Lift Coefficient Lift Quantity Momentum Flaps Slots Slats

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} • C 1 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 29 th • 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.