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The Private Pilot License Written Exam – General Knowledge

General Knowledge

General knowledge is the fourth section of my study notes for the private pilot license written exam. There are 17 sections in the Sharper Edge Exam Guide:

  • Basic Definitions and Terminology
  • Lift
  • Drag
  • Effect of CG Location on Cruise Performance
  • Range Performance
  • Endurance
  • Climbing Flight
  • Descending Flight
  • Stalling
  • Turning Flight
  • Stability
  • Flight Controls
  • Engines and Engine Handling
  • Propellers
  • Flight Instruments
  • Flight Operations and Aeroplane Handling
  • Human Factors

Some of the questions in this section also refer back to sections 2 & 3, or to a flight instructor, meaning you won’t find the answers in this section.


Basic Definitions and Terminology

(Sharper Edge question 88).

  • Chord is a straight line from leading edge to trailing edge;
  • Camber line is the line that runs through the center of the wing from leading edge to trailing edge, midway between the upper and lower wing surfaces; it is not a straight line, but one that reflects the curvature of the wing;
  • Camber is the measurement, expressed as a percentage, of the deviation between the chord line and the camber line. The measurement used is the maximum deviation between the two divided by the length of the chord line;
  • airfoil camber and chord

  • Angle of attack is the angle formed by the chord line and the line of relative airflow; it changes as the attitude of the aircraft changes;
  • Lift is the force acting perpendicular to the relative airflow;
  • Drag is the force acting parallel to relative airflow;
  • Center of pressure is the point where the forces of lift and drag act on the wing; it changes with changes in the angle of attack;
  • Center of gravity is the point where the aircraft would hang in balance if suspended; it changes with loading, but not with angle of attack;
  • For most aircraft to remain longitudinally stable the CG should be ahead of the center of pressure;
  • Axes of Rotation: there are three – longitudinal, lateral and vertical;
  • Longitudinal runs from the nose to the tail – changes in this are called “roll”;
  • longitudinal axis

  • Lateral runs from wingtip to wingtip; movement along this axis is called “pitch”;
  • lateral axis

  • Vertical runs up and down through the center of gravity; movement along this axis is called “yaw”;
  • vertical axis

  • All three axes intersect through the CG;
  • There are four basic forces in aviation: lift, gravity, thrust and drag;
  • Lift and gravity are different sides of the same coin; likewise, thrust and drag are related in the same way (equal and opposite);
  • Aspect ratio is a measurement of wing shape;it is a ratio of wingspan to average wing chord; short, stubby wings have low aspect ratios (span of 30 feet/average chord of 5 feet =aspect ratio of 6; span of 60 feet/average chord of 5 feet = aspect ratio of 12;
  • Laminar flow airfoil: the thickest part of the airfoil is about halfway through the wing, in comparison to a conventional wing, where the thickest part is closer to the leading edge; laminar flow airfoils reduce the turbulence in the airflow over the wing, but exhibit more drag when dirty or contaminated, and have more abrupt stall characteristics;
  • Angle of incidence is the angle between the longitudinal axis and the chord line of the wing; this is a fixed angle that does not change;
  • Dihedral is the angle between a horizontal line running from wingtip to wingtip and the angle the wing makes leaving the fuselage.

Lift

(Sharper Edge questions – none ).

A cambered airfoil will produce more lift than a symmetrical airfoil under the same conditions.
airfoil camber


Drag

(Sharper Edge questions 38,52,64,66,90,100).

Drag operates opposite to thrust, and acts in the same direction as relative airflow.

There are two categories of drag: parasite drag and induced drag.

Parasite Drag
Parasite drag is the drag all objects feel when moving through fluid (air). Parasite drag can be divided into three sub-categories:

  1. Skin friction drag
    • This is just the friction between the air and the skin of the aircraft.
  2. Form drag
    • Form drag is the friction between the air and the form of the object. Streamlined objects create less drag. Think of landing gear, with and without wheel pants.
  3. Interference drag
    • This is the drag that results from air moving over two or more objects that have been joined together. Think of wing and fuselage. Each has it’s own specific drag. Add them together and you should have total drag (the whole is equal to the sum of its parts) but this is not the case. Airflow from one object interferes with airflow from the second object, and vice versa, which adds even more drag, so that the total drag exceeds the drag from each part.

The denser the air, the higher parasite drag will be.
The more surface area of the aircraft, the more parasite drag there will be.
The higher the speed the greater the parasite drag.

Induced drag

Induced drag is a by-product of lift. More lift means more induced drag.

Anytime you need (and produce) more lift you get more induced drag. For example, a heavier aircraft needs more lift, and generates more induced drag.
As air becomes less dense the airplane needs more lift, which leads to…more induced drag.
But, induced drag decreases with increased airspeed.

Differences between induced and parasite drag:

Denser air means less induced drag, but more parasite drag.
Less dense air means less parasite drag but more induced drag.
Higher speed means less induced drag, but more parasite drag.

Total Drag
Total drag is the sum of all parasite and induced drag. Since induced and parasite drag often act differently it becomes a trade off when you try to minimize drag.

Generally speaking, drag is minimized in the middle of the speed range, when the lift/drag ratio is at it’s maximum (you’ve got the most lift possible in relation to the least drag possible).

Key points about drag:
Induced drag is a by-product of lift and increases with increases in angle of attack;
Parasite drag has three types: Skin, form and interference drag. They are unchanged by changes in angle of attack.

Ground Effect
Induced drag is created as a by-product of lift, specifically by down wash behind the trailing edge of the wing. When you’re within one wingspan of the ground the down wash has a hard time creating induced drag because the ground reduces the slower moving airflow. This means that you can generate a faster flying speed sooner, because you experience less drag. It’s good for soft field take offs. You rotate as soon as possible, and then fly just over the ground until you reach a safe climb speed. Induced drag decreases with speed, but you have to be careful to generate enough speed that when you leave ground effect the induced drag doesn’t slow you down again and cause you to sink.


Effect of CG Location on Cruise Performance

(Sharper Edge question 57,96).

This is pretty simple, and requires that you remember the properties of induced drag (it increases as the lift generated increases) and the difference between center of pressure and center of gravity.

In conventional aircraft the CoG has to be ahead of the CoP. This is because the tail creates downward lift which pushes the nose of the aircraft up. If the CoG is behind the CoP then the aircraft will have a nose up attitude that can’t be corrected (both the weight and the lift generated by the tail will be pushing the back of the aircraft downward).

In other words, the lift generated by the wing must equal the lift generated by the tail plus the weight exerted by gravity. If this is in balance the plane will maintain the desired attitude.

The further forward in the envelope the CoG is the more lift is required to be generated by the tail to keep the attitude acceptable. More lift generation means more induced drag. More induced drag means more requirement for power, and more fuel consumption.

Therefore, the closer the CoG is to the CoP the less downward lift is required by the tail. This reduces the amount of induced drag generated. Reduced drag means better cruise performance.

Put another way (see question 57) an aircraft with a forward CoG will cruise slower than an identical aircraft (same weight, etc) with a more rearward CoG.

A more forward CoG will cause an aircraft to be more stable in pitch because the forces pushing the nose down and the tail down are increased compared to when the CoG is toward the rear of the envelope. It will also use more fuel (as explained) and require a longer take off roll (the nose wants to stay down, and the extra lift required from the tail to counter this generates increased induced drag) – that’s question 96.


Range Performance

(Sharper Edge questions 37,82).

Maximum range means maximum distance flown per unit of fuel. Obviously the more efficiently you fly the better your range.

There are two things to consider: drag and power setting. Since drag and speed are related we need to pick a power setting that gives us the highest speed while still creating the least amount of drag. Engines don’t consume fuel in direct relation to fuel consumption. Every extra bit of fuel added doesn’t produce the same incremental bit of power. There is a sweet spot that produces the best ratio of fuel/power.

Keeping that in mind there are two performance charts to look at. The first is the amount of drag generated in relation to speed. We know form drag decreases with speed, but induced drag increases. This means that drag is highest at low and high speeds, and minimized somewhere in between.

A similar, although less pronounced curve can be graphed for power and speed. Low speeds require more power, and high speeds require lots of power, but in between there is a sweet spot that requires less power.

If you put both graphs side by side, or on top of each other, you will see that there is a speed range where drag is at a minimum and power is at a minimum. This is the power setting range that gives you the best range.

Maximum range is achieved at the best lift/drag ratio, but this is usually a fairly low speed (question 37).

To get absolute maximum range you want to fly with the best lift/drag ratio, which is the speed that generates minimum drag. High altitudes, with less dense air, also reduces drag (see question 82).

More weight means less range (more weight requires more lift, more lift, more induced drag, etc).

Greatest range is at higher altitudes and lower power settings.


Endurance

(Sharper Edge questions 45,81).

Endurance is a measure of time aloft, while range is a measure of distance.

The lower the power setting the less fuel consumed, which means more endurance. Maximum endurance, therefore, will be achieved at Vmp (question 45).

The minimum power required for flight increases with altitude, so while range increases with altitude, endurance does not.

Vmp means a slower speed, which means the prop is turning as slowly as possible while maintaining level flight. Add in that you get more endurance at low altitudes and you’ve got the answer for question 81 – best endurance is at minimum power setting, low altitude and with the prop turning as slowly as possible to maintain level flight.


Climbing Flight

(Sharper Edge question 44).

An airplane needs a certain amount of power for straight and level flight. To climb it requires that much power plus additional power. You can think of it like this: you need excess power to climb, which is why service ceiling is defined as the density altitude where the plane can’t climb anymore (or at least can’t climb more than 100 fpm) All it’s power is used to keep it aloft in less dense air, so there is no “excess”. (Absolute ceiling is when the plane can’t climb at all, period).

There are four forces in flight: thrust, drag, lift and gravity (or weight). In a climb the lift is (like always) perpendicular to the relative airflow, but weight forces two ways:opposite to lift, as well as straight down (gravity).

Question 44 asks about service ceiling. Remember: 100 fpm/density altitude.

Rate of climb (Vy)depends on excess power. Rate is speed – use it to get up fast.
Angle of climb (Vx) depends on excess thrust. Best angle gets you higher in shorter distance, but does so more slowly.


Descending Flight

(Sharper Edge questions 42,60,85).
This is essentially the reverse of climbing flight. You don’t need excess power.

A tail wind will increase the descent path (make the angle of descent more shallow).

A head wind will shorten the descent path (increase the angle of descent).

This doesn’t mean you’ll get down faster or slower with a headwind or tailwind. The airflow is relative, while the ground stays in the same place. In other words, with a headwind your distance covered will be less, but the time spent getting down will be the same (question 60).

You’ll glide furthest at the best lift/drag ratio (which, remember, is very close to your best rate of climb – in my C10 that’s 70 mph).

In zero wind conditions a lightly loaded and heavily loaded airplane (same type) will glide the same distance (question 44). However, glide endurance for the heavily loaded aircraft will be less (it will cover the same distance sooner (question 85).


Stalling

(Sharper Edge questions 41,46,72,84).
Stalling is dictated by angle of attack (this is question 41).

Aircraft are designed so that the wing root will stall before the wing tip. This allows the ailerons to function longer (if the tips stalled before the wing root you would have no aileron control).

Since angle of attack dictates whether the wing stalls, and wing roots generally stall first, you can understand that the wing root angle of attack will be steeper than the wing tip angle of attack.

“Washout” is the term used to describe this change in angle of attack (the reduction of it) from wing root to wing tip.

Wing roots can also have more camber than wing tips to make them stall first.

So, it is more desirable for the wing root to stall before the wing tip, and washout helps this to happen (question 46).

Stall strips are devices that make the leading edge of the wing sharper. They are installed near the wing root, and create an early separation point (the air flowing over the upper edge of the wing separates from the upper surface earlier), causing a stall, They are installed near the wing root so that the root stalls before the wing tip. Remember, causing the wing root to stall is not the same as stalling the whole wing or the whole aircraft. Stalling the root gives the pilot an indication that a full stall is imminent. Therefore: Stall strips cause the wing root to stall before the wing tip, thus giving warning of an impending stall (question 72).

The wing stalls when the center of pressure moves forward, toward the leading edge. Increasing the angle of attack causes this. When the stall occurs the CoP moves rapidly backward, which aids in recovering from the stall. Think about it: a forward CoP wants to push the front of the aircraft up, but as it moves backward it will allow the nose of the airplane to fall, which reduces angle of attack. When you recover from a stall you initially put the nose down, but you have to be careful not to put it to far down – that’s because the airplane generally wants to fly and is trying to get to the same sort of attitude that you’re trying to put it into.

So, as angle of attack increases, the CoP moves forward (question 84).


Turning Flight

(Sharper Edge questions 6,7,94).
Turning flight changes the direction that lift pressure is going. The lift vector becomes inclined, which results in some lift going straight up, to counter gravity, and some lift going perpendicular to the wing.

The result is that the lift that is perpendicular to the wing creates centripetal force that starts the turn, but that part of the lift is not keeping the plane aloft.

Therefore, you either descend in a turn or increase power or attitude.

Stall speed also increases in a turn. The greater the bank the higher the stall speed.

Turn radius is the size of the turn. Small radius = tight turn. Increasing the airspeed will increase the radius. The smallest turn radius will be achieved at slower speeds. Increasing speed increases the turn radius.

Increased bank also tightens turn radius. Steeper bank, tighter turn.

Tightest turn? Steepest bank possible at lowest speed possible, but steep banks increase stall speed, so watch out.

Rate of turn is the amount of time required to turn. Higher speeds mean lower rates of turn because you’re covering more distance at higher speeds.

Higher rates of turn are achieved at low airspeeds.
Higher rates of turn are achieved at steeper banks.
Low speeds and steep banks give the highest rates of turn, but again, increased bank means increased stall speed.

So, increasing airspeed will increase the radius of the turn and decrease the rate of the turn (question 6).

Increasing the bank increases stalling speed.
At 15 degrees the increase is about 2%;
At 30 degrees it’s about 7%;
At 45 degrees it’s about 19%;
At 60 degrees it’s about 41%;
At 75 degrees its about 100%.

Therefore, if Vs in straight and level flight is 50 knots, then in a 30 degree bank it increases by about 7%, of 3.5 knots, meaning it’s 54 knots. (Question 7).
At 45 degrees the increase would be 19% – use 20% for ease – meaning Vs would become 60 knots.

If the aircraft’s Vs in straight and level flight was 58 knots a 60 degree bank would increase it by 41%. 58 *.4 = 23.2. 58 + 23.2 = 81.2, but that’s using 40% instead of 41, so Vs at 60 degrees is actually a little higher (Question 94 asks what a Vs of 58 becomes at 60 degrees and gives 82 knots as one of the options. 81.2 is close enough).

  • 15 degrees increases stall speed 2%
  • 30 degrees increases stall speed 7%
  • 45 degrees increases stall speed 19%
  • 60 degrees increases stall speed 41%
  • 75 degrees increases stall speed 100%

Rate 1 turn:

  • A rate 1 turn means you turn 180 degrees in one minute;
  • A rate 1 turn is 3 degrees per second;
  • Divide true airspeed by 10 and add 7 knots for required bank for rate 1 turn.

You use a rate 1 turn to do a 180 when you fly into clouds or need to turn around.


Stability

(Sharper Edge questions 58,67,68,95,96,97).

Stability moves around the axis that is perpendicular to to the stability being discussed:

  • Longitudinal/pitch stability moves around the lateral axis;
  • Lateral/roll stability rotates around the longitudinal axis;
  • Directional/yaw stability revolves around the vertical axis.
  • (Question 95)

Longitudinal Stability:

  • This is pitch;
  • It moves around the lateral axis;
  • It is effected by CoG;

Lateral stability:

  • This is roll;
  • It moves around the lateral axis;
  • It is effected by dihedral and where the wing joins the fuselage;(question 58)
  • Sideslip (increasing lift on the lower wing) contributes to self-correcting.

Directional stability:

  • This is yaw;
  • It is provided by the stabilizer;
  • It rotates around the vertical axis;
  • CoG influences stabilizer performance;
  • Forward CoG means more stabilizer effect;
  • Rearward CoG diminishes stabilizer effect.

All axes pass through the CoG. (Question 97).

A forward CoG will cause the aircraft to be more stable in pitch (more inputs needed to make a change), use more fuel (more induced drag from more elevator lift) and require a longer take off roll. (Question 96)

There are two terms describing how the aircraft behaves in response to a disturbance (an input control or an external input): static response and dynamic response.

Static response is what the aircraft does in response to the disturbance. If it returns to the undisturbed state it is said to be statically stable. (Question 67)

Dynamic response is what follows. This response takes the form of oscillations. If the aircraft oscillates regularly, neither increasing or decreasing, after the initial disturbance, it is called “neutral stable behaviour”; the oscillations are stable through their cycles. If the oscillations gradually reduce in amplitude it is called “dynamically stable”; the oscillations reduce in a stable fashion until they disappear entirely. If the oscillations increase it is called “dynamically unstable”. A dynamically unstable plane would obviously be hard to fly. Most light aircraft are dynamically stable. (Question 68).


Flight Controls

(Sharper Edge questions 39,53,61,69).
Flight controls are the moving parts of the airplane that control how it moves. They are:

  • Rudder
  • Elevator
  • Ailerons
  • Trim, balance, servo and anti-servo tabs
  • Flaps

Rudder
Rudder is controlled by foot pedals. It controls movement around the vertical axis (yaw or directional movement). It counter-acts propeller slipstream. Slipstream spins around the fuselage, forcing the tail to the right and the nose to the left. The rudder can counter-act this (right rudder, as in when you take off). The rudder also balances the turn (it’s what you do to keep the ball in the middle). Some rudders have a trim tab (my 150 has one that you adjust on the ground).

Elevator

  • The elevator controls movement around the lateral axis.
  • Lateral axis controls pitch
  • The elevator creates downward lift in a conventional aircraft
  • The downward lift creates lateral stability
  • Changing the amount of lift created will pitch the aircraft up or down
  • This allows the plane to climb or descend
  • Trim tabs allow back pressure on the elevator to be minimized

Ailerons
Ailerons control movement around the longitudinal axis – roll
They also cause the airplane to turn
They can also cause sideslip and yaw, and lead to spiral dives
They act in opposite directions – one creates lift on one wing while the other decreases lift on the opposite wing
Increased lift creates increased induced drag
That means less drag on the opposite wing
Together these forces cause the plane to yaw toward the side with more drag (opposite to the direction of the intended turn)
This is what causes unbalanced turns, so we use the rudder at the point to counter-act the yaw
This yaw is called “adverse yaw”
Because it is predictable the ailerons can be constructed so as to compensate for it
Differential Ailerons:
The upgoing aileron (the decreased lift wing) goes up higher, causing more form drag
This compensates for the increased induced drag on the opposite wing
The downgoing aileron (the increased lift wing) goes down less, leading to less induced drag, which compensates for the increased form drag on the opposite wing
The effect is more balance
Frise Ailerons
These do the same thing in a simpler way: the downgoing wing aileron has the aileron go up
It’s leading edge protrudes down and creates a bunch of form drag
The effect is balance

Mass Balancing of Controls
The CoG of a contro surface must be ahead of its hinge point or it will develop a flutter and eventually self-destruct.

Trim Tabs, balance tabs, servo tabs and anti-servo tabs
The force on the control surface can be large, because the surface is large.
It’s moment is close to the hinge line
It can be balanced, for better feel to the pilot, by a smaller tab placed further back from the hinge line
This principle can be used in different ways

A trim tab helps push a control surface in the direction the pilot wants it to go.
The trim tab is set opposite to the direction of the control surface.
It is used when the control moves the control surface itself.

A servo tab is used when the control moves the servo tab
The servo tab then moves the control surface
The servo tab moves in the opposite direction as the control surface itself.

An anti-servo tab is the opposite (duh)
It moves in the same direction as the control surface
They increase control forces to increase the feel to the pilot

Balance tabs reduce control forces
When set up like servo tabs they do the same thing but…
They are not connected to the control column or yoke
The control surface is.

A balance tab can also be like a frise aileron, especially on a rudder
the rudder control surface moves one way
A tab on the rudder ahead of the hinge point move the other way
That reduces control surface pressure


Engines and Engine Handling

(Sharper Edge questions 2,3,4,5,8,15,43,51,62,65,73,87,89,90,92).


Propellers

(Sharper Edge questions 14,91).


Flight Instruments

(Sharper Edge questions 1,9,20,21,22,23,24,25,35,36,47,55,59,78,83,86 ).


Flight Operations and Aeroplane Handling

(Sharper Edge questions 11,18,19,26,33,54,75,80).


Human Factors

(Sharper Edge questions 12,16,17,27,28,29,30,31,32,35,48,49,56,63).


My name is Rob Chipman and I’m a realtor and pilot based in Vancouver, BC. I AM NOT A FLIGHT INSTRUCTOR AND I AM NOT OFFERING FLIGHT INSTRUCTION! I am sharing my study notes and other things I’ve learned while getting my education as a pilot. You’re welcome to make use of this information, but do not treat it as expert advice.

I really enjoy flying, real estate and the Chilcotin.  My company is Coronet Realty Ltd., located at 3582 East Hastings Street, Vancouver, BC, V5K 2A7. I have a C-150L that I own with two other pilots, based out of Pitt Meadows. Do not hesitate to contact me by email if I can help you do anything, especially if its likely to be interesting or concerns selling remote property in British Columbia.

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