fluid mechanics physics 4sl

One of the most important applications of fluid dynamics is in the design of airplane wings. In this SLP, we’ll introduce some basic terminology and take a quick look at the relationship between angle of attack, airspeed, and lift.

Go to the NASA GRC (2010) link on the Background page, which is a simulation called FoilSimII, created and maintained by the NASA Glenn Research Center.

Basic terminology (click “Geometry” in the upper left hand view.)

• Airfoil: The wing.

• Leading edge: The forward (rounded) part of the wing.

• Trailing edge: The aft (thin) part of the wing.

• Chord: The distance between the forward and aft edge of the wing.

• Angle of attack, AOA (In the simulation, it’s called Angle): The angle in degrees between the chord and direction of flight, relative to the air. At higher values of AOA, the wing is taking a bigger “bite” of the air.

• Camber: The downward curvature of the airfoil, measured as a percent of chord.

• Thickness: The maximum distance between the upper and lower surface of the airfoil, measured as a percent of chord.

Read all the instructions carefully. Set up the simulation as follows:

• Student version: Stall model

• Metric units

• Input:

Size:

Chord = 2.00 m.

Span = 10.0 m (Distance from wingtip to wingtip.)

Area = 20 m^2

Aspect ratio (AR, defined as span / chord) = 5

AR correction = ON

Shape/Angle:

AOA (Angle) = 5 deg.

Camber = 5%

Thickness = 10%

Flight test:

Earth Average day

Assume that the lift needed to maintain level flight is 20,000 N. On the “Flight test” page, adjust the speed (km/h) until lift is just over 20,000N (it won’t be exact.) Record the speed.

Go back to the “Shape/Angle” input page, and change the AOA to 6 degrees. Go back to the “Flight test” page and find the airspeed necessary to maintain just over 20,000 N of lift. (It will be lower than it was at AOA = 5 deg.) Repeat for the following increments of AOA: 7, 8, 9, and 10 degrees. Notice that the wing stalls just before 10 degrees. At this point, the lift drops (the simulation is wrong) and the aircraft begins to lose altitude. Record your data in a table.

Repeat all of the above for camber = 20%. Record your data in a table. After you’ve collected all your data, plot speed (Y axis) vs. AOA (X axis) for camber = 5% and camber = 20%. Discuss the advantages of a high camber wing when an airplane is operating near stall speed. (Note that the flaps that extend from the trailing edge of jetliner wings increase the effective camber.)

Some notes on the simulation:

For all of its apparent complexity, the simulation is actually too simple. The wing is rectangular, without sweep or taper. There’s no aircraft fuselage interfering with lift. The calculations are based on air as an ideal fluid, with no viscosity; hence, no boundary layer and no loss of lift when the wing stalls. Just the same, the simulation is an excellent teaching tool. You should explore some of the many informative web pages that are linked to the simulation