Instruments Questions

[piper pervert]

Hi,
I'm currently swotting up for my instruments exam in October,rightly or wrongly im using a couple of different sources for practice feedback questions and i am getting varying answers.Just a couple of examples:

Q. An a/c flying true track of 360 from 5S to 5N.What is cahnge in apparent wander rate?

1 set of notes say 0 deg/hr and the other says -5deg/hr.

The second is regarding the apparent indications of a classic Artificial Horizon during a turn.I believe everyone agrees that at 360 all is well,but some books say at 90 deg pitch up bank low,some say pitch up bank too high etc.

Both sources are from very reputable uk ground schools but they are contradicting eachother.If anyone can shed light on either of this probs i would be v v grateful.

Cheers Guys

PP

[oxford blue]

Neither answer is correct. At latitude 5ºS, Earth Rate is +1.3º/hour. At latitude 5ºN, Earth Rate is -1.3º/hour. The change is therefore -2.6º/hour.

However, the question apparently exists in the common question bank with incorrect answers. It may be a mistranslation of the meaning of the question from the original French. We have brought it to the attention of the JAA but we do not know whether they have done anything about it.

As for the second problem, the CAA has issued clarification about it by letter, so we know what the authoritative answer is. If your FTO is giving you any other version, it is wrong.

Turn through 90 - indicates nose up and bank angle too low
turn through 180 - indicates nose up and correct bank angle
turn through 270 - indicates nose up and bank angkle too high
on rolling out on original heading - attitude and bank angle are correctly indicated.

[Cabotage Kid]

I am a bit confused by your answers to the first question so am unsure about mine but here goes:

Apparant wander is transport+earth. There is no change of long s no transport to owrry about. Earth Wander is 15 * sin(lat). 15*sin(5S) = +1.3 deg/hr.

Moving from 5S to 0 N/S would be a -1.3 change and to 5N would be -2.6 deg/hr. I don't see where 5 deg/hr comes from (apart from being 2.6 * 2...but why?)

If your reputable school's feedback is BGS then follow that, their feedback is excellent. Got me 97% in Instruments.

If you understand precession and that the gyro spins CW then you can figure out the second question. At the four cardinal points CW it is: 1) correct 2) pitch up & underturn 3) pitch up max & turn correct 4) pitch up and overturn.

[piper pervert]

Thanks chaps,i hope that the 5S/5N doesn't come up this time,it did the first time i took it and I plumped for the 0 dg answer.There was much debate afterwards between our instructors but no definitive conclusion was drawn.

[OneMileHigh]

I'm going to have to disagree with Oxford Blue on this one:

The question as I have seen it is for a flight directly North from 5S to 5N and asks what is the expected drift of a DI.

For any such calculation the Earth rate is taken at the mid lat position, in this case 0N/S where Earth rate wander is zero. There is no transport wander to consider.

I agree that wander at 5S would be an increase of 1.3 degrees per hour, and at 5N it would decrease at the same rate, but that would not cause a total drift of 2.6 degrees. They would in effect cancel out.

[OneIn60rule]

the first one I'm not 100% sure about. However I recall that I showed it to my instructor and he said that there isn't any.

Second one is definately like this>

90 degrees will give high pitch and LOW bank

Pitch Bank
all the others are like so> 270 HIgh High
180 HIgh none
360 none none
090 High low.

[Cabotage Kid]

One mile high,

The actual would be -1.3 for 5N, the question posed here is asking for the difference so the difference from 5S (1.3) to 5N (-1.3) would be -2.6 = -1.3 - 1.3 and not 0 = 1.3 - 1.3.

I can't see how there wouldn't be any drift at 5N or 5S as the equation the CAA expect you to use is 15*sin(lat) for Earth Rate.

[oxford blue]

The question as originally asked by piper pervert asked what is the change in apparent wander rate. I believe that that was also the original wording in the Common Question Bank. In that case, the answer I gave (-2.6 degrees/hour) was correct and no correct answer option was given by the JAA. The nearest correct answer was -5 degrees/hour, but that was only the 'least worst' option of those given.

When we queried the question, I don't think we got a satisfactory reply. but I believe that the question has now been changed to "What is the average apparent wander rate", not "What is the change in apparent wander rate". In this case, the correct answer would be zero.

[OneMileHigh]

This perfectly illustrates why feedback questions must be treated with caution.

They are totally reliant on the memory of the students who sit the exams. It also shows how vulnerable we can all be to not reading the question properly, and in this respect I must offer my apologies to OB.

The answers to these feedback questions are also subject to how the person providing the answers reads the question, and in the original case reported by PP it would seem that two people interpreted this question differently in the two sets of feedback papers.

We are all in this together, and I wasn't trying to points score in my original contibution to this thread.

Basic DI drift calculations are quite easy if a set methodology is maintained, but so much can depend on how any particular question is read.

One last thing is the CAA responses to any challenges made. They will accept it when a question is deemed incorrect or unfair, but they are very careful to avoid giving any clue as to just how a question is phrased.

BTW: When 6000 question are compiled in the CQB they have stated that the CQB will be made public. What's the betting they stop adding questions at number 5,999!!!