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Lecture 8 Finish Aerodynamics of Maneuvering Flight The Flight Environment Flight Safety & Airports Chapter 4 (A,B), Jeppesen Sanderson Chapters 5 and 15, Kroes and Rardon Descending Flight

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Lecture 8

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Lecture 8 l.jpg

Lecture 8

Finish Aerodynamics of

Maneuvering Flight

The Flight Environment

Flight Safety

&

Airports

Chapter 4 (A,B), Jeppesen Sanderson

Chapters 5 and 15, Kroes and Rardon


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Descending Flight

  • When descending, the weight of the plane can be divided into two components – one perpendicular to the flight path, the other acts forward along the flight path.

  • The second component acts to increase airspeed. If you do not want to increase speed you have to reduce engine thrust in a descend.


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Gliding (1)

  • In case of the engine fails you are forced to descend without engine power. This is called gliding.

  • You might want to glide as long a distance as possible to find a safe landing place.

  • The particular AoA that gives you the maximum lift-to-drag ratio (L/Dmax) will give you the maximum gliding distance and the best glide speed.

  • If you are too fast, parasite drag increases; and if too slow, induced drag increases. Both will reduce the glide distance you can get. (Fig3-57)


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Glide speed and glide distance (3-57)


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Gliding (2)

  • There are several factors affecting gliding:

    • Glide angle – the angle between the glide path and the horizon is called the glide angle. The smaller the glade angle the less drag and the longer gliding distance.

    • The loading (thus the weight) of an airplane affects the best glide speed but do not affect the best glide distance. Two identical planes with different loads start gliding from the same altitude can attain the same best glide distance.

    • Wind – a headwind will decrease your glide distance and a tail wind will increase it.


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Turning Flight (1)

  • During a turn, because the plane has rolled, lift is broken up into two components – one vertical component that opposes the weight; the other one acts horizontally and provides the centripetal force that causes the plane to turn. (Fig 3-62)

  • With the original AoA the vertical component becomes less than the weight. If you want to maintain altitude while turning you have to increase the AoA until the vertical component alone equals the weight.


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Turning Flight (3-62)


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Turning Flight (2) – Adverse Yaw

  • In a turn, e.g., turning to the left, the right aileron is lowered while the left is raised.

  • This results in the right wing having a larger AoA than the left wing. Thus the right wing has a larger lift.

  • However, this also results in the right wing getting a larger induced drag, causing the plane to yaw to the right. This is called an adverse yaw, since it is undesirable.

  • To compensate for it, the left rudder peddle has to be pressed to turn the rudder to the left.


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Turning Flight (3) – Adverse Yaw

  • This produces a left yaw for the plane which compensates for the adverse yaw to the right.

  • When this compensation is done to the correct amount, the nose of the plane will point to the direction it turns (instead of yawed to the right).

  • After the desired turn is achieved both the ailerons and the rudder have to be turned to the opposite side momentarily to resume wing-level flight.

  • This whole process, when done correctly, is called a coordinated turn.

  • Rudder coordination is especially important for sharp turns with large AoA.


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Load Factor (1)

  • Load factor is the ratio between the lift provided by the wings and the weight of the plane.

  • In straight and level flight at constant speed the load factor is 1. The unit used is often called G’s.

  • However, during turns, or up and down flight, the load factor can differ from 1 (i.e., it is not 1 G).

  • The difference (between lift and weight) is called the G-force and is due to acceleration (change of speed or direction). This is similar to riding a rollercoaster.

  • When a plane suddenly descends from level flight the load factor is less than 1 G. When it suddenly ascends the load factor becomes larger than 1 G. These happen commonly in turbulent flight.


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Load Factor (2)

  • When you make a turn the airplane rolls (see Fig 3-62 earlier). The amount of roll is called the bank angle (angle between the wings and the horizon).

  • If you want to keep the altitude during the turn you have to increase the lift so that the vertical component of the lift equals the weight. Thus the lift is larger than the weight and the load factor is larger than 1.

  • Larger the bank angle sharper the turn smaller vertical component of lift  larger lift needed to compensate for the vertical component to balance the weight larger the load factor. (Fig 3-68)


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Load Factor vs Bank Angle in turn (3-68)


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Load Factor (3)

  • Thus in sharp turns (large bank angles) the wings can be supporting a load that is significantly more than the weight of the plane (even the pilot and passengers can feel it).

  • The larger load factor also increases stall speed (i.e., the plane will stall even at a higher speed).

  • How large a load factor can a plane withstand before structural damage occurs?

  • Small planes certified in the normal category can stand 3.8 positive and 1.52 negative G’s. Utility category planes can stand 4.4 positive and 1.76 negative G’s.


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Load Factor (4)

  • Examples of load factors


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Flight Safety

  • Collision avoidance

    • VFR and IFR

    • Visual scanning

    • Right-of-way rules

  • Taxiing in the wind


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Collision Avoidance – VFR & IFR

  • Besides controlling his/her own plane with coordinated flight a pilot has to consider other planes around and avoid collisions.

  • Majority of mid-air collisions occur within five miles of an airport, during day time, and in VFR (Visual Flight Rules) conditions.

  • Visual Flight Rules (VFR) refers to the regulations that governs flying that relies on visual observations, instead of on instruments, which is governed by Instrument Flight Rules (IFR).


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Collision Avoidance - VFR

  • There are some minimum requirements on cloud conditions and visibility requirements for flying with VFR.

  • If the weather does not reach these minimum requirements IFR has to be used.

  • Although the term VFR (or IFR) means the kind of rules, it is sometimes also used to describe the minimum weather requirements for flying under VFR, and is also used to describe the flight plan.


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Visual Scanning (1)

  • Generally you have a field of vision (maximum seeing range) of about 200○.

  • However, at any moment, you can focus sharply only at about 10○, at the center of your visual field, and it requires time to focus.

  • Under VFR your are required to scan the sky with short, regularly-spaced eye movements. Each scanning step should not be more than 10○ apart, and should focus for at least 1 second.


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Visual Scanning (2)

  • One of two scan patterns can be followed as shown in Fig 4-1.

  • The hardest object to notice are those on the side that shows no motion.

  • The would be the case is coming towards you directly from the side.

  • If the other aircraft shows no lateral or vertical motion, but increasing in size, take immediate avoiding action.


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Required Visual Scanning Patterns (4-1)


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Right-of-way Rules (1)

  • When two planes are on a collision course there are clear rules for each of the two planes involved on what they should do. These are the right-of-way rules:

    1. A plane in distress (under serious problem) has the right-of-way over all other planes.

    2.If two planes are approaching each other head-on, both planes turns to its own right side.


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Right-of-way Rules (2)

3.When aircrafts of different categories are converging, the least maneuverable aircraft has the right-of-way.

4.When two aircrafts of the same category are converging, the aircraft on the other’s right side has the right-of-way (Fig 4-5).

5.If one aircraft overtakes another, the one being overtaken has the right of way.


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Right-of-way Rules (4-5)


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Taxiing in the Wind

  • Strong wind around the wings and horizontal stabilizer during taxi on the airport can lift the airplane.

  • In the worst situation, the plane can roll over.

  • Proper use of the ailerons and elevator can help counteract the wind.

  • Fig 4-8 shows what you should do under different directions of winds.


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What to do under strong winds from different directions (4-8)


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Airports

  • Controlled and Uncontrolled Airports

  • Runway Layout

  • Traffic Pattern

  • Runway to use

    • Wind and Noise

  • Airport Visual Aids

    • Runway markings

    • Taxiway markings

    • Ramp area

    • Airport signs

  • Airport Lighting


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Controlled and Uncontrolled Airports

  • A controlled airport has a control tower.

  • All aircrafts in the vicinity are subject to instructions issued by air traffic control (ATC) from the tower.

  • A two-way radio is required for all pilots operating in a controlled airport.

  • An uncontrolled airport does not have a control tower. Pilots have to determine the active runway and how to enter and exit the traffic.


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Runway Layout

  • If there is only one runway, it is always built in the direction such that you can take off and land in the direction of the prevailing wind (heading the wind).

  • If there are more than one runway, the main one is in the direction of the prevailing wind, with the other runways aligned with other common wind directions.

  • Runways are always marked with a number referenced to the magnetic north.


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Runway Layout (1)

  • The number indicates the direction you are heading towards if you use that runway. It is rounded off to the nearest 10゚, and with the last zero omitted.

  • Thus a runway heading towards 268○ is rounded off to 270○ and is numbered 27.

  • A runway heading towards 93○ is Runway 9.

  • Since the two directions of a runway is 180○ apart the numbers on the two ends of each runway is differed by 18. (Fig 4-11)


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Runway Marking (4-11)


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Runway Layout (2)

  • If there are two runways parallel to each other, e.g., towards north (360○), then one is labeled left and the other right, i.e., they are 36L and 36R.

  • If there are three parallel runways, the middle one is labeled center, e.g., 18L, 18C and 18R.


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Traffic Pattern (1)

  • How aircrafts land on a runway is well fixed in an orderly manner. This is called the traffic patterns.

  • The traffic path is designed to be a rectangle, with the runway in the middle of one side.

  • A plane landing on the runway should enter the “Downwind” leg, which is opposite to the runway side.

  • Then it should turn about 90○ to the “Base Leg”, which is perpendicular to the runway. (Fig 4-13)


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The Standard Traffic Pattern (4-13)


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Traffic Pattern (2)

  • The plane then turns about 90○ into the “Final Approach” which aligns with the runway. Then lands towards the runway at a 3○ angle.

  • Extending in front of the runway is the “Departure Leg” which is used by planes taking off from the runway.

  • If after take off, the plane wants to remain in the traffic pattern, it turns 90○ into the “Crosswind Leg”.


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Which Runway to Use?

  • Generally you will be assigned a runway so you can take off or land into the wind.

  • As for which runway you will be assigned might also depend on whether there is a neighborhood that might be affected by the landing planes, or planes taking off.

  • In certain period (e.g., at night) you might be assigned a runway so as to avoid the noise disturbance to the neighborhood.


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