January 03, 2005

Calculating the Crosswind components

Follow-up to Crosswind Circuits – Lesson 14 from Christine's Flying blog

Cessna 152 has maximun crosswind component of 12 kts. Before taking off I need to ensure that the crosswind component of the wind is less than 12kts

Calculation- The Sixths Rules of Thumb

First calculate angle between runway and wind direction . Taking lesson 14 as example wind direction 270 deg runway is 230 deg – therefore angle = 40 deg

then apply rule

if angle = 10 deg then crosswind component = 1/6 wind strength
if angle = 20 deg then crosswind component = 1/3 wind strength
if angle = 30 deg then crosswind component = 1/2 wind strength
if angle = 40 deg then crosswind component = 2/3 wind strength
if angle = 50 deg then crosswind component = 5/6 wind strength
if angle = 60+ deg then crosswind componnet = wind strength

So at 40 deg and 17 kts wind strength – crosswind component = ~ 12kts


- 14 comments by 0 or more people Not publicly viewable

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  1. Alan Messenger

    I use a version of this based on quarters because I find it easier when confronted with a new airfield and the high workload of arriving somewhere different. If you look at your watch, 15 minutes = quarter of the wind strength, 30 minutes = half, 45 minutes = 3 quarters anything more assume full wind strength. It's not quite as accurate as yours but it does the trick and is easy to remember!

    Regards
    Alan

    11 Feb 2006, 14:55

  2. sham

    Hi
    Simple way to remember the six rules of thumb
    10 = 1 = 1/6
    20 = 2 = 2/6
    30 = 3 = 3/6
    40 = 4 = 4/6
    50 = 5 = 5/6
    60 = 6 = 6/6
    Happy flying.
    Ps how u getting on – i'm at 50 hours and getting ready for first solo nav
    cheers
    sham

    01 May 2006, 15:53

  3. Peter

    Hi,
    here is another method that is quite accurate to figure out crosswinds and it works great for me:

    The formula is: WA + 20 = %WV

    Take the angle between the wind and the runway (WA), add 20, and you have the crosswind in percent of the wind vector (WV).

    Example:
    runway 31 wind 270/10 WA + 20 = %WV 40 + 20 = 60% of 10kts = 6kts

    runway 24 wind 270/12 WA + 20 = %WV 30 + 20 = 50% of 12kts = 6kts

    runway 18 wind 260/08 WA + 20 = %WV 80 + 20 = 100% of 8kts = 8kts

    Calculating the crosswind is the sinus function of the wind angle, therefore another way to simply figure out crosswind is to know 4 sinus numbers. The 4 sinus numbers of 30, 50, 60, and 80 degrees.

    sin30 = .5 (with a wind from 30 degrees the cwc is half the total wind)
    sin50 = .75 (with a wind from 50 degrees the cwc is 3/4 the total wind)
    sin60 = .9 (with a wind from 60 degrees the cwc is the total wind minus 10%)
    sin80 = 1.0 (any wind of more than 80 degrees and your cwc is the total wind)

    Looking at my numbers here, it looks more complicated than previous suggestions, but it really depends on how accurate you want to be and what method you feel most comfortable with. I use my method all the time and I can figure this out within 2 seconds. I have another method of determining head wind component to calculate my target and reference speeds but that would probably go to far.

    Anyway happy landings everybody.
    Peter

    18 Jun 2006, 18:39

  4. Jason

    Good suggestions in this thread. I hadn’t seen the one from Peter before. Nice! Here’s a link that has a flash lesson on calculating crosswind components: www.faagroundschool.com

    It is free but you do need a high speed connection.

    05 Dec 2006, 14:31

  5. DTC

    Here is a method an E6B computer might use to calculate crosswind. It is found in only one other place online, where it is scheduled for deletion.

    For a heading (H), wind direction (D) and wind speed (S), the crosswind component© can be found with:

    C=sin(abs(H-D)*S)

    28 Jan 2007, 17:56

  6. Simon

    Im trying to get to grips with this heres a sample question I had but I cant get it to correspond to the possible answers I keep getting 21.6666666

    You are on runway 01 and are ready for departure. The surface wind is 060 at 26 kts. What is the crosswind component of this wind?
    A 23 kts
    B 20 kts
    C 17 kts
    D 25 kts

    Can anyone help me please. Email me with help as this is really confusing me.

    Thanks

    S

    18 Sep 2007, 11:54

  7. Brad

    You must be in radians mode or something… If your claculator has a little “r” on the screen then you are definitely in radians mode. Depending on your calculator you have a few options. You can either convert the degrees (060-010 = 50 by the way) to radians, or you can switch your calculator into degrees mode and try your calculation again. I would switch to degrees mode and try again. To convert 50 degrees into radians, multiply by pi/180, there should be a pi symbol on your calc, if not, use 3.141

    26 * cos(50) = 16.712… rounding brings us up to 17.

    03 Oct 2007, 20:13

  8. David

    The correct answer is B 20 kts.

    10 Oct 2007, 23:52

  9. David

    Headwind component is simply the angle of the headwind calculated in the same method. Note that the headwind + the crosswind do not equal the wind speed. You can do this on the back of a traditional E6B, or Google “crosswind component” and one of the first sites listed is a nice chart, which shows the 1/6 method above to be pretty close.

    11 Oct 2007, 01:56

  10. John

    Simon, I think the answer to your question is in fact A – 23 knots. I’ve tried various methods including rules of thumb, crosswind charts and online calculators and the answers are consistently slightly more than 22knots. Any exam paper is going to expect you to round your answers in the ‘safe’ direction, which in this case it upwards; ie. assuming more rather than less.

    Your answer of 21.666 looks like you’ve used the ‘sixths’ rule of thumb and calculated 5/6 of 26 knots. While this is close enough to fly with, it’s right in the middle between 2 of your exam question answers. The people who write these papers know all the rules of thumb and just love to do this to students! For exams, use only approved methods of calculation..
    :)

    07 Nov 2007, 12:43

  11. John

    Caution! the method quoted by Peter above (WV + 20) is inaccurate and gives significantly lower crosswind figures than it should.

    The actual figures for his examples are:
    R31 270/10 = 9kts (he said 6)
    R24 270/12 = 11kts (he said 6)
    R18 260/08 = 7kts (he said 8)

    Using Peter’s method with Simon’s question gives 18kts, when the answer is in fact 23kts.

    It may not seem like much, but it can easily be the difference between a ‘sporting’ crosswind approach and landing and exceeding the crosswind limit of your aircraft with disastrous results. The limit for a PA28 is 17kts (only 12kts for a 152 I think).

    It just serves to reinforce the lesson that you should always be sure of the information you’re being given. Too many NTSB reports hint at people taking off with planning calculations based on heresay or incorrect data.

    One of the calculators I found today is here
    http://www.paragonair.com/public/aircraft/calc_crosswind.html

    Blue Skies :)

    07 Nov 2007, 12:56

  12. Julietxray

    The maths (useful for exams, excel etc)

    Headwind=(wind strength*cos(wind direction-runway direction) positive value headwind, -ve value is a tailwind

    Crosswind=(wind strength*sin(wind direction-runway direction) positive value crosswind is from the right, -ve from left

    Runway and wind both magnetic

    e.g.
    Wind direction = 070
    Wind strength = 20kts
    Runway = 09

    Headwind = 20*cos (70-90) = 18.79 (Headwind)

    Crosswind = 20*sin (70-90) = -6.84 (from the left)

    My E6B computer prefers to show Headwind as a negative value, though it uses the same sign for left and right, to give a negative result for Headwind and a Positive for Tailwind alter the formula to:

    Headwind=(wind strength*cos(wind direction-runway direction-180) gives a positive value for a tailwind, -ve for headwind

    Headwind = 20*cos (70-90-180) = -18.79 (Headwind as displayed by units such as the CX-2)

    23 Nov 2007, 22:56

  13. Julietxray

    I should just add the answer to the question asked above was 20kts

    Crosswind = 26*sin (60-10) = 19.9 kts

    ;0)

    23 Nov 2007, 23:14

  14. JScarry

    I agree with 13 above. the answer is B 20 kts.

    Look on the back of your E6B for the Wind Correction Chart. The difference between the Runway 01 or 10 degrees and the wind of 60 degrees is 50 degrees. Look for 50 degrees in the column headings. Then look for the windspeed on the row headings. There is no wind speed for 26 kts but the crosswind component for 20 kts is 15 and the crosswind component for 30 kts is 23. 26 kts is 60% of the way from 20 to 30 kts, so the answer is 60% of the way from 15 to 23.

    60% of 8 = 4.8. Added to 15 = 19.8 kts crosswind component.

    This is an approximation to Juliexray’s answer since the chart isn’t really linear but for most purposes it is close enough.

    04 Dec 2007, 00:16


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