What is Max Drift?

[757_wannabe]

Ok, forgive my ignorance here but i am about to start Nav soon and everyone keeps going on about max drift! Would anyone be able to spend the time to explain? If so i would very much appreciate it. I see there are a few threads on calculating it but i do not understand its use.

Many thanks in advance

[langleybaston]

Max Headroom's cousin?

[Piltdown Man]

It's the drift you would experience with a 90˚ crosswind at the airspeed you are flying. As this is the maximum value, your actual drift will vary from this value to zero as your heading/track changes in relation to the wind.

[SkyCamMK]

For light aircraft use wind velocity x 60 over TAS

w/v = 20 kts TAS = 120 so dMax = 20X60/120 = 10 degrees

So if wind is on beam use 10 degrees as drift if on nose = zero and then use either clock or other system to interpolate. e.g. 0-30 deg =.5, 30-60 deg = .7 0r >60 deg off 0.9 until at 90 deg off use dMax

[blueplume]

Easy formula:

60 / TAS x Windspeed

Example:

for the average light a/c and ease of demonstration assume TAS of 120 kts
and W/V 240/20, Runway 27

therefore 60/120 = 0.5 x 20 = 10 degrees maximum drift.

Actual wind only 30 degrees off Rwy alignment. Use the clockface analogy to work out what you actual drift would be:

30 degrees taken as ~50% of maximum drift (30 minutes on a clock = half of an hour, 45 minutes (degrees) .75 max drift, 60 degrees + = max drift, accurate enough for most situations)

50% of 10 degrees = 5 degrees heading correction, fly 265 to track 270.
Remember that drift is from Heading to Track, in this case starboard drift because the wind is from the left, for which you want to correct.

Headwind/tailwind/crosswind components are functions of sine/cosine but the above is accurate enough for quick calculations.

[BoeingDreamer]

Does also depend on your TAS.

Example 120 it's TAS, your max drift will be 50 % of your wind component. So if wind is 20 kts, max drift will be 10 degrees.
This is an approx rule of thumb to use, that gives you a good enough drift correction estimate. If TAS is less, the max drift will be a little more, 100 kts is approx. 12 degrees.

And then you use the clock rule to estimate your actual drift o current heading.

[Gulfstreamaviator]

Never mind, I will go back in doors now...

glf

[757_wannabe]

AHH got it now thanks very much everyone makes sense now!

all the best

[Vik_atpl]

60 / TAS x Windspeed

or

half windspeed if your mind is alseep :=

[GradSolutions]

Application of the 1 in 60 Rule. Divide 60 by your TAS. Multiply the forecast wind speed at your chosen altitude by this factor. This is the maximum drift correction (in degrees) you will need to apply when the wind direction is perpendicular to your track. When the wind is at any other angle to your track, use your favourite mental approximation method for crosswind components (e.g. 1/2 at 30, 3/4 at 45, all at 60, or the clock code thingy) and apply that to the max drift angle.

[Neptunus Rex]

Or:

Max Drift = Windspeed / TAS (nm per minute)

Worked a treat for calculating the heading to roll out on after the turn on RW13 at Kai Tak, to be followed by the TLAR technique.

[UAV689]

The way I was taught in the university air squadron by old school RAF instructors was

Windspeed / your tas (in miles per minute)

E.g. 120 knot cruise, 20kt wind = 20/2 miles Per minute 10 degrees max drift if the wind was blowing 90 degrees across your track.

But it rarely is...

So look at your watch...

If the wind is 15 deg off your track, apply a quarter of max drift
If it is 30 degrees off track, apply half max drift

If the wind is 45 degrees off track, apply 3/4 of max drift.

If it is between 60 and 90 degrees off, use all max drift.

That is one of the reason the RAF pilots start flying an a/c with 120 kt cruise, then 240 kt cruise, then 480 kt cruise! It makes the math simples!!! 2 miles a min, then 4, then 8!

[Sciolistes]

I like Neptunus' formula best. Thinking in miles per minute is more flexible than thinking purely in knots, especially for later when you may want to mentally calculate intercept rates, distances, rates of descent/climb and ATC estimates.