Maximum Drift
 

Hi

There is a max drift calculation for a given wind speed...

anyone know what it is?

Thanks

Max drift when wind is at 90 degrees to heading. A triangle of vectors will give the answer for given wind and aircraft speeds, headings will be irelevant for this example, so its a triangle of speeds.

Pilot16

Hopefully what you are looking for is the rule of thumb that the max drift will be about half the wind, so if e.g. you have a 20kt crosswind component, the drift will be 10 degrees.

This is pretty close for a standard school plane going at about 100kt. For 150kt the max drift is about 1/3 of the crosswind.

These simple rules are as accurate as the winds aloft forecast.

I learned that the drift is three-quarters of the wind speed when your track is at 90 degrees to the wind, half the wind speed when at 45 degrees. It seems to work. But as I've said on another thread, the difference in both methods is less than 5 degrees usually, and you don't need to be more accurate than that in practice.

windspeed x TAS
------------------------
60

or put another way...

windspeed x (TAS / 60)

So if you have a rough GS of 90kts....then MD is 2/3 of the windspeed....

if you aircraft is travelling at 120 kts then MD is 1/2 of the windspeed

Also you dont need to be that accurate about it - the met man isnt and nobody told the choatic system we know as the weather (including wind) to behave either :)

Hope this helps,
FF

and whirlybord...I think 'dont need to be more accurate than 5 degs is wrong...not tried an instrument approach down an ILS recently??!?

Fly 5deg off and thats bye bye ILS...flying accurately matters - the only reason people cant fly headings properly is...

1. Failing to pick ground features to track to
2. Poor scanning of instruments in either visual or instrument flight.

If my student can accurately fly 5 deg off all the time then they certainly can fly 0deg off all the time too...

You can then use the sixths rule for estimating drift angle.

ie.

if the wind is 10 deg from track use 1/6 max drift
20 deg....2/6 max drift
30 deg....1/2 max drift
etc

up to 60 degress afterwhich point you use max drift.

It always amazes me how well this works.

Yep that 'rule of sixths is the clock stuff i was talking about - 30 deg = 1/2, 40 deg = 2/3

FormationFlyer

You are absolutely right about it being possible to hold a heading precisely; the difference is that on an ILS you only have to do it for a few minutes at most, and you have done your checks well before you get there, so you can concentrate on the job. You also have a clear visual reference: the CDI or the HSI bar, plus the heading bug, most club planes don't even have a heading bug. I doubt many people can fly better than +/- 5 deg en-route and if they did they would not enjoy the flight very much.

Agreed. But i found it quite remarkable how many pilots cant even manage +-5deg ;)