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TOW CHART QUESTION-PPL EXAM PREPS

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MEADE1990 created the topic: TOW CHART QUESTION-PPL EXAM PREPS

Hi Folks,

Long time procrastinator, first time caller. Working my way through to my PPL exam and im doing ok. This question popped up in the third practise exam. Could someone take a look and maybe explain how the answer is anything but 1030kg? Looking forward to finding out where I have gone wrong.

Meade
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Bosi72 replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

I made the same error when doing quickly for the first time.

However, after doing slowly, I found an error at the very beginning, between 1st press.height/temp chart and 2nd toda chart. In first chart 4.5mm is the distance from 2nd vertical line in press.height/temp chart and intersecting 25C diagonal line. The same 4.5mm is the distance between 2nd vertical line in toda chart above and intersecting 900m diagonal. The resulting line overlaps the 3rd horizontal line from the bottom of toda chart, then goes straight from the 2nd (long dry grass) onto the level slope chart which intersect level diagonal at the 2nd vertical line from right. Then going down overlapping the 2nd vertical from the right and goes down and intersect 4th horizontal line from the bottom of the tow chart which is actually 1000kg.

To summarize, if you try going from 1000kg backward, you will find the error you made at the first attempt.

As many things in aviation, a small mistake at the beginning, can have serious consequences at the distance..

Hope I help.
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MEADE1990 replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

G'day Bosi72. Thanks for your reply! I've done this on the computer now and I still get the same number... Can you take a look when you get a minute?

Meade
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John.Heddles replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

What was your climb weight limit, again ? I don't recall seeing it mentioned in your first post .....

Engineering specialist in aircraft performance and weight control.
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MEADE1990 replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

The correct answer is 1000kg, I can only seem to get 1030kg. I can only work off the info given in that question.
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John.Heddles replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

I'm giving you a hint but you are not seeing it ....

1030kg is fine but it is only half of the answer to be considered. You must ALWAYS check for a climb-limited takeoff weight for this aircraft. All the information is there.

Looking at the sample use of the chart -

(a) the runway-limited weight is around 1010kg shown as A

(b) the climb-limited weight is around 1085kg shown as B

The lesser of the two (in this case runway-limited takeoff weight) is the answer required.

Now, again, what was the climb-limited weight for your exercise ?

If you can't quite see it, we will work it through step by step so that it all becomes clear ...

In essence, you are not using the chart correctly. Perhaps a quick review of the notes in Bob's book would assist ?

Engineering specialist in aircraft performance and weight control.
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Bosi72 replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

Thanks John
Explanation is on page 205. I thought the line follows the climb weight limit at the end, but it actually goes from intersection of cwl and "our" line.
Cheers
Stjepan
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MEADE1990 replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

Ah John! You have all those titles in your name for a reason! I have been neglecting that side of the chart completely! Thank you for pointing that out, much appreciated (with only days to go I might add)

Meade
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John.Heddles replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

Good to see it's now under control.

Stjepan - glad we have that minor point of confusion resolved, now.

Meade - for this aircraft and this question, you are climb-weight limited. That is to say, it doesn't matter how long the runway is, you can't use the runway limit weight because the aircraft will be staggering once you get off the ground ...

It can be a bit confusing when you are starting out due to the fact that the old DCA-style P-chart combines two totally separate performance charts as overlays (solely for real estate convenience - ie to use less area on the bit of paper so that the chart detail can be made larger). It is easier if you start out with the charts presented separately so that there is no confusion. However, you need to run BOTH sets of calculations EVERY time for this aircraft and then see which gives the lower weight which then becomes the limiting weight for the occasion.

As a sideline note, Bob refers to the DCA format as "Cessna" charts for administrative convenience. It doesn't really matter what one calls them. There is a range of styles used in presenting takeoff and landing data, including the two typical sorts of presentation you see in this training arena.

All you needed to do in your (very nicely done) example is run up the density height line to the climb weight limit overlay line (at around the intersection of 6000 ft Hp and 10 deg OAT) and then run across to the right to read off the climb weight limit at around 1000 kg (similar to the example line at B in the base chart).

Keep in mind that some aircraft are NEVER climb limited while some are climb limited some of the time (generally for hot and high conditions).

On another point, you will occasionally be asked what the climb capability is. Such questions generally are unanswerable unless you are right on the climb weight limit (in which case you can assume a climb capability of 6% gross) or qualify your answer along the lines of "greater than xx%" where xx% (or whatever equivalent value is sought) relates to the underlying basic 6% requirement.

The climb requirement thing is made a little more obscure as it was specified in the old (and post-Yates Report binned) CAO (ANO) 101.22 certification requirements. All that remains is the CAO 20.7 operational requirements which often (but incorrectly) are assigned certification significance.

Engineering specialist in aircraft performance and weight control.
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MEADE1990 replied the topic: TOW CHART QUESTION-PPL EXAM PREPS

Thanks again for your help fellas, I sat the exam this morning, 56 out of 56!
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