University Carleton Department of Electronics
ELEC4600 Navigation M.R. Edwards
Assignment 2 2008
Data: 1 NM = 1.151 mi. = 1.852 km 1 NM = 1 minute of arc (approx) Earths rate of rotation: 15.05107 deg/hour g = 32.2 ft/sec = 981 cm/sec a = 3443.9 NM = 6378.2 km c = 2.9979 x 108 m/s 1 General a. What are the four requirements for approval of a navigation system for IFR (instrument ight rules) ight on domestic airways? Give a denition for each requirement b. Why is Magnetic instead of True North used as the reference for air navigation in most of North America? c. What is the term for the difference between Magnetic North and True North? d. An pilot is using a TACAN for navigation and obtains an indication that the distance from the facility is 60 NM and the bearing from the station is 150(M). Draw and label a diagram showing the lines of position resulting from this information. Comment on the geometry of the resulting x. 2 Relative Navigation Systems a. What information does a VOR provide to a pilot? ATC has give an aircraft a vector (heading) of 051 to intercept airway V316 (096 radial from the Ottawa VOR). What will be the relative bearing to the Ottawa VOR when the aircraft has reached the airway? How else could the pilot determine that the aircraft had reached the specied radial? b. In what two forms is this information displayed? c. Give one advantage and one disadvantage of ADF. d. Many DME transceivers display speed as well as distance. An aircraft is ying at 36000 Ft (approx. 6NM) at a groundspeed of 450 knots on a track which leads over the DME; the DME distance readout shows 10NM. What speed does the DME display show? e. Draw and label a diagram of the spectrum of a VOR station operating at 114.6 MHz
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f. The squitter rate for a DME is nominally 2700 pulse pairs/second. (i) Why is it advantageous to have a constant squitter rate? (ii) if the number of interrogations from aircraft is less than 2700 per second, how does the DME ground station make up the rest? (iii) If the number of interrogations from aircraft exceeds 2700 per second, how does the DME ground station decide which to ignore? (iv) The squitter rate for a TACAN is 3600 pulse pairs/second. What accounts for the extra pulse pairs? g. An aircraft receiver produces the demodulated signals from a TACAN as shown below. What is the bearing from the station? Draw a diagram showing the station and the resulting line of position.
TACAN COMPOSITE SIGNAL 2 1.5 1 0.5 0
Amplitude
0.5 1 1.5 2 2.5 3 0 ARG MRG ARG ARG ARG ARG ARG ARG ARG
50
100
150 200 250 15 Hz PHASE ANGLE(degs)
300
350
3 LORAN C a. The coverage plot for LORAN C shows that the useful range is signicantly greater over the North Atlantic than over North Ontario. Why is this?
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4 GPS a. In a Local Area Differential GPS system the error component due to ionspheric effects degrades primarily with distance from the reference station? Why? b. If a GPS receiver has a recent almanac, the time to determine a position after turn on is less than if it does not. Why? c. The Russian equivalent of GPS is called GLONASS. The system designs are quite similar except that, instead of using one frequency and multiple codes, GLONASS uses one code and multiple frequencies. The GLONASS code is a simple m-sequence. Why is this feasible GLONASS for and not for GPS which uses the more complex Gold code? d. An aircraft is in a position such that there is a DME at a bearing of 020(M)and a range of 50 NM and another one at a bearing of 090(M) and a range of 60NM. (i) What is the HDOP for this geometry? Hint: draw a diagram rst! (ii) If the bearing to the rst DME changed to 060(M), would the HDOP increase or decrease? Note: it is not necessary to do the calculations (iii) If, in part (ii), a third DME were acquired at a bearing of 180(M), would the HDOP increase or decrease?
Note: A
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a a 21 1 = ------------------------------------ 22 a 11 a 22 a 12 a 21 a a 12 11
5 INS a. What is the underlying principle of inertial navigation? b. Give two reasons why is it necessary to perform an alignment before using an INS for navigation? c. Why is alignment difcult to achieve at latitudes above (70 N)? d. What are three advantages of inertial navigation? e. What are two disadvantages of inertial navigation? f. Derive the expression for Schuler oscillation. g. During the alignment an INS measures the rates of rotation about the x and y axes required to keep the platform level are: x = 7.4107 /hour y = 6.2187 /hour what is (i) i) the wander angle ? (ii) ii) the latitude ?
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h. The value of g decreases with altitude. It is necessary to correct for this in a strapdown INS and not in a gimballed system. Why? i. . The stable platform INS architecture can be implemented using only two accelerometers. The strapdown architecture requires three. Why? j. A strapdown INS is installed in an aircraft such that the x axis coincides with the fore-aft (roll) axis of the aircraft (forward positive) , the y axis coincides with the lateral (pitch) axis (right wing positive) and the z axis coincides with the yaw axis (down positive). In the diagram, the aicraft, seen for the rear, is in level ight and is turning with 30 of bank angle. The accelerometer measures an acceleration of -1132.76 cm/sec2 and the y acce...