Transcript Week 7 Lecture

AVAT11001: Course Outline
1. Aircraft and Terminology
2. Radio Communications
3. Structure, Propulsion, Fuel Systems
4. Electrical, Hydraulic Systems and Instruments
5. Air Law
6. Aerodynamics: Basics
7. Aerodynamics: Performance
8. Human Factors
9. Meteorology
10. Loading
11. Take-off and Landing Performance
12. Navigation
Stuff to read
• Required Reading: BAK Chapter 6, pp.
196-228
Questions from the Reading
1. How does a pilot enter a climb?
2. What causes stall?
3. Why must the pilot not use the ailerons
during the stall recovery?
4. What is a steep turn?
5. Why is it generally unwise to close the
throttle before commencing the landing
flare?
Climbing
• If you wish to gain altitude, you should:
– Increase power
• A climb at a given airspeed requires more thrust than level
flight at the same airspeed
– Increase attitude
• When thrust is increased it can have 2 effects: it will increase
airspeed and/or it will increase altitude. You can use the
pitch attitude to hold a given airspeed and let the thrust
increase altitude
– Trim
• Once you are established at the airspeed and climb rate you
desire, you can use the trim controls to relieve the amount of
force you need to apply to the control yoke
The Physics of Climbs
• Forces
– See Figure 6-61 page 197
– During a steady climb, the forces are balanced (they sum to
zero)
• Velocity is constant, it just contains an upward component
• Potential energy is increasing, this requires power
• Power
– See Figure 6-65 page 199
– Power is thrust multiplied by velocity
– Power can be used to change the energy of the vehicle
• It can be used to increase the kinetic energy (= ½mv2) by increasing
velocity
• It can be used to increase the potential energy (= mgh) by
increasing altitude
Airspeed
• There are different airspeeds used for climbing
• See Figure 6-60 page 196 and Figure 6-65 page
199
– Vx, the best climb angle speed
• This speed occurs when you have the most excess thrust.
• You get the most altitude gain for the least horizontal
distance covered
• If thrust is much greater than weight, you can climb vertically
(no horizontal distanced covered)
– Vy, the best climb rate speed
• This speed occurs when you have the most excess power
• You get the most altitude gain in the least amount of time
Descent
• If you wish to lose altitude, you should:
– Decrease power
• A descent at a given airspeed requires less thrust than level
flight at the same airspeed
– Decrease attitude
• When thrust is decreased it can have 2 effects: it will
decrease airspeed and/or it will decrease altitude. You can
use the pitch attitude to hold a given airspeed and let the
thrust decrease altitude
– Trim
• Once you are established at the airspeed and descent rate
you desire, you can use the trim controls to relieve the
amount of force you need to apply to the control yoke
The Physics of Descents
• Forces
– See Figure 6-69 page 201
– During a steady descent, the forces are balanced (they sum to
zero)
• Velocity is constant, it just contains a downward component
• Potential energy is decreasing
• Power
– The power required for a descent is less than the power required
for level flight
– This is not shown on the power required figure, but you can
understand that it takes no power for a rock to fall from the sky.
– As you descend, you must be careful to not let your speed
become too great
• The potential energy lost by descending will be converted into
kinetic energy unless you take action to balance the forces
velocity
Turns
• To cause an object to turn, a
force must be applied
perpendicular to the velocity of
the object
• Think of a ball on a string
desired
path
force
required
to turn
– To swing the ball in a circle, the
string needs to apply a force in
towards the centre of the circle
• For aircraft, this force is
supplied by banking the wings
and using a horizontal
component of the lift force
– See Figure 6-76 page 205
velocity
force
required
to turn
Steep Turns
• Turns are classified by the amount of bank angle used
– Medium level turn: level flight with a 20° to 30° bank angle
– Climbing turn: during a steady climb, keep the bank angle 15° or
less to maintain the climb rate
– Descending turn: keep the bank angle 30° or less to avoid high
descent rates
– Gliding turn: keep the bank angle less than about 30°
– Steep turn: a turn of 45° or more
– Maximum rate turn: a turn which will change your heading as
quickly as possible. Only used in emergency situations, like
collision avoidance
• The greater the bank angle, the more difficult it is to
maintain level flight in a turn
– See Figure 6-88 page 215
Stalls
• Stalls occur when the angle of attack exceeds
the critical stall angle
– See Figure 6-21 page 179
• Most aerofoils have the property that the lift
coefficient, CL, increases as the angle of attack
increases.
• Eventually, the airflow over the top of the aerofoil
will separate and lift will be lost.
• This will occur at a specific angle of attack that is
a function of the shape of the aerofoil
Stall Speed
• The speed at which a stall will occur is a function of
many variables
–
–
–
–
–
Weight
Load Factor
Bank Angle
Power
Flap Setting
• When stall speeds are calculated for aircraft operating
manuals they often assume the worst case to produce
conservative numbers
– Often you can fly below the listed stall speed without stalling.
Especially if you have power on and are below the maximum
weight
– You may still manage to stall the aircraft above the listed stall
speeds. Especially if you have a high load factor (i.e. during a
steep level turn)
Spins
• Spins are complex aircraft motions in which all of the
following occur:
–
–
–
–
–
Rolling
Yawing
Pitching
Slipping
Rapid descent
• They are usually caused when one wing stalls before the
other
• To recover from a spin:
–
–
–
–
–
Centre the controls
Close the throttle
Apply full rudder opposite to the direction of the yaw
Apply forward pressure until the rotation stops
Recover from the dive (gentle aft pressure on the control yoke)
Spiral Dives
• Spiral dives occur when the aircraft begins to bank. If
you bank the aircraft and make no power or pitch
changes, you will begin to descend. As the descent
begins, the aircraft speeds up and the turn tightens.
• Spiral dives are very different from spins
– Spiral dives begin slowly, usually starting from high speeds
– Spins begin suddenly, usually starting from slow speeds
• To recover from a spiral dive, roll the wings level
– The danger of the spiral dive comes from a pilot noting a high
descent rate and pulling back on the controls. This only tightens
the dive and makes things worse if you do not level your wings
first.
For next week…
• Required Reading: BAK Chapter 8, pp.
247-284