wind deviation calculation

[long final]

I am trying to create an excel plog program and wondered if anyone ( not being that mathamatically minded! )could provide me with the calculation for wind deviation from given direction, speed and track, if indeed it is possible.
Regards
LF

[Code Blue]

Is this any use?

I found this in an older text and cannot say I've used it but:
let WA = Wind direction - Course
let WS be wind speed
let TAS = True Air Speed

then Wind Correction = ARC Sin ( sin (WA) * WS/TAS)

rgds
CB

[tacpot]

The Excel formula would therefore be
=(ASIN(SIN((H20-G20)*PI()/180)*J20/D20)*180/PI())

Where:
H20 is the cell containing the wind direction
G20 is the cell containing the track required
J20 is the cell containing the windspeed
D20 is the TAS.

'cos the Excel trig functions work in radians.

When I have figured out the Groundspeed calculation I will post this also.
:)

[long final]

Thanks Chaps, I havn't had time to try it yet, but it certainly looks impressive. :D
I'll let you know how it works out
Regards
LF

[long final]

It works just fine thanks. Look forward to the groundspeed trig.
Much appreciation.
LF

[Noggin]

What exactly is Wind Deviation?

[Kermit 180]

I think in a round about way they refer to drift, or deviation from track due to wind, and the calculation to work out the heading required to hold off that drift. Look forward to the groundspeed solution!

Kermie ;)

[long final]

Just as Kermit says.
Echo the groundspeed.
LF :p

[Noggin]

Can't understand why you need a computer to solve such a simple problem. No doubt you like to sleep standing up in a hammock!

[long final]

A genius in our midst! I want to make the computer do something, that for each leg of a trip, takes me a min or so. So a 10 leg return trip with varying winds and speeds takes ..... Until I am able to solve trig equations in me 'ed govnor I will just have to enter a couple on numbers and have that little box do all the calculating and writing type stuff. Then I get to stay in bed just that little bit longer. Hammocks, too high - thats 'cos I'm Lazy - the whole point of the excercise. ( Or could it just be for reliabilities sake ?!? )
LF ;)

[Recover]

You don't need a computer, LF. try a bit of this:

Max drift (ie the maximum amount you'd drift if all the wind was crosswind)can be calculated by dividing the wind speed by your airspeed in NMs per minute. Strictly speaking it should be TAS, but unless you're planning on going really fast or high the 'normal' 90,120 or whatever will work quite well.

So you're in a TB10 trolling along at 120kts. So that's 2 miles per minute. Wind off the chart is 20 knots, so max drift is 10 degs.

All you need to gauge now is how much of that max drift to take into account and this is where an imaginery clock face comes to hand.

If you think of the number of degs off your track that the wind is blowing (eg track 180, wind 195, wind angle=15) then the clock face represents the proportion of max drift to be applied.

So: 15 degs wind angle is 15 minutes on the clock. That's one quarter of the clock face, so one quarter of max drift.
20 degs, 20 minutes, one third of max drift.
30 degs, 30 minutes, one half and so on.
Once you get to 45 degrees of wind angle you just take the whole lot of max drift.

A quick eg then.

Track:180. Wind: 195/20. TAS/IAS:120.
So: max drift=20/2...10 degs.
Wind angle is 15 degs....quarter of the clock...quarter of max drift...2 & a half degs. Let's call it 3. So your hdg should be 183 (If it's anything like my driving then anywhere between 180 & 190 would be great ;))

This method can also be used to work out your groundspeed, but using the wind speed instead of max drift. The only thing is you need to take the wind angle away from 90 to get the proportion of the clockface. It becomes obvious if you consider that wind all across doesn't affect groundspeed.

In the example above, wind angle is still 15 degs therefore 90-15=75. This is > 45 so you'd apply the whole lot of wind to your airspeed. ie 120-20....your G/S = 100kts.

One more eg and I'll shut up:

Track:330. Wind:020/30. TAS:90

---max drift:30/1.5=20 degs

So wind angle is 50 degs. That's > 45 so all the drift applies. Hdg:350.

90-50=40. 40=2/3rds of the clockface so 2/3rds of 30 kts is 20. 90 TAS-20: G/S=70.

Try it with a whizz wheel (CRP thingy), you'll be surprised how accurate it is.

Obviously with a tail wind you'd add the proportion of the wind.

There's no need to get your head in the cockpit. Just some simple maths and an imaginary clock...it works well. It's good for calculating crosswind components for T/O and landing as well.

Toodle pip,

Recover

[Noggin]

If you really must use a computer there is a cheap program called NAV BOX, does it all for you. However, if you can't do it in your head, the computer is not much use when you are in the air and discvover the Met man tells lies.

Simple rules of thumb work, Work out max drift (2/3 WS at 90 Kts)Apply as: 0-30 degrees off= 1/3; 30-60 =2/3; 60-90 =All.

For Groundspeed use Max WC = Wind Speed Apply as: TAS +/- From 0-30 degrees off = All. 30-60 = 2/3; 60 -90 degrees = 1/3.

You should be able to calculate the wind in the air on your first leg, and then apply it on the next leg.

PPLs get too bogged down with the Prayer Wheel, the RAF hardly use it!.

[ 18 November 2001: Message edited by: Noggin ]

[long final]

ok ok ok.
Lets clear this up.
Thanks for all the advise re calculation, I have to point out that I am well able to do all the calc necessary in me noggin, on the ground and in the air if necessary ( as noggin points out - the met man is not the most acurate being around. )

This mental working will be as correct as any PPL will need nearly always. My situation though is this.

1. I am tight - I know there are packages you can buy, but I am intending to make my own.

2. I'm Lazy - Whenever I fly, unless I am sure of the visual route - I will draw my lines, measure my distances, angles and such and write it all in my plog. Then before the flight look at the WX and, as you say, mentally add a correction - that I know will be within a degree or so - write it in, then do the time. Ok so far? Pretty standard stuff. It's just that when I get home I throw it all away and forget about it. So the jist is that I intend to type all the details into a plog once, and keep em to use again. (Just having to change the wind speed and direction every time I fly that route - everything else is either already there or recalculated for me ) Saves me time is all. The drawing lines bit is the fast bit - and as you say noggin, I also aviod the wheel if I can.

Soooo, the initial post was along the lines of, if I am going to do a plog program, it might as well caluclate the CORRECT variation for me and do all the groudspeed EXACTLY. The Trig. Calc's for these problems I didn't know - read couldn't be bothered ( ref. Lazy ) - and thought someone might well have already done the graft - enter tacpot - many thanks by the way tacpot.

Hope this clears it all up, and again thanks for all reposnses. :)

Im off to sunny Blackpool now to scare some clouds - happy flying. ;)

LF

ps. Still after the groundspeed trig.!! Anyone?

[ 18 November 2001: Message edited by: long final ]

[tacpot]

Apologies for the delay.

The Groundspeed trig goes as follows:

GS=(D20*SQRT(1-(SIN((H20-G20)*PI()/180)*J20/D20)^2))-J20*COS((H20-G20)*PI()/180)

where:

D20 is the TAS
H20 is the Wind Direction
G20 is the Desired Track
J20 is the Wind Speed

The basic calculation was lifted from http://www.best.com/~williams/avform.htm#Wind

so respects to Ed Williams for understanding the trig.

Actually Ed's calculations include a subtle test to ensure that the course can actually be flown. e.g. if the w/v is 100Knots from 270degrees, and your TAS is 90Knots you cannot fly a course of 270 - cos you will be going backwards
:eek:

I omitted this test from my spreadsheet on the basis that I would never plan to go flying in a wind that was capable of pushing me backwards!

Enjoy

[Land After]

Any chance of posting the completed spreadsheet for an equally tight pilot who's thought about attempting the excel plog, but not got around to writing it?

[long final]

Tacpot, thanks again for your help. I havn't had time to try it yet, but will post my findings!

Land After - if you have not already recieved one, drop me a mail and I will post you mine as soon as I have finished it.

Regards
LF

:p

[Clouded Yellow]

Well done tacpot. I've put it all in an Excel spreadsheet, and it works just fine.

[long final]

Ditto Tacpot & Clouded Yellow - this internet thing might just catch on yer know :D - Thanks TP
Regards
LF

[long final]

If anyone is interested in a basic plog Excel prog you can now download it from our website.
Think it all works out ok - but test it

Excel plog (http://www.thebarlick.com/downloads.htm)

Regards
LF

[Land After]

Long Final et Al,

Thanks for your combined efforts on this and taking the time to post - it's saved me a wet Sunday afternoon slaving over a hot keyboard! :)