Transcript Lift Coefficient & Lift Quantity Momentum, Flaps, Slots

Lift Coefficient & Lift Quantity
Momentum, Flaps, Slots,
Slats,& Spoilers
Lecture 5
Chapter 2
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.
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.
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.
Figures 2-43 & 2-44
• CL V. (0) –Lift coefficient versus angle of
attack for typical curve of a wing{Figure 243}
• C1 V. < - Lift coefficient versus stall for a
typical airfoil section
• C= wing lift coefficient
• c= coefficient of airfoils section
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.
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)
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
Types of Flaps
continued
• 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
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?
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.
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.
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.
Any Questions?
• Let’s review
• Test is Tuesday 29th
• Chapters 1&2
– Test questions will be from text, power points,
lectures/ visual aids.
– True/False, Multiple Choice/ Fill-in/ Short
Answer/ Matching are all possible!
Quiz on Lecture 5
Chapter 2
Please take out a sheet of paper
Include today’s date and your name
Quiz on Lecture 5
Chapter 2
• Define momentum.
• Draw,label, & explain two types of flaps
discussed today and in the text.
• Compare and contrast slots and slats.