Principles of Flight Tim Freegarde

Principles of FlightPrinciples of Flight

Tim FreegardeTim Freegarde

www.uskgc.co.uk


• 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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TerminologyTerminology• 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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1. aerofoil lift & drag depend upon Angle of Attack2. aerofoil lift & drag vary as airspeed2

3. Newton was right

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• balanced flight• balanced flight wings levelwings level

steady turnsteady turn

• stability in• stability in

pitchpitch

bankbank

the whole gliderthe whole gliderforces onforces on

bits of the gliderbits of the glider

yawyaw

• changing• changing

pitchpitch

bankbank

yawyaw

elevatorelevator

aileronsailerons

rudderrudder

tailplanetailplane

dihedraldihedral

finfin

SITUATIONSSITUATIONS

Forces in level flightForces in level flight

• aerodynamic force balances weight• Newton: no acceleration

aerodynamic force produced by glider’s

wings

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WEIGHT

LIFT

WEIGHT

DRAG

• split into LIFT and DRAG:• LIFT: perpendicular to airflow• DRAG: parallel to airflow

airflow relative

to glider

TRIANGLE OF FORCES

• glide angle L:D

DL

L

D

1. Name the forces on a glider when it is flying straight at a steady speed.

Forces in a steady turnForces in a steady turn

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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?

• greater lift needed to balance weight

• need higher speed or angle of attack

• horizontal part for centripetal force

AerofoilAerofoil

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AerofoilAerofoil

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AerofoilAerofoil

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• at given AoA, lift airspeed2

• at given airspeed, lift and drag varywith AoA

• L/D varies with AoA (D L2)AIRSPEED

AerofoilAerofoil

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AIRSPEED

• at given AoA, lift airspeed2

• at given airspeed, lift and drag varywith AoA

• L/D varies with AoA (D L2)

AerofoilAerofoil

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• 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

Force distributionForce distribution

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• 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?

Control surfacesControl surfaces

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• downward deflection increases angle of attack

• lift is increased

• upward deflection decreases angle of attack

• lift is reduced

Pitch control – effect of elevatorPitch control – effect of elevator

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13. How does an elevator work?

Roll control – effect of aileronsRoll control – effect of ailerons

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Roll control – effect of aileronsRoll control – effect of ailerons

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Yaw control – effect of rudderYaw control – effect of rudder

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Yaw control – effect of rudderYaw control – effect of rudder

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Effects of controlsEffects of controls

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AEROFOILS•aerodynamic force depends upon airspeed

angle of attackPRIMARY EFFECTS•elevator pitch•aileron roll•rudder yaw

SECONDARY EFFECTS•aileron adverse yaw•rudder roll

Secondary effect of aileronsSecondary effect of ailerons

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Secondary effect of aileronsSecondary effect of ailerons

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8. Why do you normally apply rudder when applying aileron?

Secondary effect of rudderSecondary effect of rudder

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Yaw stability – effect of finYaw stability – effect of fin

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STABILITY•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?

Bank stability – effect of dihedralBank stability – effect of dihedral

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• 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

LIFT

WEIGHT

Dihedral angle

Roll stability (damping)Roll stability (damping)

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• downgoing wing experiences higher AoA

• downgoing wing produces more lift

• torque reduces rate of roll• will not level wings

Pitch stability – effect of tailplanePitch stability – effect of tailplane

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• 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?

Pitch stability – C of GPitch stability – C of G

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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?

StallStall

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• lift no longer increases with AoA• airflow separation and turbulence• drag increases• ailerons less effective

StallStall

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• a glider can stall at any speedin any attitude

• high AoA: slow flightsteep turnshigh g manoeuvrestaut winch cablerapid pitch rotation

StallStall

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9. How can gliders stall at higher speeds?

SpinSpin

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• one wing stalled• less lift, so descends higher AoA• wing stall sustained



10. Why does a glider spin?

Limiting speedsLimiting speeds

• Vs 1g wings-level stall speed

• Va no single control can overstress aircraft

• Vne never exceed (CS22: full elevator1/3 aileron or rudder)

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DG300-17www.dg-flugzeugbau.de

SB9Akaflieg Braunschweig

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?

DragDrag

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• induced drag• induced drag

• profile drag• profile drag • form drag• pushing air aside• form drag• pushing air aside

• interference drag• airflows meet• interference drag• airflows meet

• skin drag• boundary friction• skin drag• boundary friction

• leakage drag• high-low pressure• leakage drag• high-low pressure

• depends on AoA• depends on AoA

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?

7. Why put sealing tape between the wings and fuselage?

The glider polarThe glider polar

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• sink vs airspeed for given loading

15. Why is the best glide angle given by the tangent to the polar curve?

6. At what speed is total drag at a minimum?

• 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• www.carrotworks.com

[email protected]

Books and websitesBooks and websites

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Principles of Flight Tim Freegarde