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 2-43} 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 Split Slotted 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.