Two navigation course note books

MOpenshawB19211117-180404-01.pdf

Title

Two navigation course note books

Description

Book 1 - contains notes on basic earth geography, direction on the earth's surface, terrestrial magnetism, maps and projections. map symbols, latitude and longitude, triangles of velocity and reporting. There is a team list at the back.

Book 2 - contains notes on types of navigation forms, air positioning dead reckoning. fixes, plotting position lines, navigation projections (Mercator), bearings, conversion angle, plotting great circle bearings, principles of aircraft instruments, airspeed and altitude calculations, plotting.

Creator

Publisher

IBCC Digital Archive

Contributor

Anita Raine
David Bloomfield

Rights

This content is available under a CC BY-NC 4.0 International license (Creative Commons Attribution-NonCommercial 4.0). It has been published ‘as is’ and may contain inaccuracies or culturally inappropriate references that do not necessarily reflect the official policy or position of the University of Lincoln or the International Bomber Command Centre. For more information, visit https://creativecommons.org/licenses/by-nc/4.0/ and https://ibccdigitalarchive.lincoln.ac.uk/omeka/legal.

Format

Two handwritten notebooks of 36 and 60 pages and covers respectively.

Language

Identifier

MOpenshawB19211117-180404-01

Coverage

Transcription

[cover of the manual]

[page break]

Lea Green 6767
[underlined] Forms of the Earth [/underlined]
It will be necessary to consider some of the general features of the spherical world over which the navigator will flie. The earth is actually an oblate spheroid but the difference between it and an actual sphere is so small that for all practical navigation purposes the earth is considered a perfect sphere. The equatorial diameter of the earth aproximately [sic] 7926 st.mls and the polar diameter 7899 st.mls approx. The flatness occurring in both polar regions is known as the earth’s compression.
[drawings showing polar diameters & a Great circle]
[underlined] Def [/underlined]
A great circle is a circle on the surface of the earth the plane of which passes through the earths centre.

[page break]

[underlined] Def [/underlined] A small circle is a circle on the surface of the earth the plane of which does not pass through the earth’s centre.
[drawing showing small circles]
[underlined] Def [/underlined] a parallel of latitude is a small circle parallel to the plane of the equator.
[drawing showing the equator & the parallels of latitude]
[underlined] Def [/underlined] A meridian is a semi great circle joining the geographical poles of the earth
[drawing showing meridians]
[underlined] Def [/underlined] The equator is that great circle which is at right angles to the earth’s axis of rotation.
In order to facilatate [sic] the fixing of positions on the earth’s surface, the earth is imagined to be covered with a graticule.
[underlined]Def [/underlined] Graticule is the network of lines formed on a sphere by meridians of longitude and parallels of latitude.
[drawing showing graticule]
[underlined] Def [/underlined] The Prime meridian is the meridian which passes through the telescope at Greenwich observatory.
[underlined] Def [/underlined] A rhumb line is a line on the surface of the earth that cuts all meridians at the same angle.
[drawing showing the Rhumb line]

[page break]

[underlined] Direction on the Earth’s surface. [/underlined]
The earth rotates once in 24 hrs about its axis.
[underlined] Def. [/underlined] The geographical axis of the earth is the diameter about which it revolves.
At each extremities of the axis we have the geographical poles North and South. The earth rotates from West to East, owing to this rotating, heavenly body appear to rise in the East and set in the West. From any point on the earth the North pole [deleted] lui [/deleted] lies due North and the South pole due south. We now have four definete [sic] directions North, East, South and West these are known as Cardinal points or directions, it should be noticed that these directions are at right angles to each other. We can now obtain directions half way between those given above and we now have North East, South East, South [deleted] Ea [/deleted] West and North West, these are known as Quadrantal points or directions.
By convention, in Air Nav. directions are measured in degrees [underlined] clockwise [/underlined] from True North or by directions of local true meridians (000o or 360o). All directions must be expressed as three figured groups, i.e. due East would be 090o(T).
[drawing showing quadrantal points and cardinal points]
[underlined] Terrestial Magnetism [/underlined]
The earth is a magnet with all the charecteristics [sic] properties of any other magnet, a compass needle anywhere on the earth’s surface will align itself with the earth’s magnetic field at that is under the sole influence of the earth’s magnetic field is known as the local magnetic meridian. Hence a magnetic meridian will be:- [underlined] Def [/underlined] The direction of a freely suspended compass needle under the sole influence of

[page break]

the earth’s magnetic field.
Since the earth’s magnetic [inserted] poles [/inserted] are not coincidence [deleted] corin [/deleted] with the earth’s geographical poles it will be seen that a compass needle that has aligned itself with the earth’s magnetic field would not necessarily lead us to true north.
Consider the true meridian at a place, it will make an angle with the local magnetic meridian, this is the angle of variation. In travelling from one place to another we are interested in the relationship of directions with the true meridians. In flying when using a magnetic compass it is essential that the variation for the flight are known.
[underlined] Def [/underlined] Variation is angle in the horizontal plane between the true meridian and the direction of a freely suspended compass needle under the sole influence of the earth’s magnetic field. It is measured East & or West – according to whether the compass needle points East or West of the true meridian.
N.B. East & or West indicates correction made to magnetic readings to give true readings.
Magnetic survey charts have been prepared showing variations at all places, lines on these charts joining places of equal variation are known as Isoginals.[sic]
[underlined] Def. [/underlined] An Isoginal[sic] is line on a map or chart at all places on which variation has the same value.
[underlined] Def [/underlined] An Agonic line is a line [deleted] joing [/deleted] joinging places of zero variation.
There are four methods by which variation can be shown on map or chart, they are:-
(1) [underlined] Isoginal [sic] and [deleted] Io [/deleted] Agonic lines [/underlined]
[drawing of the isoginal and agonic lines]
(2) [underlined] Compass Rose [/underlined]
[drawing of the compass rose]

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[underlined] Marginal Diagram [/underlined]
[drawing showing degrees of margin]
[underlined] Statement in Words [/underlined]
[underlined] VARIATION [/underlined]
[drawing showing the magnetic field, angle of variation and the compass needle alignment]
[underlined] Annual change of variation [/underlined]
The magnetic poles do not remain in one position but travel round earth’s geographical axis completing one cycle of travel in 960 yrs. Hence variation at any place is changing continually. In England this change is at the rate of 11’ decrease per year, when taking variation on a map, therefore the date of the magnetic survey shown on the isoginals [sic] should be noted and the necessary correction made to bring the variation up to the date of use of the maps.
The primary cause of variation is the non-incidence of the magnetic poles and geographical poles, variation is also caused by the very uneven distribution of metallic ore in the earth’s crust.
All plotting in the R.A.F.is measured using true direction and since observations made during flight are obtained from a magnetic compass the necessity for correct knowledge of variation will be realised. When converting magnetic readings to true readings and vicesa-versa. the following ryhme [sic] should be observed.
[drawing showing degrees of variation to the west and the best]

[page break]

[underlined] Deviations [/underlined]
A compass needle is affected only by the earths magnetic field will along the local magnetic meridian. Under these circumstances the only correction that need be applied to obtain the true meridian will be the local variation.
Unfortunately this state of affairs no longer exist when the compass needle is placed in an aircraft, for there magnetic influences which will influence the compass needle and deflect it from the [deleted] to [/deleted] magnetic meridian. (ie deviate)
[underlined] Def [/underlined]
Deviation is the angle in the horizontal plane between the magnetic meridian and he direction of particular compass needle, influence by magnetic fields other than the earth’s magnetic fields. It is measured in degrees East &- or West – according to whether the compass needle points East or West of the magnetic meridian.
When converting compass readings to magnetic and vice-versa the following ryhme [sic] should be observed.
[drawing showing West – Best and East – Least degrees]
[underlined] Bearings Courses and Tracks [/underlined]
[underlined] Def [/underlined] The track of aircraft is the angle between a meridian and actual path traced by the aircraft over the ground it is measured 000o to 360o in a clockwise direction.
[drawing showing actual path of A/C over ground]
[underlined] Def [/underlined] The course of an aircraft is the angle between a meridian and the direction of the longitudinal axis of an aircraft, measured clockwise from 000o to 360o.
[drawing showing direction of longitudinal axis]

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Def Drift is angle between Co and Tr of an aircraft, it is measured in degrees from Port (left) or Starboard (right) according to whether aircraft drifts to right or left of the course.
[drawing showing aircraft drifts in degrees]
Def Great circle bearings of an object from an aircraft is the angle at the observor [sic] between his meridian and the arc of a great circle joining him to his object measured in a clockwise direction from 000o to 360o.
[drawing showing the object measurement in degrees]
Def. the rhumb line of [deleted] met [/deleted] mercatorial [sic] bearing of an object from aircraft, is angle at observor [sic]between his meridian and the rhumb line joining him to the object, measured 000o to 360o in a clockwise direction.
[drawing showing reciprocal angles]
B bears from A 060oT.
A bears from B 240oT.
[underlined] Def [/underlined] Back bearing is the direction observed from an aircraft of an object over which t has previously passed with any intervening alteration of course.
All angular measurements of bearings, courses or tracks must e given three figured references ie a clockwise direction of 2o will be written 002o
[drawing showing back bearings]

[page break]

[underlined] Maps Charts and Projection [/underlined]
Mathematical Cylinderical [sic] Projection
[drawing charting degrees]
Def A projection is an orderly system of representing the surface of the earth on a plane surface.
To represent the surface of the earth on a flat surface giving an exact reproduction s impossible.
In Air Navigation projections are divided into two groups (a) navigation (for plotting) (B) [deleted] Fro [/deleted] Topographical (for map reading)
[underlined] Navigational Projection [/underlined]
The [deleted] usual [/deleted] actual projection usually used is the mercators:
In flying from one place to another along a great circle track (ie) (shortest [deleted] plar [/deleted] distance between any two places) we are continually crossing meridians which owing to their conveying at the poles are changing the angle they make with our tracks as we change position, therefore it must be apparent that to maintain a great circle track we must be continually changing course which cannot be considered a satisfactory state of affairs.
This difficulty is overcome by flying along a rhumb line track which owing to the fact that it cuts all meridians at the same angle does not necessitate changing course. It must be appreciated that the rhumb line has a certain disadvantage it is not the shortest distance between ant two places ie Calshot to New York great circle 2976n.m. rhumb line 3088n.m.
Generally speaking the saving in distances by following a great circle track in flights up to 100mls is not worth the additional trouble involved.
It is obviously a great help if a rhumb line can be laid down on a map by simply drawing a straight. If it is to be a straight line then all meridians it crosses must be parellel, this is one

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of the major properties of mercators [sic] projection.
[underlined] Properties [/underlined] [deleted] of [/deleted] [circled number] 1 [/circled number] meridians are parellel [sic] equidistance straight lines, it follows, that a rhumb line must also be a straight line.
[circled number] 2 [/circled number] Great circles appear as curves convex to nearer poles.
[circled number 3 [/circled number] Parellels [sic] of latitude appear as parellel [sic] straight lines increasing in distance apart as poles are approached.
It is orthomorphic (shape preserving for small areas)
Parellels [sic of latitude are small circles and also rhumb lines.
Equator is a great circle and also a rhumb line
Meridians are semi-great circles and also rhumb lines.
[underlined] Topographical Projections [/underlined]
A topographical projection is that projection which is used to project a topographical map, usually modified polyconic or cassinis. [sic]
A topographical map is a map that shows details of land features (topography used for map reading). The majority of topographic map projections are [deleted] ortho [/deleted] orthomorthic [sic]. The different projection used for these maps differ only in minor details which do not concern the practical [deleted] nov [/deleted] navigator.
[underlined] Properties [/underlined]
[circled number] 1 [/circled number] Scale is taken as constant over each [deleted] so [/deleted] separate sheet.
[circled number] 2 [/circled number] A Rhumb line appears as a concave curve.
[circled number] 3 [/circled number]Straight lines may be regarded as great circles.
[drawing showing great circle and a Rhumb line]
Meridians appear as straight lines converging at the poles, and parrllels [sic] of latitude appear as curves concave to the nearer pole. By steering a constant course (Rhumb line) a navigator must expect to be on the equator side of a great circle track borne between two points on a topographical map.
Representative fraction (natural scale) which expresses the ratio between two points on the map

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to the actual distance between the same two points on the earth’s surface i.e. 1/250,000 1/500,000. Graduated scale lines show actual length on map of ground units of length in Km, S.M. or N.M.
[drawing of a scale]
[underlined] Statements in words [/underlined] ie 1/4=ml
[underlined] Relief [/underlined]
[underlined] Contours and form lines. [/underlined]
The presentation of an imaginary line at the same height above mean sea level. Contours are accurately surveyed measurements and must [deleted] I [/deleted] not be confused with form lines which are only approx. contours.
[drawing showing contour lines]
[underlined] Layer Tinting [/underlined]
Is a system of [deleted] relief [deleted] representing relief on a [inserted] map [/inserted] by application of layers of tint between adjacent contours lines. The tint usually intensifying with each successive increase in height.
[drawing of tinting layers]
Spot Heights actual height of one particular point above mean sea level. 700ft
Hachuring is a method of showing relief by shadowing with short disconnected radiating from peaks and high ground, not used on [deleted] topog [/deleted] topographical maps owing to idefinete [sic] nature, used on plotting charts to give approx. position of high ground.
[Pencil drawing]

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Hill Shading:- imagine a bright line shining across a map, shadows cast by high ground are shown on a map. Difficulty is experienced when shadow obliterates detail and its therefore not extensively used, however it is still found on old continental maps.
Def. Vertical Interval is difference in level between two adjecent [sic] contours.
Def. Horizontal Equivilant [sic] is difference in plan between two adjecent [sic] contours.
Gradient VI/HE
[drawing showing vertical interval & horizontal equivilant [sic]]
[underlined] Latitude and Longitude [/underlined]
Def. the latitude of a place is the angle at the centre of the earth subtended by the arc of a meridian intercepted between the parellel [sic] of latitude passing through the place and the equator. It is measured in degrees 000o to 360o according to whether the place in North or South of the equator.
Def:- the longitude of a place is the angle at the centre of the earth subtened [sic] by the smaller arc of the equator intercepted between the prime meridian and the meridian passing through the place. It is measured in [deleted] dre [/deleted] degrees, 0o to 180o East and 0o to 180o West according to whether the place is East or West of the prime meridian.
[drawing showing lines of latitude and longitude]
The change of latitude between two places is the angle at the centre of the earth subtened [sic] by an arc on a meridian intercepted between the two parellels [sic] of latitude passing through the two places. It is measured in 0o degrees and named North or South according to the direction followed in making the change.
The change of longitude between two places is the angle at the centre of the earth of subtened [sic]

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by he shorter arc of the equator intercepted between the two meridians passing through the two places, it is measured in degrees and named East or West according the direction followed in making the change,
[drawing showing equator interception]
Subtraction is involved where lat and longitude are of the same name. Addition where latitude and longitude are opposite names.
[underlined] Exceptional [deleted] Promb [/deleted] Problem [/underlined]
Place from 164o 00’E
Place to 120o 00’W
284o
Def:- we require angle subtened [sic] by smaller arc, this is obviously the larger one. Rule:- where change of longitude exceeds 180o subtract it from 360o and change direction, ie 360o 00’ – 284o 00’, change of direction 076o 00’E.
Magnetic Field
The earth’s lines of force are vertical to the surface at the magnetic poles and parellel [sic] to the surface midway between them. A freely suspended compass magnetic needle which has aligned itself with the earth’s line of total magnetic force on a journey from one magnetic pole to the other would therefore [deleted] aligned itself with the [/deleted] by being vertical to the earth’s surface and then pass through decreasing angles of depression until it became horizontal, and then the angle would increase slowly until over the other magnetic pole the needle would be vertical again. The angle such a needle makes with the horizontal at any point on the earth’s surface is known as the angle of magnetic dip.
Def:- Magnetic dip is the angle of depression below the horizontal at an observor [sic] of the earth’s total magnetic force.
Def:- An Isoclinal is line drawn on a map or globe chart joining all places of equal magnetic dip.

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Def. The uncemtrical [sic] line round the earth’s surface joining all places where [deleted] eq [/deleted] magnetic dip is zero is known as the magnetic equator.
Def:- The magnetic equator is a line joining all places where the direction of the earth’s magnetic field is horizontal and magnetic dip is zero.
Def. The magnetic poles are those two positions where the [deleted] tw [/deleted] direction of the earth’s magnetic field is vertical and magnetic dip is 90o.
The magnetic system of a compass is so balanced on it’s pivot that it always remains practically horizontal. It is thus more suitable for indicating direction than a compass needle inclined at the local magnetic dip.
Triangle of Velocities
Def. Velocity is the rate of change of position in a given direction.
Def. A vector is a graphical representation of a velocity
There are six variable factors which affect an A/C in flight, each of which has an effect on other five.
They are.
[circled number] 1 [/circled number] Course (Co) } componate [sic] velocity
[circled number] 2 [/circled number] True Air Speed (TAS) } componate [sic] velocity } W/V
[circled number] 3 [/circled number] Wind Direction (W/D) } W/V
[circled number] 4 [/circled number] Wind Speed (W/S) } W/V
[circled number] 5 [/circled number] Track (TR) } resultive [sic] velocity
[circled number] 6 [/circled number] Ground Speed (G/S) } resultive [sic] velocity
It should be noticed in above there are three speeds and three directions. Thus bearing in mind that a vector represents speed and direction enables us to construct three vectors.
Co and TAS for one vector
W/D and W/S for one vector
Tr and G/S for one vector

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It essential to realise that the arrangement of the above vector factors can never be altered (ie) the TAS is always laid off along the course it cannot be laid off along the track.
It is an actual fact that if four of above factors are known the other two may be found by a scale drawing of the triangle of velocity. There are in the RAF three triangles each involving the solution of two factors when other four are known. All directions used in plotting are clockwise angular measurements from true meridian.
Triangle no 1
To find course and ground speed given Tr, TAS and W/V.
[circled number] 1 [/circled number] Draw in a true meridian from some suitable [inserted] point [/inserted] on this meridian (point of origin) lay off Tr any length measured in a clockwise direction from true meridian.
[circled number] 2 [/circled number] [deleted] Measure down wind [/deleted]
From the same point on meridian lay off W/D, remember wind is from direction given and that this triangle must blow away from origin point.
[circled number] 3 [/circled number] Measure down wind from the point on meridian a distance to suitable vector scale to represent W/S. mark in this point.
[circled number] 4 [/circled number] Centre this point and radius the given TAS to some vector scale as used before and make an intersection in the map.
[circled number] 5 [/circled number] Join this point to the down wind point of wind vector, this will be the course, the clock wise angle may be measured from the True meridian.
[circled number] 6 [/circled number] Measure along Tr to scale as used in the distance from point of origin to the intersection of track. This will be G/S.
Therefore we have now found the two desired factors. Co (t) and G/S.
In all triangles the resultant vector (Tr and G/S) will always be shown with two arrowheads, the component will be marked with one arrow head each. It must be continually born in mind that while the course and track directions are to directions given, the wind direction is always from the direction given (it is commen [sic] knowledge that a N.E. wind is coming from N.E.)

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[4 drawings]
[6 identification symbols]
RADIO W/T
[3 identification symbols]
RADIO D/F
[13 identification symbols]
25 EFTS
Navigation Computer
Co, track and Ground Speed, given TAS, TC and W/V.
1. Set TAS
2 Set wind true direction against true course arrow from TAS point draw in wind vector to scale, mark wind vector with an arrow pointing down
3 Mark track with a pencil mark, set this against lubber line, read off degrees of drift from end of wind vector port or starboard.
4 Set required track against drift scale at the drift already found; now adjust dail [sic] slightly to make the drift on drift scale agree with the drift at the end of the wind vector.
Types of compass in general use in RAF in Pilots type :- the function to indicate the magnetic meridian for steering and setting courses. P4. Large type pilots compass, has four magnets, expansion chamber fitted with a grid ring graduated from 0o to 259o in division of 2o each.
P6 Small pilot nav. compass fitted with two magnetic and an expansion device which we call a sylphon [sic] [deleted] II [/deleted] tube.

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Reporting Position
P.8. Basically the P6 but constructed partly of bakerlite.
P.7. Basically the P6 but has a glass bottom and a mirror for horizontal readings
P.9. Basically the P8 but has a glass bottom and a mirror
Observor [sic] type compass:
Function for taking bearings and sights and for checking courses, fitted with an azimuth circle with prison sights.
02 and 02A; large type compass four magnets and an expansion chamber, and the only difference is the mark on the azimuth circle (between 02 and 02A)
06, hand bearing compass, has no azimuth circle, fitted with glass bottom, torch and a handle, for use at night, has no deviation card, also fitted with two magnetic compass card is mounted on top of magnet system
Reporting Position
RAF Lettered Co – ordinate method
RN Lettered Co – ordinate method
Bearing and distance method
Pinpoint
Lat and Long
RAF METHOD
The degrees parellels [sic] and meridians are each given two code letters, the intersection of a meridian and parellel [sic] being given a four figure [deleted] referce [/deleted] reference the code letters of the parellel [sic] being given first. In the R.A.F. method the S.W corner of the degree square in which the position is situated is first reported followed by CH Long and CH Lat (first) in mins between S.W corner and position. The mins of CH Lat being given first, the whole being given a four letter and a four figure reference.
Royal Navy

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TEAM
J. Bassett – W. GOOD – T. ORPIN – M. EVANS – N. HALE – G. TAYLOR “WICKET KEEPER” – R. WRIGHT – R. BOLT – D. BUCK – R. EVANS – J. BEARD [underlined] 12TH MAN. “JOE EVANS” [/underlined]
Webber ? – Nicholson – R. Evans [tick] – M. Evans [tick] – B. Peters ? – J. Bassett [tick] – T. Orpin [tick] – G. Taylor [tick] – J. Beard [tick] – R. Wright [tick] – R. Bolt [tick] – D. Buck [tick] – B. Good [tick] – N. Hale [tick] – J. Newbolt. – J. Evans [tick]

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B G 40 Homils [sic]
2 – 4 – 6 – 7 – 11 – 13 – 16 – 22 – 23 – 35 – 43 – 44 – 54 – 60 – 63 – 65 – 74 – 82
6 – 13 – 15 – 17 – 19 – 20 – 24 – 26 – 28 – 44 – 45 – 49 – 62 – 74 – 76 – 77 – 88 – 100

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[cover of the book]

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[chart showing degrees, vectors and co-ordinates]
[underlined] Form 316 [/underlined]
[chart showing degrees magnetic and steer by compass degrees]
100o(M) = 10/45 x 1/1 = 5/9 = [circled number] 1 [/circled number] 340o(M) = 25/45 x 2/1 = 1 6/9 = [circled number] 2 [/circled number]
Dev = 0o Dev =
[therefore symbol] Co (c) 100o
Vet Vector Scales
[circled number] 1 [/circled number] 1 degree of longitude to 60 units of speed
[circled number] 2 [/circled number] 1 degree of longitude to 120 units of speed

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Air Position
[underlined] Find Position by DR [/underlined]
At any time it should be possible for the navigator to calculate his position from [deleted] has [/deleted] what has already occurred during the flight. The principle underlying the calculation of the D.R. position is as the air position of the a/c can be worked out from observation of the true course, TAS and h time, then if the W/V is known and appro. [sic] wind effect is applied to the air position the ground position of the a/c is determined. This principle can be applied in the two following ways
[circled number] 1 [/circled number] When Track and G/S are observed
[drawn scale]
The navigator observes that his a/c has travelled from A to C in a certain time is N mins by calculating the ground speed the navigator can determine a distance C to Z for any time interval T mins. Z is therefore DR position for that a/c. This process is often adopted in practice when a/c maintains a TAS and height and no a/c keeps [deleted] cons [/deleted] constant and no change in W/V is experienced as soon as any material conditions of flight change such simple calculations become impossible.
2. Air Plot
During operational flying it may be necessary to alter course TAS and height frequently, provided navigator keeps accurate log of the courses, TAS, times and heights of the a/c and provided he knows the W/V he can find his DR position at any time. An air plot consists of laying down T courses and their respective air distances assuming a complete absence of wind, any point on the air plot is an air position, by taking on his air plot is an air position at the time of his required DR position and laying off from it a distance representing the total calculated effect of the wind since the

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commencement of the air plot, the navigator will obtain a DR position the accuracy of which depends on the accuracy of the W/V.
[drawing showing different plotting positions]
If an air plot is kept for a considerable time the W/V [deleted] varv [/deleted] will varie [sic], in this case the effect of the wind which must be applied can most easily be found if a separate plot is kept of the W/V found during the air plot, The winds are laid off in sucession [sic] as they are experiences and when DR position is required the wind effect is measured from the start of the wind plot to the point on the latest wind corresponding to required time.
An air plot is always made using true courses.
[deleted] On this [/deleted]
Unless absolutely [deleted] impp [/deleted] impossible an air plot should be kept in flight particularly when a number of courses are being flown
Advantages of an air plot.
1. Easy to keep and subject only to errors in drawing.
2. An air position can be quickly found from it.
3. If W/V is known the DR position can be found.
4. A W/V can be found at any time by comparing air position with a fix.
5. It promotes a keen interest in checking TAS courses and times.
6. It gives the pilot the greatest possible freedom of action so necessary in operational flying when maintenance of tr is impossible in the face of enemy opposition.

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An air plot should be restarted every time an accurate fix is established, errors are therefore reduced to a [deleted] me [/deleted] minimum. Never start an air fix from a DR position.
Method of Wind finding
1. Tr and G/S method
[drawing showing tr and G/S method]
Track and G/S can be measured most accurately from two reliable pinpoints obtain while flying a straight course [deleted] and [/deleted] a constant air speed Note :- Tr and GS found by use of such instruments CS and Bl or drift recording are unreliable for wind flying as it is usually impossible for the pilot to fly as accurately as these methods demand.
Air pilot method.
This is a very valuable method of finding wind provided plotting and timing are accurate and a reliable fix is f used. It is based on a comparison between air position of aircraft and its ground position whenever latter becomes known, the distance and direction of the ground position from the air position is clearly the effect of the wind since air plot was begun, the wind speed is then found by simple proportion.
[drawing showing plotting with wind effect for 25mins]
The number of alterations of course have o effect on wind found so long as air plot [deleted] o [/deleted] is kept accurately, if however air plot [inserted] is [/inserted] maintained for a considerable time the aircraft may experience a gradual chane [sic] of W/V and wind found will only be a mean W/V.
Multiple drift method.
Procedure :- steer on three courses in turn

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each being at least 50o apart from the others, note drift on each course.
CoT220o Drift 5oP Course(T) 310o Drift 9oP
Co(T)090o Drift 11oS.
[drawing 3 different courses]
Chose a suitable vector scale and describe a circle with radius TAS and centre O. From the circumference draw in the first Co to 0, lay off the other two Co’s in turn from the circumference to the centre from the point where each course leaves the circumference lay off the drift. It will be found that the 3 Tr’s thus drawn intercept possibly in a cocked hat at W it will bow be seen that we have three vector triangles of which OW the wind vector id common. This vector OW gives the wind direction measured from the centre outwards and it’s speed on the vector scale. The courses plotted on the TAS circle must be true courses.
The Drift and wind lane
[drawing showing the drift and wind lane]
This method is valuable for navigation over the sea at a height not access of 1500ft since data must contain a drift reading the method is impracticable when course of aircraft is either up or down or nearly so by measuring the drift the track of the aircraft can be determined by observing the compass or other means the direction of the wind lane can be determined which gives the wind direction on the surface of the sea as a general rule over the sea the wind direction at 1500ft is about 10o more than at the surface this tendency to veer can be applied to

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imeadiate [sic] heights by simple proportion but is to uncertain for heights above 1500ft since course and TAS, track and wind direction are known the wind speed and G/S can be calculated by plotting or CSC.
Position lines
A line drawn on a map or chart at some point upon which the aircraft is known to have been at a particular time.
Methods of obtaining
A position can be obtained in the following way by making visual or radial observations on a known object.
1. By Transit Bearing.
[drawing of a line of transit]
When two objects on earth’s surface appear to be in one straight line they are said to be in transit. The line joining two objects produced gives a position line. Transit bearings are written naming nearest object for example 0900 LTV 0 LTHO. The accuracy of the method is as high as +2o or -2o.
2. Compass Bearing.
If the compass bearing of an object is obtained by means of a bearing [deleted] ca [/deleted] compass and [deleted] oleva [/deleted] deviation for magnetic course of the aircraft and variation are applied to [deleted] the bearing true [/deleted] convert the bearing true, the reciplical [sic] of his bearing from the object is a position. the accuracy of this method is plus or minus 2o.
[drawing By W/T Bearings]
Position lines may be obtained by DF W/T, these bearings may be transmitted from a W/T station which itself takes the bearing of the a/c by DF and then ells the a/c what this bearing is

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together with the class and the time at which it was taken. Accuracy of 1st class bearing is with +or- 2o, and a 2nd class bearing + or – 5o.
4. Relative bearing
[drawing of bearings]
If the horizontal angle between a/c head and an object is measured by a DF loop or a bearing plate and if the true course of the a/c is applied then the principal of the bearing laid off from the object is a position line. The accuracy is not less than +or -2o.
5. Plan Range.
[drawing curved line]
If plan range of an object is observed from an a/c the circumference of a circle with centre the object and radius the range may be regarded as a position line.
6. Astro [deleted] Navigation [/deleted] observations
[ink mark]
[drawing of 3 lines]
It is possible to obtain positions lines by observation of the heavenly bodies. Such observations need more skill than those already described, such a position line may be considered in average conditions to indicate the centre of a band of position some 10mls wide any where the a/c might be. Note the width of the band depends on the skill of the observor [sic] the accurate maintanece [sic] of straight and level flight during observation and the [deleted] position [/deleted] [inserted] precision [/inserted] of the instruments used
Use of single position lines
1. Confirming Track
[2 drawings showing tracking lines]

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If navigator obtains a position line for example that is parellel [sic] or nearly parellel [sic] to his track the position line will serve to indicate within it’s limits of accuracy whether or not he is on track.
2. Finding G/S.
If navigator obtains a position line that is at or nearly at right angles to his track his G/S may be calculated from distance run between his last known position and the interception of his DR track and position line.
Use of multiple positions lines
If more than one position is avaible [sic] at any instant the [deleted] fos [/deleted] position of the a/c may be fixed with a certainty which depends on the accuracy of the position and their inclination to one another.
Cocked Hat
It is most improbable that if ore than two positions are avaible [sic] they will intersect at one point. Since the bearings are subject the errors already stated they will most probably form a triangle known as a cocked hat. The actual position is always taken as centre of triangle.
[underlined] Range and bearing fix [/underlined]
[drawing showing lines that cross]
If while observing the bearing of an object it’s plan range from a/c is also measured the position of the a/c may be fixed. Position is recorded as a bearing and distance.
[underlined] Fix by Simultaneous bearing [/underlined]
[drawing fixing a bearing]
If navigator is able to take instantaneous bearing of two or more objects the intersection

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of the plotted positions lines constitutes a fix since it is the only point in commen [sic] to the sevral [sic] lines drawn. It is not advisable to use position lines that differ by less than 45% from one another and no reliance what ever can be placed on a fix when the position lines meet at an angle of less than 30o. When taking simultaneous bearings the fix is timed at a moment when the object of the beam is observed since it’s bearing is changing most rapidly
[underlined] Transferring Position Lines [/underlined]
[drawing position lines]
Simultaneous bearings are seldom obtainable n flight there will usually be a time interval between then which cannot be neglected since the a/c has moved some s=distance between the taking of the bearings this difficulty is overcome by transfering [sic] the position lines. This can be done because a position of the a/c from the object, therefore if the object were moving on a track parellel [sic] to that of the a/c and at the same ground speed the bearing of the a/c from the object would remain unchanged over any interval of time. AX equals position line at 0900 BY equals transfered [sic] position always signified by double arrow. AB equals distance run by a/c along it’s track in two minutes. A position line can also be transfered [sic] in the case of an a/c whose Tr or G/S or both have been changed. To transfer a position first transfer to the position of alter course and then along 2nd tr at second G/S.
[underlined] Running Fix [/underlined]
When the position of an a/c is determined by transfering [sic]one or more position lines to cut another position line then intersection of such lines is known as a running fix. A bearings of two or more

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objects .
[drawing of intersection lines]
From A a point where the position lines cuts the tr mark off along the tr a b which is the distance [inserted] run [/inserted] in the time interval between the two bearings through B draw a line parellel [sic] to the first bearing which will cut the second bearing a L then L is the fix required.
B [underlined] Bearings on one object [/underlined]
The principal of the running fix can be applied when two or more bearings are taken of a single object. The method employed is the same as that used in previous example each position line being transfered [sic] along the tr for it’s individual time interval.
[drawing showing bearings on more than one object]
Transfer positions lines XA and XB along the Tr for distance run in 20 mins and 10 mins respectively where they cut position lines XC is the fix at the time position line XC was taken.
D. [underlined] Find Tr when Tr and G/S are unknown [/underlined]
If three position are obtained from one or more objects the tr of an a/c may be found as follows select a suitable lineal scale of time units for example 1 min to 1cm and mark off on a ruler or suitable straight edge the number of time units between the successive position lines and adjust it’s inclination until its marks upon it coincide with their appropriate position lines the inclination of the ruler then gives the direction of tr which is correct within the accuracy of the timing and of the observations.

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It is also possible to determine a position by used of this method of determining the tr. Suppose a known position A at 1200hrs and at 1220hrs and 1230hrs the navigator obtains bearings of an object B. Since the a/c was at A at 1200hrs the line joining A to B may be regarded as a position line at 1200hrs hence by procedure just described he tr of a/c is obtained.
[drawing showing the 3 different times and positions]
Through A draw a line parellel [sic] to the Tr so obtained this line represent actual Tr of the a/c cutting position lines at CD which may be considered. G/S may be found by measuring distance AD which has been run in 30 mins.
[underlined] Doubling Angle on the bow [/underlined]
Obtaining a fix by this method depends upon accurate timing of observations, the time is taken at which a bearing of an object makes a chosen angle with the track of between 30o and 80o. The angle on the bow is observed to increase as the object is approached and passed the time when the angle is double that of the original angle is noted. At this moment the a/c is a distance from the object equal to the distance run between the two observations calculated by G/S and time because triangle formed by the Tr and the two position lines is Isosceles.
[drawing of lines to form a triangle with the angles and times]

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[underlined] Fixing Position [/underlined]
Fixing position depends on sevral [sic] factors such as visibility and whether or not the area over which the a/c [deleted] ab [/deleted] is flying abounds in land marks. The methods of fixing positions are summarised in order of the reliability under all circumstances.
[circled number] 1 [/circled number] [underlined] Visual fixes [/underlined] best not allways [sic] availible [sic] owing to bad visibility or lack of permanant [sic] ground features. They are obtained (a) map reading b visually observed position lines.
[circled number] 2 [/circled number] [underlined] Astro fixes [/underlined] the average navigator can obtain position of an accuracy within 10 mls using two position lines the fix obtained is accurate to within 12 mls.
3. [underlined] DF W/T fixes [/underlined] these suffer from many defects, in ideal conditions however DF fixes can be accurate usually a DF fix is regarded as having an error of about 20 mls which error depends on the distance between the a/c and W/T station.
[underlined] Plotting Position lines [underlined]
So for position lines have been considered as curves or straight lines drawn on paper to represent certain ranges or bearings, these bearings can be represented in different ways according the map projection being used. A [deleted] pro [deleted] position line can be one of three types 1. Arc of great circle. – 2 Arc of small circle – 3 Arc of a curve of equal bearing
[underlined] Arc of a Great Circle [/underlined]
A transit is shortest line joining two origins and must therefore be a arc of a great circle and therefore the position line is actually a great circle arc but owing to it’s short length is plotted as a straight line, also a DF W/T bearing is a great circle bearing since wireless waves travel
The plotting of great circles depends on the [deleted] ma [/deleted] projection of the map of chart in use (1) On all Topographical map, layed [sic] of direct from meridian of origin as a straight line in direction of the a/c.
(2) [underlined] On Gnomonic Chart. [/underlined]
Same as for the topographical

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map, a distorted compass Rose applicable to position of origin may have to be used.
3. [underlined] Mercators Chart [/underlined]
(A) Calculate DR position of a/c (b) Calculate CA (c) Draw Rhumb line bearing from the origin by applying the conversion angle to great circle bearing at the origin.
[underlined] Navigational Projections [/underlined]
Air navigators are primarly [sic] interested in Rhumb lines but they frequently have to consider great circles as for example plotting bearings of an a/c obtained from a DF station. On the mercators projection the Rhumb line is drawn as a straight line bat [sic] a great circle is a curve convex to nearer pole that is on polar side of Rhumb line. Often on long flights it is better to fly a great circle instead of the usual Rhumb line track because of distance saved by so doing. In this case it is necessary to have a map or chart on which great circles appear as straight lines
[underlined] Gnomonic Projection [/underlined]
A map produced by this projection provides these very facilities unfortunately shapes bearings and areas are all distorted and there is no uniform scale of distance. There are 3 different types Polar, Equatorial and general, the only [deleted] w [/deleted] one used for

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ordinary navigation is Polar Gnomonic in which the pole is the centre of the map the map sheet making a tangent with the earth at the pole. Points on the earth are projected by drawing a line from the centre of the earth through the point and on to the map. Meridians will be straight lines radiating from the pole will parellels [sic] of latitudes will concentric [inserted] circles [/inserted] with centre the pole.
[drawing showing Mercators projections]
Placed on a true cylindrical projection which may be compared to a cylinder wrapped round the earth and joining it along the equator. Meridians and parellels [sic] of latitude then transfered [sic] from the earth and projected to the inside of the cylinder as seen by an observor [sic] with eye to the centre of the globe, with this projection distance between parellels [sic] increases between N and S of the equator and it is imposible [sic] project further areas. On the globe all meridians and parellels [sic] of latitude cut each other at right angles. An extremely important navigational requirement is that angles any where on the earths surface shall be correctly represented on the projection satisfies these requirements
Properties.
In mercators projection longitude scale is consisted all over the chart where as latitude scale varies with the latitude. True shape is preserved at cost of area

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hence near land masses near poles appear as huge continents though they are quite small. Thus we find that the mercators projection possess following charectaristics [sic].
1. Scale not consistent
2. Bearing straight line – Rhumb line
3. Area not equal
4. Shape true
It found by mathematical calculation that the increase in distance between parellels [sic] of lat. varies as the secant in latitude. This knowledge is used to make tables [inserted] of [/inserted] meridianal [sic] parts or mercaorial parts are number of times the length of one minute of longitude is contained in the projected distance from the equator to any [inserted] particular [/inserted] parellel [sic] of latitude.
Example if one minute of longitude – 0.02” then the distance from the equator and 30o N is 0.02 times mercatorial part for 30o that equals 0.02 x 1876.67” (taken from table) which equals 37.5334”
[underlined] Use of Mercators Projection Scale [/underlined]
On the earth the length of minute of latitude is nearly constant and consquently [sic] it forms a convenient measure of distance, on the land the length of a minute of longitude decreases. Being equal roughly to one minute of lat. at the equator but zero at the poles. On mercators projection these conditions are apparently but only apparently reversed since a minute of lat increases steadily N and S of the equator while the minute of longitude is constant all over the chart, never the less the physical scale of distance it so increases N and S of the equator on the projection therefore it is necessary to use the latitude sub division as a measure of distance. On the other hand it is necessary to use a uniform scale for solving triangle of velocity problems and for this purpose the longitude scale admirable.
[underlined] Measure of Distance [/underlined]
When measuring distance of mercator

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it is essential that the distance be taken from the latitude scale opposite length to be measured, all distances measured from latitude scale are in NM therefore if SM are required the special scale must be used.
[underlined] Bearings [/underlined]
On mercators all bearings measured from straight lines are Rhumb line bearings and are the same no matter from what meridian the measurement is made. It is therefore obvious that the plotting of Rhumb line Bearing present no difficulty however a great circle cuts successive meridians at different angles since all meridians are parellel [sic] a great circle will be a curved line convexed to nearer pole. The drawing or measurement of great circle bearing therefore calls for a special procedure.
Convergency [sic]
The reason why a great circle cuts successive meridian at different angles is that on the earth meridians are not parellel [sic] but are inclined at angles to one another. The inclination between any two meridians is called their convergency [sic] and it represents the angular difference between a great circle bearing measured at either meridian.
[drawing showing converging lines]
AB CD are meridians and CXY is convergency [sic] being difference between angle AVX and CXZ.
At the equator which all meridians cut at right angles there is no convergency [sic] where as at the poles the angle between any two meridians amounts to the change of longitude between them. Thus the value of convergency [sic] is a fraction of the CH of longitude and evidently varies with angle of latitude just as the sign of any angle varies, that is to say convergency [sic] at Lat 0o – 0 convergency [sic] at Lat 90o = Ch of long

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In fact for all practical purposes it can be said that value of convergency [sic] between any tow places at different latitudes on the earth is given by the formula convergency [sic] = Ch Long x Lin mean lat example :- what is convergency [sic] between A25o30 mins N 05’20W B41’20 N 1640E. Convergency [sic] = 22 x Sin33 – 22 x 0.54464c= 12o
[underlined] Conversion Angle [/underlined]
While the great circle are joining any two places on the earth cuts successive meridians at different angles the Rhumb line between them makes same angle at all meridians and consequently curves towards the equator. In so doing angles are made at both ends of the great circle and these angles for all practical purposes are equal to each other. This angle is called conversion angle and is equal to half convergency [sic].
[drawing showing converging lines]
Here two places in the northern hemisphere are considered WXYZ are the meridians at A and B respectively and MN is draw through B parallel to WX. ABQ is great circle passing through AB. ARBT is Rhumb line passing through AB, AP and LBS are tangents to Rhumb line at A and B it follows that angles WAP and YBL are bearings of Rhumb line ARBT.
[symbol for therefore] YBL = WAP N
It has been stated that the angles between Rhumb line and Great Circle are equal. Let them be called “C”
Then BAP = ABS – C
But opp. angles are equal ABS = LBQ = c
Now WAP = WAB +c

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Substituting in (1)
YBL = WAB+c
But WAB = NBQ (corresponding angles)
and NBQ = MBL +c
Substituting in (2)
YBL = MBL+2c
But YBL = MBL + [deleted] YMB [/deleted] YBM
[symbol for therefore] YBM = 2c
[symbol for therefore] convergency [sic] = 2c
[symbol for therefore] CA equals 1/2 ch long x sin mean lat.
Example what is conversion angle to apply between A3515S 1045E B.2545S 0215W. CA = 6.5 x .51504 = 3o to nearest degree.
[underlined] Abac [/underlined]
[3 scales showing CH long, CA & Mean lat]
To avoid calculating C/A u special facilities are provided for the navigator. On all plotting charts will be found an Abac, the use of the Abac is quite simple, a line is drawn joining Ch of [deleted] log [/deleted] long. on the top [deleted] b [/deleted] scale to the mean lat on the bottom and the CA is read from the point where this line cuts the centre scale. If Ch of long is on top side of scale the CA is also read from the top side and vicsa [sic] versa. if Ch of long is under 4o multiply by 10 and divide by 10 CA so found.
[underlined] Plotting of Great [deleted] G [/deleted] Circle bearings on mercators [/underlined]
Since the Rhumb line between two places always lies on that side of the great circle nearer the equator it is true to say that the great circle bearings of all places of any way E of observer in N hemisphere are less than Rhumb line bearings and all places W. are greater than the Rhumb line. In the S hemisphere the reverse is true. A simple rule for applying [inserted] CA [/inserted] to a great circle is Northern Hemisphere as 0o – 180o – ADD
180o – 360o = SUBTRACT
Southern Hemisphere = 0o – 180o = SUBTRACT
180o – 360o = ADD

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[underlined] Plotting a Great Circle on Mercators Projection [/underlined]
Lay off a complete [inserted] great [/inserted] circle bearing between any two places. Firstly lay off on a Gnomonic chart the Great circle bearing between the two places which will be a straight line a number of intermediate points are chosen and their lat and long obtained. These positions are then transfered [sic] to the mercators chart, and a curved lie is drawn free hand between the two places joining all the intermediate points.
[graph with 4 points marked on it]
Lay off only part of Great Circle bearing between two places namely a short arc at either of the two places. Join both places be a straight line (rhumb line) and determine CA. If a short line is drawn at either place in direction of the other and inclined towards the nearer pole so as to make an angle with the Rhumb line equal to CA such a line may be considered for all practical purposes to represent a short arc of the great circle between two places.
[graph showing GC arc at 2 points]
The Air Speed Indicator
Principle
The principle of the instrument is to measure the difference between the pressure set up by airflow past the a/c due to the movement the a/c through the air and that of the surrounding air. If a tube with one end closed has other open end pointing against current of air the air pressure inside the tube will be greater than that outside. The value of this excess of pressure in the tube depends upon the velocity of the air current and the density of the air. It is clear therefore that if the tube is kept facing into the air flow and a suitable pressure gauge is connected to the closed end the gauge can be collarbrated [sic] to measure

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the speed of the air relative to it.
[drawing showing air flow]
In the ASI. the open end of tube known as Pitot head is mounted on the a/c in airflow and is connected to a suitable pressure gauge in cockpit. The instrument has to measure the difference between the pressure built up inside the [deleted] su [/deleted] tube and the average pressure outside. Inside the cockpit of a/c in flight The airflow past the machine generally produces a region of low pressure, the extent of which depends on so many factors that it essential for the instrument to be independent of it. For this reason the low pressure side of the instrument is connected to a second tube called the Static Pressure Head which [inserted] is [/inserted] fixed to a point adjacent to Pitto Head. The Static Pressure Head is closed at the end which faces into the air flow but is pierced by numerous small radial near that end. The [deleted] Pitto [/deleted] Petot and Static Pressure Heads together form a unit which is called the Pressure Head. Pressure Gauge consists of an air tight chamber divided into two equal partments [sic] by means of a sensitive Diaphram or capsule, the Pitot Head is connected to one compartment and Static Pressure Head to the other, any variation of pressure in either tube causes a movement in the Diaphram to which is attached to a mechanism furnished with a needle which revolves over the dial of ASI.
[underlined] Altimeter [/underlined]
The principle of the instrument is that of the Aneriod [sic] Barometer but the dial instead of measuring inches of mercury is [deleted] calarba [deleted] [inserted] calibrated [/inserted] in inches equivalants [sic] heights. The pressure of the atmosphere is due to the weight of air above and gradually diminishes as height increases. The pressure of the air can be expressed in terms of millibars, pounds

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per sq ins or in the length of a column of liquid it can support. The average pressure at M.S.2 is about 10[deleted] 0 [/deleted] 13 millibars, 14 3/4 lbs per sq in or 30” of mercury.
[drawing showing vac capsule]
The instrument contains a round flat capsule made of thin corr [sic] metal from which all the air has been extracted. One side of the capsule is fixed to the instrument case while the other side is free to move. The instrument is connected to the Static Pressure Head so that the pressure surrounding the capsule is that of the surrounding air. A leaf spring is provided to prevent capsule collapsing [deleted] s [/deleted] as the atmospheric pressure decreases the capsule expands and the resulting movement is amplified and transfied [sic] by simple mechanism to a pointer revolving over a dial which is graduated in terms of height. Incorporated in the instrument is a compensator bar composed partly of steel and partly of brass which by reason of different exspansion [sic] of [deleted] m [/deleted] these metals counteracts & effects of [deleted] tempan [/deleted] temperature changes in the mechanism of the instrument.
[underlined] Calibration Laws [/underlined]
The relation between pressure and height is not a constant one but depends upon temperature, not only at given height but also at all points between that height and ground and upon pressure at ground level. Which factors change according to met. conditions. In order to calibrate an altimeter it is necessary to assume certain standard conditions of the atmosphere, correction can then be made to allow for the conditions actually observed. There are two calibration laws induced known as he Isothermal and I.C.A.N. laws.
[underlined] Isothermal Law [/underlined]
This law based on the assumption that the temperature at all heights is 10oC, no attempt has here been made to approximate to the average actual temp.

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found, [inserted] with [/inserted] the result that this law requires very large corrections especially at high altitudes.
[underlined] I C.A.N [/underlined]
This law assumes that the temp falls uniformly at rate of 1.98% per 1000ft from 15oC at M.S.L. to minus 56.5oC at 36[inserted] o [/inserted] 90ft above which remains constant at 56.5oC. This relationship is not necessarily the most accurate that could be found, but it represents with fair accuracy average conditions over the whole world and is greatly superior to the Isothermal assumption.
[underlined] Errors of Altimeter [/underlined]
(1) error due to variation of air temperature. Altimeters are calibrated to read correctly when the atmosphere is at a certain standard condition of these condition varie [sic] a correction must be applied to indicated height.
(2) Error due to lag. The mechanism of the altimeter is not sufficiently sensitive to record pressure changes quickly, for rapid ascents or descents there us sometimes a considerable lag therefore during rapid climbs the altimeter will read low and during dives read high
Error due to differences to surface pressure. The question of error due to surface pressure changes is of practical importance in flying, if the surface pressures change the altimeter will read incorrectly to the extent of 30’ for every millibar change in pressure and a correction must be made. When flying from high to low pressure altimeter reads low, if aerodromes are not at same height above MSL allowance must be made for the difference in height between the two dromes.
[underlined] Operation [/underlined]
In General the altimeter will indicate the height of the a/c at any moment, but the point above [deleted] tl [/deleted] which the is measured will depend on the manner is which the altimeter is set. If the dial is adjusted before taking off so that the pointer reads zero the altimeter will indicate during flight the height above the home aerodrome does not change during the flight will return to zero at landing on same drome. If the height above

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sea level is required during flight the altimeter must be set before taking off so that the pointer indicates the height of the aerodrome above sea level. If this is done the height of the a/c above sea level will be shown at any moment during the flight, provided the sea level pressure does not change.
[underlined] Computation Height and Air Speed [/underlined]
Unfortunately the ASI suffers from 3 defects :-
1. The instrument may suffer from constructional defects that cause instrument error, which can however be calibrated
2. The Petot Head may be effected by air eddies set up round the a/c, this gives rise to what is known as position error which can be tabulated for each type of a/c
3. The instrument cannot be fully compensated for changes of air density. Thus changes of atmospheric pressure and air temperature that occur in changes of height may cause a convergence between actual air density and the density assumed for calibration of the instrument giving rise to an error in its reading. This error can be allowed for in its process
[underlined] Derivation of TAS. [/underlined]
naturally all nav. calculation are concerned with TAS which can only be obtained at present by applying a number of correction to the instrument readings, TAS is derived in following stages
I.A.S. :- a reading of a particular [deleted] instruts [/deleted] instrument uncorrected
RAS :- IAS corrected for position and instrument errors
TAS :- RAS computed for height and temperature
To find TAS
add to RAS = 1.75% of RAS per 1000ft example RAS – 180 knots Height 8000ft
TAS = 180 + 18 [deleted] 0 [/deleted] [inserted] 1 [/inserted] x [deleted] 1.75 [/deleted] [inserted .35 [/inserted] / 10 [deleted] 0 [/deleted] [inserted] 1 [/inserted] x [deleted] 8 [/deleted] [inserted] 4 [/inserted]
= 180 + 25.2
= 205

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[underlined] Calibration of ASI [/underlined]
ASI should be calibrated regularly the setting of the pointer cannot be adjusted but check readings can be recorded and used for compiling a table for air speed corrections. When making a correction card for instrument error correction it is advised to include a position correction as well, so that instrument and position error are allowed for in one single operation.
[underlined] Height [/underlined]
The effect of temperature on the variation of pressure with height has an important bearing on the readings of the altimeter. The altimeter is graduated assuming an ideal atmosphere the temp of which is taken 50oF. Any change [deleted] can be[/deleted] in temp means that a correction has to be made and approx. rule for allowing for this [deleted] change [/deleted] [inserted] effect [/inserted] of temp is to subtract or add 1% of indicated height for each 5oF by which the mean temperature from the a/c to the ground is [deleted] blo [/deleted] below or above 50oF. Example indicated 5000ft mean temp 30oF
Height = 5000 – 5000 x 4 / 100 x 6
Height = 5000 – 200
= 4800ft
C.S.C.
Description
The instrument consists of the following main parts. (1) Bearing plate (2) Base plate (3) Gi/S bar.
The earing plate sliding up and down base plate, the wind co stud can be located in any position on the bearing either by moving it along the wind plate relative to the bearing plate. The air speed is marked off on either side of the base plate in mph and knots. To set TAS move bearing plate co until pointer registers required speed. The ground speed bar is swivelled up the top of the base plate so that it moves over the bearing plate and is connected to the track and drift pointer. The slot in the G/S bar is to fit over the wind stud and the G/S is marked down the bar on either side of the slot in mls per hour of knots. The drift scale is found on either side of the course pointer and is marked in Port of S. drift.
Analogy to triangle of velocities
The course and TAS vector is represented by a line drawn from

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speed bar swivel to the centre of the bearing plate through the course pointer. The track and G/S vector is p represented by the G/S bar from the swivel to the wind stud. The W/V vector is represented by the wind slot, from the centre of the bearing plate to the wind stud.
Method of determining
A. Course and G/S
(1) Set [deleted] true [/deleted] TAS (2) move wind stud to outside position and revolve wind plate until wind stud is against required wind direction on bearing plate (3) move wind stud along wind slot to required speed (4) Place ground speed bar over wind stud (5) Set track against T pointer (6) Read off True course against C (7) Read of G/S against centre of wind stud.
(B) Tr and G/S
(1) Set TAS (2) repeat as in A (5) Set true course against C (6) Read off Tr against T (7) Read off G/S against centre of wind stud
(C) W/V given Tr, G/S, Co TAS
(1) Set TAS (2) Set true course against C (3) Push wind stud to edge of wind plate. (4) Set track against T by moving G/S bar (5) At G/S mark wind point [deleted] m [/deleted] by a small dot on wind plate in centre of G/S bar channel (6) Move wind stud to centre of bearing plate and put G/S bar over it (7) Turn bearing plate until wind point appears in centre of the channel of the G/S bar and between the wind stud and C (8) Read off wind direction at C (9) Read off Wind speed along scale of G/S bar between wind stud and wind point.
D W/V by Multiple drift.
(1) Set TAS (2) Push wind stud to edge of wind plate but do not revolve wind plate through out operation. (3) Set first course at C (4) move ground speed bar and set drift at T (5) Draw a pencil line down the centre of G/S bar channel (6) Set 2nd course at C (7) Set second drift at T (8) draw 2nd pencil line (9) Set third course at C (10) Set third drift at T (11) Draw third pencil line (12) Move wind stud to centre of bearing plate and place G/S bar over it (13) Revolve bearing plate until centre of cocked hat comes in the centre of the

[page break]

G/S bar channel between wind stud and C. (14) Read wind direction at C (15) Read wind speed along scale [deleted] ab [/deleted] on G/S bar between wind stud and centre of cocked hat.
C W/V by drift and wind lane method
(1) Set TAS (2) Set True course at C (3) Push wind stud to edge of plate (4) Set track against T by moving G/S bar (5) Draw pencil line down centre line of G/S channel 6. Put wind stud to centre and place G/S bar over it (7) Set wind lane earing against C (8) Draw a pencil line down centre of G/S bar (9) Revolve earing plate if necessary until intersection of two lines comes in centre of G/S and Channel between wind stud and C (10) Read off wind speed along G/S bar and direction at C.
[circle with degrees marked around edge]
[chart for IAS and RES readings]

[page break]

G/S 130 Knots W/V [deleted] 174o 48 knots 176o 22o [/deleted] 152o 23 knots TR 079o Co (T) 088o
ETA = 113 / 130 X 60 / 1 – = 678 / 13 = – = 13 9/13 – = 14
ETA = 133 / 130 X 60 / 1 – = 798 / 13 – = 61 5/13
Time taken to Y is 61 mins
Expected time to cross at Y [deleted] 0743 hrs [/deleted] 0716 hrs
Co (m) 224o Tr 201o G/S 133 knts ETA 0800 hrs
TT = 92 / 133 x 60 / 1 – = 5520 / 133 – 41 67/133 – 42
TAS = 130 + 130 x 1.75 / 100 x 3 – = 130 + 117 / 8 – = 145 knots
Tr 289o Co (c) 310o G/S 131 knots ETA 0906 hrs
TT = 98 / 231 x 60 / 1 – = 5880 / 131 – = 46
GS = 102 / 1 x 60 / 45 – = 6120 / 45 – = 136 knots
Base at Exeter and orded [sic] to patrol channel to CAS light to Position X 4957 (N) 0014(W) Returning to Lincoln by Ipswich – W/V 270/20 knots
RAS 120 Knots 5000ft set course 1100 hrs
TAS Co (C) G/S ETA
At 11.20 receive MFB to proceed to Position Y 5005N 0140(W) circle smoke float for 5 mins and then s/g
CO (c) ETA Position Y
1135 loop bearing of Eiffil [sic] tower at 110 1/2o at [unreadable wording] light W/T bearing of 242o [unreadable wording] and W/V.
[unreadable wording] for Y using new W/V.
[unreadable wording] DR position 1140. Arrive at Y [unreadable wording] for X
[unreadable wording] ETA
[unreadable wording] at X on ETA s/c Ipswich using W/V [unreadable wording]
[unreadable wording] CO(C) ETA
Arrive Ipswich ETA sc Ipswich CO(C) ETA

[page break]

[equations / working out / corrections]
Co (C) 193o
ETA 0426 hrs
5047N 0027 E
W/V 113 27 knots
5033N 0020E
ETA = 0427
CO(C) = 187o
CoC 340o
ETA 0533 hrs
5031N 0045W
0613 hrs
Based out Norwich receive orders to bomb at bap d’antifer [sic] W/V 123o 21 Knots Height 5000 RAS 156 knts S/C at 0319 hrs. Co(C) ETA TARGET.
At 0355 Dungeness bears 116o(T) 0401 bears 069oT. FIX 0401 hrs W/V. 0407 AC for TARGET using new round DR 0407 Co(C) ETA. After bombing target s/c for NAV LIGHT 0510 hrs. What is Co(C) ETA (NAV) 0521 Beachy 042o (M) 0525 bears 059o(M) 0530 Beachy 081o(M) FIX 0530hrs Is it necessary to alter course for nav. Reach NAV 0534 hrs and s/c BOR using W/V 047o 35 Knts CO(C) ETA.

[page break]

[multiple equations and working out]
TAS 181 knts [tick]
Co(c) 110o [tick]
ETA 1932 hrs [tick]
Co(C) 200o [tick]
G/8 205 Knts [tick]
ETA 2000 hrs [tick]
G/S APPROX 215 Knts
FIX 5020B 01E [tick]
W V 333 24 knts [tick]
ETA 2022 hrs
TAS 192 knts
GS 180 knts [tick]
Co(c) 291O [tick]
ETA 2040 hrs [tick]
G/S 184 [tick]
W/V 354o 33 knts
DR.POS 4937N 01323 OW [tick]
Co(c) 314 [tick]
ETA 2040 mins [tick]
WV 272o 22knts
FIX 5028N 0227W [tick]
POS 5028N 0259W
[chart showing Ques No, working, Sub ques no & answers]
RAS = 124 X
TAS = 124 + (124 X 7 / 400 X 1) – = 124 + ( – = 130 Knots
(A) TAS 130 Knts
VAR 12o W – Co(M) 236o – DEV 1o E – Co(C) 256o
(B) CO(T) 224o
(C) co([deleted] m [/deleted] [inserted] c [/inserted]) 256o

[page break]

[chart showing Ques No, working, Sub ques no & answers]
[circled number] 1 [/circled number] RAS = 142 – [therefore symbol] TAS = 142 + (142 x 7 / 400 x 4 / 1) – = 152
DISTANCE 30NMS TIME 15 MINS – [therefore symbol] G/S = 120 KNTS
W/V 248o 50KTS
2.
VAR 11ow – COM 128o – [therefore symbol] CO(M) 139o
DISTANCE 86NM [deleted] TIME [/deleted] G/S 182KTS – [therefore symbol] TRIP TIME 26 MINS
a Tr 114o – b Co(T) 128o – c VAR 11oW – d CO(M) 139o – E DEV 0o – F CO(C) 139o – G DISTANCE 86NM – H G/S 182KTS – I 26MINS – J ETA 1046hrs – K DRIFT 14Os

Collection

Citation

B Openshaw, “Two navigation course note books,” IBCC Digital Archive, accessed December 8, 2019, https://ibccdigitalarchive.lincoln.ac.uk/omeka/collections/document/17296.

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