General Navigation questions.

[Mohit_C]

Hi all,

I'm back with 4 questions from the Volare questions that I have a few doubts with.

Q378) In a remote indicating compass system the amount of
deviation caused by aircraft magnetism and electrical
circuits may be minimised by:
A) the use of repeater cards (mark scheme answer)
B) positioning the master unit in the centre of the aircraft
C) using a vertically mounted gyroscope
D) mounting the detector unit in the wingtip
-> I would say D.

Q481) The alignment time, at mid-latitudes, for an Inertial
Reference System using laser ring gyros is
approximately:
A) 5 MIN (mark scheme answer)
B) 10 MIN
C) 20 MIN
D) 2 MIN
->My GeneralNav book says for IRS: Equator = 5 min, 70º latitude = 10 min, 70-78º latitude = 17 min. My Instrumentation book says: Equator = 2.5 min, 45º latiude = 5 min, 60 º latitude = 10 min. Now is there an actual formula to calculate this time for alignment as there seems to be differences between textbooks (at least mine)?

Q247) At what approximate latitude is the length of one minute
of arc along a meridian equal to one NM (1852 m)
correct?
A) 30°
B) 45° (mark scheme answer)
C) 0°
D) 90°
-> I don't actually understand why it's 45º. All latitudes are along a meridian and one minute of arc will always equal one NM along a meridian.

Q251) In which two months of the year is the difference
between the transit of the Apparent Sun and Mean Sun
across the Greenwich Meridian the greatest?
A) June and December
B) April and August
C) February and November (mark scheme answer)
D) March and September
->Well the "True Sun" and "Apparent (fictitious) Sun" meet at the Aphelion (Cancer) and Perihelion (Capricorn) and the "Mean Sun" and "Apparent Sun" meet at the Equinox Aries and Libra. Well I would guess that the greatest difference would be in Cancer (Summer in Northern Hemisphere) and Capricorn (Winter in Northern Hemisphere) = A.

Thanks.