Lift Coefficient

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Lift Coefficient Lift QuantityMomentum, Flaps,
Slots, Slats, Spoilers

• Lecture 5
• Chapter 2

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Lift Coefficient Lift Quantity

• Force pressure x area
• The amount of lift obtained from a wing should be
  proportional to the dynamic pressure of the wing
  area.
• The lift coefficient measures the portion of lift
  of the resulting force being transformed.

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Example

• If a rectangular wing can be bounded by a wall in
  a wind tunnel, it essentially has no tips, and
  simulates a section of an infinite wing.
• Measuring the lift in this manner the dividing it
  by the dynamic pressure and wing area yields the
  lift coefficient associated with the airfoil.

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Example continued

• There is no span effect because there is no tip
  to form a vortex and induce downwash.
• This is how airfoil data can be collected in wind
  tunnels.
• Plotting lift coefficients versus angle of attack
  to determine lift properties of airfoils.

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Figures 2-43 2-44

• CL V. (0) Lift coefficient versus angle of
  attack for typical curve of a wingFigure 2-43
• C1 V. lt - Lift coefficient versus stall for a
  typical airfoil section
• C wing lift coefficient
• c coefficient of airfoils section

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Momentum

• Momentum is a physical quantity defined as mass
  times velocity.
• A mass of air moving at a certain speed has
  momentum.
• When momentum changes a force is exerted and is
  expressed as the rate of momentum change.

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Flaps

• The flap is the moveable portion of the airfoil
  that is deflected through some angle from the
  original chord position to yield a higher camber.
• Page 49 figure 2-46 shows the trailing edge in
  the normal position and the extended position.
• Notice the effective chordline increase because
  the camber is increased. (deviation of the
  midline from the chordline)

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Types of Flaps

• Plain
• Separate structure hinged to deflect
• Split
• Only the lower surface deflects
• Slotted
• Move slightly aft as they deflect, opening a
  small slot allowing more air over the flap

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Types of Flapscontinued

• Fowler
• Flap moves aft a considerable distance as it
  moves down, increasing the wing area
• Slotted-Fowler
• High life producer
• Double-Slotted-Fowler
• Even greater lift producer

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Flapped V. Unflapped

• Why do we use flaps?
• When do we use flaps?
• Look at figure 2-48 p. 51
• This graphs lift curves for flapped and unflapped
  airfoils
• What do you notice on this graph?

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Slots

• Slots are leading edge devices that allow air to
  flow from the lower surface to the upper surface
  at high angles of attack.
• The higher pressure air from the lower surface
  has more energy which delays the separation of
  airflow on the top surface delaying the stall.
• Slots create excessive drag at low angles of
  attack.

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Slats

• Slats are a way of avoiding the excessive drag
  characteristics of the slots.
• The slat is a leading edge section that will open
  into a slat at low speeds but close at high
  speeds.

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Spoilers

• A spoiler is a destroyer spoiler of lift.
• Spoilers project upward into the airstream,
  blocking the flow on the top surface.
• This spoils lift.
• Spoilers may be deployed for primary roll control
  instead of deflecting ailerons.
• There are problems associated with using the
  spoilers for primary roll control.

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Any Questions?

• Lets review
• Test is Tuesday 29th
• Chapters 12
• Test questions will be from text, power points,
  lectures/ visual aids.
• True/False, Multiple Choice/ Fill-in/ Short
  Answer/ Matching are all possible!

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Quiz on Lecture 5Chapter 2

• Please take out a sheet of paper
• Include todays date and your name

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Quiz on Lecture 5Chapter 2

• Define momentum.
• Draw,label, explain two types of flaps
  discussed today and in the text.
• Compare and contrast slots and slats.