hPa 500 hPa 18300 ft 5600 m 300 hPa 30050 ft 9160 m 100 hPa 53080 ft 16180 m 27ft / hPa 73 ft / hPa
10、 Pressure as a function of geopotential altitude (International Standard Atmosphere) 2. Pressure and altitude : the altimeter Pressure altitude Zp(p) is the altitude corresponding to pressure p in the ISA model. Example :Zp 10 000 ft p = 697 hPa The term Flight level (FL) is also used. Flight Level
11、is the pressure altitude expressed in hundreds of feet. Example : FL 100 means Zp 10 000 ft. At a given pressure altitude, temperature is sometimes expressed as a difference between actual temperature and ISA temperature. Example : At FL 100 (Zp 10 000 ft), ISA temperature is - 5 C (268 K). ISA+15 c
12、onditions means that actual temperature at FL100 is 15 higher than ISA temperature, or +10C (-5+15) 2. Pressure and altitude : the altimeter Static pressure p is measured through static ports. International Standard Atmosphere is used to convert pressure p into pressure altitude Zp(p). Indicated alt
13、itude : Zi = Zp(p) - Zp(pc). The altimeter setting, noted pc, is a pressure value selected by the crew, allowing to ajust to current conditions. Altimeter setting pc Zp(pc) Pressure pPressure altitude Zp(p) 2. Pressure and altitude : the altimeter 1000 hpa 900 hpa 800 hpa 0 2000 ft 4000 ft 6000 ft 0
14、 5 4 3 2 1 6 7 8 9 ALT 1 030hPa 000 4 ft 5 pc Zi Zp(p) Static pressure p Indicated Altitude Zi Indicated altitude : Zi = Zp(p) - Zp(pc) 2. Pressure and altitude : the altimeter Altimeter settings : Standard setting : 1013.25 hPa Indicated altitude is pressure altitude. QFE is the current static pres
15、sure on the airport : On ground, indicated altitude is zero. QNH is defined in order to read airport elevation on ground. Zi (p, QNH) H at low altitudes, But, at higher altitudes, altimeter indication is affected by temperature conditions (in cold conditions, altimeter indication is higher than actu
16、al altitude). 2. Pressure and altitude : the altimeter The real atmosphere may differ from the ISA model : pressure at sea level : usual range from 980 to 1050 hPa, much lower values in cyclones, temperature at sea level, altitude for minimal temperature (tropopause) may be lower than 8 km or higher
17、 than 15 km compared to the 11 km ISA value. Consequences : Difference between pressure altitude Zp and geopotential altitude H may exceed several thousands feet QNH setting corrects the difference between actual pressure at sea level and ISA pressure (1013.25hPa), in ISA temperature conditions, an
18、altimeter set at QNH will indicate actual geopotential altitude But, it is not possible to correct temperature error : in cold air, an altimeter set at QNH will indicate an altitude higher than actual altitude 2. Pressure and altitude : the altimeter Static pressure measurements may be affected by :
19、 Instrument / sensor error Static source position error : influence of airflow around the airplane p = pport - p p1 p2 p Undisturbed flow 2. Pressure and altitude : the altimeter Static source position error calibration methods Airplane aerodynamic field (wake) Cone Pressure transducer Height above
20、ground z (radio altimeter, GPS, ) Pressure and temperature on ground pG, TG Pressure at A/C altitude obtained from z, pG, TG and T (temperature at A/C altitude) 2. Pressure and altitude : the altimeter Applicable at sea level, in ISA conditions, between 1.3 Vs in landing configuration and 1.8 Vs in
21、clean configuration. Note : 30 ft error at sea level is equivalent to 123 ft error at FL400. -90 -60 -30 0 30 60 90 50100150200250300 Indicated Air Speed (kt) Maximum position error (ft) Static source position error FAR/CS 25 requirements 3. True airspeed and indicated airspeed Ground Speed and True
22、 Air Speed True Air Speed, TAS or V, is A/C velocity relative to the air Ground Speed, GS or Vk, is A/C velocity relative to the ground. May be measured by inertial or radio navigation sensors (GPS, DME, etc). Units for speed : 1 kt = 1852 m/h = 0.5144 m/s is the drift angle. d d True Air Speed V Wi
23、nd WGround Speed Vk 3. True airspeed and indicated airspeed At low Mach numbers, Bernoullis equation is valid : pt = p + V2 = p + q q is the Kinetic pressure :q = V2 aerodynamic efforts are proportional to q Static port p Static pressure p (static temperature T) Pitot tube pt Total pressure pt (tota
24、l temperature Tt) Total pressure and static pressure 3. True airspeed and indicated airspeed The principle for indicated airspeed (noted Vi) is to convert p into an airspeed indication : Vi (p) At low speeds, when Bernoullis equation is valid, it is possible to use kinetic pressure definition, with
25、air density ISA value at sea level : p = 0Vi2 Pitot tube Static port p = pt p V2 ptp IAS 3. True airspeed and indicated airspeed Equivalent airspeed (EAS), noted EV, is the airspeed corresponding to a given kinetic pressure at s.l. in ISA conditions : q = V2 = 0 EV2 EV = V Indicated Airspeed (IAS),
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