Stuck!
 

Stuck on a question on my flight planning... can someone explain how this graph works given the information etc?

Hope this is the right place to post this....

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I think you are missing some of the input data for that question.

Based on the information given, it doesn't seem possible.

Dividing the total moment by all up mass gives the arm as 42in.

This is not on the graph.

Yep. Seems like a duff question.

CofG is 42 inches aft of datum which is way off the chart and my experience tells me that with a graph like that, even with a very unusual loading you cannot even get the CofG that far forward - unless you fill the back with helium balloons or something.

(Oh, and for your conscience: yes, this is the right place to post questions like this. Even better now that I won a Sharp LCD TV...:})

Hi Dave,

The image does not seem to come across legibly, but in general:

The weight and balance "envelope" as depicted is showing you the maximum permissible center of gravity limits relative, and up to, the maximum gross weight. The actual aircraft weight for the proposed flight, once known by calculation, is plotted up the left side of the graph. Using the calculated C of G (from loading charts provided elsewhere for you, you will have calculated the total aircraft C of G position (doing so may require calculating the moment too, and working backward a bit). You then locate the C of G position along the weight line which you have identified on the chart.

If the plotted C of G position lies outside (left or right) the "envelope" entirely, flight is not permitted. (if it's too high, you're too heavy!) If the plotted point lies inside the "normal" envelope, you may fly the aircraft as a normal category aircraft, and only perform the manuevers stated in the limitations for that type of flight. If the plotted point lies within the "utility" portion of the envelope, additional manuevers (probably including spins) will be permitted. This is to be taken to mean that spins would not be permitted if the C of G point is in the normal envelope. Generally, if it is in the "utility" you may also fly as a "normal" category, though you might be having seat occupancy limitations.

Refer to the actual flight manual (if applicable) for the real information, as what I have told you is only the concept.

If that does not answer the question, let us know in greater detail what you need to know.

Pilot DAR

Something wrong with those figures - I suspect that the 58800 figure is wrong.

This is exactly what i thought...... total mass of the plane divided by the total moment should give you the moment of the datum, but 42 shows nowhere on the graph... that's why I was confused... thought I was doing something wrong, couldn't even find it in my PPL manuals.. :ugh:

As I said before, I suspect that you may be missing more elements of the question. Or as has been mentioned the moment data could be wrong.

That's off a website designed for your ppl. That's also everything that came with the question..

Is there any sort of forum associated with that website, or contact details for the people who run it?

I would flag this up as a dodgy question, and see what they say.

I could try, other than that question the site is very good.

www.pplquiz.co.uk

Dave,I tried the demo and it seems a good site although I found an error with another unrelated question but can't remember what it was now
I used www.airquiz when I was a student and found it to be very useful.
Good luck
Lister

Do you have a PPL confuser?

I found mine very useful when I did my PPL.

Yeah, got one of those too.

It's a dud question: Bin it and move on............

Cusco.

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Can anyone tell me the calculations to working this question out?

1013-992 = 21mb

21mb x 30 = 630ft

630 + 968 = 1598ft

Edit... PPLQuiz giving me wrong answers again. Im presuming the last caluclation of an addition is correct?

PPLQUIZ said 338 was the right answer :bored::bored::bored:

What is pressure altitude Dave?

If you were on the ground you would find your pressure altitude by setting 1013 on the altimeter subscale. So you need to add any difference between your current setting and 1013 if lower or deduct it if higher.

Well, bose-x's calculation is wrong ... as are all of the possible answers given!

Pressure altitude is what the altimeter reads if 1013mb is set on the sub-scale.

If the altimeter reads zero when 992mb is set, it will read 630ft with 1013mb set.

The airfield elevation is a distractor in this question. Unfortunately, it also distracted the questioner!

Uh? Where does it say the altimeter is set to zero?

I just ran the question through my E6B and it came up with the answer that I gave.

The question does not ask what the altimeter would display it asks the pressure altitude. In which case I am pretty sure that both the question and my answer add up....

What does QFE mean?

I think you need to read the question.

bose-x, I did!

The question as stated is 'what is the pressure altitude at an aerodrome where the QFE is 992mb.' The only possible answer (at 30ft per mb) is 630ft.

I just put the question through my E6B on my iPhone and the ASA CX2 pathfinder and the answer came up as 1598ft.

So one of us is not reading the question correctly.....

The question:

An aerodrome elevation is 968ft and the QFE is 992mb, what is the aerodrome pressure altitude?

A 1598ft
B 338ft
C 720ft
D 1270ft

Or one of us doesn't really understand altimetry! ;)

Clearly, which also apparently means none of the software developers who have written the software I have plugged it into have an understanding either.....

Let's try phrasing the question slightly differently.

If the outside air pressure is 992mb, how high are we above 1013mb?

Your right bose-x, its much easier if you draw it out as a diagram..

http://img255.imageshack.us/img255/9...gramap1.th.jpg


This looks right to me.. maybe an easier way to view it?

Yep, looks right to me. Perhaps my old fashioned view of Altimetry as opposed to Islander2's works?

bose-x, I'll give you a clue.

Your E6B and CX2 are suffering from garbage in == garbage out!

You are misreading aerodrome QFE as aerodrome QNH.

As you wish mate. My E6B has to 2 entries for a pressure altitude question.

Pressure - Pressure is 992
Altitude - 968ft

My simple understanding is that if you are 968 ft and the pressure at 968 ft is 992 if you add 21mb to that then the pressure altitude is 1598 ft. You have added 630 feet by taking it to 1013 which gives you the pressure altitude. Pressure altitude being a common datum rather than QNH.

The question does not say anything about an altimeter it just asks what the pressure altitude is based on the figures given.

I just plugged in the 2 figures from the question and out popped an answer of 1598ft which was the same as my original old fashioned calculation and as answer A on the quiz.

I clearly do not understand how you are working it out. But please feel free to edify us.

I thought I had!

All you need to do is answer my rephrasing of the question:
... and then explain why you think that's a different question from the one posed.

I say again, your answer is based on the the 992mb pressure being at sea level ... whereas the question says that it is the pressure at aerodrome level.

You have lost me completely.....

Ah well, I'll bail out then. It only remains for me to wish Dave luck in his exams ... you can still pass even if you get the altimetry questions wrong!

I understand it like this.


Your stood at an aerodrome which is 968ft above mean sea level. You have an altimeter in your hand. In order for it to read 0 then you must set 992mb.
Now, the question is asking for the aerodrome pressure altitude.

"pressure altitude is the indicated altitude when the altimeter is set to an agreed baseline pressure setting" In our case, this is 1013mb.

So, were stood at the aerodrome and it wants the aerodrome pressure altitude. So to set 1013 from 992 we need to go up 21mb. 21mb at 30ft per second is 630ft.

Now are we to believe because we have been given the QFE the altitude is 0, well yes.. Hmm interesting, whilst typing this out i actually understand what Islander is talking about...

How the hell does PPL quiz get 338mb? That wouldn't be pressure altitude, that would be mean sea level altitude right?

Explain why?

It wants the pressure altitude at the aerodrome.

So it wants the altitude when you set the altimeter from QFE of 992mb to 1013mb..

Dave, I'm heartened, you've got it!

Their answer of 338ft is a nonsense. That is actually the height of the 1013mb pressure level above MSL (QNH is 1024.27mb), which is a meaningless number.