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