航空专业英语教学课件：Principles of Flight

1、PRINCIPLES OF FLIGHTObjectives Airfoil design characteristicsFour forces in flightWingtip vortices and precautions to be takenLoad factors in airplane designAirplane stability and controllabilityAirfoil design characteristicsWing is a low drag device shaped to get a positive pressure lifting action

2、from below and a negative pressure lifting action from aboveDrag on a hand or carAirfoil design characteristicsAir molecules are stationary and were moving through itTwo neighbor molecules want to end up next to each other at the trailing edge of the wingThe on going over the top has to move fasterB

3、ernoullis principleWhen a fluids velocity increases, pressure decreasesWing is basically half of a venturiLow pressure above the wing, high pressure belowAirfoil design characteristicsChord line runs from the leading edge to the trailing edgeAngle of attackCamber is the curvature of the wingGenerall

4、y, the upper half is more curved than the lowerCamber line is where all distances on either side of the line are equalFour forces in flightThrustLiftDragWeight The sum of all upward forces equals the sum of all downward forcesThe sum of all forward forces equalsthe sum of all rearward forcesThrust F

5、orward force produced by the powerplant and propellerThrust must be exerted in order for the airplane to moveThrust To maintain a constant airspeed, thrust and drag must be equalIf in level flight, the engine power is reduced, thrust decreases and the airplane slows downIf thrust is less than drag t

6、he airplane will decelerate until its airspeed is insufficient to support itThrust If in level flight, the engine power is increased then thrust increases and airspeed increasesAs long as thrust is greater than drag, the airplane will accelerateThrust and AOAStraight and level flight can be sustaine

7、d at speeds from very fast to very slowMust coordinate angle of attack and thrust in order to hold level When airspeed is low, what must we do with our angle of attack to maintain level flight?Increase angle of attackWhy?Thrust and AOAWhen airspeed is low, AOA must be relatively high to increase lif

8、tIf thrust decreases and airspeed decreases, lift becomes less than weight and the airplane descendsDuring straight and level flight, if thrust is increased, what must we do to our AOA?Decrease it If we increase thrust without decreasing AOA, the airplane will climbMust decrease AOA to keep lift equ

9、al to weightWeight The combined load of the airplane itself, the crew, fuel, and cargo or baggageWeight pulls the aircraft downward because of gravityOpposes lift and acts vertically downward through the airplanes center of gravityWeight If in stabilized level flight, when lift is equal to weight, t

10、he airplane wont gain or lose altitudeIf lift becomes less than weight, the airplane loses altitudeIf lift is greater than weight, the airplane gains altitudeLift Produced by the effect of the air acting on the wingOpposes the downward force of weightL = 1/2 V2CLSWhich of these variables can we chan

11、ge?Angle of attackAirspeed Lift Any time you move the control column fore or aft, the angle of attack changesAs angle of attack increases, lift increases with all other factors being equalProportional to the square of the airplanes speedAn airplane traveling at 200 knots has 4 times the lift as the

12、same airplane going 100 knots if the angle of attack and other factors remain constantLift Plane cant stay at a constant altitude and keep the same angle of attack if speed is increasedLift would increase and the plane would climbTo maintain the balance of lift and weight if speed is increased, what

13、 must we do?Decrease angle of attackFor every angle of attack, theres a corresponding indicated airspeed required to maintain unaccelerated flightDrag A rearward force caused by disruption of airflow by the wing, fuselage, and other protruding objectsOpposes thrustWhat kinds of drag do we have?Induc

14、edParasite Total drag = induced drag + parasite dragParasite drag Form dragBased on the size and shape of the plane, how well streamlined and amount of frontal areaParasite dragSkin friction dragCaused by friction between a fluid and the body of the surface moving through itParasite dragInterference

15、 dragWhen airflow around different parts of the plane interact with each otherInduced dragResult of creating liftWingtip vortices wash over the wing effectively bends the lift vector backwardsInduced dragDecreases with airspeedThe lower the airspeed, the higher AOA needed to produce liftHigh AOA mea

16、ns lots of liftBig pressure differentialBig wingtip vorticesLots of dragWingtip vorticesSpanwise flowHigh pressure air hits the bottom of the wing and moves out to the tipLower pressure at the root due tohigh AOAAir goes from higher low pressure tolower low pressureHigh pressure tries to go to low w

17、hich results in wingtip vortices and the path of least resistance is the wingtipIn order to create lower pressure and lift on top of the wing, it needs to be at a higher angle of attackCauses a greater pressure differential and stronger wingtip vorticesPlane has the worst wingtip vortices when its h

18、eavy, clean, and slowWhen does this occur?Why heavy, clean, and slow?Avoiding wingtip vorticesTakeoff before the plane in front of you and climb out on a steeper pathLand after the plane in front of you and come in on a higher glide pathVortices sink so avoid themA light quartering tailwind will kee

19、pvortices on a runway so be careful ifthis condition existsWhat else can we do to reducewingtip vortices?WingletsInterrupt wingtip vorticesCan increase fuel efficiency at high speeds by 16-26%Induced dragGround effectReduced downwash means less induced dragCan fly at a lower AOA because vertical com

20、ponent of lift moves forwardLift increasesGround effectWhen the airplane is near the ground, we get what is called “ground effect”Ground disrupts wingtip vortices which reduces downwashGround effectFeels like a cushion of airYoull notice ground effect when the airplane is within one wingspan of the

21、groundLoad factors in airplane designLoad factor is the ratio of the total load action on the airplane to the gross weight of the airplaneA load factor of 3 means the total load on the planes structure is three times its gross weightManeuvering speedMaximum speed where full, abrupt control movement

22、in the pitch axis will result in an aerodynamicstallof the aircraft prior to exceeding the design load limitVA2 = VA W2 / W1VA2 = Maneuvering speed (at this weight)At 2550 lbs, VA is 105 knotsWhat is VA at 2300 lbs?99 knotsLoad factor increases with bank angleAs we turn, lift gets split into 2 compo

23、nents: vertical and horizontalIn order to maintain altitude, we must keep the vertical component of lift the same as it was in straight and level flightHow do we do this?Equal and oppositereactionLoad factor increases with bank angleAirplane stability and controllabilityControllabilityThe capability

24、 of an airplane to respond to the pilots inputStabilityThe inherent quality of an airplane to correct for conditions that disturb its equilibriumThe tendency to return to equilibrium2 kinds of stabilityStatic Dynamic Static stabilityThe initial tendency the airplane displays after its equilibrium is disturbedStatic stabilityPositive static stabilityThe tendency to return to the original state of