Transcript Week 6 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.
169-195
Sir Isaac Newton
• Newton was one of those really brilliant types born in the
1600’s (mathematician, scientist, all around smart guy)
• He came up with some general rules about the way
objects move about and today these are called Newton’s
Laws of Motion
– 1st Law: An object in motion will remain in motion and an object
at rest will remain at rest unless it is acted upon by an external
force
– 2nd Law: Force is proportional to the time rate of change of
momentum
• Momentum is mass times velocity: p = mv
• If mass is assumed to be constant, Newton’s 2nd can be written: F =
ma
– 3rd Law: For every action, there is an equal and opposite reaction
• These 3 laws are used by scientists and engineers today
to explain many physical phenomena, including how
aeroplanes fly
Forces
• Forces push and pull on objects and
change their accelerations
– When you push against a box, you are
exerting a force on the box, causing it to
accelerate
Moments
• Moments occur when the force does not act through the
point of rotation of the object. As a result, there is a
twisting motion produced by the force
– Moments are also called torques. When you apply a force to the
end of a wrench, you will create a torque to turn the bolt
– The greater the distance between the point of application of the
force and the point of rotation, the greater the moment produced
– Unconstrained objects, like aircraft, rotate about the centre of
gravity
Force
Moment
Vectors
• Forces and moments are what is known in
mathematics as vector quantities
– Vectors have magnitude and direction
– Typically, they are represented as arrows
• For moments, the direction of the arrows follows
the “right-hand rule”
– If you point the thumb of your right hand in the
direction of the moment, the fingers of your right hand
point in the direction the twisting occurs
Direction of moment
Direction of twist
Forces Acting on Aircraft
• Weight
– Magnitude is proportional to mass
– Direction is toward the centre of the earth
• Lift
– Magnitude is proportional to dynamic pressure
– Direction is perpendicular to the relative wind
• Drag
– Magnitude is proportional to dynamic pressure
– Direction is parallel to the relative wind
• Thrust
– Magnitude is a function of throttle settings
– Direction is typically fixed relative to the airframe
• Side Force
– Magnitude is proportional to dynamic pressure
– Direction is perpendicular to lift and drag
• See Figure 6-4 page 173
Moments Acting on Aircraft
• For balanced flight, the sum of the moments is zero
• The flight control surfaces are used to generate
moments so the aircraft can turn
• Pitch Moment
– This rotates the aircraft about an axis that runs through the wings
causing the nose to move up and down
• Roll Moment
– This rotates the aircraft about an axis that runs from the nose to
the tail causing the wings move up and down
• Yaw Moment
– This rotates the aircraft about an axis that runs vertically through
the aircraft causing the nose to move left and right
• See Figure 6-5 page 173
Airfoils and Lift
• Airfoils generate lift by altering the airflow
to create lower pressure on the upper
surface than on the lower surface
– This results in a net force
– See Figure 6-6 page 174
• Terminology
– See Figures 6-15 and 6-16 page 177
– Understand all the terms used in these
Figures
Various angles and what they mean
• Angle of attack, Alpha, a
– This is the angle between the chord line and the relative wind
• Pitch attitude angle, Theta, q
– This is the angle between the chord line and the horizon
• Flight path angle, Gamma, g
– This is the angle between the relative wind and the horizon
•
a+g=q
chord line
chord line
q=5
a=8
horizon
relative wind
chord line
horizon
horizon
g = -3
relative wind
relative wind
Drag
• Drag is the force that is resisting the
aircraft movement
• It has several sources and there are
different types of drag
– Induced drag
– Form drag
– Skin friction drag
– Interference drag
Drag and L/D
• Minimum Drag
– See Figure 6-37 page 186
– Note that the minimum drag does not typically occur
at the lowest flight speed
• Best Lift-to-Drag ratio
– See Figure 6-40 page 187
– The angle of attack which gives the best L/D makes
the most efficient use of the airframe
– This is the angle of attack you would use if you lost
power to give you the best glide range
Inceptors and Effectors
Inceptor
Effector
Primary Effect
Secondary Effect
Control
Column/Stick
Forward/Aft
Elevator or
Stabilator
Generates pitch
moments to change
attitude
Changes flight path angle
and velocity
Control
Column/Stick
Right/Left
Ailerons
Generates rolling
moments
Also produces some yaw
moments
Rudder Pedals
Rudders
Generates yawing
moments
Also produces some roll
moments
Throttle lever
Throttle valve
Changes fuel flow to
alter thrust
Often will also produce a
pitch moment, will change
airspeed and flight path
angle
Mixture lever
Mixture valve
Changes fuel-to-air
ratio altering engine
efficiency
Changes engine power and
engine cooling
Flap lever
Flaps
Deploys flaps to
Increases drag and changes
increase lift by
the stall angle of the wing
changing wing camber
Balance and Trim
• Balance is when the sum of forces and moments
on the aircraft is zero
– From Newton’s 1st Law of Motion, this means the
aircraft will “remain in motion”. It will continue to
move as it is moving, without changing its speed or
flight path.
• Trim is when the aircraft is balanced and the
pilot does not need to exert forces on the
controls
– Many aircraft are equipped with trim wheels or knobs
that move small pieces of the primary control
surfaces. These small pieces, sometimes called “trim
tabs” exert force on the control surface to hold it in
place. See Figure 6-54 page 193
Straight and Level
• Straight and level flight means that you are not
turning and your flight path angle is zero
– Steady, Straight, and Level (SSL) means that you are
not accelerating either (not changing speed)
• If you wish to change your airspeed while
maintaining level flight, you will need to change
your pitch attitude and angle of attack
– See Figure 6-57 page 194
Flight path control
• Most aircraft do not have a single inceptor to
directly control flight path angle
• Instead, flight path angle and velocity are
controlled by using power and pitch attitude
• Typical pilot technique:
– Use power to control airspeed
– Use pitch attitude to control flight path
• As you gain experience as a pilot, you learn how
to balance these two controls to get the desired
effects
For next week…
• Required Reading: BAK Chapter 6, pp.
196-228