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ATPL theory questions

Old 29th Apr 2017, 14:13
  #1081 (permalink)  
 
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Well yes but the wording is a bit confusing
Adding a simple how does it change *over time* would be much clearer.
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Old 29th Apr 2017, 15:56
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The fact that many students make the mistake of assuming that the question requires a comparison between lrc and mrc, may be interpreted as evidence that the question is defective. But it is also possible that the real problem is the way in which many students are addressing the questions. There is actually nothing in the question to suggest that the lrc.mrc comparison is intended.

Students often make the same error with questions along through lines of *increasing flap angle in straight and level flight will?* many student pick answers such as *increase in lift* or *the aircraft will climb*. But these options ignore the clue *in straight and level flight*.

Although the lrc question has probably been deleted from the cqb by now, I believe that it should be retained in commercial question banks in order to illustrate the danger of misinterpreting questions.
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Old 1st May 2017, 16:11
  #1083 (permalink)  
 
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I have question that really I can't find answer for it which is :

Q: During a pre-flight inspection it is noticed that the nose oleo strut extension is 2" instead of the
normal 6", but there is no sign of oil leakage. This indicates:

A. an internal oil leak
B. gas charge pressure too low
C. gas charge pressure too high
D. tire pressure too low

I am not sure but I think the correct answer is "B" PLEASE HELP ME
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Old 2nd May 2017, 09:44
  #1084 (permalink)  
 
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Well, Let’s look at the options and see what we can deduce from them.

The length of the oleo is determined by the amount of oil and gas within it and the weight of the aircraft pressing down upon it. Any loss of oil or gas will reduce the length. Any excess of oil or gas will increase the length.

It is also worth noting that if the low gas charge pressure has been caused by a small gas leak, this leak will not be visually detectable. But an oil leak would be evident from the oil deposits in the area of the leak.

An internal (option A) leak would allow the oil and gas to mix, but would not change their total volume, so this would not change the oleo length. So option A is incorrect.

The length of the oleo is determined by the amount of fluid and gas which is held within it. So the tyre pressure (option D) is incorrect.

If the gas charge pressure is too high (option C) the oleo length will be greater than normal. So option C is incorrect.

If the gas charge pressure is too low (option B)the oleo will be shorter than normal, so this is the correct option.
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Old 2nd May 2017, 16:33
  #1085 (permalink)  
 
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Thanks , it was so useful

umm another question

When an aircraft employs static vents either side of the fuselage to minimize pressure errors it is
called:?

A.Static equalization
B. Pitot correction
C. Static balancing
D. Dynamic balancing

actually this is the first time hearing about static equalization
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Old 2nd May 2017, 20:33
  #1086 (permalink)  
 
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Could anyone explain the difference in the usefulness of geocentric and geodetic (or geographic) latitude ?
I have remembered the 11.6 minutes maximum difference due to earth being oblate, and the difference in the definition, but I really don't see the point of geodetic latitude.
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Old 3rd May 2017, 05:20
  #1087 (permalink)  
 
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It's because the earth isn't round - if it was, we would just use geocentric. Instead we have to draw a tangent at the horizon, then a line 90 degs to that, and the angle where it meets the horizontal at the centre of the Earth is the geodetic. The difference for our purposes is negligible, and if the earth were the size of a billiard ball you wouldn't notice any difference between it and the others on the table.

I don't see much point to it (for the exams at least), except maybe to say that the mathematical model inside the GPS (based on the World Geodetic Standard established in 1984) is different enough for you to be careful if your track takes you near to the boundaries of airspace or danger areas.
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Old 3rd May 2017, 16:24
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To amplify Paco's response, the orthogonality of geodetic coordinate axes simplifies the Euclidean norm. Using an orthogonal system is equivalent to setting the angle(s), between principal axes, in the law of cosines to 90 degrees. That is, coefficient F in the metric tensor is zero when geodetic latitude is used instead of geocentric latitude, see equation 34 et seq in Thomas, P.D. (1952). Conformal Projections in Geodesy and Cartography. Special Publication No 251. US Department of Commerce.

A further disadvantage of using skew coordinates (i.e. geocentric latitude) is that each point on the height axis has a different latitude, except at the equator and poles.
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Old 3rd May 2017, 17:58
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To clarify :

I'm assuming the geodetic coordinate axes at point P on the surface of the earth are :
- The perpendicular to the plane of tangency at P (up or down)
- On the plane of tangency a north vector
- A third vector determined with right hand rule
Whereas the geocentric axes at the same point would be
- A "vertical" on a line from center of the earth to P (up or down)
- A North vector
- An East or West vector

At this point I'm wondering why this second system of axis has a complicated Euclidean norm.
Maybe the North vector remained the same as in the first system of axes, then it means that the system of geocentric axes is not orthogonal (there is a small residual angle)

Is it correct up to this point ?

If yes, the other option would be to modify the North vector, to make it perpendicular to the line from the center of the earth. Then the North vector would go either into or out of Earth, and this is obviously a problem because it means that if you're travelling north or south at constant altitude then you actually have a vertical speed in this system of axes...

Regarding your last line : Up to reading your message I thought that GPS coordinates were actually the coordinates of the point, on the surface, of which we're vertical. But it's quite evident that it wouldn't work that way.
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Old 4th May 2017, 01:58
  #1090 (permalink)  
 
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I'm assuming the geodetic coordinate axes at point P on the surface of the earth are ...
The curvilinear geodetic coordinates are simply longitude, geodetic latitude, and height. Your description is for an ENU or NED frame.

Whereas the geocentric axes at the same point would be
- A "vertical" on a line from center of the earth to P (up or down) ...
Yes but this radius vector is not normal to the surface at P. Any other point Q along the surface normal to P has a radius vector with a different direction (i.e. different geocentric latitude). Contrast this with the fact that the geodetic latitudes of P and Q are the same. In other words, varying height has the major advantage of leaving geodetic latitude unvaried, which is a property of orthogonal coordinates.

At this point I'm wondering why this second system of axis has a complicated Euclidean norm.
Additional terms are needed to account for the change in geocentric latitude with changing height.

... I thought that GPS coordinates were actually the coordinates of the point, on the surface, of which we're vertical.
That is correct. WGS 84 coordinates are geodetic and therefore orthogonal.
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Old 9th May 2017, 20:01
  #1091 (permalink)  
 
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Selfin, you seem very knowledgeable

Another question or two about gen nav :
Why would twilight be shorter at the equator ? It seems logical to me that in winter, twilight should be longer and shorter in summer : earth's inclination about the ecliptic gives a "pseudo latitude" that's higher in winter and less in summer, providing higher insolation.
It's just as the ecliptic was a fictitious equator.
Does it work like that ?

A question in the database asked the date of the perihelion.
Why would this be of any importance when talking about gen nav ? The same course that states that perihelion/aphelion are of no importance to seasons and that their two values are very close (earth's orbit has very little excentricity)

Thanks
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Old 10th May 2017, 14:38
  #1092 (permalink)  
 
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Polish ATPL PERFORMANCE

Does anybody know where I can find graphics that fit best with the "new" graphic questions in the Polish ATPL performance exam? I use aviation exam and mainly the SEP graphics match with the real test questions but the rest not. Does anybody know a better matching question bank? Thanks a lot!
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Old 10th May 2017, 21:00
  #1093 (permalink)  
 
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What's so different or special with these graphic questions? I would like to know because I am sitting my Performance exam in a few days.
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Old 11th May 2017, 02:53
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Why would twilight be shorter at the equator ? ... It seems logical to me that in winter, twilight should be longer and shorter in summer
There's an answer to that here, and in the final two pages of chapter 8 in Henning Umland's Short Guide to Celestial Navigation. Umland has neglected refraction (34 arc minutes) and one semi-diameter (16 arc minutes) of the sun, so a better value in lieu of his 24 minutes is 20.7 minutes, i.e. the centre sun travels through a local vertical arc of 5.17 degrees instead of 6 degrees during civil twilight.

A similar derivation is in WM Smart's Textbook on Spherical Astronomy (art 33, p 51). Corrections for altitude are available in the UK Air Almanac, p 68 of 2017 edition; see also fig. 3 on p 69 for twilight duration in the Arctic depending on latitude and time of year. Despite the restricted latitudes in those figures the duration of twilight, on the condition of a sunrise existing (viz., upper limb touches the horizon), is shortest near the equinoxes.

Why would [the perihelion] be of any importance when talking about gen nav?
It's of absolutely no importance. Probably an inside joke among Vulcan navigators ( Le Verrier).

you seem very knowledgeable
I'm afraid that is merely one of those internet mirages.
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Old 20th May 2017, 21:27
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Can anybody explain this ?
https://i.gyazo.com/735e4490a9888a16...ddc5296a5f.png

I'm doubting this is the correct answer.. I don't see why it would be desirable to spiral towards the NDB
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Old 21st May 2017, 09:22
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The following two questions which are/were in the CQB require students to distinguish between HOMING and TRACKING. I have no idea where they got these definitions from (probably a 1950's RAF navigation course).

Question 1.
Which statement is correct for tracking towards an NDB in an area with constant wind and constant Magnetic Variation?

Correct answer given by the database:

The Relative Bearing of the NDB should be equal (in magnitude and sign) to the experienced Drift Angle

Question 2.
Which statement is correct for homing towards an NDB in an area with constant wind and constant Magnetic Variation?

Correct answer given by the database:

The Relative Bearing of the NDB should be kept 000 deg;

These two questions have caused much head scratching among students in the past and will probably continue to do so in the future.
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Old 22nd May 2017, 08:49
  #1097 (permalink)  
 
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Homing is adjusting for wind by keeping the needle on the 0. This results in a phenomenon called the curve of pursuit (otherwise called bird-dogging) which takes you away downwind from an airway centreline - it was a common problem for bomb aimers, and why tracking is best, where you offset for wind and fly a straighter course.
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Old 22nd May 2017, 09:10
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it was a common problem for bomb aimers
So the authors of the question didn't get it from a 1950's RAF course, but from a 1940's course!
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Old 22nd May 2017, 09:13
  #1099 (permalink)  
 
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Yep! I saw the term in a Lancaster manual! But it is used in the US and Canada.
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Old 22nd May 2017, 11:13
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Oh, I thought that questions about INS were old, I stand corrected
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