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Principles of Flight Tim Freegarde www.uskgc.co.uk
Bronze - Principles of Flight - Windrushers GC
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Principles of Flight what you need for the Bronze exam
useful knowledge for flying terminology principles how it all works Q. Questions from Bronze & Beyond
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Terminology acceleration aerofoil aileron airspeed angle of attack
attitude bank centre of mass/gravity centre of pressure chord control deflection drag (induced, profile, …) elevator fin flutter fuselage glide angle/slope laminar flow lift load factor minimum sink pitch polar curve roll rudder skid slip span spin stability stall tailplane turbulence Va Vne vortices washout wing yaw yaw string
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Principles of Flight aerofoil lift & drag depend upon Angle of Attack
aerofoil lift & drag vary as airspeed2 Newton was right
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Principles of Flight SITUATIONS forces on the whole glider
bits of the glider balanced flight wings level steady turn changing pitch elevator bank ailerons yaw rudder stability in pitch tailplane bank dihedral yaw fin
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Forces in level flight aerodynamic force balances weight
Newton: no acceleration aerodynamic force produced by glider’s wings glide angle L:D D L TRIANGLE OF FORCES WEIGHT split into LIFT and DRAG: LIFT: perpendicular to airflow DRAG: parallel to airflow airflow relative to glider LIFT DRAG 1. Name the forces on a glider when it is flying straight at a steady speed. L D WEIGHT
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Forces in a steady turn greater lift needed to balance weight
need higher speed or angle of attack horizontal part for centripetal force 2. Name the forces on a glider when it is in a well banked turn at a steady speed. 3. Why does a glider increase its speed in a turn unless you move the stick back?
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Aerofoil
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Aerofoil
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Aerofoil at given AoA, lift airspeed2
at given airspeed, lift and drag vary with AoA L/D varies with AoA (D L2) LIFT or DRAG AIRSPEED
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Aerofoil at given AoA, lift airspeed2
at given airspeed, lift and drag vary with AoA L/D varies with AoA (D L2) LIFT or DRAG AIRSPEED
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Aerofoil in steady flight, for every angle of attack there is an airspeed at which the lift will support the weight at other speeds, the glider will climb or fall, changing the AoA
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Centre of Gravity/Mass
Force distribution glider weight acts through Centre of Gravity/Mass wing lift acts through Centre of Pressure pitching torque if displaced tailplane provides balance Centre of Gravity/Mass 12. What is the purpose of a tailplane?
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Control surfaces downward deflection increases angle of attack
lift is increased upward deflection decreases angle of attack lift is reduced
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Pitch control – effect of elevator
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Pitch control – effect of elevator
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Pitch control – effect of elevator
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Pitch control – effect of elevator
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Pitch control – effect of elevator
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Pitch control – effect of elevator
13. How does an elevator work?
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Roll control – effect of ailerons
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Roll control – effect of ailerons
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Yaw control – effect of rudder
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Yaw control – effect of rudder
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Effects of controls AEROFOILS
aerodynamic force depends upon airspeed angle of attack PRIMARY EFFECTS elevator pitch aileron roll rudder yaw SECONDARY EFFECTS aileron adverse yaw rudder roll
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Secondary effect of ailerons
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Secondary effect of ailerons
8. Why do you normally apply rudder when applying aileron?
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Secondary effect of rudder
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Yaw stability – effect of fin
tendency of aircraft to recover when upset tail fin (vertical stabilizer) has angle of attack to airflow lateral aerodynamic force creates torque glider weathercocks back to point into airflow 11. What is the purpose of a glider's fin?
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Bank stability – effect of dihedral
tendency of aircraft to recover when upset LIFT bank without yaw results in sideslip sideslip steepens AoA of lower wing lower wing produces more lift torque tends to return glider to wings level slip will cause weathercock into turn Dihedral angle WEIGHT
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Roll stability (damping)
tendency of aircraft to recover when upset downgoing wing experiences higher AoA downgoing wing produces more lift torque reduces rate of roll will not level wings
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Pitch stability – effect of tailplane
tendency of aircraft to recover when upset tailplane AoA increases more significantly than wing AoA tailplane moment increases more than wing moment torque pitches nose down 12. What is the purpose of a tailplane?
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Pitch stability – C of G STABILITY
tendency of aircraft to recover when upset CG behind aft limit light/unstable in pitch prone to spin CG ahead of forward limit heavy/too stable in pitch difficulty rounding out 14. What is the effect on stability of reducing the cockpit load?
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Stall lift no longer increases with AoA
airflow separation and turbulence drag increases ailerons less effective
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Stall lift no longer increases with AoA
airflow separation and turbulence drag increases ailerons less effective a glider can stall at any speed in any attitude high AoA: slow flight steep turns high g manoeuvres taut winch cable rapid pitch rotation
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Stall lift no longer increases with AoA
airflow separation and turbulence drag increases ailerons less effective a glider can stall at any speed in any attitude high AoA: slow flight steep turns high g manoeuvres taut winch cable rapid pitch rotation 9. How can gliders stall at higher speeds?
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Spin one wing stalled less lift, so descends higher AoA
wing stall sustained 10. Why does a glider spin? a glider can stall at any speed in any attitude high AoA: slow flight steep turns high g manoeuvres taut winch cable rapid pitch rotation
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Limiting speeds Vs 1g wings-level stall speed
Va no single control can overstress aircraft Vne never exceed (CS22: full elevator 1/3 aileron or rudder) 17. What name is given to the maximum speed at which it is safe to use full deflection of any one control without damaging the glider? 18. What is the maximum airspeed and maximum manoeuvring speed of the glider that you normally fly? SB9 Akaflieg Braunschweig DG300-17
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Drag induced drag depends on AoA profile drag form drag
pushing air aside skin drag boundary friction interference drag airflows meet leakage drag high-low pressure 7. Why put sealing tape between the wings and fuselage? 4. How does the profile drag change with airspeed between the stall and VNE? 5. How does the lift-induced drag change with airspeed between the stall and VNE?
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The glider polar sink vs airspeed for given loading
6. At what speed is total drag at a minimum? 15. Why is the best glide angle given by the tangent to the polar curve?
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Books and websites phyweb.phys.soton.ac.uk/quantum/lectures/gliding/principles.pptx phyweb.phys.soton.ac.uk/quantum/lectures/gliding/principles.ppt phyweb.phys.soton.ac.uk/quantum/lectures/gliding/principles.pdf
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