Drift Angel and Ground speed

[Coldbear]

Hi,

I'm new here and I'm starting my pilot training this winter, but a got two small questions regarding drift angel and ground speed. I know these are depending on the wind situation. I know you can do this with a nav computer, but I don't have such yet. How should I calculate these figures by hand?

Martin
(EKRK, Roskilde, Denmark)

[Oktas8]

Hi Coldbear,

Although you asked to calculate the figures by hand, a numerical solution is quite complicated - it depends on left or right drift, and whether you have a head or tail wind. The graphical solution is easiest, and is quite accurate provided you measure angles carefully.

Regarding the graphical solution: If you already thoroughly understand the wind triangle, don't bother reading the rest of this!

So, to begin. Draw a line of length equalling TAS, with the direction representing HEADING. Put a single arrow representing the way the aircraft is travelling through the air.

From the beginning of the TAS line (not the end, but the beginning), draw another line. This one has length equalling GROUNDSPEED, and direction TRACK. Put two arrows on this line, representing the direction the aircraft is travelling over the ground.

The angle between these lines is drift angle. (Technically, drift angle is from heading to track, not the other way around.)

The third line, wind, is the line starting at the end of the TAS line and going to the GS line. This line should have three arrows, pointing from TAS to GS. It will have length equal to wind speed, and direction equal to wind direction.

If you have any two of these lines, you can get the third line by drawing carefully to scale.

Hope this helps,
cheers,
O8

[hugh flung_dung]

You can use basic trig or you can use the same techniques that you will use when you learn to plan diversions:

First calculate the drift when at 90 degrees to the wind, this is maximum drift (MD) and is very close to windspeed*60/TAS.

You can now very easily estimate the proportion of MD or windspeed in the air using a DI or protractor - but really this needs a picture to explain ... ask your instructor (unless someone can tell me how to attach a picture)

With simple maths:
If the wind angle (angle between track and wind) is A, the drift angle is now MD*sine A.

If the wind speed is V, the head/tail wind component is V*cosine A. Subtract or add this to your TAS to get groundspeed.

HTH
HFD

[foxmoth]

After finding your Max Drift an easy way to find how much to apply is to use the "clock" system. if angle between heading and wind is greater than 60 degrees this equates to 60 minutes on a clock face and you apply Max Drift (MD), if the angle is 45 degrees = 45 mins = 3/4 round the clock face and so you apply 3/4 MD.
Similarly 30 degrees = 30mins = 1/2 MD
20degrees = 20mins =1/3 MD.etc.
To get head or Tail component take the wind/heading angle away from 90 then apply the clock in the same way to windspeed.
This is not exact but will get you within a couple of degrees even in a strong wind. (Substitute windspeed for MD in the first part and it will give you Xwind component - handy if you are landing in a crosswind):ok:

[hugh flung_dung]

A surprising number of people have difficulty even doing the sums associated with the clock method. If you use the DI there are no sums at all, just a visual proportion to judge (I wish I knew how to post a picture without having to host it on a website:confused: ).
Once you've got the groundspeed this can be converted to time using 6 minutes = 10% of groundspeed.

Hey presto, the whole triangle_of_velocities task completed accurately and without sums ...
... and not a wizz wheel in sight.
It makes me wonder why we teach the wizz wheel ...

HFD

[Coldbear]

Thanks a lot. I will see if I can make some kind of a program that calculate all this automaticly

[hugh flung_dung]

Sorry Coldbear but a program is exactly what you DON'T need (besides, there are zillions already out there). Learn the simple visual/mental techniques and then you will be comfortable using them in flight with everything else that's going on.

HFD

[Mintflavour]

Hi
A new one that I believe works to calc drift angle. Note it is pretty accurate for 90 knot AS, other speeds above and below this you need to use a little sensible compensation.

The Angle between track wind direction (head wind or tail wind so you cant have a greater angle than 90 degrees)

divide this by 10

Wind speed divide by 10

Then multiply the two together equals drift angle.

Example

A/C Heading 030, Wind is 060/15

Wind angle is 30 degrees from right

30/10=3 15/10=1.5

3x1.5= 4.5

Therefore a correction of 4.5 degrees to the right is required yo account for drift.

This is easy enough for training aircraft that generally cruise around 90kts.

All the Best

mint

[Oktas8]

Coldbear - I have to agree with hugh_flung_dung.

The best way to becoming an expert is to get a navigation computer, and learn to use it quickly and accurately. You'll do better in the exams, and then when you've got a license you can stop using it and find the answers with quick mental arithmetic.

If you start using electronic flight planning software now, it will take much longer to be able to be quick & accurate in the air.

If you're into sines and cosines, of course write your own program! But don't actually use it for flights - learn the basics first.

best of luck,
O8

[foxmoth]

Mental calcs are very quick with practice and I always teach my students to use them to x check the wizzwheel workings.

[Whopity]

I thought a Drift Angel was a female navigator!

With one of those you'll never need a computer!

[Onan the Clumsy]

it depends on left or right drift What am I missing here?

:confused:

[Oktas8]

it depends on left or right drift

It's not enough to tell your spreadsheet that the wind angle is wind minus heading, or wind minus track. What is 355 - 010 to a computer? Certainly not 15°, that's for sure!

So for an automated program to work, the programmer has to calculate the angle between vectors for any combination wind, track, heading. If you're using MS Excel, that might mean using if...then statements depending on whether the wind is coming from the left or right. There are other ways of programming it too, but that's the example I was referring to.

Hopefully the final answer comes out correctly regardless of left or right drift - then you know you don't have any errors. :)

[Onan the Clumsy]

Oh sorry, I thought it meant "to the aircraft in the air"

However you can use the MOD function in the spreadsheet to work with the 360 degree boundary

[Mintflavour]

Leicester aero club have already done a plog in excel that calculates Drift etc

follow this link

http://www.leicestershireaeroclub.com/download.htm

Its down fall is that you can put a massive crosswind @ 90 degrees but your ground speed is hardly affectted.

mint

[VeeAny]

This may help when checking your answers from the CRP-5.

http://www.griffin-helicopters.co.uk/navtriangle.asp

V.