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Lecture X:
Wind Factors
AIRCRAFT WEIGHT &
PERFORMANCE
Wind
Understanding Wind
• Wind is defined as the horizontal movement of air relative
to the earth's surface.
• Airplane speeds up or slows down according to the speed
and direction of the wind.
• Since a flying airplane is suspended in the air, the air can
be considered to be still and the plane moving, but since
the aircraft has to go front one ground location to another
the wind speed and direction effect how the airplane is
flown
• Thus, changes on wind speed and direction has a marked
impact on aircraft performance.
Understanding Wind
• In terms of direction, three types of wind are Head
Wind, Tail Wind & Cross Wind.
• Other types are wind also included Wind Shear &
Jet Stream.
Wind Direction
Headwind
• Head wind refers to the wind blowing opposite to
aircraft motion.
Tailwind
• Tail wind refers to wind blowing along aircraft
motion.
Crosswind
• "Crosswind" is the wind component at right angle
to the flight path, causing an aircraft to drift either
to the left or right of the intended path.
Wind
Wind Shear
• Wind shear is a sudden change in wind speed and direction
will cause the plane to lose or gain airspeed and ground
speed instantly.
Jet Stream
• The term "jet stream" is often used to describe the general
flow of upper atmospheric winds. But it has a specific
meaning of upper atmospheric winds blowing faster than
57 mph. Jet streams play a key role in the weather by
steering storms and also helping determine where storms
form. Usually, when meteorologists talk about "jet stream"
winds, they're talking of winds more than 20,000 feet
above the ground
Wind Speed and Aircraft’s Speed
• Wind speed is the speed of wind, the movement of air or
other gases in an atmosphere.
• It is the average velocity at which the air travels over a
one-minute period and is measured in nautical miles per
hour (NM/H or knots).
• Aircraft’s speed is the speed of an aircraft. It can be
measured based on ground or air around it.
• The speed of the aircraft relative to ground over which it is
flying is referred as GROUND SPEED.
• The speed of the aircraft relative to the air around it is
referred as AIRSPEED.
relationship between ground
speed, airspeed, and wind speed
• Ground speed (Vground), is air speed (Vairspeed), plus or
minus wind speed (Vwind) relative to the direction the
aircraft is traveling
• Based on above equation, obviously seen that the changes
of wind speed and direction will affect the aircraft’s ground
speed.
• For example, if the wind blows in the opposite direction as
the plane's motion, Vwind will be a negative number.
• Thus, to calculate ground speed just subtracts the wind
speed from the airspeed.
relationship between ground
speed, airspeed, and wind speed
• Flying directly into the wind (head wind) will cause the
ground speed to be slower than the airspeed. If you are
flying 100 mph into a 20 mph headwind, your ground
speed will be 80 mph.
• Flying with a wind from behind (tailwind) will cause the
ground speed to be faster than the airspeed. If you are
flying 100 mph with a 20 mph tailwind, your ground speed
will be 120 mph.
How does wind affect
aircraft performance?
Wind Effect
• Referred to as wind effect, the speed and direction of the
wind will alter the progress of any aircraft in flight.
• Before each flight the pilot gets forecasted wind speed and
direction to determine the estimated compass heading and
ground speed of the aircraft.
• Although an aircraft has its own engine power, the pilot
must compensate for the wind speed and direction, in
order for an aircraft to maintain the performance &
desired course.
• This is because the changes of wind has a direct effect on :
• LIFT Produced By The Wings
• The SPEED of an airplane.
Wind Effect on LIFT Produced By
The Wings
• Wind speed and direction can affect the lift produced
by a wing.
• Let say, for take-off, airplane need to generate excess lift to
become airborne.
• Note that, airplane’s wing can only create lift if air is
moving over it (headwind).
• Referring to lift equation L=Cl½ρV²S , clearly seen that
the Lift force depends on the square of the airplane speed
relative to the air (Vairspeed) .
• Remind again, take-off with headwind will reduce ground
speed, which in turns reduce the take-off distance but still
move with required take-off speed. This is reason why
airplane require headwind for take-off.
• Head wind conditions also important during climb, descent
and landing.
• This is because headwind will increase climb
angle/descent angle and cause shorter take-off/landing
distance while reduce ground speed.
Wind effect during take-off
• Headwind will increase the airplane performance by
shortening the takeoff distance and increasing the angle of
climb.
• However, a tailwind will decrease performance by
increasing the takeoff distance and reducing the angle of
climb.
Wind effect during landing
• A headwind will increase airplane performance by
steepening the approach angle and reducing the landing
distance.
• A tailwind will decrease performance by decreasing the
approach angle and increasing the landing distance.
• Again, the pilot must take the wind into consideration
prior to landing.
Wind detector
Wind sock and AWOS: Indicate wind direction & speed
to guide pilot determine the correct runway to use for
landing and take off
Wind Sock
Automated Weather
Observing Systems
(AWOS)
Wind Effect on Airplane’s Speed
• Wind speed and direction also can affect the speed of
the airplane especially during cruise.
• Let's assume that the aircraft's cruise speed, or its speed
relative to the local air, is 500 mph.
• Let us also assume that the plane is traveling in the same
direction as the wind such that it experiences a tailwind of
100 mph.
• Since the wind and vehicle both move in the same
direction, their velocities add together, and the ground
speed becomes 600 mph.
Effect of tailwind on ground
speed
Wind effect during Cruise
• A tailwind will increase performance by increasing the
ground speed, which in turn reduces the fuel requirement
for the flight.
• A headwind will decrease performance by reducing ground
speed, which in turn increases the fuel requirement for the
flight.
Effect of headwind on ground
speed