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AE 1350 Lecture Notes #10

AE 1350 Lecture Notes #10. TOPICS TO BE STUDIED. Take-off and Landing Performance There is considerable variations due to pilot technique ground conditions FAR 25 regulations cover how take-off and landing distances must be computed.

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AE 1350 Lecture Notes #10

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  1. AE 1350 Lecture Notes #10

  2. TOPICS TO BE STUDIED • Take-off and Landing Performance • There is considerable variations due to • pilot technique • ground conditions • FAR 25 regulations cover how take-off and landing distances must be computed. • In your design, estimate wing area S to meet specified take-off and landing distances.

  3. Takeoff Performance Theory We attempt to compute the ground roll as accurately as possible. Add an extra 20% distance to account for transition and climb. Rotate to take-off Transition and climb 20% of total takeoff distance, from experience Ground Roll 80% of total takeoff distance, from experience.

  4. Ground Roll Let v be the aircraft speed. dv/dt = a where a= acceleration of the vehicle a= (All horizontal forces acting on the aircraft) / (Mass of aircraft) Assume “a” to be a constant. Integrate: v = at Velocity at lift-off vLO = a tLO Integrate again: d = 1/2 a t2 dLO = 1/2 a t2LO = v2LO/(2a)

  5. Ground Roll (Continued) From the previous slide, the total roll distance is dLO = 1/2 a t2LO = v2LO/(2a) a = Acceleration of the aircraft due to horizontal forces on it. These forces are: Thrust, Drag, Ground Friction Thrust far exceeds the other two factors during takeoff. Thus, a = T/(Aircraft Mass) = T g/ (W) Then, total roll distance is dLO = v2LO/(2a) = v2LO. W/(2Tg)

  6. Ground Roll (Continued) Total roll distance dLO = v2LO. W/(2Tg) The pilot usually lifts off at 1.2 times stall velocity. Stall velocity VStall is defined from: 1/2 r V2Stall CLmax S= W V2Stall= W/(1/2 r CLmax S) v2LO =(1.2 VStall)2 = 1.44 W/(1/2 r CLmax S) Then, dLO = v2LO. W/(2Tg)= 1.44 (W)2 / (TgrS CLmax) Include factors of safety for transition and climb: Take-off Distance, in feet = 37.5 (W)2 / (TsS CLmax) = 37.5 (W/S) /[(T/W)s Clmax] where s = Density Ratio = r/rSea-Level,,W in lbs, S in square feet

  7. Landing Performance There is considerable scatter in landing distances due to use of spoiler, brakes, reverse thrust, human factors ground conditions : wet runway , dry runway

  8. FAR-25 RegulationsLanding Performance Vapproach=VA=1.3 Vstall for civilian aircraft Vapproach=VA=1.2 Vstall for military aircraft Vapproach=VA=1.1 Vstall for carrier based aircraft 50ft Ground Roll Total Landing Distance, in feet = 0.3 (Vapproach in knots)2 These results are empirical, because of variations in pilot technique.

  9. Lift Coefficients for your Design • For fighter design, use the following Clmax • With flaps up, 1.2 - 1.8 • With flaps down, during take-off: 1.4 - 2.0 • With flaps down, during landing: 1.6 to 2.6 • For transport design, use the following Clmax • With flaps up, 1.2 - 1.8 • With flaps down, during take-off: 1.6 - 2.2 • With flaps down, during landing: 1.8 to 2.8

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