AE 1350 Lecture Notes #10

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# AE 1350 Lecture Notes #10 - PowerPoint PPT Presentation

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

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.
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.

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)

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)

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

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

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.