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Aerodynamics Workbook

VIEWS: 31 PAGES: 46

  • pg 1
									                               Aerodynamics Workbook




   Aerodynamics Workbook
                                     Aviation 271
                                           R Preston
                                             2010




Study guide and assignments for Avia 271

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                                  Aerodynamics Workbook

Preface
This workbook supplements the text Aerodynamics for Professional Pilots. My hope is that you will use it
as part of your effort to build a coherent understanding of theory of flight that is satisfactory for a
college educated aviator.

This is a workbook – as such it is up to the reader to fill in the important concepts. The intent is that this
workbook will inspire deeper thought about how airplanes fly and why they are designed the way they
are.

This subject is one that can consume your mind totally for years and still leave you with only a partial
understanding of how airplanes fly. Fortunately you can fly quite effectively only knowing what happens
and not why it happens, but humans like to explain things. Sadly many incorrect explanations have
become entrenched in flight training. Therefore the main objective of this course is to at least make you
aware that things do not work in the way intuition says and hopefully you will recognize incorrect
explanations in the future.

For those who want to actually understand how an airplane flies you must commit yourself to bringing
your understanding into line with Newton’s Laws. You must also commit to the fact that Physics is
universal and therefore your explanations must transcend airplanes and apply equally to all physical
systems. Therefore I recommend thinking not just about how airplanes fly but also about how bicycles,
cars, boats, trains, etc work. Explaining how a unicycle is ridden is a good challenge for your
understanding. Even something as simple as a child’s swing is instructive. If you limit yourself only to
explaining flight you will undoubtedly have to rely upon memorizing explanations presented to you by
others and run the risk that if the explanation is wrong you won’t realize it. That state of affairs is quite
possibly necessary if you lack either the time or inclination to think things through for yourself. But do
me one favor: if someone asks you why an airplane flies the way it does just tell them “I don’t know.”




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                                                   Aerodynamics Workbook

Table of Contents
Preface .......................................................................................................................................................... 2
Introduction .................................................................................................................................................. 4
The Atmosphere ........................................................................................................................................... 7
The Aerodynamic Force ................................................................................................................................ 8
Definition: Lift and Drag ................................................................................................................................ 9
The Lift Equation ......................................................................................................................................... 11
Forces in Climb and Descent ....................................................................................................................... 14
Stability and the entry to a climb ................................................................................................................ 18
Directional Stability and Turns .................................................................................................................... 24
Lateral Stability ........................................................................................................................................... 28
Stalls and Spins............................................................................................................................................ 30
Drag ............................................................................................................................................................. 33
Lateral Stability ........................................................................................................................................... 40
Longitudinal Stability .................................................................................................................................. 42
Directional Stability ..................................................................................................................................... 43
High Speed Flight ........................................................................................................................................ 44
Multi Engine Flight ...................................................................................................................................... 45




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                                  Aerodynamics Workbook


Introduction
To fly an airplane all a pilot actually needs to know is the observable consequences of manipulating the
flight controls. No theoretical knowledge is actually needed. However, Transport Canada requires that
pilots posses some theoretical knowledge.

I learned that the word “theory” has an important meaning:




I am committed to developing a theory that is consistent with the observable facts and consistent with
accepted scientific theories – in particular Newton’s Laws.

Newton’s First Law is:




I have learned that a rigid body always has two types of motion and these are:




I am committed to reminding myself, when I wonder why things happen, that these two motions are
completely and totally independent of each other. I know that often the two motions are closely
coupled, for example a car driving around a curve in the road is translating along a curved path while
rotating around its normal axis, but even though the two motions start and stop at the same time they
are independent and as such require independent explanations. I realize that the rotation in this
example is uniform and as such governed by Newton’s First law; but the translation is accelerated and as
such governed by the Second law.

Newton’s Second Law is:


The unit of force in this course will be the pound (lb)
                                                    2
The definition of a pound is: lb = slug x ft/sec




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                                  Aerodynamics Workbook

I learned that the laws of physics are universal. As such my understanding of how an airplane flies must
be consistent with how cars drive and boats float etc. If I try to visualize how a force affects an airplane I
will remind myself that it is wise to also ask how a similar force would affect other vehicles. An
inconsistency in my beliefs is a sure sign that I have slipped into a mistaken understanding.

I know that Newton’s Second law tells me that a force will accelerate an object. This is most obviously
apparent when the force acts directly at the objects center of gravity since the acceleration is purely in
translation. If the force is not precisely aligned with the center of gravity we say that the force has a
moment.

A moment is:




When a moment acts on a rigid object there will be a rotational acceleration, which means:




I must remind myself that when an object rotates at a constant rate it is governed by Newton’s First
law – which means there is NO MOMENT. Sometimes (often actually) this will compel me to explain
why there is no moment: two good examples of this are:

The front wheels of a car produce no “turning moment” when a car drives around a curve in the road,
because:




The ailerons on an airplane produce no rolling moment when an airplane rolls at a constant rate,
because:




When asked what turns an airplane, the fin or the elevators? I know that the answer is neither, despite

the intuitive appeal to the contrary, because to believe so would violate Newton’s ______________ law.



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                                  Aerodynamics Workbook

In everyday life when we say an object accelerates, we usually mean that its speed changes. But I
remind myself that the actual definition of acceleration is:

a = ∆V / t
Change in velocity is by definition:

∆V = V2 – V1
On the back of the facing page I have drawn a diagram that reminds me, and can be used to convince
others, that when a force acts perpendicular to the motion of an object it pushes the object around a
curved path. This is called a Centripetal force and the result is known as centripetal acceleration. The
formula is:

Aac = V2 / r

Fac = mV2 / r


Newton only gave us two laws, but he also gave us a principle that is so important that many people call
it the third law. The Third Law is:




The third law reminds us that if we “push” something it will “push back” Thus it is true that when the air
pushes up on our airplane the airplane pushes back down on the air. Consequently, if we could see the
air it would be travelling downward behind an airplane in flight since the airplane pushes as it passes by.

The Third law applies to moments as well as forces. For example when the engine applies a moment to
the propeller the propeller applies a moment back on the engine “twisting” it in the opposite direction.




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                                  Aerodynamics Workbook

The Atmosphere
I learned that the most important properties of the atmosphere in aerodynamics are

_____________________ and ______________________.




Air pressure comes in two types: Static and Dynamic

Static Pressure is:




Dynamics Pressure is:


Static pressure is the result of gravity affecting the atmosphere. At sea level ISA the static pressure of

the atmosphere is ___________________ lb /ft2.


                                                                            3
At Sea Level ISA the density of the atmosphere is 0.002378 slugs / ft




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                                    Aerodynamics Workbook

The Aerodynamic Force
Any solid object displaces (replaces) the air. When the object moves it leaves a “void” in the air that we

call a _________________. Even though this void fills in quite rapidly there is a small reduction in air

pressure in the volume that the object has just vacated.


I have drawn a diagram here of a ball moving through the air and I can use it to explain to someone why
an aerodynamic force forms.




Relative wind is by definition:




A wing is strategically designed so that the pressure drops more on one side than the other. I have
drawn a diagram below that I can use to explain to someone why a wing produces lift.




A ball can produce lift if it spins. This is because:




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                                 Aerodynamics Workbook

Definition: Lift and Drag
I know that Lift and Drag are components. As such this equation is true:



Lift + Drag =
Drag always acts parallel to the __________________ wind, which is the same as saying it acts opposite

to the _____________________


Lift acts perpendicular to the _____________________ wind and the true airspeed. As such is it true

that Lift is always _________________________ to drag.


The following force diagram shows TAS for an airplane in a 45° climb. I also drew in the aerodynamic

force and the lift and drag.




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                                  Aerodynamics Workbook

The diagram below shows an airplane at 4 specific points during a “perfect” loop. I have drawn in the lift
and drag vectors at each point.




I can explain why LF must change throughout the above loop.




At the entry point to the loop this airplane is accelerating upward at a rate equal to _______ g, which

means the vertical speed would increase __________________ ft/min each second.




55KEAS equals ____________________ ft/min. At one g this speed is reached in ____________ seconds.

If it takes an airplane 12 seconds to reach this speed on takeoff I can say it is accelerating at

___________ g. If the airplane weighs 2100 pounds thrust + drag must be _______________ pounds.




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The Lift Equation

The Lift Equation is:

L = CL x S x ½ ρV2

½ ρV2 is known as the _________________________.
The units of dynamic pressure should be _______________________________ in this course. In order to

get the desired unit Velocity must be in units of ______________________




If I multiply area x pressure I get: ___________________________

The symbol   S in the lift equation represents ________________________
The units of wing area are: ______________________

Coefficient of lift CL is unit less
In almost all cases the simplest way to use the lift equation is to take advantage of the concept of
equivalent airspeed (EAS)

EAS means:


To use EAS in the Lift Equation I must convert to units of ft/sec. To do this:




Any airplane (Cessna, Piper, or Beechcraft. etc) cruising at 100 KEAS experiences a specific dynamic
pressure, here is my calculation:




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                                  Aerodynamics Workbook

A jet cruising at Mach 0.8 at FL400 under ISA conditions has a true airspeed of ____________ KTAS,

which is an equivalent airspeed of _______________ KEAS, which is __________________ ft/sec. Here

is my calculation of the dynamic pressure (notice that I made sure to show the units)




My Cessna 172P Manual shows the wing area on page _____________. Wing area is __________ ft2.

Using the lift equation I completed the following table for a Cessna 172 at W = 2400lb.

Velocity (KEAS)      Velocity ft/sec      CL          AOA
       100

       90

       80

       70

       60

       51



The slope of the CL vs. AOA graph for an airplane with straight-wings is ________________

The slope of the CL vs. AOA graph for an airplane with swept-wings is less




When I look at the diagram of a loop (earlier in this book) I can calculate the required angle of attack for

a C-172 to enter this loop, it is _____________ degrees and at the top of the loop, where lift is zero, the

required angle of attack is ________________ degrees. On the up and down lines the lift is the same as




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                                   Aerodynamics Workbook

in cruise, which means ____________ degrees angle of attack. In no case does the airplane come close

to stalling.




Stall speed is defined as:




The lift equation can be re-arranged to find stall speed. The equation is:




Maneuvering speed is defined as:




The definition of Va is in the CARS, specifically:




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                                 Aerodynamics Workbook

Forces in Climb and Descent
The tilt table taught me the basic relationship between L + W + T + D in climbs and descents

I know that a scale doesn’t show the weight of the object on it, it actually shows _______________,

because it works based on Newton’s ________________ law.


In a climb:
Thrust is _______________________ than drag

And Lift is _____________________ than weight

In the case of a space shuttle at launch lift = _________________

and thrust equals ____________________ plus ___________________

In a descent:
Thrust is _______________________ than drag

And Lift is _____________________ than weight



To get an airplane to descend I must either reduce __________________ or increase _______________




In a climb or a descent velocity is uniform which means that climbs and descents are governed by

Newton’s _____________________ law.


I know that vertical speed and horizontal speed are components of True Airspeed. By component I
mean:




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                                Aerodynamics Workbook

This diagram explains the relationship: Vertical Speed + Horizontal speed = ________________




The diagram below started exactly like the one above except that I added Weight, Lift and Excess Thrust.

By Excess thrust I mean:




From the above diagram I can show that the two triangles are similar and as such the relationship
between excess thrust and vertical speed is:




Using the above I can say that for an airplane climbing at 75 KEAS and 500 ft/min and weighing 2400lb
the excess thrust must be:




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An airplane climbing at 75KEAS and 500 ft/min is achieving a climb angle of ______________ degrees.
The ratio:

VS/TAS = Sin(_________)
To use the above equation Vertical Speed (VS) must be converted to knots, this is done by:




The diagram below shows TAS, VS, and HS as well as L, W, and excess thrust for an airplane in a descent.




When a pilot pushes forward on the control column of an airplane in cruise it descends. The explanation
for this is:




Zooming means:




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                                 Aerodynamics Workbook

This diagram show the forces L + W + D in a power off glide. I also drew in TAS, VS and HS.




Using the above diagram I can prove that glide ratio equals L/D ratio. Here is my proof.




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Stability and the entry to a climb

To enter a climb or descent the velocity of the airplane must be changed – to be precise the direction of
flight must be deflected up or down respectively. To do this lift must be increased or decreased. This
change in lift is needed only for a few seconds, which exactly corresponds to the amount of time it takes
for the Vertical speed to change from zero to the steady value in the climb or descent.

I learned that an object falling at 1g reaches a velocity of _________________ ft/min in one second. By

comparison vertical speed in a C-172 typically changes at a rate between 150 and 200 ft/min/sec; that is

to say ~0.1g.


I know that an airplane such as the C-172 cruises at a typical CL of _____________ and thus to increase

lift by 10% the CL need only rise to ____________. This requires a change in angle of attack of only

_______________ degrees.




From the demonstration of the glider on the zip-line I learned that airplanes are longitudinally stable.

This means that the airplane will rotate to line up with the ___________________




When entering a climb the pilot increases the angle of _________________ slightly, which increases lift
as needed to change the velocity vector from level flight to the climb angle. The rest of the pitch-up to
the climb attitude is explained by:




Once established in the climb the lift needed is ____________ than weight, but the pilot must adjust the
angle of attack to match the desired climb airspeed. This is no different than in level flight.




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I understand that a C-172 cruising at 100KEAS and wishing to enter a climb at 75KEAS and 500 ft/min will
go through a series of angle of attack changes and lift changes; here is my full description of what
happens and what the pilots role is, as well as what the role of stability is:




To achieve the steepest possible angle of climb the necessary physics situation is:




                                Here is a graph showing Tx vs. Velocity




                                The 45° down-slope point would be Vy. I can explain this


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The thrust vector on most light aircraft passes quite close to the CG. On Cessnas it is almost right

through the CG, on low wing single engine airplanes the thrust vector is usually slight ______________

the CG.




If thrust vector is above CG is increased the result is a pitch moment that results in a ___________ angle

of ____________. The magnitude of the change is very small. Below I have drawn a diagram showing the

case of an airplane with thrust 4 inches above CG and the tail force 120 inches behind the Lift force. This

airplane has a leverage of ______________.




The above airplane has a stabilizer surface area of 30 ft 2. For above airplane if thrust is increased 150
pounds and speed is 80KEAS the angle of attack of the stabilizer would change _________ degrees. Here
are my calculations and notes about this:




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Because physics is universal the same forces acting on an airplane have the same results they would on
a car or bicycle. If someone is confused by the above explanation about how much the airplane pitches
and that it results in only a small change in angle of attack I will use the example of a car or motorcycle.
Here is a diagram showing how weight is transferred from the front wheels to the back wheels as thrust
is added.




I will also point out that a car only piches nose up and climbs when the road does. The same will be true
for an airplane. Ie. It will not pitch nose up until AFTER is starts to climb. I am well prepared to explain
why is starts to climb:




Induced lift happens with slipstream flows over the _______________. Twin engine airplanes have lots
of this, but many single-engine airplanes do as well, especially if they are low ____________.



Induced lift increases lift. The consequences of this induced lift on pitch attitude are (with my
explanation):




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On many single-engine airplanes the slipstream flows over the stabilizer. In such cases increased thrust
comes with increased airflow over the stabilizer. The consequences of this are:




To fully clarify my theory of how an airplane responds to application of thrust I predict that a jet fighter
with the thrust vector passing through the CG and no change in airflow over either the wing or tail
would behave as follows when thrust is increased:




My theory states that if slipstream flows over the wing and also over the stabilizer the response to an
increase in thrust would be:




My theory takes into account that lowering the gear adds drag below the CG and therefore I predict the
following results of lowering the gear:




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                               Aerodynamics Workbook

On most airplanes lowering flaps causes the nose to pitch __________________ and the airplane should
descend. The C-172 is an exception, my explanation is:




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                                   Aerodynamics Workbook

Directional Stability and Turns
Directional stability means:




The fin is the primary reason airplanes have directional stability. The fin prevents the airplane from

____________________.




An airplane placed in a banked attitude turns. Stabilities role in this is:




I remind myself that there are two motions going on when an airplane turns. One is accelerated and one
is not. One is governed by Newton’s first law and one by the Second law. Here is the full explanation:




If someone tries to convince me that the elevators are “turning the airplane” I will explain to them that

there certainly is a need to increase angle of _______________ in a turn because increased

_____________ force is needed. But I will explain that this is needed in order to generate centripitel




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__________________ toward the center of the turn. This however does not actually cause the rotation

of the airplane (which is what the word “turn” means.)




Aileron drag causes the phenomenon known as __________________________________



To counter it most airplanes have ___________________________ ailerons or ____________________
ailerons, or both.



Coordinating a turn means:




In a turn the outer wing flies faster than the inner wing. In level flight both wings would be an the same

angle of attack if the ailerons were neutral. If the speed difference is significant the result is a tendency

for the airplane to roll ____________________________ the turn. To counter this the pilot would need

to _____________________. If instead the pilot used the rudders to maintain bank the result would be

__________________________________




In a climbing turn an effect known as the spiral staircase effect tends to ___________________ the

angle of attack of the outer wing. If the pilot allowed this to actually happen the result would be

_________________________. The pilot prevents this by:




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In the diagram below I drew in Lift and Force of Centripetal acceleration (Fac). I also labeled the angle of
bank (b)




I know that weight and mass are related by the equation:

W =mg
Since I know that Fac is equal to mV2/r and from the diagram above it is also equal to _______________
I can set these two observations equal to each other and prove that:


Radius of turn =




The value of g in the equation is usually 32.1 ft/sec2, which means I have to convert speeds to ft/sec to

use the equation. The radius will come out in units of ________________



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Opposite is a diagram of an airplane flying a 360 turn at rate one. This turn takes ______________ hours
to complete.



I know that distance = Vt and in the case of a 360 turn it also equals 2πr. Setting these two equal to each
other and solving for radius I get:




In this equation Velocity can be entered in units of knots as long as time is in time units of
____________.



Consider this:

Time for a 360 = circumference of the circle / velocity

Circumference = 2πr

Substituting the equation for r I developed above here is the equation for time to make a 360:




Notice that one of the “V”s cancelled out. Thus time to turn is proportional to ______________ while

radius of turn is proportional to _________________________




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Lateral Stability
Airplanes have a lot less lateral stability than either longitudinal or directional. The reason is:




The designer of an airplane usually has to accept either spiral divergence or Dutch roll instability. Spiral
divergence is usually thought to be the lesser of these two evils. My explanation is:




This is how a spiral dive develops:




Airplanes have some combination of ___________________________, ______________________ or

_____________________________, which give them “dihedral effect.”




Because of dihedral effect the pilot can cause an airplane to _________________ by using the rudders.

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The ball in the Turn Coordinator is often called a slip indicator, however this is a poor name because the

airplane slips when the ball is centered any time:




The tilt table caused me to realize that any time the pilot applies rudder the airplane will slip unless the

airplane is __________________ toward the _________________________.




On a single-engine airplane doing a climbing-turn stall demonstration as angle of attack is increased

asymmetric thrust increases because of _____________________ factor. Assuming the pilot centers the

ball the airplane will slip to the ________________ which increases angle of attack on the

_______________ wing, especially in airplanes with lots of dihedral. As a result the amount of aileron

needed to keep bank steady is not the same in a left and right climbing turn. Consequently it can be

difficult to predict which wing will stall first, but the outer wing is more likely to stall in a

_______________ turn (assuming the ball is centered.) But, if the ball is not centered all bets are off.




A slipping airplane descends more steeply because:




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Stalls and Spins
Stall speed is defined as:




CLmax means:




Stall angle of attach changes when flaps are extended (ailerons are a type of flap for this purpose.) With

flaps extended stall angle of attack ______________________ but CLmax increases.


Stall speed equation is really just the Lift Equation rearranged with CL set to CLmax. Here is is:




Maneuvering speed is closely related to stall speed. Here is my explanation:




If the pilot holds and airplane in a stall the angle of attack can be forced beyond the stall angle of attack.

In this case CL _________________________ but it is likely still much higher than in cruise. Lift settles in

to a constant value once the vertical speed stabilizes. The airplane descends very steeply due to

___________________________________________. The airspeed indicator is usually eratic due to

position error but the actual EAS is slightly ________________________ the published stall speed as the

airplane plunges earthward. To “break” the stall the pilot must ________________________________.




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The large increase in drag when stalled is due to:




Vortex generators are supposed to delay the stall by:




Slats will delay the stall by:




Ice or other contaminants on the leading edge of the wing affect stall by:




If a stalled airplane rolls or yaws the down-going wing experiences __________________ angle of attack

which _______________________ the stall on that wing. The result is increased ________________

which exasperates the situation. The result is a rolling and yawing tendency known as a ____________




The term autorotation is applied to spins. This means:




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Below is a diagram showing the forces in a turn. You can see that in a level turn Lift is more than weight

the equation for lift in a turn is:




Load Factor (LF) is defined as:




The equation for load factor in a turn is:




Applying the LF equation to the stall speed equation I developed an equation for stall speed in a turn.

The equation is:




Using the equation I know that in a 30° bank turn stall speed increases by ____________ and in a 45°

bank turn stall speed increase by ________________.


Load factor in a 60° bank turn is ________________ g.




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Drag
Drag is by definition:




Drag is a component of the ________________________ force.


The two types of drag are _______________________ and ________________________


Parasite drag is a measure of how streamlined an object is. To be streamlined the object should be

shaped like:




The coefficient of Parasite Drag (CDp) is constant. It changes only when:




Parasite drag is proportional to _____________________________


Induced drag is defined as:




A wing tip vortex is:




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The wingtip vortex reduces the lift produced near the wingtip. Thus the pilot must increase the angle of

attack to compensate. This is known as _____________________ angle of attack.




Induced drag is ______________________ proportional to ____________________________


At the minimum drag speed _________________________ drag equals ___________________ drag.


Aspect ratio is defined as:




High aspect ratio increases maximum ____________________ ratio. But, the high aspect ratio airplane

generally needs to operate a higher CL to be efficient.


A jet transport flies at high altitude where the TAS is high but EAS is relatively _______________


High wing loading (WL) increases the CL the airplane cruises at. Wing Loading is defined as:




Wing loading for a C-172 is:


Wing loading for a B747 is 150 lb/ft2


Notice in the stall speed equation, which I have written below WL appears as part of the equation. I

have circled it:




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A total drag curve looks like this:




Power is defined as:




To convert the drag curve to a power curve all you have to do is:




For a jet, fuel flow is proportional to ________________________



For piston and turbo-prop airplanes, fuel flow is proportional to ______________________



Jet engines get more efficient at lower temperatures but piston engines __________________.



Given a choice a high manifold pressure and ________________________ is more efficient than the
opposite.


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The problem with the above fact is that the engine may run rough (or worse.)

On a Fuel Flow vs. Velocity graph ___________________________ is always at the bottom of the curve,

while maximum range is found by _____________________________________




With a headwind best range speed should be ____________________, on the graph this is found by:




Endurance is __________________ affected by wind.




A piston airplane gets maximum endurance at ____________________ altitude, and jets and turbo-

props get best endurance at ____________________________ altitude.


For a piston airplane, in the “real world”, the best range cruise altitude is the one

with________________________


For jets flight for range is more complicated because range ______________________ with altitude, but

a strong headwind might limit how high you should fly.


For a jet best glide speed should be the same as ____________________________ speeds.


For a piston airplane L/Dmax corresponds to maximum glide and also maximum _________________


To explain why best range speed might not precisely equal best glide speed for a C-172 I realize the CDp

changes following and engine failure because:




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The drag curve changes with weight. This diagram shows how:




The drag curve changes with altitude. This diagram shows how:




Streamlining reduces ______________________ drag.


Streamlining means:




A boundary layer is:




Boundary layers can be turbulent or ______________________.

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Laminar flow is desirable because it:




Laminar flow is sometimes not desirable because:




Vortex generators are:




The purpose of vortex generators is to:




Slats create slots. Slots are:




The effect of slots on the stalling angle of attack is to:




An airplane with slots is potentially tricky to land because:




Fowler flaps are:




The benefit of Fowler flaps is:




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Winglets are used to create thrust by drawing energy out of the __________________________


Winglets work most effectively on airplanes that have a strong vortex – which maens they operate a

______________________ angle of attack.


Winglets are therefore most effective on slow flying airplanes or ones with _____________ wing

loading.




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Lateral Stability
It is difficult to give an airplane natural Lateral Stability because:




All lateral-stability design-features depend on the airplane __________________ when banked.

The three design features that connect slipping to banking are:




An airplane with any of the above design feature will _________________ in addition to yawing when

rudder is applied. How much it rolls is a measure of the _______________________ effect.




A spiral dive occurs naturally in airplanes that have limited lateral stability, here is my explanation of
how a spiral dive develops:




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A Dutch Roll is the result of too much __________________________ stability or not enough

_______________________ stability.




I describe a Dutch Roll as:




A yaw-dampener is a device that artificially increases _____________________________.

Failure of the yaw-dampener on a large airplane often leads to ________________________

To stop a Dutch Roll:




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Longitudinal Stability
Longitudinal stability means:




An airplane cannot be flown without longitudinal stability because:




Too much longitudinal stability would make the airplane ________________________________

Stick Force means:



Powered controls means:



An airplane that has insufficient longitudinal stability would behave:




Center of gravity is the main determinant of longitudinal stability. My explanation is:




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Directional Stability
Directional Stability is defined as:




The main design feature that gives airplanes directional stability is:




An airplane is un-flyable unless is is directionally stable. If not it would not _____________ when
banked.



A lot of directional stability ______________________ the tendency to spiral dive. While this may not
be optimum a pilot can generally live with this deign flaw because the alternative would be:




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High Speed Flight
Swept wings increase the_______________________________


Critical Mach number means:




A shockwave is:




A Normal Shockwave is _______________________________________________, it can only occur in

Transonic flight, which means:




Oblique shockwaves occur in __________________________ flight. They create drag, but not as much

as normal shockwaves because:




Supersonic airplanes usually have swept wings – but they can be designed with straight wings provided

the wings have ______________________ leading edges. This might be OK for a ___________________

but on an airplane this is undesirable because:




Highly swept wings increase lateral stability often causing the airplane to suffer from______________

roll tendency.




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Multi Engine Flight
Climb performance decreases markedly following an engine failure because:




To maximize climb performance drag must be kept to a minimum following an engine failure. This is

done by:




Using rudder causes a slip – I explain this as follows:




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Vmc is defined as:




The conditions for Vmc are:




The effect of weight on Vmc is:




If I bank more or less than 5° toward the good engine the effects on Vmc would be (because):




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