Slide 1

Steady Gliding Flight (Un-powered)

Slide 2

Descending (the Glide)What is the descent???

Slide 3

Descending (the Glide)• In a power-off, or gliding descent thrust is reduced to zero. • Weight, Lift and Drag are balanced.• Weight is balanced by the resultant of lift and drag.• Potential energy is converted to kinetic energy.

Slide 4

Power-off descent (Glide)In the power-off descent,

SinWD

CosWL

T

0

Slide 5

Power-off descent (Glide)

• Example: An aircraft weighing 30,000 N descends with engines off at a glide angle of 3°. Find the drag and lift components that act during the glide.

Glide Angle•Equilibrium glide angle can be calculated by

•The glide angle is strictly a function of the lift-to-drag ratio•The higher the L/D the shallower the glide angle.

DL

Tan

L

D

Cos

SinTan

1

Glide Angle

Slide 7

Gliding Range

•Distance is maximum when gliding angle is minimum

•Maximum L/D gives maximum range•L/D depends only on AoA and Maximum L/D is obtained at minimum drag speed.•Max distance will be at H x L/D (Max)

D

L

TanH

R

R

H

Cos

SinTan

1

Slide 9

Rate of Descent

• V= glide velocity• Vs=rate of descent

SinSC

CosWV

SinVVHowever

SC

CosWV

CosWSVCL

Ls

s

L

L

2

,

2

2

1 2

Airspeed on Gliding Distance

Slide 10

Slide 11

Gliding endurance

• For maximum endurance - rate of descent should be minimum

• Minimum power speed under straight & level conditions.• For max endurance Vs must be min.• the minimum power required (maximum endurance) occurs

when is a maximum.

Slide 12

Effect of Weight on Gliding Performance

• The speed at which best L/D varies with the weight.• Increase weight will need to increase required speed.• At heavier weight, it will glide faster.

Slide 13

Effect of Wind on Gliding Performance

• The only factor which affects the gliding angle and so the gliding distance.

• The aircraft with tail wind descends with higher groundspeed than the aircraft which is descending into the wind or in the still air so travels further while descending at the same rate.

• When the aircraft’s flaps are lowered the L/D will be less than with the ‘clean’ wing. Therefore, the glide ratio will be less and the glide path will be steeper.

Slide 14

Effect of Wind on Gliding Performance

Slide 15

Slide 16

Formulae