Take-off and Landing Flashcards
Name the four stages of take-off
Ground run
Rotation
Flare
Initial climb
What happens during ‘ground run’
When the a/c accelerates from rest to rotation speed, Vr
When this is happening, assume a/c attitude, Cl and Cd are constant
What is the a/c attitude
other way of saying angle of attack
What happens during ‘rotation’
a/c is rotated to increase the angle of attack and Cl until lift exceeds weight.
the a/c is still in contact with the ground and just elevates its nose upwards
What happens during ‘flare’
a/c follows a circular arc to change the climb angle from zero to desired climb angle
What happens during ‘ initial climb’
a/c climbs at a steady angle and speed until it clears the screen height
What is the screen height and what is its typical value
the height at which the a/c needs to climb so as to clear obstacles around the air field.
typically 15 metres
Name the forces acting on the plane during ground run
Ground friction, drag, lift, reactant force from the ground, weight, thrust
State the relationship between Thrust and velocity
T = To - k(V^2)
T - thrust
To - static thrust
k - constant
V - velocity
Equation to calculate ground run
given in exam
x = - 1/2B * ln(A / A + B(Vr^2))
x = distance B = constant calculated A = constant calculated Vr = rotation speed
A =
(To - μmg ) / m
B =
K + 0.5 p S (Cdg - μClg)
- ———————————–
m
Which is the largest stage of take-off
ground run
What is assumed during ‘rotation’ and how does this allow a simple calculation to be made to find distance traveled in this take-off stage
The a/c angle of attack is assumed to rotate at 3 degrees per second. The desired angle of attack is usually 12 degrees and so it is said that rotation takes 4 seconds. Knowing this and the speed of the a/c, distance traveled can be measured.
Equation to find distance traveled during ‘ rotation’
x2 = Vr * 4
Vr - Velocity at rotation
4 - time taken in seconds for rotation to take place
What is said about Cl at the end of the rotation
Cl = Cl - unstick
which is then assumed to stay constant during flare and initial climb
What type of acceleration does an a/c experience during the ‘flare’ maneuver’
Centripetal acceleration. This is normally quoted as a gravitational factor.
e.g. Δ n*g
Δ n is normally around 0.2
How is the centripetal acceleration calculated during ‘flare’
Vr^2
Δ n*g = ———-
R
Equation for calculating distance traveled during ‘flare’
x3 = R*sinθ
or is θ is small ….
x3 = R*θ
Equation for distance traveled during initial climb
given in exam
hs - R( 1 - cosθ)
x4 = ————————
tanθ
where:
hs - screen height
R - radius of circle taken during flare
θ - angle of attack
Name the four stages of landing
- Approach
- Flare
- De-rotation
- Ground run
Things to bare in mind with landing
- Distances more affected by pilot technique
- Coefficient of friction includes rolling and braking
- Friction much more affected by weather
- Deceleration limited by passenger comfort
- Brakes and reverse thrust have delayed action
