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What A Drag!

What A Drag!. -DRAG. Energy is neither created or destroyed…visited earlier in the semester. How does a car as an energy system lose energy? FRICTION: Where does friction exist in a car? Apply this to the simple technology system of a dragster.

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What A Drag!

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  1. What A Drag!

  2. -DRAG • Energy is neither created or destroyed…visited earlier in the semester. • How does a car as an energy system lose energy? • FRICTION: Where does friction exist in a car? • Apply this to the simple technology system of a dragster. • The friction is not totally lost, it leaves the system, yes, but in the form of heat.

  3. -DRAG • Thrust is created by the jet engines and must overcome the retarding force known as drag/wind resistance. • There are three main categories of drag – induced, interference and parasite. • Total Drag = Dind + Dinf + Dpar

  4. -DRAG • Induced drag is that drag which is attributed to the production of lift. • The magnitude of induced drag decreases as the airspeed increases. • Water skiers experience this phenomenon when being pulled by a boat. Starting at rest, and mostly submerged, the skier feels a massive amount of drag while being pulled through the water. As the speed increases, the skier skims over the surface of the water and the drag is significantly reduced.

  5. -DRAG • Because of the high speed at which jet transport aircraft cruise, induced drag makes up less than one-quarter of the total drag. • Parasite drag is made up of three components. • Skin Friction • Profile Drag • Interference Drag

  6. -DRAG • Skin friction is the resistance air molecules encounter as they flow over the aircraft's surface. • Notice the smooth seams of the aircraft's skin; this design minimizes the skin friction.

  7. -DRAG • Profile drag, also called form drag, is caused by the air pressure in front of the aircraft. • Fast moving aircraft are designed to be sleek to minimize the frontal area and the profile drag.

  8. -DRAG • The third component is interference drag. • If the aircraft's components disrupt the air's smooth, or laminar, flow, the cost is paid in interference drag. • The landing gear is raised into the body of the aircraft after takeoff to decrease this drag. • Passengers can feel the airflow smooth when the landing gear is retracted.

  9. -DRAG • Interference drag is also demonstrated by cross winds. • As a body travels through motionless air, the resultant drag is the fluid particles hitting against exposed surfaces of the object. • If there were a cross wind, that portion of the total drag factor would be interference. • The velocity in which the cross wind “interferes” with the object causes greater drag.

  10. -DRAG • The thin air at high altitudes reduces parasite drag. • Flying at 40,000 feet, the air has one-fourth the density as at sea level. • If jet transport aircraft could fly as high as space shuttles, they could shut down the engines and coast, since no drag exists if there is no air around the craft.

  11. -DRAG • Induced drag decreases and parasite drag increases with airspeed. • Total drag is the sum of the induced and parasite drag components. • What happens in the wind tunnel? • The slowest speed an aircraft can fly is known as the stall speed. • Total drag is very high at the stall speed because of the induced component. As the airspeed increases, the drag decreases to a minimum point. • As the airspeed continues to increase above this point, the parasite drag causes the total drag to increase.

  12. -DRAG • Total Drag = DInd + DInf + DP. • Principle of Parasite drag is such that Parasite Drag quadruples as Wind Speed doubles. • So, when you get your dragster to the wind tunnel, you need to test at 25 mph, record the drag. • Turn wind speed up to 50, record drag. • If initial drag is 5 grams, then the second reading is 20. If there is a breach of this principle then there is something wrong. • Where is the additional drag coming from? • Examine our equation: Total Drag = DInd + DInf + DP

  13. -DRAG • So it must be coming from induced drag. • Induced drag is that drag which is attributed to the production of lift. • How did I get lift? • Angle of attack. • Make sure the bottom of your dragster is parallel with the ground. • By reducing your angle of attack and controlling the shape of your dragster, you minimize the production of lift.

  14. -DRAG • Aircraft designers are making airliners more and more efficient. • Reducing the total drag of an aircraft allows it to travel faster and use less fuel. • Aeronautical engineers know that air resistance is a real drag!

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