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 177 (Blackpool Airport) SQN. SENIOR CADET TRAINING contents
1.1 latitude and longitude 1.2 speed 1.3 corrections 1.4 time 1.5 exam style questions 2.1 vectors and velocities 2.2 the triangle of velocities 2.3 other factors 2.4 exam style questions 3.1 definitions 3.2 the one in sixty rule 3.3 applications of the 1 in 60 rule 3.4 exam style questions 4.1 compass forces 4.2 the direct indicating compass 4.3 the gyro magnetic compass 4.4 inertial navigation systems 4.5 to the future (and beyond) 4.6 exam style questions 5.1 VMC and IMC 5.2 wind 5.3 shallow fog 5.4 precipitation and icing 5.5 exam style questions 1.1 latitude and longitude
The latitude and longitude grid divides the Earth into degrees (o) and minutes ( ’). Every one minute of latitude is equivalent to one nautical mile of the Earth’s surface, whereas 1 degree of latitude equals 60 nautical miles. ‘
We measure the distance between two positions on the aeronautical chart using a ruler, dividers or a piece of paper, and then use the nautical mile scale which is shown on every meridian to work out the actual distance. The nautical mile scale If two places are on the same meridian, then it is even easier to calculate the distance between them. For example, if one airfield has a latitude of N40o29’ and another N51o24’, we first write both latitudes in minutes, by multiplying the number of degrees by 60 and adding the result to the number of minutes. Degrees N40o29’ ‐ 40 x 60 = 2400 + 29 = 2429 N51o24’ ‐ 51 x 60 = 3060 + 24 = 3084 Minutes We then take the two results away from each other to give the actual distance in nautical miles (nm): 3084 – 2429 = 655 nm. Questions
1. What does 1 degree of latitude represent? 2. Glasgow is due North of Plymouth with latitudes of 55o50’ and 50o25’ respectively. What distance are the two places apart? 1.2 speed
The units of speed in aviation are nautical miles per hour, also known as knots. To measure speed, we use an Air Speed Indicator (ASI) to measure the dynamic pressure (the pressure caused by the aircraft’s forward movement). This involves measuring the difference between the pressure of the air surrounding the aircraft (static pressure) and the air captured in the Pitot tube (static and dynamic pressure). This means that there is both static and dynamic pressure above the diaphragm and only static pressure below it. The two static pressures cancel each other out and the diaphragm, therefore, moves according to the dynamic pressure. This is displayed as Indicated Air Speed (IAS). Questions
1. What are the unit of speed used in aviation? 2. Draw a copy of an ASI, labelling the locations of the static and dynamic pressures. 3. How do we calculate the Indicated Air Speed (IAS)? 1.3 corrections
There are two types of error: 1. Pressure Error – due to sensing the incorrect values for Pitot and Static Pressure. 2. Instrument Error – Caused by poor manufacturing tolerances when the aircraft was built. It is possible to measure both of these errors by testing the aircraft under controlled conditions. This is showed on the calibration card, displayed in the cockpit next to the instrument. IAS + Pressure Error + Instrument Error = CAS (Calibrated Air Speed)
The higher an aircraft flies, the less dense the air becomes. To obtain the True Air Speed (TAS) from the CAS, therefore, you need to correct the air density changes. If the aircraft is flying at speeds greater than 300kts then there is also a compressibility error as well, caused by air becoming compressed in the Pitot Tube. CAS + Density Error + Compressibility Error = TAS (True Air Speed)
Questions
1. An ASI has an instrument correction factor of +3kts and a pressure correction factor of ‐1kts. If the instrument reads 130kts what is the CAS? 2. When does a compressibility error occur in flight? 1.4 time
KEY POINT
In aviation, we always use the 24 hour clock which is set to GMT (Greenwich Mean Time) which is also known as universal Time (UT). British Summer Time / Daylight Saving Time is ignored Speed, Distance and Time If we know how far an aircraft has travelled in a certain amount of time, we can calculate it speed using: Speed (TAS) = Distance (nm) Time (hours) If we know the aircraft’s speed and how long it has been flying for, we can also work out how far it has travelled using: Distance (nm) = Speed (TAS) x Time (hours) Similarly, to work out how long it will take an aircraft to travel a certain distance at a specific speed we can use: Time (hours) = Distance (nm) Speed (TAS) Questions
1. What names are given to the time used in aviation that ignores British Summer Time? 2. If an aircraft is travelling at 20kts over a distance of 40nm, how long will the journey take? 3. How fast will an aircraft have to travel to cover a distance of 500 nm in 2 hours? 1.5 exam style questions
1. One degree of latitude is equal to: A.
B.
C.
D.
1/10,000 part of the distance from the North Pole to the Equator 360 nms 60 nms 60 km 2. In Germany, Kiel is due north of Warzburg. If Kiel’s latitude is 54 20N and Warzburg’s is 49 48N, how far are they apart? A.
B.
C.
D.
272 nm 2720 nm 27.2 nm 227 nm 3. How fast must an aircraft fly to cover 1200nm in 3 hours? A.
B.
C.
D.
400mph 800kts 400kts 3600kts 4. What time is used as standard in military and commercial aviation? A.
B.
C.
D.
Greenwich mean time (universal time) European daylight saving time The time of the country over which the aircraft is flying British Summer Time 2.1 vectors and velocities
KEY POINT
A velocity is a speed also given with a direction. This can be represented by a line called a vector. The bearing of the line relative to true north represents the direction and its length represents the speed. True North True North Shorter line = slower speed Longer line = faster speed
Questions
1. What is a velocity? 2. What two things does a vector show and how does it show them? 2.2 the triangle of velocities
The Air Triangle Heading & True Air Speed
Drift Wind Speed & Direction Track & Ground Speed (GS)
Heading & True Air Speed The Heading is the direction in which the aircraft is pointing. The TAS is its speed through the air, including all the necessary corrections. Wind Velocity Represents the wind strength and the direction that it’s blowing from. Track and GS This represents the direction and speed the aircraft is actually moving across the ground. Drift KEY POINT
This angle, between the heading and track vectors, is the angle at which the aircraft is being blown sideways. Questions
1. Draw and label a copy of the air triangle. 2. What is the difference between the heading & True Air Speed and the Track & Ground Speed? 3. What is drift? 2.3 other factors
Computers Navigators often use the Dalton hand computer. In commercial aircraft, the onboard electronic computers continually solve the triangle. Magic Numbers Magic numbers make the mental arithmetic easier. Although you can learn the table below, it is possible to work out the right hand column by simply dividing the GS by 60! GS nm/min GS nm/min 60 80 90 100 120 150 180 1 1 ⅓ 1 ½ 1 ⅔ 2 2 ½ 3 210 240 300 360 420 480 540 3 ½ 4 5 6 7 8 9 Estimated Arrival Time (ETA) KEY POINT
Knowing your ETA is important for fuel calculations (checking that you have enough fuel to complete the journey) and for Air Traffic Control purposes. If the aircraft does not arrive on time, then ATC will take overdue emergency action. Questions
1. If you are travelling at a GS of 150, how long will it take you to travel 10nm? 2. Why do you think that it would be important to notify ATC if your ETA changed? 3. Other than for ATC purposes, why is knowing your ETA useful? 2.4 exam style questions
1. A velocity consists of: A.
B.
C.
D.
Speed and direction together Speed only Several speed vectors together Direction only 2. In the Air Triangle of velocities, DRIFT is: A.
B.
C.
D.
The angle between heading and track vectors The bearing of the wind vector The angle between the wind and track vectors The angle between heading and wind vectors 3. You fly between two features on the ground, and note that it takes you 3 minutes. If the features are 18nm apart, what is your groundspeed? A.
B.
C.
D.
180kts 280kts 54kts 360kts 4. ETA calculations helps the crew to determine that: A.
B.
C.
D.
The drift is correct They are flying the shortest route The wind velocity will not change The aircraft has sufficient fuel to reach the destination 3.1 definitions
Track Required This is the line drawn between the departure airfield and the destination. TRACK REQUIRED
Departure Airfield Destination Airfield
Track Made Good If the aircraft drifts off track and we establish our position overhead a unique feature (called a pinpoint), the Track Made Good (TMG) is the line joining the departure airfield and the pinpoint. TRACK MADE GOOD Pinpoint
Departure Airfield Destination Airfield
Revised Track This is the line drawn from the pinpoint to the next turning point. REVISED TRACK Pinpoint
Departure Airfield Next Turning Point /
Destination Airfield
3.2 the 1 in 60 rule
The 1 in 60 rule states that if an aircraft flies a Track Made Good 1o in error from the required track, then after 60 miles the aircraft will be one mile off the required track. This rule, however, only works for track errors up to 23o. This can be represented using a triangle: Pinpoint Distance off the required track Track Error Angle Closing Angle Distance travelled Distance still to travel Questions
1. What is the main limitation of the 1 in 60 rule? 2. Draw a triangle to show the main principles of the 1 in 60 rule. 3. Label the TMG (Track made good) on your triangle. 3.3 applications of the 1 in 60 rule
You can use the 1 in 60 rule to find how far an aircraft is off the required track and how far it must turn to rejoin it at the next turning point. For example, imagine that after 20 miles, the aircraft is 4 miles off the required track, and has a further 40 miles to fly, what angle must the aircraft turn to rejoin the required track at the next turning point? 1. Represent the information as a triangle: 4
20 40
2. Take each triangle separately Left Hand Triangle: •
Extend the triangle to make a triangle with a 60 mile base: • If a 20 mile run produced a 4 mile error, a 60 mile run (3 times as far) will give a 12 mile error (3 x 4) Therefore, the track error angle is 12o
12
4 20
60
Right Hand Triangle •
Extend the triangle to make a triangle with a 60 mile base: •
If a 40 mile run produced a 4 mile error, a 60 mile run (1.5 times as far) will give a 6 mile error (1.5 x 4) Therefore, the track error angle is 6o
6 4 40
60
KEY POINT
CLOSING ANGLE + TRACK ERROR ANGLE = AMOUNT NEEDED TO TURN TO REGAIN THE REQUIRED TRACK AT THE NEXT TURNING POINT
Therefore, 6 + 12 = 18o needed to turn to regain the required track. 3.4 exam style questions
1. The track drawn on a map, between the departure airfield and the destination is known as: A.
B.
C.
D.
Heading required Track required Track made good Revised track 2. An aircraft flies a track made good, 3 degrees in error from the required track. Using the 1 in 60 rule, how many miles will the aircraft be off track after 60 miles of flying? A.
B.
C.
D.
1nm 6nms 3nms 2nms 3. An aircraft flying from A to B, after flying 30nms, has a track error of 10 degrees. How far is the aircraft off track at the time of the fix? A.
B.
C.
D.
6nms 2nms 5nms 3nms FIX 4. An aircraft flying from A to B finds that after 40nms it is 6nms right of track. If it has a further 30nms to travel, by how much does the pilot need to turn, to regain the intended track at B? A.
B.
C.
D.
24 degrees right 18 degrees left 21 degrees left 12 degrees left 4.1 compass forces
The Earth Lines of Force The above diagram shows a compass’ magnetic field. You can clearly see that the lines of force are only parallel to the earth’s surface at the Equator! The directional force that makes the compass needle point north gets progressively weaker as you get closer to the poles. Indeed, once the angle of dip (the angle at which the lines of force point downwards) exceeds 75o, the compass becomes virtually useless! Questions
1. Draw a diagram to show the Earth’s magnetic field. 2. Define the term ‘angle of dip’. 3. At our latitude, the angle of dip is approximately 65o. Will a compass work properly at this latitude? 4.2 the direct indicating compass (DIC)
The points of the compass are printed around the equator of the ball. The magnet is hidden inside the ball. The magnetic heading is shown against the index mark on the bowl. Limitations of the DIC
Advantages of the DIC
The DIC can only give readings in straight and level, un‐accelerated flight. The DIC is very simple and, therefore, reliable. It is affected by the magnetic fields emanating from the metal the aircraft is made from and its electrical circuits. It is cheap and lightweight. The magnetic field does not have enough torque to repeat the heading to other crew positions. It does not require any form of power and will, therefore, work even after a total power failure. The DIC can only give the magnetic heading. Above 70o North and South of the Equator, the DIC becomes sluggish because of weak directional forces. Questions
1. What are the main parts of the Direct Indicating Compass (DIC)? 2. An aircraft designer wants to choose a compass to use in a new aircraft. Explain the advantages and disadvantages of him choosing a DIC. 4.3 the gyro magnetic compass (GMC)
Components 1. The magnetic detector (flux valve) which electronically senses the direction of the Earth’s magnetic field. This is situated in the wing tip where it is less affected by other magnetic fields. 2. A turn / accelerator cut off switch. 3. A gyroscope, which always points to the point in space. 4. As the GMC has more torque than the DIC, it is also possible to use various compass repeaters around the aircraft. The outputs can also easily be modified to display the True heading. How does the GMC work? The basic principle of the GMC is that it uses the long‐term accuracy of the detector unit combined with the short‐term accuracy of the Gyro. In straight and level, un‐accelerated flight, the gyro is constantly corrected by the magnetic detector. During a turn, however, when the detector unit is unreliable, the turn/accelerator cut out switch allows the gyro to operate on its own until the turn is complete. Over such a short period of time, the amount of error caused by the uncorrected gyro is insignificant. Gyro Errors There are two types of gyro error: 1. Real Errors – caused by inaccuracies during manufacturing. 2. Apparent errors – caused because we fly around a rotating earth. We easily correct for the apparent errors and they are automatically compensated for using a correction box which is built into the compass system. Questions
1. The GMC was designed to improve on the DIC. In what ways has this been achieved? 2. Describe how the GMC works in straight and level, un‐
accelerated flight. 3. A pilot wishes to make a turn. Draw a flowchart to show how the GMC operates during this period. 4.4 inertial navigation systems
The most obvious problem with using any navigation system which relies on magnetic north to find true north is that our knowledge of the variation is rarely better than 1 degree. Although this doesn’t appear to be that important, it can cause hourly position errors of up to 6nm! Where am I?
KEY POINT
The inertial navigation system (INS) provides the True heading without the need of a magnetic detection system. As a result, providing you know your starting position, you can be certain of your position at any moment in time. The INS is a lot more accurate, providing positional information to accuracy of less than 1nm every hour! Questions
1. Complete the following sentence: An INS works by using computers to keep a record of the aircraft’s movements from a known _______________ _______________ 2. Why is the Inertial Navigation System so important for an aircraft? 3. What is the main advantage of using an INS? 4.5 to the future (and beyond)
Older inertial navigation systems are prone to breaking down and take an enormous amount of time to service. Modern inertial navigation systems, however, greatly enhance reliability and reduce servicing overheads (without affecting the accuracy). Modern computers can also carry all the details of the aircraft’s direction and attitude, which can be very useful. Combining an INS with a modern satellite navigation system will also be able to provide a powerful and accurate navigation/attack system. This can be used world‐wide and will be very resistant to jamming. Questions
1. What are the main problems associated with older Inertial Navigation Systems? 2. Describe another technological advancement which will become much more common in the future and its advantages over present systems. 3. Name and describe the two different types of error associated with gyros. 4.6 exam style questions
1. When would a Direct Indicating Compass be most accurate? A.
B.
C.
D.
In a steady descent In a turn In un‐accelerated flight In a steady climb 2. Which of the following is one advantage of a gyro‐magnetic compass, over a Direct Indicating Compass? A.
B.
C.
D.
A gyro‐magnetic compass can feed compass repeaters around the aircraft A gyro magnetic compass is cheaper A gyro magnetic compass does not work during turns and accelerations A gyro magnetic compass requires no electricity 3. As a compass nears the Magnetic North Pole, the compass detector will try to point at the magnetic material inside the earth. This tilting is called: A.
B.
C.
D.
Wander Dip Variation Drop 4. Which of the following is not a component within a Gyro‐magnetic system? A.
B.
C.
D.
A suspended magnet A gyroscope A flux valve magnetic detector A turn/acceleration cut out switch 5.1 VMC and IMC
Basic trainers so not have sufficient instruments to fly in cloud and their student pilots also rarely have enough experience. KEY POINT
As a result, beginners may only fly in Visual Met Conditions (VMC) with good visibility and a cloud base that is satisfactory for the aerodrome controller. This is important, because trainee pilots do not want to lose sight of the aircraft from anywhere in the (visual) circuit. If the weather is worse than this, then the aircraft must have the necessary instruments and the pilots must have suitable instrument ratings to fly in such conditions. Such conditions are known as Instrument Met Conditions (IMC). Questions
1. What are the weather conditions associated with VMC? 2. What two things are needed for an aircraft to fly in IMC? 3. For what two reasons can beginners not fly in IMC? 4. Name and describe the two different types of error associated with gyros. 5.2 wind
Aircraft always take off and land into wind. This is because when taking off into a strong wind, an aircraft will reach its flying speed very quickly and will, therefore, require a much shorter take off run. If an aircraft was to take off downwind, it might even reach the end of the runway before gaining the necessary flying speed! As a result, runways are always built to take into account the direction of the prevailing winds. However, as it is very unusual for the wind to blow exactly along the runway, we often have to calculate the crosswind and head wind. A Windsock
Headwind Component RUNWAY Wind direction Crosswind Component Take the angle between the wind direction and runway heading (headwind component) and use the following table to work out an approximate value for the crosswind component: Angle between wind direction and runway heading Crosswind component 0o ‐15o
15o ‐30o
30o ‐45o
45o ‐60o
60o and above Zero ¼ of wind strength ½ of wind strength ¾ of wind strength Full wind strength Questions
1. Why should a large aircraft never take off downwind? What are the advantages of taking off into wind? 2. The angle between the wind direction and the runway heading is 31o and the wind speed is 40kts. What is the crosswind component? 3. Why do you think that windsocks, such as the one shown above, are so important on airfields? 5.3 shallow fog Shallow fog normally forms during the early evening and often creates a very shallow layer close to the ground. KEY POINT
For a pilot looking down from above, this fog will be virtually invisible. Once the aircraft joins the glide slope approaching the runway, however, the pilot is looking through the fog at a much shallower angle and, as a result, the fog appears to suddenly become much thicker. This slant visibility is known as the Runway Visual Range (RVR). If this is less than 800m, then landings can be extremely difficult or even impossible. From an aircraft looking down from above, the fog looks to be invisible. From an aircraft looking through the fog at a shallow angle, it looks to be much thicker, making landings hazardous. LOW LEVEL FOG
LOW LEVEL FOG Runway Runway
Questions
1. When does shallow fog normally form? 2. What is the RVR? 3. By drawing two labelled diagrams, explain why from an aircraft directly above the fog, it looks to be invisible, but from an aircraft about to land, it looks to be much thicker. 5.4 precipitation and icing KEY POINT
Precipitation is the name given to any moisture that falls from the earth’s atmosphere, such as rain, snow and hail. If the precipitation is frozen when the aircraft is in the air or the ground level temperature is less than 0oC, then the precipitation will start to stick to the airframe. This can cause serious problems, and hence any lose snow must be brushed off, or, if it has stuck to the airframe it must be treated with anti‐
icing fluid before the aircraft is allowed to take‐off. Why is Icing such a Problem? As ice sticks to the wing surfaces, their shape starts to change and no longer resembles an aerofoil and, therefore, no longer generates as much lift. The problem is made worse because the weight of the aircraft also increases as the ice sticks to the airframe. This means that in icing conditions, the weight is increasing as the lift decreases! The icing can also affect the aircraft’s control surfaces and radio aerials as well as the engine performance. Questions
1. Give 3 further examples of precipitation, other than the ones listed above. 2. An aircraft, about to take off from Blackpool Airport, discovers that the airframe has become severely iced overnight. What must be done before the aircraft can take‐ off? 3. Why can icing be such a major problem for aircraft? 5.5 exam style questions 1. In order to fly in a Visual Circuit, a trainee pilot requires: A. Good visibility and no cloud in the sky. B. Good visibility and no wind. C. Visibility and cloud base conditions to meet the aerodrome controller’s requirements D. No wind. 2. The wind is blowing directly down the length of a runway. What is the crosswind component? A.
B.
C.
D.
½ wind speed Equal to the wind speed Zero ¾ wind speed 3. The collective noun for rain, sleet, snow and hail is: A.
B.
C.
D.
IMC Precipitation VMC Participation 4. What effect can icing have on the aerodynamics of an aircraft? A.
B.
C.
D.
Lift will decrease and weight will increase The windscreen may freeze over There will be no adverse effect upon the aerodynamics Ice forming on the leading edge of the wing will increase lift