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Takeoff and Landing P Charts

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wabigail created the topic: Takeoff and Landing P Charts

Any advice for being able to accurately interpolate values on the P charts? I cannot find any examples anywhere, they have been the bain if my existence. Also, they’re giving winds that are upwards of 60° off the runway heading, I have no idea how to calculate the headwind component for this. Any help would be appreciated
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  • John.Heddles
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John.Heddles replied the topic: Takeoff and Landing P Charts

May I suggest that you post two or three specific examples with which you have been working along with some description of how you have been approaching the problems ? That way, our comments will relate to what you have been doing previously and should provide more learning value for you.

accurately interpolate values on the P charts

Graphical work is fairly standard and a bit of practice will sort out your problems. Some performance charts are well-drawn, others are pretty dreadful. That is an unfortunate fact of life in the piloting world, I'm afraid. With such charts as you post, we can to and fro until you get the basics well under control.

winds that are upwards of 60° off the runway heading, I have no idea how to calculate the headwind component

This is a resolution of vectors problem. Once you get on top of the technique, it is just a matter of step 1, step 2 and your answer tumbles out of the other end.

Please do post several scanned examples and we can go from there ....

Engineering specialist in aircraft performance and weight control.
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bobtait replied the topic: Takeoff and Landing P Charts

The wind component table in the AIP GEN 2.6 or most flight computers have a conversion scale to solve the component problem.


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  • John.Heddles
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John.Heddles replied the topic: Takeoff and Landing P Charts

Adding to Bob's comments, we will show you how to figure the components exactly, providing you have a Jepp CR style computer. Dead easy technique and quicker than pulling out the AIP page.

Engineering specialist in aircraft performance and weight control.
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wabigail replied the topic: Takeoff and Landing P Charts

Thanks for your reply, as these were CASA exam questions I don’t have them. But some of the figures were PH 3500ft, 080/15, 1.2% slope, runway 02/20 can’t remember exactly what the runways were but made up one, no mention of particular aerodrome. But the winds were at 60° off the runway. Both questions I encountered were using figures where you’d have to interpolate the values in each box.
One of the questions was using the Cessna style takeoff charts, where as the other was using the echo landing chart
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  • John.Heddles
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John.Heddles replied the topic: Takeoff and Landing P Charts

OK, I presume that you are studying with Bob's books.

How about you scan a couple of charts from the book, work some made up examples, and then post your manuscript workings of those.

The only way we can help you, effectively, is by working through examples with you .... a bit like being able to watch over your shoulder in class while you do the work yourself and we can comment along the way.

If you are using someone else's books, scan the charts from that material - makes no difference to the story.

Engineering specialist in aircraft performance and weight control.
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wabigail replied the topic: Takeoff and Landing P Charts

I’ll endeavour to get it to you when I can.
Adding onto my previous comments, yes I am using bobs books, and PPE.
Was there anywhere within the book that talks about interpolation of charts, finding xwind/headwind components using an E6B (ASA version). I have a rough idea of how to get a reasonable answer, although unfortunately I’ve come straight from RPL so I’m finding it difficult trying to learn these charts with no prior experience that would have otherwise been gained doing PPL
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  • John.Heddles
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John.Heddles replied the topic: Takeoff and Landing P Charts

Interpolation needs to be sensible, but not of microscopic precision. Generally, chart parametric lines aren't too wildly non-linear so a linear interpolation is OK. Some comments on interpolation in this thread FYI

bobtait.com.au/forum/performance/6817-echo-loading#13455

I gather that Bob's current books have some words regarding the sloping rule trick.

Most folk use the cheat sheets shown in Bob's earlier post. However, if you happen to be using the CR whizz wheel, you can do the exact trigonometric calculation on which the cheat sheets are based. The Dalton whizz wheel (eg the ASA device), however, is a straight graphical wind solution so there is no need for the trigonometry - so you miss out on that trick.

Don't fuss too much about missing PPL, I could run you straight to the ATPL exam without any of the lower licence work. Not a good idea, but doable.

Engineering specialist in aircraft performance and weight control.
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wabigail replied the topic: Takeoff and Landing P Charts

How would you go about interpolation the Echo P charts for instance? The grids aren’t exactly even (11mm for the PH, slope % near radiates outwards from a single point off the page I would suspect?, also wind speed are 1mm apart on the takeoff chart)
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  • Qfly

Qfly replied the topic: Takeoff and Landing P Charts

Here is a little trick I learned back in the early 90’s for roughly calculating headwind comps:
Take 115 minus the angle between RWY and wind. Then work the % of the wind;

Example:
RWY 140
Wind 170
Wind speed 40kts

Easy Maths Now:
170 –140 = 30
115 – 30 = 85
85 x 40/100 = 34kts
H/W = 34kts

And another;

RWY 280
Wind 220
Wind speed 20kts

280 – 220 = 60
115 – 60 = 55
55 x 20/100 = 11kts
H/W = 11kts

I traditionally try and work out stuff in my noggan before checking with the CR3 and charts. What Bob and John suggest is great advice, but try the above mentioned method from time to time even just to get a rough idea and increase your speed for these calcs. Hope this helps.
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