Ted Neale's Air Navigator notebook
Title
Ted Neale's Air Navigator notebook
Description
Ted Neale's course notes for Course 19 Air Navigator including details of corrections and adjustments to be applied to readings and calculations of positions.
Creator
Date
1943-08-23
Coverage
Language
Format
One notebook with handwritten notes
Publisher
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.
Contributor
Identifier
MNealeETH1395951-150731-051
Transcription
A.O.S.
Course 19. AIR. NAVIGATOR.
42. AIR. SCHOOL.
PORT ELIZABETH.
SOUTH AFRICA.
23rd August 1943
1395951.
Neale. E.J.H.
[page break]
Maps & Charts.
[underlined] MAP READING.
Before Flight. [/underlined]
Make sure that you know if it is metres or feet, know all conventional signs, including any unusual ones peculiar to the map in use. Insert any secret information, lightly in pencil, according to a private secret code. [underlined] eg [/underlined] 25 miles due East of actual position.
Aquire [sic] a true sense of map scale.
On 1 million 1 inch = approx 16 miles.
‘’ 1/2 ‘’ ‘’ = ‘’ ‘’ 8 ‘’
‘’ 1/4 ‘’ ‘’ = ‘’ ‘’ 4 ‘’
Aquire a true sense of map direction. The direction of North should never be in doubt. Draw in route with time or distance marks if possible (draw tracks in first). Study the route carefully, select suitable land-marks and put a pencil ring round those not clearly marked, put an E.T.A. against each. Study relative forms of landmarks, as they will appear in flight. Fold map so that area required is easily accessable [sic], preferably with distance scale shown
[page break]
[underlined] MAP READING.
During Flight. [/underlined]
Orienteering the map helps in recognising relative position of features, essential in identifying road & rail junctions, may usefully be dispensed with when not lost, to give ease in reading names and bearings.
Use time marks to anticipate land marks, such as towns, rivers & coast lines, particularly at night.
Provided the general position is known always read from map to ground. Mountains appear in plan below the A/C in elevation at a distance.
[page break]
[underlined] Procedure When Lost. [/underlined]
[circled 1]. Draw a circle of uncertainty round D.R. position, radius 10% air distance flown since last fix.
[circled 2]. Orient map by means of compass.
[circled 3]. Look around horizon for 2 or 3 prominent land-marks, estimate their bearing & distance, pin-point yourself by reading from map to ground.
[circled 4]. Failing this adopt a positive plan
a/. Fly in the direction of some prominent feature, e.g. river, mountain or coastline, follow this until recognised.
b/. commence organised search.
c/ circle some local feature until it is recognised or until plan is ready. to make map reading easiest & so assist recognition, fly from S to N over landmarks N.B. pay particular attention to air plot never fly aimlessly to inspect features on the horizon.
[page break]
[underlined] Map Reading by Day. [/underlined]
For good results, always observe down sun.
[underlined] In Good Visibility
Landmarks [/underlined]
a/. [underlined] Mountains and hills. [underlined] give general position only, very difficult to use for P.P. get impression of contour shapes.
b/. [underlined] Water. [/underlined] Rivers lakes canals etc N.B. bridges & Gorges. beware of floods & droughts.
c/. [underlined] Railways & Roads. [/underlined] do not P.P. without orienting map.
N.B. Distinguishing features d/. [underlined] Towns & Villages [/underlined] (alter shape).
e/. [underlined] Woods. [/underlined] alter shape. on modern target maps reliability symbols are used
f/. [underlined] Golf Courses & Race Courses [/underlined] very visible from the air
g/. [underlined] Sea Marks [/underlined] a/. Coastlines very visible
[page break]
due to breakers. b/ Sandbanks, rocks, shoals. N.B. STATE THE TIME.
c/. Light houses & Light Ships
d/. Marine Lights (shaded on top may not be visible when directly overhead.)
e/. large buoys
f/. Cliffs.
g/. Sea traffic.
In Poor Visibility use map reading in close conjunction with D.R.
By night always observe up Moon.
[underlined] Map Reading by night. [/underlined]
a/. Always observe up moon.
b/. Visibility may increase by night.
c/. Anticipate features.
d/. When you acquire night eyes dont [sic] spoil them by using the light.
e/. Coast always almost visible.
f/. difficult to distinguish details (due to cloud shadows).
[page break]
g/. Town lighting, decreases after midnight.
h/. Fires & ACK ACK
i/. Aerial Beacons & Marine Lights
[underlined] Lights at sea. [/underlined]
abbreviations in 1234 Chapter 3 para 19 Visibility of Marine Lights calculated for a height of 15 feet above sea, visibility is affected by Met conditions & humidity, changes of refraction, height of the observer & state of the tide.
[underlined] Reporting Position. [/underlined]
1/. Pin Point, accurate, non secret, may be difficult to find
2/. Bearing & distance, not easily estimated over 10 miles. a/. from landmark, non secret. b/. from lettered datum point, secret.
3/. Latitude & Longitude not secret, but accurate
4/. R.A.F. lettered co-ordinates.
[page break]
[diagram of lettered grid with point marked]
Each meridian & parallel alloted [sic] 2 letters (changeable). Give co-ordinates of intersection of Parallel & meridian S.W of position [underlined] MF – PR [/underlined] followed by minutes of [underlined] latitude & longitude. [/underlined] This is the same for both N & S hemisphere.
5/. The Naval Method. Bearing & distance from nearest intersection 255 JBZB 3 miles.
6/. Modified British Military Grid. Great Britain divided into 6 500Km squares, lettered LM, QR, BW & I
[page break]
b/. each 500 Km square divided into 25 100 Km squares & lettered, called Primary
c/. each 100 Km square divided into a hundred by 10 Km squares & numbered called Secondary
d/. the 10 Km squares can be subdivided into units by inspection or by instruments In reporting position give two letters & 4 figure coordinates of Pin Point from the S.W. corner.
[underlined] N.B. [/underlined]
always give Easting before Northing. Be certain if bearings refer to GRID NORTH or TRUE NORTH.
The TRUE origin passes through the I.O.W.
The FALSE origin passes West of the Scilly Isles.
[page break]
[underlined] Maps & Charts in use in the R.A.F. [/underlined]
Plotting sheets.
1/. 1 – 1,000,000. reference G.S. G.S. 4080. It covers all operational areas, Main ground features only shown, spot heights in metres ABAC scale for conversion angle, compass roses 1 – 2 or 3. Isogonals for every one degree, 10 minute graticule, marginal statute & nautical mile scale varying with Latitude. Ch Long in time as well as arc, 3 main parallels marked plainly for use with astrograph. Cheap & easily produced.
Scotland N.W 54N 13’W
All BRITISH ISLES & IRELAND. covered by 2 sheets.
2/ 1 – 500,000 BRITISH ISLE. The sheet is similar in all particulars to 1 – 1,000,000 & is used mainly for training.
3/. 1 – 2,000,000 G.S.G.S. 5012. new series small scale plotting charts, similar to 4080. * cannot be used with astrograph. Almost any European target can be reached on a single sheet.
[page break]
Used for Mosquitos & Pre flight Plan Sheet No NW 46/8 covers the area from Dublin to Konisberg 8W - 21W scale 2,000,000 at 56N. Spot heights in metres, hachuring for mountains, heavy coastline no radio broadcast stations, improved shapes of town, statute miles scale in body of sheet.
[underlined] Topographical MAPS. [/underlined]
1/ 1 – 1,000,000 GSGS 2758 modified Polyconic projection, once used for navigation, superseded by GSGS 4080. suitable for high altitude map=reading. More detail than plotting chart. No 10 minute graticule, heights in feet, covers Europe & Great Britain. Revised 1 – 1,000,000 new series being produced to cover main operational areas of Europe, based on old 1,000,000, with redesigned sheet lines, unimportant details removed roads & railways emphasised, purple layering incorporated.
[page break]
2/ 500,000 GSGS 4072 Modified Polyconic Great Britain & Europe, map reading at moderate height & short distance navigation 10 minute graticule 1/2 isogonals. heights in feet. distinctive colours for main features In Germany woods not marked in green as they are too numerous to serve as land marks, main outline only shown.
3/. 1/250,000 GSGS 3982. [deleted] Modified Polyconic. Europe, does not cover great Britain, but being extended to cover France & Ireland, used for map reading when approaching target & over industrial areas. 10 min graticule, Ht in metres.
4/. 1/4 in ORDNANCE SURVEY AIR EDITION CASSINI’S PROJECTION. Map reading only 10 min graticule on some sheets, British Grid on others. Magnetic variation on compass rose. Grid deviation at side of sheet.
1/4 in O.S. [underlined] Special. [/underlined]
Similar to above but layout conforms with 1/4 million series.
[page break]
Target Maps. reliability symbols being introduced.
BONNES PROJECTION. SOUTH AFRICAN.
[underlined] Admiralty charts. [/underlined]
Mercators Projection, only nautical mile scale, no accurate land details except sailing marks. Compass rose graduated true & magnetic, magnetic inside true with variation indicated.
Admiralty Plans.
Small charts on large scale, usually of harbours, suitable as target maps, no latitude or longitude scale, distances in nautical miles & cables. 10 cables In mile.
Marine Contoured Maps.
For use in minelaying flights, depth of water shown by layered colours, beaches & banks visible at mean low water, grey stippled, land details shown accurately, taken from 1/4 million air maps. To cover all coasts from Spain
[page break]
to 64N, including the Baltic. Norwegian sheets layered for a ground height. Barmouth sheet produced for training. Gnomonic Charts.
[underlined] CONVENTIONAL SIGNS. [/underlined]
[symbol] LAND AERODROME.
[symbol] LANDING FIELD.
[symbol] AIRSHIP BASE.
[symbol] WATER SEAPLANE ANCHORAGE.
[symbol] AERODROME (WATER)
[symbol] CONSPICUOUS OBJECT.
[symbol] AIRSHIP HANGAR
[symbol] AIRSHIP. MOORING MAST.
[symbol] MARINE LIGHT
[symbol] MARINE LIGHT VESSEL.
[symbol] CHURCH WITH TOWER OR SPIRE
[symbol] POWER CABLE. OR OVERHEAD RAILWAY.
[symbol] ARIEL [sic] CORRIDOR
[symbol] PROHIBITED AREA.
[page break]
[symbol] AERODROME CONTROLLED AREA.
[symbol] AIRPORT WITH CUSTOMS FACILITIES.
[symbol] (AERODROME) DANGER AREA (SAFETY HT MARKED).
[symbol] EXPLOSIVES AREA.
[symbol] BALLOON OBSTRUCTION BEACON.
[symbol]AIR OBSTRUCTION. MORE THAN 200 ft. [underlined] unltd. [/underlined]
[symbol] ‘’ ‘’ ‘’ ‘’ ‘’ LIGHTED
[symbol] NON AERONAUTICAL RADIO STATION.
[symbol] AERONAUTICAL COMMUNICATION.
[symbol] AERONAUTICAL D/F OR BEACON.
T. Communication M. Met N. Non directional D Track indicating A Landing Approach R Gonioltric.
[symbol] HALF SUBMERGED WRECK.
[symbol] WRECK. DEPTH OF WRECK AT LOW WATER
[symbol] WRECK LIKELY TO FOUL ANCHOR.
[symbol] DANGEROUS WRECK.
[page break]
Mercators Projection.
Similar to the TRUE CYLINDRICAL projection. It has a rectangular graticule, rhumb lines are straight lines, angles on the Earths circles are correct. The chart length of 1 min longitude is constant, therefore latitude scale increases towards the Poles. No Constant Scale, but at any latitude the scale is the same for all directions for short distances. For small areas orthomorphic, for large areas shape distorted. GRATICULE easily constructed, the Great circles are curves convex to nearer pole. Polar areas cannot be shown.
[underlined] Principle of Construction. [/underlined]
Cos 0 ‘’ 1
Cos 90 equals 0
Sec 0 ‘’ 1
Sec 90 ‘’
On the Earth, distances between meridians varies as cos latitude i.e. maximum at equator, zero at poles. On Mercators, meridians pull apart until parallel. To counteract this & preserve constant bearing, the parallels of
[page break]
latitude are pulled apart proportionately. The distance between parallels varies as sec latitude.
[underlined] To construct a Mercators Chart. [/underlined]
Between Latitudes 52N 53N, & longitude 0 & 1W. Scale 1,000,000 at 56N
Distance between Meridians at Equator = 60nm
‘’ ‘’ ‘’ ‘’ 56N = 60 cos 56 = 32.55n.m.
Scale 1/m means 1,000,000’ on ground = 1” on chart.
33.55n.m on ground = [calculation] on chart = 2.44”
[diagram]
[calculation]
[page break]
The Mercators Graticule may also be constructed by using meridiurnal [sic] parts from Norris [sic] or INMANS Tables.
Und
TOPOGRAPHICAL MAPS. [/underlined]
Simple Conical.
[diagram]
Scale correct along meridians & standard parallels, incorrect along other parallels. Greatest error on parallels furthest from the standard. This projection is good for countries with a small change of latitudes. Direction correct on Northerly or Southerly. not orthomorphic.
[page break]
Straight lines almost Great Circles.
[underlined] Method of Recognition. [/underlined]
Parallels are arcs of concentric circles. Meridians converging straight lines.
[underlined] Polyconic. [/underlined]
[diagram]
Each parallel constructed with its own centre ie more than one cone used
[underlined] Properties [/underlined]
Scale correct along all parallels & central meridian. Not orthomorphic
[page break]
more so than simple conic. Suitable for small areas [inserted] not equal areas [/inserted] (as parallels not arcs of concentric circles) but nearly so. Near Central meridians straight lines approx G.Cs.
[underlined] Recognition [/underlined]
Parallels evenly spaced, non-concentric arcs, Meridians Curved.
[underlined] International Modified Polyconic. [/underlined]
Agreed to by international conference, basis of all 1,000,000 maps of Europe & many other parts of world. Each sheet constructed seperately, up to 60 N & S latitudes, each sheet covers 4 latitude by six degrees longitude, in higher latitudes 4 latitude by 12 longitude. 1,000,000 series recognisable by this.
Turn over for sketch.
[page break]
[diagram]
[[underlined] Construction [/underlined]
Central Meridian correctly drawn to scale. Two standard parallels correctly drawn N & S. calculate positions of Meridians, draw meridians as straight lines. Transfer correct length of central meridian to two degrees east & 2 west of centre, redraw parallels, draw in rest of graticule
[underlined] Properties [/underlined]
Scale correct at standard parallels & Standard Meridian, slightly incorrect elsewhere, each sheet almost orthomorphic
[page break]
& equal area. Straight lines are almost great [symbol]
[underlined] Recognition [/underlined]
Dimensions of the Graticule. Parallels are arcs of non concentric circles. Meridians straight lines. Advantages of I.M.P. Straight lines approx G [symbol]. Scale very nearly constant. Ground W/T bearings laid off direct.
9 Ajacent [sic] sheets almost fit, 5 sheets fit exactly.
[underlined] Disadvantages [/underlined]
Rhumb lines not straight lines, bearings [underlined] must [/underlined] be measured against the meridian midway along track.
[underlined] Note [/underlined]
To plot T.M.G. find angle as above, draw to the next meridian, lay off angle again & so on.
[page break]
BONNES PROJECTION.
Maps of Suid Africaa.
Suitable for narrow countries where change of latitude is greater than change of longitude. In broad countries obliquity of Meridians at edges causes distortion.
Method of Construction
One standard parallel meridian at centre. Draw in central meridian, divide for latitude. Draw in concentric parallels of latitude, divide for longitude, draw in meridians.
[underlined] Properties [/und]
Scale correct along parallels & central meridians only. equal area, distortion at edges, therefore not orthomorphic and sheets do not fit.
[page break]
[underlined] CASSINI PROJECTION. [/underlined]
Used with 1/4” ordnance Survey maps of GT Britain. a Mathematical Construction.
[underlined] Properties [/underlined]
Central Meridian correct, others too long. Meridians curve inward toward poles. Edges of map do not coincide with meridians. + or – 4 degrees of deviation at edges. Equal Area.
[underlined] TRANSVERSE MERCATOR or GAUSSE CONFORM [/underlined]
[underlined] Properties. [/underlined]
Central Meridians straight, others curves, curved inward toward the poles. Parallels concave to nearer pole. Equator straight line. Grt [symbol] central Meridian & all Grt [symbol] perpendicular to it are straight lines, all other Gt [symbol] curved. Rhumb lines curved except for central Meridian & equator. Scale varies all over the sheet increasing with distance from Central Meridian. Bearing, shapes and Areas. Projection is
[page break]
limited in practice to 3 either side of Central Meridian. So maximum Scale error is less than 1%, so that bearings Shapes & Areas may be accepted as correct.
[underlined] Suitability. [/underlined]
Especially suitable for griding [sic], as can be extended N & S indefinitely, & if central meridians are sufficiently close, adjacent sheets fit E & W. The Union is mapped on 2 strips, North Africa on 5 strips.
[underlined] GNOMONIC PROJECTION. [/underlined]
Gnomonic is a Tangential Projection. Grt [symbol] are straight lines, bearing scales, shapes & areas, all distorted, except at point of origin. Distorted Compass rose.
[underlined] CAPTAIN OF AIRCRAFT MAP. [/underlined] Small scale Mercators plotting objects on which captain can lay off required tracks. (it measures 15’ x 12’) and all relevant information, such as Ack-Ack & etc.
[page break]
Curve of Equal Bearing.
[diagram]
A Curve of Equal Bearing is a line from all points on which the Gt [symbol] bearings of a given position on the Earths Surface are equal. It constitutes the position line
[page break]
obtained from a loop bearing.
[underlined] In Plotting W/T Position lines [/underlined]
1/ D/F W/T Bearings
A/ On a topographical Map Plot direct from D/F Station.
B/ GNOMONIC Chart Plot direct from D/F W/T Station. Distorted compass rose or protractor maybe needed
C/ On mercators (see Chapter 3 Para 38)
[diagram]
Case 1/ With conversion angle of less than 4, find D.R. posn, calculate conversion angle, apply conversion
[page break]
angle to Gt [symbol] bearing & plot from D/F station. (Draw Sketch to ensure that conversion angle is applied correctly).
Case 2/
Conversion angle more than 4. Find D.R. posn, calculate conversion angle & plot as above, at D.R. LONGITUDE apply conversion angle again in the same sense to obtain position line.
2/ Plotting Loop Bearings
A/ On topographical map, add true course. Calculate & Apply convergency or transfer Meridian, Plot reciprocal from W/T station.
Where the angle of convergency may be greater [underlined] ie [/underlined] more than 4, Plot position line as above at D.R longitude apply angle of convergency of opposite sign
[underlined] Plotting Loop bearings on Mercators [/underlined]
When conversion angle is small [underlined] ie [/underlined] less
[page break]
than 4 5 or 6. add true course, apply conversion angle (draw sketch). Plot reciprocal from D/F station.
Case B/. When conversion angle is large, add true course, apply conversion angle, plot reciprocal from D/F station, apply conversion angle of opposite sign to get Curve of Equal bearing position line.
[diagram]
[page break]
[underlined] Scale of Map. [/underlined]
[diagram]
Cloud Shadows masking town & making woods Difference of Map reading in Summer & Winter, difference of droughts drying up of rivers, also of colours of green leaves. Map read down sun. Low sun throws a lot of shadows. Map reading is better at greater hts.
Circle of Uncertainty, 10% of Air distance from last fix from D.R posn.
[page break]
[calculations]
[page break]
[calculations]
[page break]
E. T. H. NEALE
[page break]
[underlined] Astro Theory. [/underlined]
[underlined] NAUTICAL MILE. [/underlined]
Arc or distance on Earths surface subtended by an angle of 1 minute at the centre of the Earth, thus an angle of 1 will subtend an arc or distance equal to 60 nautical miles. Hence distance can usually be expressed in terms of degrees & minutes.
[underlined] Declination. [/underlined]
Is celestial latitude & corresponds with terrestrial latitude & is measure from 0 - 90 N or S.
[underlined] Precession of the Equinox]. [/underlined]
Precession of First Point of Aries Westward at the rate of 50 secs of ARC per annum.
[underlined] Right Ascension [/underlined]
Is 360 - SHA *
[underlined] GHA ARIES. [/underlined]
Angle From GM to FP [symbol]
[page break]
The Astro graph.
The sub stellar may be located for any instance of time & circles drawn from this common centre with various radii are position circles corresponding to various observed altitudes of the body. These concentric position circles made with the S.S.P over the face of the earth from E to W as the earth moves from W – E. If a film were made upon which circles were drawn for small stars as would be visible at various times in a certain locality & these circles were thrown by a projector onto the chart of the locality then by rotating the film from E to W to keep the centres of the circles coincident with the appropriate S.S.P’s the projected curves could be used as a visual guide for plotting actual posn lines from the observed altitude of the selected star, this is what a navigator does
[page break]
when using the astrograph. The time scale on the film is aligned with the appropriate meridian on the map & when suitably adjusted for GMT of observation the centre of the projected arc is coincident with the proper sub stellar point of the star, the astrograph film gives arcs of altitude for 2 stars & in addition Q correction for Polaris observation where these are possible.
The instrument projects star curves. (circles of equal altitude on the 1,000,000 plotting sheet it is used in conjunction with the air almanac which is used to adjust star curves to the time of observation, this is done by using 1/. a setting longitude 2/. a G.M.T. with a corresponding A.M.T. for a particular setting longitude, these are given for every night of the year.
[page break]
1/.
Wind all film to right hand spool
2/. Undo 6 retaining screws & remove astrograph base, which carries spool brackets
3/. Pull out right hand adjusting knob & remove full spool.
4/. Pass the end of the film beneath the right hand roller & friction pad & insert in gap between glass plates.
5/. Push the film towards the empty spool, depressing the left hand friction pad beneath the roller to assist passage of film.
6/. Insert the end in the empty spool, & insert new spool in right hand bracket.
7/. Take up the slack with the left hand spool
8/. Refit base to astrograph body.
NOTE. This is not an easy operation during flight & should not be attempted unless absolutely necessary. It is better to carry a
[page break]
reserve astrograph
To Fit the Astrograph.
1/. Join up height bar by screwing up two pieces, make certain you have the correct gauge, MKIA & MKIB
2/. Using height bar directly under each levelling screw of the mounting ring in turn, adjust so that gauge will just pass between the tip of the screw with the bottom of the gauge on the Chart table
3/. Tighten up lock nuts with the spanner provided & recheck with height gauge.
4/. See that dummy plug is in voltage socket not in use. (most modern A/C 24 volts Anson 12 volts).
5/. Attach the Astrograph to the mounting ring so that the levelling screws register in the hole, slot & plane
6/. Plug in to A/C supply, switch on to check.
[page break]
[underlined] Action before Flight. [/underlined]
Look in astrograph tables, (in Air Almanac or A.A.) under date of intended flight, take out a suitable setting longitude, (somewhere near area in which flight is taking place). & the corresponding GMT & AMT. mark in heavily with a thick pencil, the meridian of the setting longitude on the chart for its full length. In a clear space on the left hand side of setting longitude mark GMT of the hours during which you expect to use the astrograph on the right hand side of line, mark in corresponding hours A.M.T.
[diagram]
[page break]
Fix chart under astrograph & adjust to bring time scale on to central latitude line of chart, these must coincide exactly, Convert G.M.T. of first observation to A.M.T. (to nearest hour) & set this to the setting longitude, note the stars for which the curves are given at this time, & approx azimuths & altitudes. Make sure that they can be recognised when required.
[underlined] Action during flight. [/underlined]
1/ Take first altitude & note GMT
2/ Convert GMT of sight to AMT
3/. Set this A.M.T. against setting longitude.
4/. Draw in position line obtained from stars altitude.
5/ Take second sight & note GMT
6/. Convert this G.M.T. to AMT. & set new A.M.T.
7/. Draw in second position line obtained from second stars altitude. Third position line may be made by taking
[page break]
altitude of polaris & noting G.M.T convert this to AMT & set it. Take Q corn from above time scale in vicinity of fix or DR Posn apply according to sign to observed altitude of Polaris & obtain latitude
Points to be noted when using an astrograph
[circled 1]
When switching on astrograph, note which two stars are in use. If about to change, then wait until change takes place
[circled 2]. Do not wind film past stop mark.
[circled 3]. Do not forget when drawing in position line to notice direction of increasing altitudes
[circled 4] Care should be taken when bulb is changed, new bulb must be cleaned,
[circled 5]. See that you have correct latitude band for chart in use, if not parallels of latitude will not coincide.
[circled 6]. If longitude does not come on chart half hourly setting longitude can be
[page break]
found by adding 7 31’ to tabulated longitude adjusting the G.M.T appropriately adding 30 mins in W & subtracting 30 mins in E
[circled 7]. In astrograph tables left hand page is for west setting longitudes & right hand page for east setting longitudes, dates are given at the head of the column each of which is headed by hours of A.M.T. It must be noted that the corresponding Greenwich date to the GMT is indicated in heavier type it is the first in East long & second in West.
[page break]
“Z” CORRECTION
This is divided into 2 parts coriolis & gyro wander. These are calculated by use of the tables at the back of the air almanac.
[underlined] Coriolis “A” [/underlined]
This is the tendency of a mass to move to the right of its intended path when travelling N or S along a meridian in the Northern hemisphere. In the southern hemisphere it is a tendency to go to the left when travelling N or S.
[diagram]
[page break]
[diagram]
[underlined] Coriolis ‘A’ [/underlined]
This is due to the different speeds of rotation round a spinning axis of a point on various parallels of latitude. A mass when travelling along a meridian from one parallel to another, tends to retain its old speed of rotation & therefore to leave its path along the meridian. The greater its speed in travelling N or S the greater its tendency.
[page break]
[underlined] Coriolis “b” [/underlined]
So the tendency of a mass to move to the right of its path when travelling along a parallel of latitude in the N. Hemisphere or to the left in the Southern. (See diagram over page).
In the case of an A/C travelling in an E to W direction its speed of rotation will increase, therefore centrifrugal [sic] force will be increased. an A/C will tend to go off into space, at right angles to the axis of spin. This force C.F. could be resolved into 2 forces, V a tendency of the A/C to climb & CBE a tendency to go to the right of its path. When travelling from [deleted] W to E [/deleted] E to W the speed of rotation will be decreased and as the counter balancing effect of gravity & centrifrugal force will be upset, leaving a negative C.F. acting towards the [deleted] radius [/deleted] AXIS of spin.
[page break]
This can be resolved into G a tendency of the A/C to dive & C.B.E. a tendency to go to the right of its path. (the greater the A/C speed, the greater the tendency.) When not travelling along a meridian or parallel of latitude, it may be seen that a combination of coriolis “A” & “B” will affect the A/C. it can be shown that this combination will always be a constant
Now these tendencies of climbing or diving, turning to the right or left will unconsciously be corrected by the Pilot, but the effect will get through to the liquid in the bubble chamber of the sextant, causing the liquid to move to the right side of the A/C (In the N. Hemisphere) & the bubble to the left, thus the observer has to tilt the top of the sextant to the left side of the A/C to keep the bubble in the centre of the chamber, this tilt will be in the nature of 4’ in English latitudes and about 3 min to the right in these latitudes
[page break]
but it will always be there. It can be seen that this tilt will not affect fore & aft shots & will be maximum on the beam. In other words it depends on the relative bearing of the star.
[underlined] Gyro Wander [/underlined]
All directional gyros tend to wander from their constant direction in space, due to precession and other causes, having to be reset every 15 minutes or so, but this wander is going on for the whole time & the pilot while following this direction gyro is unconsciously turning to Port or Starboard by a slight amount per minute, in other words, the same effect as Coriolis. If the D.G. is wandering to Port, the pilot will turn to port, the liquid in the bubble chamber will go to Starboard & the bubble to port, In other words the same effect as Coriolis in the N Hemisphere, If the Gyro wander is to Starboard it would tend to counter act coriolis effect, the opposite will hold good in the Southern hemisphere (note sighns of coriolis & Gyro Wander tables in back of AA)
[page break]
If D.R Compass is in use Gyro wander will be nil & Coriolis effect only will have to be considered.
[underlined] EXAMPLE. [/underlined]
TAS 174 K Gyro WANDER 04 p/min
Co 180 T Az of Star 078 Lat 50N.
Table 1/.
Coriolis Effect. +3’
Gyro Wander. +4’
Combined Effect (Table 1) +7’
Relative bearing of start (Az) 078 - 180 [symbol] (heading of A/C) = Relative bearing 258
Z correction = 258 for +7” (Table 2) = -6 1/2’
Method of Checking Gyro Wander
S/C Synchronising Direction Gyro, Fly on D.G for 20 minutes & recheck Co on compass. The number of 0s
[page break]
that the heading of the A/C has changed divided by the time (in mins) will give the amount of wander per minute.
[underlined] EXAMPLE [/underlined]
0900 S/C 090M
0920 Course 096M
Gyro Wander = 6/200 /min
0.3 per min to Starboard.
[underlined] Sextant Correction [/underlined] AP 1234 Page 155
[underlined] Dome Refraction. [/underlined]
When taking a sight thru [sic] a standard Perspex dome as fitted to an A/C the rays of light from the star are bent or refracted by the Perspex thus giving inaccurate readings, all domes should be calibrated for this & a correction card placed in the A/C by the dome.
[page break]
A correction table is given in the Air Almanac, but this is only to be used if none other is available. to calibrate the dome place the A/C in a flying posn & take sights at various altitudes which after applying sextant correction will give the error, reverse the sign to get the correction.
[underlined] APPLYING ERRORS TO Ho IN ORDER. [/underlined]
1/. APPLY SEXTANT CORRN
2/. Z Corrn
3/. Dome Refraction
4/. Pin A or Q corn.
[underlined] Rising & Setting of the Sun. [/underlined]
A knowledge of this is sometimes necessary when sometimes planning a flight. The times are tabulated in the Air Almanac in L.M.T for the respective visible phenomena as observed from places on the Greenwich Meridian.
[page break]
If there were no refraction, sunrise & sunset would occur when the centre of the sun was horizontal to an observer at sea level, due to refraction the centre of the sun appears to be well above the horizon at these times & the visible phenomena occurs when the sun’s centre is about one degree below the horizontal
[underlined] Twilight. [/underlined]
The beginning of morning & the end of evening twilight are tabulated to give some indication of the amount of light that is available before sunrise & after sunset, AP 1234 page 85 paragraph 42. As the time of sunrise, sunset & twilight at any place changes only a minute or so from day to day the tabulated L.M.T of these occurrences at places on the Greenwich Meridian, may be
[page break]
taken as approximate L.M.T. for all places on the Earth at Similar Latitudes, Interpolation may be necessary as between tabulated latitudes.
[underlined] N.B. [/underlined] In all places in the world on any given parallel on a certain day the sun will rise or set at the same L.M.T.
[underlined] Example Sunrise [/underlined]
What is L.M.T, the G.D & G.M.T, the ZD & ZT of sunrise at a place 47N & 32E on 1st June 1943.
45N 0417’
50N 0356’
In Ch Lat 5N the change in time is -21 mins
‘’ ‘’ ‘’ 2N ‘’ ‘’ ‘’ ‘’ ‘’ 21x2/5 ‘’ = -8 mins
At 47N on Greenwich Meridian the sun will rise at 0417-8 = 1409 [sic]
[page break]
At 47N 32E the sun will rise at 0409 L.M.T.
LONG in TIME -2.08
GMT 0201 1-6-43
Zone = -2
ZT = 0401 ZD 1-6-43
SUMMARY OF SIGHTS TO 31-10-43
[table]
[page break]
[underlined] PZX TRIANGLE. [/underlined]
It is used to work out the AZIMUTH and altitude of a heavenly body from an assumed posn in the vicinity of which (60 miles)the observer is known to be. Done by use of A.A. & ANT tables.
[underlined] Intercept. [/underlined]
The AZIMUTH & ALTITUDE (which give ZENITH DISTANCE] of a star is calculated for the time the true altitude was observed, this gives the bearing & distance of the sub stellar point from the assumed position, this position being in the vicinity of the observers actual position.
[diagram]
[page break]
the calculated altitude is compared with the true observed altitude & any distance between them is due to the difference in Radii of the two position circles. [underlined] ie [/underlined] position circle through the assumed position & assumed position through the observer. If the observed altitude is greater than the calculated altitude, this means that the true zenith distance must be less than the calculated zenith distance. The radius of the observers position circle must be less than the radius of the assumed position circle & so the observers position line must be towards the star by a distance equal to the difference between calculated & observed zenith distance, In other words between calculated and observed altitude. When the observed altitude is less the opposite will apply and
[page break]
the observers position will be farther away.
[diagrams]
[page break]
[diagram]
[underlined] Perihelion [/underlined] occurs when the Earth in a point in its orbit when it is nearest the sun (approx 4th JAN). [underlined] APHELION [/underlined] occurs when the Earth is on a point in its orbit it is farthest from the sun (approx 4th July).
[underlined] Moonrise & Moonset. [/underlined]
The moon moves round the Earth from West to East & from new moon to new moon the period is approximately 29 days, the average lunar day is 24 hrs 50 mins, therefore the moon rises & sets on an average of 50 mins later each day, and on some days will not rise, or will not set on others. The times tabulated in the air almanac is for the visible phenomena & is in
[page break]
L.M.T. for places on the Greenwich Meridian. The rapid movement of the moon around the Earth as compared with the earths rotation round the sun, causes difficulties when calculating times of moonrise or moonset for places not on the [underlined] Greenwich Meridian [/underlined]. Owing to the revolution of the Moon in the same direction as the revolution of the Earth, the earth has to spin through more than 360 between two successive moonrises or moonsets. There is always therefore a time lag in the phenomena connected with the moon.
Sketch is seen as from above N. Pole, O is the centre of the Earth. G1/ is the position of the Greenwich Meridian at 60N lat at the time of the moonset of the 22-2-43, 24 hours later greenwich Meridian will be at G1/ again but the moon will be at M2/ & moonset will not occur, moon will set on the 23-2-43 when the
[page break]
meridian has moved to G3 & the moon will be at M3. thus moonset will occur at 2100 hrs on the 23-3-43. The difference between the L.M.T of moonrise or moonset on one day & the L.M.T of the same occurrence on the next or preceding day varies and at some times is more than an hour.
[diagram]
In the above figure moonrise is at 23,30 on the 26-4 on the Greenwich Meridian. On the 27-4 at 2330 hours the moon will be at M2 & therefore moonrise will not have occurred on the Greenwich Meridian. Moonrise will not occur on the Greenwich
[page break]
Meridian until it is at G3/. and the moon at M.3, which will be at 0035 hrs on the 28-4, Therefore there is no moonrise on the Greenwich Meridian on the 27-4. The local date & L.M.T of moonrise & moonset at places east or West of Greenwich differ from the dates & times tabulated in the A.A. by a proportion of the daily lag concerned, the AA provided a table of distances, (approx half the daily lag) the correction is applied direct to the L.M.T. of the phenomena on the meridian at Greenwich to obtain the L.M.T on the observers meridian, therefore at places east of Greenwich the phenomena will occur at an earlier L.M.T than at Greenwich and the correction is to be subtracted, at places West of Greenwich it will be at a later L.M.T. than at Greenwich and the correction added, the rule is add if the longitude is West, subtract if East.
[page break]
[underlined] Example. [/underlined]
[calculation]
[page break]
[calculation]
[deleted] [calculation] [/deleted]
[page break]
When planning a long flight it may be useful to know when & where to expect the sun or moon to rise or set, if it were simply a case of arriving at some destination, say before sunset, the time to leave could best be calculated by working back from destination to starting point.
[underlined] Example [/underlined]
Suppose a flight of 5 hrs duration must be completed by sunset which occurs at 1800 hrs LMT on long 33E & the start point is in Long 50E. What is the latest time of depart in LMT.
[calculation]
[page break]
[calculation]
[diagram]
[page break]
[underlined] Polaris [/underlined]
If there were a star at the [inserted] celestial [/inserted] Pole suitable for observation, the altitude of the star would be the observers latitude. Polaris is not at the pole, but very near it, a small correction called Q can be worked out which when added algebraically to the correct observed altitude of Polaris, converts it into a quantity equal to the observers latitude.
Declination of Polaris is approx 89 so it is always within 1 of the celestial pole, one degree on the earth equals 60 nm therefore sub stellar point of Polaris describes a circle round the pole of approx 60nm radius
[page break]
[diagram]
P is Pole, Px stars meridian. The distances XZ & PZ are very large compared with PQ with centre & radius XZ cut PZ at T, then triangle XZT is an isosceles & PT is true Q corrn/.
Note
As we normally work with altitudes and latitudes in this case Q corrn would be minus, were the star at X1 Q corrn would be positive
[page break]
[diagram]
P equals N Pole, [symbol] = Polaris. Z = observer, draw XR perpendicular to PZ, point T is found by radius [symbol]Z & centre Z, cutting ZP at T, in practice RT is very small & can be ignored
[page break]
therefore P.R equals Q corrn/, but PR equals P[symbol] cos [symbol]PR (cos LHA[symbol]) P[symbol] is constant (Polar distance Polaris)
LHA[symbol] = LHA[symbol] + SHA[symbol]
SHA[symbol] is constant, therefore we can tabulate Q corrn against L.H.A.[symbol]
[underlined] Note. [/underlined]
Strictly speaking Q corrn depends upon Latitude, but tables assume a latitude of 45N, the tables may be used without appreciable error from 15 - 70N. It is important to remember that Polaris observation is the only observation (astro) worked out with D.R. Longitude
[page break]
If assumed posn is 100 miles out from ASSUMED [underlined] psn. [/underlined]
[diagram]
May be due to one of two things in Fig I. the azimuths from the assumed and actual positions are
[page break]
not parallel, therefore when drawing in position line from azimuth from the assumed position, this position line will be inclined at a small angle to the true position line.
In fig II. error is due to the fact that the azimuth is the arc of a Great Circle and not a rhumb line as plotted on a mercators chart/
[underlined] Note [/underlined]
When using assumed positions large distances from the actual position another error may occur, due to the arc of the position circle being a straight line. If this occurs sights should be reworked near actual position
[underlined] Reasons Why altitudes of less than 15 or more than 80 are rarely use in astro nav.
Less than 15 [/underlined]
When a body is low in the sky
[page break]
there is a large amount of refraction in the sky which will be difficult to calculate for different heights at which the A/C is flying.
[underlined] altitudes greater than 80 [/underlined]
In the case of an altitude of 80 the radius of the position circle is only 600 miles therefore a straight line can only be used as a position line over very short distance, in other words the azimuth is changing rapidly.
[underlined] Maximum Declination of Sun, Moon & Stars. [/underlined]
Maximum Dec of moon is 28 1/2 Moons orbit is inclined at 5 1/2 to the sun, maximum declination therefore is 28 1/2 minimum 18
Maximum declination of star is 90 but it depends on its position on the celestial concave.
Maximum declination of sun is 23 1/2.
Course 19. AIR. NAVIGATOR.
42. AIR. SCHOOL.
PORT ELIZABETH.
SOUTH AFRICA.
23rd August 1943
1395951.
Neale. E.J.H.
[page break]
Maps & Charts.
[underlined] MAP READING.
Before Flight. [/underlined]
Make sure that you know if it is metres or feet, know all conventional signs, including any unusual ones peculiar to the map in use. Insert any secret information, lightly in pencil, according to a private secret code. [underlined] eg [/underlined] 25 miles due East of actual position.
Aquire [sic] a true sense of map scale.
On 1 million 1 inch = approx 16 miles.
‘’ 1/2 ‘’ ‘’ = ‘’ ‘’ 8 ‘’
‘’ 1/4 ‘’ ‘’ = ‘’ ‘’ 4 ‘’
Aquire a true sense of map direction. The direction of North should never be in doubt. Draw in route with time or distance marks if possible (draw tracks in first). Study the route carefully, select suitable land-marks and put a pencil ring round those not clearly marked, put an E.T.A. against each. Study relative forms of landmarks, as they will appear in flight. Fold map so that area required is easily accessable [sic], preferably with distance scale shown
[page break]
[underlined] MAP READING.
During Flight. [/underlined]
Orienteering the map helps in recognising relative position of features, essential in identifying road & rail junctions, may usefully be dispensed with when not lost, to give ease in reading names and bearings.
Use time marks to anticipate land marks, such as towns, rivers & coast lines, particularly at night.
Provided the general position is known always read from map to ground. Mountains appear in plan below the A/C in elevation at a distance.
[page break]
[underlined] Procedure When Lost. [/underlined]
[circled 1]. Draw a circle of uncertainty round D.R. position, radius 10% air distance flown since last fix.
[circled 2]. Orient map by means of compass.
[circled 3]. Look around horizon for 2 or 3 prominent land-marks, estimate their bearing & distance, pin-point yourself by reading from map to ground.
[circled 4]. Failing this adopt a positive plan
a/. Fly in the direction of some prominent feature, e.g. river, mountain or coastline, follow this until recognised.
b/. commence organised search.
c/ circle some local feature until it is recognised or until plan is ready. to make map reading easiest & so assist recognition, fly from S to N over landmarks N.B. pay particular attention to air plot never fly aimlessly to inspect features on the horizon.
[page break]
[underlined] Map Reading by Day. [/underlined]
For good results, always observe down sun.
[underlined] In Good Visibility
Landmarks [/underlined]
a/. [underlined] Mountains and hills. [underlined] give general position only, very difficult to use for P.P. get impression of contour shapes.
b/. [underlined] Water. [/underlined] Rivers lakes canals etc N.B. bridges & Gorges. beware of floods & droughts.
c/. [underlined] Railways & Roads. [/underlined] do not P.P. without orienting map.
N.B. Distinguishing features d/. [underlined] Towns & Villages [/underlined] (alter shape).
e/. [underlined] Woods. [/underlined] alter shape. on modern target maps reliability symbols are used
f/. [underlined] Golf Courses & Race Courses [/underlined] very visible from the air
g/. [underlined] Sea Marks [/underlined] a/. Coastlines very visible
[page break]
due to breakers. b/ Sandbanks, rocks, shoals. N.B. STATE THE TIME.
c/. Light houses & Light Ships
d/. Marine Lights (shaded on top may not be visible when directly overhead.)
e/. large buoys
f/. Cliffs.
g/. Sea traffic.
In Poor Visibility use map reading in close conjunction with D.R.
By night always observe up Moon.
[underlined] Map Reading by night. [/underlined]
a/. Always observe up moon.
b/. Visibility may increase by night.
c/. Anticipate features.
d/. When you acquire night eyes dont [sic] spoil them by using the light.
e/. Coast always almost visible.
f/. difficult to distinguish details (due to cloud shadows).
[page break]
g/. Town lighting, decreases after midnight.
h/. Fires & ACK ACK
i/. Aerial Beacons & Marine Lights
[underlined] Lights at sea. [/underlined]
abbreviations in 1234 Chapter 3 para 19 Visibility of Marine Lights calculated for a height of 15 feet above sea, visibility is affected by Met conditions & humidity, changes of refraction, height of the observer & state of the tide.
[underlined] Reporting Position. [/underlined]
1/. Pin Point, accurate, non secret, may be difficult to find
2/. Bearing & distance, not easily estimated over 10 miles. a/. from landmark, non secret. b/. from lettered datum point, secret.
3/. Latitude & Longitude not secret, but accurate
4/. R.A.F. lettered co-ordinates.
[page break]
[diagram of lettered grid with point marked]
Each meridian & parallel alloted [sic] 2 letters (changeable). Give co-ordinates of intersection of Parallel & meridian S.W of position [underlined] MF – PR [/underlined] followed by minutes of [underlined] latitude & longitude. [/underlined] This is the same for both N & S hemisphere.
5/. The Naval Method. Bearing & distance from nearest intersection 255 JBZB 3 miles.
6/. Modified British Military Grid. Great Britain divided into 6 500Km squares, lettered LM, QR, BW & I
[page break]
b/. each 500 Km square divided into 25 100 Km squares & lettered, called Primary
c/. each 100 Km square divided into a hundred by 10 Km squares & numbered called Secondary
d/. the 10 Km squares can be subdivided into units by inspection or by instruments In reporting position give two letters & 4 figure coordinates of Pin Point from the S.W. corner.
[underlined] N.B. [/underlined]
always give Easting before Northing. Be certain if bearings refer to GRID NORTH or TRUE NORTH.
The TRUE origin passes through the I.O.W.
The FALSE origin passes West of the Scilly Isles.
[page break]
[underlined] Maps & Charts in use in the R.A.F. [/underlined]
Plotting sheets.
1/. 1 – 1,000,000. reference G.S. G.S. 4080. It covers all operational areas, Main ground features only shown, spot heights in metres ABAC scale for conversion angle, compass roses 1 – 2 or 3. Isogonals for every one degree, 10 minute graticule, marginal statute & nautical mile scale varying with Latitude. Ch Long in time as well as arc, 3 main parallels marked plainly for use with astrograph. Cheap & easily produced.
Scotland N.W 54N 13’W
All BRITISH ISLES & IRELAND. covered by 2 sheets.
2/ 1 – 500,000 BRITISH ISLE. The sheet is similar in all particulars to 1 – 1,000,000 & is used mainly for training.
3/. 1 – 2,000,000 G.S.G.S. 5012. new series small scale plotting charts, similar to 4080. * cannot be used with astrograph. Almost any European target can be reached on a single sheet.
[page break]
Used for Mosquitos & Pre flight Plan Sheet No NW 46/8 covers the area from Dublin to Konisberg 8W - 21W scale 2,000,000 at 56N. Spot heights in metres, hachuring for mountains, heavy coastline no radio broadcast stations, improved shapes of town, statute miles scale in body of sheet.
[underlined] Topographical MAPS. [/underlined]
1/ 1 – 1,000,000 GSGS 2758 modified Polyconic projection, once used for navigation, superseded by GSGS 4080. suitable for high altitude map=reading. More detail than plotting chart. No 10 minute graticule, heights in feet, covers Europe & Great Britain. Revised 1 – 1,000,000 new series being produced to cover main operational areas of Europe, based on old 1,000,000, with redesigned sheet lines, unimportant details removed roads & railways emphasised, purple layering incorporated.
[page break]
2/ 500,000 GSGS 4072 Modified Polyconic Great Britain & Europe, map reading at moderate height & short distance navigation 10 minute graticule 1/2 isogonals. heights in feet. distinctive colours for main features In Germany woods not marked in green as they are too numerous to serve as land marks, main outline only shown.
3/. 1/250,000 GSGS 3982. [deleted] Modified Polyconic. Europe, does not cover great Britain, but being extended to cover France & Ireland, used for map reading when approaching target & over industrial areas. 10 min graticule, Ht in metres.
4/. 1/4 in ORDNANCE SURVEY AIR EDITION CASSINI’S PROJECTION. Map reading only 10 min graticule on some sheets, British Grid on others. Magnetic variation on compass rose. Grid deviation at side of sheet.
1/4 in O.S. [underlined] Special. [/underlined]
Similar to above but layout conforms with 1/4 million series.
[page break]
Target Maps. reliability symbols being introduced.
BONNES PROJECTION. SOUTH AFRICAN.
[underlined] Admiralty charts. [/underlined]
Mercators Projection, only nautical mile scale, no accurate land details except sailing marks. Compass rose graduated true & magnetic, magnetic inside true with variation indicated.
Admiralty Plans.
Small charts on large scale, usually of harbours, suitable as target maps, no latitude or longitude scale, distances in nautical miles & cables. 10 cables In mile.
Marine Contoured Maps.
For use in minelaying flights, depth of water shown by layered colours, beaches & banks visible at mean low water, grey stippled, land details shown accurately, taken from 1/4 million air maps. To cover all coasts from Spain
[page break]
to 64N, including the Baltic. Norwegian sheets layered for a ground height. Barmouth sheet produced for training. Gnomonic Charts.
[underlined] CONVENTIONAL SIGNS. [/underlined]
[symbol] LAND AERODROME.
[symbol] LANDING FIELD.
[symbol] AIRSHIP BASE.
[symbol] WATER SEAPLANE ANCHORAGE.
[symbol] AERODROME (WATER)
[symbol] CONSPICUOUS OBJECT.
[symbol] AIRSHIP HANGAR
[symbol] AIRSHIP. MOORING MAST.
[symbol] MARINE LIGHT
[symbol] MARINE LIGHT VESSEL.
[symbol] CHURCH WITH TOWER OR SPIRE
[symbol] POWER CABLE. OR OVERHEAD RAILWAY.
[symbol] ARIEL [sic] CORRIDOR
[symbol] PROHIBITED AREA.
[page break]
[symbol] AERODROME CONTROLLED AREA.
[symbol] AIRPORT WITH CUSTOMS FACILITIES.
[symbol] (AERODROME) DANGER AREA (SAFETY HT MARKED).
[symbol] EXPLOSIVES AREA.
[symbol] BALLOON OBSTRUCTION BEACON.
[symbol]AIR OBSTRUCTION. MORE THAN 200 ft. [underlined] unltd. [/underlined]
[symbol] ‘’ ‘’ ‘’ ‘’ ‘’ LIGHTED
[symbol] NON AERONAUTICAL RADIO STATION.
[symbol] AERONAUTICAL COMMUNICATION.
[symbol] AERONAUTICAL D/F OR BEACON.
T. Communication M. Met N. Non directional D Track indicating A Landing Approach R Gonioltric.
[symbol] HALF SUBMERGED WRECK.
[symbol] WRECK. DEPTH OF WRECK AT LOW WATER
[symbol] WRECK LIKELY TO FOUL ANCHOR.
[symbol] DANGEROUS WRECK.
[page break]
Mercators Projection.
Similar to the TRUE CYLINDRICAL projection. It has a rectangular graticule, rhumb lines are straight lines, angles on the Earths circles are correct. The chart length of 1 min longitude is constant, therefore latitude scale increases towards the Poles. No Constant Scale, but at any latitude the scale is the same for all directions for short distances. For small areas orthomorphic, for large areas shape distorted. GRATICULE easily constructed, the Great circles are curves convex to nearer pole. Polar areas cannot be shown.
[underlined] Principle of Construction. [/underlined]
Cos 0 ‘’ 1
Cos 90 equals 0
Sec 0 ‘’ 1
Sec 90 ‘’
On the Earth, distances between meridians varies as cos latitude i.e. maximum at equator, zero at poles. On Mercators, meridians pull apart until parallel. To counteract this & preserve constant bearing, the parallels of
[page break]
latitude are pulled apart proportionately. The distance between parallels varies as sec latitude.
[underlined] To construct a Mercators Chart. [/underlined]
Between Latitudes 52N 53N, & longitude 0 & 1W. Scale 1,000,000 at 56N
Distance between Meridians at Equator = 60nm
‘’ ‘’ ‘’ ‘’ 56N = 60 cos 56 = 32.55n.m.
Scale 1/m means 1,000,000’ on ground = 1” on chart.
33.55n.m on ground = [calculation] on chart = 2.44”
[diagram]
[calculation]
[page break]
The Mercators Graticule may also be constructed by using meridiurnal [sic] parts from Norris [sic] or INMANS Tables.
Und
TOPOGRAPHICAL MAPS. [/underlined]
Simple Conical.
[diagram]
Scale correct along meridians & standard parallels, incorrect along other parallels. Greatest error on parallels furthest from the standard. This projection is good for countries with a small change of latitudes. Direction correct on Northerly or Southerly. not orthomorphic.
[page break]
Straight lines almost Great Circles.
[underlined] Method of Recognition. [/underlined]
Parallels are arcs of concentric circles. Meridians converging straight lines.
[underlined] Polyconic. [/underlined]
[diagram]
Each parallel constructed with its own centre ie more than one cone used
[underlined] Properties [/underlined]
Scale correct along all parallels & central meridian. Not orthomorphic
[page break]
more so than simple conic. Suitable for small areas [inserted] not equal areas [/inserted] (as parallels not arcs of concentric circles) but nearly so. Near Central meridians straight lines approx G.Cs.
[underlined] Recognition [/underlined]
Parallels evenly spaced, non-concentric arcs, Meridians Curved.
[underlined] International Modified Polyconic. [/underlined]
Agreed to by international conference, basis of all 1,000,000 maps of Europe & many other parts of world. Each sheet constructed seperately, up to 60 N & S latitudes, each sheet covers 4 latitude by six degrees longitude, in higher latitudes 4 latitude by 12 longitude. 1,000,000 series recognisable by this.
Turn over for sketch.
[page break]
[diagram]
[[underlined] Construction [/underlined]
Central Meridian correctly drawn to scale. Two standard parallels correctly drawn N & S. calculate positions of Meridians, draw meridians as straight lines. Transfer correct length of central meridian to two degrees east & 2 west of centre, redraw parallels, draw in rest of graticule
[underlined] Properties [/underlined]
Scale correct at standard parallels & Standard Meridian, slightly incorrect elsewhere, each sheet almost orthomorphic
[page break]
& equal area. Straight lines are almost great [symbol]
[underlined] Recognition [/underlined]
Dimensions of the Graticule. Parallels are arcs of non concentric circles. Meridians straight lines. Advantages of I.M.P. Straight lines approx G [symbol]. Scale very nearly constant. Ground W/T bearings laid off direct.
9 Ajacent [sic] sheets almost fit, 5 sheets fit exactly.
[underlined] Disadvantages [/underlined]
Rhumb lines not straight lines, bearings [underlined] must [/underlined] be measured against the meridian midway along track.
[underlined] Note [/underlined]
To plot T.M.G. find angle as above, draw to the next meridian, lay off angle again & so on.
[page break]
BONNES PROJECTION.
Maps of Suid Africaa.
Suitable for narrow countries where change of latitude is greater than change of longitude. In broad countries obliquity of Meridians at edges causes distortion.
Method of Construction
One standard parallel meridian at centre. Draw in central meridian, divide for latitude. Draw in concentric parallels of latitude, divide for longitude, draw in meridians.
[underlined] Properties [/und]
Scale correct along parallels & central meridians only. equal area, distortion at edges, therefore not orthomorphic and sheets do not fit.
[page break]
[underlined] CASSINI PROJECTION. [/underlined]
Used with 1/4” ordnance Survey maps of GT Britain. a Mathematical Construction.
[underlined] Properties [/underlined]
Central Meridian correct, others too long. Meridians curve inward toward poles. Edges of map do not coincide with meridians. + or – 4 degrees of deviation at edges. Equal Area.
[underlined] TRANSVERSE MERCATOR or GAUSSE CONFORM [/underlined]
[underlined] Properties. [/underlined]
Central Meridians straight, others curves, curved inward toward the poles. Parallels concave to nearer pole. Equator straight line. Grt [symbol] central Meridian & all Grt [symbol] perpendicular to it are straight lines, all other Gt [symbol] curved. Rhumb lines curved except for central Meridian & equator. Scale varies all over the sheet increasing with distance from Central Meridian. Bearing, shapes and Areas. Projection is
[page break]
limited in practice to 3 either side of Central Meridian. So maximum Scale error is less than 1%, so that bearings Shapes & Areas may be accepted as correct.
[underlined] Suitability. [/underlined]
Especially suitable for griding [sic], as can be extended N & S indefinitely, & if central meridians are sufficiently close, adjacent sheets fit E & W. The Union is mapped on 2 strips, North Africa on 5 strips.
[underlined] GNOMONIC PROJECTION. [/underlined]
Gnomonic is a Tangential Projection. Grt [symbol] are straight lines, bearing scales, shapes & areas, all distorted, except at point of origin. Distorted Compass rose.
[underlined] CAPTAIN OF AIRCRAFT MAP. [/underlined] Small scale Mercators plotting objects on which captain can lay off required tracks. (it measures 15’ x 12’) and all relevant information, such as Ack-Ack & etc.
[page break]
Curve of Equal Bearing.
[diagram]
A Curve of Equal Bearing is a line from all points on which the Gt [symbol] bearings of a given position on the Earths Surface are equal. It constitutes the position line
[page break]
obtained from a loop bearing.
[underlined] In Plotting W/T Position lines [/underlined]
1/ D/F W/T Bearings
A/ On a topographical Map Plot direct from D/F Station.
B/ GNOMONIC Chart Plot direct from D/F W/T Station. Distorted compass rose or protractor maybe needed
C/ On mercators (see Chapter 3 Para 38)
[diagram]
Case 1/ With conversion angle of less than 4, find D.R. posn, calculate conversion angle, apply conversion
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angle to Gt [symbol] bearing & plot from D/F station. (Draw Sketch to ensure that conversion angle is applied correctly).
Case 2/
Conversion angle more than 4. Find D.R. posn, calculate conversion angle & plot as above, at D.R. LONGITUDE apply conversion angle again in the same sense to obtain position line.
2/ Plotting Loop Bearings
A/ On topographical map, add true course. Calculate & Apply convergency or transfer Meridian, Plot reciprocal from W/T station.
Where the angle of convergency may be greater [underlined] ie [/underlined] more than 4, Plot position line as above at D.R longitude apply angle of convergency of opposite sign
[underlined] Plotting Loop bearings on Mercators [/underlined]
When conversion angle is small [underlined] ie [/underlined] less
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than 4 5 or 6. add true course, apply conversion angle (draw sketch). Plot reciprocal from D/F station.
Case B/. When conversion angle is large, add true course, apply conversion angle, plot reciprocal from D/F station, apply conversion angle of opposite sign to get Curve of Equal bearing position line.
[diagram]
[page break]
[underlined] Scale of Map. [/underlined]
[diagram]
Cloud Shadows masking town & making woods Difference of Map reading in Summer & Winter, difference of droughts drying up of rivers, also of colours of green leaves. Map read down sun. Low sun throws a lot of shadows. Map reading is better at greater hts.
Circle of Uncertainty, 10% of Air distance from last fix from D.R posn.
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[calculations]
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[calculations]
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E. T. H. NEALE
[page break]
[underlined] Astro Theory. [/underlined]
[underlined] NAUTICAL MILE. [/underlined]
Arc or distance on Earths surface subtended by an angle of 1 minute at the centre of the Earth, thus an angle of 1 will subtend an arc or distance equal to 60 nautical miles. Hence distance can usually be expressed in terms of degrees & minutes.
[underlined] Declination. [/underlined]
Is celestial latitude & corresponds with terrestrial latitude & is measure from 0 - 90 N or S.
[underlined] Precession of the Equinox]. [/underlined]
Precession of First Point of Aries Westward at the rate of 50 secs of ARC per annum.
[underlined] Right Ascension [/underlined]
Is 360 - SHA *
[underlined] GHA ARIES. [/underlined]
Angle From GM to FP [symbol]
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The Astro graph.
The sub stellar may be located for any instance of time & circles drawn from this common centre with various radii are position circles corresponding to various observed altitudes of the body. These concentric position circles made with the S.S.P over the face of the earth from E to W as the earth moves from W – E. If a film were made upon which circles were drawn for small stars as would be visible at various times in a certain locality & these circles were thrown by a projector onto the chart of the locality then by rotating the film from E to W to keep the centres of the circles coincident with the appropriate S.S.P’s the projected curves could be used as a visual guide for plotting actual posn lines from the observed altitude of the selected star, this is what a navigator does
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when using the astrograph. The time scale on the film is aligned with the appropriate meridian on the map & when suitably adjusted for GMT of observation the centre of the projected arc is coincident with the proper sub stellar point of the star, the astrograph film gives arcs of altitude for 2 stars & in addition Q correction for Polaris observation where these are possible.
The instrument projects star curves. (circles of equal altitude on the 1,000,000 plotting sheet it is used in conjunction with the air almanac which is used to adjust star curves to the time of observation, this is done by using 1/. a setting longitude 2/. a G.M.T. with a corresponding A.M.T. for a particular setting longitude, these are given for every night of the year.
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1/.
Wind all film to right hand spool
2/. Undo 6 retaining screws & remove astrograph base, which carries spool brackets
3/. Pull out right hand adjusting knob & remove full spool.
4/. Pass the end of the film beneath the right hand roller & friction pad & insert in gap between glass plates.
5/. Push the film towards the empty spool, depressing the left hand friction pad beneath the roller to assist passage of film.
6/. Insert the end in the empty spool, & insert new spool in right hand bracket.
7/. Take up the slack with the left hand spool
8/. Refit base to astrograph body.
NOTE. This is not an easy operation during flight & should not be attempted unless absolutely necessary. It is better to carry a
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reserve astrograph
To Fit the Astrograph.
1/. Join up height bar by screwing up two pieces, make certain you have the correct gauge, MKIA & MKIB
2/. Using height bar directly under each levelling screw of the mounting ring in turn, adjust so that gauge will just pass between the tip of the screw with the bottom of the gauge on the Chart table
3/. Tighten up lock nuts with the spanner provided & recheck with height gauge.
4/. See that dummy plug is in voltage socket not in use. (most modern A/C 24 volts Anson 12 volts).
5/. Attach the Astrograph to the mounting ring so that the levelling screws register in the hole, slot & plane
6/. Plug in to A/C supply, switch on to check.
[page break]
[underlined] Action before Flight. [/underlined]
Look in astrograph tables, (in Air Almanac or A.A.) under date of intended flight, take out a suitable setting longitude, (somewhere near area in which flight is taking place). & the corresponding GMT & AMT. mark in heavily with a thick pencil, the meridian of the setting longitude on the chart for its full length. In a clear space on the left hand side of setting longitude mark GMT of the hours during which you expect to use the astrograph on the right hand side of line, mark in corresponding hours A.M.T.
[diagram]
[page break]
Fix chart under astrograph & adjust to bring time scale on to central latitude line of chart, these must coincide exactly, Convert G.M.T. of first observation to A.M.T. (to nearest hour) & set this to the setting longitude, note the stars for which the curves are given at this time, & approx azimuths & altitudes. Make sure that they can be recognised when required.
[underlined] Action during flight. [/underlined]
1/ Take first altitude & note GMT
2/ Convert GMT of sight to AMT
3/. Set this A.M.T. against setting longitude.
4/. Draw in position line obtained from stars altitude.
5/ Take second sight & note GMT
6/. Convert this G.M.T. to AMT. & set new A.M.T.
7/. Draw in second position line obtained from second stars altitude. Third position line may be made by taking
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altitude of polaris & noting G.M.T convert this to AMT & set it. Take Q corn from above time scale in vicinity of fix or DR Posn apply according to sign to observed altitude of Polaris & obtain latitude
Points to be noted when using an astrograph
[circled 1]
When switching on astrograph, note which two stars are in use. If about to change, then wait until change takes place
[circled 2]. Do not wind film past stop mark.
[circled 3]. Do not forget when drawing in position line to notice direction of increasing altitudes
[circled 4] Care should be taken when bulb is changed, new bulb must be cleaned,
[circled 5]. See that you have correct latitude band for chart in use, if not parallels of latitude will not coincide.
[circled 6]. If longitude does not come on chart half hourly setting longitude can be
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found by adding 7 31’ to tabulated longitude adjusting the G.M.T appropriately adding 30 mins in W & subtracting 30 mins in E
[circled 7]. In astrograph tables left hand page is for west setting longitudes & right hand page for east setting longitudes, dates are given at the head of the column each of which is headed by hours of A.M.T. It must be noted that the corresponding Greenwich date to the GMT is indicated in heavier type it is the first in East long & second in West.
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“Z” CORRECTION
This is divided into 2 parts coriolis & gyro wander. These are calculated by use of the tables at the back of the air almanac.
[underlined] Coriolis “A” [/underlined]
This is the tendency of a mass to move to the right of its intended path when travelling N or S along a meridian in the Northern hemisphere. In the southern hemisphere it is a tendency to go to the left when travelling N or S.
[diagram]
[page break]
[diagram]
[underlined] Coriolis ‘A’ [/underlined]
This is due to the different speeds of rotation round a spinning axis of a point on various parallels of latitude. A mass when travelling along a meridian from one parallel to another, tends to retain its old speed of rotation & therefore to leave its path along the meridian. The greater its speed in travelling N or S the greater its tendency.
[page break]
[underlined] Coriolis “b” [/underlined]
So the tendency of a mass to move to the right of its path when travelling along a parallel of latitude in the N. Hemisphere or to the left in the Southern. (See diagram over page).
In the case of an A/C travelling in an E to W direction its speed of rotation will increase, therefore centrifrugal [sic] force will be increased. an A/C will tend to go off into space, at right angles to the axis of spin. This force C.F. could be resolved into 2 forces, V a tendency of the A/C to climb & CBE a tendency to go to the right of its path. When travelling from [deleted] W to E [/deleted] E to W the speed of rotation will be decreased and as the counter balancing effect of gravity & centrifrugal force will be upset, leaving a negative C.F. acting towards the [deleted] radius [/deleted] AXIS of spin.
[page break]
This can be resolved into G a tendency of the A/C to dive & C.B.E. a tendency to go to the right of its path. (the greater the A/C speed, the greater the tendency.) When not travelling along a meridian or parallel of latitude, it may be seen that a combination of coriolis “A” & “B” will affect the A/C. it can be shown that this combination will always be a constant
Now these tendencies of climbing or diving, turning to the right or left will unconsciously be corrected by the Pilot, but the effect will get through to the liquid in the bubble chamber of the sextant, causing the liquid to move to the right side of the A/C (In the N. Hemisphere) & the bubble to the left, thus the observer has to tilt the top of the sextant to the left side of the A/C to keep the bubble in the centre of the chamber, this tilt will be in the nature of 4’ in English latitudes and about 3 min to the right in these latitudes
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but it will always be there. It can be seen that this tilt will not affect fore & aft shots & will be maximum on the beam. In other words it depends on the relative bearing of the star.
[underlined] Gyro Wander [/underlined]
All directional gyros tend to wander from their constant direction in space, due to precession and other causes, having to be reset every 15 minutes or so, but this wander is going on for the whole time & the pilot while following this direction gyro is unconsciously turning to Port or Starboard by a slight amount per minute, in other words, the same effect as Coriolis. If the D.G. is wandering to Port, the pilot will turn to port, the liquid in the bubble chamber will go to Starboard & the bubble to port, In other words the same effect as Coriolis in the N Hemisphere, If the Gyro wander is to Starboard it would tend to counter act coriolis effect, the opposite will hold good in the Southern hemisphere (note sighns of coriolis & Gyro Wander tables in back of AA)
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If D.R Compass is in use Gyro wander will be nil & Coriolis effect only will have to be considered.
[underlined] EXAMPLE. [/underlined]
TAS 174 K Gyro WANDER 04 p/min
Co 180 T Az of Star 078 Lat 50N.
Table 1/.
Coriolis Effect. +3’
Gyro Wander. +4’
Combined Effect (Table 1) +7’
Relative bearing of start (Az) 078 - 180 [symbol] (heading of A/C) = Relative bearing 258
Z correction = 258 for +7” (Table 2) = -6 1/2’
Method of Checking Gyro Wander
S/C Synchronising Direction Gyro, Fly on D.G for 20 minutes & recheck Co on compass. The number of 0s
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that the heading of the A/C has changed divided by the time (in mins) will give the amount of wander per minute.
[underlined] EXAMPLE [/underlined]
0900 S/C 090M
0920 Course 096M
Gyro Wander = 6/200 /min
0.3 per min to Starboard.
[underlined] Sextant Correction [/underlined] AP 1234 Page 155
[underlined] Dome Refraction. [/underlined]
When taking a sight thru [sic] a standard Perspex dome as fitted to an A/C the rays of light from the star are bent or refracted by the Perspex thus giving inaccurate readings, all domes should be calibrated for this & a correction card placed in the A/C by the dome.
[page break]
A correction table is given in the Air Almanac, but this is only to be used if none other is available. to calibrate the dome place the A/C in a flying posn & take sights at various altitudes which after applying sextant correction will give the error, reverse the sign to get the correction.
[underlined] APPLYING ERRORS TO Ho IN ORDER. [/underlined]
1/. APPLY SEXTANT CORRN
2/. Z Corrn
3/. Dome Refraction
4/. Pin A or Q corn.
[underlined] Rising & Setting of the Sun. [/underlined]
A knowledge of this is sometimes necessary when sometimes planning a flight. The times are tabulated in the Air Almanac in L.M.T for the respective visible phenomena as observed from places on the Greenwich Meridian.
[page break]
If there were no refraction, sunrise & sunset would occur when the centre of the sun was horizontal to an observer at sea level, due to refraction the centre of the sun appears to be well above the horizon at these times & the visible phenomena occurs when the sun’s centre is about one degree below the horizontal
[underlined] Twilight. [/underlined]
The beginning of morning & the end of evening twilight are tabulated to give some indication of the amount of light that is available before sunrise & after sunset, AP 1234 page 85 paragraph 42. As the time of sunrise, sunset & twilight at any place changes only a minute or so from day to day the tabulated L.M.T of these occurrences at places on the Greenwich Meridian, may be
[page break]
taken as approximate L.M.T. for all places on the Earth at Similar Latitudes, Interpolation may be necessary as between tabulated latitudes.
[underlined] N.B. [/underlined] In all places in the world on any given parallel on a certain day the sun will rise or set at the same L.M.T.
[underlined] Example Sunrise [/underlined]
What is L.M.T, the G.D & G.M.T, the ZD & ZT of sunrise at a place 47N & 32E on 1st June 1943.
45N 0417’
50N 0356’
In Ch Lat 5N the change in time is -21 mins
‘’ ‘’ ‘’ 2N ‘’ ‘’ ‘’ ‘’ ‘’ 21x2/5 ‘’ = -8 mins
At 47N on Greenwich Meridian the sun will rise at 0417-8 = 1409 [sic]
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At 47N 32E the sun will rise at 0409 L.M.T.
LONG in TIME -2.08
GMT 0201 1-6-43
Zone = -2
ZT = 0401 ZD 1-6-43
SUMMARY OF SIGHTS TO 31-10-43
[table]
[page break]
[underlined] PZX TRIANGLE. [/underlined]
It is used to work out the AZIMUTH and altitude of a heavenly body from an assumed posn in the vicinity of which (60 miles)the observer is known to be. Done by use of A.A. & ANT tables.
[underlined] Intercept. [/underlined]
The AZIMUTH & ALTITUDE (which give ZENITH DISTANCE] of a star is calculated for the time the true altitude was observed, this gives the bearing & distance of the sub stellar point from the assumed position, this position being in the vicinity of the observers actual position.
[diagram]
[page break]
the calculated altitude is compared with the true observed altitude & any distance between them is due to the difference in Radii of the two position circles. [underlined] ie [/underlined] position circle through the assumed position & assumed position through the observer. If the observed altitude is greater than the calculated altitude, this means that the true zenith distance must be less than the calculated zenith distance. The radius of the observers position circle must be less than the radius of the assumed position circle & so the observers position line must be towards the star by a distance equal to the difference between calculated & observed zenith distance, In other words between calculated and observed altitude. When the observed altitude is less the opposite will apply and
[page break]
the observers position will be farther away.
[diagrams]
[page break]
[diagram]
[underlined] Perihelion [/underlined] occurs when the Earth in a point in its orbit when it is nearest the sun (approx 4th JAN). [underlined] APHELION [/underlined] occurs when the Earth is on a point in its orbit it is farthest from the sun (approx 4th July).
[underlined] Moonrise & Moonset. [/underlined]
The moon moves round the Earth from West to East & from new moon to new moon the period is approximately 29 days, the average lunar day is 24 hrs 50 mins, therefore the moon rises & sets on an average of 50 mins later each day, and on some days will not rise, or will not set on others. The times tabulated in the air almanac is for the visible phenomena & is in
[page break]
L.M.T. for places on the Greenwich Meridian. The rapid movement of the moon around the Earth as compared with the earths rotation round the sun, causes difficulties when calculating times of moonrise or moonset for places not on the [underlined] Greenwich Meridian [/underlined]. Owing to the revolution of the Moon in the same direction as the revolution of the Earth, the earth has to spin through more than 360 between two successive moonrises or moonsets. There is always therefore a time lag in the phenomena connected with the moon.
Sketch is seen as from above N. Pole, O is the centre of the Earth. G1/ is the position of the Greenwich Meridian at 60N lat at the time of the moonset of the 22-2-43, 24 hours later greenwich Meridian will be at G1/ again but the moon will be at M2/ & moonset will not occur, moon will set on the 23-2-43 when the
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meridian has moved to G3 & the moon will be at M3. thus moonset will occur at 2100 hrs on the 23-3-43. The difference between the L.M.T of moonrise or moonset on one day & the L.M.T of the same occurrence on the next or preceding day varies and at some times is more than an hour.
[diagram]
In the above figure moonrise is at 23,30 on the 26-4 on the Greenwich Meridian. On the 27-4 at 2330 hours the moon will be at M2 & therefore moonrise will not have occurred on the Greenwich Meridian. Moonrise will not occur on the Greenwich
[page break]
Meridian until it is at G3/. and the moon at M.3, which will be at 0035 hrs on the 28-4, Therefore there is no moonrise on the Greenwich Meridian on the 27-4. The local date & L.M.T of moonrise & moonset at places east or West of Greenwich differ from the dates & times tabulated in the A.A. by a proportion of the daily lag concerned, the AA provided a table of distances, (approx half the daily lag) the correction is applied direct to the L.M.T. of the phenomena on the meridian at Greenwich to obtain the L.M.T on the observers meridian, therefore at places east of Greenwich the phenomena will occur at an earlier L.M.T than at Greenwich and the correction is to be subtracted, at places West of Greenwich it will be at a later L.M.T. than at Greenwich and the correction added, the rule is add if the longitude is West, subtract if East.
[page break]
[underlined] Example. [/underlined]
[calculation]
[page break]
[calculation]
[deleted] [calculation] [/deleted]
[page break]
When planning a long flight it may be useful to know when & where to expect the sun or moon to rise or set, if it were simply a case of arriving at some destination, say before sunset, the time to leave could best be calculated by working back from destination to starting point.
[underlined] Example [/underlined]
Suppose a flight of 5 hrs duration must be completed by sunset which occurs at 1800 hrs LMT on long 33E & the start point is in Long 50E. What is the latest time of depart in LMT.
[calculation]
[page break]
[calculation]
[diagram]
[page break]
[underlined] Polaris [/underlined]
If there were a star at the [inserted] celestial [/inserted] Pole suitable for observation, the altitude of the star would be the observers latitude. Polaris is not at the pole, but very near it, a small correction called Q can be worked out which when added algebraically to the correct observed altitude of Polaris, converts it into a quantity equal to the observers latitude.
Declination of Polaris is approx 89 so it is always within 1 of the celestial pole, one degree on the earth equals 60 nm therefore sub stellar point of Polaris describes a circle round the pole of approx 60nm radius
[page break]
[diagram]
P is Pole, Px stars meridian. The distances XZ & PZ are very large compared with PQ with centre & radius XZ cut PZ at T, then triangle XZT is an isosceles & PT is true Q corrn/.
Note
As we normally work with altitudes and latitudes in this case Q corrn would be minus, were the star at X1 Q corrn would be positive
[page break]
[diagram]
P equals N Pole, [symbol] = Polaris. Z = observer, draw XR perpendicular to PZ, point T is found by radius [symbol]Z & centre Z, cutting ZP at T, in practice RT is very small & can be ignored
[page break]
therefore P.R equals Q corrn/, but PR equals P[symbol] cos [symbol]PR (cos LHA[symbol]) P[symbol] is constant (Polar distance Polaris)
LHA[symbol] = LHA[symbol] + SHA[symbol]
SHA[symbol] is constant, therefore we can tabulate Q corrn against L.H.A.[symbol]
[underlined] Note. [/underlined]
Strictly speaking Q corrn depends upon Latitude, but tables assume a latitude of 45N, the tables may be used without appreciable error from 15 - 70N. It is important to remember that Polaris observation is the only observation (astro) worked out with D.R. Longitude
[page break]
If assumed posn is 100 miles out from ASSUMED [underlined] psn. [/underlined]
[diagram]
May be due to one of two things in Fig I. the azimuths from the assumed and actual positions are
[page break]
not parallel, therefore when drawing in position line from azimuth from the assumed position, this position line will be inclined at a small angle to the true position line.
In fig II. error is due to the fact that the azimuth is the arc of a Great Circle and not a rhumb line as plotted on a mercators chart/
[underlined] Note [/underlined]
When using assumed positions large distances from the actual position another error may occur, due to the arc of the position circle being a straight line. If this occurs sights should be reworked near actual position
[underlined] Reasons Why altitudes of less than 15 or more than 80 are rarely use in astro nav.
Less than 15 [/underlined]
When a body is low in the sky
[page break]
there is a large amount of refraction in the sky which will be difficult to calculate for different heights at which the A/C is flying.
[underlined] altitudes greater than 80 [/underlined]
In the case of an altitude of 80 the radius of the position circle is only 600 miles therefore a straight line can only be used as a position line over very short distance, in other words the azimuth is changing rapidly.
[underlined] Maximum Declination of Sun, Moon & Stars. [/underlined]
Maximum Dec of moon is 28 1/2 Moons orbit is inclined at 5 1/2 to the sun, maximum declination therefore is 28 1/2 minimum 18
Maximum declination of star is 90 but it depends on its position on the celestial concave.
Maximum declination of sun is 23 1/2.
Collection
Citation
Ted Neale, “Ted Neale's Air Navigator notebook,” IBCC Digital Archive, accessed October 30, 2024, https://ibccdigitalarchive.lincoln.ac.uk/omeka/collections/document/16387.
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