Langley Flying School Private Pilot Groundschool Manual Sample ...

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Private and Recreational Pilot Groundschool Manual Page 50Langley Flying School, Inc.StallsStalls occur at the critical angle of attack, at which point the airflow over the wing becomes chaotic and the wingscan no longer produce sufficient lift to counteract weight.As the airfoil approaches the stalling speed, the point of transition, or separation point, moves forward enough toexceed the design factor of the wing.The stalling angle is usually 20. Since most aircraft lack angle-of-attack indicators, airfoil angle is measured byindicated airspeed (IAS).As a rule, aircraft will usually stall near the stalling speed published in the Pilot Operating Handbook (bottom ofgreen line on an Airspeed Indicator); however, IAS does not always indicate angle of attack, as in the case of a highspeedstall.Factors that affect the StallSnow, frost, ice and dirt:All of these disrupt the laminar flow and therefore reduce airfoil lift capability. It is illegal to fly with snow, frost, orice adhering to “critical surfaces” of the aircraft 27 — “wings, control surfaces, rotors, propellers, horizontalstabilizers, vertical stabilizers or any other stabilizing surface of an aircraft.” Contamination to the extent ofmedium to coarse sandpaper will reduce lift by 30% and increase drag by 40%.ABC of GlocationForward C of G requiresgreater tail-loading,increasing aerodynamicweight. Total lift requiredis therefore increased.C of GlocationRearward C of G requires less tail-loading,decreasing aerodynamic weight. Total liftrequired is therefore decreased.If both aircraft are traveling at 100 KTS, Aircraft Amust have a higher angle of attack than Aircraft B.Aircraft A is therefore closer to the critical angle ofattack and therefore has a higher stalling speedWeightIncreased weight requires increased lift; therefore thecritical angle of attack (stall) will occur at higherairspeeds. Stated another way, if two aircraft aretravelling at the same airspeed, but one is heavier thanthe other, the angle of attack of the heavier aircraft isgreater than the lighter aircraft and therefore that muchcloser to the critical angle of attack.Centre of GravityStalling speed increases as the aircraft C of G movesforward. As the C of G moves forward, the negativelift generated by the horizontal tail surface will have tobe increased. Any increase in the negative liftproduced by the tail will effectively increase theaerodynamic weight of the aircraft—producing thesame effect as described above with respect to weight.Conversely, stalling speeds decrease as the C of Gmoves aft as less negative lift is required from the tailand the aircraft is aerodynamically lighter. While thebenefits of a rearward C of G is a lower stall speed, theadverse result of a rearward C of G is less stability asthere is less tail force that can be manipulated by thepilot through elevator or stabilator control. 28TurbulenceUpward vertical gusts abruptly increase the angle ofattack beyond the stalling angle, irrespective ofairspeed.27CAR 602.1128 Additional discussions of this appear on P. 93.© 2012 David L. Parry
Private and Recreational Pilot Groundschool Manual Page 51Langley Flying School, Inc.Angle of Bank in Level Flight0 o Bank 20 o Bank 40 o Bank 60 o Bank 80 o BankLoading: 1.0 g Loading: 1.06 g Loading: 1.31 g Loading: 2.0 g Loading: 5.75 gAerodynamic Weight:2000 lbs.Stall Speed: 55 KTSAerodynamic Weight:2100 lbs.Stall Speed: 56.6 KTSAerodynamic Weight:2620 lbs.Stall Speed: 63 KTSAerodynamic Weight:4000 lbs.Stall Speed: 78 KTSAerodynamic Weight:11,500 lbs.Stall Speed: 132 KTSTurnsLIFTWEIGHTDuring a turn in level flight, greater lift is required tooffset increased effective aerodynamic weight of theaircraft in the turn. Because the angle of attack of anaircraft must be increased to offset the increasedaerodynamic weight (resultant force of a turn), the wingis closer to the critical angle of attack and therefore closerto a stall, despite a constant airspeed. Accordingly, thereis an increase in the relative stall speed of an aircraft in alevel turn. The formula to determine increased stallspeed is as follows: normal stalling speed times thesquare root of the load factor equals banked stall speed.Thus, an aircraft with a stall speed of 50 KTS and in a60-bank turn (load factor of 2.0) will stall at 71 KTS.FlapsLIFTWEIGHTVERTICALCOMPONENT OF LIFT(effective lift)CENTRIFUGALFORCERESULTANTFORCEAn increase in airfoil lift isproduced by the use ofSimple Flapflaps, and the stall speed isdecreased by their useSlotted Flap(bottom of white line on anAirspeed Indicator). TheSplit Flapextension of flaps has theeffect of increasing therelative angle of attack ofFlowler Flapthe airfoil. Induced drag isalso increased. Some flap designs incorporated slots,which permit the compressed air under the wing tomigrate through the slot to the upper surface of the flaps.These are referred to as slotted flaps. Some flap designsallow the flap surface to move rearward as it extends—the feature is referred to as a Fowler Flap.SpinsSpinning is defined as autorotation that develops after an aggravated stall (a wing dropping during a stall).The downward moving wing has a higher angle of attack and more induced drag than the upward moving wing andtherefore acquires a greater stalled condition. Spinning involves simultaneous roll, yaw and pitch as it develops ahelical or corkscrew path nose down.An incipient spin is the autorotation prior to a vertical descent path, while a fully developed spin begins once the© 2012 David L. Parry
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