Mass and balance new question

[Zsoti89]

Hello
first of all thank al of you who’ll answer and try to help me understand this one. I started studying mass and balance but I got stuck with this one.
Thats the question.
The CG limits are from 5 inches forward to 7 inches aft of the datum. If the MAC is 41 inches and its leading edge is 15 inches forward of the datum what are the CG limits as %MAC?
Thank you for your answers.

[TryingToAvoidCBs]

It helps to draw it out.

I havn't done this stuff for a while, but I'm fairly sure the forward CoG is 10" behind the leading edge and the rear CoG of 22" aft of the leading edge.

If the MAC is 41" then:

Forward limit %MAC = 10/41 = 24%
Rearward limit %MAC = 22/41 = 53%

[Zsoti89]

Thank you so much. Now I understand.
Could you please help me with this one please? I made it but my answer is slightly more than it should be just wonder if I did something wrong.
The question is.
an aeroplane has a zero fuel mass 47.800 kg and a performance limited TOM of 62.000 kg. The distances of the leading edge and trailing edge of the MAC from the datum are 16 m and 19.5 m. What quantity of fuel in imperial gallons must be taken up to move the CG from 30% MAC to 23%MAC if the tank arm is 16 m aft of the datum and the fuel SG is 0.72?

thank you.

[omi787]

Hello mate can you explain how did you get the 22 inches? i am aware you added the 15 and the 7 but why exactly ?
thank you.

[RichardH]

Because LE is 15" forward of datum & rear limit is 7" aft of datum = 22" from LE.

[omi787]

Because LE is 15" forward of datum & rear limit is 7" aft of datum = 22" from LE.
thank you very much Richard, it made sense after i drew it.

thank you.

[VariablePitchP]

Thank you so much. Now I understand.
Could you please help me with this one please? I made it but my answer is slightly more than it should be just wonder if I did something wrong.
The question is.
an aeroplane has a zero fuel mass 47.800 kg and a performance limited TOM of 62.000 kg. The distances of the leading edge and trailing edge of the MAC from the datum are 16 m and 19.5 m. What quantity of fuel in imperial gallons must be taken up to move the CG from 30% MAC to 23%MAC if the tank arm is 16 m aft of the datum and the fuel SG is 0.72?

thank you.

What an absolutely ridiculous question.

[john_tullamarine]

What an absolutely ridiculous question.

With respect, may I suggest that you might be missing the point ?

Theory stuff is just that and not to be confused with flying. The aim is to establish that the student (exam candidate) knows, and is competent to play with, a reasonable amount about the stuff. Often, if one were to be practical or otherwise close to Industry reality, it might be a tad difficult to make that assessment.

Practical stuff is for simulators and line checks.

I've not looked at the question in detail and it may well be inconsistent but that is not the philosophical point here.

Perhaps one might style the question as being not overly Industry practical ?

[VariablePitchP]

What an absolutely ridiculous question.

With respect, may I suggest that you might be missing the point ?

Theory stuff is just that and not to be confused with flying. The aim is to establish that the student (exam candidate) knows, and is competent to play with, a reasonable amount about the stuff. Often, if one were to be practical or otherwise close to Industry reality, it might be a tad difficult to make that assessment.

Practical stuff is for simulators and line checks.

I've not looked at the question in detail and it may well be inconsistent but that is not the philosophical point here.

Perhaps one might style the question as being not overly Industry practical ?

They’re doing ATPL exams, the P standing for pilot, not philosopher. There’s about 5 different steps in that question, 5 of which you would *never* do in normal line flying, and at best a couple of which you might do if you’re in the small % of people that work for Tim’s Twin Taxis or Claire’s Cargo Carriers.

The question is based on something like a 737, in Europe, where fuel is given in KGs… The nonsense about calculating moment arms etc, totally unnecessary and I imagine written by someone who’s at best had a fable on fight sim.

There seems to be this obsession with making the questions difficult, why?! Flying is pretty easy… If the exams reflect that then that’s absolutely fine…

[paco]

I quite agree with VP. This would be horrendous time suck in an exam. As a matter of interest, what answer did you get?

[john_tullamarine]

They’re doing ATPL exams, the P standing for pilot, not philosopher.

True. However, both questions are dead simple and well within the grasp of a private pilot, providing he/she understands what is meant by MAC and is able to run a simple load sheet. It would be quicker just to do the problems rather than argue why they are stupid.

5 of which you would *never* do in normal like flying

Let's not worry too much about how we might count steps. However, as I see it, the steps required are straightforward and perfectly relevant to normal flying, regardless of aircraft size. Perhaps I am getting a bit slow in my dotage and you can show me which bits are those which one "would never do in normal (like) flying" ? For that, I would be very grateful.

There seems to be this obsession with making the questions difficult,

If one has a basic understanding of what is required to solve the problem, the questions cited are extremely simple. They would only be difficult for those who have an inadequate understanding of what is required.

This would be horrendous time suck in an exam

Not really. The first question should take, perhaps, 20-30 seconds to read and draw the story in a simple sketch and, perhaps, another 20-30 seconds to figure the answers. The second question requires one to realise that the datum needs to be relocated to the LEMAC but then is absolutely dead simple. Unfortunately, the question has no solution due to the RTOM's being too limiting. If the RTOM were a bit higher, though, all would be fine.

As a matter of interest, what answer did you get?

For the first question, as for post #2. However, one would normally give the answer, at the least, to the first decimal.

For the second question, it doesn't have a solution as the numbers don't work.

As to whether this question is practical, of course it isn't. I have 50 years' worth of weights and other engineering and I can't ever recall seeing any aircraft with such a station arrangement. As I suggested before, though, the aim is to test some fundamental knowledge in the theory training and examinations. The practical stuff is the province of the sim and the line check.

I can remember (only just, this far removed in time) on my B727 ground school, the instructor's observing that none of us would be permitted to fail the exams - if we needed to fail the endorsement, the checkies would address that requirement in the sim and the local proficiency work following the exams.

I made it but my answer is slightly more than it should be just wonder if I did something wrong.

Your comment suggests that you probably have the MAC thing well and truly under control. Let me guess, you were a bit under 350 kg fat on the RTOM ?

[paco]

For the time suck comment I was referring to the second question - by the time the candidate realises it's a waste of time, better questions could have been answered. The various stages required should be one mark questions. It looks like a simple moving mass question, in that the C of G has to be moved 7%, but it isn't.

[john_tullamarine]

For the time suck comment I was referring to the second question

Noted - my error.

by the time the candidate realises it's a waste of time, better questions could have been answered.

The question took me a similar time to the first to sort out - about 30 seconds to run up a quick sketch (for those folk who don't draw a sketch, you are just making things difficult for yourselves, quite unnecessarily). It was obvious that the solution was q.e.d. if the datum were to be moved. The sums took about 10-15 seconds to do to the point where it was evident that the question was flawed. The question, as they say, is money for jam and dead easy to do.

I would suggest that the question is anything but a waste of time. It has some unusual characteristics which have a very useful learning outcome. So far as the error in the question is concerned, that would have been simple finger trouble on the part of whoever wrote the question, allied with either no/inadequate checking prior to publishing the question - I think most of us have been guilty of such things over the years.

The various stages required should be one mark questions.

If you prefer. However, I would put the question as being worth, maybe 2 marks in a typical exam so not really worth the effort in making the change ?

It looks like a simple moving mass question,

Why ever would you think that ? If you did, then you would be off on a tangent with no solution in sight.

in that the C of G has to be moved 7%,

Indeed. However, one can ballast (in this case by adding fuel) to achieve the goal.

but it isn't.

That ought to have been evident from the initial assessment of the question.

Perhaps you might post your solution and we can offer constructive critique ? That way there is a positive learning outcome for those who might be interested in this thread ?

Unfortunately, far too many pilots try to learn too little about weight control and then find themselves thrashing about in a bog when hunting for problem solutions. With a bit of background understanding, weight and balance stuff is easy peasy and absolute money for jam in the examinations.

[VariablePitchP]

5 of which you would *never* do in normal like flying

Let's not worry too much about how we might count steps. However, as I see it, the steps required are straightforward and perfectly relevant to normal flying, regardless of aircraft size. Perhaps I am getting a bit slow in my dotage and you can show me which bits are those which one "would never do in normal (like) flying" ? For that, I would be very grateful.



Bless my phone’s spellcheck it subbed ‘line’ for ‘like’ which doesn’t help. The question is based around a 737/A320 type aircraft. In such an aircraft the most you’d be expected to do on the load sheet is to work out where to sign it. With Airbus now completing the fly smart rollout the days of doing that are also in the past. Take off calculations are just punching stuff into an iPad.

Granted, you could theoretically work for Bill’s Boeings who operate one 727 from a shed in and therefore do it all in house, but the returns from these exams are diminishing every day.

Learning in extreme detail how the inner workings of gyroscopic instruments work… Why?! It’s just wasted knowledge which is dumped the second the exam is gone.

I’d argue the six months full time groundschool could be stripped right down to 3 or 4 exams you could do in two or three months. It’s not 1971, we need to accept that.

It would be interesting if courses like MPLs could start like that. Flying a 320 for easyJet at the end of the course? Great, you can immediately write off 75% of the content as a total waste of time as it is as relevant to your day to day operating of the aircraft as a strong grasp of Swahili would be, the latter probably being more interesting to learn!

[john_tullamarine]

Bless my phone’s spellcheck

Don't you just hate that characteristic like poison ?

The question is based around a 737/A320 type aircraft.

That's understood and quite fine. However, for the purpose of the theory work, it really doesn't matter if we were to use a Vanguard for the sample aircraft. Or a Grand Commander. Or whatever.

In such an aircraft the most you’d be expected to do on the load sheet is to work out where to sign it.

Hopefully your comment is tongue in cheek. Else one could only caution that such an attitude would not fare well at court following a mishap ....

With Airbus now completing the fly smart rollout the days of doing that are also in the past. Take off calculations are just punching stuff into an iPad.

Were we to progress along that line of reasoning, then we would be better served dispensing with the theory work altogether and doing it the way one sees with many folks on PCs .. give it a run and figure it all out on the fly. Not the best if the JB kit fails in flight and you are left with only mandraulic alternatives ....

the returns from these exams are diminishing every day.

The returns should be the acquisition of potentially useful knowledge but I guess we must be from different philosophical backgrounds ?

Learning in extreme detail how the inner workings of gyroscopic instruments work… Why?! It’s just wasted knowledge which is dumped the second the exam is gone.

Perhaps your training was far more maintainer based than what we have over in the Antipodes for the pilot folk. The typical pilot systems work is relatively trivial, geared very much toward block diagrams which have only the vaguest relationship to the real kit and only intended to provide the pilot with a notional overview of what is what ...

the six months full time groundschool could be stripped right down to 3 or 4 exams you could do in two or three months.

With the caveat that I haven't seen your requirements, I would opine that a sensible ground school program PPL through ATPL can be done and dusted in, perhaps, 3-4 months fulltime.

a total waste of time as it is as relevant to your day to day operating of the aircraft as a strong grasp of Swahili would be,

I can only opine that your comment is one which gives me great sadness. In long gone days, the pilot sought excellence rather than mediocrity. I guess the name Gann would mean naught to you ? There are numerous others who were in the same class of pilot.

The old greybeards who trained me were from the same mould. I guess I can only suggest that their wisdom in respect of attitude has rubbed off somewhat. I don't suggest that we need to know how to build the aircraft (as pilots) but it really can be useful to know just a little bit more than "light comes on, press button A".

I suppose that we will just have to continue to agree to disagree. I can only hope that you aren't faced with really out of left field problems during your career. Sioux City, the Hudson, and so on, come to mind. Knowing a bit more than the bare bones stuff might not get you home on the day ... but it has a significantly higher correlation than coming from a technically impoverished background. Just the way it is, I'm afraid.

[rudestuff]

Has this thread drifted to ATPL bashing? Great!
My no. 1 problem with the EASA/CAA system is a complete lack of clarity and a mismatch between what is taught and what is tested.

The FAA has a simple system that works: the FAA thenselves publish a series of handbooks telling you everything you need to know. Then the FAA give you a written and verbal test only on stuff that is in that book. No teach - no test.

The CAA/EASA publish a very vague list of learning objectives upon which they will test. The various training organisations have to essentially guess what they have to teach based solely on feedback leading to
huge volumes of material and pointless questions like who walks the ICAO Presidents dog.

A fATPL holder might know the orbital height and inclination of a GPS satellite but have no idea how that data is presented in the cockpit. It would be much more useful to know 100% of a relevant volume of information than 75% of a largely irrelevant volume of information.

[paco]

Hear, hear - the schools need the databases as much as the students do :) There is an LO in met about estimating relative humidity from temperature and dewpoint, for which the actual calculation is over a page long. Nowhere do they mention that there is actually a rule of thumb, and that is what should be used. Coming from the old UK and Canadian systems myself, I support rudestuff's comments. However much EASA tries to denigrate the FAA system, the truth is that theirs is not better by any means, certainly in terms of standardisation between checkrides. Questions that are more practical revolve around stuff like - you don't have enough fuel to get from A to B - how many 45 gallon drums would you have to preposition somewhere along the track in order to get there?

Talking of gyros, I remember saying in one of the RMT meetings at EASA that gimbal orientation was useless knowledge for pilots and why are we asking about it, and the KLM and Lufthansa reps got nearly apoplectic when insisting that it was vital. Go figure. And do the DVLC ask about when the department was established when you go for your driving licence? No.

[VariablePitchP]

The question is based around a 737/A320 type aircraft.

That's understood and quite fine. However, for the purpose of the theory work, it really doesn't matter if we were to use a Vanguard for the sample aircraft. Or a Grand Commander. Or whatever.

In such an aircraft the most you’d be expected to do on the load sheet is to work out where to sign it.

Hopefully your comment is tongue in cheek. Else one could only caution that such an attitude would not fare well at court following a mishap ....

the returns from these exams are diminishing every day.

The returns should be the acquisition of potentially useful knowledge but I guess we must be from different philosophical backgrounds ?

Learning in extreme detail how the inner workings of gyroscopic instruments work… Why?! It’s just wasted knowledge which is dumped the second the exam is gone.

Perhaps your training was far more maintainer based than what we have over in the Antipodes for the pilot folk. The typical pilot systems work is relatively trivial, geared very much toward block diagrams which have only the vaguest relationship to the real kit and only intended to provide the pilot with a notional overview of what is what ...


If this was what and how it was taught, and what was tested, then that would be brilliant. An actual overview. I’d have no problem with that sort of teaching, block diagrams as you say.

But in today’s exam regime your students would all be dropping out of your school after bombing the exams for not being able accurately calculate declination angles in the polar regions using nothing more than a pencil sharpener and a rubber band.

It would be equally fine to use any aircraft, provided that detailed questions weren’t based around the specific fit of, say, a Vanguard. The actual questions aren’t generic, they’re not an overview, they’re not just broadly theoretical. They’re ridiculous. Recently the aircraft in vogue was the 737-400, you better know it’s memory items and understand it’s avionics fit to be able to pass.

As Rudestuff uses in their example you will literally be expected to recall the orbital parameters of GPS satellites, the exact frequencies and layout of an ILS array, and learn to memory(!) the exact number of fire extinguishers and crash axes an aircraft with 300-349 seats must be fitted with. You will be tested to a level of detail that most staff involved in the production of parts couldn’t answer at.

And your comment about the use of modern load sheets missing the point about what you actually do in real life. You get the load sheet, sense check it, sign it. The computer does a far better job than a pilot at calculating trim effects of 5 tonnes of fish than we would do with a dry wipe pen, laminated load sheet and some red string.

I’ve no doubt that people were devastated at the removal of sextant useage techniques from the syllabus or the loss of the need to learn morse code. It’s always going to be the same, an inability to embrace change and progress, regardless of what the change actually is.

When the NDB is finally removed from service and the questions taken out of the exam bank we’ll have the same old comments ‘it’s terrible, how could Sully possibly have landed in the Hudson without knowing the frequency band of inner, middle and outer market locator beacons?!?!’

[john_tullamarine]

I offer no comment on the regulators and their approach to exams. Unfortunately, exam content is something which we are not able to influence.

In regard to the last however many posts addressing the iniquities of the syllabus and examination system, the thread appears to have lost track of the OP's original questions.

Perhaps the more general examination discussion might be better addressed in separate threads while this thread finalises some answers to the OP's questions ? Who knows ? Perhaps some might learn something from the exercise ?

So far as specific training is concerned, there are two concerns/goals -

(a) the student should end up knowing a range of things which have some relevance to the job. This ought not to be just "light comes on, press button A" but extend to things a little more general in application

(b) whatever the exams are up to, the student needs to end up with adequate specific and directed knowledge to secure a pass. I suggest that this is much the same in any jurisdiction. I concur with the observation that some of this might well be subject to a post exam data dump.

[paco]

Of course, forgot about the OP -

m = d
M D

m is how much to add
m is the weight of the aircraft
d is the change in C of G (7% or .245 m)
D is the change in distance (.805 m).

m = .245 x 47800 = 14547 kg or 20205 ltrs or 4535 Imp gals
.805


tabbing may be a bit off

[john_tullamarine]

14547 kg

Indeed. Very slightly more involved (less intuitive) than necessary to obtain the answer, but, no matter. Likewise, one might prefer to round it off to 14548.

However, somewhat in excess of the RTOM, as declared, so of not much value to the question ?

[paco]

If memory serves I got 14547.2 something, but rounding off would depend on the answers available. The conversion to imp gals is also completely unnecessary just for a one mark question. Also, don't know why they bothered with the PLTOM. Just in case I ever become a question writer again :) how would you have approached it?

[john_tullamarine]

Only two considerations from my point of view:

(a) make sure that the question is "doable" by running some tests to check for stupidity. The RTOM mismatch, really, was unforgiveable.

(b) the use of distractors and other nonsense is fair game in larger questions given that the real life job of flying involves a lot of being stuffed about often with only half of the story. However, it is rather pointless to do so unless the answer is to be a full written solution and marked by a human who can assign credit for what is done sensibly.

For the student to lose all marks for, say, a single mistake in a lengthy theory exam question is, to me, not on. I don't see much benefit in theory exams which have a sudden death outcome. As I suggested earlier, sweaty exercises in the box are the place for that sort of pressure, providing that the examiner sets the problem and then sits back, holds his tongue, and observes the performance. Screaming skulls have no value as I see things.

[paco]

Thanks for that - I was told that they left my questions last for review because they knew they would be sensible - the same went for the other UK writers, but since we got chucked off the database after Brexit the quality has fallen off a cliff.

[john_tullamarine]

.. the way of the world. We greybeards progressively get eased out and the expertise of decades goes with it.