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## KDR question using ERSA wind table

• Carly
• Topic Author

### Carly created the topic: KDR question using ERSA wind table

Hi Bob and team,

Id love some help with the following KDR

Calculate head, tail or crosswind component - Part 61 MOS Unit 1.7.1 PNVC, 2.4.4
2.4.4 Calculate headwind, tailwind and crosswind components given W/V and HDG using:
(b) conversion and wind component tables in ERSA.

I am able to calculate the head/tail wind and crosswind on the flight computer given heading and wind, however part B asks me to calculate this from the ERSA wind component tables.

Is it accurate to use this table given the wind and heading for an in flight situation, not a runway? and wouldn't I want to know the difference between the wind and my track, not heading?

Hopefully this makes sense, feeling a little confused!

Thank you!

Carly

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 365

### John.Heddles replied the topic: KDR question using ERSA wind table

Is it accurate to use this table given the wind and heading for an in flight situation, not a runway?

It doesn't matter one iota whether you are on a runway or in flight.

All that is required is that you can resolve a vector quantity (in this case, wind velocity) into its components (H/W or T/W and X/W). You can do that using the whizz wheel either graphically (Dalton style) or quasi-trigonometrically (Jepp style) - the answers should be the same, any round off errors excluded.

Alternatively, you can do the sums using look up tables (such as the ERSA wind component table). I haven't checked that table's accuracy but I presume it is OK - in this case, you should get the same answer for tabulated angles. If you interpolate for intermediate angles, there will be a small error associated with linearising the trigonometric equations (which is transparent to you when using the tables).

However, I note that the reference to "heading" for the runway is confusing as you are considering track (ie you are taking off or landing along the runway direction.

and wouldn't I want to know the difference between the wind and my track, not heading?

If you run the sums with respect to heading, you are looking to find the wind components along (H/W or T/W) and at right angles (X/W) to the heading direction. If you run the sums with respect to the track, then the components are in relation to the track. Of course, it makes more practical sense to run the sums with respect to track as that relates to where you want to end up going ...

Note that, if you do run the sums with respect to track, you also need to figure out the TAS components so you can add and subtract consistent quantities. This is what the Jepp's effective TAS is all about. Might be worth digging out your Jepp manual and having a revision of how the sums are worked out on the Jepp.

Engineering specialist in aircraft performance and weight control.